QB Patrol boot cowl

[Pbruce]

I’m just starting my boot cowl and I’m finding there are many decisions to be made. In the interest of making good ones, I have some questions of Patrol builders:

the attached photo is from the online building assistance pages. The builder has used Groups CS screws and nutplates to attach boot cowl and firewall. I think the instruction pamphlet which came with my plans details it this way too. Seems like a good idea to make things removable, except that the windshield will be glued down onto the boot cowl anyway, so the panel cannot be removed. Is there any reason to not just rivet the boot cowl down, at least along the top?

Are 1/8” aluminum rivets appropriate for the boot cowl-to-firewall join?

Would there be much value in splitting the boot cowl sides from the top and making them removable? (I’ll have access from the inside as I’m planning snap-in blanket panels on the interior fuselage sides under the instrument panel).



thanks.

[Archer39J]

That picture is my 4-place so I'm not positive if the patrol is the same. The angle of the boot cowl and the firewall flange is such that there's s gap between them and I'm not sure how riveting would look, but I think some people have done that.

Even with the windshield installed I figured it was a good idea to use screws to make it removable. I wish now that I had put a split after the bend somewhere below the upper door hinge so I could just remove those to access the back of the instrument panel. I'd want that split to overlap too. I think I can get enough access undoing the bottom screws and peeling it up but I'm not sure.

[Bcone1381]

The Patrol Book is my source document for the Windshield. It does not have us gluing it, rather fabricating a Back-Up Strip and a Windshield Fairing on the front. These parts are held in place to the boot cowl with machine screws and nut plates. This is from p.52 of the Patrol Book. I fabricated my back-up strip from Fiberglass rather than AL.


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[Mark Goldberg]

Pat, the windshield is sandwiched in place at the bottom between the fiberglass piece you make for the outside and the aluminum or fiberglass back up piece on the inside bottom of the windshield. The windshield is attached with screws on the sides to the vertical formers. These attach holes in the windshield are bigger than the screws. Then use rubber or nylon line as kind of bushings for the screws to help with the uneven expansion/contraction of it all as the parts heat and cool.

The boot cowl attachment to the firewall does need to be flush head screws or rivets. Because the cowl fits over it at the firewall. Mark

[Pbruce]

Guys, all of these comments are extremely helpful, both in correcting some of my misunderstandings, and also giving me ideas.

Thank you all very much!

It does indeed seem worthwhile to go through the effort of nut-plating the boot onto the firewall, and probably making the side panels removable.

Archer 39, nice work! I really like the way you built that access panel above the instrument panel. I will try to emulate it.

happy summer, all!

[TimTall]

I did the same thing with the access panel above the instrument panel. Looking back, it probably wasn't worth the trouble. It's tricky getting the screws all lined up without the windshield. It would be very difficult re-installing that panel with the windshield in place. If you're planning on installing steam gauges it's more necessary. If you're installing glass you'll have a handy 10" hole in the panel that you can work through easily. It takes about 5 minutes to pull a Dynon display out - similar for all the others i'd assume.

I debated for a while about making the boot cowl sides removable. While it might be useful occasionally, i didn't think it was worth the bother. I hope I don't regret that some day but so far no issues getting at anything that needed tweaking through the doors or through the EFIS hole.

[alaskabearhawk]

FWIW Ken Scott made a removable panel in his boot cowl. To open the panel he pulls the piano hinge pin out. He says he likes it and makes it easy to inspect everything forward of the door post. On the downside it's one more vector for water intrusion, but he has a hangar so it's not an issue for him.

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[Bcone1381]

My Windshield install went pretty well. A big part of this process is making sure all the stuff that is close by play well with each other. Mainly the doors, and wings.

The aft side edges of the windshield interacts with the L & R side hinged windows. I installed the windshield in place using screws on two aft sides and top mount, and trimmed the aft sides of the windshield so that it nests well with the side window frames when they are closed and latched. I think it was essential for me at my skill level that my side windows and main cabin door were skinned and clecoed, and fit up prior to doing this. (All my windows and door need are paint and final riveting.)

Once clearance between these pieces was assured, the final trimming done, I drilled the sides and nut plated the former to secure it with machine screws IAW the patrol book. Next up was to fabricate the Fairing and Back-up Strip.

I applied 2" cellophane packaging tape as my release agent to the boot cowl and the windshield. I applied artist clay to the fillet between the windshield bottom and boot cowl along with some epoxy/flocked cotton mixture where there was larger gaps near the side posts.

I used 8.8oz bidirectional Fiberglass cloth from Spruce, and Aeropoxy Epoxy. 1Qt of epoxy resin is plenty. This epoxy is mixed by weight so I weigh the cloth first, then mix up 1.1 times that weight of epoxy and it gives me less than 10% extra after saturating the cloth. Between two layers of 4 mil hardware store plastic sheeting I saturate a single large piece of cloth with epoxy. I pour the epoxy onto the cloth. The top sheet goes over it, then I spread the epoxy into the cloth using a plastic squeegee.

After the cloth is saturated between the plastic, I mark my pattern of the piece I want onto the visqueen and cut it out with a pizza cutter type fabric cutter. Preimpregnating the cloth this way a no mess, clean way to do a wet layup. I apply the saturated cloth to the areas one piece at a time. When the saturated cloth piece is layed down, I remove all air bubbles and ensure 100% contact using a hotel key card and my fingers.

I did the inside back-up strip first, using 5 layers of glass cloth on the inside as I understand one layer is about the same as .010 thick aluminum. The outside got 8 layers IAW the patrol book. After the glass cloth was applied I put peel ply cloth on top of the layup so that the cured surface has an appropriate surface to recieve more coatings, and to reap the benefits of removing the excess epoxy.

After the layup was cured the position of the windshield in my humble opinion is all set. I want it going exactly back in this spot every time its put in. To facilitate duplicating the fairings position on the boot cowl I didn't move a thing until I match drilled each end of the fairing to the boot cowl with a no. 40 drill. Then I removed the fairing and windsheildeld. Then I match drilled the back-up strip to the boot cowl. Everything fit back on real nice. The fit is outstanding. Now I'm in the process of installing nut plates to secure the two piece to the boot cowl. By the way, the cured piece will pop right off the celophane tape.

If your at OSH, and this method is of interest to you, hunt down a compsites class/demonstration by Scott VanderVeen. He is excellent.


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[Mark Goldberg]

Very good description of what you did Brooks. I have done this about 95% the same way. I have done aluminum back up on the inside however. Mark

[Lee]

Pat, we seem to be at the same place on our builds. Here is what I am doing with my boot cowl. I started with the factory pieces which placed 2 seams under the windscreen which meant that I couldn't remove either the top piece or either of the sides without first removing the windscreen. My solution was to make a new top center piece from a full 4' piece of aluminum. this moved the seams to just below the upper door hinge. The result is that the windscreen now sits entirely on the top center boot cowl section which will be riveted to the firewall. The side pieces can now be easily removed if need be. The top center piece inside of the windscreen can also be removed if needed. Maybe I am over thinking this, but I am happy with the way its coming out. The pix show the before and after. Lee

[Pbruce]

Thanks Lee. I have a few questions for you. Send you a PM. Thanks. It’s looking good!

[davzLSA]

Hey Pat, I just finished my boot cowl. I split it on the sides and made the side panels removable. I also made a frame for my instrument panel and screwed it to the top cowl skin. My instrument panel is now a separate panel I can remove if needed. The top cowl skin can stay on, and I will still have fairley easy access to the rear of the instrument panel. I have pictures posted on my thread if you are interested.

[Pbruce]

Definitely interested!