News:




  • October 23, 2018, 12:27:07 AM

Login with username, password and session length

Author Topic: Unequal panels  (Read 1865 times)

Offline Charlie Pate

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 260
Unequal panels
« on: June 08, 2006, 12:57:35 PM »
 Many planes are built with the inboard wing panel longer than the outboard wing
panel.
The reason for this is said to equalise lift on both wings as the outboard panel
moves faster than the inboard panel.
If this be true, why doesn,t the same thing apply to the stab;or , why don,t we make the inside stab panel longer to give equal lift like the wing?
 Just a thought.


Offline minnesotamodeler

  • 2014 Supporters
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2335
  • Me and my Chief Engineer
    • Minnesotamodeler
Re: Unequal panels
« Reply #1 on: June 08, 2006, 03:58:09 PM »
I don't think anyone has an answer for you!  I have heard this apparent inconsistency discussed before, but never with any kind of resolution.  Maybe you ought to do some experimenting with it and see how (if) it affects flight characteristics.

--Ray
--Ray 
Roseville MN (St. Paul suburb, Arctic Circle)
AMA902472

Offline Tom Dugan

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 175
Re: Unequal panels
« Reply #2 on: June 08, 2006, 07:48:41 PM »
Charlie,

I am far from the expert but I can tell you that Ray has summed it up in a few short sentences.  This comes up in all the forums and there is definately a difference of opinion.  I think you will see that it is the older models that have very obvious offset.  The purpose was to create extra lift to counteract many of the forces acting on a CL plane.  The plan or kit you are looking at probably has 2" offset and again is an older design kit.  It seems that newer designs do not have offset and if they do it may be 1/2".  In the forum discussions I have seen offset boils down to three choices and for the most part are personal preference.  Those choices are:

1.  Leave the offset in the kit as it was designed.  The designer decided that it gives the plane the best flight characteristics.

2.  Thinking about offset currently is that if you put offset in, only 1/2" is really needed.

3.  No offset is needed.

These choices are what Ive taken away from the several threads that Ive read so far.  I know this doesnt answer your question but current opinion is split just about evenly around these personal preference choices.

Thomas

Offline Russell Shaffer

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1335
Re: Unequal panels
« Reply #3 on: June 08, 2006, 08:42:52 PM »
I always thought it was to offset the weight of the lines.  Same reason for tip weight.  But I'm certainly no aeronautical engineer.
Russell Shaffer
Klamath Falls, Oregon
Just North of the California border

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #4 on: June 08, 2006, 11:53:14 PM »
Many planes are built with the inboard wing panel longer than the outboard wing
panel.
The reason for this is said to equalise lift on both wings as the outboard panel
moves faster than the inboard panel.
If this be true, why doesn,t the same thing apply to the stab;or , why don,t we make the inside stab panel longer to give equal lift like the wing?


    That's a very interesting thought. I have come to the opinion that this effect is responsible for the common need to have a larger outboard flap.

      Brett

Offline Bill Little

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12813
  • Second in COMMAND
Re: Unequal panels
« Reply #5 on: June 09, 2006, 07:09:43 PM »
    That's a very interesting thought. I have come to the opinion that this effect is responsible for the common need to have a larger outboard flap.

      Brett

Brett,

Since the reaction of the airplane is to nose out when up is applied and nose in when down is applied  (counterclockwise flight), doesn't the increase in outboard flap area help to some degree to offset this?  It seems to me that with a larger outboard flap area, when the flaps are deflected it almost gives an "aileron" effect to the plane.  I do not see the added flap area outboard to be of that great an advantage in level flight other than to maybe support a *little* more tip weight..

Am I way off base here??

(Sorry Charlie)

Bill <><
Big Bear <><

Aberdeen, NC

James Hylton Motorsports/NASCAR/ARCA

AMA 95351 (got one of my old numbers back! ;D )

Trying to get by

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #6 on: June 09, 2006, 11:57:45 PM »
Brett,

Since the reaction of the airplane is to nose out when up is applied and nose in when down is applied  (counterclockwise flight), doesn't the increase in outboard flap area help to some degree to offset this? 

   I don't think so - the extra drag, if any, will nose the airplane out with turns in either direction, so it will make one direction worse.
     Note I didn't commit myself to which direction it yaws in corners. There is more than one effect, and I'll let Ted and Al argue over that one some more.


