Dave,
Talk to a bunch of experienced small aircraft engine mechanics. The consensus I've gotten was: just spin it up, you won't hurt it. (Being a chicken-hawk, I never followed up on that advice and cruised faster than 2400 rpm, though.) Most of the mechanism is identical between the C-85 and the O-200 which is allowed to spin faster. That's even a bit more so for yours with the O-200 crankshaft. But isn't it less stress for the engine to have 4800 explosions a minute, each at a power level of 70% than to have 4200 explosions a minute, each at a power level of 75%? (. . . to develop the same total power.) [Numbers just made up off the top of my head.] I'd stay with the same pitch, enjoy the improved climb and let it lounge along in most flying. When needed for a cross country trip, then you can spin it up to 2500 rpm. That wouldn't be as fast as having a coarser pitch prop and spinning at 2500 rpm but I always preferred being nice to my engine. (Hey, mechanical people - would it be reasonable to even spin the C-85/O-200-crank engine up to 2575 rpm with a less stress-demanding climb prop?) Dave, please talk to mechanics and make your own decisions. I am NOT any kind of expert on engines. Ed > -----Original Message----- > From: Dave English [mailto:[email protected]] > Sent: Sunday, January 24, 2010 9:35 PM > To: Ed Burkhead > Subject: Re: [ercoupe-tech] Re: PROP PITCH > > Ed, > > "If you turn 2400 rpm, your speed should be about the same, maybe exactly > the same as if a C-85 or C-75 were turning the same prop the same rpm." > > I think you are probably correct there. I hadn't really though of it in > those terms, but the speed at which the prop turns governs the thrust it > produces. The new engine will be working less hard (more torque per > revolution) than the old engine. To see a cruise benefit, I would have to > re-pitch the prop, which I may do after evaluating the pro/con. > > Spinning the engine faster is not authorized because it's still a C-85, > although theoretically it should be physically able to run at the 2750 O-200 > limits. But I can potentially run at the recommended O-200 cruise RPM of > 2500 and stay under the C-85 2575 limit. > > I really hate the way wheel pants look on the Ercoupe. They are too bulky > looking and destroy the balance of the aircraft. They remind me of looking > at a woman with a beautiful shape but fat ankles! > > Later, > Dave > > . > ----- Original Message ----- > From: "Ed Burkhead" <[email protected]> > To: <[email protected]>; "ety" <[email protected]> > Sent: Sunday, January 24, 2010 9:16 PM > Subject: RE: [ercoupe-tech] Re: PROP PITCH > > > > > > > > Dave, > > > > If you turn 2400 rpm, your speed should be about the same, maybe exactly > > the same as if a C-85 or C-75 were turning the same prop the same rpm. > > > > If you move through the air faster without changing the airframe, you'll > > need to expend more fuel. If you are willing to burn the fuel, you can > > get cruise speed improvement from spinning the engine faster. > > > > Your climb with the C-85/O-200-crank engine should climb better and > > owners report significantly better climb (though I'm always skeptical of > > self-reported improvements. > > > > The Kinney wheel pants haven't been reported to provide much if any > > speed improvement as they were designed without benefit of aerodynamic > > software or wind tunnel. > > > > Mark Huesden installed a new windshield that has a much milder slope, > > extending forward almost to the fuel cap. He's done some other things I > > can't itemize. > > > > Ed > > > > >
