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Propeller, number of blades, another aspect

Old 08-13-2014, 03:54 PM
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Default Propeller, number of blades, another aspect

This entire thread is hypothetical, I'm trying to describe one aspect and would like your input.

The most efficient propeller if there are no limitations would be the 1 bladed prop with a counterweight. This prevents the propeller from running into it's own turbulence. However real world applications come with limitations.

In this case I'm on the subject of multirotors. Here each propeller has to fit between the other propellers. This means the propellers have a very strict maximum diameter.

Say we want to carry a payload (camera, LEDs or a fluffy unicorn, whatever floats your boat) we need more lift. Of course we will give the aircraft more powerful engines but just blasting more power will not always solve the problems. Because of the diameter limit to the propeller, a more powerful engine can't be paired with a larger propeller. Instead the more powerful engine will take the same propeller as the original weaker engine, but spin it faster. You could of course try with propellers with a different pitch but spinning a prop very fast doesn't nessecarily move more air, at least not so much more air that the more powerful engine gives you as much additional lift as you had hoped.

So I'm imagining another solution. We would need a way to let the more powerful engine work optimally at the same rotation speed as the weaker engine but still move more air. Simplified; we need to give it more resistance.

As I wrote we can try to adjust the pitch BUT pitch is more often associated with the intended speed through the air, isn't it? A fast aircraft will need a steep pitch since the air is already blowing against the propeller as the plane flies. The slow flyers need a flat pitch, using a steep pitch with a slow moving aircraft would be like putting sideways paddles on the prop; instead of forcing the air backwards it would just start spinning the air around creating a mini tornado. Here I exaggerated but the point being that optimum propeller pitch has more to do with the airspeed at which the given propeller should work best, and less to do with the power of the engine. Or am I missing something?

We can't increase the propeller's diameter because then it would bump into the other propellers.
We'll only get a little help by finding the optimum pitch propeller for this new motor. The pitch should still be optimised for a hovering multirotor platform, similar to that of a slow flyer.

What is left is to add more blades. Even though a 2 bladed large diameter propeller would be optimal, we could use a propeller with more blades to achieve a similar effect, couldn't we?

With this in mind I have been looking for 5 or 6 blade rc propellers, but I can't seem to find any.

Does anyone here know of any place where you can get 5 or 6 blade propellers?

Sincerely yours.

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