I was wondering if the muffler is supposed to be contained in the planes cowl or if it is alright to have it sticking out the side of the plane. The plane is a cmp p51-d 50 and the engine is a magnum .46xls. As the plane is constructed it only allows for inverted installation of the engine. Any help or advice would be appreciated.

Well, first of all, you can mount the engine any way you wish to. You can orient the engine mount pretty much any way you wish, but it requires some modification to the firewall to accomodate the mounting bolts. You will have to punch out the old blind nuts, patch the holes, then re-drill out the new holes and pull through new blind nuts. It's a bit of a chore, but you can do that.

This would help you mount the engine so that the muffler will exit out the bottom if you wish.

But, to answer your first question, though, the muffler can exit anywhere you really want it to, out the side, if that's how it is intended to be, but it shouldn't be inside the cowl. It will make quite a mess if it was inside the cowl.

CGr.

Thanks a bunch CGr that fully answers my question. Now I can continue my build with confidence.

No sweat. All you have to do is decide how you want the engine mounted. They generally consider the typical mounting configuration and build them that way. The firewall is generally set up for the correct thrust angle so if you want to rotate the engine, well, all you have to do is re-set the engine mount on the firewall and go from there.

There is a posting somewhere here in the beginners forum about replacing the blind nuts and filling in the holes. I won't go through that because I just don't remember how the poster did it, but a little searching can lead you to what was recommended for filling the blind-nut holes. But, from what I remember, you can make plugs and epoxy them in place in the old holes, then place your new mounting position, marking the firewall for the blind nut center, drill out the hole, and pull in the blind nut.

Pulling in the blind nut, if you are not familiar with that, is an easy process where you drill out the hole to the diameter recommended for the diameter of blind nut you are using, then using a bolt with a washer, put the blind nut on the BACK side of the firewall, thread the bolt with the washer, and screw it in till the blind nut hits the firwall. Then you carefully and steadily, pull the blind nut into the hole. You can use a drop or so of epoxy on the blind nut to hold it in place.

The key part of this is to pull it fully until the backing plate on the blind nut is securely against the back of the firewall. The epoxy will hold it there (you don't need a lot of epoxy, just enough to coat the blind nut and not to much so it comes out of the front of the firewall (forms a lump so the engine mount is not square).

One little thing here. The firewall thickness should be more than the blind nut so it does not protrude out the front of the firewall. You can dry-run this before applying the epoxy so you are clearly assured that the blindnut does not protrude out the front of the firewall. If it does, you can always grind some of the blind nut so that it does not stick out. You want the firewall flat and flush so tha the engine mount does not slant one side or the other, you want it flat and flush with the firewall.

Oh my.. this gets sort of lengthly. But, you can most likely make sense of it and see what I mean as you look over what you are trying to do.

Let us know what you come up with. Pictures are always appreciated...

Later gater.

CGr.

Dang lost my post.

Hey CGR,
One thing I did on the 4* (which is according to the manual) was to pull the bind nuts like you say, but then counter bore the holes on the back of the engine mount, so the shaft of the blind nut sits inside the mount, so they don't rock or stand off the firewall. This way, you don't have to grind the nut and ruin the starter threads on it.
Regards,
Curtis

Yeah, Curtis.

I was trying to think of that method. I've read that here on RCU. That's probably the best way to do this. I'm sure the OP will be able to use this as well as many of us. I did the mount without grinding off the blind nut surfaces, but it was a pain in the butt. I read the 'countersink' method somewhere but just didn't remember the particulars. You only have to be carefull you deep you countersink. That should really help the OP out with his engine mount changes.

CGr.