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Author Topic: Dennis Adamisin: Clipped flaps...a discussion???  (Read 15553 times)

Offline Steve Helmick

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Dennis Adamisin: Clipped flaps...a discussion???
« on: July 26, 2007, 10:50:34 PM »
Dennis has mentioned modifying several ARF's by clipping and fixing the tips of the flaps, I think making them into adjustable tabs. Maybe...but I'd have to go check those threads. Stated purpose and result is said to be reduced control handle loads (i.e., "power steering") required to turn the model.

I find this interesting...and puzzling...as I have personally heard PW state that he tried that and returned to making the entire flaps moveable. Also, have read that Ted Fancher did the same experiment, and also preferred the entire flaps moveable, and returned to that setup. I am not 100% certain what their objections were, but I think consistency, possibly caused by the adjustable tabs flexing in difficult conditions, but I'm just not sure. I do not want to 'start something', just seek enlightenment... HB~> ouch! HB~> ouch! HB~> ouch!  H^^ Steve
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Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #1 on: July 27, 2007, 03:56:55 PM »
Yo Steve!  glad to offer my opinion, unfortunately a LOT of electrons will be sacrificed in the process, I do not know how to answer this curtly.  There are a lot of facts, factors and "factoids" that play into this discussion.  Hope I can do them justice while keeping it as brief as possible.  Also I have shamelessly dropped some names in this piece, hope those folks chime in too to add or subtract to what I said about their experiences!

First the premise: When a wing produces lift it sheds vortexes (mini-tornados) of air off the wing tips.  The vortex is relatively high energy air with curling, highly 3 dimensional flow.  If you have a control surface like a full-span flap or aileron in the vortex then you have to turn that vortex when you deflect the control surface, but the vortex resists getting turned!  Result for the CLPA flyer, you get a very "heavy" feel, and probably a hard time doing a decent square corner.  If you cut off the flaps you miss the vortex, and improve the control effort and corner.

If you have ever heard about people doubling up the number of hinges at the tips of their flaps - they did it because the tip vortex was beating the heck out of the hinges at the tips of their full span flaps!

In his article on the Olympic, there was a side bar to the main article where Bob Gialdini advised that lengthening the flaps (versus the design as published) would result in a slower corner and smoother flight.  About this time my brother had built a Nobler modified to mimic the Olympics.  His bird was very heavy and needed all the lift it could get, however, as built with full span flaps, the bird couldn't get out of its own way and would scarcely turn a round loop under 45 degrees.  He cut off about 5 inches of flap and the bird got CORNER.  It was still too heavy though...

As I reported here in StuntHanger, my Oriental ARF as built with full span flaps flew nice but had a propensity for 88 degree square corners - it was hard to pull on it hard enough to get a decent square.  I cut 4" off the flap and the bird got corner, so much in fact that I had to then go and round off the leading edge to prevent it from stalling!  Then I built the Cardinal (also reported here in the Hanger), and did not bother waiting to fly before cutting off the flaps and rounding the LE, and it flies great.  Thge Cardinal was also the first time I set-up the cut off portion of the flap as a trim tab - of course the wing is dead straight and no tab was required!

Before I built the Oriental I noted that several folks in the StuntHanger reported better corners after they reduced the flap throw, and I surmise, reduced the effect of the vortex on the flap.
 
So HOW MUCH do you cut?  Certainly, the experience Ted Fancher documented on his Imitation article is the BEST practical knowledge out there.  If you haven't seen that I will try to summarize:  Ted built the Imitation with segmented flaps, whereby he could change the span of the flaps.  He reported that the shorter span flaps allowed the Imitation to turn harder corners, but loss of "feel" cost him precision in round maneuvers.  His conclusion was that "too much was probably better than too little" flap span.  However, even his "full span" flap config actually stopped at the swept wing tips - so he was likely still out of the trailing vortex - or at least missing the worst of it.  I never asked Ted if he did this, however it might have been feasible to get back the FEEL with the short flaps if you also change ratios and added flap throw.  I think the extra throw would manifest itself as drag - more than lift - and it MIGHT help prevent wind-up in maneuvers???

A tangent: I have built birds with partial span NARROW CHORD flaps that were almost unflyable - NO feel whatsoever!  However, also note that narrow chord does not get you out of the vortex, only shortened span.

One more big factor at work: structural rigidity of the flaps.  After some bad experiences with the controls "washing out" on early kit-built stunters the Adamisin designs have all featured very "stiff" control systems.  I have seen airplanes with thin full span flaps where the pilots claimed they had no trouble making corners, yet if you held the tip of the flap rigid the root of the flap could move through some 20-30 degrees deflection with little resistance from the tips!  These guys were in effect achieving partial span flaps the hard way, though they were also the guys who had trouble flying in the wind.

Now the OPPOSING POV; most notably what Al Rabe has written here & other places about full span flaps.  Al maintains that the full span flap is necessary to maximize lift.  Note also that Al gets VERY insistent on have structurally rigid flaps, and likes LOTS of line tension - which would help him apply enough force to overcome heavy control loads.  Its tough to argue with the success of Al's designs, however I would suggest that the last couple of inches of the wing (including the full span flap) are not generating much lift due to the highly 3D flow of the vortex - I think he could cut an inch or three off his flaps and never miss it from the standpoint of lift, but the control feel would change a LOT - however I do not expect Al will be cutting off any flaps in the foreseeable future!

So now, back to your original statements including Paul Walker's experience:  I have been away for awhile and have not talked to Paul since...1985??!  Thus this is purely speculation; Paul has always used powerful set-ups and LOTS of line tension - the full span flaps probably help with the feel under high line tension - and helps him make an Impact!

Historically there have been losts of successful airplanes with full span faps and lots with partial span - ultimately the answer lies with the pilot.  For my part the only question I ever ask myself is how much to cut?

Ultimately I think the "best solution" might be really mundane.  When I read about people putting 51's (or more) into smallish airplanes like Cardinals & Tutors, I think what they are doing is gaining line tension to overcome heavy control loads or other trimmable problems.  Sure, it can work, at least while the line tension is there, but when the lines get loose (and they WILL), control authority diminishes - and these guys start looking for 60's or bigger to replace the 51's they are using in a 40 size airplane!  Thus I would suggest a better course of action would be to trim-out the bird in a low power mode, then apply engine power to your heart's content...
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline don Burke

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #2 on: July 28, 2007, 08:47:18 AM »
Dennis,

To me, you've made a very good explanation about tip vortexes affecting the flap load.   As far as steps to minimize the effect, I have wondered why more don't use swept back tips ala F1 racer NEMESIS instead of the "traditional" configuration.  The swept back tip is designed for exactly that purpose, minimize the effect of tip vortexes.  A swept tip combined with ending the flap at the last straight wing rib would accomplish the intended purpose.  That remaining portion of the TE outboard of the flap could be used as a fixed adjustable trim tab.

Or is it that no one has done it and won a major event, yet? (The chrome eagle principle)

don Burke AMA 843
Menifee, CA

Offline Jim Pollock

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #3 on: July 28, 2007, 10:51:09 AM »
Yo!  Steve,

I don't think so..... See picture below!



Offline RandySmith

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #4 on: July 28, 2007, 11:25:24 AM »
"""'The swept back tip is designed for exactly that purpose, minimize the effect of tip vortexes.  A swept tip combined with ending the flap at the last straight wing rib would accomplish the intended purpose.  That remaining portion of the TE outboard of the flap could be used as a fixed adjustable trim tab.

Or is it that no one has done it and won a major event, yet? (The chrome eagle principle)"""'


HI

What you just described  is  the  SV series  planes,  Vector  SV-11  etc.  They have all been that way  since the early 1980s.   If you  look at the  tips  on my  KATANA   SV-22  and  a  few  others  they have the  best tip design that I saw  when  wind tunnel  test were  being  ran on many many tip shapes.
This tip shape is  very similar  to modern Racing planes , The POND Racer used them and many others, Nemesis  used tips  that  although  more  scimitar  shaped  does  the  exact same thing.  You will also see them on some high performance Gliders
This  tip  produced  the  smallest vortices  and  had the  least amount  of parasitic  drag. I agree   with what Dennis  stated  about not moving the tips of the flaps.  I have tried it many times  both ways, and  the turn and  "feel"  is  better.  What i did end up doing  was  to calculate the full span flap area  then build that exact are into just the movable portion of the flaps.  That worked  much better  than  just cutting and  fixing the  ends.
Also I have  had  ZERO  problems  with the tips  moving or flexing.  many many planes at the NATs  have  used this  arrangement  for years, and  there has  been about 4500  SV  planes  built and  flown this  way

Regards
Randy

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #5 on: July 28, 2007, 02:44:31 PM »
Good feedback folks!

It would seem that the next logical step WOULD be to sweep the trailing edge of the tip back.  I have never done that and have been making some sketches.  Then I see the pix Randy posted and... THATS IT! BW@

Really should include the tail in this discussion too - for the same reasons.  Virtually every airplane I have built I used horn balances on the elevator - I now believe this was the wrong thing to do.  I learned in RC sailplanes that horn balances can actually reduce control effectiveness while creating a lot of drag.  What I should have done is cut the balance off the elevator and glued it to the stab.  Take that a step farther and copy (uhh, I mean reverse engineer) a shape similar to that Randy's Katana pix onto the now fixed stab tip.  I don't think I would make that fixed tip much more than 1 to 1.5" wide tho... old habits die hard!

 
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline phil c

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #6 on: July 30, 2007, 07:25:08 AM »
Given that planes with almost every concievable tip shape fly extremely well, I'd have to say that tip shape is more a matter of taste than any real aero advantage.  Randy, you'd have to publish some wind tunnel data on actual wings of model size with these tips showing how the performance improvement was measured.  Aerodynamic measurements are just too dependent on the actual size of the wing to scale well.  Just look at the data on wing thickness.  Thick wings work better on model sized wings, which was measured by NACA back in the 30's.  But some of the reports, corrected for wing span and tip effects, show that thinner wings have better lift/drag ratios.  Hence all the old-timers with thin wings.  Thin should fly faster, and the NACA reports appeared to confirm that, so all the better.   Unfortunately, it was a wrong.  Lots of modelers, and full scale designers, have made major errors trying to apply full scale data to smaller planes flying at lower Reynolds numbers.

Regarding cutting the flaps short of the tips, I believe Paul W. covered that in his Impact article.  When the flaps were shortened to get the tips of them out of the tip vortices the plane lost some lateral stability and had more wiggles in certain maneuvers.  This may be due to the fact that the flaps themselves generate their own tip vortices.  If the flap is just slightly shorter than the wing, 2-3 inches, you'd end up with two vortexes at each tip which could interfere with each other.  Separating the flap tips from the wing tip by 1/3 span or so keeps the vortices apart so they don't interact and makes shortening the flaps another tool for trimming the control feel to suit the pilot.
phil Cartier

steven yampolsky

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #7 on: July 30, 2007, 12:58:41 PM »
There are two points that I haven't seen anyone address in this discussion:

1) Deflected flaps lower wing's AOA. If flaps are fixed near the tips, that portion of the wing will be effectively stalled in a turn thus decreasing roll axis stability.
2) Fixing flaps near the tips while keeping elevator area the same, changes the flap-to-elevator lift ratio. Let me explain. Deflected flaps increases wing's lift. It also creates negative pitching moment. Stab and elevator are sized large enough to compensate for negative pitching of deflected flaps plus create positive pitch rotation. If a section of flaps are fixed, the amount of negative pitching moment is decreased. More of elevator's positive pitching moment is used to rotate the model(better corner).


