Cowling attachment to firewall

[Nev]

One of my mentors mentioned using camlocs to attach the top and bottom engine cowls to the firewall, and also to attach them to the nose bowl. While I intend using camlocs to retain the side cowls, I wasn’t sure if they had sufficient strength to hold the cowling in place. I see that Vans often use a piano hinge to retain the cowls to the firewall and themVans instructions show this method.

Does someone have experience with either method that can comment ? Just to clarify, I’m not referring to keeping the cowl doors closed, but the attachment between the upper and lower cowls at the front and aft ends.

Thanks.

[Mark Goldberg]

I have always used flat head screws to attach my cowl to the firewall Nev. Either #6 or #8. With nutplates installed on the flanges of the firewall. I have never seen what you are contemplating. I am not saying it is a bad idea, but just have always done it the same way.

When I built an RV8, I did not use the piano hinge style attachment of the upper to lower cowl. It is a clean method but I remember RV owners pulling hard to get that piano hinge wire out. And have heard of broken piano hinge loops. I am sure it is fine, but I chose another way. Mark

[Nev]

Thanks Mark, I gather most Bearhawks use machine screws and that’s what I had planned. But I thought I’d look into the Camloc idea in case he’s onto something that I hadn’t considered. He said it makes removing the cowling a very quick exercise, but wasn’t sure if the firewall flange was wide enough to support Camlocs,

[davzLSA]

Hey Nev, I like your thoughts about cam locks. But they are mucho expensive and they are a pia to install.

[Nev]

All good data points Dave, thanks. I’m sitting in front of the engine waiting for the solutions to come to me

[svyolo]

I was considering the piano hinge, at least for the upper cowl, and maybe the cowl doors. The curvature of the lower cowl makes me want to use screws.

[geraldmorrissey]

I had Camlocs holding the cowl on at the firewall on my Cessna 150. Plus I had them going down the sides between the upper and lower halves. I have seen them on 172's. Made removing the cowl a breeze. One of the neat features of the Camloc's I had was the adjustability. I was able to adjust the cowl up and down, side to side so the cowl fit the spinner perfectly. Easy to install but a royal pain to initally adjust, but after that, they were a joy. I will definitely have them on my Patrol. I think I spent 2 or 3 days dinking around adjusting them but after that they held the position until I sold the plane years later. The front end of the Cessna cowl was fiberglass and I used screws to hold that end together.
Gerry
Patrol #30

[Nev]

Good to know thanks Gerry, exactly what I was after.

[PaulSA]

Getting on to this part soon. I've already bought Camlocs for the doors but intend to hold the bottom cowl on with screws/nutplates. I'm sure Camlocs would work fine but the bottom cowls don't need to come off too often and Camlocs don't come cheap!

I've used piano hinge on my RV-10. Once you get the hang of it and the pins have worn in a bit, it doesn't take long to get them in or out. With fibreglass, you can cover the rivets and get a very clean look but you are going to see the rivets on a metal install so I don't see the benefit - other than cost.

[geraldmorrissey]

One other thing you might consder is getting the winged Camloc's for those parts of the cowl that will be opened during preflight. That way you don't need a screwdriver and they can be released with gloves on. As for cost, in the grand scheme of things, a few bucks extra on a $75,000 airplane doesn't amount to much.
Gerry
Patrol #30

[Nev]

I’m planning to use the winged ones on the opening cowls, good idea thanks.

[Battson]

I started out with the winged ones, however I changed to the screw-head ones second time around.

Reasons:
1. The aesthetic is much nicer
2. Flush mounted means they don't catch on aeroplane covers when parking up overnight
3. Most aircraft engines do not need to be checked before each flight, most manufacturers don't require it

After realising that nobody else is doing it every day on their certified aircraft, and 8 years of finding nothing whatsoever, I was happy to open the engine once every dozen flights instead of every preflight. This is even more true when you own your own plane, you develop a greater understanding of the airframe - it's sounds and vibrations. Normal indications. You would notice immediately if something was not right. This is more likely than seeing something amiss when you open the cowl.

[svyolo]

I have never owned an airplane, but was thinking using a piano hinge on the upper center part of the cowl to make removal easier. The #8 recommended screws and nut plates go thru the top of the cowl, boot cowl, and firewall flange. I was thinking pulling the piano wire out the side was easier than removing screws from above.

Any thoughts on this, or anyone else do it that way?

