Howard Rush's flaps

[Howard Rush]

Hmm.  Here's a thread with my name on it, yet I didn't start it.  I see why you'd make it a separate topic, but please don't put my name on something I didn't write.

[Matt Colan]

What about a bigger prop, I've heard bigger prop = more stability, and less prop = more corner.

[Jim Pollock]

The new flaps are straight from the plans, right Howard?

Jim Pollock 

[Randy Powell]

Howard,

I thought the old orange plane was more tractable with the 40 VF

[Doug Moon]

Infinitely stiff flaps are a GOOD!  They wont ever give up.  They wont change over time with wear and they wont be suspect in really wet weather.

You could fix this problem the old school way.

First off disco the diffusers.  Tape them or connect them in some way you know wont give way under flying conditions.

Fly the plane and take note.  

Then, right there at the field, with a straight edge and a #11 slice off an 1/8" from the TE on both flaps.

Fly again and take note.  

Repeat until they are the size they need to be.  Then build new ones using the same method as before only to the new size.  

BUT..............Before you can try this you must be certain this truly is the problem.

The plane I had at the nats this year will not fly on a hard point with cables.  It is simply not flyable in competition.  Believe me I tried to get it to work Because it is an over the counter handle I can use again and again.  It wasnt just me either who noticed it.  Others were commenting on having trouble with angles and so on.  After about 50+ flights and many different setups and a contest with poor results trying to make it work I gave up and returned to solids and a bar handle.  All was good again.  

This year at the nats Steve's plane was still new with only about 30 flights on it.  Continuous movement with the LO finally delivered the sweet spot where it would go where you pointed it.  Before it was a battle everywhere.  Flyable but you had to stay on it and you always felt it would not do 2 in row in the same place.

Many many many variables cause this odd trim issue.  I am sure with PW on the scene you guys have it nailed down pretty close.

Please keep us in the loop.

[Brett Buck]

Infinitely stiff flaps are a GOOD!  

  Not if the flaps were sized assuming they would flex!

   Brett

[Brett Buck]

What about a bigger prop, I've heard bigger prop = more stability, and less prop = more corner.

    You are only looking at one dimension. That's kind of true if you only look at pitch, but the more prop, the more yaw disturbance you have. Bob's airplane may have had a variation on that problem.

    Howard's prop is already a lot bigger than mine, on the same engine at about about the same weight.

    Back in the good old days 25 years ago, the only way to get more performance was to go for more diameter. Now, you can get whatever kind of performance you need with any reasonably-sized prop, so there's little reason to shove on as much diameter as you can, which in turn allows you to use smaller props with less trim penalty.

    Brett

[Doug Moon]

 Not if the flaps were sized assuming they would flex!

   Brett

Yes but with the torque tube they were assumed to not flex, or did you mean the original designed flaps on the plan.  

Also it would be nearly impossible to actually know how much they would flex.  Not really anything out there installed on a stunt plane today measuring such items as flap flex and then giving report.  If there is I havent heard about it, which means I missed it and that is entirely possible.  I would love to see it.  I think that would be cool!

Just thought of another fix for Howard's issue.  He said the flight characteristics were worse with the tabs taped in place.  Make them, the tabs, twice as long as they are now.  Reducing the flap effectiveness.

Or,

Bring in more elevator, also reducing flap effectiveness.

  

 

[Brett Buck]

Yes but with the torque tube they were assumed to not flex, or did you mean the original designed flaps on the plan.  
 

   They are the same size as the original, I think, sized by trial and error.

Just thought of another fix for Howard's issue.  He said the flight characteristics were worse with the tabs taped in place.  Make them twice as long as they are now.  Reducing the flap effectiveness.

Or,

Bring in more elevator, also reducing flap effectiveness. 

   Already did that, I think.

     I forgot, I am supposed to send Howard some inflight pictures to examine the flap/elevator travel.

     Brett

[RC Storick]

The absolute biggest problem with the trim on my viper is too fast controls. If I were 25 years younger it might work. Second problem is procession as Brett pointed out. I was a good experiment. I learned a lot.

[Brett Buck]

The absolute biggest problem with the trim on my viper is too fast controls. If I were 25 years younger it might work. Second problem is procession as Brett pointed out. I was a good experiment. I learned a lot.

      I would also suggest that getting rid of the fin offset would be goal #1. That was the one thing that couldn't easily be changed in the field, but I think that was the biggest issue.

