Rotors

Re: Rotors

Postby jander14indoor on Wed Feb 22, 2012 11:55 pm

It would PROBABLY improve the air flow to fit them flush between the spars. Lower drag > more efficient. As to how to cut them it should be possible to rig up a jig, but these are compound cuts. Hmmm, have to think on that. Anyway, right now I cut, try fit, cuss, cut, try fit, cry, I get there.

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Re: Rotors

Postby thedoctor on Thu Feb 23, 2012 12:11 am

To cut my ribs so that they lie flush between the rotors, I normally just take a piece bigger than the rib size i will actually need (bigger in length) and let the ends overlap the spars. I then take one of those nice straight edge (long chisel) blades and line it up flush with the lower spar. Then, keeping the blade at the same angle as it was before, I cut the rib; that way, it should be at the correct angle. I then glue this correct end at the right angle and cut the rib end for the upper spar in the same way. I use something like those blocky Pentel erasers to provide support for the rib while i cut it. If you do this correctly and don't do dumb things like gluing the bottom end of the rib so the rib isn't lying against the spar anymore, you should get ribs with ends that match pretty dang close the angles of the spars and thus lie flush between them well. There are probably more precise ways of doing this than the way I do it (I hope you could understand all that mess), but that's how I've been doing it, and it gets good results. Just be warned that it gets much harder to cut ribs this way the closer you get to the center of your rotor because the angles become so steep.
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Re: Rotors

Postby illusionist on Thu Feb 23, 2012 11:12 pm

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.
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Re: Rotors

Postby thedoctor on Thu Feb 23, 2012 11:26 pm

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.

Well I've never done that because I've never tested anything to that extent, but I guess if you make the fixed rotor fit into the motor stick like 3D puzzle pieces that might work...or you could just attach them with ambroid cement and use acetone when you want to take the rotor off, but that might damage the motor stick after a while. As of right now, that's all I can think of...
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Re: Rotors

Postby chalker7 on Fri Feb 24, 2012 12:59 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.

Sure, if you made a couple large paper tubes like you might use in Wright Stuff you can make rotors that plug in and out.
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Re: Rotors

Postby jander14indoor on Fri Feb 24, 2012 11:02 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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Re: Rotors

Postby illusionist on Fri Feb 24, 2012 11:49 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).

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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

Postby Skleintop3141 on Sat Feb 25, 2012 12:01 pm

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

Postby blue cobra on Sat Feb 25, 2012 2:47 pm

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

Postby illusionist on Sat Feb 25, 2012 3:02 pm

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

Postby Skleintop3141 on Sat Feb 25, 2012 3:13 pm

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

Postby illusionist on Sun Feb 26, 2012 7:05 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

Postby chia on Sun Feb 26, 2012 8:28 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

Postby thsom on Mon Feb 27, 2012 2:06 am

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

Postby chia on Mon Feb 27, 2012 2:14 am

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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