# What is a typical compression ratio in light turboprop aircraft propellers? [closed]

Does anyone happen to know a rough estimate of a typical light turboprop aircraft propeller's compression ratio? Something with 6-12 seats like a Cessna Caravan or Piper Malibu. Doesn't need to be that accurate but something spinning around 1800-2000 rpm at sea level ISA?

• Welcome to aviation.SE! I edited your question to (hopefully!) make it a little clearer. If I got it wrong then you can just roll back my changes or edit it again. Your title mentioned the Malibu, which is the PA-46, but you had tagged it PA-32, which is the Cherokee Six. I guess you intended the PA-46 because I think you're asking about light turboprops but again, don't hesitate to correct it if I'm wrong. – Pondlife Nov 12 '20 at 20:58
• @Pondlife Turns out they really meant propeller compression ratio. – Sanchises Nov 13 '20 at 9:49
• Mikey, please edit your question per your comment below. – Michael Hall Nov 13 '20 at 18:26

By first principles, one simply expects the pressure difference to be thrust $$T$$ divided by disc area $$\pi r^2$$. Due to the fact that the propeller "sucks" ahead and "blows" behind itself, we'd expect to see about half of this pressure difference as a pressure drop ahead of the propeller and the other half as a pressure increase behind the propeller. The effective compression ratio $$n$$ in ambient pressure $$p_0$$ is then

$$n=\frac{p_0+T/(2\pi r^2)}{p_0 - T/(2\pi r^2)}$$

To see what thrust is created for a given amount of power, you can use this excellent answer by Peter Kämpf.

• We need an expression to relate thrust to power, as power is known, not thrust. – Efe Ballı Nov 13 '20 at 12:45
• That equation is for static thrust. I guess the OP wants to get the power in flight, which is given in the linked answer. Thanks for your comment! – Sanchises Nov 13 '20 at 12:47
• Couldn't get the equation in the proper form, so I removed it. You're right, it is for static thrust, but to me it is really unclear what the OP asks in terms of flight conditions. – Efe Ballı Nov 13 '20 at 12:49

Welcome.