Steve

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #8 on: July 30, 2007, 03:48:29 PM »
Sorry that is  just wrong, if you are directing this at my Airplanes

Randy, I am not directing my comments at your designs. I was rather thinking of clipped flaps in general. I think your designs are VERY well balanced. I also like wingtip shapes on your designs: tapered out tips prevent generated vortexes from reaching the wing's lifting surface.

The first portion of your  statement is  not  correct, the tips  are  not  stalled.  If the tips  were  stalled  you would  have  a bobble in the corners  where  the  wing would be  dropping.

Let me correct myself then. I did not mean the wingtips but rather outer portions of the wing that have fixed flaps. With that corrections in place, the parts of the wing without deflected flaps will stall before wing sections with flaps.

I have very carfully calculated the  flap area I need to match both weight and  ratio  of  elev.  flaps.  As long as the SV series is  built in the  given weight range  all is  good,  If it is  grossly heavy the flaps  need to be  increased in size or span.

I am actually thinking of tests where a flap sections were made fixed, decreasing overall flap area. This actually brings another quetsion. What's better: narrow full span flaps or wide half span flaps of the same area?



Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #9 on: July 31, 2007, 10:32:35 AM »
Steve H.  Looks like you got the DISCUSSION you were looking for!


Steve Y: If outer portion of the wing with fixed flap is at lower AOA then it is FARTHER from stalling than the flaped part, i.e. like using wash-out - not necessarily a bad thing.


Phil C: I agree that the differences between the "best" and "worst" wingtips is not very big - not likely to be the difference between success or failure.  However I think CLPA design has been refined to the point where all further "improvements" occur at the margins - and hopefully you line up enough directionally correct factors to yield a benefit.

I wish Paul W would check in, I would like to have him expand on his conclusions - what is described could easily be construed as a mini-stalling behavior caused by the now more ferocious corner.  I experienced that even with the Oriental, where when the corner was improved the bird started to stall - necessitationg a correction to the wing leading edge shape which solved the issue.


Steve Y. Short fat flaps versus long skinny ones - whew, now THAR's the rub!  Here's another one - do you think the flaps are there for LIFT or for DRAG?  I think the answer is mainly for lift - but the drag does not necessarily hurt either!  For the reasons I laid out I will never consider using FULL span flaps.  I have wondered about using relatively narrow flaps with a LOT of throw - maybe 3:2 versus elevator (insted of the "normal" 2:3 or 1:1) to increase the drag component.  If using wide flaps I would want to restrict the deflection - and probably get a GREAT lift component.  Wide flaps and a lot of throw sounds like too much control effort.

SO many ideas, so little time...!

Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

steven yampolsky

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #10 on: July 31, 2007, 12:04:57 PM »
Steve Y: If outer portion of the wing with fixed flap is at lower AOA then it is FARTHER from stalling than the flaped part, i.e. like using wash-out - not necessarily a bad thing.

Dennis, I wrote that deflected flaps lower AOA, not fixed flaps. To be honest I don't remember the reason why( think it has to do with ability of a wing to develop lift beyond 10-12 degrees AOA). I am drawing this from memory when I flew full size airplanes.
Full size airplanes use flaps to keep the wings from stalling. They also use thicker airfoils at the tips. So, say if you were to use NACA 22% airfoil at the root and NACA 28% at the tips, regardless of the shape of the wing(tapered or straight), the 22% section will stall before the 28% one.

Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #11 on: July 31, 2007, 10:29:41 PM »
Yo Steve!  glad to offer my opinion, unfortunately a LOT of electrons will be sacrificed in the process, I do not know how to answer this curtly.  There are a lot of facts, factors and "factoids" that play into this discussion.  Hope I can do them justice while keeping it as brief as possible.  Also I have shamelessly dropped some names in this piece, hope those folks chime in too to add or subtract to what I said about their experiences!

First the premise: When a wing produces lift it sheds vortexes (mini-tornados) of air off the wing tips.  The vortex is relatively high energy air with curling, highly 3 dimensional flow.  If you have a control surface like a full-span flap or aileron in the vortex then you have to turn that vortex when you deflect the control surface, but the vortex resists getting turned!  Result for the CLPA flyer, you get a very "heavy" feel, and probably a hard time doing a decent square corner.  If you cut off the flaps you miss the vortex, and improve the control effort and corner.

If you have ever heard about people doubling up the number of hinges at the tips of their flaps - they did it because the tip vortex was beating the heck out of the hinges at the tips of their full span flaps!

HI DENNIS (ALL CAPS TO DIFFERENTIATE BETWEEN DENNY'S COMMENTS AND MY OWN)

INTRIGUING STUFF, ESPECIALLY THE COMMENTS ABOUT THE EFFECTS OF VORTICES ON FLAP LOAD.  HAVE TO ADMIT I'D NEVER CONSIDERED THAT ASPECT.

I'M NOT SURE I AGREE, HOWEVER, THAT SHORTENING THE FLAPS TO LESS THAN FULL SPAN WOULD COMPLETELY ELIMINATE ANY SUCH EFFECT ON CONTROL LOADS.  OUT HERE ON FLYING CLOUD ISLE IN FOSTER CITY WE GET TO WATCH HUNDREDS OF AIRLINERS APPROACH SFO EVERY DAY (ONE'S JUST GOING BY OUTSIDE MY DEN DOOR RIGHT THIS SECOND).  THE BAY AREA ALSO HAS A COMMON WEATHER PHENOMENOM OF COASTAL STRATUS MOVING IN AND OUT MOST EVENINGS.  THIS RESULTS IN AN AIR MASS READY TO FORM CLOUDS AT THE LEAST PROVOCATION.

JUST SUCH A PROVOCATION ARE THESE LOW FLYING AIRLINERS WITH GEAR AND FLAPS OUT STARTING THEIR FINAL APPROACH.  I HAVE SEEN LITERALLY HUNDREDS OF EXAMPLES OF "VISIBLE VORTICES" TRAILING OUT BEHIND THESE SHIPS OVER THE 35 YEARS WE'VE LIVED HERE.  WHAT IS PARTICULARLY IMPRESSIVE IS SEEING THE "DUAL" VORTICES OFF OF EACH WING ON HEAVILY LOADED SHIPS, ESPECIALLY 747S.  THE DUAL VORTICE IS THE RESULT OF ONE FORMING AT THE WINGTIP (WELL OUTSIDE THE FLAPS) AND A SECOND FORMING RIGHT AT THE OUTER EDGE OF THE EXTENDED FLAPS THEMSELVES.  BECAUSE THE EXTENDED FLAPS ARE WELL BELOW THE "UNFLAPPED" OUTER WING WHICH CONTAINS THE AILERONS, THERE ARE, IN EFFECT, TWO WINGS; A HIGHLY CAMBERED ONE FROM THE WING ROOT TO THE END OF THE OUTBOARD FLAP (747S HAVE TWO FLAP SEGMENTS, INBOARD AND OUTBOARD; BOTH OF WHICH ARE IN THE INNER ONE HALF OR SO OF THE WING SPAN); AND A "SECOND" UNCAMBERED WING OUTBOARD OF THE FLAPS.  BOTH PRODUCE THEIR OWN DISTINCTIVE VORTEX.

THERE IS A VERY PROMINENT VORTEX AT EACH LOCATION.  ALTHOUGH I HAVEN'T EQUIVILANT "EVIDENCE" OF THE SAME SORT OF THING WITH PARTIAL SPAN STUNT FLAPS, THERE IS NO REASON TO THINK THE SAME EFFECT WOULDN'T EXIST.  PERHAPS YOUR WIND TUNNEL EXPERIMENTS SHOWED A DIFFERENT RESULT.  I'D BE INTEREST TO KNOW IF YOU EXPERIENCED IT.

In his article on the Olympic, there was a side bar to the main article where Bob Gialdini advised that lengthening the flaps (versus the design as published) would result in a slower corner and smoother flight.  About this time my brother had built a Nobler modified to mimic the Olympics.  His bird was very heavy and needed all the lift it could get, however, as built with full span flaps, the bird couldn't get out of its own way and would scarcely turn a round loop under 45 degrees.  He cut off about 5 inches of flap and the bird got CORNER.  It was still too heavy though...

As I reported here in StuntHanger, my Oriental ARF as built with full span flaps flew nice but had a propensity for 88 degree square corners - it was hard to pull on it hard enough to get a decent square.  I cut 4" off the flap and the bird got corner, so much in fact that I had to then go and round off the leading edge to prevent it from stalling!  Then I built the Cardinal (also reported here in the Hanger), and did not bother waiting to fly before cutting off the flaps and rounding the LE, and it flies great.  Thge Cardinal was also the first time I set-up the cut off portion of the flap as a trim tab - of course the wing is dead straight and no tab was required!

Before I built the Oriental I noted that several folks in the StuntHanger reported better corners after they reduced the flap throw, and I surmise, reduced the effect of the vortex on the flap.
 
So HOW MUCH do you cut?  Certainly, the experience Ted Fancher documented on his Imitation article is the BEST practical knowledge out there.  If you haven't seen that I will try to summarize:  Ted built the Imitation with segmented flaps, whereby he could change the span of the flaps.  He reported that the shorter span flaps allowed the Imitation to turn harder corners, but loss of "feel" cost him precision in round maneuvers.  His conclusion was that "too much was probably better than too little" flap span.  However, even his "full span" flap config actually stopped at the swept wing tips - so he was likely still out of the trailing vortex - or at least missing the worst of it.  I never asked Ted if he did this, however it might have been feasible to get back the FEEL with the short flaps if you also change ratios and added flap throw.  I think the extra throw would manifest itself as drag - more than lift - and it MIGHT help prevent wind-up in maneuvers???

YOU'RE RIGHT, DENNY, THE IMITATION DIDN'T HAVE FULL SPAN FLAPS.  THE TIPS (VERY MUCH LIKE THE SHAPE ON RANDY'S VECTOR SERIES) ARE SWEPT FOR ENHANCED ASPECT RATIO EFFECTS (AND  I LIKE THE LOOK OF THEM!)  THE ONLY SHIP I'VE FLOWN IN THE LAST NUMBER OF YEARS WITH FULL SPAN FLAPS WAS THE REFINISHED FINAL EDITION ON WHICH I LENGTHENED THE FLAPS TO FULL SPAN BECAUSE I WAS CONCERNED ABOUT WING LOADING.  TODAY, I FEEL THAT CONCERN WAS MISPLACED.  FWIW, THAT SAME AIRFRAME WON THE NATS WITH THE PARTIAL SPAN VERSION IN 1995 (WHEN IT WAS A RED, WHITE AND BLUE "GREAT EXPECTATION") AND AGAIN ONE YEAR EARLY IN THE NEW CENTURY WITH THE FULL SPAN FLAPS AND THE PURPLE "POND SCUM" PAINT JOB.  AS YOU STATE, FLAP SPAN ISN'T A DEAL BREAKER EITHER WAY.

