Sikorsky X2 coaxial heli developments.
Originally Posted by Glory
No retractable u/c,
Cool!
-- IFMU
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Glory, what you are not understanding is that this prototype helicopter has the potential to significantly improve top speed without severly affecting it's primary role as a VTOL machine compared to other helicopters. This technology is also scalable to medium size and larger helicopters. Such machines would be more expensive to operate, but would have a great impact on the flexibility of the helicopter concept. There is also no compromise to the helicopter's ability to autorotate.
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I made a recent decision to get back into engine design (as well as returning to Cambridgeshire), and am enjoying the challenges associated with the role. That said, i wish the guys at Sikorsky-Schweizer rapid prototyping facility in Horseheads (N.Y.), and Sikorsky's flight-test facility at West Palm Beach (Fla.) every success in expanding the envelope of what promises to be an amazing actual flying machine!
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I made a recent decision to get back into engine design (as well as returning to Cambridgeshire), and am enjoying the challenges associated with the role. That said, i wish the guys at Sikorsky-Schweizer rapid prototyping facility in Horseheads (N.Y.), and Sikorsky's flight-test facility at West Palm Beach (Fla.) every success in expanding the envelope of what promises to be an amazing actual flying machine!
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Mart,
At this years Annual AHS Forum,
'Nikolsky lecturer and former Sikorsky engineer Dr. Ken Rosen told the audience, "We have a wonderfully creative workforce... What is missing is leadership." He contrasted yesterday's drive for tiltrotors and X-Wings with today's "sparkling mediocrity" and he noted, "When a company is in the hands of active exciting leaders, thats when a concept can take hold."'
Dr. Ken Rosen also said "We are not in a sunset industry..."
It would be interesting to know who he meant by "We", particularly when considering that there are 60,000 American engineering students in universities as compared to 900,000 Chinese engineering students in universities.
Mart, this is no time to leave Aerodynamics.
I made a recent decision to get back into engine design ... and am enjoying the challenges associated with the role.
'Nikolsky lecturer and former Sikorsky engineer Dr. Ken Rosen told the audience, "We have a wonderfully creative workforce... What is missing is leadership." He contrasted yesterday's drive for tiltrotors and X-Wings with today's "sparkling mediocrity" and he noted, "When a company is in the hands of active exciting leaders, thats when a concept can take hold."'
Dr. Ken Rosen also said "We are not in a sunset industry..."
It would be interesting to know who he meant by "We", particularly when considering that there are 60,000 American engineering students in universities as compared to 900,000 Chinese engineering students in universities.
Mart, this is no time to leave Aerodynamics.
Viewing the photos of the flight (which were accompanied by all of the "best ever" required comments to get the bonus) I would suggest move the pilot station to the back cockpit and use vertically challenged pilots to avoid a decap during maneuvers.
The Sultan
The Sultan
Originally Posted by The Sultan
Viewing the photos of the flight (which were accompanied by all of the "best ever" required comments to get the bonus) I would suggest move the pilot station to the back cockpit and use vertically challenged pilots to avoid a decap during maneuvers.
-- IFMU
IFMU
There are stiff rotors, but no actual rigid rotors. Simple dynamics. Helicopter history has shown everyone underestimates the flexing of the blades. Proto 60, 61 63 and 64 are clear evidence of this.
The Sultan
There are stiff rotors, but no actual rigid rotors. Simple dynamics. Helicopter history has shown everyone underestimates the flexing of the blades. Proto 60, 61 63 and 64 are clear evidence of this.
The Sultan
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Widgeon
Yes. State Farm was the first company to ever provide tip-weight insurance for helicopters.
It can be seen in the picture that the craft has exceptionally heavy tip-weights, for dynamic stiffness. The insurance was to protect the company, should the tip weights come off during flight.
_____________
Trivia.
The following was only a rumor.
A few years ago the blade manufacture for the X2 produced a prototype UAV. It had extruded aluminum blades. Then steel shafts were epoxied into them as leading edge weights. Rumor has it that during a display in front of armed services personnel the epoxy in one of the blades cracked and launched its shaft.
I wonder if the insurance company would have paid if some of the generals had been 'shish kabobed' with the flying shaft.
I wonder is the State Farm Insurance sign has any significance
It can be seen in the picture that the craft has exceptionally heavy tip-weights, for dynamic stiffness. The insurance was to protect the company, should the tip weights come off during flight.
_____________
Trivia.
The following was only a rumor.
A few years ago the blade manufacture for the X2 produced a prototype UAV. It had extruded aluminum blades. Then steel shafts were epoxied into them as leading edge weights. Rumor has it that during a display in front of armed services personnel the epoxy in one of the blades cracked and launched its shaft.
I wonder if the insurance company would have paid if some of the generals had been 'shish kabobed' with the flying shaft.
