I was hoping I might get some help with a project I am working on. I am building a GP Christen Eagle and am placing a US Engines 41 on the nose. I have been reading a lot of posts from people flying this plane who have experienced cabine cracking and failure as well as other structural problems from vibration.

For starters I am mounting my engine using a GP large engine isolation mount to reduce vibration and potential problems with that issue. Has anyone else built this plane and done the same and if so what kind or results did you achieve?

The real question I am here for is that I would like to modify the stock muffler and place a spray bar in it for a smoke system. Since the stock muffler has a baffle in it with a screened hole in the center I was unsure where the spray bar would be most effective and the correct location for placement. I know some engines have experienced problems with smoke oil being sprayed into the exhaust port so if the correct place is on the engine side of the baffle I can install a spray bar the does not have holes facing the piston.

If it is better placed on the outboard side of the baffle that is moot but also does anyone know if the internal baffle is needed for proper engine operation? Since only a portion of the muffler receives exhaust gasses due to the baffle and hole cut in it should the spray bar also be restricted to the size of the opening?

I would be happy to post some photos if anyone would like to visually see what I am referring to.

Thanks for any help and input...

Charlie

The internal baffle is robbing your engine of performance...and quieting things down a bit. Typically injecting the smoke oil into a nice hot spot in the exhaust, close to the exhaust port on the cylinder, but 'aiming' it away from the cylinder should work fine. I'd be surprised if a spray bar as described would get you any better results than a simple inlet nipple attached for injection....but i haven't experimented much with that stuff.

Edit** Also, beware of some soft mounting...it can actually end up transmitting MORE of the harmful vibrations to your airframe and equipment. Generally, a properly tuned engine, and balanced prop/spinner combo will offer good results on an appropriately sized airframe as compared to the power.

Chad

Chad,

You think it is safe then to remove the baffle from the inside of the muffler? I am not too concerned about power as this plane will be plenty fast with the engine stock. Most smoke mufflers I have ever had any experience with had a bar going across the entire muffler that had holes in it and most were fed from opposite sides. I guess I could just put the nipple on and have it spray down across the path of the exhaust port which would probably be a far easier modification.

I want to make sure that if I remove that baffle that is does not cause engine overheating due to leaning out the ratio more than I can compensate for...

Thanks for your input.

Charlie

I haven't heard of any other reason to remove the baffle, other than attempts at increasing performance. Maybe leaving the baffle in place will trap more exhaust heat and burn off the smoke oil better?!?!?

I've seen aftermarket mufflers with smoke 'coils' which preheat the oil before injection, and compared them to bone stock and simple B&B exhuast diverters with a nipple near the mounting flange...and I couldn't tell a difference in smoke quality at all. The difference that at times you CAN tell, is that the preheating coils 'can' decrease performance similar to baffles...etc.

Chad

Can you use any nipple or is there a special SMOKE Nipple that needs to be used?

I am wanting to tap a straight pipe coming out of a G62 in the stock location for a YELLOW Aircraft AT 6, for smoke.

PS:
Hi Chad..........................COKE PLANE doing OK?

Hey Roger, long time no talk to! I have completely gone through the plane a-z, made a few changes and updates, and all is well. It has yet to fly after the updates, but that is only because the weather hasn't been friendly to me. I'll definitely keep you posted when I get the chance. I'll have to crash one of your camping trips too and get some flying in.

Anyway...about the smoke nipple...I've recently been using the std Great Planes\DuBro 'pressure tap' I believe they are called, and they work fine. I believe the size is 8/32 from memory. I just know for best results, tapping it into the mounting flange, pointing slightly away from the cylinder has worked well. At least this is what has been working well for me.

Chad

Thanks for the input. Think I will just try tapping a nipple into the top of the muffler above the exhaust port and spray down into the stream of exhaust gasses. I will leave the baffle in unless I run into any engine performance problems. Who knows, maybe too much smoke may actually inhibit the flow of exhaust and cause overheating which would require removing the baffle...

Charlie

Leave the baffle, it won't be a problem.

Will do, thanks...