I recently recieved (form Leonard) one of Big Art's tube mufflers for a Fox 35.
Where should I put the pressure nipple for muffler pressure - what size hole do I need (pref in inches) - I take it the thread is 4-40.
Tony
Pressure nipple
Stuka Stunt Main Forum · 4 of 4 known posts recovered
There are several brands that work. We usually use a DuBro 241 which is a 6-32 thread. There are 4-40 thread versions that work just as well.
The "normal" location is in the tube, itself. Most are angled at about a 45 degree angle towards the body and you can drill and tap right in the middle of the valley between two fins. Use the paper gasket and it will seal just fine.
Normal lore says you should not put the pressure fitting in the stack leading to the muffler as this is a lower pressure area(due to the faster exhaust gas speed). We have tried it, however, and have found no difference in performance. There is more "meat" in this area to drill and tap and it is a little easier as well.
So take your choice. Put the fitting where it works best for you. There is no real "right" or "wrong" way of doing it.
Leonard Neumann
Leonard Neumann
Tony, Len,
One thing worth looking at during tap location selection is the attitude the engine will be mounted in versus where the pres. tap will actually be once installed and motor is bolted to the airframe. It may be wise not to allow the pres tap or related tubing to become the "low point in the pres. line loop going up to the tank. Reason: After the engine is run, and the residue oil migrates to the lowest point in the muffler it may run into the pres. tap/tubing, and congeal, thus blocking off the tap, ..ergo no positive pres. on the system. Could lead to a bad engine run, perhaps loss of the aircraft in an inverted pass or what have you. Locate the tap at a place where it will not become the "P-trap" like your kitchen sink has, and inadvertently block off the system. This could be more the case after extended lay-up of the airplane between flying sessions. Something to consider anyway. Regards.
Tony
One thing worth looking at during tap location selection is the attitude the engine will be mounted in versus where the pres. tap will actually be once installed and motor is bolted to the airframe. It may be wise not to allow the pres tap or related tubing to become the "low point in the pres. line loop going up to the tank. Reason: After the engine is run, and the residue oil migrates to the lowest point in the muffler it may run into the pres. tap/tubing, and congeal, thus blocking off the tap, ..ergo no positive pres. on the system. Could lead to a bad engine run, perhaps loss of the aircraft in an inverted pass or what have you. Locate the tap at a place where it will not become the "P-trap" like your kitchen sink has, and inadvertently block off the system. This could be more the case after extended lay-up of the airplane between flying sessions. Something to consider anyway. Regards.
Tony
I tried a few locations when I first tried muffler pressure and came to the conclusion that it does not really matter where the pressure nipple is.
I get the impression that you don't need much pressure to get the benefits, just as well as I would not think the pressure in the muffler is very high anyway....great big hole at the back open to atmospheric pressure......
What I do now is to put it where it does not show up too much as I don't like tubing all over the place, that is, I put the nipple on the face of the muffler that faces towards the engine.
Just my 2 Penny-worth.
I get the impression that you don't need much pressure to get the benefits, just as well as I would not think the pressure in the muffler is very high anyway....great big hole at the back open to atmospheric pressure......
What I do now is to put it where it does not show up too much as I don't like tubing all over the place, that is, I put the nipple on the face of the muffler that faces towards the engine.
Just my 2 Penny-worth.
Dave Moffitt