Rudder yaws plane correctly but then drops oposite wing?

[MG1500]

My Vermont belle 1300 with Axi 2920-10 on ten cells flys great except when I use rudder. When using it either left or right it yaws the plan in the correct direction but if held, makes the oposite wing drop (and yes it is hooked up correctly and there is no mix with the ailerons). Why would this happen and is it correctable? Maybe because of the lack of dihedral?

Thanks for any help you may have . . .

[kato145]

Could be cross-control stall. Where the oppsite wing stalls if the AOA is to high. Don't know, with out seeing it. Does it drop when in a turn? or Are you trying to do a manuver like a kinfe-edge pass? Are the wings normal in chamber or do they have a curve on both sides??

[pmackenzie]

My Vermont belle 1300 with Axi 2920-10 on ten cells flys great except when I use rudder. When using it either left or right it yaws the plan in the correct direction but if held, makes the oposite wing drop (and yes it is hooked up correctly and there is no mix with the ailerons). Why would this happen and is it correctable? Maybe because of the lack of dihedral?

Thanks for any help you may have . . .
The Vermont Belle is a low wing with very little dihedral. This causes adverse roll with yaw inputs. There are two solutions to minimize this:
Add dihedral, or using a computer radio mix in some aileron with the rudder.
Pat MacKenzie

[jb753]

I have flown a couple of large glow powered Fly Babys that have the same characteristic. If you hold full right rudder, while flying fast, the left wing drops and the plane flies straight ahead or turn slightly to the left (opposite rudder input). The rudder works normally at low speeds. On the Fly Baby, I think that it is a combination of the high mounted fin and rudder along with damming up air against the side of the fuselage on one side with low pressure on the other wing caused by the yawing of the fuselage.

[Dereck]

Pat
I've got an own-design aerobatic that does exactly what you describe. Turns out the dullard who builds my models didn't prop up both ends of his custom dihedralled building board, and thus the wing has only half the specified dihedral.

Any application of rudder results in a slow and unpleasant roll away from rudder - this is not fun in knife edge flight, when the model tries to roll inverted on application of top rudder.

Suggestions? I've built enough flat winged models to know that it doesn't really work in practical applications, but it is an easy way out for idle builders or those seeking a cheap production method - no dihedral bracing being needed.

Idea - strip the wing, saw it in half, add some dihedral, brace to similar standards as used by designers who care, and recover.

Idea - computer mixing, as suggested above, might work if the trait is not too bad.

Idea - sell this thing and build yourself a model designed by someone who cares more about performance than profit.

To quote my Granny - "If you want anything doing right, do it yourself"

Regards

Dereck

[Gordon]

Thank goodness!!

I found the same effect with a scale model of the Miles M20 WW2 experimental fighter, but nobody else would own up to the problem, far less believe me.

Pat MacKenzie is right. I cured my model by sawing the wing at the centre-section and adding dihedral. It took two attempts to eradicate the problem .....

Gordon

[Dereck]

Hi Gordon
We're describing a method often used by pattern fliers in the good old days before computer radios!

FWIW - ways back before I left England, I designed a couple of sports models with 'everything on the thrustline" - wing and tailplane - with dihedral-free wings. This is the opposite of the Belle, as described by MG1500. Despite common wisdom - this layout was, I believe, used in a US pattern design and several derivatives called the "Eyeball". This layout is not all that neutral and all of mine could be rolled happily, if slowly, using just the rudder, which was close to equally divided in area above and below the thrustline.

From my experiences, the only way a 'flat' wing would work is if it was placed about halfway between the thrustline and the 'conventional' location of a low-winger - or about halfway up my present model's battery pack!

There are a lot of factors involved in this to determine the exact dihedral to give a 'neutral' rudder response of yaw only, with no secondary effect of rudder application. Those who can do the math involved - I salute you!

The rest of us will have to rely on computer coupling or an evening's work starting with a saw :eek:

Idle thought, at the usual internet cost ;) - my Four Star 40 with a 53" span, vice the usual 60", has close to neutrally pure yaw response from its rudder. It's parallel chord, taper-free wing has two degrees of dihedral.

D

[MG1500]

Thanks to all responders. I will try to rudder/aileron mix first but won't that make knife edge a problem?

[pmackenzie]

Thanks to all responders. I will try to rudder/aileron mix first but won't that make knife edge a problem?
The goal is to get the right amount of mix so that the adverse roll goes away. This should improve the knife edge.
Pat MacKenzie

[flypaper 2]

Ikarus Shockfliers, with the mid, flat wing will do a 360 flat turn in about three ft.dia. Good example of what they will do when up properly.

[Mike4122KSA]

My Formosa did that before I did a mix. Now, knife edges are good, and hammerhead/stall turns are perfect.

[MG1500]

Thanks everyone - - if it stops raining this weekend (again!) I will see how the mix works.

[PGR]

I experienced exactly the same problem with my new Mamba from N.E. Sailplanes. Knife-edge slips and flat turns were a two-thumb ordeal at best. I spent this morning dialing in some rudder-aileron mixing and now, both maneuvers still require two thumbs but they're no longer an ordeal.

I was able attain one-thumb knife edge or flat turns but not both at the same time. What I now have is an acceptable compromise between the two and I can deal with the residual roll with the mixer 'tween my ears.

Pete