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This message was automatically forwarded on behalf of Bill Bayne. Please address any responses to the mail list or directly to Bill at: [EMAIL PROTECTED] -----Original Message----- From: William R. Bayne [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 22, 2006 11:08 AM To: Ed Burkhead Subject: Re: [COUPERS-TECH] C-85 STC, Performance, Props rlytech Hi All, Somebody is missing something here, and maybe it's me; but the "Technically none" comment would seem applicable only in the eyes of the FAA (which is not always the world in which we live and fly). With this STC, the C-85 prop is retained. "...increased displacement and increased compression" equal increased "oomph". The proportion that translates (respectively) to horsepower and/or torque is, in part, determined by cam design and, in part by the rpm allowed by a given prop. If that prop was a "cruise" prop (courser pitch that will not redline) before, the added "oomph" will allow the same prop to achieve greater rpm than before. The Continental C-90 power curve directly translates all additional rpm into additional horsepower. In a "which comes first, the chicken or the egg" scenario, the added torque from increased displacement and increased compression makes it possible for the engine to turn a given prop faster. The "balance point" between increased horsepower (from increasing rpm) and increasing resistance from higher flight speed (from aerodynamic drag) moves up the power curve, and all of that rpm increase directly translates into increased HORSEPOWER. Yes, climb performance is likely improved; but it may now also be possible to redline the engine because more power from the greater displacement and efficiency at any given rpm is available. By having the prop tweaked, the increase can be optimized for cruise or for climb or split between them according to owner preference (within allowable static limits, of course). There is ample evidence that new postwar Ercoupes at 1260 lbs. with 75 HP and the "steel" MLG had a maximum speed of approximately 125 mph. I would estimate the later forged aluminum MLG and the fatter "doughnut" fairings ("doughnuts" were previously up in the wing) to carry a 3 mph penalty. Accordingly, I would expect a straight, properly rigged and aerodynamically "clean" Ercoupe (no fixed trim tabs, huge venturis, MLG landing lights or forests of antennas) with this STC optimally set up should allow cruise capability near that Alon claimed (but few seem to routinely achieve) with similar climb performance. Accordingly, IMHO, the "bang for the buck" for an Ercoupe in good condition is probably greater from this STC than any other single option at overhaul time. I'll go even further. If one were to STC a 73" prop on this installation, (the greater diameter is more efficient, per Fred Weick), I would expect above speed in cruise at approximately 85 hp rpm/fuel consumption levels with the Stromberg carb. The "factory" wood Sensenich prop selected for the C-75 allowed upwards of C-85 rpm at full throttle, and Fred would cruise at that rpm when he did not choose better economy or range flying cross country. Fred's actual words to me, as I recall, were to the effect that "I thought owners would rather have a 75 hp installation that actually gave them 85 hp, but I was all wrong. They wanted to SAY they "had 85 hp regardless of how well it performed". He was NOT a fan of the conversion of the C-75 to the C-85 on the Ercoupe, and seemed to regard the C-85 in the E Model as a marketing ploy that actually decreased performance (by that time he was no longer at Erco). I believe an examination of the logs of HIS Ercoupe would show it was never converted from 75 hp to 85 hp while he owned it (which would be absolute confirmation of this). Let the flames begin! Regards, William R. Bayne <____|-(o)-|____> (Copyright 2004) -- On Feb 22, 2006, at 08:59, John Cooper wrote: > At 02:39 AM 2/22/2006, Anne and John wrote: >> So, how much extra horsepower can really be expected from this STC, >> or how much bang for the buck ??? > > Technically, none. Given the physics of fixed pitch props and the > fact that your RPM limit doesn't change, you get the same power. > What changes is how much of that power is available at less than full > power conditions. This is due to the increased torque capacity from > the increased displacement and compression ratio. Read: improved > climb performance. > > John Cooper, A&P > Skyport Services ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
