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Bill Biggs wrote: > So if I take my check ride with the FAA, and he tries to bust me > for exceeding RPM limits I can refer to WRB as "approved data" > Yea Right, and pigs can also fly. Guys, I've been out of town so forgive me, please, if I'm not quite in synch with the debate. If I'm correct, this is a quick summary of the discussion: Bill Bayne mentioned that Fred Weick chose the prop for the C-75 so that it would spin to high rpm on takeoff and could over-rev in cruise, thus giving C-85 performance with the C-75 engine. Others, including John Cooper discussed the STDS and mentioned the static rpm requirements. Several are giving Bill Bayne a hard time for "advocating" illegal setup of the aircraft and claiming that it can't be done without being illegal. Bill Bayne is defending himself. ___________________________ Well, I do remember Fred Weick saying something to the effect that he chose the prop for the C-75 equipped Coupe so that it would spin faster, giving better climb and could over-rev in cruise if you didn't pull back on the throttle. Yeah, guys, I think Bill Bayne is substantially correct in his assertion. Here's some discussion: In STDS A-718, it says: Engine limits For all operations, 2300 r.p.m. (65 hp.) (S/N 1 thru 112) For all operations, 2275 r.p.m. (75 hp.) (S/N 113 and up) Farther down, it says: 2. Propeller - fixed pitch metal, McCauley 1A90CF or 1B90CM 26 lb. (-32) (a) With Continental C-75 series engines only static r.p.m. at maximum permissible throttle setting: not over 2100, not under 1950. No additional tolerance permitted. Diameter: not over 73 in., not under 71 in. Thinking about it, I would think that if I had a static rpm on the ground in still air of 2100, then at 70 mph climb, I might be coming close to 2275 rpm and getting full power from my C-75. When I reached altitude, leveled off in cruise, I'd have to pull back the throttle to avoid over-revving the engine. Thus, I could climb near the 2275 red line and cruise near the 2275 read line in a plane that meets the STDS A-718 static rpm of 2100. If I'm not mistaken, that's what Bill is asserting. I think he's right. Now, comparing that with the C-85 with the standard prop, most planes will get a static rpm near 2100 (allowed range, per A-787 is not over 2225, not under 2025). So, if the C-75 prop gives static rpm of 2100 and the C-85 prop gives static rpm of 2100, you might have similar performance. Again, I think this is what Bill Bayne is asserting. REALLY, guys, I don't think he's advocating anything illegal. But Fred Weick was a propeller expert - he REALLY wrote the propeller textbook. He chose the propeller for the earlier Coupes under the rules then applying to get the best performance with climb near red-line and cruise near red-line. And red-line of 2275 just doesn't over stress that engine. You are NOT being told to cruise above the red-line. You are being told that Fred Weick advocated cruising the C-75 AT the red-line. Hope I've added something to the discussion. Ed Burkhead http://edburkhead.com ed -at- edburkhead???.com (change -at- to @ and remove "???") ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
