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Thread: 3 Piece Boot Cowl - A Handy Design

  1. #1
    Darrel Starr's Avatar
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    3 Piece Boot Cowl - A Handy Design

    For those of you building or planning to build a Super Cub or similar plane, I would like to recommend building your boot cowl in three pieces. The top piece rolls around the top of the firewall. The two other wrapper pieces slip under the top piece then meet at the bottom in the middle. Dakota Cub builds boot cowls of this general description. Husky boot cowls are in 4 pieces. If you design it to screw together with nut plates on the firewall, you can easily repair it or reach parts hidden underneath.
    I really didn't think I would ever take mine apart but after a couple years of use, paint started to bubble around screws. The problem turned out to be a mistake I made when prime painting the parts. I first primed with self etching VariPrime, which is a dark tan, then sprayed over that with white PolyFiber Epoxy primer. I didn't properly prep the surface and the paint separated between primer coats.
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    It was relatively painless to unscrew the two boot cowl wrappers and the false boot cowl pieces also.
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    Since I wanted Bob Schefter in Fergus Falls to strip and repaint the parts and since his shop is off airport, having the parts in small pieces rather than flying the SC into Fergus Falls meant that he could use his paint booth and get a nice smooth dirt free surface.
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    Anyway, just one example of why I'm glad the boot cowl comes apart.
    Also, imagine if the rear seat heater box needs repair, not a problem - just take off the right side boot cowl wrapper and have at it.
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  2. #2

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    I second to what Darrel says. I made my boot cowl for my -12 too. Instead of using a 3 piece, I made a 2 piece using a pattern off the old one with posterboard. The top "saddle" piece will make the boot cowl easier to fit because instead of working with 2 big pieces, you are working with 3 smaller pieces. I realized this when I was trying to fit my boot cowl to the frame. If I have to take my boot cowl off the frame like Darrel has had to do, I will have to take my windshield off. For securing the boot cowl to the 3/8 channel, nut plating the channel is the way to go.

    Every restorer has a "If I had to do it over again, I would do this different..." list. a 2 piece to 3 piece boot cowl would most likely be on my list.

  3. #3
    Bugs66's Avatar
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    That's how I did mine. Very convenient.

  4. #4
    SpainCub's Avatar
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    Darrel, thank you for your contribution! I always take something away of great value with your posts! and great picture to back your explanation... that really helps us technically illiterates.

  5. #5
    Darrel Starr's Avatar
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    Spaincub, thanks for your comment; Much Appreciated.

  6. #6

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    Wish Piper had done it that way...
    Remember, These are the Good old Days!

  7. #7
    kase's Avatar
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    Just had a guy make one like that for my cub.
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  8. #8
    Dave Calkins's Avatar
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    Darrell, a nylon washer under the screw heads will help keep your paint nice....Husky's have them......I put nylon washers under every screw on new paint on Cessna's, for sure, every one!

  9. #9
    AkPA/18's Avatar
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    Another cub??? Looks good Alan!

    Mark
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    Takeoffs are optional--Landings are mandatory

  10. #10
    kase's Avatar
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    No just doing a little repair work. Started out with a craked tailpost. Ended up adding a 3 ft metal belly to the tail and a new boot cowl cause I didnt like the way the other one fit.

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  11. #11
    Darrel Starr's Avatar
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    Dave, I do use nylon washers under all of the screws -- but the paint lifted anyway, no cure for a bad bond short of stripping it off.

  12. #12

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    Hi Darrel,

    I'm quite new to Supercubs and whilst waiting on a PA18 kit I've ordered, I'd like to buy a pan-box brake to make a 3 piece cowl and some smaller projects whilst building. What width do you think I'll need for the this cowl work? I'm currently looking at a 50" and a 36" unit.

    Thanks

  13. #13
    Gordon Misch's Avatar
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    Darrel hasn't been on the site for a number of years, but I've been hampered by a brake / roll that is too small. Get the bigger one unless there's a good reason not to.
    Gordon

    N4328M KTDO
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  14. #14
    Steve Pierce's Avatar
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    I have an 8' brake and a 6' press brake. The 50" will work perfect for most Cub work.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  15. #15

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    a four foot shear is handy - if you have no other uses it for it other than your cub project, it’s probably not worth it...quality tin snips work just fine.