  The asymmetrical torque in *roll* from the effect Charlie mentions results in the airplane rolling away from you (as if you had more tip weight) on either insides or outsides. The larger outboard flap counters this.

    I have done some pretty crude experiments with this in the last few years, with stab/elevator extensions on the inboard side. They were so cursory that I didn't really prove anything one way or the other. It's a very minor effect, and to really make a complete experiment you really need to replace the outboard flap with one the same size as the inboard.

      Brett
   

Offline Bill Little

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12813
  • Second in COMMAND
Re: Unequal panels
« Reply #7 on: June 10, 2006, 10:17:28 AM »
   I don't think so - the extra drag, if any, will nose the airplane out with turns in either direction, so it will make one direction worse.
     Note I didn't commit myself to which direction it yaws in corners. There is more than one effect, and I'll let Ted and Al argue over that one some more.


  The asymmetrical torque in *roll* from the effect Charlie mentions results in the airplane rolling away from you (as if you had more tip weight) on either insides or outsides. The larger outboard flap counters this.

    I have done some pretty crude experiments with this in the last few years, with stab/elevator extensions on the inboard side. They were so cursory that I didn't really prove anything one way or the other. It's a very minor effect, and to really make a complete experiment you really need to replace the outboard flap with one the same size as the inboard.

      Brett

Thanks, Brett.  I had not figured the drag of the flap, just the increased size. 

Haven't seen Ted and Al discuss all the "P" words in quite a while!

The experiment you speak of would seem to have been simple with something like Ted's Imitation and the variable flap size set up he started with.  (??)

Bill <><
Big Bear <><

Aberdeen, NC

James Hylton Motorsports/NASCAR/ARCA

AMA 95351 (got one of my old numbers back! ;D )

Trying to get by

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #8 on: June 10, 2006, 01:49:14 PM »

The experiment you speak of would seem to have been simple with something like Ted's Imitation and the variable flap size set up he started with.  (??)


   We would have to have thought of it before the airplane met it's demise.

    It was one of the points of evidence in the idea. The airplane was rather famous for outrageous twist in the fuselage, and it tended to be in the direction indicated by the lift asymmetry in the tail. If you see the tail twisted 20-30 degrees, you can figure it's putting a lot of torque on the rest of the airplane.

      Brett

Offline Terry Fancher

  • AMA Member
  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 15
Re: Unequal panels
« Reply #9 on: June 13, 2006, 10:08:39 AM »
Thanks, Brett.  I had not figured the drag of the flap, just the increased size. 

Haven't seen Ted and Al discuss all the "P" words in quite a while!

The experiment you speak of would seem to have been simple with something like Ted's Imitation and the variable flap size set up he started with.  (??)

Bill <><

Bill,

We're keeping our powder dry! >:D >:D >:D

Ted  p.s. The "currently being contemplated" twin Imitation will not have the tail twist problems addressed by my esteemed colleague.  It will, in fact, have a built up fuse (and may actually have a slightly longer inboard stab/elev.  As you might have guessed, Brett and I have spent more than a few minutes discussing the possibility)

p.p.p.s.  Actually, I thought the Imitation was famous for being a truly great design and flying outstanding patterns. ::) ::) ::) .  Guess maybe I was blinded by the twisting tail.  8)

Offline Bill Little

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12813
  • Second in COMMAND
Re: Unequal panels
« Reply #10 on: June 13, 2006, 12:08:36 PM »
Hi Ted,

ALL of the Imitations I have seen in the air have been outstanding flyers!  So much so that I have sheeted a set of ancient foam cores to biuld an OS 40VF piped version.  Probably leaving it as a profile!

Bill <><
Big Bear <><

Aberdeen, NC

James Hylton Motorsports/NASCAR/ARCA

AMA 95351 (got one of my old numbers back! ;D )

Trying to get by

Offline Terry Fancher

  • AMA Member
  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 15
Re: Unequal panels
« Reply #11 on: June 13, 2006, 12:50:32 PM »
Hi Ted,

ALL of the Imitations I have seen in the air have been outstanding flyers!  So much so that I have sheeted a set of ancient foam cores to biuld an OS 40VF piped version.  Probably leaving it as a profile!

Bill <><

Bill,

I'm sure you'll enjoy it.  I probably flew my original at least twice as many flights as any other airplane I've built.  It was the easiest airplane to fly well I've ever flown and wasn't critical to trim.  My favorite configuration was with the Enya .46 four stroke that was an absolutely perfect combination despite the resulting high weight (about 62 oz with the four stroke up front and the weight in the tail necessary to balance it).  YOu could do any maneuver you wanted any size you wanted and it just kept chugging along.

