Sikorsky X2 coaxial heli developments.
There is a new X2 video on aero news network. Views of the cockpit, closeups of the head ect. They posted it Thursday 3/20 on aero-news tv, article title is "Aero-TV Gets A Close Look At Sikorsky's Exotic X2!"
http://www.aero-news.net/
-- IFMU
http://www.aero-news.net/
-- IFMU
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Hub Fairings
Which one are they going with?
Sikorsky's patent 7,229,251 ~ Rotor hub fairing system for a counter-rotating, coaxial rotor system, ->[Images], ->[Drawings] show a number of interesting and radical aerodynamic considerations.
Sikorsky's patent 7,229,251 ~ Rotor hub fairing system for a counter-rotating, coaxial rotor system, ->[Images], ->[Drawings] show a number of interesting and radical aerodynamic considerations.
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The patent can be seen on google with full images
here is a link to the images
http://www.google.com/patents?id=Aje..._pages&cad=1_1
The fun starts after fig. 3a
here is a link to the images
http://www.google.com/patents?id=Aje..._pages&cad=1_1
The fun starts after fig. 3a
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Congratulations X2 team for being the star of HeliExpo 2008! Thanks also to Peter Grant for giving a clear overview of the project development status. I wish Sikorsky every success with this clever development of the advancing blade concept.
CEFOSKEY, i'm actually glad the fairing wasn't there for all the publicity. Those rotorheads are extremely clever and it would be a shame to hide them. That said, the weathervane fairing is also a very clever development, and i can't wait to see it installed. What was the thinking behind the opposed twin cambered horizontal aerofoils on the patent? Are you trying to ensure flow stability behind the mast, like the doghouse platform on a single rotor mast design? I am also trying to work out what is the function of what looks like cooling fins in the position to be occupied by the fairing? They look a little too complex to just be bearing mounting flanges. Is the weathervane motorised, so that what is seen is a mounting spline?
I also notice the patent helo looks interestingly like an X2 development of S76 - now that would really be something!
CEFOSKEY, i'm actually glad the fairing wasn't there for all the publicity. Those rotorheads are extremely clever and it would be a shame to hide them. That said, the weathervane fairing is also a very clever development, and i can't wait to see it installed. What was the thinking behind the opposed twin cambered horizontal aerofoils on the patent? Are you trying to ensure flow stability behind the mast, like the doghouse platform on a single rotor mast design? I am also trying to work out what is the function of what looks like cooling fins in the position to be occupied by the fairing? They look a little too complex to just be bearing mounting flanges. Is the weathervane motorised, so that what is seen is a mounting spline?
I also notice the patent helo looks interestingly like an X2 development of S76 - now that would really be something!
The patent can be seen on google with full images
here is a link to the images
http://www.google.com/patents?id=Aje..._pages&cad=1_1
The fun starts after fig. 3a
here is a link to the images
http://www.google.com/patents?id=Aje..._pages&cad=1_1
The fun starts after fig. 3a
Edited to add: Doh. Should have read the whole of the proceeding post before posting.
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CEOFOSKEY,
Thanks for the additional information.
On a related subject;
A rotorhub provides no lift and much drag. For a number of years now an idea has been bouncing around my few remaining neurons. It consists of giving the "doughnut fairings" a larger diameter and thereby a shallower elliptical X-section.
If this "doughnut" was allowed to teeter as it rotated and it was held up at the front-end of the mast, it might act as a lifting body.
Dave
Thanks for the additional information.
On a related subject;
A rotorhub provides no lift and much drag. For a number of years now an idea has been bouncing around my few remaining neurons. It consists of giving the "doughnut fairings" a larger diameter and thereby a shallower elliptical X-section.
If this "doughnut" was allowed to teeter as it rotated and it was held up at the front-end of the mast, it might act as a lifting body.
Dave
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So how about it S-76 drivers: Would you swap your ride for an otherwise similar machine, but that could get the boss there at >4 times UK motorway speeds? 
CEFOSKEY, thanks for the explanation. Even the plain vanilla fairing looks good, but those vortex generating turning vanes are a nice touch. I'm still confused by what looks like corrugation on the rotor shaft between the hubs. This is inside the machined casting structure for attaching the fairing bearings.
Dave, the hub fairing works best by blocking the blade root vortices which would otherwise form. Simply avoiding the fountain effect will improve rotor efficiency. It is a mechanically very simple way to achieve a useful gain.
CEFOSKEY, thanks for the explanation. Even the plain vanilla fairing looks good, but those vortex generating turning vanes are a nice touch. I'm still confused by what looks like corrugation on the rotor shaft between the hubs. This is inside the machined casting structure for attaching the fairing bearings.
