Why not just rubbing alcohol and not deal with the poisons of brake cleaner
Yeah, but you cant have a party afterwards with the brake cleaner ...
Aileron Hinge Design
- Thread starter Ollie Krause
- Start date
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Ollie,
Ambitious project! You did not say where you are from nor which set of ultralight rules you are living with. There is a big difference - US rules are 252 lb airframe weight, Euro rules are much more substantial birds.
The designs of Steve Wittman (airplanes in the Smithsonian among others) used torque tube actuation, no needle bearings, and my plans for Steve's Buttercup seem to indicate tube in tube, just like his tailfeathers and in other designs mentioned above.
You can see similar schemes in
Common designs even in much heavier airplanes are tube in tube, bolt in tube, short lengths of extruded piano hinge, Oilite bronze bushings on bolts, and self-aligning bearings. All rely upon a bit of lube as they are all sliding friction, not a rolling element bearing in the bunch. Given the low forces and very low sliding velocities for an ultralight, rolling element bearings add useless weight, cost, and build complexity.
Billski
Tornado Flyer
Active Member
Rubbing alcohol has a high water content and could cause corrosion.
Ollie, the digital rendering that you show in a recent post has the rear of the main wing rib surrounding ("cupping") the front of the aileron.
This tells me that you need the aileron to rotate around its own leading edge tube... meaning the hinge axis needs to be inside the center of the aileron leading edge not just in front of it.
If that is true, that configuration will drive more of your hinge design than anything else. You won't be able to use U-brackets, piano hinges, eye bolts.
In order to hinge the ailerons as you drew it in your rendering, you will need a long U-shaped strap that runs back from the wing, around the leading edge of the aileron, and then back to the wing. Inside this U-strap you will need a piece of low friction plastic tube, Teflon or Delrin, that acts as the bearing between the metal parts. Then you will need a spacer block between the wing t railing edge tube and the aileron bushing (the piece of Teflon tube) to keep the aileron in it's hinge strap.
This is the way many high performance and aerobatic airplanes are hinged. However it is more complicated and labor-intensive than what this airplane probably needs. It is likely over-engineering for an ultralight.
So based on your layout, what I would do is remove the "cove" or close-fitting curve at the back of the main wing ribs. This will allow the aileron to be hinged using the U-brackets or eye bolts.
This tells me that you need the aileron to rotate around its own leading edge tube... meaning the hinge axis needs to be inside the center of the aileron leading edge not just in front of it.
If that is true, that configuration will drive more of your hinge design than anything else. You won't be able to use U-brackets, piano hinges, eye bolts.
In order to hinge the ailerons as you drew it in your rendering, you will need a long U-shaped strap that runs back from the wing, around the leading edge of the aileron, and then back to the wing. Inside this U-strap you will need a piece of low friction plastic tube, Teflon or Delrin, that acts as the bearing between the metal parts. Then you will need a spacer block between the wing t railing edge tube and the aileron bushing (the piece of Teflon tube) to keep the aileron in it's hinge strap.
This is the way many high performance and aerobatic airplanes are hinged. However it is more complicated and labor-intensive than what this airplane probably needs. It is likely over-engineering for an ultralight.
So based on your layout, what I would do is remove the "cove" or close-fitting curve at the back of the main wing ribs. This will allow the aileron to be hinged using the U-brackets or eye bolts.
This is one of the hardest things for engineer types to learn. A long time ago on RAH* one of the posters said: "Anything more than 'good enough' is unprofessional"
It was, and still is, excellent advice....provided you can define exactly what is 'good enough'.
*RecAviationHomebuilt Usenet group
Who was it that said that... Chuck S, Badwater Bill, Oysterhouse?
I don't honestly remember. They were a regular contributor, but I don't think it was one of those 3 memorable individuals.
Been struggling with that very concept the last couple of days. The last guy to work on the project had a pretty low bar for 'good enough'.
I fear my bar setting may be wasting time........
Dan Thomas
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Corrosion in plenty of places, yes, but in aileron piano hinges that are out in the rain anyway?
Rubbing alcohol is 70% isopropyl, the rest mostly water and a bit of glycerin.
Ollie Krause
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Oops I totally missed that! Thanks for the advice and I'll go implement those changes. My concern though is that by removing the cupping, a notch will be formed at the leading edge of the aileron and disrupt the flow of air across the control surfaces and also create additional drag because of a low pressure pocket. I honestly have no clue though so any insight into that would be helpful. Thanks!
poormansairforce
Well-Known Member
What you have is the same design as the Minimax. Not bad just different. The pivot just needs to be a the radius center of the d tube. Easy to make since you don't need to bend anything.
Ollie Krause
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Oki doki so I removed the blind cove and instead used a circular pattern to simulate aileron deflection to cut away exactly what is needed (see attached photo). Does this seem like a viable solution?
