Dark Wombat,

It probably isnt the motor stuttering. What happens is when wind hits the rotor disk, can change the lift produced. The effects are varied depending on the angle that the wind hits the rotor disc and the direction it comes in from.

Wind blowing level into advancing blades causes a gain in lift, into retreating blades you get a drop in lift. Its most noticable in a hover. The good news is that since you've managed to notice it, it means your getting pretty good at hovering. It means you've managed to get your hover stable enough to start noticing changes in the heli's aerodynamics. Beginners learning to hover usually dont notice it that much because the heli is moving all over the place anyway.

Im sure youve heard about retreating blade stall. With these micro heli's its actually possible to get retreating blade stall in a hover! Retreating blade stall normally occurs at high forward speed. The air is moving in over the retreating blade at such a high speed that the blade loses lift and "stalls". The heli will roll violently to the right. I was outside hovering in a really strong wind after a local hurricane. Im not positive, but I honestly believe I experienced retreating blade stall in a hover. I had the nose into the wind, and the heli pitched right REALLY quick. I tried it again with the tail into the wind, and sure enough it tipped left.

As far as the vibration problem. Ive actually been checking the blades that come from the factory. Ive found a couple of sets that had a warped blade. Occasionally I've also found that both blades have the same warp or twist. I think they match them up at the factory as best they can. When you just swap out one blade, its most likely a result of one of the blades having a slightly different "warp" than the other blade. Ive even found one set of flat blades in a crash kit that had one severly warped blade. I would recommend checking out the blades before you purchase them. Look for the best set you can find. Anytime you change out blades it normally requires readjustment.

Also dont just weigh them, BALANCE them. Make sure that they balance good. You can have two blades that weigh the same, but have them out of balance. You could have a blade that weighs 10 grams, but has the weight concentrated in the tip and another one of the same weight, but the weight is concentrated near the root.

If you want to get an idea of how this works. Get your heli all trimmed out. Now obviously the flybar weights are the same weight. Move one of the weights in a little. Now rev it up.. It will shake like CRAZY. Each end of the flybar weighs the same, but the weight is off center.