Engine power question???

wrote:
I own a Cessna 150 with a 150 HP engine installed (0-320- E2D)

The STC states the static RPM is not to be over 2250 RPM.

My airplane meets the Static RPM Requirement.

My question is am I getting the full 150 HP on takeoff??? turning
2250 RPM

When rolling down the Runway the Tach reads about 2250 RPM

During stable Cruise the engine spins up to 2600 RPM ++ full
throttle : no problem

It seem's to me that the engine should turn much faster like 2700
RPM or so for 150 HP??? on takeoff Just like a Cessna 172!

Turning 2250 RPM seems like I am not getting the full rated engine
HP??? perhaps 125 HP or so???????

What sets the engine RPM?? is it the diameter of the prop?? or is
the Throttle travel
limited???

Why would the STC limit the Static Engine RPM to 2250 RPM???

is it because the Tip of the props may exceed speed of
sound ????

The STC states the Prop is a Mccauley 1C172/TM not over 74 inches
not under 72.5 inches.


Thanks for input

It forces you to use a certain minimum prop pitch to avoid overspeeding
it in flight.

An O-320 makes 120 hp at 2300 rpm and 26". At wide open throttle at SL
and 2250 it is probably around 130 hp. Add a couple thousand feet and
125 hp at the start of the roll sounds about right.

Any fixed pitch airplane is the same. A 150 with a stock O200 doesn't
have 100 hp available while static either, probably more like 80-85. So
all things being equal you still have 50% more power available than stock.

With all the old wives' tales about running constant speed engines
"oversquare" (rpm below mp) it's amusing to note that fixed pitch
aircraft are way oversquare all through their takeoff and climb phase
until they're going fast enough.

John