Bill asked: > Can the group give me a concensus of what the rpm should > be with a C85, full throttle, on climb out?
Bill, That's going to depend on 1. prop pitch 2. airspeed 3. aircraft gross weight at that moment 4. altitude 5. temperature. If you are heavy and climbing steeply with a coarse (cruise) pitch prop, the rpms will be fairly low. If you are light, doing a cruise climb, near the ground at low temperatures (winter), you might have a fairly high rpm on climb. I'd normally expect something in the 2200 to 2300 rpm for a C-85 engine at full throttle. As Ralph said, the test of your engine health and prop pitch comes in a zero wind, full power static run up on the ground. CAUTION! Make absolutely sure the pavement is solid (not chipping) and that there's no gravel anywhere within a yard of the prop's lowest point. If you are doing the runup on grass, look under the grass to see if there's loose gravel there. (I got several prop dings from a runup on grass where there was hidden, loose gravel under the grass.) The prop will pick up gravel and chunks and damage itself. Ideally, you make the static rpm test at zero wind. Since zero wind is so rare, if the wind is mild, turn the plane so the wind comes exactly from the side of the prop and you'll get an accurate enough reading. If the wind is strong, do the same for a quick check but come back on a low wind day and do it again for an accurate reading. With the C-85, the static rpm limits on a Coupe are listed by prop in Aircraft Specification A-718 (for the C and CD) and in A-787 for the D and all later models. (Links to these Aircraft Specifications are on my Coupe webpage at: http://edburkhead.com/Ercoupe/index.htm.) As an example, with the McCauley 1A90CF or 1B90CM props on the C-85 engine, the static rpm limits are: not over 2225, not under 2025. With my extreme climb prop, a McCauley 1B90CM pitched to 7146, my static runup was right at 2225 rpm. The same prop, pitched to 7152 will probably be at the bottom end of the range at 2025 rpm. Be aware that a cruise prop may get you pitiful speed if you have a heavy plane. Your climb would be pitiful and you might not have enough horsepower to pull the plane up to the prop's ideal speed. I've known cruise pitch Coupes that could barely get to 90 mph flying level with full power. My extreme climb prop would cruise 100 mph at 2400 rpm with the engine not working very hard. The 7148 and 7150 pitch props come in between with the 7148 usually cruising @2400 rpm and 104 mph and the 7150 pitch usually cruising @2400 rpm and 108 mph. You should know your healthy-engine static rpm so, if you are suspicious, a static rpm test will tell you if your plane is putting out full power. But, as for climb rpm? That's much harder to say. Ed Ed Burkhead http://edburkhead.com/Ercoupe/index.htm East Peoria, Illinois ed -at- edbur???khead.??com (remove the ? marks and change -at- to @)
