Control surface stress in wing warping

[Wufnu]

I've slowly been accumulating information and parts on a proposed build of a 31cc Ryobi powered foamy Fokker E.I-IV and plan to use wing warping. One thing I am unsure of is how much force the wings will put upon my servo and how large (or many) a servo to use.

I plan to wire the controls in a circuit fashion with control cables for the leading and trailing edges of both wings.

I thought perhaps someone in this forum would have experience with this.

[Sparky Paul]

There's two problems with wing warping; a structure flexible enough to permit the distortion, and stiff enough to not flutter at flight speeds.
The WWI wing-warpers pulled on the trailing edge wires for control, the leading edge wires were fixed structural supports.
I'd suggest trying a flat-plate wing of Depron, before going into more complexity.
A stiff wing spanwise, but flexible chordwise.
A normal servo might be sufficient for a small test test vehicle.
Look at the wing structure of the Fokker E.III, that obviously works, but might be difficult to achieve in model sizes.
I believe Arizona Models makes a wing-warping E-III... ?

[Wufnu]

Just the trailing edge? Well now, that only makes things 100% easier. :) I didn't notice that when I was looking at pictures to see how it was all rigged up, I don't know how I didn't, but it's good news to me.

I was thinking of using a single HS-755, I'll have to calculate surface area to be sure.

Thanks!

[Sparky Paul]

On the Eindecker, there's a bellcrank on the control column at its bottom.
Each side of the bellcrank is connected to a similar crank on the aft landing gear support tripod, with cables.
This lower bellcrank has the warping wires to the points on the aft spar which warp the wing.
The warp wires on the top of the wing run thru a pulley at the apex of the upper support, and merely slide back and forth as the wing warps.
In essence, the warp mechanism pulls the trailing edge on one side down, the motion transfers to the other wing across the upper support.
The forward wires rig the wing dihedral, and are one continuous loop on each side of the plane with a turnbuckle controlling the tension in the pair on each side.
My buddy Dick Skoglund tried a warping wing on one of his Eindeckers, and found the structure when covered was too stiff to permit much control at all, with the wing rigged at the scale zero dihedral.
He'd made the wings seperate per full-scale, the spars plugging into sockets in the fuselage sides, and could change the rigging to add some dihedral, so the rudder had some rolling effect in addition to the warping of the wing.
From the Squadron-Signal "Fokker Eindecker in Action"..

[Wufnu]

"This lower bellcrank has the warping wires to the points on the aft spar which warp the wing.
The warp wires on the top of the wing run thru a pulley at the apex of the upper support, and merely slide back and forth as the wing warps.
In essence, the warp mechanism pulls the trailing edge on one side down, the motion transfers to the other wing across the upper support."

That is exactly what I had in mind, only with the front and back. In fact, this is the same way I rigged up my pull-pull ailerons on a recent glider conversion (except I rigged the wires to fuse-mounted control horns, convenient way to run wire), to prepare myself for this very thing :) So glad I don't have to do the front as well. It's still quite a ways in the future, I just do a little work on it here and there.

Thanks, again.

[Sparky Paul]

I noticed an article on a full-scale replica of an E-III in the latest "Air Classics".. built from factory drawings and blueprints done in 1919.
The wing warps 3 inches at the tip. Not a serious amount on about a 6 foot chord, but probably all a structure could withstand and not get totally limp.
The flier says it's a good airplane.. but Frank Tallman says of the one he flew, it felt like it wanted to swap ends at any given moment.
The pilot had to hold the rudder in place with his legs, the elevator in place with his arms, and fight the roll to the right induced by the motor rotating in its bearings... "Fatiguing airplane to fly" from a British evaluation in 1914.
The "Immelmann turn" as we fly it probably was beyond the capability ot the E-III.. both vertically and in roll.
On one of my websites:
http://www.angelfire.com/indie/aerostuff/eindeckero.htm

[vintage1]

I am fairly sure from early literature that the WWI Immelman turn was more like a pull up to a 'zoom' and application of elevator and rudder to complete something like a snap roll - the idea being that you ended up behind someone chasing you, with altitude and speed..

What is did NOT do was reverse direction as the modern manouver does. There is no point in that as a combat manouver.


Today maybe a split S does the same job, but in those days negative G cut the engine and threw the pilot out..if it didn't snap the wings.

[Wufnu]

From what I read, and this is from memory, he used it after he zoomed his victim. He used his speed energy and went back up, hit the old rudder and elevator, and found himself in a position to either make another pass at his victims tail or get in the sweet spot easily if his victim decided to turn after he passed.

From what I remember from the book that came with the original "Red Baron" game they had him going up to a stall, applying full rudder before the apex, and going from there depending on where your enemy is at the moment. Sorta like a hammerhead, I believe.

Would also like to say that with the wing warping anyone that tried to roll out of an inverted loop in a Fokker Eindecker was a fool.. and probably died doing it :(

http://www.furball.warbirdsiii.com/krod/ACM-immelman.html

[Wufnu]

Oh yah:

"The flier says it's a good airplane.. but Frank Tallman says of the one he flew, it felt like it wanted to swap ends at any given moment.
The pilot had to hold the rudder in place with his legs, the elevator in place with his arms, and fight the roll to the right induced by the motor rotating in its bearings... "Fatiguing airplane to fly" from a British evaluation in 1914."

No doubt, you've got a full flying rudder and a stabilator with a rotary engine. Youch :( You gotta watch the ball or the plane will yaw right out from under you, no vertical stabilizor. Always controlling, no rest, so I can only imagine. I'm going to build me one, one day. Not a model, either ;)

[fhhuber506771]

I have a book dated 1924 (written by a british WWI pilot) with some drawings of how they accomplished some of the maneuvers.

The immelman drawing has a dive, half loop and then half-snap-roll. It DID reverse direction, and if it was from a diving pass at an opponent, it regained altitude (trade airspeed for altitude because the engine wasn't going to pull you up that fast) and did set them up for a second diving pass. The end result looks a lot like the second half of a "modern" Cuban-8 using a half-snap.

Note.. the rotary-radial (or however you want to designate it...)with the crankcase spinning around the crankshaft gave you a lot of torque to use to snap the plane around when it was near stall. The pilots either learned to USE that torque for faster maneuvering or they didn't last long.