Pacific Flyer story

[asra]

quote:Originally posted by Whitelighter69I didn't know you could overpower a gyro!!! What flying characteristics does it produce???????Hi Gavin,just a quick summary of what we are all going on about....Gyro's have a "Centre of Gravity" (like everything).If you have an engine positioned so that its line of thrust is significantly above the CofG, and the rotors get "unloaded" due to pilot error, or wind shear, or something,and you put too much power on, and you don't apply the correct piloting technique in time,then the thrust can roll the whole machine forward around the CofGresulting in a probably fatal crash. Its called PPO - power push over.This may be highly speculative, as there are not many survivors of PPO to discuss it with.There is an excellent paper about the theory of it on the asra site under technical papers - stability, by Jean Fourcade.The solution is to get the thrustline of the engine to pass near to or below the CofG. The the engine thrust tends to push the nose up, rather than down, which is inherently stable.High thrustline, or low CofG can also be corrected by good pilotting technique, if you are experienced and know what to react to, and how to react, or by lowering the line of thrust, or by raising the CofG, or both.Tim's point is that Raising the CofG makes the machine less stable on the ground, and there is a limit to how far you can lower the prop without turning it into a rotary hoe.There are other ways to improve ground stability, but most cost something in weight. So if you want it stable in the airand on the ground, then you lose out on power and agility. But then, instability in the air is more likely to be fatal than on the ground. Thats just damned expensive.You should have seen my instructor jump when I tapped forward on the stick a little too sharply, which results in rotor becoming unloaded, etc. He knew the feel of the warning signs. I didn't, and probably still won't recognise it soon enough to correct.The risk of PPO can also be reduced by a good horizontal stabiliser, a fair way back where it has lots of leverage to resist sudden attitude changes. But of course this makes the machine more stable and less fun to fly.There is also a torque effect from the engine, so a big powerful engine can cause the machine to tilt sideways, which isn't really a problem, but adds another variable that an inexperienced pilot has to come to terms with, and affects the way the machine turns left and right.All in all, PPO is a relatively rare occurrence. (we think. There are enough crashes where we don't ever know the reasons.) Several factors have to come together, and the pilot has not fail to compensate soon enough. Its not a worry experienced pilots.Suppose the change of it happening is about once in a thousand hours,and it takes about a thousand hours before you get enough experience to deal with it. Then, if you are Mr. average and lady luck is playing fair, then you are probably OK. But if the situation occurs in the first hundred hours, then you are proabably toast.Personally, I'd rather adjust the machine than take the risk.Sure all the experienced guys can tell you its not a problem.It wasn't a problem for them now, and lady luck didn't shaft them in their early days.The people I want to hear from are the theoreticians who know how to avoid the problem (Jean Fourcade), or the people who had it happen to them and somehow managed to live to tell the tale,or to the ghosts of the others. Anyone know a good medium?Not such a quick summary after all. sorry.Serverlan

[asra]

[Tim]

quote:Originally posted by Johnit is unfortunate that as gyros have been 'improved' since Bensen, stability has apparently suffered. John, I do not believe that this is so. The earlier style machines that I flew were so short coupled and without stabilizer that they required constant pilot attention in just about any conditions. Most of the more up to date machines will fly hands off, and in the case of machines like Bill Drewery's, Robby Glen's and the Hunter Valley's two seater, if a student starts porpoising, all the instructor has to do is to put one finger on the stick and hold it dead still and the porpoising instantly stops. Surely this attests to a degree of stability. I used these machines as a sample because they are what is considered to be "high thrust line"I believe that the main problem with stability of the newer machines is their greatly improved performance and speed capability, and the fact that any "level" of pilot can get one in the air so easily that you can fly without having spent many hours learning the tedious basics.Tim McClure

[asra]

[asra]

tim there is no way in hell anyone could fly my gyro hands free before it went to paulw drewery

[Tim]

G'day Bill. Your Gyro was the same configuration as Robby Glen's so it should have been able to fly hands off. Of course you would have to trim it correctly first, the same as you would for any gyro. I am glad to hear that you are enjoying flying it.Tim McClure

[asra]

John said, "If you want stability for cruising around, then tractor is the way to go, if you want it agile, then you want something like the 'Feral'." What if someone wanted something in between, where then.[?]Aussie Paul.[]www.firebirdgyros.com

[asra]

tim you would think ross would be able to trim it then and i can tell he would never try itw drewery

[asra]

Yeah Paul, I guess you then want the prop in the middle, a bit inconvenient if that's where you want to sit.What I was actually driving at, was that with a tractor it's much easier to get a decent arm for the Hz stab to work on. Now while in many ways CLT is desirable in all aircraft, there are plenty that use other ways of achieving acceptable stability.As people move to more powerfull engines and/or bigger props to me it seems that these are more easily accomodated up the front. This of course could be a bit of a worry for those of us who want to mix it with pelicans[:0]John EvansThink logically and do things well, think laterally and do things better.