Asymmetrical wing length vs. symmetrical wing length

[Skip Chernoff]

I'm certain this topic has come up, so please forgive me for asking. All of  the full fuselage stunters I've ever built had a longer inboard panel.Recently I noticed a number of "symmetrical" length wings on various planes.I have three questions (1) when did this change take place? (2) Why did this occur?(3) Is the stunt community finding that symmetrical length wings fly better? Just Curious....PhillySkip

[Perry Rose]

On question 3, I am not able to tell the difference. I would have to build two of the same model with the wings installed equal and unequal and fly them to see if I could tell the difference. I recall more than one reason for the unequal wing panels. The first I heard was that the longer inside wing was to support the weight of the lines then, later on it was that the outside wing flew faster and produced more lift so it had to be shorter.

[GallopingGhostler]

I'd be curious too. Designs such as Hal DeBolt's All American in all sizes has a longer wing inboard panel than outer. He states that he did this so that no rudder offset was required, no tip weight required either. Of course, I noticed that he set his planes up to fly clockwise to take advantage of the engine's torque. Nowadays we all fly counterclockwise.

Should one do away with the offset and make the All American wing symmetrical, with tip weight, engine thrust offset and rudder offset?

[Garf]

Should one do away with the offset and make the All American wing symmetrical, with tip weight, engine thrust offset and rudder offset?

Then you can't use it to fly OTS.

[Tim Wescott]

I think that the "big boys" use a small amount (an inch or so) of asymmetry.  I haven't flown an All American, but I've heard a number of comments on the difficulties caused by the extreme amount of asymmetry in that design (and if you "correct" it then you can't fly it in OTS, unless you can document someone flying it that way by December of 1952).

Basically, if you're not extreme about it, a little bit of asymmetry is more or less a trim issue.  Probably no matter what, it's something that you trim around because it's not something that you can exactly change easily at the field.

[Paul Smith]

I look at it this way.

Assume the engine is going 60 MPH in a 60 foot circle.  So with an average size stunter the center of the inboard wing is going about 59 MPH and the outboard is going 61 MPH.  So very clearly, the outboard is going farther and faster and making more lift and drag.

So you can compensate by adjusting the size of the wings or by adding enough tip weight to waste the excess lift on the outboard side.

Another way is to imagine that you have a wing flying in a circle with no fuselage.  It will have CENTER of Lift that is slightly outboard due to the speed differential.  The smart designer would find the center of lift and place the fuselage upon it.  Thus with the CG and CL aligned, there would be no rolling moment either in level flight or during maneuvers.

[john e. holliday]

Doesn't a full symmetrical air foil have to fly a very minor positive angle for lift?

[Randy Powell]

You need more tip weight with equal span panels.

[Tim Wescott]

Doesn't a full symmetrical air foil have to fly a very minor positive angle for lift?

Yes.  I'm not sure how that pertains to this discussion, though.

I'm pretty sure that when we fly level, the flaps are trailing down.  If you read Paul Walker's trim chart, one of the cycles in there is to adjust the flap-elevator ratio while tweaking the elevator bias so that the plane is riding dead-level both upright and inverted.  Too much flap-elevator and it'll be nose down upright and inverted; too little (or with a flapless stunter) the nose will ride high both upright and inverted.

[Andre Ming]

The only actual "stunt" type plane I ever finished and flew was a .35 Magician with a Fox 35 Stunt on it. The Magician has an asymmetrical wing design as I recall. Good memories with it. Stable flier, easy to fly, and so forth. Perhaps "one of these days" I'll build another Magician.

[Ted Fancher]

The thing you have to be aware of (and correct for if, like the All American, stock asymmetry is excessive) is the fact that the greater the asymmetry the less tip weight you can carry to adjust for the speed/lift differential.  The All American is the historically perfect example.   At some degree of asymmetry (the AA Sr had a full three inches on just a ~50" span and is the poster plane for what I'm about to write) the spanwise center of gravity will have to be "inboard" of the fuse because the much more than necessary extra inboard wing will now be producing more lift than the outboard and could...if taken even further require weight to be added to the inboard wing to keep the wings level during maneuvering.  That would suck but not as much as building it per the plans but using nor (or even very little) engine offset.

The bigger problem (displayed by every AA Sr. built per the plans) is that the spanwise CG can and most likely will end up "inboard" of the thrust line of an engine mounted with little or no offset.  The result of this problem is that, upon release, the thrust--being outboard of the spanwise CG--will do its best to accelerate the nose inward toward the pilot rather than straight ahead as more or less demanded by our Jurassic era control system which doesn't adapt easily to slack lines.  This has resulted in many an AA Sr. visiting the airman in the center of the circle despite his/her best efforts to outrun  the dang thing.

The solution is to defy Brett Buck and all the other experts (such as myself) who preach minimal aerodynamic offsets on our Hot Shot stunters and mount your Fox .35 in the AA Sr. with decided out thrust (four or five degrees) so that the thrust line will pass inboard of the (necessary) spanwise CG location for performing tricks with level wings.  Were it not for those pesky "rules" the better solution would be to move the stock wing about two inches outboard resulting in a more modest one inch of asymmetry.  Alas, you're unlikely to slip that big a change past the OTS ED.

