Tina
Senior Member
Understood Ferran, I see your point and more to think about when it comes to helicopter verse auto gyro. I am still new to all this and learning more all the time.
Dennis and Tina, the autogyro is older (first flight in 1923) than helicopter (first real flight in 1936). But once the helicopter was a fact, just at the end of WWII, all the investigation efforts were directed to helicopters and the gyro was entirely forgotten. Mr. Bensen found a new application to an existing technology; by really he didn’t created anything.
Our gyro blades are not innovations, in fact the airfoil (everybody uses the same one) was developed a lot of years ago and there are not investigation and development programs in benefit of autogyros. This is a very different history from helicopters. Isn't it?
Ferràn
Dennis,
IMHO, a partially powered rotor, plus pusher propeller, may be the most efficient for higher cruise speed.
Dave
[...] mechanical losses in driving the main rotor via a transmission are far less than aerodynamically driving it via autorotation.
Dennis, we are comparing helicopter versus gyro performances. Obviously the rotor tail sucks more power hovering than at cruise speed (8% versus 4%). But it still sucks a 4% of the required power in cruise. And tail rotor’s drag is bigger (much bigger) than vertical fin’s one. And helicopters have vertical fins too. But this is only part of the story.
Have you ever heard about inherent side slip? The tail rotor is always producing a lateral thrust, in order to compensate main rotor torque over fuselage. But you cannot compensate a torque (what main rotor is doing) with a moment (what tail rotor is doing). The undesired result is sideways translating tendency that must be compensated by tilting the main rotor. In other words, all conventional helicopters are always flying whit a side slip. And this creates more drag and reduces overall efficiency.
Dennis,
Thanks for sharing your experience.
How much power do you think would need to be applied directly to the gyro rotor (i.e. PPR) to achieve the same cruise efficieny as a helicopter? That is, assuming all other things being equal (weight, drag, etc.)
I'm not questioning anyone's credentials, but I find it hard to believe that Dennis Fetters' statement on tail rotor power needs:
depending on gross weight, a tail-rotor uses 20% to 25% or even more of the power needed to hover
is perhaps too general. Good performance in hovering flight is a key feature of rescue helicopters, and the fact is that the conventional 'Sikorsky', i. e. main + tail rotor configuration has been used for S&R helicopters, both light and heavy ones. I find it hard to believe that S&R helicopters may need such a big fraction of its power for the tail rotor while hovering.
Perhaps there are other factors here, apart from gross weight, like boom length and tail rotor diameter.
Rgds
XXavier