# What is the static thrust of a Piper Arrow III?

I want to find out what's the static thrust of a Piper Arrow III (non-turbo) with Mc Cauley propeller at T/O (max) power as function of the air density.

I can't find it in the manual, I know the engine is rated at 200 HP and had a look at some formulas but they require some other parameters like the propeller efficiency which I can't find.

• use 50% efficiency. Then you will be wrong by at most a factor of 2. On a more serious note: The definition of efficiency breaks down at zero speed. A lower value than 50% will be likely. Please see here for some more data. Apr 22, 2020 at 19:19
• Weird, according to this dept.aoe.vt.edu/~lutze/AOE3104/thrustmodels.pdf I should take a 90% "We can estimate the actual static thrust is 90% of that or 1116 lbs."
– Gus
Apr 25, 2020 at 7:19
• I'm rather surprised to read that. GA propeller efficiency rarely exceeds 85% and twist is matched to cruise speed, not the static case. Especially fixed-pitch propellers have poor efficiency at zero speed. Here is a NACA report on old measurements of static thrust. See point 5 of the conclusions. Apr 25, 2020 at 7:44
• Yes, I read that one as well. Still I must be missing something. If we take a 0.5 for the static thrust we get (with a 6.12 blade) a value of 750 lbs, but then after releasing brakes at 40 knots it would be 814 lbs according to the thrust formula (n * P / v). I can't make sense of it. To me after releasing brakes and speed builds up, the thrust should reduce. What am I missing?
– Gus
Apr 25, 2020 at 8:09
• Constant speed or fixed pitch prop? Apr 25, 2020 at 9:38