Boot Cowl Construction

[Ray Strickland]

Looks really good. You set a high bar for those that follow.

[svyolo]

Reading some boot cowl threads, I decided to make sure my panel and firewall flange didn't move while fabricating. I wanted to make sure they were in the right place. I bolted a piece of plywood with big stringers to make the firewall flange square, and then used some scrap (I create a lot) angle from the firewall tubing to the instrument panel. Both are pretty rigid now.

[jaredyates]

Thank you so much Archer39J for posting the pictures here, and for allowing us to add them to the builder manual entry on the boot cowl here:

https://bearhawk.tips/3136

Please keep up the good work!

[Archer39J]

Oh cool, thanks for sharing real-world performance!

[Archer39J]

Yeah that certainly does help, I did something similar for the cabane pass through.

[BravoGolf]

That's the general idea. There's a thread here where Battson talks about his but I don't think I bookmarked it. Here's a VAF thread that briefly discussed it, apparently it's standard on RV-8s? It's easy enough to remove and install I'll for sure do a comparison when I get flying.

http://www.vansairforce.com/communit...=116609&page=3

I had problems with CHTs on my RV-7 and installed one to clean up the exit area. My pre and post flight test showed CHTs 15-20 degrees cooler. Which means I can climb continuously and not have to level off early.

[svyolo]

Brooks, I was going to use doorskins but it looks like they are getting hard to find. Other than that, making a bunch of small pieces into 1 larger panel was my plan.

[Bcone1381]

This is great, Dave! I've been dreading this part of the build as others have told me the the documentation and manuals are inadequate. Your pics and description are going straight to my file library!

Dave;

The boot cowl I did was enjoyable to me. I think the process I used was part of my success. I made each panel out of poster board first....twice. The first paper version had numerous small pieces of pasteboard taped together. The second was made of a larger single panel. To thicken and strengthen the poster board I married two together with 3m spray glue. After the second paper panel was made, fabricating the real thing was not very stressful, and I knew where the issues were and how to mitigate those problems. I admit that having access to a sheet metal roller at my local Eaa chapter was helpful in the upper corner areas..

[jaredyates]

Let's see if we can roll the helpful info into the manual too!

[svyolo]

Dave;
I read that thread a while back. Interesting read. I will probably do a similar "lip". I have also been thinking a bit about cooling. To cowl flap or not? I want to err to the side of simple. Having to be an active part of my engine cooling system is not something I want to be, if I can help it. I will come up with a power setting and speed to descend such as not to shock cool the engine. I think it is also pretty easy to set up the EFI mixture to closer to peak EGT during the descent. That should also help to keep the engine from cooling to rapidly. I will do that by picking a small range of power settings that I will use for the descent, and set the A/F in that range to not cool the engine excessively. It will be automatically done when you set that range of power. Running "full rich" or LOP both are designed to help cool the engine. In the descent, the opposite is the case. You want to keep the engine warm.

Right now I think I will size the cowl exhaust to what I think will work everyday in moderate temps. I will also install a pair of louvers in the lower half of the cowl, but will plan on blocking them off most of the time, and opening them for flying in higher ambient temps.

Anyway, that is the current plan. I am definitely willing to listen to any other ideas.

[Archer39J]

I see a radius in the tunnel opening. Do you think it will help with smoothing the flow of the air exiting your cowl and contribute to better cooling?

That's the general idea. There's a thread here where Battson talks about his but I don't think I bookmarked it. Here's a VAF thread that briefly discussed it, apparently it's standard on RV-8s? It's easy enough to remove and install I'll for sure do a comparison when I get flying.

http://www.vansairforce.com/communit...=116609&page=3

[tailwind]

I see a radius in the tunnel opening. Do you think it will help with smoothing the flow of the air exiting your cowl and contribute to better cooling?

[robcaldwell]

This is great, Dave! I've been dreading this part of the build as others have told me the the documentation and manuals are inadequate. Your pics and description are going straight to my file library!

[Archer39J]

Archer39j, I like the Venturi roll on the firewall exit. You may have this in mind but don't forget to roll all edges so the panels hug down tight. Nice work ! Stinger

I've not seen that done on boot cowl skins, though I recall the manual mentioning breaking the boot cowl extension panels 1/4" about 5 degrees. I didn't do that as everything seems to lay flat and seal well enough for my eye. The gaps look much more pronounced in the photos than in person. I've seen others take extra steps to make these panels sit flush with each other, figured I'd try overlapping them first and I think it turned out well enough for me.

That said at least on the forward center piece I may put in a RTV gasket between where it overlaps the side panels to avoid water wicking up under there, on final install maybe.

[stinger]

Archer39j, I like the Venturi roll on the firewall exit. You may have this in mind but don't forget to roll all edges so the panels hug down tight. Nice work ! Stinger