Rotors

jander14indoor
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Re: Rotors

Post by jander14indoor » February 24th, 2012, 7:02 am

Brute force, since the motor sticks are fairly trivial, make a bunch of motor sticks and fix different pitch rotors as usual. Then mix and match the pitch of the free rotor to optimise flight. Nothing says equal pitch rotors are the best choice (hint, the air going past the lower rotor has already been accelerated by the upper rotor, importance depends on how close the rotors are).

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illusionist
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Re: Rotors

Post by illusionist » February 24th, 2012, 7:49 am

jander14indoor wrote:Brute force, since the motor sticks are fairly trivial, make a bunch of motor sticks and fix different pitch rotors as usual. Then mix and match the pitch of the free rotor to optimise flight. Nothing says equal pitch rotors are the best choice (hint, the air going past the lower rotor has already been accelerated by the upper rotor, importance depends on how close the rotors are).

Jeff Anderson
Livonia, MI
Yup, I remember the discussion from last year. My rotors are at opposite ends of the motor stick, so I don't think it'd be too beneficial in my case.
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Re: Rotors

Post by Skleintop3141 » February 25th, 2012, 8:01 am

In the rules it states "The helicopter may use up to three fixed pitch rotors, not exceeding a maximum diameter of 35.0 cm." Does this mean in total the rotors must not exceed 35.0 cm or that each rotor may not exceed 35.0 cm?

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Re: Rotors

Post by blue cobra » February 25th, 2012, 10:47 am

illusionist wrote:Thanks, and another thing.
I believe this was brought up in last year's thread, but never received an answer-
Is there a way to mount the "fixed" rotor onto the motor stick temporarily so that you can swap it out for a rotor with a different pitch during testing? I was thinking about maybe creating some notches and tying it on with thread, but it seems very weak.
I did this last year. I used some light 1/32" balsa to make a 3 sided U-shape that fit on my motor stick, and glued the fixed rotor to that. Then I put little 1/32" pieces of balsa on my motor stick above and below where this fixture goes so I can get it in the same place every time. Put your rotor fixture on the motor stick, and secure with orthodontic elastics or something similar.
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Re: Rotors

Post by illusionist » February 25th, 2012, 11:02 am

Skleintop3141 wrote:In the rules it states "The helicopter may use up to three fixed pitch rotors, not exceeding a maximum diameter of 35.0 cm." Does this mean in total the rotors must not exceed 35.0 cm or that each rotor may not exceed 35.0 cm?
Each individual rotor must be less then 35.0cm.

And thanks blue cobra, I'll try it out.
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Re: Rotors

Post by Skleintop3141 » February 25th, 2012, 11:13 am

illusionist wrote:
Skleintop3141 wrote:In the rules it states "The helicopter may use up to three fixed pitch rotors, not exceeding a maximum diameter of 35.0 cm." Does this mean in total the rotors must not exceed 35.0 cm or that each rotor may not exceed 35.0 cm?
Each individual rotor must be less then 35.0cm.

And thanks blue cobra, I'll try it out.

Thank you :)

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Re: Rotors

Post by illusionist » February 26th, 2012, 3:05 pm

Okay, so I can fly successfully for a little over 1 minute on 3/16 rubber and now I really want to move down to 1/8, but 1/8 doesn't seem to have enough power to turn the rotors.

The issue is, I'm not sure what rotor angle/dimensions to use. I've tried a 3cm vertical distance (vd) with 13cm tip distance to a 2cm vd with 12cm tip separation (with which I'm getting about 40 seconds). Should I try a smaller vertical spacing (which I think would be too small if I go any further) or a smaller tip spacing resulting in smaller rotor surface area?
Some other info- Heli Weight: 3.51g Rubber: 1.6g

I know it sounds like I'm asking for a definitive answer (which I know is something that you can't give), but I just want a direction to go in from some of the more experienced members.
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Re: Rotors

Post by chia » February 26th, 2012, 4:28 pm

Wow, your rotors are really wide! Mine tend to be 3-4 cm vd and 8 cm tip separation. I've experimented a little, but that seems to work well, at least with 1/8 rubber.
I know I don't have as much experience compared to who you're technically asking, but I think you're right about not lowering the vertical distance any more, so I guess you might want to try a smaller tip separation?
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Re: Rotors

Post by thsom » February 26th, 2012, 10:06 pm

When you guys use helical rotors, what are your main beams? If they are 1/8 by 1/8 wouldn't that get really heavy because you would have four pieces of 1/8 by 1/8 balsa wood of say 36-37 cm length each?

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Re: Rotors

Post by chia » February 26th, 2012, 10:14 pm

thsom wrote:When you guys use helical rotors, what are your main beams? If they are 1/8 by 1/8 wouldn't that get really heavy because you would have four pieces of 1/8 by 1/8 balsa wood of say 36-37 cm length each?
I use 1/16 by 1/16, though I believe some use 1/32 by 1/16. I can't imagine 1/8 by 1/8 is terribly aerodynamic, and the extra strength really isn't necessary.
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