Last edited by Dave_Jackson; 1st Sep 2008 at 00:03.
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The Sultan, as a fan of the ill fated AH-56 Cheyenne i feel your advice is well worth heeding. The big difficulty is that the longer the rotor mast, the more flexibility you design into the rotor system. I imagine that the current design came after a lot of careful consideration, and simulation, of the dynamics. From the pace to date, i don't imagine Sikorsky will be rushing the flight test program until the dynamics are proven out. Maybe CEFOSKEY can give us more insight into the passage of the program from CAD to test?
CEFOSKEY, i'm looking forward to that video! Just knowing that X2 is a real flying machine is exciting enough, but one of my favourite MPEGs is a highspeed flyover of Commanche at West Palm Beach - the noise alone is amazing!
Dave, despite Nick's kind help, i was recently passed over by Westlands. Being honest, from BAE experience, i suspect that a paycut would have been required. My current role allows me to gain the experience in analysis and test that i crave, while being able afford the cost of UK living. Actually my first job has tempted me to write my own Vortex Panel Method software:
Vortex Panel Method
CEFOSKEY, i'm looking forward to that video! Just knowing that X2 is a real flying machine is exciting enough, but one of my favourite MPEGs is a highspeed flyover of Commanche at West Palm Beach - the noise alone is amazing!
Dave, despite Nick's kind help, i was recently passed over by Westlands. Being honest, from BAE experience, i suspect that a paycut would have been required. My current role allows me to gain the experience in analysis and test that i crave, while being able afford the cost of UK living. Actually my first job has tempted me to write my own Vortex Panel Method software:
Vortex Panel Method
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Slowrotor, i have no wish to start that debate again, but the Hiller photo can be seen as a demonstration in the difference between statics and dynamics. What it really comes down to is how much the blades weigh in comparison with the two guys straddling them. The deflection can be proportioned to frequency, which from the photo implies a relatively high frequency 1st order flapping mode.
My earlier debate with Dave was that this still does not significantly reduce the pitch link lead angle. Basically one 1/4 cycle of the spin and bending stiffened blade is not much less azimuth than the 1/4 cycle of a spin only stiffened blade, for such a long blade. So dynamically even a high effective hinge offset blade can be seen as relatively soft.
Don't forget that for a blade strike to occur you really need two things: reduced g on the fuselage and large cyclic inputs causing blade flexure. For the first point i'm sure we can rely on Chief TP Kevin Bredenbeck not to rush into anything without thinking about it. For the second point i'm sure that a relatively stiff rotor will reduce the cyclic input required for a given pitch/roll rate. There is the uncertainty of a new FBW system, but this will have had most of it's shakedown on the Schweizer 333 development prototype.
All in all guys, lets not hex this thing before Sikorsky have had a chance to prove it.
My earlier debate with Dave was that this still does not significantly reduce the pitch link lead angle. Basically one 1/4 cycle of the spin and bending stiffened blade is not much less azimuth than the 1/4 cycle of a spin only stiffened blade, for such a long blade. So dynamically even a high effective hinge offset blade can be seen as relatively soft.
Don't forget that for a blade strike to occur you really need two things: reduced g on the fuselage and large cyclic inputs causing blade flexure. For the first point i'm sure we can rely on Chief TP Kevin Bredenbeck not to rush into anything without thinking about it. For the second point i'm sure that a relatively stiff rotor will reduce the cyclic input required for a given pitch/roll rate. There is the uncertainty of a new FBW system, but this will have had most of it's shakedown on the Schweizer 333 development prototype.
All in all guys, lets not hex this thing before Sikorsky have had a chance to prove it.
Last edited by Graviman; 2nd Sep 2008 at 11:13.
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Mart,
The Vortex Panel Method software looks interesting.
Have you seen the the freeware program NVFoil, and had a chance to compare the two?
You may be underestimating the rigidity of Sikorsky's ABC blades.
[Source ~ Rotor-Wing Aerodynamics ~ W.Z. Stepniewski / C.N. Keys ~ Book I]
Sikorsky S-69 (XH-59A) ABC ~ Flapping hinge offset: Flapping frequency ratio (v/n) ≈ 1.4 [p.39]. From the graph [ p.18] it appears that the equivalent (virtual) flapping hinge offset will be approximately at 50% of rotor radius.
The information that is available on the new X2-ABC indicates that Sikorsky is increasing the rigidity even further.
This page on phase lag may be informative
Dave
The Vortex Panel Method software looks interesting.
Have you seen the the freeware program NVFoil, and had a chance to compare the two?
You may be underestimating the rigidity of Sikorsky's ABC blades.
