Oh no..... You are opening a heated topic here Bruce!
Bruce, IMHO here is my answer.
Any of todays "
typical " sport gyroplanes -
and these include everything from Bone Stock RAF2000's, to Early Bone Stock Aircommands, to Bandits, Bensens, Ken Brock Machines, Dominators, Sparrowhawks, Sportcopters, Falcons, Sportsters, Twinstars, etc..... etc.... - Can be flown with a reasonable safety margin no matter if they have a horizontal stab and no matter if the thrustline is centered with the Vertical CG or not.
What does it take to fly any gyroplane?
Training.
With proper training, you can fly any gyro. The fact that a gyro has a thrustline offset, or no stab..... or has all the modern advancements in design such as CLT and a good effective stab, A gyro is still a gyro and they will all
basically fly the same.
With the proper training, you can learn to fly a machine with a high thrustline such as the RAF, and even without the addition of a horizontal stab. People have done it for years, and people will likely continue to do so for the forseeable future.
Now there is a catch!
No matter how much training you recieve, a gyro with a high thrustline can, and still wants to do the dreaded power pushover. It is only your training to respond to the machine in certain situations that prevents the power pushover from happening. So in a nutshell, it will always be up to the pilot to insure that the gyro remains in normal flight, and it is really the pilot that makes these ships stay in the sky. Again, this is possible with the right kind of training and the proper amount of training.
The difference a CLT - centerline trust - arrangement makes on a gyroplane is it eliminates the possiblity of the power pushover. When you understand what a power pushover is.... it is clearly obvious why the CLT gyro can not do it.
A power pushover - also called a buntover - happens when the rotordisk is unloaded and the engines power setting is still at a mid to high setting. There is many situations where the rotor can unload... Such as at the top of a fast steep climb, in a strong downdraft, in stormy or gusty wind conditions, AND most popular is once pilot induced osicilations are allowed to get to the point of something simular to the fast climb and pushover at the top of the climb.
When the rotordisk is unloaded, the gyro experiences more or less a G factor of zero. You feel like your floating, such as at the top of a hill when riding a roller coaster. Since the gyros weight is normally suspended - for a lack of a better term - from the rotor, the rotor is normally under at least 1 positive G. As the gyro flys around the rotor is holding the gyro under the rotor, and it is making lift, just like the wings on a airplane. This lift factor also called the rotor thrust vector, is what sort of magically allows any gyro to fly. Even gyros with no horizontal stabs and with the thrustline placed above, below or on the vertical center of gravity. In other words, the rotors thrustline vector can allow what is more or less a out of balance gyro fly, and even fly reasonably well.
When you unload the rotor, experience Zero G, or whatever you want to call it.... You
TAKE AWAY the rotor thrustline vector. When you take the RTLV away you basically take away any stability factor the rotor blades add to that gyro. When this happens the gyro is nothing more than a go kart in the sky that is basically out of control until you reload the rotor and get the RTLV back into effect.
The bad thing about a High Thrustline gyro, such as a RAF2000, is that during the time the blades are unloaded and the RTLV is gone the gyro is now going to fly, react and respond to forces as they happen based around the gyros
VERTICAL CENTER OF GRAVITY. So if you find through hangtests and caculations that the VCG of your RAF2000 is located 12 inches below the location of the center of the prop - which is where the thrustline is - then the propellers thrust is pushing the the gyro higher than the CG, creating a forward tumbling force that can and will become a Power pushover- Bunt over.
It is the same as grabbing a basketball and pushing on the top third of the ball... it will roll forward quite easily. Push on the middle of the ball and it will just want to slide fowards, not roll at all.
The Centerline thrust machines are designed to place the Vertical center of gravity inline with -
or in some cases like my Dominator, slightly above -
the Thrustline.
In doing this, the CLT gyro, if flown into a condition that results in the rotors unloading, it does not have any force trying to tumble it foward into a bunt, even if the power if left at maximum power. It is this that makes the CLT gyro not able to Bunt Over and this is the reason the Sparrowhawk exists. To offer what the RAF offers but to do it in a design that eliminates the possibility of Bunt overs.
Don't forget that once a Buntover begins, there is absolutely no recovery and nothing you can do to save yourself. It has also been caculated that on a high powered machine such as the RAF2000 that it only takes a fraction of a second to Buntover, once the rotors are unloaded if the power setting is at a high setting when the rotors become unloaded. So there is no recovery, and little time to react on the onset of a unloading.
Again like I said in the beginning of the post, if your properly trained, you can normally detect and prevent the rotor from ever becoming unloaded to begin with, and you could very possibly fly a HTL gyro like a RAF2000 till you are too old to get in the seat and reach the starter button. BUT..... then again, we are all prone to screw up at some point or another. It is possible to get behind in flying the gyro and end up unloaded and in a Buntover. It has happened to several experienced gyropilots, several high time airline pilots flying gyros, and many many Newbies to gyros.
It is alot like handling a loaded and cocked handgun with no safety switch. If your trained and careful you can handle that gun forever. But the one time your careless, that gun can and will go off. A HTL gyro is EXACTLY the same. For this reason, I and many many others believe the best choice in gyroplanes FOR EVERY PILOT, NEW TO FLYING GYROS OR NOT, is a CLT machine. It is safer than a HLT machine without dispute.
A horizontal stab is also a not needed item on a gyroplane. All a Horizontal stab does is to dampen the gyro airframe in pitch. It makes PIO less possible and helps smooth out the ride in gusts and thermals. It does the same thing as a Shock aborber does for your screen - storm doors. It just dampens things.
So far most Horizontal stabs are not powerful enough on their own to counter a Buntover at slow speeds. At very highspeeds, a properly designed and installed stab can make enough force on it's own to counter the force of a HTL in the event that the rotor becomes unloaded. But again, at the slower speeds a stab is just a shock absorber in pitch and makes getting into a Zero G situation more difficult, by making the gyro fly more stable.
Even a CLT gyro benifits from a Horizontal stab. It dampens the gyro in pitch and makes for a smoother ride.
So these are just some facts and thoughts to maybe help you with your decision. Again, any gyro can be flown with enough proper training. A HTL gyro can buntover, a CLT gyro can not. Any gyro with a Horizontal stab will fly better and have a more stable ride than one without.
You will read alot of comments on stability on this forum. Some people I think are confused on what stability is. To some folks stability is just a gyro that flys reasonably well and you can trim it out and fly hands off for periods of time. To others a stable gyro is one that can be flown for long periods of time with the control stick locked in position, preventing it from moving to counter pitch excursions. Me myself, I consider a gyro to be stable only if it can not or is extremely highly unlikely to be possible of going into a mode of flight of which there is no recovery - A Bunt over on a gyro, or say for example a spin in a airplane with the CG past aft limits....