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Author Topic: tongue vs tube  (Read 1221 times)

Offline Chris Belcher

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tongue vs tube
« on: September 15, 2017, 09:58:45 AM »
I have a Brodak 40 in Gieseke Nobler that is speeding up during flight. Set up is;
stock venturi, TT 11x4.5 prop, PM 10/22 fuel, uniflow with pressure.
The issue is it is going from 5.4 second laps to 5.0 or faster by the end of the pattern.
Now, I tried a tongue muffler and it made it worse..like 5.4 to 4.8...put the stock muff back on and it goes from 5.4 to 5.0, not as bad but still speeding up more than i like, and I much prefer the run (minus speed up)  with the tongue)
I did find a leak in the uniflow solder joint at the front of the tank,fixed that thinking it would solve the issue but...nope. This plane flies really well and I do like a LITTLE speed up at the end but the clover can be exciting at 4.8 to 5.0. I will try bypassing the copper tubes that run through the fuse next outing, maybe an air leak there. Am I expecting too much for a run to go from 5.4 to 5.2? I know it's only 2/10 of a second but at 5.0 it's hard to keep shaped right starting at the vert 8s.....at least that's what I'm blaming on this week ;D
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Offline Steve Helmick

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Re: tongue vs tube
« Reply #1 on: September 16, 2017, 10:44:33 PM »
Everything I've read about the B.40 is that 1) They take a good bit of running to get really broken-in. If it's a new engine, that's top pick. 2) The stock tube muffler reportedly works much better than a tongue muffler. 3) From local observation, the TT 11x4.5 is about max load, so if it's not loosened up enough, or the venturi size smaller than stock or nitro content not enough, it's overloaded. PM 10/22 should work real well. 4) Tank or fuel system leak. Could be internal to the tank, perforated uniflow tube, etc. 5) Double Star (who makes B.40's) spraybars have been known to have burrs inside that do weird stuff. Putting in a Randy Aero NV Assy. would be a good option. 6) You're running a fuel filter? What kind? Is it near the engine or muffler? Can it be leaking or absorbing heat and vaporizing the fuel later in the flight?

A lot of these same ideas were put forth when Walter Hicks posted about Mike Massey's .46LA powered Trophy Trainer...we never got to find out what fixed the weirdness, because Mike went and converted it to electrons. Some of us were looking to find out what fixed the problem, and we were left frustrated. If there's something I forgot, maybe you can search for that thread and check my recollection. I hope we'll get a good report this time!

The Gieseke Nobler is a favorite Classic of mine, so please post pictures!
y1 Steve

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Offline Chris Belcher

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Re: tongue vs tube
« Reply #2 on: September 17, 2017, 05:56:47 AM »
Today I am bypassing the tubes that go through the fuse wall. If that doesnt do it ill pull the tank or.replace. Will post pics
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Offline RandySmith

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Re: tongue vs tube
« Reply #3 on: September 17, 2017, 11:09:33 AM »
Quote from: Chris Belcher on September 17, 2017, 05:56:47 AM
Today I am bypassing the tubes that go through the fuse wall. If that doesnt do it ill pull the tank or.replace. Will post pics

I would suggest  changing  the  tank, fuel line, filter, see  then if you have a different  results,  Most of these problems are almost  always , fuel delivery problems

Randy
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