Coaxial RC Helicopter weirdness

[Wolfala]

Hey ya'll,

I was bored today, so I went out flying a Coaxial electric RC helicopter to remove the boredom. The winds were calm outside - everything started off ok. Hovered for about 30 seconds to adjust the trim, and then climbed the aircraft up to about 20 meters to maneuver it around. After a little while, I started a descent at around 3 meters per second. The descent rate seemed to increase, and I thought it was maybe settling with power, so I pitched forward and increased the power to the rotors. The engines spooled up and I could hear the rotors beating - when at around 10 feet there was a very loud CRACK. Both rotors stopped dead, and it crashed to the ground.

After the initial WTF and thinking I was in some sort of vortex ring state I thought it was not mast bumping because the tail is still attached. And the pictures I took showed the tail clean. But when I looked at the rest of it, the top rotor seemed to impact the lower rotor with literally 1 rotor slicing into the other. I thought the whole point of coaxial rotors was so that even if they are both coning they won't intersect paths. And this was a case where the rotor was mostly not underload, until I applied power to arrest the descent.

Anyways, on to the pictures.

http://s145.photobucket.com/albums/r207/wolfala/RC%20Helicopter%20rotors/










Hypothetically, if 1 rotor was spooling up faster then the other during the application of power - could 1 rotor have found itself coning into the others area of rotation? I don't know how else to look at it since I am not a helicopter guy.

Wolf

[GtoRA2]

I have one like that, and it wouldn't fly because on rotor hub had stripped and was spinning inside the gear so everything looked ok but one rotor never spun up fast enough to get it airborne.

[Yossarian]

I have a very simple R/C helicopter (it coincidentally has two main rotors as well), where a similar thing happened.  It was flying in midair and suddenly the rotors stopped spinning and it crashed.

When I looked inside it, what had happened was the motor was dead (I forgot exactly what caused it).  Check your motor, and see if there are any obstructions inside of the motor, and if not you may want to try replacing the motor.

<S>

Yossarian

P.S. I just read the rest of your post more carefully...but I don't see how one motor could have sped up more...

[Wolfala]

I was just told something that caught me by surprise by another helicopter guy.

His response was essentially like this:

"I fly RC helicopters, and what you encountered is normal for coaxial birds. Few things to remember, the bottom blade will get loaded before the top blade. Because of that as soon as you apply power, the bottom baled will cone up, and then Baam.. crash.

 

With coaxial helicopters, power should be applied slowly and descent should be gradual, no way around it.

 

You selected coaxial heli for ease of flying and in return you got some limitations including: no aerobatic performance, blade strikes for abrupt control changes, docile performance. On another hand, the learning curve is quick and the positive feedback gets you flying again.

 

Good luck with the next flight."

[Kaw1000]

I use packing tape on my rotor blades on my CX2

Its the tape with the string in it. Just run a strip of tape
on the underside of rotor blade the trim with a exacto knife.

Makes the blades stiffer and stronger...less breaks and bending

[Maverick]

I have a Cx2 as well and had the blade impact thing happen more than once. I learned that jamming the power was not a good way to save it. The other thing you did was to jam it into forward flight. The sudden inputs caused the rotor clack. The blades are not terribly rigid in the mounting and flex quite a bit.