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Piano Hinge for Engine Cowl

SeanB

SeanB

Well Known Member
Hey,

I am getting ready to final attach (hopefully) the engine mount so I can install the landing gear and engine on my RV7. I've read archived threads stating the bottom of the piano hinges (vertical ones) can be very difficult to access for riveting with the mount in place. I would like to install those hinges in advance.

I see in Drawing 45, the end of the hinge run (bottom end) is where the curve starts, near the gear leg. I'm trying to determine how high to go with this piece of hinge.

  • Anyone have a measurement of what worked for you?
  • Pics?
  • Or, could I estimate and leave the hinge material a little long, then attach the bottom "challenging" areas with rivets, the top remains clecoed, and I can trim later?

Thanks!
 
Skybolt Fasteners

Piano hinges were one of the items I failed to master during my -8A build, so I went with Skybolt fasteners. No regrets - and as I recall, they have kits assembled for various RV 's.
 
I think you’d still want to put the flanges for the skybolts on before hanging the engine mount. Not sure exactly how high up they start, however.

Edit: I've thought about it more (did the lower firewall with hinges and top with skybolts)... the side hinges, at least on the 8, were able to be riveted with the mount in place. The skybolt tabs needed the mount in place to make sure that the receivers wouldn't interfere, but then the mount needed to be taken off to actually rivet them in that area at least.
 
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For the bottom cowl hinges, use the MS20001P material, not what Van?s sent you: MS20001P aluminum hinge is extruded. The closed hinge loops cannot be pulled apart. Furnished with hinge pin. Anodized finish.

Carl
 
Sean, I'm at the same place as you on my build. For the reasons you mentioned, I decided to go with the Skybolt fasteners for the firewall (top and bottom), and hinges along the sides where the cowling is split. I called them last week to order and they gave me 15% off that kit.

Have not installed them yet, but from reading the instructions you will probably want the engine mount installed to determine where to put the flanges (if you go that route).
 
After spending all but about 1 year since 1994 with RV cowl hinges, I see no reason to spend extra $hundreds on 1/4 turn fasteners that tend to fall out & get lost. ;-) Some say potato...

You're right; you can't rivet the bottom end of the side hinges with the mount in place, and the rest won't be that easy, either.

To your question, my side hinges (on the -7) end even with the bottom edge of the side skin. No memory of what the plans show; that's just where mine are.

On removing the mount: There's a lot of chicken/egg in this area. I used clecos to hold mine until I finished fitting the cowl, because I was worried about how much shim to use to keep the variable thickness fiberglass even with the fuselage sides. So my mount has been on/off several times, which hasn't been that big a deal, at least to me. But... clecos don't pull down the stack of skin/shim/hinge as tightly as rivets, so.... mine's still not perfectly flush; the cowl is now very slightly proud of the skin where they meet.

Here's a thought that I wish I'd had earlier: It's easier to build out the fiberglass thickness to meet the line of the side skin (too much shim thickness), than to shave off glass and rivet heads to reduce the cowl's thickness.
 
I hope this doesn?t distract from the O.P.'s question too much, but has anyone that's running the S.J. cowling and plenum "not" installed a piano hinge "or" sky-bolt...or any other faster for that matter, on the upper cowling/firewall location? Unlike a standard cowling where the baffles seal up to the inside of the upper cowling as the inlet air comes in and pressurizes everything, the S.J. cowling and plenum setup confines all of that incoming air in the plenum, so the top cowling really isn't subjected to any internal pressure pushing up on it like with the standard cowling/baffle setup. So, if the top and bottom cowling are fastened together in the standard way with piano hinges or some other kind of faster, does the top of the cowling really need to be secured at the firewall location? I saw a YouTube video where the cowling was installed in this fashion, but it was on a much slower bush style aircraft.

Thanks,
Mark
 
unusual pressures

Mark33 said:
...So, if the top and bottom cowling are fastened together in the standard way with piano hinges or some other kind of faster, does the top of the cowling really need to be secured at the firewall location? ...
Click to expand...
Mark, interesting question - my concern would be that in areas like that there are a lot of unusual pressures, could be positive, could be negative, and if there is no cowl attachment there you would see the cowl either expand out or get pushed in - neither of which would be good. There could also be some movement there that would rub things, and that might rub you the wrong way.
 
rv8ch said:
Mark, interesting question - my concern would be that in areas like that there are a lot of unusual pressures, could be positive, could be negative, and if there is no cowl attachment there you would see the cowl either expand out or get pushed in - neither of which would be good. There could also be some movement there that would rub things, and that might rub you the wrong way.
Click to expand...

Thanks Mickey,

Yeah, I was thinking about the same things you listed. I think that at the very least you'd want to give that back edge of the top cowling a little bit of support and incorporate a little "lip" for it to ride on so that it's just not flopping in the breeze.

Mark
 
Mark33 said:
I hope this doesn?t distract from the O.P.'s question too much, but has anyone that's running the S.J. cowling and plenum "not" installed a piano hinge "or" sky-bolt...or any other faster for that matter, on the upper cowling/firewall location? Unlike a standard cowling where the baffles seal up to the inside of the upper cowling as the inlet air comes in and pressurizes everything, the S.J. cowling and plenum setup confines all of that incoming air in the plenum, so the top cowling really isn't subjected to any internal pressure pushing up on it like with the standard cowling/baffle setup. So, if the top and bottom cowling are fastened together in the standard way with piano hinges or some other kind of faster, does the top of the cowling really need to be secured at the firewall location? I saw a YouTube video where the cowling was installed in this fashion, but it was on a much slower bush style aircraft.

Thanks,
Mark
Click to expand...

Short answer - no! Do not do this. Cowl internal pressure is but one force on the cowl.

I have a lot of time with the James Cowl and can tell you all hinge fasteners are required.

Carl
 
Pillowing

Thanks for the replies so far. If I were to install Skybolts, is there ?pillowing? or ?puckering? of the fiberglass compared to piano hinge? Skybolt appears to have the metal flanges in separate pieces. Maybe I could rivet the lower vertical ones, then install engine mount? Finish the others with mount attached later?

Thanks!
 
SeanB said:
Thanks for the replies so far. If I were to install Skybolts, is there ?pillowing? or ?puckering? of the fiberglass compared to piano hinge? Skybolt appears to have the metal flanges in separate pieces. Maybe I could rivet the lower vertical ones, then install engine mount? Finish the others with mount attached later?

Thanks!
Click to expand...

Use screwdrivers as temporary pins and put your motor mount in place. Then, visualize the places (near the corners of the mount) where you won't be able to squeeze or drive rivets with the mount in place. Attach hinge or whatever attachment hardware you need in those areas prior to final attachment of the engine mount.
 
Sean,

What do your James Cowl instructions say to do? Mine instructed me to fit and install the top cowl first. That obviously meant that it had to be attached to the fuselage in a stable manner, in order to fit the lower cowl.

Also, don't forget that there's still significant pressure on the top cowl, even if you're using a plenum. Reference all the issues people have had with the oil door bulging out in flight. It's outside the high pressure plenum area on the 4 cyl engines.

Charlie
 
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