All kidding aside, Brett's admonition about the flexible aft fuse is real.  From the pilot's perspective it never bothered my with my original but, from watching others fly theirs, it was very real.  Anything of reasonable weight that can be done to add some torsional rigidity would probably be worth it.

A local flyer, Paul Pomposo, has been flying one of late with a piped VF and seems to like it a lot.

Ted

Offline L0U CRANE

  • AMA Member
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 888
Re: Unequal panels
« Reply #12 on: June 18, 2006, 02:01:08 PM »
Hi, all...

I favor unequal  wing panel physical lengths that are dynamically equal in area, considering the span and flight radius.

There's no single rule of thumb for that condition, although many models are very similar in layout, line length and span, so for them the same solution works or is very close.

As I recall, many designers went to equal-physical-length panels for appearance reasons, then found that they needed quite a bit more tipweight than the (properly sized) unequal panels did. I think, also, experimenting with larger outboard flap area also began with "equal span panels," then was found useful for "unequal-span-panels."

If the panel area is split properly to each side of the fuselage, many of the lift, drag and thrust problems are pretty well resolved.

Since the line weight acts vertically, and line drag in flight acts horizontally, we can static-balance the effect of line weight with tipweight (I presume the model carries half and I carry the other half. Of course, that applies  less and less as the model moves higher on the flight hemisphere, but it is a starting point.)

We deal with the horizontal effect of line drag with CG position vs leadout guide location, and a few other things...
\BEST\LOU

Offline Paul Smith

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4669
Re: Unequal panels
« Reply #13 on: July 13, 2006, 04:58:32 AM »
I built a certain combat design with 1.5" of offset.  I built a lot of 'em, maybe 20 or so.

Just as an experiment, after listening to this "equal panel" jive, I built one with equal panels. A total disaster !!!  It came on the lines like crazy.  I had to add 2 ounces of tip weight. 

Reason ?? Simple.  The outboard wing is going faster and makes lot more lift.  In tight turns, it makes so much excess lift, it will come into the centre and EAT YOU.

I cured it by cutting 1.5" off the outboard wing and return the tip weight to normal.

The old masters got right.  Some kits are made equal just to minimize production cost.
Paul Smith

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #14 on: July 18, 2006, 03:07:43 PM »
I built a certain combat design with 1.5" of offset.  I built a lot of 'em, maybe 20 or so.

Just as an experiment, after listening to this "equal panel" jive, I built one with equal panels. A total disaster !!!  It came on the lines like crazy.  I had to add 2 ounces of tip weight. 

Reason ?? Simple.  The outboard wing is going faster and makes lot more lift.  In tight turns, it makes so much excess lift, it will come into the centre and EAT YOU.

I cured it by cutting 1.5" off the outboard wing and return the tip weight to normal.

The old masters got right.  Some kits are made equal just to minimize production cost.

     This experiment tells us very little about the topic. I don't think that anyone would be remotely surprised that if you took a working design, and cut an inch and a half off of one wing,  that it wouldn't work and/or need a lot of tipweight. Now, if you had some observations about how it flew once you put in sufficient tip weight, then, that might tell us something.

   The lateral CP of the wing is offset from the geometric centerline of the wing by differential speed effects. However, the "old masters" were off by factors of 3-10 in the amount of differential needed, depending on the design. The right answer, at least to balance the speed differential,  for ~35-sized planes, is on the order of 1/2".  And, the "old masters" completely missed the exact same effect on the tail, resulting in designs like the All-American.


Over the years,  cut-and-try experimentation determined that  we needed for various "warts" on the outboard flap. Now we know why.

     Brett

Offline Steve Fitton

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2129
Re: Unequal panels
« Reply #15 on: July 23, 2006, 10:37:29 PM »
Is the current Infinity using equal panels?
Steve

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 13267
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Unequal panels
« Reply #16 on: July 25, 2006, 07:24:10 PM »
Is the current Infinity using equal panels?

Hi Steve
Not speaking for Brett, but i have  tried about adozen differant wing panel lenghts, and  also equal panels. I have found  that  about 3/4 inch to be  perfect  on 59 to 61 inch span planes.

Regards
Randy

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #17 on: July 25, 2006, 07:40:38 PM »
Is the current Infinity using equal panels?