AS YOU STATED, HOWEVER, I'M FIRMLY IN THE CAMP OF THOSE WHO AGREE WITH THE INCREASED RESPONSIVENESS OF PARTIAL SPAN FLAP CONFIGURATIONS ... ASSUMING ADEQUATE LIFT CAN BE GENERATED BY THE LESSENED "CAMBERED" SPAN THAT RESULTS.  I DO BELIEVE, HOWEVER, THAT THE INCREASED RESPONSIVENESS IS THE RESULT OF A REDUCED NEGATIVE PITCHING MOMENT THAT RESULTS FROM LESS OF THE SPAN BEING EQUIPPED WITH FLAPS.  I HADN'T PREVIOUSLY CONCERNED THE FLAP LOADS ASSOCIATED WITH VORTICES AND WILL HAVE TO GIVE THAT SOME THOUGHT (WHILE STILL REMEMBERING THE DUAL VORTICES I SEE OUT OUR FRONT WINDOWS)

I STRONGLY BELIEVE THAT, WITH MODERN POWERPLANTS, MANY OF OUR HISTORICALLY LOW WING LOADING DESIGNS PRODUCE WAY MORE LIFT THAN IS NECESSARY TO SUPPORT THE SHIP IN EVEN THE TIGHTEST CORNERS WE CAN FLY RELIABLY CLEANLY.  GREAT ADVANTAGES CAN BE OBTAINED BY REDUCING THE AMOUNT OF THE WING WHICH IS FLAPPED AND THUS INCREASING THE PITCH RATE OBTAINABLE WITH LESS CONTROL INPUT (WHILE STILL PRODUCING THE LIFT REQUIRED TO CARRY THE AIRPLANE IN THE HIGH G CORNER).

I'M VERY MUCH IN YOUR CORNER IN TERMS OF USING NO MORE FLAPPED SPAN THAN NECESSARY TO PRODUCE THE LIFT REQUIRED FOR THE TIGHTEST CORNERS THE PILOT CAN FLY WITH PRECISION.

A tangent: I have built birds with partial span NARROW CHORD flaps that were almost unflyable - NO feel whatsoever!  However, also note that narrow chord does not get you out of the vortex, only shortened span.

WE VERY MUCH AGREE ABOUT THE VIRTUES OF FLAP DEFLECTION FOR INCREASED CONTROL FEEL.  I BELIEVE THE GREATEST PART OF THAT FEEL IS THE RESULT OF THE NEGATIVE PITCHING MOMENT OF THE CAMBERED SURFACE (PLUS, OF COURSE, THE RAW CONTROL LOADS ASSOCIATED WITH MOVING A LARGE SURFACE AGAINST THE AIRFLOW)AGAIN, I'D HAVE TO BE CONVINCED THAT THE VORTEX DOESN'T STILL EXIST AT THE END OF THE FLAP, REGARDLESS OF HOW MUCH UNFLAPPED SPAN CONTINUES OUT TO THE TIP (WHERE THE PRIMARY VORTEX WILL STILL EXIST).

One more big factor at work: structural rigidity of the flaps.  After some bad experiences with the controls "washing out" on early kit-built stunters the Adamisin designs have all featured very "stiff" control systems.  I have seen airplanes with thin full span flaps where the pilots claimed they had no trouble making corners, yet if you held the tip of the flap rigid the root of the flap could move through some 20-30 degrees deflection with little resistance from the tips!  These guys were in effect achieving partial span flaps the hard way, though they were also the guys who had trouble flying in the wind.

AGAIN, WE'RE IN PRETTY MUCH TOTAL AGREEMENT.  IT IS WORTH NOTING, HOWEVER, THAT THE BERRINGERS HAVE BEEN VERY SUCCESSFUL USING "FUNGIBLE" TINY FLAPS ON THEIR WORLD CHAMPS PEDIGREED DESIGNS.  I DON'T NECESSARILY AGREE WITH THAT APPROACH BUT CAN'T ARGUE WITH THEIR SUCCESS.

Now the OPPOSING POV; most notably what Al Rabe has written here & other places about full span flaps.  Al maintains that the full span flap is necessary to maximize lift.  Note also that Al gets VERY insistent on have structurally rigid flaps, and likes LOTS of line tension - which would help him apply enough force to overcome heavy control loads.  Its tough to argue with the success of Al's designs, however I would suggest that the last couple of inches of the wing (including the full span flap) are not generating much lift due to the highly 3D flow of the vortex - I think he could cut an inch or three off his flaps and never miss it from the standpoint of lift, but the control feel would change a LOT - however I do not expect Al will be cutting off any flaps in the foreseeable future!

I THINK I'D BEST NOT COMMENT ABOUT MY DIFFERENCES WITH AL REGARDING FLAPS AND FLIGHT TRIM.  SUFFICE TO SAY I'D STAND RIGHT BEHIND YOU AS YOU DEBATE WITH HIM.

So now, back to your original statements including Paul Walker's experience:  I have been away for awhile and have not talked to Paul since...1985??!  Thus this is purely speculation; Paul has always used powerful set-ups and LOTS of line tension - the full span flaps probably help with the feel under high line tension - and helps him make an Impact!

Historically there have been losts of successful airplanes with full span faps and lots with partial span - ultimately the answer lies with the pilot.  For my part the only question I ever ask myself is how much to cut?

Ultimately I think the "best solution" might be really mundane.  When I read about people putting 51's (or more) into smallish airplanes like Cardinals & Tutors, I think what they are doing is gaining line tension to overcome heavy control loads or other trimmable problems.  Sure, it can work, at least while the line tension is there, but when the lines get loose (and they WILL), control authority diminishes - and these guys start looking for 60's or bigger to replace the 51's they are using in a 40 size airplane!  Thus I would suggest a better course of action would be to trim-out the bird in a low power mode, then apply engine power to your heart's content...

BOY, WE REALLY AGREE ON THESE COMMENTS.  BRETT AND I WORKED WITH YOUNG PAUL FERRELL TO HELP HIM MAKE HIS CARDINAL MORE USER FRIENDLY WITH A MUCH SMALLER ENGINE.  INADEQUATE LINE TENSION TO DEFLECT THE CONTROLS WAS A BIG PART OF THE REASON PAUL WAS HAVING TROUBLE FLYING REPEATEDLY GOOD MANEUVERS.  GIVEN THE SMALLER ENGINE AND THE MODEST LINE TENSION AVAILABLE, WE APPROACHED MODIFYING THE AIRPLANE BY REDUCING THE SIZE AND DEFLECTION OF THE FLAPS.  WE REDUCED THE THROW TO THE MINIMUM AVAILABLE WITH THE HORNS ON BOARD AND, FRANKLY, WHACKED 3/4" OFF THE TRAILING EDGE OF THE FLAPS.  THE RESULTING AIRPLANE HAD MORE THAN ENOUGH LIFT TO CARRY IT THROUGH PATTERNS THAT WERE NOW SMALLER AND MORE PRECISE THAN ACHIEVABLE WITH THE "STOCK" LARGE AREA FLAPS.  WE DID NOT REDUCE THE SPAN SIMPLY BECAUSE IT WAS EASIER TO TRIM THE TRAILING EDGE AND THEN RE SEAL THE MONOKOTE COVERING.

THE RESULT WAS A VERY FLYABLE AIRPLANE WITH MODEST BUT ADEQUATE LINE TENSION THAT DID PAUL VERY PROUD DURING THE WALKER FLYOFF AFTER HIS VICTORY IN SENIOR IN 2006.

GREAT THREAD!

TED FANCHER


Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #12 on: July 31, 2007, 10:59:34 PM »
Dennis has mentioned modifying several ARF's by clipping and fixing the tips of the flaps, I think making them into adjustable tabs. Maybe...but I'd have to go check those threads. Stated purpose and result is said to be reduced control handle loads (i.e., "power steering") required to turn the model.

I find this interesting...and puzzling...as I have personally heard PW state that he tried that and returned to making the entire flaps moveable. Also, have read that Ted Fancher did the same experiment, and also preferred the entire flaps moveable, and returned to that setup. I am not 100% certain what their objections were, but I think consistency, possibly caused by the adjustable tabs flexing in difficult conditions, but I'm just not sure. I do not want to 'start something', just seek enlightenment... HB~> ouch! HB~> ouch! HB~> ouch!  H^^ Steve

Only partially correct, Steve.  I did, in fact make the flaps on the long lived Final Edition (nee Great Expectation) full span when I installed a new vertical stab and refinished some of the "pond scum" paint job.  This was an experiment after flying David Fitz' Stargazer (a "similar" design) equipped with full span flaps that was able to turn well controlled corners somewhat tighter than mine.  The results were inconclusive and I've reverted back to the partial span preference on the few ships I've worked with since.

It's my opinion that stunt guys overthink the flap thing.  I've stated before and will reiterate, flaps are nothing more than parts of the wing that happen to be hinged so as to allow the airfoil to change camber, thus modifying the lift of which the flapped part of the wing is capable with a given angle of attack.  Their primary value is allowing the designer/pilot to obtain the lift required for flying high g maneuvers from a smaller overall area.  An additional advantage is  the resulting negative pitching moment which allows airplanes with a further aft CG to retain control feel without needing to be "nose heavy" to do so.  A distinct advantage in high winds.

This combination of factors allows the informed designer to balance the size of the wing itself with the size (chord or span, in my estimation ... within practical reason) of the flaps to produce a ship which provides adequate but not excessive lift (yes, Martha, there is such a thing as excessive lift for precision flight) and provides the control feedback desired by the pilot for precision control of the pitch rate of the airplane while he does the tricks.

I further think there is merit in the use of flaps to reduce the area of the wing necessary to produce the required lift.  The bigger the wing the greater the effect upon it of high winds and turbulence.  If the required lift can be produced by a smaller overall surface area the controlability of the airplane will be improved under adverse conditions.   This, I believe, is the primary advantage of a flapped stunt ship, a smaller wing necessary to fly a higher weight competitively.

Ted

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #13 on: August 01, 2007, 07:40:51 PM »
Hmm I posted a reply here a few hours ago, must have been lost when the site went down...?

Ted:
NO DOUBT the dual (or more) vortices exist.  I think by shortening the flap then you only have to carry THAT vortex on the flap, plus the one that exists at the flap ROOT.  I am supposing that the flap vortex by itself is significantly less energy than the flap and wing vortices together... that make sense?

No doubt you are also right about the negative pitching moment - but I cannot get a handle on how powerful that is.  For example, when I was flying RC sailplanes with flaps, ANY input of flap required corrective DOWN elevator to keep from ballooning.  BTW just a couple degrees of flap on a sailplane has a big effect on minimum sink or maximum GO!

I also wanted to mention that one reason I may be more sensitive to cutting down the flaps is that traditionally have flown stuff on the botttom end of the power spectrum  For Instance, the Walker Cup winning Magister carried 54 oz on 630 squares and used a OS S35.  This is not too far from Randy's birds at 675 squares - but I think he is using a little more power (like maybe 100% more!) than I did!

Come to think of it, the Oriental with the LA 40 is probably the MOST powerful CLPA bird I've ever had!  LL~
Denny Adamisin
Fort Wayne, IN

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Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #14 on: August 02, 2007, 12:52:57 PM »
Hmm I posted a reply here a few hours ago, must have been lost when the site went down...?