    I still think the 65 with a 40VF prop and any necessary adjustments to make it work would end up being absolutely *awesome*. I guarantee you'd win the "horsepower sound" award with that thing 8-stroking at 11000 rpm. Everybody else would run away because they were scared.

   Overall, there's absolutely nothing wrong with it that couldn't be fixed  - and if nothing else it would be an excellent experiment.

     Brett

[Ted Fancher]

 

Then, right there at the field, with a straight edge and a #11 slice off an 1/8" from the TE on both flaps.

Fly again and take note.  

Repeat until they are the size they need to be.  

Doug,

Bravo!

Ted

[Randy Powell]

I get kidded about using a small prop on a 65. I listen to the guys that know this stuff, like Ted and Brett and Paul. I've had good luck running the smallest (diameter) prop I can get away with.

[Mike Ferguson]

    I still think the 65 with a 40VF prop and any necessary adjustments to make it work would end up being absolutely *awesome*. I guarantee you'd win the "horsepower sound" award with that thing 8-stroking at 11000 rpm. Everybody else would run away because they were scared.

Out of curiosity, what would the "ballpark" starting point for a setup like this be?

RO-Jett 65, Bolly "toothpick" prop ... what else?

[Randy Powell]

Mike,

My last plane I was using an Eather 3 blade undercamber 12 x 4 cut down to an 11.5. Worked pretty well for me.

[Paul Walker]

?  What did he specify as being "unsuitable"?  Do the flap tabs taint it in some way?  Does it require a VF to be perfect?

VF required...No
Tabs tainted....No

I originally described the situation at the flaps being too stiff. That's exactly what it feels like. However, fupon urther evaluation, it could be a "bind" in the control system somewhere. I suspect the flap horn area.  It turns acceptably well, but will not stop very well. There is also a hint of hunting in level flight, which might be excess friction in the control system somewhere.

The friction or bind doesn't make it unflyable, in fact it flies fairly well. However, the friction or bind it has will keep him out of the winners circle until it is resolved. Hopefully the root of the problem will be found soon, fixed, and he will be back to practicing for the TT's shortly.
(in our 100 degree heat as well!)

[Bradley Walker]

Controls are like tires.

You could have 5000 HP but if you cannot hook up, it aint worth a @#$%.

[Brett Buck]

However, fupon urther evaluation, it could be a "bind" in the control system somewhere. I suspect the flap horn area.  It turns acceptably well, but will not stop very well. There is also a hint of hunting in level flight, which might be excess friction in the control system somewhere.

   I don't suppose that the hinges could be binding because the wing is flexing, the flaps aren't, could it?

    Brett

[Ted Fancher]

Naw,

Just do what Dougie said.  Buy #11 blades by the boxful and start trimming. Excessive pitching moment from too much area/flap deflection/flap size makes accurate exits from corners more difficult becuase it alters the relationship between the direction the airplane is "pointed" and the direction it is going.

If, for instance, anyone wants to improve the flyability of their ARF Cardinal profile, trim a minimum of 1/2" off the trailing edge of the flap.  Better yet, slice it off in stages and test fly as Dougie suggested.  Note the improvement in the corner size, exit and control input required as you progress.  The improvements I more or less guarantee you'll experience are the result of reduced pitching moment from a wing which is developing more lift and pitching moment than required to fly corners of the desired radius.

After first flying (later) Senior National Champion Paul Ferrell's Cardina we went the full Monty, cutting a full 3/4" off the trailing edge and never looked back.

Another big plus is reducing the chord of the flaps simultaneously reduces the twisting moment that was the reason Howard went to the carbon tube spar in the first place.  Thus the smaller sized flaps will be both more appropriately sized for the necessary lift and will be more consistent in producing that lift because of a reduced load induced washout when deflected.

T

[Dennis Adamisin]

After first flying (later) Senior National Champion Paul Ferrell's Cardinal we went the full Monty,

T

TOO MUCH information...!              

[RandySmith]

"You could fix this problem the old school way.
First off disco the diffusers.  Tape them or connect them in some way you know wont give way under flying conditions.
Fly the plane and take note. 
Then, right there at the field, with a straight edge and a #11 slice off an 1/8" from the TE on both flaps.
Fly again and take note. 
Repeat until they are the size they need to be.  Then build new ones using the same method as before only to the new size. 
BUT..............Before you can try this you must be certain this truly is the problem."

