Thrust setting

[glum]

Hi All,

I'm looking for some help with the term 'thrust setting'. I am familiar with fixed wing aircraft but know almost nothing about rotorcraft, and have a design project for a tilt-rotor aircraft, which of couse has elements of both.

My project is for the cockpit, specifically focussing on the displays, and I am trying to define the parameters for displaying thrust. Does such a term exist with rotors, or is it purely a turbine / turbojet term?

Thanks for any advice,

Glum.

[Agaricus bisporus]

Turbine Helicopters and some turboprops use Torque expressed as a percentage of each engine's output often using a dual gauge, ie superimposed needles to ensure easy power balancing. I'm sure you'll find details of torque gauges with a websearch.

[ShyTorque]

"Thrust setting" isn't a term generally used for helicopters.

As Agaricus said, "torque setting", or "percentage torque" is more common.

Having said that, the RAF's version of the Puma (HC1) doesn't have a torque gauge and on those aircraft the term "degrees of collective pitch" is used instead.

[Two's in]

Most rotorcraft have power units that are governed to accommodate a variable load at a (fairly) constant engine speed. Simply put, the engine load controls the fuel input to the engine at a given speed, or speed range to be more accurate.

In hovering flight the "thrust" will be a function of engine/transmission torque, and the principle is that the engine governor ensures that sufficient power is delivered to maintain a given pitch setting. This negates the need for the pilot to have to control the "throttle" in addition to the other controls, as was the case on earlier helicopters.

In fixed wing flight it is likely that airspeed will need to be variable, not fixed, so with the propulsion units tilted forward you could vary the speed by adjusting the governor datum via Engine Control Levers.

The complexity of sensing what mode the engine governors need to be in as a function of power unit angle and control input is not trivial, and is probably a software function within the FCS.

[HeliComparator]

Rather than just looking at torque, you might like to consider a First Limit Indicator type system as fitted to the later Eurocopter helis, and I think the EH101. THe FLI indicates the proximity to the first limit, whether it be torque, N1 or TOT. In a typical engine / transmission combination, the limiting parameter can be any one of those three depending on density altitude. The pilot is really only interested in how much further he can push the thrust lever/raise the collective (which increases blade pitch angle and hence thrust and drag of the rotor system), not which parameter happens to be the limiting one at the time, so it makes for a much better HMI.

I am not sure what the accepted terminology is for a tiltrotor, but rather than "thrust setting", perhaps "power setting" is a more universal concept that could apply to the tilt rotor in both its modes.

HC

[glum]

Thank you gents, that was just what I was looking for. :ok:

[AnFI]

for a given attitude the thrust is approximately constant - regardless of power. (if nil acceleration)

[Non-PC Plod]

An alternative to the "first limit indicator" nomenclature is "power index", which is now used on A-W types. - Again measures torque, temperature and gas generator speed.