Once again, this forum is mainly peacefull homebuilding oriented, not high speed warrior rotorcraft... You certainly saw the video on the GYRODYNE, this craft with two tandem seats: it's all we need!!!:violin: :der:Andre, OK but if we are going to get serious I've got to vote against the Coaxial configuration.
For homebuilt rotorcraft; the thrust-to-power ratio is a serious concern, particularly when using 2-stroke engines (not mandatory). The coaxial has a significantly inferior thrust-to-power ratio in comparison to bilateral twin main rotor configurations. For private purposes, at 100 mph, it's not a problem...
For fast future craft (that's out of concern!!!); I suspect that the coaxial, such as Sikorsky's X2 may have a terminal problem (AMEN!). The earlier Sikorsky S-69 ABC was unable to achieve the top speed objective, due to excessive vibration. It had provisions for vibration damping devices but for some reason they never added them.
The following is copied from PPRuNe. It may explain the reason for this problem and an inability for the coaxial configuration to excape it.
"Consider the side of the craft coaxial ABC] where the upper blades are advancing and the lower blades are retreating, during cruise. The use of ABC means that the upper (advancing) blades are providing most of the thrust. The lower (retreating) blades are meeting the airflow with a sharp leading edge.(????)
We know that a sharp leading edge can only operate within a small range of AOA. We also know that there is an amount of time required for the sectors of an airfoil to recover from a stall. In addition, we know that the lower blades on this side of the craft are passing in and out of the thrust of the upper blades 8 times per rotor revolution (FALSE, at cruise, no blade passes in the downwash of the upper blades!!!!).
IMHO, it is reasonable to assume that segments of the lower retreating blades will passing in and out of stall, at rates of up to 8 times per RRPM."
The bilateral twin main rotor configurations should not be subjected to this specific concern.(for homebuilding purposes: too complex, too large, not compact enough, too much dead weight, too much airframe blown during take off, etc...and above all: i don't like side by side rotors, except synchropters...)
A side-by-side helicopter with an empty weight that is nearly half that of a comparable coaxial means that many of your concerns are, or can easily be, eliminated.too complex, too large, not compact enough, too much dead weight, too much airframe blown during take off, etc.
I believe that my remarks and information are directed at the coaxial configuration. They are not the promotion of any specific configuration.Sorry Dave, this thread deals with homebuilt coaxial helicopters
Cita, I respect you because of your impressive background, and do not mean to contradict you. However, all the photos and videos I have seen show Mr. Schöffman hovering just a few feet above ground -- less than his own body height. Do you have better pictures or videos?"out of ground effect" is roughly 1 1/2 times rotor diameter.With only 2.13 meters diameter,Mr. Schöffman flies regularly out of ground effect.
I have seen him reaching a height of about 10 meters last year in Wels (Austria).
Having observed it at close range, do you think it could be improved to a notable degree?Bruno,
Thanks for the flowers!
"Herr Schöffman" would be flying "out of ground effect" theoretically speaking when his feet would be roughly 1.2 m above the ground.
Even this short clip shows Mr. Schöffman a few times higher than this.
I agree though that even the 30+ hp he's using seems marginal with the extreme small rotor diameter and I guess that the 10m altitude I saw last year is probably the best he can do under near perfect conditions.
I had the chance to examine his little helo and the simplicity in both design and construction is beyond believe.
Although very sencitive (spelling?) I'm surprised at how well he's able to control the craft,after all 2.13 m diameter is VERY small,even for a UL helo.