aileron controls in solid core wing?

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raymondbird

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Thinking of building a Rutan style outer wing for my replica fighter but can't use his torque tube method of aileron actuation. Anyone have any ideas on the best way to install a bell crank/push rod setup in such a solid foam core wing?

Thanks
 

TFF

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The choices is a cove along the wing trailing edge where hinges are, external control runs, or carve out the core along with appropriate adjustments.
 

Jay Kempf

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What style of controls do you wish to use? Pushrod and bellcrank, cables and pulleys?

The general method is to plan a recess for the bellcranks and access covers. Then hotwire a channel and insert a light weight tube to line the hole. You have to do the math on reinforcing the edges of the access cover hole in the skin.

Bede used coaxial drives for aileron and flap where the aileron torque tube is carried on bearings right through the flap leading edge so that everything rides on coaxial bearings. Both control horns are inboard in the fuselage at the wing root. Simple and bullet proof system but not light.
 

Victor Bravo

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Bury a 2 inch thin wall plastic tube in the foam core (between the root and the bellcrank) before glassing the core. Dig out a hole in the foam mid-span to glass in a plywood plate to mount the bellcrank. Then bury another 2 inch plastic tube from the bellcrank to the trailing edge.

Run your 3/4 or 7/8 steel or aluminum push-pull rods through the center of the plastic tubes. Mount the bellcrank onto the plywood plate.

Wrap two layers of non-structural glass cloth over the exposed section of plastic tube where it exits the wing near the aileron, turning it into a protective and somewhat drag reducing faring.

Make sure to build a removable cover over the bellcrank plate so you can inspect/adjust/replace the hardware at the bellcrank.
 

raymondbird

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What style of controls do you wish to use? Pushrod and bellcrank, cables and pulleys?

The general method is to plan a recess for the bellcranks and access covers. Then hotwire a channel and insert a light weight tube to line the hole. You have to do the math on reinforcing the edges of the access cover hole in the skin.

Bede used coaxial drives for aileron and flap where the aileron torque tube is carried on bearings right through the flap leading edge so that everything rides on coaxial bearings. Both control horns are inboard in the fuselage at the wing root. Simple and bullet proof system but not light.
I like that system but just the worry about increased risk of flutter with torque tubes. So I've read about anyway. Oh, and I have prefered cables to the bellcrank and then a push rod to aileron but all push rods sounds great like VB describes and less foam to be removed I think.
 
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raymondbird

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Bury a 2 inch thin wall plastic tube in the foam core (between the root and the bellcrank) before glassing the core. Dig out a hole in the foam mid-span to glass in a plywood plate to mount the bellcrank. Then bury another 2 inch plastic tube from the bellcrank to the trailing edge.

Run your 3/4 or 7/8 steel or aluminum push-pull rods through the center of the plastic tubes. Mount the bellcrank onto the plywood plate.

Wrap two layers of non-structural glass cloth over the exposed section of plastic tube where it exits the wing near the aileron, turning it into a protective and somewhat drag reducing faring.

Make sure to build a removable cover over the bellcrank plate so you can inspect/adjust/replace the hardware at the bellcrank.
Thank you Sir! That is exactly what I was looking for.
 

wsimpso1

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You need a spanwise pass between root and aileron bellcrank, and you need a chordwise pass between the aileron bellcrank and the aileron cove. Spanwise pass can be put in with the same hotwire saw template you cut the main parts of the cores with. Vari-Ez/ Long-Ez/ Cozy/ Defiant, etc do a small one for wiring, to tip lights and rudder cables, you might need two, one for wiring, one for pushrods. The chordwise one can be cut with a core drill made from steel tube. It will look like a long hole saw. These passes will require enough clearance for the tubes to move while the bellcranks and idlers swing through their range.

You will also need a small equipment bay for the bellcrank and an inspection cover for that space. I make mine for trim tab motors etc by cutting out a block of foam that is the size of the bay, a few inches on a side and the depth of the foil, cover with duct tape, and insert in the opening in the foam. Build up your spars, laminate the skins, then cut out the opening to the bay. Pull the taped foam out, glass the inside of the bay, bond your bellcrank mount to the liner, make a cover of laminate, and bond in flanges on the edges. Flox fit the edges of the door, Click-Bond nut plates, and fair the wing including the covers.