Ted:
NO DOUBT the dual (or more) vortices exist.  I think by shortening the flap then you only have to carry THAT vortex on the flap, plus the one that exists at the flap ROOT.  I am supposing that the flap vortex by itself is significantly less energy than the flap and wing vortices together... that make sense?

No doubt you are also right about the negative pitching moment - but I cannot get a handle on how powerful that is.  For example, when I was flying RC sailplanes with flaps, ANY input of flap required corrective DOWN elevator to keep from ballooning.  BTW just a couple degrees of flap on a sailplane has a big effect on minimum sink or maximum GO!

I also wanted to mention that one reason I may be more sensitive to cutting down the flaps is that traditionally have flown stuff on the botttom end of the power spectrum  For Instance, the Walker Cup winning Magister carried 54 oz on 630 squares and used a OS S35.  This is not too far from Randy's birds at 675 squares - but I think he is using a little more power (like maybe 100% more!) than I did!

Come to think of it, the Oriental with the LA 40 is probably the MOST powerful CLPA bird I've ever had!  LL~

Good thoughts, Denny.  Here's my take on some of them.

My guess is that the vortex is the result of all of the lift up to that point of the wing span.  The vortex is the result of high pressure air on the bottom of the wing trying to get to the low pressure on the top of the wing.  The "vortex" is, I believe, the result of the natural spanwise flow of the air (air doesn't go straight parallel to the fuselage but tends to move towards the tips).  Because of that spanwise movement the "low pressure" the air is seeking is back towards the fuse.  The fact that the airplane is constantly moving forward combined with this "inward" movement makes the spiral.  I can't quantify or send you to a source off the top of my head but I think it is logical to expect the vortex at any point of the span to be the result of the air pressure change up to that point.

The effect of flaps on pitch has been discussed on the forums a number of times and your response is always one of the confusing factors.  Negative pitching moment is, in fact, a significant factor.  Just make a flying wing out of any old flapped clunker you've broken the fuselage on.  Such a  "flying wing" maneuvers in the pitch axis solely based on the pitching moment of the cambered airfoil that results when we deflect the flaps (except we now call them elevators 'cause the tail's gone!). 

The fact that the sailplane pitches up when flaps are extended is the result of a different aerodyamic reality that takes place when flaps are deflected.  Lowering flaps changes not only the camber of the airfoil but also its angular relationship to the stabilizing surface.  The net effect is increased decalage between the two.  Thus, when you drop the flaps, the angle of attack of the wing increases proportionately to the flap extension while that of the tail does not.  The tail is, in effect, applying "up" elevator to the airframe itself and the nose will pitch up in response. 

The other thing that happens is that drag increases and the airplane will gradually slow and the effect of the increased decalage on the vertical flt path will be different.  Generally speaking the body angle will moderate and the airplane will either slow down to maintain the desired altitude or, if the airspeed is maintained (without power adjusstment) the ship will descend.

The initial pitch reaction in any case is a function of the angular change between the lifting surface and the stabilizing surface when the flaps are deployed.

Oh, boy.  I well remember your slightly horsepower challeged long wing stunters.  I could almost feel you cringe when big Art would "richen" up the needle on that sweet little OS so you'd have to "work just a bit harder".  By the way, I bet there's more than coincidence between your comments about the efficiency of camber changes on sailplanes and your use of high aspect ratios on your large area but "lower than modern" horsepower attached to the nose of them.

Am I wrong?

Ted

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #15 on: August 02, 2007, 06:14:42 PM »
Ted:

Actually, as I recall when you first saw the long-winged Orange Crate you asked "Where's the tow hook???  LL~

Exploraion of the higher AR came from a need to go somewhere I had not gone before.  The AREA was "normal" (567 squares vs prior designs 580) but the area was spread over a longer span.  The trump card was better span loading, but I just built the durned things too heavy! pull the nose up and its just HP versus gravity!

Your description of sailplane trim is spot on.  Implicit in that is when re-trimmed with the flaps deployed, the fuselage assumes a nose-down inclination versus the no-flap trim condition.  I guess I always thought the pitching moment would have a more powerful effect - but then the effect from the stab (the up elevator you described) probably overpowers the flap PM, especially on a long-tailed sailplane...

I'm going to dig through some of the aero books and see what I can find about the effect of flaps on spanwise flow!  I know I am a little concerned about it on my next-on the board Sheeks Swinger with the swept wing!  BTW that thing calls for full span narrow chord flaps.

Ah yes an S35 with a 10-6EW, tuned to fly 6+ second laps to "make him work".  Looking back I think both the best part AND the biggest problem with that set-up was that it was completely refined and locked-in; I was using EVERYTHING available without a lot of room to maneuver as far as alternate props, fuels, & what not.  As you know I always had trouble building light enough to give me some tunable features.

BTW, I'm trying to resurrect the 33 YO TriStar that I flew at the 1974 NATs.  I think that makes it a contemporary of - Moby Dick?  So far I ripped out the original LG and the built in and rusty fuel tank.  Discovered some oil soaking that has to be fixed - gonna take some work to set it all right.  Anyhow, if I may invoke that immortal phrasing, I'm looking forward to flying the "Charles Atlas-ized" TriStar!

BTW, you folks DO have sealed hingelines as standard equipment, right???   mw~
Denny Adamisin
Fort Wayne, IN

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Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #16 on: August 02, 2007, 09:12:13 PM »

BTW, you folks DO have sealed hingelines as standard equipment, right???   mw~


Just so you know, Denny.  After that lunch you and I shared a hundred or so years ago I've gone to sealed hingelines off the board and never looked back.  Not only that, whenever I wrote about sealing hinge lines for "publication" I don't believe I've ever failed to give you credit for slapping me in the fact with the obvious.  Don't know if you recall but I'll bet my face got that deer in the headlights look when you first brought up the subject.  In other words, why on earth would anyone "ever" build a ship intended maximize control surface lift for maneuvering and "NOT" seal the hinglines.  A total "no -brainer" which apparently perfectly describes my mental state prior to that lunch.

Shoot, I even sealed them on the Strega for the Great American ARF OFF.  Don't know if Uncle Jimby caught that "extra effort" or not. 

Ted

P.s. by the way, if you've still got one of those long winged critters hanging around, put in something like Randy's ultra light .40 and watch it come alive.  As you know, the long winged things produce the lift they need at lower angles of attack and, with just a touch more "poop", the vertical issues go away.  Could be a world beater, or at least a nats beater ... again.

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #17 on: August 03, 2007, 03:55:51 PM »
Ted;
Yup, I've been sealing the hingleines on the Brodak ARF's too.  Don't know if they really need it & DON'T CARE!  I consider the hinge seal to be just as fundamental as making the surface movable in the first place.

I don't remember you having a deer in the headlights look, but I do remember your tail was draggin because you had just lost a promising new bird and were really dissappointed to have to go back to a bird you really did not like.  I also remember seeing you a few weeks later at the NATs grinnin like the proverbial cat wot got the canary!  YES you were generous with your praise, but the real discoverer was my brother Arch who sealed up my first Eclipse to get it to fly.

If/when I can resurrect the old TriStar I want to fly that without (as built in 1974) and with seals.  Has kinda always bothered me WHY it took us (collectively) so long to "discover" seals, and how many birds I have flown without seals that could have been just a little bit better!

Ditto the power-up.  Eclipse 3 is still hanging in Big Art's basement and is stilll in great shape - but it is 24 years old.  Also has a built in 3.5 oz non-uniflow tank.  Do I try to salvage or start anew?  When I built that one I cut out TWO sets of ribs & spars...!

Sorry all, seems I have wandered WAY off the thread... :-[
Denny Adamisin
Fort Wayne, IN

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Offline Larry Wong

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #18 on: August 03, 2007, 07:39:51 PM »
Ok Guys what do you use to seal hinge line and do you do both elevator and flaps? every time I try to seal hinge line the controls seem tight. HB~>  ???
Larry

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Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #19 on: August 04, 2007, 10:53:33 AM »
Ok Guys what do you use to seal hinge line and do you do both elevator and flaps? every time I try to seal hinge line the controls seem tight. HB~>  ???

Hi Larry,

I use Crystal Clear packing tape.  It comes in appx three inch widths and the package is green and white at OSH.  I pull off a couple of feet of it and stick it to my glass topped work bench.  I cut it in appx one inch strips and then cut individual chunks of each strip to fit "between" the hinges on every hinged surface I can find!  Do NOT put the tape over the hinges.  It will stick to the hinges and disrupt control movement.  The tiny unsealed percentage of hinge gap that remains isn't worth worrying about.

As you state, you must be careful that the tape doesn't interfere with smooth operation anywhere else as well.  Here's my method.

With the airplane upside down, I use a good sized rubber band wrapped around the tip of the stab and elevator to hold the controls fully deployed in the proper direction to open up the desired hingeline for sealing (full up elevator to seal the elevators and full down to seal the flaps).  I cut a piece of reasonably thick balsa, a couple of inches wide, at an angle so it has a wedge shape end-grain end with an angle to it.  The angle needs to be sharp enough that you can push the wedge completely into the open hinge line.  This is used to force the tape as deep as possible into the hinge spacing. 

Take up a proper sized section of tape and carefully let it touch the most convenient surface, i.e. either the stab or elevator and as parallel as possible to the hingeline itself for neatness.  While holding the opposite edge of the tape lightly to keep it from touching the other surface, take your wedge of balsa and push the tape down into the hingeline completely.  You'll sometimes find it trying to attach to the other surface but usually a firm push with the wedge will detach it and allow the tape to go into the hingeline as desired.  Now, simply push the wedge forward against the second surface to attach it.  Roll the remaining tape onto the second surface so it adheres with no air bubbles (again, for neatness).

The next step is important ... and a bit of a pain.  After EACH segment is attached, remove the rubber band and test the controls for binding, sticking or "noise".  If there is any resistance -- do it over again.

You'll find that you'll get pretty good at this and doing a whole airplane won't take more than an hour or so.

Ted Fancher

Offline Peter Germann

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #20 on: August 05, 2007, 10:04:38 AM »
3M makes the ultrathin tape I'm using to seal hinges since a long time. Never had it come off or break:

850 Polyester Tape  Trans.  D.C. Part No 021200-0741
Roll 1 in x 72 yd
Thickness is 2/1000 in or 0.06 mm

regards,
Peter Germann

Offline don Burke

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #21 on: August 05, 2007, 10:09:53 AM »
Re: tape, the electric foamies use a clear tape that conforms really nicely to the surfaces and gaps.  It's a lot more flexible than the packaging tapes.  It's sold in one form by DU-BRO.
don Burke AMA 843
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steven yampolsky

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #22 on: August 06, 2007, 03:24:00 PM »
Re: tape, the electric foamies use a clear tape that conforms really nicely to the surfaces and gaps.  It's a lot more flexible than the packaging tapes.  It's sold in one form by DU-BRO.

I used this tape on my last model and found it to be too thick to the point where it interfered with controls. I had to re-tape everything with regular packing tape.

Offline Steve Helmick

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #23 on: August 16, 2007, 10:00:35 PM »
Yo!  Steve,

I don't think so..... See picture below!



