I finished my RV-9A nearly three years ago.
Since then I fly mainly @3.000 feet @ 21 MAP and 2.350 RPM with 120 knots indicated and 25/26 liters per hour fuel burn.
I like the low noise 2.350 RPM and don't like to see 35 liters on fuel flow.
I am also slightly disappointed to be 20+ knots away from Van's published speed.
So, now that I am building the -4 I looked again at the engine/propeller selection section and I found something I already knew but I didn't focused on. Van's says that the main advantage of a C/S propeller is selecting high MAP and low RPM, thus saving fuel and reducing engine wear, the added value of a C/S being the possibility to achieve less than 75% power at altitudes lower than 8000 feet wihout reducing MAP.
Now, I tried to have full MAP (28+) and reducing RPM but I am a bit afraid to go under 2300 RPM. There is an old story about non going with RPM below the MAP (if 25 then not below 2500; if 21 not below 2100, etc...).
Before attempting the ultimate test (28 MAP and 2200 or less RPM) to achieve the best compromise, is this procedure harmful fon the engine?
Thanks.
Camillo
Since then I fly mainly @3.000 feet @ 21 MAP and 2.350 RPM with 120 knots indicated and 25/26 liters per hour fuel burn.
I like the low noise 2.350 RPM and don't like to see 35 liters on fuel flow.
I am also slightly disappointed to be 20+ knots away from Van's published speed.
So, now that I am building the -4 I looked again at the engine/propeller selection section and I found something I already knew but I didn't focused on. Van's says that the main advantage of a C/S propeller is selecting high MAP and low RPM, thus saving fuel and reducing engine wear, the added value of a C/S being the possibility to achieve less than 75% power at altitudes lower than 8000 feet wihout reducing MAP.
Now, I tried to have full MAP (28+) and reducing RPM but I am a bit afraid to go under 2300 RPM. There is an old story about non going with RPM below the MAP (if 25 then not below 2500; if 21 not below 2100, etc...).
Before attempting the ultimate test (28 MAP and 2200 or less RPM) to achieve the best compromise, is this procedure harmful fon the engine?
Thanks.
Camillo