Some might advocate a thin cover glued on with silicone seal. You will want to work out the pressures at your Vne, the forces of those pressures on your cover area, and make that call.

Billski
 

BoKu

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On Dick Schreder's gliders, he ran the push-pull tube for the aileron up the flap cove. The only aileron control inside the wing is a bellcrank that drives the final drive pushrod. You could do something like that; make the flap cove a bit deeper than it would otherwise be, and carve out a box in the foam core for the bellcrank.
 

Bill-Higdon

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On Dick Schreder's gliders, he ran the push-pull tube for the aileron up the flap cove. The only aileron control inside the wing is a bellcrank that drives the final drive pushrod. You could do something like that; make the flap cove a bit deeper than it would otherwise be, and carve out a box in the foam core for the bellcrank.
Someone did a similar aileron control on a KR(can't remember it was a 1 or a 2) where they replaced the cable that runs between the 2 aileron bellcranks with a push pull tube.
 
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Jay Kempf

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I like that system but just the worry about increased risk of flutter with torque tubes. So I've read about anyway. Oh, and I have prefered cables to the bellcrank and then a push rod to aileron but all push rods sounds great like VB describes and less foam to be removed I think.
Flutter is speed and torsional stiffness dependent. But in the end good balancing is the best mediation. If you have a low aspect ratio, stiff wing you should be able to pick a big enough coaxial tube set to ward off flutter. But you still have to do the math. Carbon fiber is very stiff in torsion. There are tubes manufactured to work as sets. Not cheap though or you could make your own with one of the mandrel or lost foam methods.
 

raymondbird

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Flutter is speed and torsional stiffness dependent. But in the end good balancing is the best mediation. If you have a low aspect ratio, stiff wing you should be able to pick a big enough coaxial tube set to ward off flutter. But you still have to do the math. Carbon fiber is very stiff in torsion. There are tubes manufactured to work as sets. Not cheap though or you could make your own with one of the mandrel or lost foam methods.
Great info and can't thank all of you enough! The Cozy plans I have show an aluminum torque tube, so maybe with big carbon tubes and good balancing, like you say, it would be stiff enough. Will have to think on that for awhile as definitely the easiest way. The wing is low AR and will be very stiff.
 

bhooper360

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I have a similar project, sort of. I have not imposed any constraints about the weight, cost, or flutter resistance.

You see the way he sets up the Giles, with the bellcrank is in the fuselage. It's almost irrelevant whether you do a torque tube or a push/pull this way, it's the same number of linkages, and in either case we assume the aileron is very stiff. So I deferred this option until I work out the controls. Other things I haven't decided:

  • What material to make the bearings out of for the carbon fiber tube (PTFE?)
    • Is PTFE superior to bearing bronze for 6061 or 3140?
  • In which directions, if any, will the phenolic blocks require fiberglass reinforcement?
  • Is a 1" bond area sufficient to cause the carbon torsion tube to fail somewhere else?
These are magic 8-ball questions, to get a sense of where I am in the planning process. No real answer is solicited.

w/r/t maintenance hatches: The Dark Lord of Composites requireth a sacrifice of 32 black spiders and one (1) small kitten per fastener. Anyway the composites are very likely to be dropped or fallen on top off within a month. It'll be much faster to chainsaw the old wing in half and build a new one.

Pencil drawing is mine, the other graphic is from the Giles G-200 build manual.

push pull.jpg
File_000.jpeg
 

BoKu

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What material to make the bearings out of for the carbon fiber tube (PTFE?)
I would not under any circumstances run a carbon fiber push-pull tube through any kind of plain bushing. The material is too soft to have any reasonable wear life.

What I would suggest is an aluminum push-pull tube run through pushrod roller guides like these from Wicks:


I use about 20 guides like those in each HP-24 sailplane. But I make them myself instead of buying them, and mine have 6 balls each instead of just 4.

Edit add: This post has a cross-section drawing of one of those guides.
 
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