Sikorsky X2 coaxial heli developments.
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X2 rotor speeds
"No clutches, guys. The whole drive system is tied together, rotors and prop shaft."
NickLappos,
So if I understand you correctly, you're saying the X2 TD drivetrain is a single, fixed gear ratio. With rotor speed changes effected only through engine throttling (ie. like V-22), and torque split controlled through rotor and prop blade pitch settings?
It's not that a multi-speed geared rotorcraft transmission can't be made to work with a conventional friction clutch for shifting. Boeing's (unmanned) A160 uses such a system, as did the Bell XV-3 (I believe). Although neither has been/was shifted during flight on a regular basis due to safety concerns.
You also say that the ABC TD could slow the rotor to 82% via engine speed throttling, which sounds like the engine guys (Pratt?) were being very conservative, even with mid-70's turbine engine technology. I'd guess that a modern turboshaft engine with variable compressor geometry, digital FADEC and a well sorted combustor could probably run satisfactorily at 70% engine speed or less.
Would something like a 100% to 70% speed range be satisfactory for what the X2 wants to do?
Thanks for the input.
riff_raff
NickLappos,
So if I understand you correctly, you're saying the X2 TD drivetrain is a single, fixed gear ratio. With rotor speed changes effected only through engine throttling (ie. like V-22), and torque split controlled through rotor and prop blade pitch settings?
It's not that a multi-speed geared rotorcraft transmission can't be made to work with a conventional friction clutch for shifting. Boeing's (unmanned) A160 uses such a system, as did the Bell XV-3 (I believe). Although neither has been/was shifted during flight on a regular basis due to safety concerns.
You also say that the ABC TD could slow the rotor to 82% via engine speed throttling, which sounds like the engine guys (Pratt?) were being very conservative, even with mid-70's turbine engine technology. I'd guess that a modern turboshaft engine with variable compressor geometry, digital FADEC and a well sorted combustor could probably run satisfactorily at 70% engine speed or less.
Would something like a 100% to 70% speed range be satisfactory for what the X2 wants to do?
Thanks for the input.
riff_raff
Last edited by riff_raff; 27th Apr 2010 at 06:09.
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Mart,
You have previously commented on the coaxial-ABC operating in an autorotative state. You may therefore find this report of value, due to the large stall region at the root end of the retreating blades. Observations in flight of the region of stalled flow over the blades of an autogiro rotor
Dave
Do you have any section drawings available for X2 blades? ... My heli performance program can now flap a single rotor to equality, so I'd like to see how X2 lift/downwash looks with cyclic trimmed for forward flight.
Dave
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Dave,
I didn't realise blade element method went back as far as 1939. That paper ranks right up there with the paper by Doris Cohen explaining the origins of vortex panel method as applied to P45 Mustang!
The biggest difference between theory and practice is the distortion of inflow that results from ingested air passing over other blade elements first, and the distortion of outflow from fuselage/empennage. I'm going to try to account for both in my code once it starts to take shape. I briefly had the cyclic trimming to requested flight speed and climb last week - but it is early days and results are not always stable. Unfortunately my weekends are being gobbled up currently, since i am doing one last surge to get my phys degree finished.
I didn't realise blade element method went back as far as 1939. That paper ranks right up there with the paper by Doris Cohen explaining the origins of vortex panel method as applied to P45 Mustang!
The biggest difference between theory and practice is the distortion of inflow that results from ingested air passing over other blade elements first, and the distortion of outflow from fuselage/empennage. I'm going to try to account for both in my code once it starts to take shape. I briefly had the cyclic trimming to requested flight speed and climb last week - but it is early days and results are not always stable. Unfortunately my weekends are being gobbled up currently, since i am doing one last surge to get my phys degree finished.
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DATE:20/05/10
SOURCE:Flight International
Sikorsky X2 breaks helicopter speed barrier
By John Croft
Sikorsky reports that its X2 advancing blade concept technology demonstrator has achieved 168kt (311km/h) forward speed, putting the dual counter-rotating pusher-prop compound beyond the typical maximum speed for traditional helicopters and outside the reach of the company's S-76 chase vehicle's 155kt capability.