 5/8" on the wing, 0 on the tail. I'm planning to do the offset tail experiment with extensions on the tips and a new outboard flap (same chord as inboard, vice 1/1/8" larger like it is now.

    Brett

Offline Steve Fitton

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2129
Re: Unequal panels
« Reply #18 on: July 25, 2006, 10:49:46 PM »
Thanks Brett and Randy for the comments.  I'd flown equal panels for awhile, and was caught a bit suprise by how much less tipweight you carry on an offset wing like my Avanti I just started fooling with.  I was thinking the Infinity was equal span, although the fact it had offset was probably mentioned ages ago and it never registered.

Steve
Steve

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #19 on: July 26, 2006, 07:36:49 AM »
Thanks Brett and Randy for the comments.  I'd flown equal panels for awhile, and was caught a bit suprise by how much less tipweight you carry on an offset wing like my Avanti I just started fooling with.

    To first approximation, it really *is* like moving the fuselage over to act as tipweight. Figure the fuselage and all the attached parts are 75% of the weight of the airplane, maybe 45 oz of a 60 oz airplane. 3/4"x45 oz =33.75 in-oz of rolling moment. That's about equivalent to an ounce and a quarter in the tip. This is not exactly rigorous but it's close enough to explain the effect.

   What doing it to excess creates are the *secondary* effects like having the tail offset from the wing, the thrust vector not aimed through the CG, etc.

     Brett

Offline RC Storick

  • Forum owner
  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 11613
  • The finish starts with the first piece of wood cut
    • Stunt Hangar
Re: Unequal panels
« Reply #20 on: July 26, 2006, 04:58:35 PM »
I think of it just like stagger. Stagger is when a race Bike or Car is set up to turn left. The theory of it being like wing tip weight is plausible however "I think it creates more lift" Meaning less tip weight. Everyone who knows my attitude on weight knows that I think thats a good thought.  f~

By the way it's my first post in this section.  %^
« Last Edit: July 26, 2006, 05:47:30 PM by Robert Storick »
AMA 12366

Offline gordon tarbell

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 464
Re: Unequal panels
« Reply #21 on: July 26, 2006, 05:42:03 PM »
Make Right rear tire bigger car turns left.
Gordon Tarbell AMA 15019

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 13267
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Unequal panels
« Reply #22 on: July 26, 2006, 08:24:57 PM »
Thanks Brett and Randy for the comments.  I'd flown equal panels for awhile, and was caught a bit suprise by how much less tipweight you carry on an offset wing like my Avanti I just started fooling with.  I was thinking the Infinity was equal span, although the fact it had offset was probably mentioned ages ago and it never registered.

Steve

Hi Steve

In the planes I tried with equal  span  I had as much as  2  1/2 ounces  of  tip weight.  Thats  a  lottta  lead.
Everything I have built or have under constrution  use  between  1/2  to  3/4  inch  offset panels.

Brett  I actualy  had  a plane  that used offset in the  stab-elev. was 1/4 inch to be  the  same  as  the  wing? really could tell no  differance. I had  thought about trying  that again  sometime, so it will be  interesting to see  what you  find

Randy

Offline Steve Fitton

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2129
Re: Unequal panels
« Reply #23 on: July 26, 2006, 08:54:47 PM »
Randy,

  Thats about what my equal span Time Machine carries.  2.0 oz lead plus an indeterminate amount of extra in the non-hollowed outer tip.  It almost bit me in the Avanti 50 where I have taken out all but 1/4oz from the weight box but have the again indeterminate amount of weight in the non-hollowed tip.  That 1/4 oz may have to come out as well.  I should have remembered this fact with offset panels but didn't.  Now I know why your plans show the outboard tip hollowed(!)

Steve
Steve

Offline Jim Pollock

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1050
Re: Unequal panels
« Reply #24 on: August 10, 2006, 06:00:26 AM »
Brett, Steve, Ted - All

I understand the effects of wing offset and plan on using 5/8" offset on my
Excelsior.  Another offset that I may try is making the inboard tip of the Stab/elevator 1/16" lower than absolute level to help with gyrscopic precession.  Of course I don't know if that would be sufficient to help or not, but the idea is start with just a little and revise later if needed.  Is anyone else going to try stab tilt?

Jim Pollock   :!

