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Piano Hinges for Primary Flight Controls - Pro/Con?

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Topaz

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I guess that I read your text differently (as in: about the ensuing discussion about piano hinges). Darn text indeed, we should discuss this with a cold beer in the sun. (Yes, it's evening here)
Agreed. However, it's morning here and I'm procrastinating about a brochure that I've designed and had approved, but now have to do the not-fun part of stamping out copies with differing text. Hoist one for me, will 'ya? :gig:

What I meant was that it's easy to make something like designing aileron hinges too complicated. Piano hinges have quite obviously worked just fine in many an airplane, so in similar applications and with the same reasonable amount of design effort you'd use for anything else in the airplane, they ought to work fine elsewhere. As I mentioned, my dad's old Aeronca had aileron hinges that were just a couple of bolts in single shear. Optimum design? Hardly. But the airplane was forty-something years old when we got it, and the ailerons worked just fine.

By not doing that.

Simply put the full-span piano hinge in a dry mold. Align both ends and align the rest with a laser, then fix it to the mold (some screws or glue) and seal the hinging middle part, such that you can later cut the wingskin over there and not wet and glue the hinging part. This way you can align it perfectly, without any time constraint or worrying about creating a mess. By the time you're laying up (or in my case infusing), there's nothing than can be ruined anymore, except maybe mold warp. It's fairly easy to cut away a major part of the piano hinge later if one would want to.
I think I'm following you. And I highlighted 'mold warp', thinking "mold warp as in thermal expansion, for example?" I see what you're getting at, but I don't think I'm quite convinced. I agree that setting it all up and fixing it before infusion is better than the alternative I mentioned earlier, but the infusion process is going to put a lot of forces through the system, and I can see things moving around, if only a tiny little bit. Which might be enough to require scrapping the part. The great big expensive part.

I guess I'm a great skeptic about processes that require near-perfection in execution, particularly as applied to the shop of an amateur constructor like you or I. I'd much rather attach the piano hinge to the aft spar with small bolts, and then oversize the bolt holes in the hinge slightly, allowing them to be adjusted to perfection during assembly. YMMV, of course.
 

autoreply

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Agreed. However, it's morning here and I'm procrastinating about a brochure that I've designed and had approved, but now have to do the not-fun part of stamping out copies with differing text. Hoist one for me, will 'ya? :gig:
Maybe tomorrow. Tonight is GF-time. No hoisting. Not of beer at least.
What I meant was that it's easy to make something like designing aileron hinges too complicated. Piano hinges have quite obviously worked just fine in many an airplane, so in similar applications and with the same reasonable amount of design effort you'd use for anything else in the airplane, they ought to work fine elsewhere. As I mentioned, my dad's old Aeronca had aileron hinges that were just a couple of bolts in single shear. Optimum design? Hardly. But the airplane was forty-something years old when we got it, and the ailerons worked just fine.
Ah clear. There is quite a lot going on in an aileron though, like the "out of plane" bending I referred to earlier. It's often deceiving how simple such details look on a design if you know how much is involved, even something as simple as the Aeronca.
I think I'm following you. And I highlighted 'mold warp', thinking "mold warp as in thermal expansion, for example?"
Yep. Mold warp as in the whole mold being screwed up, but that has nothing to do with the hinge then.
I see what you're getting at, but I don't think I'm quite convinced. I agree that setting it all up and fixing it before infusion is better than the alternative I mentioned earlier, but the infusion process is going to put a lot of forces through the system, and I can see things moving around, if only a tiny little bit. Which might be enough to require scrapping the part. The great big expensive part.
The amount of force in infusion is massive... about 50 tonnes of force for a single wing skin. But that's deceiving. Because we basically just apply that force in holding 2 plates together (the mold and the infusion package), which sounds impressive but really isn't that much loading. We have a lot of force on the hinge, pushing it down in the mold. Thus no net deformation and in fact more resistance to deformation. The pressure on the rear and front of the hinge are there too, but they're working against each other, no net result either.

The only net force I think you will have is that of the fibers getting wet (and thus shrinking). Those are fairly sizeable forces. But the protection on the hinge itself relieves most of this by flexing/warping a bit. A 2" deep carbon hinge really isn't going to deform anymore if you screw/glue it down properly.

Did I mention I'm planning to build a H-stab first and then test it to destruction to verify production methods and my design calcs?
I guess I'm a great skeptic about processes that require near-perfection in execution, particularly as applied to the shop of an amateur constructor like you or I.
And I greatly prefer for someone to shoot down my ideas before I waste time doing something that won't work. That's why HBA is such a great place. Or you are such a great person. Where's that "love" button again?

Yes, I'm greatly under the influence, but cafeïne only ;)
 

Topaz

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Maybe tomorrow. Tonight is GF-time. No hoisting. Not of beer at least.
TMI, Jarno, TMI. :gig:

Did I mention I'm planning to build a H-stab first and then test it to destruction to verify production methods and my design calcs?
Well, I hope it works out the way you plan. I'm really glad to hear you're doing some testing on real-world parts before trying to build the whole wing.

And I greatly prefer for someone to shoot down my ideas before I waste time doing something that won't work. That's why HBA is such a great place. Or you are such a great person. Where's that "love" button again?

Yes, I'm greatly under the influence, but cafeïne only ;)
Uh huh. I'm of the opinion that you're more under the influence of "girlfriend proximity", but again that gets us back to TMI... If we hear from you again in the next two hours I'm going to be terribly disappointed. :)
 

Head in the clouds

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Brilliant! Thanks for the tip. The brake cleaner is also unlikely to contaminate composite surfaces (residue, if any, is easy to clean).
Not having read the whole thread apologies to all if I repeat wisdoms previously offered, however -

I also think this lubrication method is brilliant, thank you from me too, I love piano hinges for load spreading.

I remember people lamenting the black residue from the elements of the hinge 'working' due to their natural action or transmitted vibration. I don't know if it was previously spoken of but I was shown how to solve it by bending the hinge pin into a series of curves rather than inserting it straight, so it couldn't rattle.

As far as control surface lockup due to flexing of the wing under load is concerned, it makes no difference what type of hinges you use, if the hingeline is forced out of axis then there will be a commensurate increase of control force with a 'toggle effect' from one deflection to the other. Build stiff wings - or accept the limitations and the benefits of flexible ones.
 

Toobuilder

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Just to close the loop on this thread - I attended a EAA fly in in Bakersfield yesterday and put my eyes on a Lancair 320. The flaps and ailerons had the EXACT hinges and geometry I am asking about.

...And I thought I was being clever.

The 320 has essentially the same mission profile and wing construction as my airplane, so I'm guessing I'm going to be OK with this design.
 

N91CZ

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http://www.n91cz.com/HingePlay/HingeRepair.pdf

http://www.n91cz.com/HingePlay/hinges.htm


I just stumbled across this thread. I saw a few references of the use of piano hinges on Lancairs. Implied was that they must be ok for the application. Unfortunately this is not quite the case. Stock MS20001 hinge is holding up poorly on Lancairs. They take quite a pounding due to the torsional vibration of the engine on a very light and stiff airframe. I have spent much time helping folks replace them. The good news is that MS20001 hinge can be made to work very nicely with larger hinge pins. Unfortunately most Lancairs are still flying with stock hinge material and have severely worn hinges. The first link above shows a hinge removed with 500 hours in service -next to a new section. Almost half the aluminum is worn away.
 
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N91CZ

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Well for some reason the two links are combining to only one address. The text of the addresses is correct however.
Chris
 
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