Reduction of Condition levers

[Radar Identified]

Hello All,

My question is as follows.....

You take off with 100%. As you climb out and your speed increases you reduce to a lower percentage.

My understanding as to why this is done is on the initial takeoff as your forward speed is 0kts there is an optimal AoA for the prop. As your speed increases the AoA decreases to a point where the Prop is no longer producing an optimum amount of thrust. Therefore by reducing the condition levers you increse the blade angle and the AoA thereby resuming the optimum amount of thrust produced.

If this is correct which I am not saying it is where is the limit of reduction to benifit gained. i.e obviously by reducing to feather this does not provide better thrust. Hope the question can be understood and that the general query comes across!

Regards
R.I

[error_401]

I don't think that the aerodynamic is that much of a concern.

IMHO (actually flying a turbo-prop)

Propeller design: Is made to offer a range in which the prop can steer to maintain a maximum rpm. Be it the take-off setting, be it a cruise setting. This means that the prop itself is not limited but could (with a more powerful engine) still produce more thrust.

Back to the inital question I think that as long as the prop is able to maintain its rpm in the design range it is compensating for the effects described.

Maximum thrust with a prop aircraft is at maximum torque.
Maximum torque is usually the limiter for turbo-prop aircraft (apart from other things like Nh [high pressure stage] or ITT).
The higher propeller rpm the more power you need to achieve the same torque at the prop. This is the main reason for the high setting at take-off where you want ALL that is available.

Once established in climb you reduce to a lower propeller rpm.
1st for comfort reasons.
2nd you lower the power output on the turbine or engine to below the MCT (maximum continous thrust/torque) to keep engine lifetimes high.

Maybe there is somebody else from the propeller guild who can be more specific.

error

[zerozero]

The reason for the reduction isn't so much for aerodynamics but to reduce the noise and lower the temperature.

Actually, now that I think about it...

...a lot of the noise comes from the prop tips which could very well be supersonic. So, there's an aerodynamic aspect to it, in a backwards sort of way.

:\

[barit1]

For a free-turbine (independent power turbine) engine only:

The prop speed, and thus the power turbine speed, is controlled by the prop governor. It modulates prop blade pitch angle to hold rpm.

At start of TO, the blade pitch is fairly low, but as you pick up speed, the rpm will tend to increase as inflow speeds up. (Fixed-pitch planes routinely experience this.) But the prop governor then feeds in a steeper blade angle to hold the selected rpm.

By the time you reach cruise, the blade tips would be supersonic -
so setting a lower prop rpm is in order.

Constant-speed props are preferred for aerobatics because the pilot doesn't have to monitor rpm; it remains constant whether going uphill or downhill.