This section is intended as a layman's guide to why the CC will not 'bunt-over', allowing for its design and flying configuration (that is, it is designed not to exprience the infamous Gyro 'buntover').
TERMINOLOGY: The more technical terms used in the Gyro community include PPO (Power Push Over = 'Buntover' or 'Pushover'). And PIO (Pilot Induced Oscillations or 'Porpoising').
How does this infamous 'buntover' occur - this requires looking at a particular Gyro configuration and to best illustrate the problem, let us take consider one such 'guilty' Gyro design .. In doing so I will divide the Gyo into 3 essential elements
TERMINOLOGY:
1=Rotor Drag, 2=Parasitic Drag, 3=Propulsion Thrust Line
Because of typical design constraints the pusher prop is mounted between the rotor (drag) and the pendulum weight (mass and drag) of the Gyro. This means that the effective thrust is between two points of drag. Should the Gyro lose one or the other point of drag, at a time of high engine thrust and slow speed (minimal weather-cocking from the horizontal stabiliser assuming one is fitted) then there will be a condition where the craft could snap-roll. It is all a balance of forces and conditions.
When a gyro is travelling forward at a fast speed, there is a natural weather cocking effect taking place. The effective wind is keeping the gyro facing forward and level - all things being equal the pusher prop is providing its thrust, in balance, between the rotor drag and pendulum mass drag all impacted by the leverage of the tail horizontal stabilizer.
Now picture if either the rotor drag or the pendulum mass drag and the tail horizontal stabilizer were suddenly not there due to some unusual flight condition or mechanical failure (or in the case of the tail, design).
If the pendulum mass of the pilot were to fall away the pusher prop would be thrusting below the rotor drag and thus at slow speeds and with heavy thrust, could cause an up-and-over backward snap-roll around the rotor drag. But this particular circumstance is a most unlikely one for a number of reasons.
Conversely, if the gyro were flying forward at a slow speed and the rotor lift and drag were suddenly not there, and the engine was providing high thrust, at that instant the pusher prop could and may well spin the gyro around the mass of the pilot and craft - a forward snap-roll, or buntover.
One element not mentioned up to this point is the added complexity of the rotor gyroscopic effect called precession. As the prop thrust tries to pitch the craft forward, the rotor even though not supplying the needed lift/drag is still a spinning gyroscope and the rotor will attempt to roll left or right (depending on which direction the rotor blades spin) as soon as the tilting spindle hits the stops of the teeter hinge, brought on by the pitching action of the gyro frame as the prop keeps thrusting forward. (Most if not all gyros have, looking from above, counter-clockwise rotating rotors and so following gyroscopic precession will pitch forward then roll left).
The result of the above is that the prop is pushing forward then the rotor starts rolling left - a tumbling action results and also the rotor blades usually start hacking into the vertical stabilizer as they bend downwards (due to loss of inertia and negative Gs) and in some gyro designs the prop will also hack into the rotor blades - Altogether very ugly.
If we consider the actual dynamics of a buntover, it is a condition where the thrust line is above the instantaneous combined mass of the craft's rotor and pendulum weight (parasitic drag), and the tail horizontal stabilizer weather-cocking is insufficient to prevent the thrust pitching the craft over this instantaneous mass of the craft. Put another way ... the prop thrust force has taken the least path of resistance and combined with the rolling moment of the rotor, once the teeter stops are hit by the tilting spindle, the craft tumbles.
The buntover's violent pitching forward can also lead to a 'precession' stall of the rotor - this is most likely to occur on low inertia or lightweight rotors and happens when the bunover is so strong that the gyroscopic force from precession rapidly (split seconds) slows or simply stalls the rotation of the rotor.
If one looks closely at the CC one can see how the tail-boom was constructed to allow the 7' 10" dia prop to swing clear whilst its main thrust is right through the centerline of the craft's body.
In essence, the CarterCopter does mainly 2 and 4 and a bit of 3. But also the fact that the CC 'unloads' its rotor, combined with 2 ensures that the CC will not do CarterWheels through the sky.
Doug Marker