Tongue Mufflers

Gang --

Some dumb tongue muffler questions from the resident doofus:

1. The exhaust holes go towards the outside of the circle on a profile, otherwise gunk would build up inside? That makes a circuitous route for the pressure tap line.

2. Exhaust holes point towards the ground for inverted and upright installations, right?

3. Do you ever clean them out?

Remember, back when I was flying, only the most effete of RC flyers had mufflers of any kind.

Point the holes anyway you want to. It will work fine. You can move the pressure tap around if you wish (surely you don't want to run a STOCK muffler). You do want the tap where little or no used oil runs back into your tank from the muffler. There was something in stunt news about a flyer noticing a gradual change in how his engine was running and finding that the holes in his muffler were gummed down to a smaller diameter. He cleaned them out and all was well. I've not noticed this, but I don't run (usually) straight castor.

I doubt that the motor cares which way the thing points. I have used tongue mufflers off and on for some years and generally decide what I want kept cleanest and point the holes away from that side. Never have seen one that needed cleaning unless it was stored in the barn with the rats and bats. If it gloms up, perhaps you need to fly more often and keep it blown out.....

It is true, you can aim the muffler any way you want. The engine will exhaust fine either way. On a side engine mount (profile), if you aim the holes towards the outside of the circle you will get less "gunk" on the plane. And if the tube to the pressure tap has to bend around a little, that's fine. Some people have mounted the pressure tap on the back edge just for the sake of convenience, but I have never found the necessity of doing that.

On an inverted engine, aim the holes down and you will keep the plane cleaner. On an upright engine...aiming the holes up will keep the plane cleaner. (Yes, that's right, up!). But it might look better if they were aimed down.

It is OK to check the holes periodically to make sure they aren't becoming plugged, and it is good to blow through the pressure tap, too, once in a while. If that gets plugged up, oh, it can get exciting. (Can you say, "Lean run"?) Most people don't think to check it, but the same size tap with its itty bitty hole is used on the tub muffler as well.

If you want to see what back pressure can do to an engine run, tap a couple of holes in the tongue muffler and insert 4-40 x 1/4 bolts in the holes one at a time. When we started having our custom mufflers made, I noticed that Art Adamisin was using 10 holes and The old SST muffle of the McDonald's had 12. I figured 12 should, therefore, do it, and that's the way our first ones were made. Then when we were experimenting with the Magnum engine I decided to add another row of holes to the muffler to see how it worked. I tapped and plugged them again and ran it with 12 open. Then I opened one more, then another. We gained a couple hundred rpm each time I took a screw out. So now we make the mufflers with 15 holes open. Still, if you have got an engine that is running a bit fast for you--especially in cooler weather, that is one way to tame it. Add a couple of screws in cooler weather and take them out again in hot weather. That way you can probably get by with the same fuel and venturi size all year long.