Dave, the hub fairing works best by blocking the blade root vortices which would otherwise form. Simply avoiding the fountain effect will improve rotor efficiency. It is a mechanically very simple way to achieve a useful gain.
Last edited by Graviman; 25th Mar 2008 at 20:05.
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Mart,
The rotorhub represented 50% of the drag (parasitic only - I think) on the earlier ABC. This was a serious concern.
IMHO, a secondary concern may the rotorhub generated turbulence, plus the root vorticies, due to their interactaction with the propeller (which did not exist on the earlier ABC).
Why do you believe that the 'fountain effect' is detrimental? It is probably detrimental to a tiltrotor during hover, but it could be beneficial to a helicopter in ground effect.
Dave
The rotorhub represented 50% of the drag (parasitic only - I think) on the earlier ABC. This was a serious concern.
IMHO, a secondary concern may the rotorhub generated turbulence, plus the root vorticies, due to their interactaction with the propeller (which did not exist on the earlier ABC).
Why do you believe that the 'fountain effect' is detrimental? It is probably detrimental to a tiltrotor during hover, but it could be beneficial to a helicopter in ground effect.
Dave
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New downloads available on Sikorsky's website
http://www.sikorsky.com/sik/Attachme...07_Trifold.pdf
looks like a glamour shot with the hub fairing on.
Also some coment on the attack varient mock up. Why not have an integrated flir to reduce drag instead of the nose ball? Why have the cockpit as a complete bubble? It would seem that integrating the rear of the cockpit into the fuse would make better sense. Why have the exhaust coming out of two flaring cones? I would think that an internal vent like the Comanche had would be better. Also the tail boom could be styled to flow tapering from the rotor hub down to the tail prop. Overall the concept drawing looks cool but feels more like a franken drawing of stealth fighter jet mated to a bell cobra with x2 mechanics.
http://www.sikorsky.com/sik/Attachme...07_Trifold.pdf
looks like a glamour shot with the hub fairing on.
Also some coment on the attack varient mock up. Why not have an integrated flir to reduce drag instead of the nose ball? Why have the cockpit as a complete bubble? It would seem that integrating the rear of the cockpit into the fuse would make better sense. Why have the exhaust coming out of two flaring cones? I would think that an internal vent like the Comanche had would be better. Also the tail boom could be styled to flow tapering from the rotor hub down to the tail prop. Overall the concept drawing looks cool but feels more like a franken drawing of stealth fighter jet mated to a bell cobra with x2 mechanics.
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Dave, the fountain effect is the result of the slightly higher static pressure under the rotor forcing air past the rotor hub (now that Rotorheads have established that there is a measurable pressure increase). Since leakage causes lost lift for a given power requirement, it represents a loss in Figure of Merit. The best FM is always obtained for a uniform induced velocity. Above the fuselage this induced velocity clearly needs to be zero, but not negative.
The hub doughnut fairings, designed by CEFOSKEY, will reduce drag by reducing hub turbulence with the turning vanes forcing the flow to remain attached until the seperation point. It is like all things a compromise, but FM will go up.
I can understand how your mechanism would reduce drag, by aligning the "flying saucer" to the induced airflow. But this rotor system already has two swash plates, and i can't think of an aerodynamic way to make the fairings sit where they would need to be. The turning vanes are a simpler solution.
Bat1, great poster there.
The hub doughnut fairings, designed by CEFOSKEY, will reduce drag by reducing hub turbulence with the turning vanes forcing the flow to remain attached until the seperation point. It is like all things a compromise, but FM will go up.
I can understand how your mechanism would reduce drag, by aligning the "flying saucer" to the induced airflow. But this rotor system already has two swash plates, and i can't think of an aerodynamic way to make the fairings sit where they would need to be. The turning vanes are a simpler solution.
Bat1, great poster there.
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Mart,
Thank you for defining 'fountain effect'.
Perhaps you may wish to look a little further into the subject. You may wish to consider its effect on an 'aerodynamically dirty' underbody, such as open landing gear doors.
Perhaps a Gimbel joint at the center of the lifting-body. This will put it's 'theoretical' pitch axis at 50% of chord. Then give it a slight 'dish' shape between the four blade roots.
Dave
Thank you for defining 'fountain effect'.
Perhaps you may wish to look a little further into the subject. You may wish to consider its effect on an 'aerodynamically dirty' underbody, such as open landing gear doors.
i can't think of an aerodynamic way to make the fairings sit where they would need to be.
