Guys, I usually see you writing about your speed and rpm at 8000'. I guess that's because 8000' density altitude is usually thought of as where you will develope 75% power. Well, first off, with your forward speed, your manifold pressure will be higher due to dynamic pressure recovery so you'll be at higher power. That 8000'-75% relationship is for much slower planes. Secondly, do you really do most of your flying around 8000'? That's a pretty popular altitude region for C-172 types, so you'll have lots of traffic there. But I would think that you would use your planes mostly for cross-country flights. That's the major reason for my plane, so when I go any distance I fly at 11,500' or 12,500'. It's so much cooler there and there's lots less turbulence and traffic. In the summer, the density altitude here on the west coast is usually about 2000'-2500' higher. The other day at 12,500, OAT was 11C, ISO +20.7C, for a density altitude of 14,880' But if you limit your rpm on a fixed pitch prop to sea-level rated rpm when at 8000', you've really cut into your take-off, climb, and high-density-altitude cruise performance. If you get your prop set-up for rated rpm at high density altitude, you'll see much better all-around performance. Your engine will tolerate, with no problem, going 10% over red-line. Believe me, it won't suddenly explode the moment that needle gets slightly to the right of the red-line. Some of the helicopter versions of these engines will turn up to 3200 rpm. Sure, they might have slightly different parts, but that red-line spec is put on there for certification considerations, not as a "don't exceed or it will fall apart" warning! You do have a throttle, I hope! So get Craig to set up your prop for rated rpm at, say, 14,500' dalt, and when you fly at lower altitude, if the higher rpm alarms you, pull the throttle back a little. The RVs I've tested show a drop in speed and rpm of about 1.1%/1000'. If you get a prop that will turn 2700 rpm at 14,500' dalt, it will turn about 2900 rpm at 8000' dalt, 7.4% over red-line. Now really; when you fly below 8000', don't you pull the throttle to get the rpm at or below rated? OK then, if you get the prop so it will turn rated at 14,500' dalt, you'll just pull it back at a little higher altitude. But then, if you drop it to rated rpm at 8000' dalt, you'll be a little slower but also at less than 75% pwer. So which takes less toll on the engine, the higher internal pressures at higher power, or the higher centrifugal forces at higher rpm but lower power? Typically, over-square engines have more bearing wear from power than from CF. Actually, the piston and connecting rods experience little loading from CF as they are usually being pushed or pushing against a load!