Ted

p.s.  I no longer have my plans for the AA Sr. and can't recall if Hal DeBolt showed a lot of offset or not.  The plans do, as I recall, show the ship as he flew it, clockwise.  The torque may have helped a bit to keep the outboard wing lower until the ship accelerated but I doubt very much that it would have allowed the engine to have been mounted with zero offset like we're so prone to do with our hot shot ships.

I did pull out my (later designed) de Bolt  Stunt Wagon plans, however, which show the flip side of this discussion.  The SW had equal span wings (quite unusual for the times, I believe); employed Zero engine offset and called for four (FOUR) ounces of outboard tip weight.  By the way, no less a famous and well qualified expert than Al Rabe utilized nothing other than equal span wings and made it quite clear that significant tip weight was required to adjust the spanwise CG to compensate for the greater lift of the faster outboard wing.  As with the Stunt Wagon, no engine offset would have been required to avoid the AA Sr takeoff issues. pps, I believe my comment about Al eschewing asymmetry is accurate.  There might have been exceptions that I'm unaware of.

Of the two extremes the equal span wings and extra required tip weight is a no brainer superior approach than excessive wing asymmetry.  Some of us hot shots could probably make an argument for the superiority of more modest asymmetry, requiring less tip weight set up being closer to the ideal.  Both those approaches have admirable records over the years.  The AA Sr. approach, not so much.

[Tim Wescott]

Of the two extremes the equal span wings and extra required tip weight is a no brainer superior approach than excessive wing asymmetry.  Some of us hot shots could probably make an argument for the superiority of more modest asymmetry, requiring less tip weight set up being closer to the ideal.  Both those approaches have admirable records over the years.  The AA Sr. approach, not so much.

--> Listen to Ted <--

Well, unless he and some guy named Howard start arguing over aerodynamics.  Then grab some popcorn and a soda, sit back, and enjoy the show.
 
I am not a super-expert, although I can regurgitate things they've said.  I try to figure out who actually wins, mix in what I know about what current design trends there are, and go from there.  And for asymmetry -- it's what Ted said.

[Skip Chernoff]

Thanks all for your thoughts on this subject. Now I have another question.....Suppose you build a symmetrical ship ,how do you determine how much tip weight you actually need? Is it the old fly upright then inverted and see if you've got a high or low wingtip then add or subtract tip weight.....or will one of the pattern stunts tell you if tip weight is needed. Thanks,PhillySkip

[Tim Wescott]

Thanks all for your thoughts on this subject. Now I have another question.....Suppose you build a symmetrical ship ,how do you determine how much tip weight you actually need? Is it the old fly upright then inverted and see if you've got a high or low wingtip then add or subtract tip weight.....or will one of the pattern stunts tell you if tip weight is needed. Thanks,PhillySkip

Initially, you add a bit more (1/2 ounce or so for a 40-sized ship) than half the weight of your lines.  More is safer.

Then you go do the upside-down, right side up thing, looking for tip weight and warps.

Then, if you're a good enough pilot (or if you have helpful people looking at your flying) you watch the plane's behavior in the corners.  There's a complicated interaction of tip weight and leadout placement that, when done right, makes the corners sweet.  If you can find one of Paul Walker's trimming articles (series of, actually), then get it and study it.  He leads you by the nose through the whole process.

[Skip Chernoff]

Thanks,reading the Walker trimming stuff now.

[Mark Scarborough]

on tip weight, the point of the exercise is the add enough weight so the outboard tip is 1/2 ounce heavier than the inboard.  simply adding a half ounce to the outboard tip is NOT the answer. what about the extra finish, or heavy ribs or,,,

so as Brett describes you balance the beast  along the centerline fore and aft, then put your desired tip weight on the inboard tip ( be it 1/2 or 1 ounce, I would target starting with 1 ounce personally) then add weight to the outboard tip till it balances out. remove the inboard weight( its just there to balance ) and add the outboard weight to the tip weeight box,,
then fly,,
telling moments for tip weight, square corners, and transitions

[GallopingGhostler]

p.s.  I no longer have my plans for the AA Sr. and can't recall if Hal DeBolt showed a lot of offset or not.  The plans do, as I recall, show the ship as he flew it, clockwise.  The torque may have helped a bit to keep the outboard wing lower until the ship accelerated but I doubt very much that it would have allowed the engine to have been mounted with zero offset like we're so prone to do with our hot shot ships.

Thanks, Ted for your explanations. Outerzone has PDF plans of the AA Sr. http://www.outerzone.co.uk/plan_details.asp?ID=4684



A closer look at the downloaded pdf plans shows no engine offset. I'll be sure to include engine offset in my build.

[john e. holliday]

I don't have engine off set on my AA Sr.  Of course I take off like I'm flying a racing plane.   If you don't get ahead of them they will eat your lunch.  I have even made wheeled landings a couple of times with no bounce.