Propeller basics help!

[Djay Ahluwalia]

How does the thrust produced by a propeller differ due to

 

-the voltage/current its working at 

 

- the size of the propeller

 

 

[Bruce Richards]

It is hard to answer such a general question with anything but a general answer. So the bigger the prop the more thrust it generates. Up to a point the faster you spin it the more thrust it generates. but if you spin it too fast the thrust will drop off quickly. For the electric motors we use the higher the voltage the faster they will spin and for a given propeller the more power they will consume.

 

Not sure if this helps but feel free to ask more questions and I am sure we can answer them.

[Danny Fenton]

Generally the larger prop spinning at a lower rpm is more efficient and this is the area I try to operate my models at. The larger prop pushes a large disc of air at a lower velocity and tends to be much quieter in operation too. In my experience a quiet powertrain is usually efficient, remember noise and heat is wasted energy.

As Bruce says its a bit of a vague question, what is it you are you specifically asking Djay?

 

Cheers

Danny

[Andy Gates]

From a message I have had from Djay, he is trying to get his head around the working relationships between voltage, current, the propeller dimentions and performance of the propeller.

 

Realistically he is looking at a small powered glider but I suspect that may change when the weight and performance is taken into consideration.

[Ed Anderson]

Posted by Djay Ahluwalia on 14/05/2010 15:16:42:

How does the thrust produced by a propeller differ due to

 

-the voltage/current its working at 

 

- the size of the propeller

 

 

 This question was asked a while ago, but it is so basic that I will add a few comments.

 

The electric motor constant kV says that for each volt applied to that motor the motor will try and spin at a certain speed.  It will draw more and more current trying to hit that speed predicted by kV.  Higher voltages produce higher RPMs.  

 

So a 1000 kV motor will try to spin at 1000 rpms for every volt applied.

A 1500 kV motor will try to spin at 1500 rpms for every volt applied.

 

The wider the prop the more watts ( amps X volts) , the more amps, the motor will draw in order to try to reach the speed predicted by kV.

 

The deeper the pitch of the prop the more watts the motor will draw in order to try and reach the speed predicted by kV.

 

The faster the prop spins the more thrust and air speed it produces up to a point where it starts to approch the cavitation point.  

 

In simple terms, that is how it works.

 

Wider shallower props tend to be more efficent than smaller deeper props.

 

For gliders, where we are looking for climb rather than speed, we tend to go to wider shallower props.

Edited By Ed Anderson on 11/07/2010 18:42:45