Doug is correct about making sure that is the problem, you see this a lot with light airplanes, the lighter the plane the more the flap pitching the plane will hurt you in exits. Heavy planes generally can benefit or need more flaps.
A slider elevator horn is a good idea if you do not know what the final outcome of the plane is, or your building a new design.
I remember when many people went to the 60 engined planes, a lot of people had to add a 1\4 inch or so to the chord of the flaps to keep the plane from sinking or stalling.
I also have seen a very very light 60 inch span ship that wound up cutting the flaps at near 3\4 span and added elevator movement to get the lift balance correct......
I am beginning to think that an adjustable flap horn with an elevator slide maybe something worth while. One of the ships I have here working on has this feature, just because it is an "unknown to me, and a big departure from my usual planes
Things come full circle 

Randy

[Dennis Adamisin]

Full adjustment of flap & elevator throws are the best tool in the bag, but a little hard to retrofit.

Trouble with cutting flap chord is that you are also cutting wing area.  Thus you are changing two characteristics at the same time.  The situation Ted describes where they narrowed the flaps by 3/4" also reduced wing AREA by 40 sq in.  The trial of tabs active versus not also suggests this is not the root cause (if I read that part right)

I would (in a heartbeat) cut the flap SPAN; 5" or so off each tip.  Sure it will result in "less flapped span"...  but so what???

[Ted Fancher]

Full adjustment of flap & elevator throws are the best tool in the bag, but a little hard to retrofit.

Trouble with cutting flap chord is that you are also cutting wing area.  Thus you are changing two characteristics at the same time.  The situation Ted describes where they narrowed the flaps by 3/4" also reduced wing AREA by 40 sq in.  The trial of tabs active versus not also suggests this is not the root cause (if I read that part right)

I would (in a heartbeat) cut the flap SPAN; 5" or so off each tip.  Sure it will result in "less flapped span"...  but so what???

Whooo, boy, Denny.

I'll get back to you all on this one. 


Great subject!!!!!

TEd

[Paul Walker]

   I don't suppose that the hinges could be binding because the wing is flexing, the flaps aren't, could it?

    Brett

No, that's not it.  The carbon tube is wound at +/- 45 degrees. No 0's. It is VERY rigid in torsion, and VERY wimpy in bending....Just the way it needs to be. So the flap is "matched" in Mx bending on the wing so the hinges don't load up due to a mismatch in stiffness.

It appears that the two ball links on the flap horn were binding for some reason. He said one of the balls appeared to be rusted. He flew it this morning and now all of a sudden it was "twitchy". Indicates to me the friction is now gone. Should work now. However, he wimped out early and wouldn't fly in the 100 degree plus weather. We'll have to find out later! Me, I had to work today...

[RandySmith]

Full adjustment of flap & elevator throws are the best tool in the bag, but a little hard to retrofit.

Trouble with cutting flap chord is that you are also cutting wing area.  Thus you are changing two characteristics at the same time.  The situation Ted describes where they narrowed the flaps by 3/4" also reduced wing AREA by 40 sq in.  The trial of tabs active versus not also suggests this is not the root cause (if I read that part right)

I would (in a heartbeat) cut the flap SPAN; 5" or so off each tip.  Sure it will result in "less flapped span"...  but so what???

Boy that  sounds familiar!!

rANDY

[Mark Scarborough]

Paul,
now how long would it take for ball links to actually rust? man I am thinking years,,  

[Dennis Adamisin]

Boy that  sounds familiar!!

rANDY

I am soooooooooooo predictable! 

[Bradley Walker]

Full adjustment of flap & elevator throws are the best tool in the bag, but a little hard to retrofit.

Trouble with cutting flap chord is that you are also cutting wing area.  Thus you are changing two characteristics at the same time.  The situation Ted describes where they narrowed the flaps by 3/4" also reduced wing AREA by 40 sq in.  The trial of tabs active versus not also suggests this is not the root cause (if I read that part right)

I would (in a heartbeat) cut the flap SPAN; 5" or so off each tip.  Sure it will result in "less flapped span"...  but so what???

Full span flaps equal mucho mucho drag in the corners.  Mucho.  Not to mention huge tip vortexes when coupled to porky planes.