A follow-on flight, expected the week of 24 May, is to see X2 test pilot Kevin Bredenbeck accelerate the LHTEC T800-powered fly-by-wire pusher to 180kt, completing the third of four planned envelope expansion test phases. Phase four, which could begin as soon as mid-June, includes the first attempts to slow the X2's main rotors while opening the speed envelope to 250kt or more.
The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows.
Ahsish Bagai/Sikorsky
SOURCE:Flight International
Sikorsky X2 breaks helicopter speed barrier
By John Croft
Sikorsky reports that its X2 advancing blade concept technology demonstrator has achieved 168kt (311km/h) forward speed, putting the dual counter-rotating pusher-prop compound beyond the typical maximum speed for traditional helicopters and outside the reach of the company's S-76 chase vehicle's 155kt capability.
A follow-on flight, expected the week of 24 May, is to see X2 test pilot Kevin Bredenbeck accelerate the LHTEC T800-powered fly-by-wire pusher to 180kt, completing the third of four planned envelope expansion test phases. Phase four, which could begin as soon as mid-June, includes the first attempts to slow the X2's main rotors while opening the speed envelope to 250kt or more.
The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows.
Ahsish Bagai/Sikorsky
Article here, some more info than was in the clip in the post above:
sikorsky-x2-breaks-helicopter-speed-barrier.html
Interesting they used the photo from Airliners.net, and seem to have misspelled the photographer's name. I wonder if they goofed anything else up in their edit.
Looks like they can no longer consider using a Bell 47, R44, or Bell 206 to chase it. If this frustrates anybody they could always pick on the boorish spares in the PM article.
-- IFMU
sikorsky-x2-breaks-helicopter-speed-barrier.html
Interesting they used the photo from Airliners.net, and seem to have misspelled the photographer's name. I wonder if they goofed anything else up in their edit.
Looks like they can no longer consider using a Bell 47, R44, or Bell 206 to chase it. If this frustrates anybody they could always pick on the boorish spares in the PM article.
-- IFMU
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Originally Posted by IFMU
I wonder if they goofed anything else up in their edit.
I/C
Last edited by Ian Corrigible; 27th Aug 2014 at 18:10.
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Fantastic news!
Just when some folk were disparaging Sikorsky for technical issues that really are not that unusual for any new development.
So now begins the patient wait to see how the speed envelope unfolds.
Fingers crossed that all goes smoothly. But, remember this is a totally new type of helicopter so nothing can be rushed.
Good luck X2 development team.
Just when some folk were disparaging Sikorsky for technical issues that really are not that unusual for any new development.
So now begins the patient wait to see how the speed envelope unfolds.
Fingers crossed that all goes smoothly. But, remember this is a totally new type of helicopter so nothing can be rushed.
Good luck X2 development team.
Only 22 more knots and they reach the speed I have flown routinely in Cobras. 150+ more knots and they can see a tilt rotor pass them by if they look quickly.
The Sultan
The Sultan
I/C,
Where did that picture come from? I think that is the first pic I've seen on the web of the gear up. Looks great.
Great post Sultan. I had no idea that the cobras were so fast. Why do we even have Apaches?
-- IFMU
Where did that picture come from? I think that is the first pic I've seen on the web of the gear up. Looks great.
Great post Sultan. I had no idea that the cobras were so fast. Why do we even have Apaches?
-- IFMU
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Is Sikorsky getting some competition?
370 mph Helicopter?
370 mph Helicopter?
Vertolety Rossii (Russian Helicopter) made an interesting announcement recently in Moscow. They plan to spend $1 billion on researching what they are calling a fifth-generation helicopter. What are the requirements? It must be radar invisible, have extended range (no specifics on what that means,) be equipped with an intellectual arms system, be able to combat fighter jets and reach speeds of 370 mph. They believe that with additional government funding they could have it built in as soon as five years.
The figure of 370 mph is of particular interest to me. Currently, the speed record for a production helicopter was set back in 1986 using a modified Westland Lynx ZB500.
