Engine cowl top panel-how big?

[Pbruce]

Hey guys, I’m doing some planning on my Patrol engine cowl. I’m seeking advice: The cowl top panel (at 24”) seems to be too wide-maybe it’s for a 4-place? In any case, it seems prudent to cut it narrower in order to provide better access to the top of the engine. Maybe I’m wrong about this though, since reducing the width of the center panel would move the doors inward and up, reducing access below the engine.

I have seen build comments and instructions saying it should be about 12-13” and another which says 18” wide. My panel is currently 24” wide which brings it almost to the outer corners where the hard bend downward begins

How wide did you guys go on the center panel? Should I actually be trying to provide access the area below the cylinders through the doors? Anything else to think about? Thanks

Pat

[TimTall]

Mine is a 4-place but I seem to remember cutting that top piece to 18" wide. That gives lots of access to the top of the engine but still keeps it wide enough to put the hinge line in a good spot. I made the doors large enough that I could remove the lower spark plugs with the cowl on.

[Bcone1381]

I think your thinking is spot on to cut it narrower. Bob's Patrol Book (P.56) says the top cowl section is 12" to 13" wide. I'll be making mine that size. I recall that is the size I've seen on other Patrols. The stock sheet aluminum that comes with the kit is oversize. Access is key.
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[Pbruce]

Thanks Brooks. I just noticed the drawing calls for .025 on the bottom. Mine is .032 which might be nicer, at the expense of a few ounces. I will keep the doors full width (20” at the back I think). I’ll trim the 5’ wide bottom panel to give me something like 13-14” on the top. I assume the doors would but up against the center panel via the piano hinge and overlap 3/4” at the bottom. I really like the Piper-style latches for their ability to pull the doors down snug. I’ll try to find some.

[Bcone1381]

I am also doing the Piper style latches. I like how they draw the doors down tight and keep tension on the pieces as the latch goes over center.

A lot of places ask a pretty penny for them. I found mine on ebay a few years ago...still expensive...had to source the 1/4 turn fasteners (Southco maybe?) separately. But, Last summer at OSH I saw that B and B (A hardware dealer at OSH) had them in their tent. B&B Home (bandbaircraftsupplies.com) You might give them a call. It seems like there exists a supply of NOS of these parts around. I think Supercub, some Warrior, Tomahawk, and Stinson used them.

[Pbruce]

I gave B&B a call. I think all they had was Heartwell H-500-2. These are a nice latch, widely available at decent prices, but more suitable for oil doors, glove boxes, etc. I have been coming up pretty dry on any kind of flush-mounted draw latch. I might resort to a piano hinge with a removable hinge pin, ala Vans RV. They are a little bit more cumbersome though, almost certainly less likely to get opened routinely. I’ve got some time. I was kind of shocked at the supply/demand/ price picture. At least with experimental, we have options.

[jaredyates]

I would not use the piano hinge, one of the greatest features of the Bearhawk is the ease of opening the cowling. I'd recommend installing the quarter turn fasteners in both the horizontal mating cowl parts, and also at least one or two in the fiberglass nosebowl and in the firewall flange. In my first iteration of cowling I only installed 5 fasteners across the bottom joint, and the fiberglass distorted over time and it didn't work out well. Having some fasteners in it helps stabilize that joint. Instead of looking for a ratchet type of attachment, I'd recommend spending the time on a roller to bend the cowl so that it fits in a tidy way without needing any tension. It will take some tools and craftsmanship but could also be something you could get some help with.

[Pbruce]

Thank you Jared! That was plan B. Easily available and not too expensive as well. How many fasteners or what spacing would you recommend across the bottom of the cowl door (Patrol doors being a little shorter than your 4-place? A couple on the nose and firewall seems like a good idea. what fibreglass was distorted-the nose bowl? I didn’t quite understand that.

[jaredyates]

I used spacing around 6 inches, but would adjust that as required to make the layout even. Go in 2 inches or so at each corner and then see how many inches are left in the middle and divide accordingly. The nose bowl was the problem, if I remember correctly it slid aft under the cowl door, but it could have been the other way. The problem was definitely forward/aft movement of the section of nose bowl that sat under the cowl door.

[Bcone1381]

I used spacing around 6 inches, but would adjust that as required to make the layout even. Go in 2 inches or so at each corner and then see how many inches are left in the middle and divide accordingly. The nose bowl was the problem, if I remember correctly it slid aft under the cowl door, but it could have been the other way. The problem was definitely forward/aft movement of the section of nose bowl that sat under the cowl door.

Jared, thanks for sharing this. It is the first I’ve heard of how the nose bowl - cowl door joint might behave under load in flight. I know Mark has two nose bowls available depending on spinner type and wonder if one is stiffer than the other, Several years ago I noticed Bob’s Patrol cowl doors were secured with 1/4 turn fasteners with at least one fastener where you describe on the nose bowl area. Just another validation.

This topic brought to mind a cowl door issue that Donna shared here 5 years ago. I Thought it might be prudent to give that thread some exposure.

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/32745-learn-from-my-mistake-design-flaw

I wonder if the nose bowl can push back and wedge under the cowl door, applying force on the leading edge of the cowl door to lift it and start popping rivets off.

[Pbruce]

The wider the center section is, the stronger and more stable the whole assembly is likely to be. I might make that center piece as wide as it can be without interfering with the dipstick. Jared’s comment about a few 1/4 turn fasteners connecting the door fronts to the nose bowl seem to address this issue too.