I'm not sure how many different makers of CF stunt pipes are currently being made, but I know of Smith/PA, Brian Eather, and "ES" pipes (from Utah) are. I know Richard Oliver, Windy U., and Bill Werwage used to, or perhaps still do make 'em. I'm sure there are some others, somewhere.

My question is this: If you find the location of the first baffle and mark that, will the initial "bench trim" length be the same, given the exhaust timing? Will a minor engine size revision change it, such as going from a .46 to a .51, if the exhaust timing is the same? In other words, will Randy's chart work for other brands?  Still talking about initial bench trim length, remember.    Steve

 

Yea, I ran into this when I went from an Eather pipe to a Randy pipe. I finally got it worked out, but it took a bit. Quite a lot of pipe length variation.

So, do other pipe makers give you any kind of chart (like Randy Aero's) or any length info to help get a leg up on it and not destroy your engine by having the pipe too short to start?  Steve

    You aren't likely to destroy the engine no matter what you do to the pipe, unless you do something else bad, too, at the same time.

   Brett

I'm not sure how many different makers of CF stunt pipes are currently being made, but I know of Smith/PA, Brian Eather, and "ES" pipes (from Utah) are. I know Richard Oliver, Windy U., and Bill Werwage used to, or perhaps still do make 'em. I'm sure there are some others, somewhere.

My question is this: If you find the location of the first baffle and mark that, will the initial "bench trim" length be the same, given the exhaust timing? Will a minor engine size revision change it, such as going from a .46 to a .51, if the exhaust timing is the same? In other words, will Randy's chart work for other brands?  Still talking about initial bench trim length, remember.    Steve

     The critical factors that you have some control over are the exhaust duration and the position of the reflecting surface (length). If tuning to the first baffle is the right surface, then you can measure to the first baffle, and then figure it out. If you are tuning to the conical tail cone, measure to the centroid of the cone (2/3 of the way from the "peak" to the base of the cone). Adjust from there.

     Brett

Hey Steve:
I also got one of those Utah pipes from Norm W.   Will be trying it out in about a month on an Enya61RE /  SV-11 ARC.    What engine are you trying yours on ?

Steve, check put Macs web site advice -

http://www.macspro.com/tuning.asp

It basically states that you compare the open faced exhaust's performance to that of a full pipe length's performance by using the prop, rpm, fuel etc that you intend to use in flight and look for any increase in rpm. Seems fair enough to me.

The 'measuring from the first baffle' idea simply seems more like a convenient method to show where the testing proves the overall pipe should be positioned - it gives you a marker for reference.