  16. #16
    wireweinie's Avatar
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    Sheets of aluminum come in 4 foot by 8 foot and 4 foot by 12 foot. Get brake and shear that can handle at least the 48" distances.

    Web
    Life's tough . . . wear a cup.

  17. #17

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    I have a Niagara rotary beading tool from about 1900 that I used to do most of my light joggle work, along with the 48" brake and 52" shear I also have a set of 1/4" bead rolls, which add nice stiffeners and edges. I still want to learn to do a wire roll. Good luck, Tim

  18. #18
    Charlie Longley's Avatar
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    I am looking at rebuilding my boot cowl. What’s everyone’s thoughts on the firewall, stainless or titanium?

  19. #19

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    Have fun with Titanium...

  20. #20
    Steve Pierce's Avatar
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    I have made several firewalls from titanium. Considerably lighter and I did not find it difficult to work with, just different. Drill slow.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  21. #21
    skywagon8a's Avatar
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    There are special drills for drilling titanium. As I recall they have a very shallow angle.
    N1PA

  22. #22
    skywagon8a's Avatar
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    See if you can notice the angle of the grind on the drill in the first two pictures. The third picture is comparing the titanium grind on the left with a "conventional" grind on the right.

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    The flatter grind cuts nicely through titanium. One of my first aviation jobs was drilling holes on the production line for Sikorsky. This flat drill is what we used for drilling the firewall on the top of the S-61 fuselage. I think it was Titanium? It was long ago.
    N1PA
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  23. #23
    stewartb's Avatar
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    Quote Originally Posted by Charlie Longley View Post
    I am looking at rebuilding my boot cowl. What’s everyone’s thoughts on the firewall, stainless or titanium?
    Given the choice a couple of times I’ve chosen stainless.

    My EXP kit’s standard firewall was aluminum with fire-proof paint. I passed on that.
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  24. #24

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    Ti
    Remember, These are the Good old Days!

  25. #25
    Charlie Longley's Avatar
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    My boot cowl is in pretty good shape. Firewall not so much. I’ll probably order a Ti firewall from Atlee and just have them punch the holes I need.

    is the hole in the picture for a defroster?

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  26. #26
    Steve Pierce's Avatar
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    The fluted edge on the Atlee Dodge titanium firewall in a pain. I fit it on a Super Cub build several years ago.
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    Steve Pierce

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  27. #27
    Steve Pierce's Avatar
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    I didn't like how the boot cowl sheet metal fit around the flutes and cut them off and used a firewall channel from Clyde Smith $85. https://www.cubdoctor.com/stainless-...lls/index.html He makes a very nice set for reasonable money. Now I order my titanium from Titanium Joes ($200-300) and cut out my own firewalls. I have punches for the holes if you decide to make your own and want to borrow them. Compare to $768 plus shipping on the Atlee Dodge unit. https://fadodge.com/pa-18-titanium-firewall/
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    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  28. #28
    Steve Pierce's Avatar
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    I used nut plates in the flange so the boot cowl can be removed in sections and used PRC sealant around the flange, front and back.
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    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  29. #29
    skywagon8a's Avatar
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    Is the difference in weight between Stainless and Titanium really enough to compensate for the difficulty in working the material? What is the weight difference? Assuming the same thickness.
    N1PA

  30. #30
    Steve Pierce's Avatar
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    It is considerable but will have to look it up. I don't find it hard to work with. Shears fine, drills fine just slow down the drill and punches fine.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  31. #31
    Steve Pierce's Avatar
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    A friend just built a titanium firewall to replace the stainless firewall on his PA11/AL11 Legend Cub and he saved 3 lbs titanium vs stainless.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  32. #32
    skywagon8a's Avatar
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    Interesting, I would not have guessed it to be that much. Now I can understand the interest in Ti.
    N1PA

  33. #33
    wireweinie's Avatar
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    Mr. Pierce

    What's the proper rivet for the Ti? Monel or is there something else that is less reactive?

    Web
    Life's tough . . . wear a cup.

