Where is 'thrust' pointing?

[Dave_Jackson]

'Thrust' is considered by some as the rotor's force that is perpendicular to the tip path plane. Others considered 'thrust' as the horizontal component of the rotor's force.

Both definitions are probably valid for an airplane's propeller. Which is the correct one for a helicopter's rotor and what is the correct name of the other vector? :confused:

[Grainger]

How about "Total Rotor Thrust" for the force perpendicular to the disk ?

This can then be resolved into vertical and horizontal components.

In fact, there are two possible horizontal components - a longitudinal one for forward/back motion, and a lateral one if the helicopter is banked or traversing sideways.

[heedm]

As much as it seems like it would be convenient, there is not a universal standard for terminology, sign conventions, and variables with regard to helicopter aerodynamics. Check out Stepniewski & Keys book carefully and you'll see they aren't even consistent between their volumes.

I think of thrust as perpendicular to the tip path plane.

Whichever you use, make sure it's clear to your readers.

Matthew.

[Dave_Jackson]

Grainger & heedm


Thanks for the input.

Perhaps Stepniewski was ambidextrous. Perhaps when writing the two books, the left hand didn't know what the right hand was doing. :yuk: Bad joke.

If 'thrust' is used for the vector perpendicular to the tip path plane and 'lift' is the vertical component, would 'push' or 'pull' be an appropriate word for the horizontal component(s)?

[NickLappos]

Dave,
In general terms, the thrust that is prouced by the main rotor is the vector sum of all the forces that the rotor produces. This thrust is very roughly perpendicular to the tip path plane. If the truth be known, the thrust is a very choppy wave form, with lots of 1 per rev and N per rev content, as well as oscillating in-plane "H" forces.

For accounting the forces on a flying machine, we divide all forces into four vectors, Lift and Weight, Thrust and Drag. In this parlance, the thrust is the sum of all propulsive forces on the aircraft. For a helicopter, this is the longitudinal component of the rotor thrust, and the net propulsive force from the engine exhaust.

There is no standard term for anything on our planet, why should thrust be any different?;)

[Dave_Jackson]

Nick,

Thanks for the additional information.
I hope you had an enjoyable and rewarding trip.