Westland G-Lynx Record Holder
That aircraft managed to reach 249.1 mph. What has been preventing us from going faster? Several items, including retreating blade stall which is a problem introduced due to the advancing blade generating more lift than the retreating blade. Another thing to consider is wave drag and the problems of supersonic blade tips. Apparently, they have a plan for how to get around these problems. Maybe they will be using a tilt-rotor setup such as the Osprey V-22? If so, can you really call it a helicopter still? But wait, was the Lynx really the fastest?
Sikorsky S-69
Back in the early 1970s, Sikorsky came up with a way to eliminate the retreating blade stall problem. They developed the S-69 as part of the Advancing Blade Concept program which used a co-axial design and a “feathering” of the blades. This eliminated retreating blade stall and allowed the advancing blades to carry the load. Maximum speed is listed as 322 mph. If Kamov is involved perhaps we’ll see (or not see) an evolution of the KA-50? Alternatively, if they don’t go with a co-axial setup, I’ll be really interested to know how they overcome RBS at such a high speed. What are your thoughts?
The figure of 370 mph is of particular interest to me. Currently, the speed record for a production helicopter was set back in 1986 using a modified Westland Lynx ZB500.
Westland G-Lynx Record Holder
That aircraft managed to reach 249.1 mph. What has been preventing us from going faster? Several items, including retreating blade stall which is a problem introduced due to the advancing blade generating more lift than the retreating blade. Another thing to consider is wave drag and the problems of supersonic blade tips. Apparently, they have a plan for how to get around these problems. Maybe they will be using a tilt-rotor setup such as the Osprey V-22? If so, can you really call it a helicopter still? But wait, was the Lynx really the fastest?
Sikorsky S-69
Back in the early 1970s, Sikorsky came up with a way to eliminate the retreating blade stall problem. They developed the S-69 as part of the Advancing Blade Concept program which used a co-axial design and a “feathering” of the blades. This eliminated retreating blade stall and allowed the advancing blades to carry the load. Maximum speed is listed as 322 mph. If Kamov is involved perhaps we’ll see (or not see) an evolution of the KA-50? Alternatively, if they don’t go with a co-axial setup, I’ll be really interested to know how they overcome RBS at such a high speed. What are your thoughts?
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IMFU - From an old SAC buddy during AHS last week, but it looks like Wired has a second photo from that same shoot.
jim63 - Sounds like they're describing the Ka-90, but that's one of those "we'll believe it when we see it" programs. On the subject of hokum, Kamov is also playing with a jet-assisted Ka-50.
I/C
jim63 - Sounds like they're describing the Ka-90, but that's one of those "we'll believe it when we see it" programs. On the subject of hokum, Kamov is also playing with a jet-assisted Ka-50.
I/C
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Slowing the main rotor.
"The prototype is designed with no clutch between the main rotors and propulsor, which requires the pilot to increase forward speed through the variable pitch control on the six-bladed rear propeller. Once in the 180kt realm, the X2's computer will automatically slow the main rotors and increase collective pitch to prevent tip speeds from entering high-drag transonic region, with Bredenbeck correspondingly increasing propulsor pitch to increase the X2's speed as the propulsor also slows."
I'd be interested to see a schematic of the X2 driveline. If there is no clutching (ie. gear shifting) then the only way to reduce the speed of both the main rotors and pusher prop at the same time is by reducing engine speed, which would be rather inefficient for the turbine engine. If both main rotors and pusher prop are mechanically coupled through the drivetrain at a fixed ratio, then changing pitch of one/both will only change load, and not relative speeds.
A change in relative speeds between the main rotors and pusher prop (one speeds up while the other slows down) could possibly be achieved without gear shifting through the use of a single input/dual output differential gearset. Where each of the two output drive speeds are a function of the relative rotor and prop loads. Such a drivetrain configuration could change the relative output speeds with blade pitch (load) changes.
Or maybe Sikorsky convinced Honeywell to add a second power turbine spool to their engine so that the main rotors and pusher prop can be driven independently. Hey, just because it's never been tried before doesn't mean it won't work!