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 13267
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Unequal panels
« Reply #25 on: August 10, 2006, 12:42:54 PM »
Brett, Steve, Ted - All

I understand the effects of wing offset and plan on using 5/8" offset on my
Excelsior.  Another offset that I may try is making the inboard tip of the Stab/elevator 1/16" lower than absolute level to help with gyrscopic precession.  Of course I don't know if that would be sufficient to help or not, but the idea is start with just a little and revise later if needed.  Is anyone else going to try stab tilt?

Jim Pollock   :!


Not on purpose  !!   y1

Offline Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1944
Re: Unequal panels
« Reply #26 on: August 10, 2006, 03:08:33 PM »

Not on purpose  !!   y1

 **) ... yes, I did, I wrote it some years ago on stuka

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #27 on: August 10, 2006, 08:01:01 PM »
Another offset that I may try is making the inboard tip of the Stab/elevator 1/16" lower than absolute level to help with gyrscopic precession.  Of course I don't know if that would be sufficient to help or not, but the idea is start with just a little and revise later if needed.  Is anyone else going to try stab tilt?

   Oh my! I don't think I would recommend that. If you want to try it, I would suggest doing the old boiling water/towel trick on an existing (old) airplane and see how it works before doing it on a new one or building it in on purpose.

      Brett

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 13267
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Unequal panels
« Reply #28 on: August 11, 2006, 09:20:05 AM »
**) ... yes, I did, I wrote it some years ago on stuka

Hello Igor

One  little  problem I see with this  is  you  would need a differant  warp , or  angle  on the  stab tilt  for  2 or  3 blade  props  and  also  for  differant  diameter  props  :o
 j1

You guys let me know how this works  :-O

Offline Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1944
Re: Unequal panels
« Reply #29 on: August 11, 2006, 09:31:35 AM »
I see much bigger problem, I cannot trimm it at all (may be little bit with CG position). So if the tilt is improper or if I use another prop as you say, the only way to fix it is to cut the stab out and install it back at different angle. I do not see any advantage to the Rabe rudder beside less moving marts. ... and ... it does not look "seriosly" at all  ;D

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #30 on: August 11, 2006, 10:38:40 AM »
I see much bigger problem, I cannot trimm it at all (may be little bit with CG position). So if the tilt is improper or if I use another prop as you say, the only way to fix it is to cut the stab out and install it back at different angle. I do not see any advantage to the Rabe rudder beside less moving marts. ... and ... it does not look "seriosly" at all  ;D

      The most serious problem I see is that it's like using an H-bomb on an ant hill. Precession is a minor problem at most, and many many airplane have managed to be trimmed reasonably well without any consideration for it at all. Stab tilt (or skew) has incredible "authority" to induce yaw torques. To have even slightly off has a very large effect on the way the airplane flies.

     If you are really interested in "curing" precession the Rabe rudder is a perfectly fine solution. Plus, you can adjust it, or more likely, fix it one position when you decide it's not necessary.

     Brett

Eric Viglione

  • Guest
  • Trade Count: (0)
Re: Unequal panels
« Reply #31 on: August 11, 2006, 01:55:22 PM »
Sort of related... maybe a stretch  n~

The flapless Baron Humbug I inherited had a Rabe rudder on it. Probably came in handy when Baron had the high rpm OS FSR setup in this plane. Then he switched it over to STV60, and that's what I've been running too.  (well, actually a STV56, virtually identical run)

It took me a while to figure it out, but the Rabe rudder became not only unneeded with the ST60, but was a total detriment. I've recently reconfigured it to more of a Windy "wiggly" rudder, that moves very little, with the over all effect of some constant rudder for both up and down.   :!

Baron had it kicking so far out on "up" control that it was kiting away on insides, which is what happened when I flew it at the KOI for the first time in dead air.  %^ The air hadn't been dead for months, so I never ran into that. Boy, what a wake up call! Disaster was averted, but the flight score would not have made Baron proud.  ''

With that fixed, it actually flies pretty conventionally now, though the corners wouldn't be considered blinding. I attribute that more to material choice than design. The elevator is thin contest balsa with silkspan, and really should have been light C grain or built up. As it sits, it's thin & very flimsy.

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #32 on: August 11, 2006, 06:58:34 PM »

The flapless Baron Humbug I inherited had a Rabe rudder on it. Probably came in handy when Baron had the high rpm OS FSR setup in this plane. Then he switched it over to STV60, and that's what I've been running too.  (well, actually a STV56, virtually identical run)

It took me a while to figure it out, but the Rabe rudder became not only unneeded with the ST60, but was a total detriment. I've recently reconfigured it to more of a Windy "wiggly" rudder, that moves very little, with the over all effect of some constant rudder for both up and down.   :!