Which explains why many of these fat winged planes with full span flaps have to be built either super light or need monster power to pull them....  or why these plane keep getting smaller and smaller with bigger and bigger engines.

I will never build full span flaps ever, ever again.  Especially those "diving board" flaps that appear to almost have no taper at all all the way out to the wing tips.  those are the worst... just be prepared to get out the nitro when the weather gets hot.  My Strega would nearly fall of the sky when it was over 100.  My Shear Panic, Mr Hyde and Dr Jekyll all required *substantiallly* more HP to pull through a decent pattern.  With these designs, every time the plane hit the corner, the poor little PA 65 (sans pipe) would go neeeeeeeeeeeeee, and sounded like a deflating balloon.  In fact, they were unflyable without a pipe for the added HP or a 4 cycle. 

Of course, you have to couple 14 to 16 oz wing loading with these full span flaps, but I see no advantage unless you are intentionally *trying* to slow the engine down to keep it from winding up.

Of course, I expect to be flamed...

My new T-Rex design has flaps that are about 2/3 span and it is so easy to pull around I think it would adequate with a good 51 on a muffler....  at the same weight.

[Peter Ferguson]

I had something similar happen on my large R/C airplanes that used ball links. I think some of the balls are plated. The 4-40 bolt that held on the ball would rust which undermined the ball plating. Perhaps the hole in the ball doesn't get much plating. It wasn't concealed on those installations so I could replace it easily. I thought about using SS bolts to prevent the problem but I was suspicious about their strength (in hindsight I should be more suspicious about the non spec steel screws).

[Randy Powell]

Or, Howard could just cut them off and put on new ones (or fly the plane without them to see if the problem persists). It's not as if the design isn't well know by Howard and heck, the plane's designer is right at hand.

[Howard Rush]

I replaced the balls.  Two were tight.  One looked corroded, but may have gotten some CA on it.  This is embarrassing, because the first thing one does is to make sure the controls have no friction.  This is the first plane I've built with ball joints, and I never checked them for friction.  Could be the friction was there from the get-go as a result of the threads going in too far, pinching the balls, or it could have crept in later.  Dan Rutherford told me the trick of squeezing the socket perpendicular to the pushrod axis to free a sticky ball.  It worked on the uncorroded ball, but I replaced it anyhow.  The silver lining of this cloud is the plethora of metaphoric material for JCT ditties. 

[John Witt]

I think the balls are chrome plated brass. It's difficult to get much of the plating down the inside of the hole, so you have brass in contact with the zinc, and then steel of the screw. All it takes is a little moisture and you have a battery which will first eat the zinc, then the brass. The tin in the brass alloy can also change phases and cause the ball to slightly increase its diameter. A stainless steel screw will help, since there's no zinc plate.

I don't know how much load the ball links are under in a UC airplane, but the helo guys change them pretty frequently. Of course, they get a lot of motion in a helo. I'd bet you need to change them at least once a year in a stunter. On the other hand, helos are not tolerant of much slop, whereas a UC is probably less critical about that and some wear would help the seizing/corrosion issue.

John

[Kim Doherty]

I replaced the balls.  Two were tight.  This is the first plane I've built with ball joints, and I never checked them for friction.  Could be the friction was there from the get-go as a result of the threads going in too far, pinching the balls, or it could have crept in later.  Dan Rutherford told me the trick of squeezing the socket perpendicular to the pushrod axis to free a sticky ball.  

OK, I confess, I have been to the dark side and I like it. My name is Kim Doherty and I fly R/C helicopters. There, I've said it and I feel so much pressure has been lifted from my being.

I have been using ball links for a fairly long time. If you are going to use ball links you will most likely need to adjust them as well. You will need two tools for this. The first are ball link pliers to remove the link from the ball and reinstall it afterward. The second is a ball link resizer of the appropriate diameter to adjust the amount of friction present in the link. The resizing tool is adjustable in diameter to enable you to remove just the right amount of material. You will only need to rotate the tool a couple of times before you retry the ball. In helicopters we do not want a sloppy head but we do want it to be silky smooth. Both of these tools can be purchased at almost any hobby shop.

Kim.

[Frank Sheridan]

Hey Kim, What brand of ball links are you using these tools on?

