The idea of muffling the Fox 35 for use in sport racing was a project I undertook for pure research purposes as an academic exercise to see if it was viable. Why, one might ask?
Well, with the lack of flying sites due to noise, the abundance of unmuffled events which require hearing protection, the fact that ALL RC engines are normally muffled, well ... what exactly is our problem, I wondered? Besides, if Dan Rutherford can propose alternate (and I use the term loosely) racing ideas, why can't I? This was technically very easy to do as I already had all the required equipment on hand.
First item was to contact anyone who might have had any previous experience. The ONLY person with experience was John Thompson from the highly respected Nitroholics Racing Team. John indicated it works, but one must be aware of the engine head bolts coming loose. OK, I committed that to memory.
The muffler of choice is of course the stock Fox muffler. Perhaps others may be better, but we must start with stock equipment and go from there.
The test bed is my teenaged Top Flite Flite Streak well built by Bill Darkow & covered in tough nylon. The thick-winged Flite Streak is not a recommended sport racer but for a flying test bed, it's more than adequate. Engine was the stock Fox .35 broken in open face and using (I think) 29% castor fuel. Flying prop is an APC 9D X 8P. Open face flights indicated a speed of 24 sec/7 laps, with excellent cold starts and hot restarts. (1-3 flips). Then the Fox muffler was fitted. Performance dropped 1 second per 7 laps. A few tenths may have been lost due to the (now) nose-heavy condition, but I rather doubt it. Loss of some airspeed is of no consequence, and was expected. However, the first indication of problems was on the start and restarts. The initial start required a bit of a prime, different but not too bad, I could live with that. The hot restarts were a problem. After fueling, when flipped, most often the engine would briefly fire & die. Then I knew at least a minute of choking/priming/flipping was due. It became evident to me that if the engine did not "catch" on the first flip or two, then a minute of so of hard prop flipping /choking was in store before it would start. The engine was just asking to be primed, but with a muffler, it was too much trouble without adding a prime port (pressure tap or something). This caused me to try a variety of procedures, dry start, wet start, choke, no choke & various other combinations.
The final result was that the initial start was not so bad, but I had to be extremely careful on the pit stop. On landing, I had to carefully fuel the tank, choke twice & then flip. It sounds a lot easier than it is because even then the odd pit stop still required a minute of flipping and I hated that! I also thought that the hotter the engine ran, the more critical this hot restarting became, so I was very careful not to run the engine at full lean but rather a little bit on the rich side. As soon as the muffler was removed, all the starting difficulties instantly went away and the engine returned to its normal excellent starting characteristics.
I appeared at the Regionals in May 2005 proceeded to put in a one-flip start and 2-flip pit stop heat for a time of 5:35. It was the smoothest and quietest, flight of the entire event. It was also the second-slowest time of the event. It proved two things to me:
It is possible for a very experienced modeler to figure it out, but it would be a disaster for a less-experienced racer, especially without implementing some form of priming mechanism. It also proved ZERO interest, as nobody else has put in an official flight elsewhere. The noise level though was REALLY LOW and very pleasant. This allowed me to practice at a site that wouldn't allow louder model types. I would be very interested to see if the O.S. 25 engine would be any better to handle with a muffler in a racing environment. Perhaps some enterprising modeler will tell us??
Final thoughts: In light that quiet flight (electric) is taking the hobby by storm, I think it's worthwhile to continue endeavors that look into noise reduction, especially in "sport events." Modelers have often come up with very clever solutions to problems. I like to pursue quiet racing not because I have to, but because I CAN!
This page was upated March 13, 2006