Cowl Trimming...
 

I'm putting an OS .61FX in my GP RV-4 and the cowl will need some major cutting to pass the standard muffler through. W/O the muffler the engine fits perfectly, no trimming / cutting of the cowl involved. Problem is - when muffler is attached, I can't 'slide' the cowl on without having it tilted and angled in all different directions - so transferring lines would be difficult.

What's the best technique to find the exact 'area' to remove for the muffler?

I’ve used sheets of paper attached to the fuse to draw guidelines of the muffler and then transfer on to the cowl, but the RV-4 has a flared cowl with long ears that would make it a little difficult.

Am I missing the obvious here? Thanks!


Wiqar

RE: Cowl Trimming...
 

Kevlar,
Is it possible for you to attach the muffler once the cowl is put on? I have to do this on some of my plane, put the engine on, put the cowl on, and then attach the muffler. It might be difficult to get to the muffler mounting bolts, but sometimes this is the only option for a cowled engine.

Ken

RE: Cowl Trimming...
 

Hmmm....not a bad idea. I'll look at that tonight - I haven't trimmed the 'exhaust' hole on the bottom of the cowl yet, but there may be enough room to squeeze the muffler in there....might have to enlist the wife with her smaller hands - Hey, I'm keeping her involved (Why do you spend so much time in the basement? What do you guy's do all day?)

RE: Cowl Trimming...
 

You're a smart man Kevlar!

I always try to involve mine as well (43 years) by letting her pick from among two or three I've selected, and at times, enlist her help also. In fact, after several years away from the hobby, she's the one that bought me my first arf 3 years ago, and Christmas of 2005 an CMP Yak 54-140 for a Christmas present.

There is one thing that one must always remember, "Experience is a hard teacher. She always gives the test first and the lesson sometime later!"

Phillip

RE: Cowl Trimming...
 

I had to cut the cowl for my plane and we just cut a hole from the back of th cowl to the end of the muffler. It does not look as good but it has a lot of room for the air to exit.

RE: Cowl Trimming...
 

I mount the muffler on the engine then mount the assembly to the plane. Then, I take stiff paper (Poster board works well).. and cut it to fit the parts that stick out for sure. I tape the templet to the plane with masking tape such that I can lift it out of the way. I make sure the templet is fitting the around the protrusions, then remove the engine assembly and reinstall the cowl. The templet will not indicate the areas to cut out. I always cut a bit small and trial fit, and do final adjustments a bit at a time. I just cut a cowl where only a sliver of the muffler along the header had to be removed and a small area for the can at the opposite end. The cowl was round to make things interesting but the final fit is perfect. and unless you look up from below, you cannot see the spots I had to cut out.

This works for anything.. ie finding the exact point for a fuel filler mounted on the fire wall, needle valve extensions, spark plug access holes and so on.

Best regards,
Randy