Propeller Design

[willymesserschmitt]

Hi, I’ve been trying to design a propeller from cero, I’ve studied Theodorsen´s paper and I do understand the procedure for obtaining the optimum distributions for an specific flying condition (speed, HP, rpm), but how to design the propeller for the whole aircraft operation , because the paper gives guidance to design for an specific flying situation.
I´ve tried doing an average of the optimum chords for every flying condition, but at low speeds the chords tend to be very wide, so the resulting prop seems different in shape whit the commons props.
Perhaps Theodorsen´s method is too old, is there any other methods for prop design?
Thanks.
Willy

 

[rb1957]

i think you have encountered the crux of airplane design, being compromise. Design means making the best compromise. You can optimise the plane for a specific "point in the sky" (maybe long range cruise for a passenger transport, maybe hi-speed maneouvre for a fighter, ...) and accepting what you get at other points; or sub-optimal design, which is less than optiminal at the design point but better than the optimal design at the other points (maybe the optimal design has unacceptable landing performance). This then is why we have leading edge and trailing edge surfaces on the wing ... to improve the performance of the wing and the plane in off-design points.

not much practical help ! then in the real world you've also got the cost considerations, how expensive is something to make ? is the performance gained worth it ?

good luck

 

[willymesserschmitt]

I didn’t mention than I’m planning to make the prop variable in pitch, so I think that this solve the issue of adapting the prop for the changing conditions, hence than I m not sure about what is the correct chords distribution for this kind of prop. Of course if it were to be fixed pitch you have to decide which quality you want to give priority and having this done you have only one operating condition to select the optimum chords.

 

[reidh]

Is this a ground adjustable only propeller that you are designing?

Reidh

 

[willymesserschmitt]

I’m thinking in a flight controllable prop, but if fitted with the appropriate control system it could be made an automatic constant speed prop.