I think that was one of the Sweden Impacts (early '90's), and that was about the time PW was experimenting with the tabs vs. full span flaps. In my view, the wingtips might be very important on this flap span issue. The Impact tips look to me like they'd create a fairly large vortex, anyway. Paul is always experimenting with his old planes. They're stacked around the shop like some folks would have combat models...I'd guess at least 20 useable airframes...two being B-17's....  y1 Steve
« Last Edit: August 18, 2007, 08:41:51 PM by Steve Helmick »
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Offline proparc

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #24 on: August 18, 2007, 03:42:45 PM »
This is superb stuff Dennis D>K

Someone say - Ed Southwick?
Milton "Proparc" Graham

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #25 on: August 18, 2007, 09:21:43 PM »
This is superb stuff Dennis D>K

Someone say - Ed Southwick?

Milton:

...or Lew McFarland!  Palmer seems to have had some both ways...

BTW, the thread wsa Steve Helmicks idea, all the kudoes to him. CLP**
Denny Adamisin
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Offline Dick Fowler

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #26 on: August 19, 2007, 10:49:14 AM »
I'm surprised that nobody is using the "Windex"  or wet method for hinge sealing tape. Works the same way that it does for Monokote trim. Slide the tape into place and squeegee the liquid out from under the tape.
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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #27 on: August 21, 2007, 01:21:26 AM »
Dennis and Ted,

   Great discussion you have going here.  Please indulge me as I share some thoughts that have been buzzing around in my head ever since I took aerodynamic courses at Park’s Air College about 25 years ago. 

   I’ve been modeling since I was 7 or so and have been involved in stunt since the late 70’s although family and career have slowed my involvement over the last 10 years.  Your discussion here has rekindled many thoughts and ideas that I have wanted to share and discuss since reading my first Stunt News I the early 80s.  I just never took the time to put them down in written form and now these forums (and spell check) have taken away my last bastion of excuse!

   A common trend I have seen throughout my modeling life is that we are very effective at analyzing what our airplanes are doing but not as effective at determining why they behave as they do.  Now, I am not the leading expert in aerodynamics and stunt ships but I do want to share some of my thoughts on flaps, what they do, what they don’t do and why.  I hope that this discussion will correct some misconceptions and be beneficial to all in trimming and design.


Dennis:  First the premise: When a wing produces lift it sheds vortexes (mini-tornados) of air off the wing tips.  The vortex is relatively high energy air with curling, highly 3 dimensional flow.  If you have a control surface like a full-span flap or aileron in the vortex then you have to turn that vortex when you deflect the control surface, but the vortex resists getting turned!

Dennis, I agree with everything except one statement:  the vortex does not have to be turned. These vortexes induce drag and they rob lift by decreasing the effective wingspan, but they do not apply any forces that resist pitch.  Take a look and a video of an F-16 or other high performance fighter performing extreme high alpha (high angle of attack-AOA) maneuvers.  Many have smoke generators on the wingtips that exaggerate the visual effects of the vortices.  These vortices flow straight away from the wingtips at varying angles to the cord line depending on the AOA.  There is no curve to them indicating a resistance to pitch or rotation.  In essence, air that is already behind the wind can not exert a force on that wing.  A deflected flap will change the pressure differential between the top and bottom of the wing (the source of the vortex) and increase the magnitude of the vortex.  The vortex will also decrease the effectiveness of the flap but I do not see there being a resistance to flap movement.  Only a minute percentage of the flap’s effective area would be affected.

Steven:   Deflected flaps lower wing's AOA. If flaps are fixed near the tips, that portion of the wing will be effectively stalled in a turn thus decreasing roll axis stability.

Steven:  You are on the right track but think you remember this backwards. 

Let’s go over a few flap basics.

Pitch angel:  This is the angle between the flight path and the longitudinal axis of the airplane (the thrust line if you will).

Angle of attack – this is the angle between the relative wind –RW-(the flight path of the airplane) and the chord line of the wing.

Chord Line:  This is a line drawn from the center of the leading edge profile (the LA center line on our symmetrical stunt wings) and the trailing edge of the wing.  With the flaps in neutral, this line is the same as the center line of the airfoil as seen on the plans.  With the flaps deflected 45 degrees down, it is still defined by a straight line between these two points, but now the line is angle down.  Go to your plans and draw the flap fully deflected.  Then draw a line from the forward most point on the LE to the TE of the flap.  This is the chord line for full flap extension.  Flap deflection increases the camber of the wing by lowering the TE.

Assuming that the fuselage remains at the same angle (the relative wind does not change) deflecting the flap increases the angle between the RW and chord line, thus increasing the AOA.  This is how the flaps increase lift. 

There are only 2 ways to get a given wing to produce more lift.  You can increase the speed or increase the angle of attack. As a rule we try to avoid significant increases in speed during our maneuvers.

 AOA can be increased be increasing the pitch angle and by increasing the camber of the wing without increasing the pitch.  Notice how your flapless OTS design can be landed in a very nose high attitude after the engine dies?  As airspeed slows, you have to increase the AOA to maintain the same amount of lift.   We do this by increasing pitch.  On a flapped airplane, we increase camber by defecting a flap, also increasing the AOA.   In a square corner, we actually do both, increase both the pitch and the camber.

With the above being said, any flapless portion of the wing outboard of the flaps will have the same AOA as the flapped portion only when the flaps are neutral.  If the flaps are deflected any amount, the flapless tip will always have a lower AOA.  This may be beneficial as I will cover below.


Dennis:  I wish Paul W would check in, I would like to have him expand on his conclusions - what is described could easily be construed as a mini-stalling behavior caused by the now more ferocious corner.  I experienced that even with the Oriental, where when the corner was improved the bird started to stall - necessitating a correction to the wing leading edge shape which solved the issue.

There is no doubt that we can force or planes into an accelerated stall without too much difficulty with predictable results – the flight path will be unpredictable!  The question I have is what part the wing is actually stalled.  Is it the root, the tip or the whole wing?   This is an aspect of flap design that I am surprised to have never seen addressed.

Any wing will always stall at the same AOA regardless of the airspeed.  This is called the critical angle of attack.  Going back to our flapless OTS example, it does not matter if you stall the plane in level flight with the engine dead, 5 feet above the ground and barely moving on the upwind side of the circle or if you stall it in a blinding corner at over 60 mph.  The wing stalls both times at the same AOA. 

On a flapped plane, every time you change the flap deflection you change the camber and in effect have “new” wing.  However, for any given flap deflection, there is an associated critical AOA that never changes regardless of the airspeed.

Full size aircraft such as the Cessna singles are built with significant amounts of wash out in the wings.  The wing is actually twisted slightly from the outboard end of the flaps to the tip.  The LE is lower at the tip and the TE is higher.  The result is lower chord line at the tip compared to the root.  In a stall, the root with a higher angle of attack stalls first, with all the associated warning signs while the outer portion of the wing remains un-stalled. Designers spend a lot of time on this design feature to impart gentle, predictable stall characteristics into the plane. 

A stunter with a longer fixed flap at the tip may have the same result.  The tip with its lower AOA remains flying and producing lift while the flapped portion is stalled. 

Here is the part of flap design I have never heard addressed.  Assuming a wing has the same root and tip airfoils, and the flap chord is a constant percentage of the wing chord at any station along the span of the wing, then the AOA changes the same amount along the span of the wing for a given flap deflection. 

If a Twister wing had a constant chord flap (say 2 inches from root to tip) then at 30 degrees of deflection, the AOA would be the same at the tip as at the root.  But you say hey, the Twister has tapered flaps – approx 3” at the root and 1” at the tip.  What does that do to our AOA?  Let’s go back to our profile plan view. On the center rib, draw the root of the flap (3” chord) deflected 30 degrees and then draw the chord line as we discussed earlier.  Now draw the tip of the flap (1” chord) and again draw the tip chord line.  Because the flap tip chord is a smaller percentage of the wing tip chord the resulting AOA of the tip is less than the AOA at the wing root.  In theory, the tip should remain un-stalled and lift producing while the root stalls first.  Actually the stall would commence at the root and progress outward towards the tip as the critical AOA was exceeded progressively from root to tip.

 On a tapered wing, it the flap chord decreased as a percentage of the wing chord from root to tip we would get the same effect.  If the reverse happened - the flap chord increased in percentage of the wing chord from root to tip - then the tips would stall first resulting in potentially severe hinging and banging.  If the flap chord is a constant percentage, the theoretically the intire wing woulod stall at once.  Ted, as I recall you have used a slightly different airfoil at the tip than the root on some of your designs.  I believe the high point of the airfoil was moved forward a few percentage points at the tip.  Many factors such as this would affect the critical angle of attack for a given section along the span.  However, the premise still holds that excessive flap chord towards the tip may lead to the tips stalling before the root and manifesting itself in udesireable hinging and banging.

I wonder how many poorly cornering ships have been abandoned in the past because the flap percentages actually cause the tips to stall first instead of the root?  I have no idea.  AS I said, I have never heard this aspect of design addressed.


Dennis:  Short fat flaps versus long skinny ones - whew, now THAR's the rub!  Here's another one - do you think the flaps are there for LIFT or for DRAG?  I think the answer is mainly for lift - but the drag does not necessarily hurt either!  For the reasons I laid out I will never consider using FULL span flaps.  I have wondered about using relatively narrow flaps with a LOT of throw - maybe 3:2 versus elevator (insted of the "normal" 2:3 or 1:1) to increase the drag component.  If using wide flaps I would want to restrict the deflection - and probably get a GREAT lift component.  Wide flaps and a lot of throw sounds like too much control effort.

More flap trivia:  The first 20 degrees or so of travel flaps increase lift a lot with only a slight increase in drag.  From 20-45 degrees, lift increase very slightly with a huge increase in drag. 

Remember that flaps increase lift by increasing the AOA through a change in camber.   Let’s revisit our Twister-type wing.  If we installed 1/2” chord flaps along the whole wing and the tota; chord was say 12 inches, 20 degrees of deflection would result in only a slight change in the chord line and result in little additional lift.  If we deflected them 45 degrees there would still be only a slight change in the chord line (again with little lift) but a whole lot of drag! 

Now let’s take the a wing and install flaps that are 50% of the wing chord -six inches of wing and six inches of flap -  and deflect them 20 degrees.    Again draw the chord line and we see a much greater change in its angle.  With a larger flap chord we will see a higher angle of attack and more lift for a given angle of deflection.  Drag will increase but not as much as lift increases.   

These two examples are meant to show the extremes to make the point.  As the flap chord decreases as a percentage of the wing chord to zero, the flaps would become less and less efffective.  Inversely as the flap chord increases other negative aspects such as control forces and structural limitations would overshadow and improvements is lift.  I also do not have any idea what effect changes in flpa chord have on pitching moment - it may be positive or negaitve.  Unfortuneatly, whey designers make a significant change to flap chord, other characteristics of the model are changed as well and resulting changes to flight characteristics, either good or bad, may not be the reslult of just the flap change but of other changes in combination.  The only way to know the true changes are to change only one aspect at a time, such as you did on your Oriental project.

So Dennis, your thoughts on narrow vs wide flaps are correct.  Now I hope you understand why.

There are times we could use more drag but the example I just gave reveals that the drag we think is helping is actually working against us when we don’t want it and is AWOL when we need it.  Our planes tend to wind up in consecutive round maneuvers when control deflections are low and flap induced drag is low. Bottom line is the drag is not much help here.   The flaps create their most drag at high deflection – AKA square corners – at a time when we likely want to preserve energy for the next 17 corners of the square eight or the excruciating climb to the top of the hourglass.  I don’t know what we can do about it but I thought it worth mentioning.