    I'm not sure what you are running, but the typical Baron-recommended run for the 45FSR (11.5-4) and the typical ST60 setup are very close in terms of precession.  I think you may be jumping to a conclusion that the difference you found was a result of precession. It could have been a half-dozen other factors.

    In any case, most movable-in-flight rudders hurt more than help, but that's only because most, in fact virtually all of them, are adjusted incorrectly. It's a very powerful adjustment and you need *very very little* movement. And it's my very firmly held opinion that there's almost no good reason to have any net offset at neutral.

   If the movable rudder is hurting you instead of helping then is certain to have been incorrectly adjusted. It definitely won't jurt anything *if it's right*.

      Al's instructions for adjustment are about perfect, with only one problem - they require Al's level of knowledge and observational ability to implement. Most people, at *all* skill levels, seem to be be incapable of seeing or diagnosing rudder problems.

    I would suggest an alternate plan - disconnect the rudder and put it in a fixed position very close to 0. Then trim the airplane to the absolutely best you can do without a movable rudder. That will take about a year of flying for most. Then, and only then, take it out on a calm day, fly it a few times as is, looking for yaw. Then hook it up to the movable parts, and add *just enough* to remove the yaw you see. I promise that if the airplane is in optimum trim with a fixed rudder near 0, you will need only a teeny-tiny amount of additional movement to fix the precession. This avoids the typical problem  - where all trim problems are addressed with rudder adjustments.

   Brett

Eric Viglione

  • Guest
  • Trade Count: (0)
Re: Unequal panels
« Reply #33 on: August 11, 2006, 10:06:08 PM »
Well Brett, I don't know what to tell ya. When I got this plane, the rudder was set to move  a  LOT. And for up control, the rudder went past 0 deg, and actually was set about 2 deg past 0 deg to push the airplane IN.

I had started by working with tip weight, removing itsty bits 1/16th ounce at a time over the last year, until the wing stopped dipping at hard turns up at 45 deg, and that's when I decided to start backing off the Rabe rudder. I removed ALL tip weight eventually ( a full 1/2 ounce) and the weight box is now totally empty.

 The way it's set now, it's got about 3 deg offset at neutral, 7deg offset at max down control and about 5deg max offset at full up.  It never goes past 0 deg anymore to push the plane in, it kicks out, neutral, then back out the way I have it set now, and it is SOOOO much better it isn't funny. Very little if any yaw in the corners anymore. It used to wag it's tail like a dog. It's so much cleaner now that the corners even appear sharper.

OH...BTW, I installed the motor at 0 offset right from the beginning, and most people look at it and think it has inset because Baron sanded the ply nose ring for offset, and with the motor at 0 deg it looks like inset until you measure the prop tips. I obviously have it setup very different from the last person who owned it.

This was a very early version of the Humbug that Baron was never happy with, and didn't retro fit the ST60 till much much later, and gave up on it yet again. Not sure what the level of understanding of trim was back then, but this thing was pretty out of whack )for me anyways) when I got it. Now, in all fairness to Baron, this thing passed through other hands before I got it, and someone else very likely messed with it, and made it worse.

For what it's worth, on the "run" of an FSR vs/ST60.... Well... you may be thinking of the typical west coast Tom Lay ST60 runs you probably see locally, and if that is what your comparing to the FSR run, yes, they are probably about the same or close for procession.

But, compared to the BigJim ST60 run, the ST60 runs you will find are two very different animals. The one ST60 run is with the stock high compression head, flatter pitch run, as even Pat Johnson recently reccomended the new APC13x4w as a good choice for ST60's, and that's probably why. The second type BigJim ST60 run is low compression hemi head, low RPM run. My ST56 is running a 13x6 in the mid 8K. Nothing at all like an FSR turning an 11x4 at 10500 or even a TL ST60 turning a 13x4 at 9800. 

Mayhaps that is what you were thinking when comparing the FSR??? :!

Eric V.

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 9049
Re: Unequal panels
« Reply #34 on: August 11, 2006, 11:11:11 PM »
Well Brett, I don't know what to tell ya. When I got this plane, the rudder was set to move  a  LOT. And for up control, the rudder went past 0 deg, and actually was set about 2 deg past 0 deg to push the airplane IN.