[Howard Rush]

I'd like to know that, too.  I have plastic rod ends that I am beginning not to like.  Is anybody familiar with these? http://www.rcrockcrawling.com/product_info.php?products_id=256

My dog seems to be OK now-- a good stunt plane, but not a great one.  My fuselage has assumed the shape of a banana, although so far I can tweak the stab to maintain its alignment.  I still have the handicap of full-span flaps, and big, stiff ones to boot.  Now that the balls are free, we again compensated for the excessive flaps by moving the CG aft and increasing the elevator throw.  Then we moved the leadouts as far back as they would go.  I wouldn't have thought of this myself, but a human embodiment of the Paul Walker Trim Chart was in attendance at the field today.  Now to burn some fuel.

[Brett Buck]

Full span flaps equal mucho mucho drag in the corners.  Mucho.  Not to mention huge tip vortexes when coupled to porky planes.

Which explains why many of these fat winged planes with full span flaps have to be built either super light or need monster power to pull them....  or why these plane keep getting smaller and smaller with bigger and bigger engines.

I will never build full span flaps ever, ever again.  Especially those "diving board" flaps that appear to almost have no taper at all all the way out to the wing tips.  those are the worst... just be prepared to get out the nitro when the weather gets hot.  My Strega would nearly fall of the sky when it was over 100.  My Shear Panic, Mr Hyde and Dr Jekyll all required *substantiallly* more HP to pull through a decent pattern.  With these designs, every time the plane hit the corner, the poor little PA 65 (sans pipe) would go neeeeeeeeeeeeee, and sounded like a deflating balloon.  In fact, they were unflyable without a pipe for the added HP or a 4 cycle. 

   I think you make be missing at least some of the point. Of course, if you make wide-chord flaps that go all the way to the tip, it will be hard to turn and drag the airplane down. The fact that you have to deflect the elevator enough to generate the required rotational rate means you have to move the flaps a lot, too, far beyond what you would really need in other circumstances. That just means the flaps are too big. That's one of the basic flaws I think exists in the the Patternmaster-style airplanes. And the wider the flap chord, the larger the moment arm for the flap hinge moment. Maybe you need it with the rest of the airfoil the way it is, but that's artificially constraining the problem.

   However, you can get a more efficient (in terms of induced L/D) wing with the full-span flaps, and a narrower chord, than with partial-span flaps and a fractional span. You don't need to constrain the airfoil to the "45-degree departure angle" leading edge that leads to the odd shape forward of the high point, so you don't need to have overly large flaps to compensate, and then can adjust the flap chord/percentage of wing chord to get just enough lift.

   Having partial-span flaps is OK, obviously, but having part of the wing cambered, and part of it uncambered, is hardly a formula for reduced drag. The original idea was that gives you washout so the root stalls first, but if you are stalling, you are done anyway.

   If nothing else, the fact that you are finding the power of a PA65 inadequate for flying a stunt plane certainly suggests that there might be something a bit "off". I have as thick a wing as anyone competitive today and my airplane flew just fine with a 40VF.

   And the good reason to have full-span flaps has nothing to do with lift, drag, etc. The issue Paul found, and I (once again) copied, was that the interference between the fixed and moving part of partial-span flaps was causing a trim issue. Particularly if the fixed part is deflected, or the flaps are tweaked so that the fixed and movable sections don't line up on the inboard and outboard wings. That's the one intentional change I made from the 1998 version of my plane, to the 2006 version. This airplane is noticably smoother through the transitions of the round 8s than the old one, and no amount of trimming on the other airplane ever got rid of the little glitch around neutral. The current airplane, it's a non-event.

   Obviously there are various tradeoffs and there's no one way to do anything, but I don't think the theory you are operating on is necessarily right.

   Howard's issue seems straightforward enough, you make flaps tips deflect more, they provide more lift for a given control input, more hinge moment for a given control input, and change the turn  balance of the airplane slightly from the canonical Impact. If it was mine, I would just cut 1/8-3/16" off the flap chord at the tips and try it again.

     Brett

[Paul Walker]

My name is Kim Doherty and I fly R/C helicopters.

Well, that explains a lot!!

And I used to think that you flew electric PA planes.....


Have I got a design for you....

Just take an Impact, add an Orbit 20-16, a 4000 5S29 TP battery, our favorite ESC and Processor, have it weigh in at 62 ounces, and your eyes will be opened!  It can be done.  I have, and it works GREAT!   

Now, don't tell sparky about this new lighter electric plane.  I'll never hear the end of it!!

