Demon Lord Razgriz said:Comparing it to the X2 designs, this X3 seems to be forgetting a key detail in the X2 design. X2 has a coaxial tandem rotor, which negates the primary problem with single rotors at high speed losing lift on one side.
F-14D said:The Fairey Rotodyne (more or less) flies again!
AeroFranz said:I would extend comparisons to the even earlier Fairey Gyrodyne (spell check?). This may not fly as fast as a tiltrotor or even the X2, but there is much to commend in experimenting with something that is relatively low-risk and still delivers respectable performance.
AeroFranz said:I agree the X-2 seems to have the better solution, with higher speed potential. But there is much to commend in Eurocopter's approach. They could not rely on the wealth of data gathered by Sikorsky on the various LHX/ABC programs, yet they litterally cobbled the thing together using parts they had lying around, got the thing in the air without spending a fortune (my guess) and it most likely works.
Matej said:The small note: X-49 torque force is eliminated by the big moving surfaces inside the duct, that are changing the direction of the air flow. But how it works on the X3? The different thrust of the propellers on the each side?
Matej said:The small note: X-49 torque force is eliminated by the big moving surfaces inside the duct, that are changing the direction of the air flow. But how it works on the X3? The different thrust of the propellers on the each side?
TomS said:While the X-49A (and the notional SpeedHawk production version) has a third engine to drive the pusher, that would not absolutely necessary for other aircraft in that general configuration. I can't see any reason you couldn't have the prop driven off the same transmission that feeds the rotor (a la X2 and X3).
Demon Lord Razgriz said:Comparing it to the X2 designs, this X3 seems to be forgetting a key detail in the X2 design. X2 has a coaxial tandem rotor, which negates the primary problem with single rotors at high speed losing lift on one side. And I doubt those stub wings will generate much lift with the rotor disrupting the air flow over them.
amsci99 said:Demon Lord Razgriz said:Comparing it to the X2 designs, this X3 seems to be forgetting a key detail in the X2 design. X2 has a coaxial tandem rotor, which negates the primary problem with single rotors at high speed losing lift on one side. And I doubt those stub wings will generate much lift with the rotor disrupting the air flow over them.
"What is new on the X3 is that Eurocopter appears to be using differential power/pitch on the props to counter torque instead of a tail rotor or fantail. That looks like the big difference between X3 and the compound helos of the 1960s. Both the props and the rotor appear to be driven off a common transmission by the two turboshaft engines.
How does this compare to the US solution, the tilt-rotor? Bad news: You still have the old compound-helo problem of driving the rotor sideways through the sky, which may result in efficient cruise speed capping out at a lower figure. "
Following are the comments of Bill Sweetman on the Aviation Week ARES Blog. Pardon my ignorance, so does it mean that the X3 has to sacrifice power to counter the torque problem and any compound helicopter (including the X-49) will have a similar problem? I was always under the impression that the wings would offload the rotor at high speed and power dedicated to any torque cancellation would be reduced.
AeroFranz said:hmmm..I'm curious about the lack of wings on the X-2. I'm not saying that it needs them, there are the aforementioned increases in Wempty and download in hover, but doesn't offloading the rotor delay some of the compressibility problems at the tips (because of lower CL requirements)?
I'm trying to figure out what is being traded here by having it or not.
AeroFranz said:hmmm..I'm curious about the lack of wings on the X-2. I'm not saying that it needs them, there are the aforementioned increases in Wempty and download in hover, but doesn't offloading the rotor delay some of the compressibility problems at the tips (because of lower CL requirements)?
I'm trying to figure out what is being traded here by having it or not.
amsci99 said:Demon Lord Razgriz said:Comparing it to the X2 designs, this X3 seems to be forgetting a key detail in the X2 design. X2 has a coaxial tandem rotor, which negates the primary problem with single rotors at high speed losing lift on one side. And I doubt those stub wings will generate much lift with the rotor disrupting the air flow over them.
"What is new on the X3 is that Eurocopter appears to be using differential power/pitch on the props to counter torque instead of a tail rotor or fantail. That looks like the big difference between X3 and the compound helos of the 1960s. Both the props and the rotor appear to be driven off a common transmission by the two turboshaft engines.
How does this compare to the US solution, the tilt-rotor? Bad news: You still have the old compound-helo problem of driving the rotor sideways through the sky, which may result in efficient cruise speed capping out at a lower figure. "
Following are the comments of Bill Sweetman on the Aviation Week ARES Blog. Pardon my ignorance, so does it mean that the X3 has to sacrifice power to counter the torque problem and any compound helicopter (including the X-49) will have a similar problem? I was always under the impression that the wings would offload the rotor at high speed and power dedicated to any torque cancellation would be reduced.
TomS said:But I'm annoyed to see tilt-rotor called "the US solution" since there are plenty of US non-tiltrotor concepts (X2, X-49, Canard-rotor-wing, etc) and one European company is signed up to tiltrotor (Augusta and the Model 609).
Tailspin Turtle said:Offloading the rotor with the wing doesn't solve the compressibility problem as much as not needing the lift means you can reduce the rotor rpm to keep the advancing tip from approaching its critical Mach number. One of the benefits of the ABC is that you can slow the rotors down for high speed flight but also get lift from the rotors and not worry about retreating blade stall.
I wonder how the required power compares with a standard anti-torque tail rotor, since the moment arm is much smaller.
... troops can enter and exit side doors directly without having to worry about walking into propellers ...
AeroFranz said:Tailspin Turtle said:Offloading the rotor with the wing doesn't solve the compressibility problem as much as not needing the lift means you can reduce the rotor rpm to keep the advancing tip from approaching its critical Mach number. One of the benefits of the ABC is that you can slow the rotors down for high speed flight but also get lift from the rotors and not worry about retreating blade stall.
Oh, ok. I guess that's different but related to what I meant. Both operating CL and tip speed affect compressibility onset (I am working from fixed wing theory here, hope this is valid for rotors too). The two are related by the amount of thrust to be generated. I am not sure which is more effective in building a margin on compressibility, whether to keep RPM constant and use a lower rotor CL (thanks to wing generated lift) or viceversa.