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Mounting engine on firewall...HELP PLEASE!

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Mounting engine on firewall...HELP PLEASE!

Old 07-16-2009, 02:28 AM
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PlaneKrazy214
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Default Mounting engine on firewall...HELP PLEASE!

I purchased an 40 size f4u corsair model off ebay......the instructions are horrible. It is supposed to be an ARF but of course it is not. My problem is that I need advice on mounting the engine to the firewall. There are no predrilled mount holes and it appears no thrust angle has been built into the firewall either. Any help would be greatly appreciated. Thanks
Old 07-16-2009, 07:30 AM
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MinnFlyer
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Default RE: Mounting engine on firewall...HELP PLEASE!

Put the engine on the mounts, hold the plane nose-up and place the engine on the firewall.

Now put the cowl on and align it with the fuse.

Center the engine in the cowl, remove the cowl and mark where the engine is, then drill.
Old 07-16-2009, 09:01 AM
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Ed Smith
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Default RE: Mounting engine on firewall...HELP PLEASE!

If I may add. Do as Minnflyer describes but TACK glue the mount to the firewall with 30 min epoxy. Then it will not move while removing the cowl, engine or drilling the mounting holes. Once drilled the mount can be tapped free from the firewall.

Ed s
Old 07-16-2009, 10:11 AM
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Default RE: Mounting engine on firewall...HELP PLEASE!

One other thing i can add is with the cowl mounted take a measurement from firewall to where you want the thrust washer to be, then you can temporarally tack glue your engine to the mount and then procede as Minn has discribed.
it will allow you to make a minor adjustment later to move the motor in or out on the mount once the mount is attached to the firewall.
Old 07-16-2009, 11:59 PM
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Default RE: Mounting engine on firewall...HELP PLEASE!

Ok Thanks alot! I appreciate everyones input. Like I said, not the ARF I thought it was. This will certainly help. Knowledge is power! Thanks again
Old 07-17-2009, 05:22 AM
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da Rock
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Default RE: Mounting engine on firewall...HELP PLEASE!

While you're messing around the firewall, since it's an ARF, take a close look at that wood. If it's two layers of lite ply (the norm nowadays), you should look at it closely. Press it with a fingernail where the motor mount edges will be. Lite ply uses rather course wood in it's middle layer (and just veneer for the outer layers) and it's often got soft spots. ARFs often use just two layers for the firewall so you've really only got two layers of somewhat thick wood with 4 layers of veneer. The last one I reinforced would flex under thumb pressure. All it usually takes to reinforce is fairly thin regular ply. Regular has hardwood in it and won't fail under compression. The T-nuts do a number on liteply sometimes. (actually, it's the bolts that do the deed. They've got awesome leverage and always have.)
Old 07-19-2009, 01:47 AM
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Default RE: Mounting engine on firewall...HELP PLEASE!

ok...will do. Looks like you are correct. I shall beef it up. Thanks
Old 07-19-2009, 04:48 PM
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Default RE: Mounting engine on firewall...HELP PLEASE!

A little bit of CA on the engine mount will get the engine to stay well enough to get the position right.
Old 07-19-2009, 08:12 PM
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Default RE: Mounting engine on firewall...HELP PLEASE!

Is the whole in the firewall of an arf the thrust line? I just converted my seagull 180 to gas and centered the mounting plate side to side on the fuse and then aligned the hole in the backplate (gas mount) with the hole in the firewall and the cowl slipped on centered. Was I wrong to use that hole in the firewall as a reference?
Old 07-19-2009, 09:00 PM
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anuthabubba
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Default RE: Mounting engine on firewall...HELP PLEASE!

Just lucky.

Terry in LP
Old 07-19-2009, 09:44 PM
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da Rock
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Default RE: Mounting engine on firewall...HELP PLEASE!


ORIGINAL: tryan02

Is the whole in the firewall of an arf the thrust line? I just converted my seagull 180 to gas and centered the mounting plate side to side on the fuse and then aligned the hole in the backplate (gas mount) with the hole in the firewall and the cowl slipped on centered. Was I wrong to use that hole in the firewall as a reference?
Lucky? yeah, a bit.

Lots of motor mounts have an open center so the firewalls often have a hole there. That'd be where they expect you to route your hoses. However, it isn't a given that the mounts they expect you to use are symmetrical.

If the design calls for right thrust, that hole should be offset side to side. If it calls for down thrust, it'd be offset up/down.

Everything you assemble in an ARF needs to be checked closely. A Sukhoi ARF I assembled a couple of years back was completely hosed. The manual said there was no thrust offsets. The firewall actually had right and down thrust. The hole was positioned for up thrust and right thrust. It's always a good idea to check everything you can think of, because they don't always get everything right.
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Old 07-20-2009, 06:29 AM
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tryan02
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Default RE: Mounting engine on firewall...HELP PLEASE!

WHEW that was a close one!! Had me getting worried back double checking all my measurements it looked good fit good I now have 2 seagull models and am very impressed with there builds. Cant wait to fly this one on 26cc. Thanks for that picture really an eye opener I will be more aware of it now on builds.

I'd rather be lucky than good any day.

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