[RandySmith]

My name is Kim Doherty and I fly R/C helicopters.

Well, that explains a lot!!

And I used to think that you flew electric PA planes.....


Have I got a design for you....

Just take an Impact, add an Orbit 20-16, a 4000 5S29 TP battery, our favorite ESC and Processor, have it weigh in at 62 ounces, and your eyes will be opened!  It can be done.  I have, and it works GREAT!   

Now, don't tell sparky about this new lighter electric plane.  I'll never hear te end of it!!

I once heard someone say an Impact is a great plane between  62 and 65 ounces...

[Howard Rush]

I flew the electrical one.  It's not bad for an airplane with full-span flaps.

[Paul Walker]

I flew the electrical one.  It's not bad for an airplane with full-span flaps.

Yeah, but they're the wimpy soft kind!

[RandySmith]

I flew the electrical one.  It's not bad for an airplane with full-span flaps.

A shocking experience I would guess!!!

I know  that was  baddd

[Frank Sheridan]

Watt a shocking experience!  I just couldn't resist(or) the urge to say that.

[Bradley Walker]

   Obviously there are various tradeoffs and there's no one way to do anything, but I don't think the theory you are operating on is necessarily right.

I am in no way saying that these type flaps do not work well, they obviously do...  given you have enough juice to pull them.

I am just saying that the nearly constant chord full span flaps create way more drag than say 2/3 span flaps of the same area (even if the chord is larger). 

There is indeed a trade off...  you are saying that large chord flaps will cause large resistance at the handle in the wind...  I have not seen that myself.  Mostly what I see is what was said before, flaps being to large (given the 1/1 to ratio is assumed) for the design or the CG to far forward will cause handle loading.  In general, if the CG is too far forward or your flaps are too large, you will feel the flaps in the wind...period.

No, what I am saying is something altogether different.  For a flap of a given area (say 20%) using the large chord at the tip (and in conjunction the flap chord is then reduced at the root to compensate) the greater the drag in hard corners.  As a result more overall power is required to pull the airplane through a "non event corner".  I do believe there is some evidence from large aircraft aerodynamics to support my real world conclusions.

I have no doubt in my mind whatsoever.  I have tested several designs of this type (and other designs) keeping the engine constant.  Whereas most of you guys, have done the opposite, flown the same design with several engines.  It is a very enlightening experience.

Of course, weight is a factor too...  but my T-Rex at 67 oz is infinitely easier to pull than my Mr. Hyde at 67 oz (which was basically an Impact with a high aspect tail) or my Shear Panic, which is a UHP Impact.

On the T-Rex, I basically eliminated the tip of the flap.   Anyway, it will be out soon.  Proof is in the pudding I guess.  I think there might be a slew of vintage engines coming out of the woodwork to pull the first 300 units around.  There certainly is no need for a high zoot fuel guzzling wonder engine to pull it.

[Howard Rush]

I do believe there is some evidence from large aircraft aerodynamics to support my real world conclusions.

Well, show us then.  You got wind tunnel data, a CFD analysis, or what? 

[Bradley Walker]

Well, show us then.  You got wind tunnel data, a CFD analysis, or what?  

No, I don't have those things Howard...  I really only have second hand information from guys who designed propeller driven aircraft.

So, feel free to ignore anything that I said, since I do not have the wind tunnel up and running.

I will however stand by my assertion that I have probably tested more combinations of airplane, engines, pipes, no pipes, 4 stroke, 2 stroke, low RPM, high RPM etc on stunt planes than just about anyone in stunt (sans Randy Smith), at least in recent years.  So, for now I suppose that will have to suffice.

I do not think it takes a genius to know that full span flaps create more tip vortexs than less than full span flaps.  As far as I know (in the world of real airplanes) it is common knowledge that tip vortexs equal turbulence which equal drag...

...but then I am not a super aerodynamic rocket scientist and do not claim to be one.

[Paul Walker]

I do not think it takes a genius to know that full span flaps create more tip vortexs than less than full span flaps.  As far as I know (in the world of real airplanes) it is common knowledge that tip vortexs equal turbulence which equal drag...

