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All Forums >> RC Airplanes >> RC Warbirds and Warplanes >> 2 Questions...
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2 Questions... - 7/16/2002 10:25:50 PM   
jack01



Posts: 808
Joined: 5/3/2002
From: Memphis, TN, USA
Status: offline 		Four strokes have headers anyway. The header is the pipe that connects the engine to the muffler. For smoke, you'd probably have to go with a good smoke muffler. I'd check for a PITTS muffler first. You can put smoke on anything if they make a smoke muffler for your engine. You can also make your own smoke muffler, but it's very diffucult on four strokes.
       Post #: 1

2 Questions... - 7/17/2002 12:38:51 AM   
FHHuber



Posts: 4931
Joined: 1/1/2003
From: gone, , USA
Status: offline 		You're running the O.S. .72 FS if I remember... There are headers available for it... they are EXPENSIVE! one version is $65. You DON'T need it unless you want to go into competition flying. You can adapt the original muffler and header for smoke easilly. Take 1/16 ID soft brass or copper tube, and wrap at least 4 turns tightly around the header pipe. Drill and tap the muffler for a second "pressure" fitting. Use the new tap for your muffler pressure, and T that to pressurize the smoke tank too. Use the original pressure tap for the smoke injection. Tygon (clearish yellow normally at the hobby shop) tube goes from the smoke tank to the pump, to the flowcontrol valve, then a connector to a short piece of neoprene to the tube wrapped around the headder, then neoprene to the "pressure" fitting. Tygon will melt off the muffler and preheater. (that tube around the header) Neoprene will be weakened and ruined by the smoke fluid. I am using a TME smoke pump... its expensive, at about $100 for the full kit with pump, controller, some fittings, valve and a check valve. And you have to put a second RX battery in the plane... With the smoke on... you will lose up to 40% of the engine power due to increased backpressure due to the fluid expansion.

(in reply to jack01)
       Post #: 2

2 Questions... - 7/17/2002 3:11:21 PM   
FHHuber



Posts: 4931
Joined: 1/1/2003
From: gone, , USA
Status: offline 		that's about the result I've been getting with my O.S. .91 FS, using the stock muffler. I've switched to a Mac's tuned pipe (probably the same one that would fit the .72...) But I had a problem with the smoke fluid eating the fuel tank I used for the smoke fluid. (the thin walled Sullvan's are NOT resistant to smoke fluid... even if you replace the plug with a gasoline type... the plastic softens and expands, releasing the plug... I haven't put the replacement , DuBro, tank in yet.) Fortunately.. the .91 is so much excess power in the Dr1... with smoke on and full throttle...it was flying just right for scale performance. (which I get at just under half throttle without smoke... but power/rpm increases less as you open the throttle more.)

(in reply to jack01)
       Post #: 3

2 Questions... - 7/18/2002 2:01:46 PM   
FHHuber



Posts: 4931
Joined: 1/1/2003
From: gone, , USA
Status: offline 		I'm using a pump AND backpressure to the smoke tank.... QUOTE: Tygon (clearish yellow normally at the hobby shop) tube goes from the smoke tank to the pump... Yes, you can get a $25 kit that just uses backpressure, but its not as reliable as the pump, and you won't get as much smoke volume. (fluid folw rate will be very low) If you don't port some muffler backpressure to the smoke tank... the pmp may not be able to re-prme in flight, after having been off while running at full throttle (even with the check valve, and the muffler tap being at the narrowest part of the muffler.) O.S.'s stock 4-stroke muffler builds up a LOT of backpressure. MUCH more than any 2-stroke. The engine power loss is NOT from the muffler pressure loss to the fuel tank (practically no loss by using the T.) or it would have reduced power when I simply leave the line for the smoke tank DISCONNECTED. (which only has a minor effect on long vertical ascents... I tried it.) The power loss is from increased muffler backpressure, (reducing the airflow in the engine) and possibly some cooling of the combustion chamber from backflow of the exhaust mixed with smoke fluid. (possible...not very likely with a 4-stroke... backpressure would have to be VERY high)

(in reply to jack01)
       Post #: 4

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