Cowl Piano Hinge Attach Choices

[Utah-Jay]

This might have been covered and I am guessing a lot of it is personal choice, but I wanted to get some opinions.

Choice 1) Rivet top cowl to piano hinge and use screws to attach the cowl door to the piano hinge

Choice 2) Screw top cowl to piano hinge and rivet cowl door to piano hinge

Choice 3) Rivet both top cowl and cowl doors to piano hinge

Choice #3 would look a lot cleaner ( I like this) but would be more of a pain to remove in one large piece.

Choice #1 would allow for taking the doors off separately when needed, and more easily than choice #2

Thoughts?

[jaredyates]

I prefer option 3. If you really need to remove the door, pull the hinge pin out.

[Battson]

This makes most sense to me, in over 10 years I have never needed to remove that pin.

Be sure to bend the pin at the front, so it can't work it's way out in flight - especially forward towards the spinning propellor.

[Nev]

I also did option 3. Like Jared, I remove the hinge wire to remove the doors separately. Put a 90° bend about 1/2 inch from the forward end of the hinge wire. Then after inserting the hinge wire, turn the end down below the cowl to stop it moving forward inflight. However now I usually open both doors to the vertical position and lift the whole thing off as one unit. Pretty easy.

[alaskabearhawk]

FWIW, I did option 2.

[TrueAirSpeed]

Jay's seen mine-option #1.

[Utah-Jay]

Seems like every option has been used, I figured so. I had not thought of the removal of the piano hinge

More food for thought.

[AKKen07]

I did #3. Removing the pin is easy as is removing the top whole. No need for screws.

[Bcone1381]

I want to help visualize this to the readers..

The Patrol Book shows an aluminum angle that connects the firewall to the nose bowl with the outboard edges of the top cowl piece riveted to that angle support. It is noteworthy that Bob calls out #8 screws (not #6 which I commonly use) for the hinge attach and the attachment to the nose bowl and firewall.

These photos are taken from Bob's Patrol Book. The last photo shows the Hinge attachment to the top cowl.
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[Battson]

I screwed the top half of my nose bowl to the top cowl, per the book. However the bottom half of the nose bowl is riveted.

I have never needed to touch those screws, and cannot imagine why they are recommended. Does anyone know why that is a screwed connection, not riveted??

[jaredyates]

During the construction on our blue plane I asked Bob about using rivets vs screws in the nose bowl and boot cowl area and he seemed not to be to worried about one vs the other. I didn't care for rivets in the fiberglass but whenever I did use them I tried to make the fiberglass a sandwich between aluminum pieces. For example, cowl skin on the outside, and a little strip of aluminum on the inside.

[AKKen07]

I screwed the nose bowl to alum parts. I find it much easier to remove if I unscrew it first. Probably just a quirk of my installation but I use them frequently.

[gregc]

I did option 3. The only difference I have from Bob's drawing is that I used the U channel that came with the kit instead of the angle bracket. The channel/door assembly is attached at each end with #8 screws. A couple of steel strips attached the the channel (a combination of Nev and Eric Newton's approach) makes it easy to lift the whole thing off.

[Utah-Jay]

Battson

Just to be clear you riveted the bottom engine cowl to the nosebowl? I had not thought of that, but it sounds like a good idea. Based on your comment above, would you also rivet the top cowl to the top nosebowl?

[Battson]

Battson

Just to be clear you riveted the bottom engine cowl to the nosebowl? I had not thought of that, but it sounds like a good idea. Based on your comment above, would you also rivet the top cowl to the top nosebowl?

If you build the cowl with overlapping C-channels per the Bearhawk Book, lapping the C-channels inside the nose bowl and firewall - then it makes it hard to remove either of the parts independently (nose bowl or aluminium cowl assembly). It comes off as an assembly 99% of the time in my experience (assuming the prop is installed, which it almost always is).

However, that C-channel overlap is not a great design in my view. I find removing and replacing the cowls extremely painful compared to certified types, because you need to slot the C-channels into place.

If I were redesigning the cowl, I would do it differently. Easy access to the engine (no risk of scratching spinner / paint etc) would be great to have.

If you are planning to use the cowl as just two parts (top part and bottom part) for maintenance, then I see no use in having screwed connections within those parts.

[Nev]

If I were redesigning the cowl, I would do it differently.

Good point, and probably an area that a few may have changed. Here's another data point.
I riveted the top cowl to the top nose nose bowl, and the bottom cowl to the bottom nose bowl. I then trimmed the C-section extrusions and fabricated lugs that they fit over. An additional countersunk screw locates and secures them to each lug (shown in one photo below).

Installing and removing them is very simple.

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[Utah-Jay]

Thanks Battson and Nev

you guys just made my life a lot easier

[arborite]

For reference, my Piper J5 cowl is built as follows:

- side cowl covers have piano hinge riveted to the top edge.
- nose bowl supports that run from the firewall out to the nose bowl have nut plates riveted to them, four per side
- top cowl has holes that align with the nut plates
- hinges have holes that align with the same nut plates
- screws inserted from the top, passing through top cowl. hinge, then through support into nut plate

sorry for no pictures. i’ll try to take some if there’s interest

[arborite]

here’s a very crude sketch. black are cowl sheet metal parts, red is hinge that is riveted to side cowl, blue is nose bowl support, green is nut plate and yellow is screw

i like this setup. in the J5, taking off the top cowl is needed just as often as the sides. access to the top of the engine for oil screen, plugs, etc needs the top cowl off. having it in three pieces is easier to handle than one big floppy piece if the hinge were riveted to both top and sides

if i want to take off just one side, it’s easy to remove the top screws from that side only and slide out the side panel. the top is held on by the other side and front/rear screws.

[Pbruce]

I seem to be missing something, conceptually: why not rivet both leaves of the hinges to their respective aluminum parts, and just pull the pin out whenever disassembly is required? Any reason why that would not work or is undesirable?
is required

[Utah-Jay]

That was not an option I had thought of, several of you do it and it is a great option.

Thanks to all