ORIGINAL: Free Bird
Dan & Ed: What's the big difference between firewall and belly mount for the nose gear? Wouldn't the firewall mount give you a little more room?
I just spoke with Dub Jett on the phone while ordering two of his high performance mufflers for my pair of OS .55AX engines. The mufflers that have flanges that fit the TT .46 fit all OS engines in that size range and work perfectly. He did add some valuable information regarding prop selection when using his mufflers. Start with an 11x6 (or less load) when using his mufflers. You should be able to richen the mixture by approximately 3000 rpm off peak with whatever size prop you run. This means that as you richen the mixture off of peak, you should be able to richen the engine to the point of about 3k rpm before the engine "falls off the pipe" (these are my words). If not, you could be in dangerous territory, especially with only a 1k rpm richening until it "falls off the pipe". All of this means that when using his Jett muffler, the recommended 12" props of any pitch are simply out of the question. I'm not including 12x4 props for 3D because this muffler is not desirable for 3D usage, which is attributable to its "pipiness" (again, my words, not Dub's). Hopefully, if I've made an error, either Bob Brassell or Dub Jett will jump in and set us straight.
Ed: I'm a little unclear on your thoughts here. I can understand backing off the needle as the engine tends to unload in flight, but 3000rpm? That seems to be a little excessive, yes?
OK, as far as the build goes, I'll start posting pics this weekend. There's a bunch of work that can be done while I decide if I want to go the retract route. There's a bunch of parts that need to be made that aren't supplied with the Erueka short kit. Also there's no BOM list which would be quite helpful. I'll make up a list as I go for those that build this kit in the future.
FB
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Believe me, Dub wasn't as confusing on the phone as what I have written. What I said was accurate. My comments are prefaced upon the understanding that the reader has some tuned pipe experience in the past.
In the interim, here is something to chew on. Dub was concerned that modelers would use the ridiculously large props that are suggested in the engine's instructions when also using one of his mufflers because that combo would not work well together. His tuned muffler is geared to work with average .40-.46 prop sizes, i.e., 10x6 to 11x6. The OS instructions list 12x7-8" props. The latter size props will drop the engine rpms down to a point that will be out of resonance for the Jett high performance muffler.
Rather than worry about the 3,000 rpm richened mixture before dropping off the pipe (out of resonance), it is better to just not load the engines up with anything larger than an 11x6. I'm sure all of this will be properly explained in the instructions included with the mufflers.
The belly mount nose gear does not eat into the tank compartment's front to back dimension, thus permitting a full size fuel tank with padding.
Ed Cregger