[Source ~ Rotor-Wing Aerodynamics ~ W.Z. Stepniewski / C.N. Keys ~ Book I]
Sikorsky S-69 (XH-59A) ABC ~ Flapping hinge offset: Flapping frequency ratio (v/n) ≈ 1.4 [p.39]. From the graph [ p.18] it appears that the equivalent (virtual) flapping hinge offset will be approximately at 50% of rotor radius.
The information that is available on the new X2-ABC indicates that Sikorsky is increasing the rigidity even further.
This page on phase lag may be informative
Dave
Don't forget that for a teetering blade strike to occur you really need two things: reduced g on the fuselage and large cyclic inputs. For the first point i'm sure we can rely on Chief TP Kevin Bredenbeck not to rush into anything without thinking about it
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212man, i've reworded that post to avoid further confusion... 
Dave, from memory the graph on p.18 of Stepniewski is a linear approximation, which is only valid at low hinge offsets. Using
(e/R)effective = 2[ (wn / W)^2 - 1 ] / [1 + 2 (wn / W)^2 ]
gives for wn/W=1.4 a value e/R=0.39 or 39% , but i came unstuck using the standard Prouty lead angle calcs for very high wn/W fan blades.
An easier simplification to work out lead angle is that wn/W of 1.4 means that 90 degrees of blade bending cycle will occur in (90 deg)/1.4 = 64 degrees of the azimuth, so requiring a delta3 angle of 90 - 64 = 26 degrees. The aerodynamic damping (Lock number) will also have a small effect by altering the simple harmonic motion phase angle, as per formula on wikipedia:
Harmonic oscillator - Wikipedia, the free encyclopedia
I'll have to figure how to convert Lock number to damping factor r at some point.
For whatever reason i've struggled to get NVfoil to run, and have found the vortex panel JAVA a nice straight forward utility for any arbitrary aerofoil shape.
Dave, from memory the graph on p.18 of Stepniewski is a linear approximation, which is only valid at low hinge offsets. Using
(e/R)effective = 2[ (wn / W)^2 - 1 ] / [1 + 2 (wn / W)^2 ]
gives for wn/W=1.4 a value e/R=0.39 or 39% , but i came unstuck using the standard Prouty lead angle calcs for very high wn/W fan blades.
An easier simplification to work out lead angle is that wn/W of 1.4 means that 90 degrees of blade bending cycle will occur in (90 deg)/1.4 = 64 degrees of the azimuth, so requiring a delta3 angle of 90 - 64 = 26 degrees. The aerodynamic damping (Lock number) will also have a small effect by altering the simple harmonic motion phase angle, as per formula on wikipedia:
Harmonic oscillator - Wikipedia, the free encyclopedia
I'll have to figure how to convert Lock number to damping factor r at some point.
For whatever reason i've struggled to get NVfoil to run, and have found the vortex panel JAVA a nice straight forward utility for any arbitrary aerofoil shape.
Last edited by Graviman; 3rd Sep 2008 at 11:24.
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Two bits of information
Jim Kagdis, advanced program manager said;
"The T800-powered X2 will fly initially with the tail-mounted propeller installed, but not connected, Kagdis says. The demonstrator will be used as a 'flying wind tunnel' to determine the aerodynamic interaction between the rotor and propulsor. Other areas on interest will include optimization of the rotor shaft angle for performance and blade tip clearance for maneuvers, the company says."
________________
The AHS Montréal – Ottawa Chapter invites you to a presentation by
Jim Kagdis – Sikorsky Aircraft Corporation, “X2 Technology Demonstrator”
Thursday October 2nd , 2008 at 5:30 pm
"The T800-powered X2 will fly initially with the tail-mounted propeller installed, but not connected, Kagdis says. The demonstrator will be used as a 'flying wind tunnel' to determine the aerodynamic interaction between the rotor and propulsor. Other areas on interest will include optimization of the rotor shaft angle for performance and blade tip clearance for maneuvers, the company says."
________________
The AHS Montréal – Ottawa Chapter invites you to a presentation by
Jim Kagdis – Sikorsky Aircraft Corporation, “X2 Technology Demonstrator”
Thursday October 2nd , 2008 at 5:30 pm
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CEFOSKEY, you missed a trick here - just slow down the frame rate until the flight looks nice and controlled. 
It may just be that this machine has a much snappier response rate than most helis, since most machines just ignore cyclic stirring. Possibly the gain factor on the control just needs to be reduced. Is this a force control sidestick or is there a reasonable amount of movement?
At this stage just some decent resolution photos would do me!
Showing engineers a low resolution blow up of what might be a helicopter doesn't do the X2 first flight justice...
It may just be that this machine has a much snappier response rate than most helis, since most machines just ignore cyclic stirring. Possibly the gain factor on the control just needs to be reduced. Is this a force control sidestick or is there a reasonable amount of movement?
At this stage just some decent resolution photos would do me!
Showing engineers a low resolution blow up of what might be a helicopter doesn't do the X2 first flight justice...