The way it's set now, it's got about 3 deg offset at neutral, 7deg offset at max down control and about 5deg max offset at full up.  It never goes past 0 deg anymore to push the plane in, it kicks out, neutral, then back out the way I have it set now, and it is SOOOO much better it isn't funny. Very little if any yaw in the corners anymore. It used to wag it's tail like a dog. It's so much cleaner now that the corners even appear sharper.

   Yeah, that's a lot more in the ball park. I was a little concerned when you mentioned the "Windy" setup. I hadn't spent a lot of time looking at the other airplanes, but I know the Testarossa had a neutral offset of about 15-20 degrees, with more movement than that.

Quote
For what it's worth, on the "run" of an FSR vs/ST60.... Well... you may be thinking of the typical west coast Tom Lay ST60 runs you probably see locally, and if that is what your comparing to the FSR run, yes, they are probably about the same or close for procession.

But, compared to the BigJim ST60 run, the ST60 runs you will find are two very different animals. The one ST60 run is with the stock high compression head, flatter pitch run, as even Pat Johnson recently reccomended the new APC13x4w as a good choice for ST60's, and that's probably why. The second type BigJim ST60 run is low compression hemi head, low RPM run. My ST56 is running a 13x6 in the mid 8K. Nothing at all like an FSR turning an 11x4 at 10500 or even a TL ST60 turning a 13x4 at 9800. 

Mayhaps that is what you were thinking when comparing the FSR??? :!


   No way - if that's what you are running it's probably even more that way than I thought.  8000 on the ground is about 8800-9000 in the air, and the FSR is running about 10800-11000 in the air. Thats only a difference of about 25%. The radius of gyrations of a 11 and 13" prop are about 2.475 and 2.92 respectively. The moment of inertia of the precession goes as the square of the radius of gyration, so the 13 has about 40% more inertia *even if the two props weighed the same*. Figure that the 13" prop probably weighs at least half again as much and it's a slam dunk - WAY more precession with a 13-6 at 8800 than an 11-4 at 11000. Looks to be about 70% more (1.4*1.5*.8 = 1.68).

     That's the sort of thing I was talking about. With the engine/prop switch, the precession went UP, not down. Maybe it might works better because the increased torque is a better  match the reduced (but still substantial) rudder movement.

     It's no wonder it didn't work before  - with far less precessional torques, the required rudder movement would have been very small indeed. But instead, it was moving A LOT.

Brett

   


   Check my math- use the equations in my design column

r_gyr = ~.225 x diameter  (from Pete Soule's testing results)

I=m x r_gyr^2

h (angular momentum) = I x omega

omega = RPM/.104666

Eric Viglione

  • Guest
  • Trade Count: (0)
Re: Unequal panels
« Reply #35 on: August 12, 2006, 09:27:30 AM »
Quote
No way - ....<SNIP> Figure that the 13" prop probably weighs at least half again as much and it's a slam dunk - WAY more precession with a 13-6 at 8800 than an 11-4 at 11000. Looks to be about 70% more (1.4*1.5*.8 = 1.68).

Hey, I was just pointing out what inheriting a ill-adjusted Rabe Rudder was like. BUT... as long as you brought it up, I just ran out to the shop and fired up the digital scale:

APC 11.5x4 = 1.4 ounces!!!!  %^
REVUP 13x6 (the one I'm running is cut down to 12.75) = .7 ounces!

That's half the weight of the FSR prop, not the other way around.

May want to recheck the math with those numbers. Besides, everyone who calculates GP always leaves out the Engines internal rotating mass. Add that at the over 2k rpm difference between the two runs. and the prop is almost along for the ride. Well, that's an exaggeration... but you get my drift.  Anyone who's had a shaft run on an FSR can attest to this as well, they are a pretty beefy motor GP wise, even sans prop. Go pop the hood of your car and stomp the gas pedal, hope you got good motor mounts, no prop attached to your car (if your cars new enough, the fan is electric and not on the water pump, heh  :P ), and the motor does the same thing as ours, right?

All I'm saying is there are a multitude of other factors for a given setup that may or may not have been at play here. For me, I can attest that from my cut-and-try experience that MY typical low RPM ST60 on a wood prop has minimal GP compared to other similar high RPM setups with carbon or nylon props.  Maybe I'm all wet, but it fits nicely into my little world.  ;)

EricV


Tags: