OS 61 VR going lean
07-05-2009 | 08:12 PM
#1
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OS 61 VR going lean
A club member is running this engine in a ducted fan and he told me the other day he was having trouble with it leaning out during flight. When questioned further he said it has a pipe , is running 10% fuel and it has no tank pressure. Is this normal to not run a tank pressure line in this application? It is not pump equipped.
07-05-2009 | 08:31 PM
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From: Colorado Springs, CO
RE: OS 61 VR going lean
Hi
All ducted fan engines need exhaust presure to the fuel tank to run reliable. No pressure, no reliable engine run. This is true for most 2 cycle engines. Only takes 1 lean run to kill a DF or high speed engine.
Vince
All ducted fan engines need exhaust presure to the fuel tank to run reliable. No pressure, no reliable engine run. This is true for most 2 cycle engines. Only takes 1 lean run to kill a DF or high speed engine.
Vince
07-06-2009 | 02:39 AM
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From: corona,
CA
RE: OS 61 VR going lean
He may have gotten that idea as the tank is ahead of the engine instead of behind it, he doesn't need pressure - not wise. But he is also probably setting his needle too lean on the ground, especially since its piped. On a propped engine, the RPM gain when the engine unloads in the air is nominally 500 to a 1000 RPM. We compensate for that increased fuel demand in the air by backing off our HSN from a maximum RPM setting. Now with a tuned pipe, the RPM increase between on the ground and "On the pipe" is significantly greater. If your friend is setting the needle like a propped plane, he is not providing enough fuel cushion for the increased RPM thru what is essentially a fixed flow fuel system.
In my younger days, I attempted controlline speed; .15's and .29's on pipes. I would have to release the planes with the engines running "dirty" rich. As the engines would unload as the plane gained speed, they would start to run cleaner and a bit faster. And when they got "on the pipe", the RPM gain was significantly noticeable. One speed merchant had an audio tach and stated he had measured the difference between maximum ground RPM and on the pipe in the air RPM on his .29's to be between 5 and 6 thousand RPM. That requires quite a bit of fuel flow compensation to provide for in setting a needle on the ground.
In my younger days, I attempted controlline speed; .15's and .29's on pipes. I would have to release the planes with the engines running "dirty" rich. As the engines would unload as the plane gained speed, they would start to run cleaner and a bit faster. And when they got "on the pipe", the RPM gain was significantly noticeable. One speed merchant had an audio tach and stated he had measured the difference between maximum ground RPM and on the pipe in the air RPM on his .29's to be between 5 and 6 thousand RPM. That requires quite a bit of fuel flow compensation to provide for in setting a needle on the ground.
