Hangar Flying => Hangar Flying => Topic started by: N210GW on June 23, 2005, 08:01:29 AM
Title: Cruse RPM
Post by: N210GW on June 23, 2005, 08:01:29 AM
I would like some user feed back on cruse RPM's. I have a Long EZ with a 0-320 and a prop that is probly beter suited for climb and no wheel pants. Curently I cruse at 140 kts true at 2500 RPM and 8000 ft . At full power I can see 3000 RPM and 170 kts. My concern is without a fuel flow gague or a manifold pressure gague how do I determine how much power I am pulling from the engine. I would apreciate some feed back on runing the engine at the higher RPM's.
Title: Cruse RPM
Post by: Anonymous on June 23, 2005, 11:10:18 AM
This won't be real accurate, but I bet its within 5%. Look at a Lycoming table that show HP, vs RPM. It doesn't make a difference what plane it comes from, as long as the engine is the same.
Extrapolate their 2700 rpm up to your 3000 rpm. The HP will increase in the same proportion. Note this ONLY works for a know throttle setting, i.e. FULL, and assumes that at the 2700 rpm point, your producing rated power.
EXAMPLE. If your cruising along at sea level, full throttle, and your engine is turning exactly 2700 rpm, then your putting out exactly 160 hp. If you changed something to increase the rpm (i.e. re-pitched your propeller), your engine will be generating more power.
I don't have the table in front of me, but I seem to remember approximately 10 HP per 100 rpm in this area of the graph.
If this is so, then if your turning 3000 rpm, then your putting out approximately 190 hp. AT SEA LEVEL, FULL THROTTLE
Stan Hall from EAA 62 in My old home in San Jose wrote a nice article on a similar subject. You can reverse the formula and back out the HP.
http://www.eaa301.org/newsletter/2003/feb.pdf
Waiter
Title: SOUNDS CLOSE
Post by: Waiter on June 23, 2005, 11:25:11 AM
I think most of the EZs are running wooden props and spinning the engines faster than rated.
I have a standard O-320 with 8.5 pistons.
My good old Great American would turn 2900 rpm at 165kts. My Prince P prop would turn 3000 rpm at 175 kts.
I currently use an MT constant speed, and turn a more civilized 2300 rpms at 165 kts.
For the same manifild pressure (i.e. throttle full) more RPMs is more power.
More RPMs means higher power, and usuall faster speed, But, this depends on how the blades are cut. I can turn my MT at 3000 rpm, and producer more power, but the airplane actually flies slower, The blades are cut for 2300rpm at 170kts, The max I can get out of it is about 180kts at 2600 rpm. If I spin the prop faster, the plane starts slowing down, back to about 160kts at 3000 rpm.