PPRuNe Forums - View Single Post - Propeller torque & engine torque
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Old 22nd Jun 2012, 12:27
  #154 (permalink)  
keith williams
 
Join Date: Jan 2011
Location: England
Posts: 661
Received 20 Likes on 13 Posts
I thought you might wish to deny one or more of your errors, so I did a search.

1. Propellers continue produce THP when the aircraft velocity is zero.


Page 1 post 8 “Not that myth again. It's disappointing to have to point out to one who calls himself an instructor that in your 'brakes on' scenario the aircraft is still producing 200 THP as well as 200 BHP because it is accelerating a mass of air rearwards in a futile attempt to turn the earth and the atmosphere in opposite directions.”

2. When an aeroplane is standing still on the ground with wheel brakes applied the THP is equal to Thrust x propwash velocity.


Page 1 post 14 “But that does not mean a stationary aircraft can do no work and therefore produce no THP!!! The work is done by moving the mass of air one way and the mass of the Earth a tiny imperceptible amount the other way.

3. If propellers produced no THP when the aeroplane is standing still on the ground, it will be impossible for the aeroplane to accelerate when the brakes are released.


Page 6 post 120 “Sure, no power is required if the aircraft is at standstill but that does not mean no power is available. OTOH power is required to accelerate the mass of the vehicle from standstill with or without aerodynamic drag. No power available = no acceleration. THP is the power available. If the aircraft has to move before you get THP then you are in a chicken and egg situation - you can't accelerate the aircraft without power but you can't have power until you move the aircraft.”



4. If THP is Thrust x TAS it will be impossible for aircraft to accelerate in flight.


Page 7 post 148 “Aircraft flying straight and level at speed Va, pilot sets new power to accelerate to Vb. Assume constant propeller efficiency between Va and Vb due variable prop. Final THP = thrust x Vb, we agree that much. Using the hypothesis you outlined above we can draw some conclusions:

The new power is set, the BHP has gone to the prop but THP doesn’t catch up until the plane reaches Vb?!

Thrust horsepower during the acceleration is less than final THP when you get to Vb?!

Thrust must have increased, but this didn’t reflect an increase in THP, this was because power was wasted in the propwash?!”



If you look at item number 2 above you will see that

Page 1 post 14 “But that does not mean a stationary aircraft can do no work and therefore produce no THP!!! The work is done by moving the mass of air one way and the mass of the Earth a tiny imperceptible amount the other way.


implies that

When an aeroplane is standing still on the ground with wheel brakes applied the THP is equal to Thrust x propwash velocity.



It really is time for you to face up to the fact that virtually everything that you have written in this thread has been nonsense.

keith williams is offline