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In a message dated 2/13/03 2:57:41 AM Eastern Standard Time, [EMAIL PROTECTED] writes: > The eye may be on the wrong ball here. No argument that turning a given > prop at a given rpm yields identical results in climb and speed from > identical horsepower. You very seldom actually get 85 hp from a 85 hp > (operate at that narrow point on the power curve). Again, fixed pitch props are strange beasts. Assume for a moment you have a C85 and a prop/airframe combo that yields exactly redline RPM at full throttle at sea level on a standard day. Power under those conditions is 85 nominal horse power. Pitch the nose up and the RPM drops off, as does the power. Pitch down and you exceed redline. Game over. Now, take that prop and airframe and put a C90 (or O200) behind it. At full throttle you will exceed redline under the same conditions. Again, game over. OR, throttle back to 2575 RPM. Power output will be exactly the same as with the C85. Why? It takes 85 hp to turn that prop/airframe up to 2575. No more, no less. What's different? Manifold pressure. The C85 will pull about 28.92 inches of manifold pressure at full throttle. The C90 will be somewhat less as it is not at full throttle. Again, pitch down and RPM goes off scale. Pitch up and RPM decreases. Here is where you can derive a benefit. Add back in the throttle you took out to stay below redline. Now you are turning 2575 legal RPM at full throttle, 28.92 inches of manifold pressure, and climbing. Power output is more than 85 hp. (but less than 95 hp, which is what the C90 can do at 2675 RPM and full throttle.) the reality, however, is that one never climbs at that speed. Back at a more realistic climb speed, say 75 - 85 mph, RPMs are much lower, and less than the 85 hp point on the C90, ergo, you are making less than 85 hp. More than the unmodified engine, though. Don't get me wrong, I think this is a great mod. All I'm saying is that most folks over state the actual numbers. Without a prop change, it is unlikely you'll ever get into a flight regieme (sp?) where you'll see more than 85 hp. With a prop change, but without exceeding the legal RPM limit, the best you'll see is about 93 hp. On a dyno, with no redline concerns, 100+ is likely, but no one flies a dyno. John ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
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