Boot Cowl Construction

[Archer39J]

After spending entirely too long on it I've finally wrapped up the boot cowl construction so I figure'd I'd post some photos. Written instructions left a lot to the imagination and I spent a bit of time looking at photos of what other folks had done, hopefully these are helpful to someone.

I opted for #6 screws and nut plates all around, more than strong enough and allow easy removal of panels in the future. I ended up not using the top panel provided with the kit as I wanted a larger opening to access the back of the instrument panel, the access panel I made is about 24" wide and runs almost to the windshield. Contrary to the manual I started with the side panels since they would be lapped by the top panels and once I had them secured I trimmed to make the top opening symmetric about the aircraft CL.

I'd read several posts about either breaking the edge of the top of the side panels or installing some angle for stiffness, but I found once everything is buttoned up there didn't seem to be a need. No discernible flex when I reef on the instrument panel and everything is rock solid. If I notice any pillowing as I load up the instrument panel I can always add some supports but I don't see that being necessary.

One thing that made this particularly fun was the fact the plane made by the front of the firewall flange isn't planar and varies +/- 1/16" or so when measured against the instrument panel. Nothing on a welded frame this size is perfectly symmetric so don't count on that... I also created quite a problem for myself and had to remake the starboard boot cowl extension panel because I allowed the firewall in that area to get kicked forward about 1/4" when I match drilled everything. I ended up putting bolts and washers through the motor mounts to suck the firewall tight against the frame and secure it while I wrapped the rest of the boot cowl and it was all good after that.

Some final cleanup to do before paint but I'm done working these for a while. With the instrument panel in place I can finally start cutting and mounting some racks

[Archer39J]

Test bump? Hmm, original post wasn't showing up in the General Discussion thread, must have been a vbulletin hiccup.

[Ray Strickland]

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

[interstate al]

Excellent pictorial! Your work looks fantastic!
I personally found the boot cowl to be one of the hardest parts to date on my LSA QB project. After I made construction paper templates it went a bit smoother!

[AKKen07]

Thanks for posting this!

[Archer39J]

Excellent pictorial! Your work looks fantastic!
I personally found the boot cowl to be one of the hardest parts to date on my LSA QB project. After I made construction paper templates it went a bit smoother!

Thanks for the compliment, I’d agree this was the most challenging part so far. I’m glad to do this before the wings as it’s a good intro to sheet metal work.

[rodsmith]

That is beautiful workmanship!

[Archer39J]

Thank you!

[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

[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.

[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!

[jaredyates]

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

[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?

[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

[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.

[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..

[Archer39J]

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

[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.

[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.

[Archer39J]

Oh cool, thanks for sharing real-world performance!