Aileron Hinge Design

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Grumpy Cynic
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Have you ever seen a clean bicycle chain?
Every time I ride. ;)

There may be some incompatibility with the carrier in bicycle chain lube but they are specifically formulated to not attract dirt/dust and the carrier evaporates fairly quickely. Some gun lubes are the same way.

To fracture an old quote:
"Test, but verify" :p
 

lr27

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It may be possible to find a standard bushing of a great material that can fit the tube and also in a 3D printed housing. I seem to recall a bearing material called Rulon, but I don't remember the properties. We used some Rulon bearings in a gigantic bagel making machine.

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Have you figured out how stiff the torque tube needs to be? How much it has to weigh to be that stiff? I suspect it will weigh more than some other sort of linkage. Other alloys of aluminum, or at least the affordable ones, will have about the same elastic modulus. 7075 or 2024 would be STRONGER than 6061, but not stiffer.
If you can make room for a really large diameter torque tube, with thin walls, and figure out how to keep those thin walls from buckling, it will be much lighter. However, it might use up a lot of design time better spent on something else. I'm not sure, but it looks like you're using a thick tube for torsional stiffness in the aileron itself. My intuition says that making it with diagonal ribs may provide more torsional stiffness for the weight.
 

lr27

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P.S. Maybe some of you guys who have been around ultralights will know whether aluminum rubbing on a plastic bearing holds up ok, or if it galls. (I hate cleaning bits of aluminum and sand out of bike brake pads, but I hate the sound of that stuff machining away the rims even mire.)
 

proppastie

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Reality check.......you do not 3D print hinges.....You make them from steel, aluminum, pieces of aircraft piano hinge material, heim bearings or other mounted uni-ball standard bearings. Some of the advice here is coming from people who have never designed anything.
 

lr27

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I think the OP was writing about the short aileron running in a bearing at each end, not a hinge as such. Nevertheless, such a bearing would have to be properly supported. If that support was a plastic housing, it would be bulky.
 

Ollie Krause

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Have you figured out how stiff the torque tube needs to be? How much it has to weigh to be that stiff? I suspect it will weigh more than some other sort of linkage. Other alloys of aluminum, or at least the affordable ones, will have about the same elastic modulus. 7075 or 2024 would be STRONGER than 6061, but not stiffer.
If you can make room for a really large diameter torque tube, with thin walls, and figure out how to keep those thin walls from buckling, it will be much lighter. However, it might use up a lot of design time better spent on something else. I'm not sure, but it looks like you're using a thick tube for torsional stiffness in the aileron itself. My intuition says that making it with diagonal ribs may provide more torsional stiffness for the weight.
We haven't done any specific calculations on the exact magnitude of the aerodynamic forces acting upon the aileron but I imagine that they will be pretty minor as the top speed will only be 54 knots. Most of our current dimensions are purely conceptual and are either based on similar aircraft, trends in design, or some basic calculations. Since I'm still a junior in high school, my math knowledge (and that of my team) is limited to that offered by a precalc class but I'd be more than willing to jump ahead and learn some new things if needed. Teaching myself calc (or other advanced math) though would be pretty inefficient and I was hoping to be able to get a closer estimate with some fluid analysis (still need to figure out how that works). Either way though, if you know any equations or can refer me to a textbook which goes over such calculations that would be great. I'll also look into using diagonal ribs or wires to improve torsional rigidity. Thanks for the suggestions!
 

BoKu

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...You will probably find that using 2024 or 7075 aluminum instead of 6061 makes the aileron stiffer (torsionally)...

A common misconception. All aluminum alloys have about the same stiffness per unit mass and per unit volume. 7075 would certainly be stronger, but no stiffer than 6061.
 

lr27

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Ollie:
A lot of times, when you're designing something, someone else has derived the formula and you can look it up. For me, it helps to have done at least some of the calculus, which makes it easier to re-derive when I forget part of the formula. Not that I remember all that much calculus any more. Having derived formulas in the past is probably good for my garbage detector. If you slip a digit when plugging numbers into a formula, it's helpful to recognize when the results are absurd.

The other day a friend of mine called me because he was all excited that he'd figured out how to store useful amounts of electrical power* in flywheel. At reasonable rpms. He was going to power his house that way, I think with charging from solar cells. It turns out almost anything is feasible if you move the decimal point enough places. BTW, I'm not saying it's impossible to store lots of power in flywheel, just that some exotic materials and very sophisticated engineering will be required. I think some utilities use fancy flywheels for evening out short term surges or sags. One constraint is the strength of materials. The stronger the flywheel, the faster you can spin it and the more energy it stores. Or releases if it breaks and causes an explosion.

