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Old Feb 16, 2012, 04:38 AM
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Slow motion coaxial video

Slow motion coaxial video

Coaxial rotor/contra-rotation RC helicopter slow mo (1 min 28 sec)
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Old Feb 16, 2012, 05:16 AM
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Zurich
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Interesting!

It is hard to tell exactly from that video, but it seems that the upper rotor has more pitch than the lower. That is the exact reverse of fullsize practice and of what is required for best performance and overall efficiency.

When correctly designed (I understand that these are toys ... but that is not a valid excuse for poor engineering), both rotors should generally have the same RPM, which also seems not to be the case here: when the lower rotor, operating in the accelerated airflow from above, has greater pitch than the upper, both rotors WILL have the same RPM. This is a proven fact and not just theory, as I often use a strobe to tune and adjust my coaxs .... and they HOP!

Lee
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Old Feb 16, 2012, 11:22 AM
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The flybar introduces drag and changes the flight dynamics of the upper head. They will never be the same rpm as the rpm of each is constantly changing to keep the helicopter pointed in a specific direction. The helicopter in the video is spinning counter clockwise. So of course the rotors are spinning at different speeds.

The only way they'd be the same rpm would be on a full sized version that had variable pitch on either one or both heads. You are over thinking these simple toys.
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Old Feb 18, 2012, 04:46 AM
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Quote:
Originally Posted by Barak1001 View Post
The flybar introduces drag and changes the flight dynamics of the upper head. They will never be the same rpm as the rpm of each is constantly changing to keep the helicopter pointed in a specific direction. The helicopter in the video is spinning counter clockwise. So of course the rotors are spinning at different speeds.

The only way they'd be the same rpm would be on a full sized version that had variable pitch on either one or both heads. You are over thinking these simple toys.
Nice try, but you are unfortunately wrong on all counts.

I humbly request you to more carefully re-read my comment and to think it over in more depth [for ex., the flybar AND the swashplate, etc., have some influence].

I totally stand by my fully researched and real-life "toy-coax"-proven statements.

Lee
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Old Feb 18, 2012, 03:03 PM
Fly em if ya got em.
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I consider Xlcrlee to be somewhat an authority on these toy copters. I remember the work he did back in the day with airhoggs. Might wanna listen to him. Lee
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Old Feb 18, 2012, 03:05 PM
Fly em if ya got em.
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Plus, I like his name. ahahahahaha
Lee
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Old Feb 18, 2012, 06:11 PM
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I don't care if he's an "authority" or not, the helicopter in the video is spinning counter clockwise, it's impossible for the rotors to be turning at the same speed. After all varying the speed of one motor is how toy coaxials yaw. The only way for both heads to have the same rpm would be for the heads to be mechanically linked, like on a variable pitch version. For instance the Helibaby which is a real life example of a single motor coaxial toy that has variable pitch on a single head to induce yaw.

Saying I'm wrong on all counts is idiotic and contrary to how these helicopters actually fly. There are real life versions of these coaxials with a single motor that worked exactly as I described. On the other hand there are no dual motor fixed pitch coaxials that can yaw without a speed difference between one head and the other.

Since I'm wrong on all counts, explain to me how the fixed pitch helicopter in the video is supposed to induce yaw with both heads spinning at identical rpm?
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Old Feb 18, 2012, 07:35 PM
Fly em if ya got em.
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I would not dare argue this with either of you. Xlclee and you are both way smarter than I am. I have only heard of one copter that deals with yaw different than what you describe about motor rpm's. I am ignorant and bow to your knowledge. Lee
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Old Feb 21, 2012, 05:45 AM
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"read carefully" includes properly interpreting the meaning of "generally", for ex.

I also stand by my previous post. IF you wish, you can likely learn something from it. Your choice.


the other
Lee
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Old Feb 21, 2012, 05:54 AM
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Syma S110G @420 to 1000 fps (4 min 34 sec)
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Old Feb 22, 2012, 06:03 AM
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Nice vid!

In a well-designed "toy" coax, except for yawing or aerodynamic trim problems, the pitches are so engineered as to generally keep the rotors at the same RPM to maximize motor efficiency and overall power usage, since the motors have the same power source. and of course, that won't happen during initial start and during landing spin-down, as the mechanical friction forces are in those cases significant, whereas in flight the aerodynamic forces (lift & drag) are far greater.

L
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Old Mar 09, 2012, 01:51 AM
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Another good video.

RC Toy chopper in flight In UltraSlo motion (1 min 9 sec)
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Old Mar 09, 2012, 07:39 AM
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So far as I can see, even this toy coax has its rotors turning generally at the same speed [watch how often they pass each other at the same circumferential points, except when yawing, etc.].

Nice vid ....

L
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