Ted:  My guess is that the vortex is the result of all of the lift up to that point of the wing span.  The vortex is the result of high pressure air on the bottom of the wing trying to get to the low pressure on the top of the wing.  The "vortex" is, I believe, the result of the natural spanwise flow of the air (air doesn't go straight parallel to the fuselage but tends to move towards the tips).  Because of that spanwise movement the "low pressure" the air is seeking is back towards the fuse.  The fact that the airplane is constantly moving forward combined with this "inward" movement makes the spiral.  I can't quantify or send you to a source off the top of my head but I think it is logical to expect the vortex at any point of the span to be the result of the air pressure change up to that point.

Ted, I would talk about this if it was not 1 am.  I’ll catch ya later on this one.

Ted:  The fact that the sailplane pitches up when flaps are extended is the result of a different aerodynamic reality that takes place when flaps are deflected.  Lowering flaps changes not only the camber of the airfoil but also its angular relationship to the stabilizing surface.  The net effect is increased decalage between the two.  Thus, when you drop the flaps, the angle of attack of the wing increases proportionately to the flap extension while that of the tail does not.  The tail is, in effect, applying "up" elevator to the airframe itself and the nose will pitch up in response.

If this were true, then why don’t our stunter’s flaps, which are a whole lot bigger and effective as a percentage of the wing’s surface, have the same positive pitching moment when deflected?  Heck, we are even helping with a half of a 25% stab standing up at 30 degrees in the prop blast.  The situation you describe above happens in all airplanes when the flaps are extended yet the result is not the same. 

I believe that this phenomenon in sailplanes is due to the physical relationship between the location of the horizontal stabilizer, its area and the resulting airflow changes from the trailing edge of the wing with flaps extended and how that air flows over the stabilizer. 

I know that in a Piper Arrow with the stab slightly higher than the wing, there is a significant pitch change with full flap extension but very little pitch trim change.  On a C-170B however, the thing about wants to stand on its tail when the first notch of flaps are applied.  It takes a whole lot of nose down trim to correct this.  However, when the 2nd and 3rd notch (30 and 40 degrees) is added, there is very little pitch up and little additional down trim in needed. 


Dennis:  Implicit in that is when re-trimmed with the flaps deployed, the fuselage assumes a nose-down inclination versus the no-flap trim condition.  I guess I always thought the pitching moment would have a more powerful effect - but then the effect from the stab (the up elevator you described) probably overpowers the flap PM, especially on a long-tailed sailplane...

Dennis, remember what the flaps do…they increase the angle of attack.  When you put the flaps down on a sail plane, you are not trying to produce more lift, but rather produce the same amount of lift at a lower airspeed.  Because the flaps increase the AOA by changing the camber and moving chord line, the pitch of the fuselage will decrease (nose low) while the AOA remains relatively high.  If you fly any airplane with flaps up and then flaps down at the same airspeed, the resultant pitch attitude will always be higher with the flaps up.  This is not a function of pitching moment or tail volume.  Remeber we increase AOA by increasing pitch or increasing camber. 

Conclusion:

Back to the issue of flaps and stunters and fixed tips and narrow and wide and deflections. As Dr. David Manor, PHD told us over and over again, there is no free lunch.  We use flaps because our planes fly better with them, but they also bring some baggage that makes our lives difficult.

Long skinny full span flaps probable are not the best answer.  Neither are very short, high chord flaps.  The optimum is somewhere in the twain.  The aero lab at Parks had a 36 inch wind tunnel capable of speeds over 120 mph.  A 60% size model of a modern stunt ship tested at 120 mph would have had approximately the same Reynolds’ number as our actual models.  I wish I could have built a test model with removable flaps, stabilizer and elevator and done tests on lift over drag, pitching moments and drag for various flap spans, chords and elevator/flap ratios.  That could have answered a lot of questions.  Instead we plod along with very educated guesses based on experience and trial and error.  There are countless other factors not addressed that have an impact on our model's flight characteristics that have not been addressed for brevity and simplicity.  When comparing two models with different flap configurations, we must consider that the changes in flight characteristic may not be due soley to the change in flaps, especially if other changes have been made as well to the stab/elevator, tip shape, weight, etc. 

One more consideration on comparing two examples of the same model with different flap configurations.  Micheal Seilig did a tremendous amount of research in the 90s on low speed airfoils for RC gliders.  He cautioned that the inability to accurately and consistently recreate/duplicate a given airfoil or design parameter using traditional building techniques could have a significant impact on the resulting flight characteristics.  A characteristic we attribute to a new flap configuration may be due to some other change introduced unitentionaly during the building phase.

We have seen many different configurations be successful, from Bob Barron’s flapless Humbug to Windy’s and L Jay’s huge flaps of the 80’s to the more traditional designs seen today.  Full span or not, large chord or narrow, all can be made to work. 

Thanks for letting stick my nose into this discussion.  I hope I have not stepped on any toes.  As I said, we observe very accurately.  I hope I have given some information to help take some of the error out of our trials. 

Wow, this got long.  Thanks for reading.

Bruce


edited for clarity

« Last Edit: August 21, 2007, 12:07:41 PM by 4-Shipp »

Offline RandySmith

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #28 on: August 21, 2007, 08:44:27 PM »
""""On a C-170B however, the thing about wants to stand on its tail when the first notch of flaps are applied.  It takes a whole lot of nose down trim to correct this""""

Hi Bruce  are you saying that if you take this airplane in perfectly level flight  and hold everything in the same postion, then lower the flaps the nose  will go up???

I took no less than a dozen airplanes up and tried this very test, every airplane I tried pitched the nose UP , I posted these results here and on SSW , the reaction I got was just to be ignored, it was almost as I had made this up    ~^ HB~>

Regards
Randy

Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #29 on: August 21, 2007, 11:27:25 PM »
Randy,

Take the stab and elevator off of those C170s and drop the flaps and see what happens.

For that matter, just leave the flaps up and see what happens when the tail is missing.

Well, on second thought.  To save wear and tear off the old body, take the stab and elevator off an old Vector, hook up the lines like you still had the stab and elevator on it and then try to take off.  Go ahead.  Give it full "up" (i.e. full down flaps).

Tell me how that works out.

If you're not that adventuresome buy somebodys old Half Fast and take it off with the "flaps" full down (i.e. "virtual" elevator full up).  Tell me how that worked out.

Ooops. forgot.  The Half Fast is a flying wing so the aerodynamics are all different, I guess. Down is up and up is down?

The combat world spent a short period of time with the hot ships being flying wings (which maneuvered via distorting part of the wing into a reverse camber).  The smart guys quickly learned that they'd get a whole lot better performance by taking the "elevator" off the trailing edge of the wing and putting it back somewhere where a good tail belonged.

The other advantage of using a tail is you're not robbing the wing of lift by trying to turn it in the same direction as the camber you've put into it.  A camber which causes the flying wing to turn (slowly, compared to its tail aft counterpart) in the desired direction.  What causes this to happen is the same thing that happens any time you extend flaps on a conventional (stabilizer aft) airplane. 

What happens to the "pitch of the airplane" (where the nose goes) is ultimately the result of the "longitudinal dihedral"  (decalage) between the angle of attack of the wing (with flaps deflected as Bruce discussed) and that of the unchanged (by your description) stab/elevator.

Dennis' statement regarding the ultimate attitude of the trimmed airplane with a relative nose down attitude is also accurate.  Approaches in low ceiling /visbility conditions in airliners are generally made with the largest flap deflection available.  Doing so lowers the cockpit (nose down attitude) and reduces the cockpit cutoff angle so the pilots have a better view of the runway when they break out of the overcast.

Fly that Cessna at 70 knots with full flaps and again with zero flaps.  The attitude that results will be quite nose low with flaps out and quite high with zero flaps.  that will be true at any airspeed that doesn't tear the flaps off the airplane (or overextend the power available from the little 145 horse Continental).

Oh, and Bruce.  I loved your post (and not only becaue it was longer than even my old forum records.  I agreed with easily 90% of it and only had a slight difference with the most of  the rest.

The one thing I think you slipped up on was your suggestion that because the flaps are bigger in area than the elevators they should overpower them (and act not unlike my above discussion about taking the tail off of a stunter and seeing what control inputs make happen).

The additional lift that results from the flap deflection is centered somewhere between 25% and 50% or so of the MAC (depending on AOA).  The arm on which it acts is the distance between that location and the Longitudinal location of the CG.  Further, the change in lift thus generated is only a part of the total lift that would have been generated whether the the ship  was flapped or not when the tail causes the AOA to increase.

The lift produced by the tail is not only generated at (several) X times greater arm from the CG but is a dramatic increase in raw lift from that required to maintain level flight.  It is this combination of  a much longer arm and (several) times greater percentage lift increase that makes flaps succomb to the will of the tail.

It is conceivable, of course, that the ratio between flap size and tail size (and deflection, etc) could be reduced to the point that the tail could "not" overcome  the pitching moment of the flaps and the nose would drop despite the best efforts of the compromised tail.  Or, the CG could be moved so far forward that a tail that would allow "modest" maneuvering on an unflapped airplane would not be able to do so with inappropriately sized flaps. 

This is, plain and simply, the reason that a lot of classic era airplanes perform best with reduced flap movement.  Their tails are typically small (as little as 15% of the wing area) and the flaps comparatively large.

The combination of the negative pitching moment of the flap induced wing camber, combined with the required forward CG to maintain an acceptable static margin for stability results in an airplane that can be literally unuseable with, for instance, a one to one flap/elevator ratio.

Bruce, I could well be missing something here (and I'm the first to admit my study of aerodynamics didn't occur at an accredited university), but I've seen and experienced way too much of this stuff (full size and stunt ship) to be easily diswayed from this point of view.

Great discussion.

Ted

Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #30 on: August 21, 2007, 11:52:44 PM »
""""On a C-170B however, the thing about wants to stand on its tail when the first notch of flaps are applied.  It takes a whole lot of nose down trim to correct this""""

Hi Bruce  are you saying that if you take this airplane in perfectly level flight  and hold everything in the same postion, then lower the flaps the nose  will go up???

I took no less than a dozen airplanes up and tried this very test, every airplane I tried pitched the nose UP , I posted these results here and on SSW , the reaction I got was just to be ignored, it was almost as I had made this up    ~^ HB~>


Just a couple of additional thoughts on this post, Randy.

Typically, pilots have used flaps as a means to help slow the airplane as we set up for landing approaches.  The common practice used to be to extend flaps close to the maximum structurally allowable extension speed, thus allowing speed to be kept up as long as possible to minimize  time enroute.  When they do that the effects of the resulting increase in decalage between the wing and tail is dramatically increased.  Lift goes up as the square of airspeed.  Because the increased lift (negative lift, a download to stabilize the wing) of the tail (due to the decalage) acts on an arm a long way from the CG the dramatic tendency you discuss is witnessed.  If, your desire was, in fact, to maintain the speed at which you deployed the flaps you would, indeed, have to trim the nose down dramatically as well as increase the engine thrust commensurately.

