The blade tips of the two rotors will be closer at the crossing azimuths on the Dragonfly then they are on the SynchroLite. This will mean that less Opposed Longitudinal Cyclic can be applied to provide yaw; because of gusts etc.

It may be necessary to use Differential Collective Pitch; but it has disadvantages. Note that the rear quadrants are the biggest concern since this is where the blade tips are closing on each.

Yaw by Tip Brake causes a rotation about the axis of the rotor with the applied brakes. This results in the desired rotation about the craft's Z-axis, but it also results in nose up rotation about the craft's Y-axis. The nose up is due to the additional torque about the Y-axis.

Yaw by Opposed Collective does not change the total torque about the Y-axis. But, it does introduce an undesired rotation consisting of a roll about the X-axis. This is caused by the unequal thrust of the two rotors.

Summation: In addition to the application of the tip brakes on one rotor, additional forward cyclic must be applied on the other rotor. This method should work during autorotative touchdown; when there is no forward velocity.

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Yaw by Differential Collective causes a rotation about the axis of the rotor with the increased pitch. This results in the desired rotation about the craft's Y-axis, but it also results in nose up rotation about the craft's Z-axis, and a roll about the craft's X-axis.

Differential Collective will increase the torque, the thrust and the coning angle on one rotor. To offset this torque and its cross-coupling to nose up pitch, forward cyclic will be required on the other rotor. To offset this thrust and resulting roll, inward lateral cyclic will be required on the other rotor.

The increased forward and lateral cyclic will elevated the blade tips at the back of this rotor, but the good news is that the increased cone on the other rotor will have elevated it's blade tips. This is good for the back, where the blades are closing but is not good for the front. At least in the front there is separating motion.

Summation: In addition to the transfer of some thrust to one rotor, additional lateral cyclic must be applied on the other rotor. This method will probably not work during autorotation touchdown; when there is no forward velocity.

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Which retains the greatest rotor to rotor clearance? Perhaps the reduction of differential collective rotor clearance should be compared to the reduction of clearance by raising the tip brakes.

Which is mechanically cleaner; the tip brake mixer or the differential collective mixer?