Regarding the U brackets, what material do you recommend? If I were to use any aluminum, I assume that I wouldn't be able to bend them myself as it would damage the fatigue strength of the metal and make them prone to breaking. I looked briefly online though and the selection for exact pre-made bracket dimensions seems a little limited. Alternatively, I could also use steel but it would add additional weight and couldn't be stainless to avoid galvanic corrosion. I don't know anything about corrosion prevention but I imagine that powder coating or galvanizing these brackets wouldn't help much as any corrosion resistant coating would be quickly worn down due to vibrations and regularly rotating. Sorry if any of these questions sound stupid and if there's any resources you can recommend me to so I don't ask the obvious I'd love to read up on them. Thanks again for all of your help!
Regarding the U brackets, what material do you recommend? If I were to use any aluminum, I assume that I wouldn't be able to bend them myself as it would damage the fatigue strength of the metal and make them prone to breaking. I looked briefly online though and the selection for exact pre-made bracket dimensions seems a little limited. Alternatively, I could also use steel but it would add additional weight and couldn't be stainless to avoid galvanic corrosion. I don't know anything about corrosion prevention but I imagine that powder coating or galvanizing these brackets wouldn't help much as any corrosion resistant coating would be quickly worn down due to vibrations and regularly rotating. Sorry if any of these questions sound stupid and if there's any resources you can recommend me to so I don't ask the obvious I'd love to read up on them. Thanks again for all of your help!
Attachments
2 books are 'must haves' if you are going to go any further than this project:
Airplane Performance Stability and Control
Theory of Wing Sections (TOWS)
These are the foundations that most of the other books are built upon. Neither is a particularly easy read but given the questions someone of your age is asking I doubt you will have much trouble.
Ollie Krause
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Thanks for the suggestions! I'll order em up.
I recommend that you go out to airports and look at a lot of airplanes and ultralights and gliders. There are many ways of skinning this cat. What you've chosen is could be made to work, but might not be the most effective combination of shapes and materials.
In most cases where the wing has a semi-circular cove and the control surface has a semi-circular leading edge, the hinge axis is arranged at the center of the radius on the control surface so the gap remains small and constant.
One important aspect of control surfaces is that they must be torsionally rigid so that they do not twist (much) in response to a moment applied at the control drive location. That usually means that the surface must incorporate a closed box or tube section with substantial torsional stiffness. Although there are tricks you can use with diagonal ribs to establish torsional stiffness without a closed section. Anyhow, the small diameter tube shown in your drawing looks to be too small to produce enough torsional stiffness for any reasonably-sized control surface.
Not necessarily a valid assumption. As long as you stay within recommended cold bend radii for the alloy, temper, and thickness, it's fine. The reason I'd use steel is because it has better resistance to wear at the bearing site with the axis pin.
Unless you live on the beach, or you know your airplane will last more than a few years, corrosion protection beyond a squirt of rattle-can primer should be pretty far down the priority stack of what to worry about. You can drive yourself nuts trying to design for forever. By the time it's a problem, it will probably be someone else's problem.
You do not need a cove or cup at the rear of the wing. A simple fairing strip (we called them "wiper seals" on the sailplanes) will eliminate the gap and discontinuity in the surface, eliminating the drag and air leakage. The front of the aileron should be round if you can do it easily enough, but even that is not absolutely necessary. I'll try to post a sketch later this evening when I get home, but BoKu and a hundred other guys on this forum can make a sketch before I can.
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Bet your head is spinning with all this help. Welcome to design.
poormansairforce
Well-Known Member
I thought it was the monkey house?
Ollie Krause
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Haha yeah I have a lot to learn. I'm going to an EAA Young Eagles event this weekend so I'll take a look around then. Thanks for everything, guys!
Ollie Krause
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Okay so I've been thinking and I noticed in the SS-1 wing video above that he just used a single aileron torque tube as his hinge. While I really like the U bracket and bolt idea for its resistance to locking with wing flex, the continuous torque tube is really enticing for its simplicity (and possibility to make friese ailerons). Since my ailerons are going to be incorporated into the wing, I could just install some nylon bushings into my ribs eliminating the need to rivet into the aft spar effectively reducing construction time and knocking a couple rows off the BOM. To help mitigate any bending, I could increase leading and aft spar thickness a bit and also make the torque tube a bit thicker. This would also increase maximum wing loading and might calm down my mom a bit if I could show her it loaded to 6g. Assuming this would curtail bending, would the simplicity at the cost of additional weight be worth it? I'm still gonna hold off on making any major design changes before I can inspect some planes in person this weekend but I wanna be a bit more knowledgeable before I show up there so I can ask more useful questions.
Excellent, while you are at Young Eagles please go out of your way to meet and speak with as many of the EAA chapter members as possible. Sooner or later you will meet several members of that EAA chapter that do know more about airplane design than some of the other members.
Start listening and learning, start figuring out who actually knows what they're talking about and who is just loud or thinks they know what they're talking about. This is every bit as important of a skill in aviation as flying or engineering
If you let this online HBA group know which EAA chapter Young Eagles event you are going to, or what airport, chances are somebody here knows somebody there, and can speed up your learning curve, etc.
One of the good things about this forum, which is the de facto equivalent of an online EAA chapter, is that when you get good avice or bad advice it will become very clear because of everyone else's reaction. If I say something stupid to you that is horrible advice, ten or twenty of these folks will jump down my throat for the world to see. You might not get that calibration as quickly in some back woods smaller EAA chapter.