If, on the other hand,  you were to wait until the minimum airspeed clean before extending the flaps the change in lift would be much less dramatic, the nose would rise only slightly before dropping to try to maintain a "trim" airspeed.  Note that with the power unchanged the only way the airplane can maintain the initial speed is to lower the nose.  A stable airplane will ultimately find a new "trim" airspeed if the trim is left as it was and the power remains unchanged.  that does not necessarily mean the altitude will remain the same, of course.

The "standard" method of flying airliners changed dramatically as  the cost of fuel increased.  The "hot dog" style of high speed til the last possible moment and then throwing out the drag just in the nick of time to land out of a stabilized approach quickly gave way to carefully planned descents that included allowing the airspeed to bleed off gradually as to the minimum speed (approximately 1.3 V sub S for the existing flap setting) before going to the next setting and allowing the same gradual bleed off; repeating until the landing flap setting and approach airspeed are obtained about a thousand or so feet in the air when VFR or just prior to the Final Approach Fix on an actual instrument approach.  Only at that point will a well planned descent require the pilot to bring the power up from idle since leaving cruise altitude.  Efficient, smooth and undemanding on the trim inputs.

Trim changes when approaches are flown this way tend to be one way only, nose up as the airspeed reduces.

I never flew an Airbus but would find it interesting (if you were able to actually "fly" it versus program surface inputs to the full time auto pilot) to see how trim needs varied from the Boeings I spent most of my time on.  The Airbus design philosophy included a very "unloaded" tail (aft CG).  There is little "pitching moment" from the displacement of CG and Cl of the wing that requires the Boeings to use a lot of negative stabilizer settings throughout the flight regime, especially takeoff and landing.  I would guess that any significant trim change made by the auto pilot would be almost exclusively the result of pitching moment arising from cambering the wing with flap extension.

Bruce might well have studied some on just this subject.  I'll also ask some of the analysts I word with at NASA who have a lot of time on Airbuses.  It's an interesting aside to this whole question.

Ted
Regards
Randy

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #31 on: August 22, 2007, 07:29:28 AM »
Ya know folks, this has been a GREAT thread - great contributions from all - congrads!  CLP**

Someone (Randy?)  noted earlier in this discussion that we spend to much time/effort discussing flaps relative to their importance. 

However, this thread started as "Why'd you cut the flaps on  ARF's" and has progressed to Airbuses & NASA!  What is really scarry is that it has done it in a perfectly logical progression!


I think that's the signal that is time to move on to another discussion !!! y1
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Bruce Shipp

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #32 on: August 22, 2007, 07:46:35 AM »
"The one thing I think you slipped up on was your suggestion that because the flaps are bigger in area than the elevators they should overpower them (and act not unlike my above discussion about taking the tail off of a stunter and seeing what control inputs make happen)."

Hi Ted,

I didn't mean to say that the flaps would overpower the elevator.  I was talking about the relative size/effectiveness of the flaps on a stunt ship vs. those on a sailplane. 

I think we all agree that aerodynamically deflecting flaps does move the center of lift aft, further displacing it from the CG and causing a nose down moment.  My point in my original post was in reference to the nose up pitch when flaps were applied on a sail plane.  My examples of the Arrow (low wing Piper) and the 170B (high wing Cessna) were offered as real world examples of two different reactions to the same control input.  Both of these aircraft have manual flaps (manufactured by the Strong Arm Flap Co.).  They have long levers in the cockpit that are used to manually lower/raise the flaps and locks to hold them in the desired position.  Consequently they can be literally moved from full up to full down in less than a second or two.  This allows us to observe the reaction to the flaps prior to any significant reduction in airspeed resulting from the increased drag. 

On the Piper, the airplane pitches noticeably down but there is little if any associated pitch trim change.  The airplane just does not want to climb with flaps .  The Cessna however will pitch up (aggressively if the flaps are applied quickly) and requires a whole lot of forward pressure to maintain level flight.  The converse happens when flaps are raised.  After a flaps 20 takeoff, if the flaps are rapidly lowered, there is a significant pitch down that can get your attention if you are still close to the ground).  The Piper does not demonstrate this characteristic when the flaps are raised.   I believe that this is a result of design (physical relation between the wing, flaps and elevators) issues where the deployed flaps affect the airflow over the tail and changes the effectiveness of the elevator. 

It must also be noted that these airplanes use different styles of flaps – both different than our stunters – and that is a factor as well.  A stunt ship uses plain flaps.  They increase the camber but not the wing area.  They are not a slotted flap either.  There is no gap at the leading edge of the flap to let air move from below the wing to the top of the flap.  We actually tape the hinge lines to prevent this. 

The Piper has slotted flaps which allow air to flow from below to above the flap at the leading edge.  I do not think that this slot would influence the shift in the center of lift as much as simple increase the effectiveness of the flap (more lift for a given deflection).  The Cessna however has slotted fowler flaps that actually move down and aft.  This also increased the wing area and brings another plate of aerodynamic goodies to the table. 

The point is that unlike the sailplane example, not all flaps on all airplanes will cause a pitch up as observed by Dennis. 

Ted, an experiment I would like to see (along the lines of your tailless trials) would be to fly a modern stunt ship with the tail in place but the elevator disconnected and fixed in neutral.   Fly it in normal battle trim but with only the flaps defected for control.  Then we could see exactly what the resulting pitch forces would be when we blast those huge (or not so huge flaps depending on the designer) 30-40 degrees up or down.  I’m starting to really wish I could get my hands on the wind tunnel!

Bruce

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #33 on: August 22, 2007, 07:56:59 AM »
“However, this thread started as "Why'd you cut the flaps on  ARF's" and has progressed to Airbuses & NASA!  What is really scarry is that it has done it in a perfectly logical progression!”

This stuff is too cool to talk about.  And while the previous discussions on flaps is great what I was hoping to pull out of this thread was discussion on the following points:

Flap chord as a percentage of the wing chord from root to tip, fixed tips vs full span flaps and the effects on cornering, stalling and hinging/banging in hard corners or turbulence.

Narrow flaps with lots of deflection vs wider flaps with less deflection and the associated effects of drag – low drag when we want high (rounds maneuvers) and high drag when we want low (square maneuvers).

Bruce  D>K


Offline RandySmith

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #34 on: August 22, 2007, 11:22:17 AM »
Randy,

Take the stab and elevator off of those C170s and drop the flaps and see what happens.

For that matter, just leave the flaps up and see what happens when the tail is missing.

Well, on second thought.  To save wear and tear off the old body, take the stab and elevator off an old Vector, hook up the lines like you still had the stab and elevator on it and then try to take off.  Go ahead.  Give it full "up" (i.e. full down flaps).

Tell me how that works out.

If you're not that adventuresome buy somebodys old Half Fast and take it off with the "flaps" full down (i.e. "virtual" elevator full up).  Tell me how that worked out.

Ooops. forgot.  The Half Fast is a flying wing so the aerodynamics are all different, I guess. Down is up and up is down?

The combat world spent a short period of time with the hot ships being flying wings (which maneuvered via distorting part of the wing into a reverse camber).  The smart guys quickly learned that they'd get a whole lot better performance by taking the "elevator" off the trailing edge of the wing and putting it back somewhere where a good tail belonged.

The other advantage of using a tail is you're not robbing the wing of lift by trying to turn it in the same direction as the camber you've put into it.  A camber which causes the flying wing to turn (slowly, compared to its tail aft counterpart) in the desired direction.  What causes this to happen is the same thing that happens any time you extend flaps on a conventional (stabilizer aft) airplane. 

What happens to the "pitch of the airplane" (where the nose goes) is ultimately the result of the "longitudinal dihedral"  (decalage) between the angle of attack of the wing (with flaps deflected as Bruce discussed) and that of the unchanged (by your description) stab/elevator.

Dennis' statement regarding the ultimate attitude of the trimmed airplane with a relative nose down attitude is also accurate.  Approaches in low ceiling /visbility conditions in airliners are generally made with the largest flap deflection available.  Doing so lowers the cockpit (nose down attitude) and reduces the cockpit cutoff angle so the pilots have a better view of the runway when they break out of the overcast.

Fly that Cessna at 70 knots with full flaps and again with zero flaps.  The attitude that results will be quite nose low with flaps out and quite high with zero flaps.  that will be true at any airspeed that doesn't tear the flaps off the airplane (or overextend the power available from the little 145 horse Continental).

Oh, and Bruce.  I loved your post (and not only becaue it was longer than even my old forum records.  I agreed with easily 90% of it and only had a slight difference with the most of  the rest.

The one thing I think you slipped up on was your suggestion that because the flaps are bigger in area than the elevators they should overpower them (and act not unlike my above discussion about taking the tail off of a stunter and seeing what control inputs make happen).

The additional lift that results from the flap deflection is centered somewhere between 25% and 50% or so of the MAC (depending on AOA).  The arm on which it acts is the distance between that location and the Longitudinal location of the CG.  Further, the change in lift thus generated is only a part of the total lift that would have been generated whether the the ship  was flapped or not when the tail causes the AOA to increase.

The lift produced by the tail is not only generated at (several) X times greater arm from the CG but is a dramatic increase in raw lift from that required to maintain level flight.  It is this combination of  a much longer arm and (several) times greater percentage lift increase that makes flaps succomb to the will of the tail.

It is conceivable, of course, that the ratio between flap size and tail size (and deflection, etc) could be reduced to the point that the tail could "not" overcome  the pitching moment of the flaps and the nose would drop despite the best efforts of the compromised tail.  Or, the CG could be moved so far forward that a tail that would allow "modest" maneuvering on an unflapped airplane would not be able to do so with inappropriately sized flaps. 

This is, plain and simply, the reason that a lot of classic era airplanes perform best with reduced flap movement.  Their tails are typically small (as little as 15% of the wing area) and the flaps comparatively large.

The combination of the negative pitching moment of the flap induced wing camber, combined with the required forward CG to maintain an acceptable static margin for stability results in an airplane that can be literally unuseable with, for instance, a one to one flap/elevator ratio.

Bruce, I could well be missing something here (and I'm the first to admit my study of aerodynamics didn't occur at an accredited university), but I've seen and experienced way too much of this stuff (full size and stunt ship) to be easily diswayed from this point of view.

Great discussion.

Ted


Ted

I can't fly a C170 with the tail missing , neither can you ,so I will pass on that, Also I never said anything about what it would fly like without the elevator and Stab gone. I full well know  exactly what would happen.
I also never said that a VECTOR  with the rear end gone would not act like the Flaps were now the elevator, I know exactly what will happen if I do that also.
My comments  were only about what happens to the pitch of the airplanes I mentioned when the Flaps were deployed without anything else changing. I never argued the fact that the reverse would happen if you removed the tail.
I also didn't say anything about any airliners, I have only flown 1 and didn't use flaps  ;D

I am also fully aware that if you try to maintain speed with the flaps down you will have  to re trim add power and pitch the nose down to fly level, I never argued that point either.
I just found it interesting that so many GA planes pitched nose up when extending flaps,Period.
 All of the other situations you wrote about I never even brought up ,about I have no disagreement with you what so ever. Everything you stated about flaps working like an elevator in those situations are 100% correct.
And by the way I have flown a stuntship that had elevator removed, it acts just as you would expect ,and is  very ugly to fly

Randy

Offline RandySmith

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #35 on: August 22, 2007, 11:26:19 AM »
“However, this thread started as "Why'd you cut the flaps on  ARF's" and has progressed to Airbuses & NASA!  What is really scarry is that it has done it in a perfectly logical progression!”