Anyway, one handy source of these formulas is Machinery's Handbook. The formulas might just lead you down the primrose path, but it may be useful to compare your calculations to the results from FEA.

Anyway, to design an entire ultralight from scratch, backed up with calculations, may be a really large project for high school. It may be better to look at a bunch of designs, pick one, and figure out what needs to be different to suit your purposes. Or you could pick some subset of the design task.

Has anyone mentioned Mike Sandlin's designs in this thread? I don't know if they've been rigorously analyzed, but I think the ones on line have flown. The drawings have lots of info in them and show ways of doing things that have been shown to work.
*Comparable to batteries or better.
 

proppastie

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You do not need any more than basic algebra, knowing a spread sheet program will help greatly. The many formulas are out there (open source for a buzz word/term) so running the numbers would be what you have to do. Basic geometry in the old days but CAD does it for you now.
Making a layout based on other designs then analysis of the loading, strength, power required, speed, climb rate, range, etc, would be a big project for anyone of us. A new grad in aero-engineering would be hard pressed to do it correctly. Frati post 88 walks you through a complete design.
Of course you probably want to jump right in and do what Peter Sripol did with his Youtube design....He did not get killed, but he did buy a light sport aircraft to fly around in and got a pilots license in a standard category aircraft.
 

lr27

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New aero engineering grads may not know very much about light airplanes. Was test flying a UAV (using radio control) for three of them once. They didn't seem to understand why I was whining about no spoilers or flaps on a design with a 20:1 aspect ratio and a small fuselage!
 

lr27

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Of course not. I was testing it for the designer/builders. As an RC motorglider it would have been pretty nice with spoilers or flaps added.
 

rdopaleo

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Hi All,

Sorry I haven't been able to post an update recently but I just finished up a rough assembly of my wing design (see attached photos). As described in a previous post, I opted to use a thick(ish) torque tube within some greased nylon bushings. The two bushings directly adjacent to the aileron have a slightly smaller ID than those at the root of the wing so that slight wing flex doesn't cause the torque tube to lock up but the aileron doesn't flop around and flutter during flight. At this point, my primary concern is that the aileron is only attached to any of the main ribs at either end making it potentially susceptible to flexing and flutter (because of it's unsupported design). This is going to be used on an ultralight aircraft flying at slow speeds where I imagine that the aerodynamic forces on the aileron won't be extreme though and I'd like to keep the design as simple as possible. Are there any other aircraft that use a similar torque tube assembly and have the aileron completely suspended between two of the main ribs or is this inherently unstable and should be avoided? When this design is used, I typically see at least 3 attachment points such as in the Belite wings or the SS-1 video linked above. Anyway any help is greatly appreciated.

My latest wing design can be viewed in 3D on my Public Onshape Document (to make up for the low resolution screen shots).
Ok lets go through this again. You are wanting to build a wing that is different from the wing designed by the man who invented the particular aircraft you hope to build and fly yes?
What is your reasoning for only connecting your main spar (torque tube) at each end?
For a moment lets say you have already built this wing, and now we will magical remove the torque tube from the wing. What keeps the ribs from falling down when we do this?

The main spars first job(there are 2 jobs) is to transfer the lift that the exterior of the upper wing creates, to the body of the aircraft and make it fly. This lift is carried by the ribs of your wing. The air lifts the skin of the wing...the skin is attached to the ribs and so the skin lifts the ribs. The ribs job is now to lift the main spar so that the main spar can lift the aircraft and that is how flight occurs. If your ribs are not attached to the spar how does your design get the lift to the spar?
 

Ollie Krause

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Yeah that's sorta what we were thinking when we started this project. We'd be lying to ourselves if we said we could design something cutting edge in terms of efficiency, weight, etc with no background in aerospace engineering. We just want to make our own design from scratch and then construct it so that we get exposure to the aircraft design process, all the technical aspects, and building experience. If the final plane comes out a little overweight, inefficient, or ugly, we'd all still be happy if it flew safely.
 

