Total Rotor Thrust question...
 

Can someone help with my question please?
When transitioning from the hover into forward, level flight....why is total rotor thrust increased? I have it in my head that it should be reduced as less power is required than in the hover. Any help would be much appreciated.
Thankyou in advance. http://images.ibsrv.net/ibsrv/res/sr...ies/thumbs.gif

Mmmmm ....

I think with your question you have to assume that there is no change in the collective pitch with the transition to forward flight.

If that is the case as the induced flow increases ... the rotor efficiency also increases and therefore the TRT also increases.

Certainly as the airspeed of the aircraft increases you could reduce power (if you wished) to the hover TRT value the aircraft would then be flying with the same rotor thrust value but at reduced power (effectively).


:}

GM - I've just answered this question on the Professional Flight Training forum. If you have, quite sensibly, decided to move it here, you should delete the other thread.

Simple terms without any fancies. If I tilt the disc forward in order to allow the rotor thrust to initiate the forward movement, the airframe will not only go up as before the forward initiation on the cyclic but will also tilt the nose downwards towards the ground. If I do not increase collective in order to increase the rotor thrust to compensate for the tendency to fly forward and downwards, i will fly into the ground as the original applied rotor thrust is now divided between lift and forward movement and thus has to be increased in order to maintain height initially.

I must have a mental block on this one. I know what happens with the various stages but I just can't picture why TRT increases as power is reduced. I will just accept it and move on!!!lol Thanks for your replies :ok:

If you think of it as - TRT increases so you have to reduce power to maintain height. (Rather than as you reduce power)

Yes?

Total Reaction on TRT
 

Spinwing, I guess I should look at my books before I comment but I'm certain that induced flow reduces as you enter forward flight and gain Transational Lift. If this is ture then in the vector diagram Total Reaction tilts towards TRT and hence an increase in TRT?

Nothing like throwing some two pence worth in the mix to liven up a debate!

PT

General Mutley,

After the initial horizontal acceleration, which will require additional TRT to maintain height - and accelerate, the horizontal component of the induced flow will cause the total reaction to tilt forwards, thereby reducing rotor drag and increasing TRT as a result. The reduction in rotor drag means that to continue in balanced flight (ie no more acceleration either vertical or horizontal) the corresponding power required to maintain rotor RPM is reduced - OR if the collective is left alone, TRT can be said to increase. This situation remains relative up until the total drag (IE rotor, profile and parasite drag) increases (as a square of the airspeed) cancelling out the benefits of the horizontal airflow component, and eventually the power required to accelerate further increases. Hence the unique shape of the helicopters power-required for level flight graph). The lowest point of which we exploit as a "Safety Speed" for performance purposes.

You need to look at the TRT and TR diagrams in a POF book and revise what happens when the horizontal component of the induced flow increases (normally by flying forwards).

Up until a couple of months ago this was gobbldee-gook to me. but I had to revise for an interview and found WJ Wagtendonks POF book a godsend. Its on the net if you google.

Having vomitted all that up bear in mind I am not an FI(H)!!!!

DB

When you are in a 'perfect' hover you are using TRT to counteract the weight of the helicopter. As you move forward you still need to have that thrust to counteract the weight of the helicopter PLUS the thrust needed to move the helicopter forward. The fact that you reduce the collective lever is not really to reduce power but because the disc is becoming more efficient due to translational lift. I think...

THANKS everyone. I just need to revisit those damn TR diagrams again. Has been helpful to read the answer in different words to those used in the books.
Cheers for all your help :ok: