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bob27s -> RE: SJ90L muffler extension ? (3/22/2006 2:53:56 PM)
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quote:
ORIGINAL: Fxrs_tim
Bob,
I'm finally getting back to work on the Curare and have discovered that I'm going to need a 1" extension on the muffler header (SJ90L) to clear the side/bottom of the fuse. I can't find the extensions on Dub's site - can you direct me?
Also, once the extension is on, will that affect performance much? If so, what prop combo do you recommend? I'll be running Powermaster 15%, plane should weigh ~8.5lbs.
Thanks!
Tim
Hi Tim....
Dub does not have a 1" extension listed on the web site. He does not make one like that. Extensions are available in 1/4" incriments.
You would not want to use a 1" extension on a standard Jett 90L setup with the jett-stream muffler if you can at all avoid it. It will really mess up the performance, expecially if you are looking for speed.
Of note, are you sure the muffler hits ? On my old Curares (one glass from hobby barn, the other wood from MK) I ran Webra 61 and OS 61FSR engines - with the stock mufflers, and both of those engines/mufflers fit without issue. The jett muffler should fit as well, unless the issue is clearing the wing ?
A few ways to get around this issue... kinda depends on what point you are at in the construction.
1) Do not side mount the engine 90 deg (horizontal cylinder). Mount it more at 75-80 deg with the cylinder slightly up. That will allow the muffler to clear the fuselage. (see blue king kobra photo and patriot/jett photo)
2) I do not recall if you are building this as a tail dragger or with the standard tricycle gear. If it is being built as a tail dragger, mount the engine at appx 135 deg - cylinder down a bit from horizontal. Align the muffler down below the fuselage along the center line. Use that nose gear area, and build in a pocket/tunnel for the muffler (sort of what Dave Brown did with the Illusion)
3) Dub has a form of adapter (usually used for bolt-on type engines like the OS FSR, Rossi, MVVS) that creates about a 1/4" extension, and also causes a 1/4" offset (toward the top of the cylinder). He may be able to make a Jett-to-Jett version of this. That might get the clearance you need. (see Patriot/Rossi 53 redhead photo)
4) You would want to consider the "little toni" exhaust extension package. Chances are this is long enough. This is a set of extensions about 3/4" long, with an additional kick-angle added. With the stock muffler, you lose about 1000 rpm, but you can go up 1" or 2" in pitch. 11x9 and 12x8 work well. The LX muffler also availble for this set up will get you about 500 of those rpm back. (see Toni photos)
Take a look at these images. Might give you an idea of what I listed.
Bob
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