Will an OS FP-20 work well on a tongue muffler?  I've got a Sig Skyray that could use the CG shifted further back, and would like to do the job by adding lightness to the front, instead of weight to the back.

On a related note, does anyone know where I can get a life-size casting of a tongue, in a reasonably easy to machine aluminum alloy?

Well, I guess that saves me from an hour spent cleaning casting sand off my tongue.

       Bill, this setup as you referred to as the BBTU was tried recently at our club. For whatever reasons, we tried everything to the letter and not so good results. I'm not here to say that it doesn't work or to argue an already proven fact. I was wondering if it was the result of us using the steel version engine. I found that mine worked much better using the tongue. I was using a Randy Smith tongue no extra holes and the holes were enlarged to 7/64th. I found the engine to be retaining to much heat. I use Powermaster fuels 10%nitro 22% oil. I found the engine to purr right along when the tongue was added. What I did find out though is that my stock muffler ISN'T the one you've mentioned above. In comparison, mine is slightly fatter and a touch shorter but other than that, they are very similar. My muffler still has all its internals intact as well with the exit being the stock size. As for my partners, everything he had was by the instructions per Brett. He even launched at the required rpm which I can't recall off the top of my head, but the plane would eventually sag. I somewhat questioned his motor as he purchased it used and really didn't know its history. Mine though was purchased by me and seldom run other that breaking it in. I'm flying a somewhat heavier kit built Flite Streak while my partner was flying a Skyray.35. I would say I had much better results using the tongue. Are most users of this engine prone to using the ABN version?Ken

hi Kenneth,

Don't know what to say.  it is opposite of any experiences I have had withe OS .2OFP BBTU.

I am no engine expert.  No great pilot either so my opinion is significantly less than most's.

I have 4 or 5 of these engines and have run all but one.  The one I haven't run is one set up by Dan Rutherford and I "won" it in a long ago contest at SSW.

The first one I used was a steel piston one that I later converted to ABN. (it was well worn when first put into use so a new S/P was thought needed).  The power was restored, but the "run" wasn't significantly different afterward..  All usage has been (so far) on what Da Dirt calls "Pukey Profiles".  All have good noses, and the fuel systems have caused no problems.  Have always used Sig 5% (or 10% when it's real hot around here)  1/2 and 1/2 "Champion", it's what I can get the easiest around here.  Never had a surprise and once the needle is set on a new plane, nothing else much is done, and no surprises have been encountered.

I am sorry that y'all had problems, I can't say what the fix would be.

I can say that the system as Brett suggests only works in the manner described using the stock parts specified. 

A couple of "guesses", if it sagged, the needle was probably too lean, regardless of "RPM", or some other fuel system gremlin could have been the culprit.  A weak engine to start with is "calling off all bets."  Don't know the fuel you used either, but as long as it was fresh, I guess it should work, ok.  The run is a constant 2 cycle.  The engine pulls a bit more going up and shuts off a bit going down.  Not a tremendous difference in the "sound".  Never used anything but a balanced 9-4 APC.

Next "installment" will be a "Super Combat Streak". liked that model since my first one in 1971.  Fun to fly and practice with!  Will probably use it for a Classic contest, too, if I fly in another contest! LOL!!

Sorry!
Bill