Mark33
Well Known Member
I have a question for all of you engine and prop gurus. I have a newly completed RV-7 with an IO-360 and a whirlwind RV-200 C/S prop. The primary problem that I'm having is that I'm only getting 2650 RPM's out of it (both on the ground and in flight) and can only achieve, on average, about 145 MPH (not knots) indicated airspeed. The engine is making good power at around 28-29" MP. I have insured that my prop cable has about 3/8" cushion in it prior to it touching the panel and the arm on the governor is making good contact with its stop. I've even tried adjusting the stop on the governor to give me some additional through, but that hasn't help any at all. I've also had a prop shop check the angles on the prop and they have insured me that it's within specification. During ground runs, and at full throttle takeoff, it will momentary flash to 2700 RPM's but will immediately come right back down to 2650 RPM's. I really wouldn't be all that concerned about it because even at 2650 RPM's it still has plenty of power for takeoff. My main concern is my cruising speed. So, I guess my main question is, is this low RPM affecting my speed any or do I have another problem? So, in other words, with all things being equal, when I roll my prop back, to lets say 2400 RPM's for cruise flight, am I getting the same effect in performance regardless if I was starting out at 2650 or 2700 RPM's? Is 2400 RPM's 2400 RPM's regardless as to where I started from? I feel like I have a race car that's not geared properly and the performance is suffering because of it. My friend also has an RV-7 with a bone stock O-360 and a fixed-pitch prop and he can literally run off and leave me behind. Something is just not right!! I don't have the wheel pants or landing gear fairings on yet and I know I'll pick up some speed once I have these installed, but I can't imagine I'll pick up much more than 10-12 MPH. I once had an RV-4 with an O-360 and a C/S prop and at full throttle when I would come back on my prop to 2350-2400 RPM's it would literally feel like something kicked it in the tail....I could feel a surge in speed. With this -7, I don't feel any surge at all and I barley pick up any speed at all when I pull the prop back. This is really frustrating and so far I'm very disappointed in the performance of this airplane. So, with all that being said, I would appreciate any help or suggestions that anyone can provide.
Thanks,
Mark
Thanks,
Mark
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