![]() ![]() So the outer tips each create a force of XY in one rotational direction while the inner tips each create a force of 1/2XY in the other rotational direction. But it has a much shorter moment arm, for our example let's say it's 1/2Y. They also create a force of X and it is in the opposite direction of the outer rotor tips. Now consider the inner ends of those rotors. Note that the direction of the force of both outer rotor tips is in the same rotational direction with respect to the center of the airframe. So the outer two tips of the clockwise rotors create a force of let's say X which is multiplied by their distance from the center Y. But the forces applied to the airframe are multiplied by their distance from the center of the airframe. The clockwise rotors are beating the heck out of the air, pushing air and creating lots of drag and the create the same force all the way around their path. The feathered counterclockwise rotors aren't creating much in the way of other forces. This means that there is no vehicle rotation due to different rotor speeds. What will happen? Seriously, think about it for a minute before reading on.įirst consider that all rotors are rotating the same speed. This won't create any lift but consider what would happen if the two clockwise rotors were set at 90 degrees pitch (straight up and down) and the two counterclockwise rotors were set at zero pitch. Or increase some, lower others, differential thrust can hold the same altitude. Differential thrust makes you go up and down. In the case of a rotor aircraft, thrust is in a downward direction. Secondly, in the example of the variable pitch, glow quadcopter, again in the process changing pitch of 2 rotors and reducing pitch of 2 rotors does create differential thrust, but it's not the differential thrust that creates the yaw. In the process of changing rotor speeds on those fixed pitch props, they do change thrust, but that's not what causes the yaw of the vehicle. Increasing the rotational speed of two rotors and slowing the others causes yaw due to conservation or rotary motion. The generalization that it's "The same as all of them, differential thrust", is still wrong.įirst of all, most quadcopters don't use differential thrust to create yaw. But nobody else was bold enough to posit an opinion on how it worked. Increase the pitch on two rotors, decrease on the other two rotors and the outer end rotor drag overcomes the inner end rotor drag, yawing the entire airframe. I'm only a physics fan (physics phan?) and an engineer who enjoys thinking out how to build things. They'll act like paddles and push the airframe in the counterclockwise direction.Īgain, I'm no expert. ![]() Since outer tips of both blades are moving in the clockwise direction with relation to the entire aircraft and they are farther out than the inner tips, they have a longer moment arm. At high pitch and at opposite corners of the aircraft, the clockwise rotors are each creating forcers other than the downward push of their rotors. But there's another force they are creating. ![]() The two high pitched rotors are doing all the work. No lift, not much drag, just hanging out. Those counterclockwise rotors aren't doing much of anything. So increase the clockwise rotors to an extreme pitch and the counterclockwise rotors to zero pitch. When I go through these kind of mental puzzles I tend to think to extremes. ![]() If you increase the pitch on the two clockwise rotors and decrease the pitch on the counterclockwise rotors so that the total lift stays constant, what happens? All of them variable pitch instead of variable speed. Two rotors going one direction, two going the other. But after you asked, I realized that it might be something different. I didn't think about it at all when I watched the video. ![]()
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