flymeaway

My Feedback: (6)

I am building a trainer with a .25 2-stroke that I'll fly in the fields behind my house - around a few neighboring houses within ear shot. I can fly electrics here no problem but am concerned with the noise of a 2-stroke. I don't want to go electric because I have the .25 laying around from another plane (that wanted to be reunited with the ground WAY sooner than I had in mind), and besides - I love the smell of burning glow fuel. I have researched on line and found very little in the way of aftermarket products for quiet pipes. One company I found is flyquiet.com - their claim is up to 10-12db quieter than stock mufflers. I'm not even sure this will be enough though. Any tricks or product suggestions?

Also, I realize that the bigger prop I use, the less RPM I will be turning and therefore creating less noise. In theory. Any suggestions on props? the plane is a 56" trainer with flying weight of around 50-60oz. Thanks.

Richard L.

My Feedback: (24)

Stick either a .40 size or a .50 size 4-stroke in it, and nobody will complain. You can then spin a larger diameter prop at a lower rpm and still continue to enjoy the smell of burning glow fuel.

MarkNovack

My Feedback: (3)

If you overload your little motor on too large a propellor you will lose not only huge amounts of performance (it may not even leave the ground) but you risk quickly burning up the motor. Try finding the correct size of three bladed propellor for your motor. You can turn the same RPM but with a smaller diameter blade the tip speed will be significantly slower resulting in far less noise. Also, go for the good muffler. I think bewteen a good muffler and 3-bladed propellor you will find that the little motor does not generate that much noise. A good 3-blade will give better performance than a two blade spinning far to slowly and your motor will than you also. Remember that a soft-mounted motor will cut your DBs also by a couple and that can be important.

Mark

tiggerinmk

Is this a modern 25 with a baffled muffler?
I ask because I've got a 15LA and an old Enya 15. The old Enya is a fair bit louder as it just has a strap on with no internal baffling.

BTW, remember that DB is a logarithmic scale, so 10-12db should make quite a difference.

A typical 25 would normally run a 9x6, as a trainer doesn't need to be fast, you could try a 10x4 or 10x5. If the engine is powerful enough for the plane you'll be chugging around at half throttle or less anyway once you got to altitude, so the amount of noise you make has probably got more to do with your flying style than the engine.....

I'd try it, then once you know how it flies and how noisy it is, you can experiment accordingly...

flymeaway

My Feedback: (6)

Thanks for the info. I didn't even think of a 3-blade prop. I am going to try that along with the aftermarket muffler. This .25 is about 15 years old, so I believe it has a muffler with no baffling - it is LOUD! I also have a .35 that is a bit older, but still runs great - I haven't run that motor in about 13 years but I recall it being slightly quieter than the .25. I am going with the .25 because I have the notion that the .35 would be too heavy for the plane. I could be wrong though - would the .35 be a better engine for this plane? Would it be queiter do you think?