  34. #34
    Charlie Longley's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    A friend just built a titanium firewall to replace the stainless firewall on his PA11/AL11 Legend Cub and he saved 3 lbs titanium vs stainless.
    Thanks for the links Steve! After sleeping on it I am going to build a 3-4 piece firewall. I have a slip roller and punches. My “welder” has a good shear I can go over and use.

  35. #35
    Charlie Longley's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    I used nut plates in the flange so the boot cowl can be removed in sections and used PRC sealant around the flange, front and back.



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    Where did that engine mount lug come from Steve? It doesn’t look stock.

  36. #36
    supercrow's Avatar
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    Quote Originally Posted by Charlie Longley View Post
    Where did that engine mount lug come from Steve? It doesn’t look stock.
    Thrustline mod.
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  37. #37

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    Hi everyone.

    For ease of future maintenance when making a 3 piece boot cowl, do you make a ''formed seal'' (I'm not sure of the term that you use?) with heatproof goop like PR812, where the boot cowl is screwed to the firewall's nut plates? Ie: goop one side, petroleum jelly the other and screw them together to form the panel seal?

    If you have a avionics maintenance issues, is it easier to make some large removeable panels on top of the dash, or do you remove the windscreen and the top boot cowl panel? I've read that some people use felt to mount the windscreen similar to a Cessna 172, yet others use a caulking compound and I'm not sure if this is a thing that once trimmed and fitted well, you never ever want to remove it again due to the risk of cracking or just being a PITA.

    What's the preference for the panel join in the wrapper? A flange / lap seam or a simple overlap with a slight panel edge break?

    I'm hoping I can modify the standard parts in my kit when they arrive to suit - they mirror the stock cub setup where the boot cowl wrapper has the fluted formed edge that folds down over the firewall.

    Thanks again

    Damian

  38. #38
    Steve Pierce's Avatar
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    Quote Originally Posted by wireweinie View Post
    Mr. Pierce

    What's the proper rivet for the Ti? Monel or is there something else that is less reactive?

    Web
    I have used standard aluminum rivets on all the ones I have built so far.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  39. #39
    Steve Pierce's Avatar
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    Quote Originally Posted by tackdog View Post
    Hi everyone.

    For ease of future maintenance when making a 3 piece boot cowl, do you make a ''formed seal'' (I'm not sure of the term that you use?) with heatproof goop like PR812, where the boot cowl is screwed to the firewall's nut plates? Ie: goop one side, petroleum jelly the other and screw them together to form the panel seal?

    If you have a avionics maintenance issues, is it easier to make some large removeable panels on top of the dash, or do you remove the windscreen and the top boot cowl panel? I've read that some people use felt to mount the windscreen similar to a Cessna 172, yet others use a caulking compound and I'm not sure if this is a thing that once trimmed and fitted well, you never ever want to remove it again due to the risk of cracking or just being a PITA.

    What's the preference for the panel join in the wrapper? A flange / lap seam or a simple overlap with a slight panel edge break?

    I'm hoping I can modify the standard parts in my kit when they arrive to suit - they mirror the stock cub setup where the boot cowl wrapper has the fluted formed edge that folds down over the firewall.

    Thanks again

    Damian
    I have not made a seal. The Short Wing Piper series have an airworthiness directive to seal the firewall with a non-hardening seal because they used a fiberglass insulation under the floor that would get saturated with fuel and oil and cause a fire hazard. I have not seen any issues. I have removed the side panels to get access to under the panel but usually access from under the instrument panel using a modified creeper that sits on the front and rear seat bases. The top panel can be removed but the windshield would need to come out. I seal around the windshield with a urethane sealant. At the over laps I brake a flange on one side for stiffness.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  40. #40
    Charlie Longley's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    I have not made a seal. The Short Wing Piper series have an airworthiness directive to seal the firewall with a non-hardening seal because they used a fiberglass insulation under the floor that would get saturated with fuel and oil and cause a fire hazard. I have not seen any issues. I have removed the side panels to get access to under the panel but usually access from under the instrument panel using a modified creeper that sits on the front and rear seat bases. The top panel can be removed but the windshield would need to come out. I seal around the windshield with a urethane sealant. At the over laps I brake a flange on one side for stiffness.
    Steve what thickness/grade of Titanium are you ordering?
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