[Battson]

I have never owned an airplane, but was thinking using a piano hinge on the upper center part of the cowl to make removal easier. The #8 recommended screws and nut plates go thru the top of the cowl, boot cowl, and firewall flange. I was thinking pulling the piano wire out the side was easier than removing screws from above.

Any thoughts on this, or anyone else do it that way?

Not a bad idea. You need to consider the U-channel which must tuck under the firewall flange, and the boot cowl which goes over the top of the flange. This is not a masterpiece of design, and it's a real fiddle to reinstall after maintenance. It's almost designed to remove paint. At the same time as that, you have to miss the prop and spinner. If you could pop the cowling into place and then attach it, without doing the U-channel overlap, it would be easier.

[svyolo]

I didn't think about the U channel, I will have to think about that one.

[Nev]

You need to consider the U-channel which must tuck under the firewall flange

What is the purpose of the U channel tucking under the firewall flange, and where is it written ? ( I found a reference in Bearhawk tips - but no pictures, but nothing in the plans.)

I have terminated all 4 of U channels before the flanges. The reason is that the thicknesses don’t match, so I’ve riveted some aluminium angle instead to extend behind the nose bowl flange. The rivets will go through the outer aluminium skin, the fibreglass of the nose bowl, and the angle aluminium. This seems to have worked very well, looks fine, and is strong.

At the firewall end, it’s different. Assuming that I use nutplates to attach the cowling to the firewall, if the U channel extends under the firewall flange, then the nutplate must be attached to the U channel in order for it to capture everything. Is this what people are doing ? This seems very fiddly. Another way would be to rivet something to the firewall flange (angle extrusion for example) with a nutplate say one inch forward. That way the whole assembly can be lifted vertically at the rear once the screws are removed.

If it doesn’t have a nutplate attached to the U channel, then how does it improve structural integrity? Is there any other way this can be done ?

[Battson]

That is what I did. I am not recommending it, however I understood it was required.

[Nev]

I found some good detail in Eric Newton’s manual regarding the engine cowling including a diagram showing how to make a steel plate (to do what I did with angled aluminium), which allows all pieces to line up.

This is on pages 4,5 &6 of the finishing manual.

Eric doesn’t show any detail (that I could see) of the rear cowling attaching to the firewall flange - specifically where the U channel attaches, so I’m still searching for ideas in this area.

[PaulSA]

The Bearhawk Fuse Builder assist manual has some info on this - P49 to 54. It looks like they are doing a lapped finish rather than flush so you may need to adjust if that's what you want.

[robcaldwell]

Yes what Paul said... I used a piece of 1/16" 4130 plate to mate the channel and the firewall flanges together. The plate is permanently riveted to the inside of the channel, and where it laps to the firewall flange, I have #10 nut plates on the bottom of the plates. I can send pics if you would like. Seems like I saw this example somewhere when I was at that point in the build, but cannot remember where...

[Nev]

I can see now where my confusion has come from. One manual shows a lapped joint with no stiffener, another manual shows a flush joint with a steel stiffener in behind.

[robcaldwell]

Maybe this pic helps a bit. Might need to zoom in to see where the plates are installed inside the channels. Here is my discussion on the engine cowling. https://bearhawk4place.blogspot.com/...e-cowling.html

IMG_2315.jpeg

[Nev]

Thanks Rob. Interestingly from the pic your U channel looks to be a bit wider than mine and this has allowed you to fit two nut-plates on the steel plate. Looks very strong. I wonder how the strength compares to that of the firewall flange and bootcowl that we attach these parts to. I’ll post pics of mine later, I’m interested to hear how you think they compare for strength.

[robcaldwell]

One of the very few things I had fabricated for me were these Channels. I took a sheet of .032 AL to a race car shop near me and asked them to cut and bend the channels. I requested extra wide for the support and what you are seeing.

[davzLSA]

You do beautiful work Rob!!

[Nev]

Here a photo of how I’ve done it. At this stage I’ve only done the two from top nose-bowl attachments, using aluminium angle pieces.

I’m interested in thoughts as to whether I’ve achieved the required level of structural integrity doing it this way, or should I be removing the aluminium angle and replacing with .032 steel ?

F82FC2C5-004A-4765-950C-4EC1451BF14D.jpeg

[Mark Goldberg]

That looks plenty strong enough Nev. Your cowling is .025 and a little .032 aluminum. This angle looks had good thickness. Mark