Claude.... I'm surprised that no one has responded to your posting. I'm not sure that I can help but I will offer several comments. You sound experienced so I won't ask if you are finding pools of gas under your quick drains or untying your tiedown ropes at the wrong end when you fly.
The McAuley recommended props(square tip) for your 85HP plane are the CM7150 for standard and the CM7148 for climb. There was no 7149 so it had to have been repitched. The original and new markings would be stamped on the prop. You didn't say if it was cut down from a 7351, used on the 75HP engine, or not. Apparently you have some question about it. As for the 6950 prop, if it is standard, it should way overrev on a C85 engine. This prop was standard on the A-D model Cessna 150's before they went to the 6948's. I tried one once on a C85 Coupe it turned up 2700RPM and produced very limited full power. It may not be legal. Some Coupes are faster than others. However a typical 85HP Coupe will fly full throttle, level flight(FTLF) at 114MPH, or so, with a 7150 prop. It will touch down, full stall at 50-55Mph. These are rough guides that can be used to check the ASI. The tachometer can't be really checked on the plane unless some source such as a drill that can turn an accurate 1300RPM can be found( it needs to be checked near the red line). If your prop is truly pitched to 7149 and the planform has not been changed, then in FTLF it should show more like 2600+ rather than 2500RPM, assuming that your engine is in good shape and properly timed. If you're using 6 gals of fuel in cruise at 2250RPM, and not just doing circuits and bumps, that would correspond to around 2440RPM with a 7150 prop(80-85%Pwr) and should be higher with a 7149 prop. When climbing out at 80MPH the tach would show about 2350-2375 RPM for a 7150 and more than that for the 7149 prop. Sounds like the words and the music don't match for that prop/tach combo, doesn't it? I'm no expert on this but I'll offer my observation on Coupe speed, a contraversial subject. All Coupes will fly at two speeds(cruise) with the same throttle setting(but not the same RPM). If you're on the lower speed just lower the nose, pick up 2-3 MPH and level out. You're faster but it's hard to hold it . Some call it "getting on the step". Actually when you fly faster in a Coupe you fly more nose down and with less drag. In my opinion it explains why when you go to an 0-200 engine the air speed increase is greater than the cube root of the power ratio increase would predict. That and removing the venturis. Power increases speed. Speed increases lift(Square law). Trim lowers nose. Drag decreases. Speed increases. There is a limit to this, of course and if I had to guess I'd say it might be around 115HP for the Coupe. And, of course, when I talk about drag decreasing I'm really talking about drag coefficient since total drag increases with speed. It's my thought that if a Coupe is substantially slower than it should be the engine/prop is wrong and/or drag is excessive. This assumes that air speed is being measured accurately. Overall trim is a factor.So is weight and irregularities in the airframe. Also, everything you hang on a Coupe that's in the airstream slows it down. Anytime you have a heavy wing and use trim tabs to bring it back up, you're adding trim drag(i've seen Coupes fly with the ball off center). Anytime you bend that elevator trailing edge down to help the trim tab get a little more nose up you may be adding trim drag(on my Alon it cost 3MPH top speed). Just two final comments. I was never able to outrun a Cessna 150 in a fair fight with my 85HP Coupe. This reply has enough contraversial state- ments to get you some responses, let's hope they address your problem. Best Regards .....Cliff
<<attachment: winmail.dat>>
