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  1. #1
    Masonhornet's Avatar
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    False firewall


    So I'm building a Kadet Senior, and would like to be able to swap engines in the future. I saw an earlier post that mentioned installing a "false firewall" to make this easier.
    I'm assuming this is a firewall that mounts to an existing firewall that's epoxied to the airframe. Is this correct and what's the most common way to accomplish this..?

    Thanks..!

  2. #2
    gene6029's Avatar
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    RE: False firewall

    Hi, i have a Kadet Senior, and have had several motors on it over the years. I just keep useing the existing firewall, but use new motor mounts each time. Occasionaly i have to drill new holes in the firewall to put blindnuts to hold the new motor mount. You could make a new firewall each time if you wanted, & just attach it to the existing one with bolts & blind nuts. I use the plastic radial motor mounts everyone sells, nothing fancy....Gene

  3. #3
    mike109's Avatar
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    RE: False firewall

    G'day

    I think that I may have posted the comment about a "false firewall". I am going to do this because one of my existing Kadets already has so many holes in the firewall that it is starting to look more like Swiss cheese than a plane.

    I will use a second piece of ply which I will bolt to the main firewall with four larger than normal bolts but I will use some spacers to keep the false wall about 1/8 inch clear of the main wall.

    I will also mount the front "cheeks" of the plane on the false wall but make it so that it overlaps the main fuse slightly. One of the false firewalls will be set up to take a radial cowl.

    The Kadet usually needs a bit of weight at the front to balance correctly so as long as I don't go mad with weight, the extra hardware should not be a problem. Kadets are light anyway and a little extra does not stop them still flying well.

    Cheers

    Mike in Oz
    \"I just had no control. Must be the radio.\" Club Saito #597 Kadet Brotherhood #66

  4. #4

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    RE: False firewall

    The fuselage is wide enough, so you might consider the very wide hardwood beam and mounting plate scheme used in the old Midwest TriSquare.

    Basically, you fit some very wide hardwood beam mounts glued to ply nose doublers, then bolt down a "U" shaped aluminum or 1/4" plywood plate that the engine is attached to to the hardwood beams. The firewall needs to be notched to accommodate the beams.

    The advantage of this scheme is there's no futzing inside the nose area when blind nuts come loose because all the bolting on an engine swap happens out in the clear in front of the firewall, the heavy strain on the firewall glue joints is distributed better to the fuselage without imposing a bending load on the center of the firewall like the stock setup does where the nylon/alum mounts are narrower than the firewall.

    If you have access to a bandsaw, aluminum mount plates are pretty easy to fab. It can be done with a hacksaw, just takes longer.

  5. #5

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    RE: False firewall

    I just buy a new mount and drill it in. If it is going to be a permanent change, I knock out the old blind nuts and fill in the old holes with piece of big kitchen match and epoxy. If you might swap back and forth, just leave the old nuts in and you can easily swap motor mounts.

    Tain't hard.

    Tom

  6. #6
    proptop's Avatar
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    RE: False firewall

    Maybe you could use one of those big, cast Aluminum clamping style motor mounts? They are common to ARF Trainers.
    http://www.hangar-9.com/Products/Def...?ProdID=HAN40M
    (just for illustration purposes, the one above is .40 sized...you probably want the bigger version )




    Or...one of the adjustable type:
    http://www.hangar-9.com/Products/Def...ProdID=HAN2033
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  7. #7
    Masonhornet's Avatar
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    RE: False firewall


    Thanks for the replies..! The more I thought about it I'm just going to continue "per the plans" with the stock firewall
    and keep things simple. I was concerned about the firewall looking like swiss cheese at some point, but I'll cross that
    bridge if I ever get there... [8D]

  8. #8
    mike109's Avatar
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    RE: False firewall

    G'day

    My reason for doing this is a bit unusual so I am not surprised you are not going to do it. I currently have four Kadets but this one is going to be my experimental plane. It will have two different wings and initially will have a Saito 90R3 radial engine inside a round cowl. Later it is going to become a camera plane with the camera where the engine normally is and the engine either over and behind the wing or it may become a twin engined Kadet.

    Cheers

    Mike

    \"I just had no control. Must be the radio.\" Club Saito #597 Kadet Brotherhood #66

  9. #9
    MinnFlyer's Avatar
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    RE: False firewall

    A better option is to use the Great Planes engine mount:

    http://www3.towerhobbies.com/cgi-bin...?&I=LXJ772&P=7

    Its width is adjustable, so if you ever swap engines, AND if the new engine is wider, you can buy an identical mount (if you need to re-drill the holes) mount it to the same blind nuts that are in the firewall, and spread it apart a little
    Mike B. AMA# 42400 www.gettingairborne.com
    Ultra Sport Brotherhood #2 - Waco Brother #188 - Cub Brother #2

    \"Those are my principles. If you don’t like them, I have others.\" - Groucho Marx

  10. #10
    mike109's Avatar
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    RE: False firewall

    G'day. Yes that would be true if I were using a single cylinder engine and I have used those in the past and they work well.

    But ...

    I want to put a Saito Radial engine and they don't use a separate engine mount - they bolt directly to the firewall and the pattern for the R90R3 3 cyinder radial is not the same as the pattern for the 90TS (twin) and different again from the Great Planes adjustable mount.

    To further complicate things, I want to make a removable nose for the plane that will fit a radial cowl and still be able to mount a single cylinder engine with the normal Kadet "cheeks".

    As I have said before, my model is going to be a work in progress and be used for experimentation and so I need a bit more flexibility than I can get with the excellent Great Planes mounts.

    This all started because my ARF Kadet has over its life had a Saito 65, then the Saito 90TS twin then an ASP 91 and most recently a Thunder Tiger 54 four stroke. I tried to put the Saito 90R3 radial in it but there were so many holes I was unable to drill holes where I needed them and at that point I decided on the removable false firewall for the next model which is currently under construction (slowly). So far I have half a wing built.

    Mike in Oz

    \"I just had no control. Must be the radio.\" Club Saito #597 Kadet Brotherhood #66


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