At the middle of the page 192 of this discussion it is the "Pendulum rocket fallacy" article of Jim Bowery.
Please read it and try to understand it.
If you can’t, let me know to help.
It clarifies, among others, the effect of the center of gravity on the stability of a rocket or of a Flyer.
For the rest you ask, here is a quote from the “Device Technical Report” (at https://www.pattakon.com/GoFly/index.html
) as filed in the GoFly / BOEING contest:
In case of malfunction of the one engine, or in case one propeller hits an obstacle and falls apart, or in case a transmission tooth belt is broken, or . . ., the “healthy” engine-propellers-set is sufficient for a safe landing.
With the one only engine running at 9,000rpm (mean piston speed: 9m/sec) and driving its two 3-blade 39’’ diameter / 28’’ pitch propellers at 3750rpm (2.4:1 reduction) the total thrust force is calculated at 250lb (115Kp), the tip speed is 195m/sec (57% of the sound velocity), the power required by the running engine is 65bhp (which means: 36.8 lb*ft (50mN) of torque from 21.5ci (350cc) capacity, i.e. 142mN/lt specific torque, which is attainable by a good 2-stroke: the 2-stroke Rotax 850 ETEC provides more than 20% more specific torque (175mN/lt).
End of Quote
And here is the Atlas human powered helicopter that won the Sikorsky prize:
It is a Portable Flyer with two pairs of counter-rotating propellers.
It flies controllably.
At 1:02 of the video you can see a square on the ground. The rider has to stay inside this 10mx10m square, otherwise he is calcelled.
The following slide is at the 1:17 of the video:
Spot on how much the rider is offset to the left of the image.
Because his Portable Flyer is near to cross the right side of the 10mx10m square, and desperately tries to correct by displacing his center of gravity relative to the overall thrust axis.