Dave
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Thanks Cefoskey,
I guess I am a little suprised that the 3d rendering of the attack version was also patented. Seems like a waste of time for just a concept drawing for publicity purposes. Though in the end whatever brings in the money is worth doing.
I guess I am a little suprised that the 3d rendering of the attack version was also patented. Seems like a waste of time for just a concept drawing for publicity purposes. Though in the end whatever brings in the money is worth doing.
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CEFOSKEY,
You are probably correct, in that the complexity etc. may not justify any possible advantage.
The idea is from the Department of Demented Designs.
It is one of many considerations for directing sufficient air at the upper quadrant of the propeller disk on the UniCopter concept. This problem may not be so serious on the X2.
The X-wing is a good looking craft. A stated objective in one of the patents was "to provide a stopped rotor X-wing aircraft with low drag and high speed forward flight, including aerodynamically efficient supersonic operation;". It appears that the craft was flown on its wings, but never flown with the rotorhead attached.
Dave
You are probably correct, in that the complexity etc. may not justify any possible advantage.
The idea is from the Department of Demented Designs.
It is one of many considerations for directing sufficient air at the upper quadrant of the propeller disk on the UniCopter concept. This problem may not be so serious on the X2.
The X-wing is a good looking craft. A stated objective in one of the patents was "to provide a stopped rotor X-wing aircraft with low drag and high speed forward flight, including aerodynamically efficient supersonic operation;". It appears that the craft was flown on its wings, but never flown with the rotorhead attached.
Dave
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Originally Posted by CEFOSKEY
How they convinced themselves this was going to work before the days of computerized CFD is beyond me.
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A drawing looking just like the rendering was patented
http://www.google.com/patents?vid=USPATD526269
Five other concept patents are listed on the unicopter website
http://www.unicopter.com/1465.html
http://www.google.com/patents?vid=USPATD526269
Five other concept patents are listed on the unicopter website
http://www.unicopter.com/1465.html
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The following article is not directly related to the ABC coaxial, however it is an interesting evaluation of the coaxial configuration.
Operational considerations for a co-axial, contra-rotating rotor.
Operational considerations for a co-axial, contra-rotating rotor.
Some of the statements there seem hokey to me. Like:
If this was true, airplanes everywhere would be stalling their propellers at high speed, as 'air blows in the direction it is blowing air.'
What about autorotation? We have batted this back and forth before, I think in this thread. Coaxes and synchrocopters are bad here. Generally they need long tails & rudders to cope. Look at the KA50, the K-max, ect. Plus I thought it was differential torque, what is this differential rotational inertia thingy he refers to?
-- IFMU
As air blows through the tail rotor in the direction it is blowing air, efficiency is lost and the rotor pitch needs to be increased (possibly leading to a tail rotor stall).
High level of yaw authority, extending well into the flight envelope. As yaw authority is not totally limited to that of the aerodynamic capabilities of a tail rotor, being dependant on that of the differential rotational inertia applied to each disc, being used to generate a yawing motion, operability extends beyond that of the tail rotor system.
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IFMU,
This is only speculation, however it would appear that the text on the web page is a slightly crude translation of writings from another language, perhaps Russian.
The first quote may relate to a Kamov affectionado believing that a helicopter with tail rotor is unable to stay on target under gusty conditions.
In the second quote he may have used 'inertia' when he meant 'torque'. I understand that the coaxial has a very powerful yaw authority, due to the differential torque. In autorotation the pedals must be reversed. It appears that Kaman and Kellett initially thought they could get away with shorter tail booms because they did not have a tail rotor. Look at the size of Flettner's vertical stabilizer.
Just speculation.
Dave
This is only speculation, however it would appear that the text on the web page is a slightly crude translation of writings from another language, perhaps Russian.
The first quote may relate to a Kamov affectionado believing that a helicopter with tail rotor is unable to stay on target under gusty conditions.
In the second quote he may have used 'inertia' when he meant 'torque'. I understand that the coaxial has a very powerful yaw authority, due to the differential torque. In autorotation the pedals must be reversed. It appears that Kaman and Kellett initially thought they could get away with shorter tail booms because they did not have a tail rotor. Look at the size of Flettner's vertical stabilizer.
Just speculation.
Dave
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The Gyrodyne QH-50 series of antisubmarine drones solved the coaxial autorotation yaw control reversal problem using rotor tip mounted drag brakes. Many QH-50 models have no directional control surfaces at all and those that do have small fixed vertical fin(s) indicating they are for forward flight stability not fundamental yaw control.
There's lots of information at http://www.gyrodynehelicopters.com/.
Bob
There's lots of information at http://www.gyrodynehelicopters.com/.
Bob