Patrol Cowling Article

[noema]

Fellow builders, here is a fairly extensive post about the cowl building process. I am using Skybolt quick-release fasteners and have added quite some details about them which I couldn't find anywhere else. They are great imho because they are adjustable.

cowl.jpg

https://xhawk.substack.com/p/cowling

[Mark Goldberg]

Looking very good Stefan. Mark

[Sierra Skydog]

Excellent post and workmanship! Thanks for sharing

[Bcone1381]

I enjoyed your cowling article. I loved your description of your quarter turn fasteners.

I work alone quite a bit. I expect I will want to install the lower engine cowl when I am alone in my shop. I want to win every wrestling match with the engine cowl. Securing it to the firewall flange will be the major struggle.

So, I am wondering what the group thinks about using quarter turn fasteners instead of Bob’s design of #8 machine screws and nut plates on the aft edge of the cowl.

[Nev]

I am wondering what the group thinks about using quarter turn fasteners instead of Bob’s design of #8 machine screws and nut plates on the aft edge of the cowl.

I really like that idea and it's something I wanted to do, but as a first timer I found it difficult to visualize how to go about it. After installing the quarter turn fasteners on the cowl doors it was all quite straight forward.

Definitely I'd be looking at doing it next time around.

[jaredyates]

If you are in position to operate a quarter turn fastener, I would think you would also be in position to put 3-4 quarter turns on a screw, which is enough to hold the cowl briefly.

If I have help available when installing the cowling I will accept it, but I almost always do it solo. On our first plane the rubber baffle strips on the front cooling inlets and on the airbox could hold the front end up long enough to put the back screws in, and this made it pretty easy. The steel tabs at the u-channels held onto the firewall flange sufficiently to keep the back end of the cowl in place even without a screw, usually. The cowl skin was dimpled, and the steel applied a little holding pressure to keep that dimple nested in the corresponding dimple at the flange.

If you want quarter turn fasteners, you can find a way to use them, but I don't think you should feel like you need to install them to get the cowl on without a fight.

Some things I would want to think about if I was using quarter-turn fasteners:

-Some of them are quite fiddly to operate. You open them, and they still get stuck in the receptacle when you try to get them out. This would be immediately apparent if you attempted to open our cowling doors, at least with the type if fasteners we have. There may be better ones, but I wouldn't want any more of these to deal with. We put up with them because the utility of being able to open the doors quickly outweighs the frustration of dealing with them.

-If you space them the same as you would the #8 fasteners, they will increase weight, perhaps by a lot.

-If you space them farther apart, will the specified cowl material thickness be sufficient to handle the more concentrated stresses? Similarly, how much edge distance margin is missing at the flange due to the much larger diameter hole for the receptacle?

-I suspect you'll spend more money. Maybe quite a bit more.

-Quarter turn fasteners were available when Bob decided not to use them. He evaluated the advantages and disadvantages and decided screws and nutplates were better. If you can get ahold of him, you could ask why he doesn't prefer them. Sometimes when I do that, I agree with his reasoning, and sometimes I don't. Usually, he exposes some insight that I had not yet considered.

All of this is not to say that nobody should ever use quarter turn fasteners at the firewall flange, but rather to say there are so many times when we might make what seems like a small change, only to find that it was bigger than we thought. If we must deviate to solve a problem, then we do what we have to do. But I try to stay cautious about making changes to solve non-problems, where the cost-benefit is much less clear.

Cowls live a hard life. They hang way out there, while only being attached at the firewall. The engine is in there moving around on the scope of centimeters at a time. We expect them to maintain contact with the rubber seals to keep cooling pressure, but yet not make contact with the aluminum parts. Then the same thing happens with the airbox interface. We want to be able to easily remove them and even more easily open large sections of them, and we routinely cycle their temperature, and they are receiving internal and external pressure pulses from each rotation of the prop. Side loads come from intentional and unintentional slips and skids.

303AP has 1350 hours, with a few various cowl patches and fixes. Right now the cowl is off and I need to add a few more.

I propose that cowls need an extra margin of respect.

[dramsey]

I am afraid to admit this but I have 72 number 8 screws holding my cowl and plenum on the Lancair IV. I dred the removal, but I have gotten good doing it by myself. I then used quarter turn fasteners on my subsequent Just Highlander build. They are a royal pain in the ***. I had beat on the cowl at times to get them to release. My neighbor put 1/4 turn on his RV10 cowl and I think he regrets it. The alignment changes every time he puts it on. Its a pain in the *** getting them to release. They hang up and he ends up beating on the cowl to get them to release. So my bias is now screws and nutplates, though I might be tempted by piano hinges like a lot of the RV community.

[noema]

That's also my impression. The quarter-turn fasteners are harder to align and tend to hang. Putting on the cowl with small drill and well-fitting drill bit is easy enough for me. Especially using a drill bit that fits well enough so the screw stays on it makes this much easier.

[Nev]

I use a little Bosch electric screwdriver too. Easy on the screws, and makes removing cowls and panels a breeze.