prop rpm question

Matt Whiting wrote:
Richard Lamb wrote:

If you can find the engine performance plots you will see that the
percent of RPM and percent of power (HP or torque) are not at all
the same thing.

And it's torque that turns the propeller (not RPM).

1000 rpm might be near 1/2 RPM, but barely 10-20 percent max torque.

At full power (torque), the prop can deliver x number of pounds
thrust for any given airspeed. That's the most you'll get.

Rolling off RPM also rolls one down the torque curve.

And you are right, it's a very non-linear curve.


Richard

ps:

also on the torque curve, note that max torque and max HP are usually
NOT found at the same RPM...

ta


It's been a while since I saw so many errors in so little text.

Matt


That RPM and torque are NOT the same thing?

Or that at full power will give deliver full thrust?

Ot that the thrust delivered changes with airspeed?

Or that it's very non linear?

Very oversimplified, but go ahead and straighten me out, Matt.

Richard

Richard Lamb wrote:
Matt Whiting wrote:

Richard Lamb wrote:

If you can find the engine performance plots you will see that the
percent of RPM and percent of power (HP or torque) are not at all
the same thing.

And it's torque that turns the propeller (not RPM).

1000 rpm might be near 1/2 RPM, but barely 10-20 percent max torque.

At full power (torque), the prop can deliver x number of pounds
thrust for any given airspeed. That's the most you'll get.

Rolling off RPM also rolls one down the torque curve.

And you are right, it's a very non-linear curve.


Richard

ps:

also on the torque curve, note that max torque and max HP are usually
NOT found at the same RPM...

ta



It's been a while since I saw so many errors in so little text.

Matt



That RPM and torque are NOT the same thing?

Or that at full power will give deliver full thrust?

Ot that the thrust delivered changes with airspeed?

Or that it's very non linear?

Very oversimplified, but go ahead and straighten me out, Matt.

Richard

Yes, horsepower and torque are absolutely not the same thing. The
following suggests that they are "At full power (torque)..."

Rolling off RPM may or may not roll you down the torque curve. If you
are running at an RPM above the torque peak, reducing RPM might actually
increase the torque available.

1000 RPM isn't 1/2 RPM. It may be close to 1/2 of the maximum allowable
RPM, which is what you hopefully intended to say.

Matt