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Prop blade loads

Prop blade loads

Prop blade loads

I'm trying to design a variable pitch mechanism for a 2-blade prop (D 1.75 m) and a 160 HP engine. The pitch mechanism should be actuated by a DC motor. Trouble is, I don't know how to calculate the aerodynamic loads which twist the blade. Best result I got so far is around 60 Nm, but I think that's to high.
I need a book suggestion or a formula or any data I can use to estimate the DC motor power,gear ratios etc..

RE: Prop blade loads

Try conservation of momentum. A standard fluid dynamics text will do.
First, do the problem twice. Once with the blade at angle "A" and then with the blade at angle "B". The difference in forces should give you a way to estimate the torque required.  


RE: Prop blade loads

I think the problem is that the centre of pressure will move along the chord of the blade as the spped of the plane and the prop change (and some other things). If it stayed in the same place the torque required would just be friction and so on, since you could line the axis of the blade up with the CP.


Greg Locock

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RE: Prop blade loads

 Don´t forget the centrifugal loads trying to fine-pitch the blades (unless you use counterweights).

RE: Prop blade loads

these are all good posts ... but get a book on propeller design if you want to design one.  there are Too many subtlities and problems in the design to answer on this typ of forum.

good luck

RE: Prop blade loads

A star for rb, really the only right answer.  Better, buy several books on prop design, and then go work for Hamilton-Standard or whoever they are today.  There's a lot of black art in getting it "just right" instead of "pretty close".

RE: Prop blade loads

Anecdotal story on prop blade loads.
I had a motor glider in my shop with a variable pitch/feathering prop made in Germany. In an accident a blade tip had been damaged.
 It was sent to a repair station and serviced.
When the aircraft was test flown, the prop would not feather, several attempts, were made which produced ominous noises from the feathering mechanism. At this point the test flight was dis-continued, the aircraft landed, and the propeller checked. The feathering mechanism was bent.
 We then discovered that the repair station had installed the counterweights on the wrong side of the prop.

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