Alternator Pulley/Cowl Contact & hinge link breakage

[Bob Axsom]

Info only:

At rest there is plenty of clearance between my alternator pulley and cowl (RV-6A) however I noticed a slight mark on the cowl and added a thin stainless steel striker plate. Now the plate is almost cut through so I have gone to a more substantial striker plate and I will dress the forward edge of the pulley tomorrow.

When I pulled the short hinge pin at the rear of the upper cowl half tonight to go to work on this problem I heard a little "tink" and I found I had experienced my first broken hinge link. I suspect I will have to go to the screw and plate nut fix that I had to use in the lower cowl.

Bob Axsom
Just over 100 hours in N710BJ

[SteinAir]

Hi Bob,

Welcome to the RV world of piano hinge cowls! I actually just had "my" first experience with broken pins on my bottom cowl, at about 300hrs. Same thing, took out the lower pins, and tink, tink, there were the eyes on the floor.

This fall at annual, ALL the piano hinges are coming off and Skybolts/Camlocs are going on. My other RV has them and I'll never again use those piano hinges on the cowl.

With these hinges, especially on the bottom of the lower cowl, for the most part there is those that have broken eyes, and those that will.

Just my 2 cents, I thought be cause I used large hinges there I would be immune, but I guess not!

Cheers,
Stein.

[Mel]

The piano hinge works great on the horizontal between the upper and lower cowls and vertically at the lower cowl to firewall attach. Everything else neds something else.
Mel...DAR

[Bob Axsom]

I would like some information on the Skybolt Fasteners. I am working on a solution to the problem that will preserve the paint job - almost have it.

Bob Axsom

[gmcjetpilot]

I have used piano hinge with great success. However I found in a few problem areas I used a different approach from stock.

One: I used stronger forged piano hinges that are solid and don't have burrs. Notice the lighter weaker rolled hinges have small burrs in the high stress corners. Consider smoothing the edges of all hinges before installing to reduce this stress concentration. They can be rough and is no wonder they crack.

The second approach is to consider counter sunk screws and nut plates vs. the expensive quick release hardware. With an electric screwdriver and limited use in a few places, this is a cheap and effective solution.

The only place I went away from the piano hinges completely was behind the spinner, where I used screws and nut plates. They are a little more of a pain to remove, but with an electric screwdriver and the lower cost it is something to consider. Also I am talking about limited use in combo with piano hinges. I used a metal reinforcement, 3 nut plates, screws and tinnerman washers on each side. Piano hinges are too weak. Again just 6 screws can be removed very fast, even by hand tools, sit flush and are cheap.


Except for the spinner, I found the standard hinges work well except for the lower aft cowl to firewall side piano hinge. I had cracking problems, ie failed lugs. The pressure inside the upper cowl, plus the external air load on the lower cowl really puts a large prying load on them. The solution was to use heavy-duty forged piano hinges. The problem went away. These solid forged hinges are awesome. They cost a little more but still cheaper than quick release hardware and I think looks better.

The last area was the aft upper cowl to firewall piano hinges. Not a strength issue but they are a pain to install thru the oil door. I still used the standard hinges but used a little flap door held with one screw in the center to access the pins from the outside, making installation easier. I would consider screws in this area next time.

The last problem with hinges is the rivets working loose. You should consider the hinges in the cowl are bonded on. Drill little weep holes in the hinge flange to allow the epoxy to flow. Cleco and clamp, than rivet. Make sure the rivet pitch is not too large and make sure you have good grip lengths and slightly over drive. So not to distress the fiberglass consider a squeezer or back driving.

Cheers George

[Bob Axsom]

Mel told me about the flange/platenut/Screw fix earlier for the lower aft hinges and I made that change before paint. It is working out very well and there was no paint pain. I will do something similar for the top but it is going to require a little finese to avoid an area repaint. I think I will cut off the links (after another one comes off) and leave the mounting flanges there as spacers. I will cantilever a flange from the fuselage skin for mounting the platenuts. Holes will be drilled in the flange to clear the existing rivet shop heads and I will countersink the skin/spacer for #8 screws (or perhaps rivets). I will drill 3/8" holes (yes with all the proper sequential steps to assure perfect alignment) in the cowl and install it with #8 stainless flathead screws and dimple washers (like the bottom).

The strike plate - uh, well we never used that 6th setting stainless butter knife anyway. A major item here was the dressing of the forward pulley edge which came to a sharp jagged edge (sort of like a hole saw) it is now smooth, rounded and less protruding than before.

Bob Axsom