Rotors

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Re: Rotors

Post by new horizon » November 4th, 2010, 8:48 am

A left handed rotor, would that be the same as a right handed rotor (the props used in wright stuff), but the angles of the two blades are flipped? Like if your right-handed propeller had a right side go downward, and a leftside that went upward, then would the left-handed propeller have a rightside go upward and a leftside go downward?

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Re: Rotors

Post by smartkid222 » November 4th, 2010, 1:00 pm

Yes i think so. I'm sure Jeff is going post a website explaining it better or copy and paste from old posts.
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Re: Rotors

Post by jander14indoor » November 5th, 2010, 3:53 am

Why, you all are doing fine. Right and left hand props just have blades flipped as already said. One provides thrust spinning clockwise, the other counter clockwise, and I can never remember which without looking and thinking.

While it doesn't really matter to the air which is free and which is 'fixed', you should be consistent otherwise you have to remember which way to wind. And it may be easier to remember which way to wind if you match the combination to your handedness. Right handers tend to wind clockwise without thinking, left handers tend to wind counterclockwise. Convention says wind clockwise, free rotor on top thrusts spinning clockwise and 'fixed' rotor below thrusting counterclockwise. Oh, and that is looking from behind or below.

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Re: Rotors

Post by Ze_Duke101 » November 24th, 2010, 5:03 pm

Hey, Im new to science Olympiad, and I want to know for helicopters, what would be better, Helicopter propellers, or an aerial screw?

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Re: Rotors

Post by calgoddard » November 24th, 2010, 6:23 pm

Use rotors. To my knowledge no aircraft, full scale or model, has every flown based on lift generated by an aerial screw of the type depicted
in the illustration you posted that was supposedly hand drawn by Leonardo DaVinci.

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Re: Rotors

Post by illusionist » December 11th, 2010, 10:17 am

For the rotors, would it be best to attach them like this:

built like the ones for the fixed rotor, except attached to a prop shaft- http://picasaweb.google.com/jeffrey.hoo ... 7835332994

or, build two blades in the above manor, but attach them only to one propeller spar? kinda like this: http://www.youtube.com/watch?v=uDhcxS_OTv8

it seems like the second type will be able to adjust for different thrust (they are flexible) but the first one is more rigid...
Any preferences?
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Re: Rotors

Post by blue cobra » December 11th, 2010, 6:10 pm

I'm not 100% sure of what you're asking.

Are you talking about building blades in one long, twisting rectangle like the picture vs. two rectangles like the video? Or were you talking about having one free and one fixed rotor vs. two free rotors?

Balsa light/thin enough for this event is probably going to be fairly flexible under the full torque of a motor, even for the type pictured in the still image. As for which design is better, that's something we'll need to find out. This is the first year Helicopters has been an official event, so anything is possible. I see both possible advantages and possible disadvantages to each of those designs, so experimentation will be a great thing for this event.

tl;dr: I don't know.
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Re: Rotors

Post by illusionist » December 11th, 2010, 7:12 pm

Yup, i meant building it like the picture, but then cutting them and attaching them like the video. I'll build two different rotors for the same helicopter body and try both... Thanks
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Re: Rotors

Post by illusionist » December 12th, 2010, 2:20 pm

Alright,my results maybe flawed, but I am getting better flight times withe rotors attached like the video. That may just be due to poor construction though.
Another question, the rules state that the rotors must be of fixed pitch. So is it fine if the rotors bend during flight since they are flexible?
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Re: Rotors

Post by jander14indoor » December 12th, 2010, 6:42 pm

OK, take this with the usual: "This is not an official clarification as this isn't the official NSO site for such." grain of salt.

EVERYTHING bends some as soon as you put a load on it. Even diamond. Everything. Even a VERY stiff rotor made of say (illegal but workable) carbon fiber.

If they interpreted simple flexing of components as variable pitch they'd have to disqualify EVERY helicopter submitted.

I suspect the rule refers more to mechanisms specifically designed to change pitch in a controlled manner with things like pivots or hinges like 'real' full size helicopters and their complicated collective controls and stuff. If you want to see an example look for variable pitch propellers used in F1D indoor free flight planes.

Again, while its a fact everything bends, the rule interpretation is an OPINION only.

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