This stuff is too cool to talk about.  And while the previous discussions on flaps is great what I was hoping to pull out of this thread was discussion on the following points:

Flap chord as a percentage of the wing chord from root to tip, fixed tips vs full span flaps and the effects on cornering, stalling and hinging/banging in hard corners or turbulence.

Narrow flaps with lots of deflection vs wider flaps with less deflection and the associated effects of drag – low drag when we want high (rounds maneuvers) and high drag when we want low (square maneuvers).

Bruce  D>K




HI Bruce

Simple solution, all we need to do is to come up with variable ratio flaps that change chord  between manouvers  HB~> HB~>   yea I'll  work on that one   :D

Regards
Randy

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #36 on: August 22, 2007, 12:09:53 PM »
We should take on something simpler - like the Designated Hitter rule...!  VD~  S?P  HB~>  HB~>  HB~>
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #37 on: August 22, 2007, 07:54:26 PM »

Ted

I can't fly a C170 with the tail missing , neither can you ,so I will pass on that, Also I never said anything about what it would fly like without the elevator and Stab gone. I full well know  exactly what would happen.
I also never said that a VECTOR  with the rear end gone would not act like the Flaps were now the elevator, I know exactly what will happen if I do that also.
My comments  were only about what happens to the pitch of the airplanes I mentioned when the Flaps were deployed without anything else changing. I never argued the fact that the reverse would happen if you removed the tail.
I also didn't say anything about any airliners, I have only flown 1 and didn't use flaps  ;D

I am also fully aware that if you try to maintain speed with the flaps down you will have  to re trim add power and pitch the nose down to fly level, I never argued that point either.
I just found it interesting that so many GA planes pitched nose up when extending flaps,Period.
 All of the other situations you wrote about I never even brought up ,about I have no disagreement with you what so ever. Everything you stated about flaps working like an elevator in those situations are 100% correct.
And by the way I have flown a stuntship that had elevator removed, it acts just as you would expect ,and is  very ugly to fly

Randy

Hi Randy,

All the other stuff was intended as an explanation of why the light planes you experimented with probably acted the way they did.  The various items you felt were unresponsive were intended to cause you and the readers to realize that a flying wing is nothing more than a stunt ship with no stab and elevator and we all pretty much know that on a a flying wing the "elevators" (what we would call flaps if there were a tail on the same aircraft) appear to act just like the elevators on a regular ship.  They go up and the ship turns inside and vice versa.  The point, of course, is that what is making them go up when the elevators (flaps) go up is the pitching moment of a cambered airfoil.  The fact that most flying wings are inferior performers to similar designs on which the elevator (flaps) are placed on a boom behind the identical wing is very strong evidence for the reality that a cambered wing will have a pitching moment and the pitch that results from it, in the absence of a tail to point the thing in the desired direction, will be pretty ordinary. (like doing an outside loop in a Piper Cub).

All of the examples were intended to make it as obvious as possible that the existence of a pitching moment in cambered (flaps extended) wings is very real and needs to be addressed by stunt designers.  That's all.

Ted

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #38 on: August 22, 2007, 10:16:59 PM »
Hi Randy,

All the other stuff was intended as an explanation of why the light planes you experimented with probably acted the way they did.  The various items you felt were unresponsive were intended to cause you and the readers to realize that a flying wing is nothing more than a stunt ship with no stab and elevator and we all pretty much know that on a a flying wing the "elevators" (what we would call flaps if there were a tail on the same aircraft) appear to act just like the elevators on a regular ship.  They go up and the ship turns inside and vice versa.  The point, of course, is that what is making them go up when the elevators (flaps) go up is the pitching moment of a cambered airfoil.  The fact that most flying wings are inferior performers to similar designs on which the elevator (flaps) are placed on a boom behind the identical wing is very strong evidence for the reality that a cambered wing will have a pitching moment and the pitch that results from it, in the absence of a tail to point the thing in the desired direction, will be pretty ordinary. (like doing an outside loop in a Piper Cub).

All of the examples were intended to make it as obvious as possible that the existence of a pitching moment in cambered (flaps extended) wings is very real and needs to be addressed by stunt designers.  That's all.

Ted


Hi Ted

Thanks for the post ,  however your preaching to the choir, I have designed stuntships  for over 3 decades and I do full well know the existence of pitching moments in cambered wings, I also know how it affects our stuntships, light  medium and  heavyweights.  I have never stated or argued the contrary.
I am also very aware that a flying wing has it's flaps(elevators) act like elevators on a regular ship, and again have never stated anything else.
Again my comments was I found it interesting that in some full  size  airplanes the very first movement the plane had when the flaps are deployed, was opposite of what many think happens,  That was it  period, I wasn't trying to say , nor did I say that Stuntships do this.....
This has been a good thread full of much information, I just hope it's been useful.

Regards

Randy

Offline Ted Fancher

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #39 on: August 22, 2007, 10:59:35 PM »


Again my comments was I found it interesting that in some full  size  airplanes the very first movement the plane had when the flaps are deployed, was opposite of what many think happens,  That was it  period, I wasn't trying to say , nor did I say that Stuntships do this.....
This has been a good thread full of much information, I just hope it's been useful.

Regards

Randy

Hi Randy,

That's exactly why I discussed the "decalage" change that results when flaps are deployed, thus increasing the angle of attack of the wing of which they are a part.  When the angle of attack of the wing increases while that of the tail remains constant it is essentially the same thing as pulling up on the elevator while leaving the flaps stationary.  The nose up pitch that comes about is transitory and diminishes as the speed moderates or the nose drops to try an retain the speed existing prior to the flap extension.  The lower the airspeed at the time you extend the flaps (above stall speed for the initial setting, of course) the less pitch up you will experience.

I think it is valuable to remember that almost anything  that changes aerodynamically on an airplane acts on everything else.  Thus, it is difficult if not impossible to define exactly what changes will take place on a variety of airplanes based on a single identical change.  Knowing that, however, does not prevent us from understanding the initial effects of any single change such as cambering a previously uncambered airfoil.

Ted

Offline captcurt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #40 on: September 06, 2007, 12:51:57 PM »
Forgive me if I missed someone else mentioning this but...

Alot of this discussion is apples and oranges.  Dennis has been doing the flap clip on some planes with modestly thin foils.  In the heat of summer, those wings need to get to a pretty high AOA to generate enough lift to turn crisply..they thus are making the vortex issue quite noticeable.  Dennis' experiments absolutely appear to make the plane fly better--I was there to see it.

But I'm not so certain that the same effect would be noted on a curretn generation foil like my Smith Katana, the TP or the Impact.  They just don't need to be driven hard enough so the difference is noticeable. 

Just my $.02 in explaining the differences in what we are experiening.

Curt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #41 on: September 07, 2007, 03:07:06 AM »
Sorry, Ty, I have not made real plans for the Macchi. All I did was stretching 3-side views found on the internet until fitting "regular" stunt numbers (more or less, that is). Google Macchi Mc 72 for details.

Peter Germann

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #42 on: September 07, 2007, 06:51:23 AM »
Beatiful model Peter:

I too enjoyed very much your Stunt News article.

Curt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #43 on: September 07, 2007, 08:18:15 AM »
Sorry, Ty, I have not made real plans for the Macchi. All I did was stretching 3-side views found on the internet until fitting "regular" stunt numbers (more or less, that is). Google Macchi Mc 72 for details.




Hi Peter

I too  really enjoyed seeing your plane, great job on a really cool airplane. It has long been a favorite of mine

Regards
Randy

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #44 on: September 07, 2007, 08:25:30 AM »
Forgive me if I missed someone else mentioning this but...

Alot of this discussion is apples and oranges.  Dennis has been doing the flap clip on some planes with modestly thin foils.  In the heat of summer, those wings need to get to a pretty high AOA to generate enough lift to turn crisply..they thus are making the vortex issue quite noticeable.  Dennis' experiments absolutely appear to make the plane fly better--I was there to see it.

But I'm not so certain that the same effect would be noted on a curretn generation foil like my Smith Katana, the TP or the Impact.  They just don't need to be driven hard enough so the difference is noticeable. 

Just my $.02 in explaining the differences in what we are experiening.

Curt




Hi Curt

I can tell you that the  SV  airfoils are much less sensitive to flap changes than the  much thinner ones, even though the SV airfoils  are  not  what I would call  fat  airfoils. I flew  Nobler type airfoils for many years , and they really respond to small changes, adding 1/8 inch across the span makes a  huge difference in how the plane flies and carries  weight and how it affects the turn, if you have a very light plane , taking away area will noticably affect the  turn also.

Offline captcurt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #45 on: September 07, 2007, 09:10:45 AM »
Hi Randy:

Yes..that is exactly what I was getting at.  The guys up here flying the SV's are continually amazed at how well the wings work...and over a really wide range of weights and speeds.

I also would not consider them to be fat foils (AKA the patternmaster-type) but significantly thicker than the classic-type Nobler etc wing.

From what I have seen, the work Dennis has been doing with the ARF flaps has been all on the classic thin foils.  His results prove to me that it definitely has a positive effect for those wings at least.

What was happening on the full flap versions on those planes was very similar to the erratic turn behaviour we would see on some un-sealed flap installations--except it didn't get better when the flaps were sealed.

Curt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #46 on: September 09, 2007, 11:30:07 AM »
Thanks Dennis:

I understand (at least to the normal full-scale pilot approximation) the theory and your discussions on the vortex turbulence.  I was trying to justify, in my own terms I guess, why many of those that HAVE tried the same experiment on moderate to fat foiled full-blown stunters, still prefer the full flap option--or see no difference.  (it does seem likely tho, that when doing the experiemnt, they would have reduced the flap areas & moments also) I recall PW has done complete test cycles with multiple flap sizes, etc so would believe that if they worked better, he would be doing that.

It seems that one of the differences that could explain why your approach is not universal could be that on the fat foiled planes, there isn't enough flap deflection required to make the vortex issue a problem.

Just one of those emperical hypotheses used to validate what we are observing--no facts--it would require some planned testing and data collection I guess.

Anyway..we sure know it worked on the Oriental that you did. 

I might go back and re-read one of Ted's Imitation articles where he used segmented flaps with joining pins to enable flap length/area adjustments--although the length or area issue might confuse the resultant root cause.

I do know that as I fly better, I use less and less control deflection. I also believe that the swept-outboard tips and tabs on my Randy Smith designs are there for this very reason.

When my next "A" stunter is finiished, we will have an opportunity to try full-span. as designed, or tabs.

Missed you at Flint yesterday but had a nice chat w/Alan and Art.

Best,

Curt

Online Dennis Adamisin

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #47 on: September 09, 2007, 10:50:35 PM »
Curt:

I'm sorry I missed Flint too.  My son came up to visit so we could watch U-M football together - talk about lost weekends!   HB~>  HB~>  HB~>




Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline captcurt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #48 on: September 10, 2007, 07:37:49 AM »
OMG..that was sick.

They will return however.!

Curt

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Re: Dennis Adamisin: Clipped flaps...a discussion???
« Reply #49 on: September 11, 2007, 03:39:59 PM »
OMG..that was sick.

They will return however.!

Curt


... but not until Carr is history!


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