Thrust produced by the propeller
 

Hi All,

Just reading through some theory notes and have come across a statement that I'm not sure about regarding propellers.

Contrary to popular belief, the thrust that moves an aeroplane forward is NOT produced by the blast of air going backwards from the propeller but rather the lift force produced by the propeller blade.

So is it true that all propeller driven aircraft are pulled through the air by the propeller or pushed through the air via the propeller.

Interested to hear people's thoughts


Thanks.......


Mr.G

:ok:

Ah, but the 'blast of air' is caused by the lift force. Propellers are mini wings. The pressure differential of the airflow over the blades causes the air to be pushed back and, thanks to Mr Newton and his 3rd law of motion, the plane to be 'pulled' forward. For a more in depth view, you'll need someone brighter than me.

The propeller is essentially a rotating wing. If you read about wings then the same theory applies to the propeller.

Bernoulli and Newton
 

This has the potential to bring out the fanatics on either side but the truth is the correct answer is "both."

There is in fact a low pressure area ahead of the prop. And you can apply Bernoulli type physics in this case.

But you can also make a case for Newton in that the prop is taking an airmass and accelerating it rearwards..."for every action there's an equal and oppsite reaction."

Definitely two ways to look at it. Two different theories describing the same phenomenon.

And now I'll wait for my lashings.

I see no reason to give you a lashing 00.

However, I have just noticed that Mr Garrison is a CPL (A) AND a CPL(H). So I'm rather surprised he asked.

Zerozero got it in a nutshell.......as he says, it's explained by Newton's Third Law.

A while ago I stumbled across this NASA web-site (not rocket science in this case, honestly - its actually a Beginner's Guide To Aeronautics) which gives some superb explanations to this and probably every other aeronautics conundrum you can think of. Give it a try.......

http://www.grc.nasa.gov/WWW/K-12/airplane/

WUT

In a wing, the airflow is turned downwards in a phenomenon we call "downwash". It is the "equal and opposite" reaction to the lift produced by the wing. They are inseparable, yet many elementary texts neglect to mention downwash.

A prop blade's downwash is called "propwash", and its lift is called "thrust". They are equally inseparable (as are the forces in the first paragraph).