Tiger Tim

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We'd be lying to ourselves if we said we could design something cutting edge in terms of efficiency, weight, etc with no background in aerospace engineering. We just want to make our own design from scratch and then construct it so that we get exposure to the aircraft design process, all the technical aspects, and building experience. If the final plane comes out a little overweight, inefficient, or ugly, we'd all still be happy if it flew safely.
I can have a hero half my age, right? I like this Ollie guy.
 

mcrae0104

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...their unique size and shape mandates that I 3D print them out of nylon (which is probably the strongest and best suited printable material for bushings).
What could possibly be so unique about these bushings that they must be 3D printed?

Ollie, I applaud your work but this premise is not true. As soon as you look at some actual aileron hinges you will see that this is not true (esp. for ultralights). Download the Falco plans if nothing else and take a look.
 

Victor Bravo

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We used some Rulon bearings in a gigantic bagel making machine.
What a wild coincidence, my good friend and the president of our local EAA chapter has been a de facto design engineer and troubleshooter of bagel machines for Thompson Bagel Machine for many years. Have you heard of Thompson Bagel Machine? Apparently they were the first to design a machine to do it.
 

wsimpso1

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Hi All,

Sorry I haven't been able to post an update recently but I just finished up a rough assembly of my wing design (see attached photos). As described in a previous post, I opted to use a thick(ish) torque tube within some greased nylon bushings. The two bushings directly adjacent to the aileron have a slightly smaller ID than those at the root of the wing so that slight wing flex doesn't cause the torque tube to lock up but the aileron doesn't flop around and flutter during flight. At this point, my primary concern is that the aileron is only attached to any of the main ribs at either end making it potentially susceptible to flexing and flutter (because of it's unsupported design). This is going to be used on an ultralight aircraft flying at slow speeds where I imagine that the aerodynamic forces on the aileron won't be extreme though and I'd like to keep the design as simple as possible. Are there any other aircraft that use a similar torque tube assembly and have the aileron completely suspended between two of the main ribs or is this inherently unstable and should be avoided? When this design is used, I typically see at least 3 attachment points such as in the Belite wings or the SS-1 video linked above. Anyway any help is greatly appreciated.

My latest wing design can be viewed in 3D on my Public Onshape Document (to make up for the low resolution screen shots).
I could not get into Onshape. I did look over your sketches. I have a few comments:

Bushings with grease? Probably work a lot better with Delrin or Teflon (they are self lubricating and way less messy than with white lubes), if you can not buy bushings to your size, you can certainly buy the plastic and spin it in a lathe. You will want a slight press fit into the wing structure, a slightly loose and trumpet shaped inside fit to the tube inside it to accommodate wing and aileron deflecting differently under aero loads.

The wing will deflect in one curve and the aileron will try to deflect in a completely different shape. Since they will try to deflect differently with only the bearing points to constrain them, the easiest scheme to make work is two points of support for the aileron, a firm connection between torque tube and aileron, and one bushing at the bellcrank for control input to the torque tube. When you put in a mid-aileron hinge point, it will carry about half the lift of the aileron plus a huge fraction of the load from the deflected wing bending the aileron to follow those three points. The bending load will be trying to bind the aileron, and may add weight and complexity to aileron design. The binding may be minor indeed in an airplane of this speed range, with control surfaces and linkages that are pretty soft in bending, so binding may be a minor issue. You will have to either estimate the deflection curves of wing and aileron and then check if the aileron can stand it.

Keeping in mind that this is a low speed airplane and does not need much stiffness for aeroelasticity effects, you will usually allow quite soft structures as long as they are strong enough.

Your rib spacing is curious to me. Normally the spacing is smallest at the root, and as wing loading drops off as you go outboard, the space between ribs can be increased. In ultralights, they usually stick to one spacing to commonize the diagonal drag/antidrag bracing. Placing an extra rib at each hinge point for the aileron is probably a good idea, but then you resume your ribs spacing scheme (whichever it is until the next interruption. You seem to have extras in the span of the aileron - why? Perhaps you have a good reason that is worth the weight...

Billski
 
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Dana

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I would be leery about using a 3D printed part for anything structural. Definitely no grease, as others have said it attracts dust and grit. Acetal (Delrin and Rulon are trade names for acetal) is a better choice than nylon; it has inherent lubricity, similar strength to nylon, and is super easy to machine.

Here is a section of the Kolb Ultrastar plans. It uses piano hinges, and the front aileron spar is the torque tube that the control horn is attached to. Crude, but it works just fine. The aileron forces aren't high at all despite being full length, and that's with a short side stick controlling them.

upload_2020-3-8_8-49-13.png
 
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