Have you ever watched a 757 land in conditions that cause the vortices to condense?  For some reason (ha) that happens in Seattle a lot, and I happen to work under the flight path of Sea-Tac airport. On the 757, the flap goes a significant way outboard on the wing, and on landing approach, with the flaps deployed, you can very clearly see the vortices coming off the end of the flap, and not the wing tip. I'm not shure that shortening the length of a flap on a stunt plane would reduce the tip vortex any.  It would probably just move it.

Regardless of this tip vortex issue, my experience is that the major turbulance left by a stunt plane comes from the prop. The bigger, the worse. It far eclipses the tip vortex issue. I had a plane made for Reno that was 725 in ^2 and 43 ounces. With the standard 11.3 dia prop, it would hit its wake in calm weather. However, switching to a 9*4 and running at 15k, I could stand still in the center of the circle in absolute dead air without fear of hitting my wake. The maneuver speed was no different prop to prop, thus the tip must have been seeing the same flow prop to prop, thus it must not have been the tips causing the issue. As soon as the prop was switched back to 11.3", the problem came back.

As far as full span vs. partial span goes, I have had trouble with some partial span flaps with consistency due to the "funny" flow that happens when the moveable flap transitions past the fixed portion. Full span flaps avoid this issue. This issue was on my '98 Nats winner. With partial span flaps, it was going to be hard making the top 20. With full span, it won. This was not just in my mind, but my coach was asking why I was having such trouble being consistent flight to flight before going to the full span flaps. I switched from flight to flight right in front of him, and he too was amazed at the difference. You may have luck with them, but I don't need that hassle to possibly come back some day. Me, I'm using full span flaps, and I have the electric power to "drive" through the terrible drag they create.....

[Bradley Walker]

I hope no is trying to say I am equating drag=bad, or that I am somehow impugning designs that use lots of drag.  That is not the case at all.

Higher drag equals need for more power...  many stunt designs are based on using drag to control speed.

[Howard Rush]

"I do not think it takes a genius to know that full span flaps create more tip vortexs than less than full span flaps.  As far as I know (in the world of real airplanes) it is common knowledge that tip vortexs equal turbulence which equal drag..."

Not very far, it appears.  Tip vortexs (vortices, we call 'em) are an inevitable consequence of lift.  The drag they cause is called induced drag, although that's sorta a misnomer.  It is, as I recall, for a stunt plane turning a corner, proportional to the square of the airplane's span loading.  You can reduce drag by a few percent by wingtip doodads like winglets or increase it by a few percent by having the spanwise lift distribution stray from the optimal elliptical distribution.  I suspect that without a lot of analysis, you can come closer to an elliptical spanwise lift distribution with full-span flaps than with partial-span flaps.  You are welcome to show me otherwise. 

Another type of drag can come from separation over the flap.  If you try to get a high Cl by deflecting little flaps a lot, you'll probably get a lot of drag.  Full-span flaps can actually have less drag at a given Cl than a wing without flaps.  I came across a paper by Wortmann in about 1976 that showed symmetrical airfoils with flaps optimized to minimize drag at small deflections.  The application Wortmann had in mind was sailplane control surfaces, but it looked like they could be used for combat models.  Phil Cartier saw the paper, too, and we both decided it was cool, but not worth the bother.

This is probably moot for stunt planes.  I don't think drag in corners is a big deal.  When I went to a bigger engine in my Impact, the most noticeable effect to me was better speed regulation in round tricks, particularly the vertical eight.  I didn't need the big engine to get around corners.  Randy Powell made some high-aspect-ratio planes that should actually have lower drag in corners than most planes.  Perhaps he'll give his observations.  Obviously, successful stunt planes have had various flap configurations.  One could probably do just fine with one partial-span flap and one full-span flap. 

[Dennis Moritz]

Nice to hear the unfolding saga of Howard's flaps. Like much else in the stunt world, seems as though it's praxis over theory. What works, works.

[Bradley Walker]

  I didn't need the big engine to get around corners. 

Sigh...  living where you live, I doubt you have any problems making thrust or HP.

Of course, the West Coasters have to go UP in nitro when they visit Muncie, we Texans have to go DOWN.  In fact, many of my friends think Muncie is the supreme source of power, thrust, and lift, and have never experienced anything better.  While your friends complain about how they are down on power compared to home.

I would really like to see if you would have the same opinion in Dallas when it is 104....about the time you hit that second square eight.  All those darn corners... and that motor just keeps slowwwwwwwing downnnnnnnn... trying to keep the speed of the airplane up.  It is pretty simple really.