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Offsetting piano hinges

Mr Charles

Well Known Member
I am in the process of upgrading my beloved 4, (not original builder), and am replacing my original poly cowl with the epoxy based one. As my original lower cowl to fuselage piano hinges had a few broken eyes, decided to go for all new piano hinges. I have researched many, many threads and have gained much knowledge. However, I can't seem to find much on offsetting the hinges and so would like some feedback.
My understanding is offsetting hides the eyelets for a cleaner look, and possibly improves strength. I reworked my old poly cowl some time ago, and offset the horizontal hinges, and felt like it helped with installation alignment...especially single person.
First, on the lower cowl to fuselage...I bought some MS20001-6 extruded (2" overall, 3/4" legs, .051 thick, .090 pin. Is this good for lower attachment? How much should I offset them? Assuming I should?
Second, on the cowl to upper fuselage...my thoughts here are that the extruded maybe not the best for the curve? Use SST? Is the increased strength of the extruded necessary at this location? I have read posts on relieving the eyelets, tapering the pin etc. for the SST. Assuming all this will work on the extruded the same?
Should I offset this hinge also? and if so how much? (With either the extruded or the SST)
And last, the horizontal cowl split...is extruded worth the extra cost? How much should I offset?

Would like to hear what others have done and any recommendations, Pros and Cons, thoughts or opinions...

Mr Charles
 
Just finished this job. What I do:
- Top cowl, 1/8? hinges per plans but I do not use the smaller pin to make the curve. I take 1/8? SS pins and turn down the last few inches to the smaller pin diameter to make the curve. This way you have full size pins along the top of the cowl - eliminates the cowl popping up that last 1/16? when the ram air pressure pushes it up.
- Lower cowl, same size hinge but do use the extruded hinge material. This eliminated the broken eye issue on my RV-10.
- Side hinge. Here is where the offset comes in. Buy a wider hinge from ACS and have eye seam just above the cowl seam.
- Side hinge pin. I never liked the front cowl pin retainer deal so on all three RVs I have the side pin come out in the cockpit. I use 1/4? aluminum tubing as the conduit in the plane, pin going through a 3/16? cut off rivet with a #40 hole that aligns the pin wiht the first eye.

Carl
 
More info please

It appears that ACS does not have the extruded with an 1/8" pin. They have one that is .180, so close... Is this what I need for the lower attachment? Or is there somewhere else to source the 1/8" pin extruded hinge?

For the top fuselage to cowl, it appears to be the same issue. The MS hinges are not available with 1/8" pin. So use the Van's 1/8" hinge here? (or from another source?)

Would there be a benefit to offsetting these two hinges any? Or any reason not to?

Was also wondering if there would be any reason to use SST hinges instead of aluminum for the top and horizontal attachments?

Charles
 
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Use the MS20001P extruded hinge with the smaller pin diameter from ACS for the bottom hinges. Hinge width the same as the stock hinge material.

For the top cowl hinge, use the stock hinge 1/8" material from Van's, but instead of using the smaller diameter pin called for in the plans, buy some 1/8 SS pin material and tapper the ends like I mentioned. Tapering the ends is not trivial - turning against a belt sander seems to be the best process.

The only hinges you want to offset are the two side hinges.

Cowl side to firewall hinges - stock hinges per the plans.

Carl
 
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