Maybe someone can shed some light on how the X2 drivetrain changes rotor speeds.
riff_raff
I'd be interested to see a schematic of the X2 driveline. If there is no clutching (ie. gear shifting) then the only way to reduce the speed of both the main rotors and pusher prop at the same time is by reducing engine speed, which would be rather inefficient for the turbine engine. If both main rotors and pusher prop are mechanically coupled through the drivetrain at a fixed ratio, then changing pitch of one/both will only change load, and not relative speeds.
A change in relative speeds between the main rotors and pusher prop (one speeds up while the other slows down) could possibly be achieved without gear shifting through the use of a single input/dual output differential gearset. Where each of the two output drive speeds are a function of the relative rotor and prop loads. Such a drivetrain configuration could change the relative output speeds with blade pitch (load) changes.
Or maybe Sikorsky convinced Honeywell to add a second power turbine spool to their engine so that the main rotors and pusher prop can be driven independently. Hey, just because it's never been tried before doesn't mean it won't work!
Maybe someone can shed some light on how the X2 drivetrain changes rotor speeds.
riff_raff
This was back at post 700.
Originally Posted by NickLappos
No clutches, guys. The whole drive system is tied together, rotors and prop shaft. My guess is that the "permanently" geared prop is a variable pitch assembly that can run at flat pitch, as well as positive (forward push) and negative (aft pull) pitch. If no prop thrust is desired, the pitch is flattened. Prop thrust could be done with a separate thrust lever in the cockpit, near the collective.
The engine governors automatically increase power as prop pitch is increased.
The engine governors automatically increase power as prop pitch is increased.
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Cattletruck, don't forget that autorotation just means that the main rotor does not require positive torque to rotate. So a clutch is not a requirement for an autogyro flight mode. I would not be surprised if during the proposed 265kias dash speed the main rotor actually supplied torque to the pusher prop.
Sultan, nobody says that 168kts is fast. But, it does prove that the technical issues have been overcome and that the ship is back on the path of a 250kts cruise. Imagine how routinely cruisiing 68+kts faster than your Cobra would feel.
Once X2 has proven itself, i would not be surprised if a 3rd generation ABC (counting S69 as 1st) began to consider what would be required to develope a rotor system which could approach turboprop speeds. Early days...
Chris, that the aerodynamics near the root are more complicated than the CFD predictions does not surprise me. I was actually impressed that the flow was sufficiently non turbulent to allow a vane type of device. Can you give any specifics of the difficulties encountered?
Sultan, nobody says that 168kts is fast. But, it does prove that the technical issues have been overcome and that the ship is back on the path of a 250kts cruise. Imagine how routinely cruisiing 68+kts faster than your Cobra would feel.
Once X2 has proven itself, i would not be surprised if a 3rd generation ABC (counting S69 as 1st) began to consider what would be required to develope a rotor system which could approach turboprop speeds. Early days...
Chris, that the aerodynamics near the root are more complicated than the CFD predictions does not surprise me. I was actually impressed that the flow was sufficiently non turbulent to allow a vane type of device. Can you give any specifics of the difficulties encountered?
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@CEFOSKY-That would be assuming 100% serviceability for conventional helicopters, which definitely is not the case!
-typical serviceability would be in the region of 75-80%.
-typical serviceability would be in the region of 75-80%.
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you're right on that one CEFOSKEY - I wonder whether the Osprey or any other tilt rotor with all that additional complexity and possible failure modes will ever reach the serviceability & reliability levels of a conventional helicopter....
And on that note, the X2 is definitely the correct way ahead
O/T - did The Sultan routinely fly at 190 kts in a Cobra? That's its listed VNE, isnt it?
And on that note, the X2 is definitely the correct way ahead
O/T - did The Sultan routinely fly at 190 kts in a Cobra? That's its listed VNE, isnt it?
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Speculations
#1
The X2 may set a new speed record; due to its very large engine.
#2
The X2 may have an overall efficiency comparable to, or below, that of the V-22.
#3
Outside funding for development will not materialize.
The added hype from #1 will be unable to cover up the aerodynamic and mechanical limitations in #2.
The X2 may set a new speed record; due to its very large engine.
#2
The X2 may have an overall efficiency comparable to, or below, that of the V-22.
#3
Outside funding for development will not materialize.
The added hype from #1 will be unable to cover up the aerodynamic and mechanical limitations in #2.
