Sikorsky X2 coaxial heli developments.
More debate
Courant article about reaching 235 kts, and debating if the X2 is a helicopter or not:
courant x2 story
Maybe they got the idea from us here!
-- IFMU
courant x2 story
Maybe they got the idea from us here!
-- IFMU
Sikorsky Aircraft's quest to produce the world's fastest helicopter raises one question above all: How fast?
As of Tuesday, the date of the X2 prototype's most recent flight, the answer was 235 knots, the latest increase in a steady advance toward the avowed goal of 250 knots, or 287 mph. That's nearly 100 knots faster than conventional modern helicopters' top speed.
Another, more philosophical question has also been popping up lately: Is the X2 really a helicopter?
Stratford-based Sikorsky, one of the world's biggest, most famous helicopter makers, says yes. But in the wonky world of aviation enthusiasts, there's debate. And Sikorsky's steady stream of public announcements about the X2's boundary-pushing progress has prompted some observers to raise the question — and answer it with a resounding no.
"The X2 is a compound aircraft, not a true helicopter," said Elfan Ap Rees, the editor of Helicopter International magazine in Great Britain, who objected after Sikorsky's July 26 statement that the X2 had reached 225 knots, setting an unofficial speed record. "…The X2 is a fine technological achievement with great promise and Sikorsky should be proud of that and not belittle its success with inaccurate claims."
The 5,000-pound, single-pilot X2 has one engine, two counter-rotating main rotors on top — and a rear "pusher" propeller to give it extra thrust.
Geoff Russell, a spokesman for AgustaWestland, a Sikorsky competitor in Europe, also said the X2 does not qualify as a "pure helicopter" because it generates power from a device other than the main rotor atop the aircraft.
"The X2 therefore will not be able to claim the speed record set by the Lynx helicopter in 1986," he said, referring to the souped-up version of a Westland helicopter still on record as the fastest.
(According to the Washington-based National Aeronautic Association, a non-profit U.S. organization that certifies aviation records, a Westland Lynx remains the record-holder for speed, at 216 knots, or 249 mph. Sikorsky plans to invite an NAA representative to attend a test flight of the X2 once it reaches 250 knots, expected later this year.)
But Sikorsky is making no apologies for its innovations, and confidently insists the X2 is no mere rotorcraft, a broad term that includes helicopters, but a bona fide helicopter.
"We stand by our claims," company spokeswoman Marianne Heffernan wrote in an e-mail.
The Fédération Aéronautique Internationale — an international organization based in Switzerland that certifies world aviation records (and which X2 critic Elfan Ap Rees serves as honorary president of the rotorcraft committee) — defines helicopter in a way that would appear to include the X2.
Section 9 of the group's Sporting Code for rotorcraft, available on the NAA website, says a helicopter is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."
By the FAI's own definition, Sikorsky's X2 seems to fit. It generates lift from its main rotors — the ones on top — which spin on an axis perpendicular to the lengthwise axis of the aircraft's body.
While the axis of the pusher prop is horizontal, like the aircraft's lengthwise axis, the pusher prop does not generate lift — only thrust, Sikorsky said. The X2 does not rely on wings for lift, or anything else; it has none.
"The X2 demonstrator is considered a pure helicopter because all of its lift is derived from its rotor system rather than being augmented by wings," Steve Weiner, Sikorsky's director of engineering sciences and head engineer for the X2, said in a statement. "No other helicopter meeting these criteria has cruised at 250 knots to date."
Other helicopter-like aircraft have traveled at 250 knots and faster, such as the V-22 Osprey, a high-speed aircraft made by a partnership of Bell Helicopter and The Boeing Co. But it has large wings and two dramatically adjustable rotors. The experimental Bell 533, which traveled at more than 270 knots, had stub wings and jet engines.
Whatever the squabbles among helicopter purists, advances in aircraft technology are blurring the lines between long-recognized types of flying machines — even for people who have been flying them for decades.
"It's actually a good question," said Jay Brown, a former Army helicopter pilot in Vietnam who is the executive director of the Combat Helicopter Pilots Association. "It's come up before when we talk about people who are eligible for membership in our organization."
Brown said his group has concluded that the V-22, for example, a so-called tilt-rotor helicopter, should not count as a helicopter, because its rotors swivel from a horizontal to a vertical orientation for forward travel.
"The V22 is not a helicopter," he said in an interview. "When it shifts from hovering flight to forward flight, it becomes an airplane." (Boeing, one of the V-22's producers, agrees, describing it as a tiltrotor aircraft that takes off and lands like a helicopter, but converts into a turboprop airplane.)
Brown says the X2, despite the pusher propeller at its rear, meets his concept of a helicopter, because its top-mounted rotor system "stays where you expect a helicopter rotor system to be."
"If you were in theory to remove the rotor system, it would stop flying," Brown said of the X2. "It has to have the rotor system spinning in order to maintain flight. I think it's still a helicopter."
The American Helicopter Museum and Education Center, near Philadelphia, keeps things simple by opting for a flexible definition.
Said president Sean Saunders, "It changes with every new invention."
As of Tuesday, the date of the X2 prototype's most recent flight, the answer was 235 knots, the latest increase in a steady advance toward the avowed goal of 250 knots, or 287 mph. That's nearly 100 knots faster than conventional modern helicopters' top speed.
Another, more philosophical question has also been popping up lately: Is the X2 really a helicopter?
Stratford-based Sikorsky, one of the world's biggest, most famous helicopter makers, says yes. But in the wonky world of aviation enthusiasts, there's debate. And Sikorsky's steady stream of public announcements about the X2's boundary-pushing progress has prompted some observers to raise the question — and answer it with a resounding no.
"The X2 is a compound aircraft, not a true helicopter," said Elfan Ap Rees, the editor of Helicopter International magazine in Great Britain, who objected after Sikorsky's July 26 statement that the X2 had reached 225 knots, setting an unofficial speed record. "…The X2 is a fine technological achievement with great promise and Sikorsky should be proud of that and not belittle its success with inaccurate claims."
The 5,000-pound, single-pilot X2 has one engine, two counter-rotating main rotors on top — and a rear "pusher" propeller to give it extra thrust.
Geoff Russell, a spokesman for AgustaWestland, a Sikorsky competitor in Europe, also said the X2 does not qualify as a "pure helicopter" because it generates power from a device other than the main rotor atop the aircraft.
"The X2 therefore will not be able to claim the speed record set by the Lynx helicopter in 1986," he said, referring to the souped-up version of a Westland helicopter still on record as the fastest.
(According to the Washington-based National Aeronautic Association, a non-profit U.S. organization that certifies aviation records, a Westland Lynx remains the record-holder for speed, at 216 knots, or 249 mph. Sikorsky plans to invite an NAA representative to attend a test flight of the X2 once it reaches 250 knots, expected later this year.)
But Sikorsky is making no apologies for its innovations, and confidently insists the X2 is no mere rotorcraft, a broad term that includes helicopters, but a bona fide helicopter.
"We stand by our claims," company spokeswoman Marianne Heffernan wrote in an e-mail.
The Fédération Aéronautique Internationale — an international organization based in Switzerland that certifies world aviation records (and which X2 critic Elfan Ap Rees serves as honorary president of the rotorcraft committee) — defines helicopter in a way that would appear to include the X2.
Section 9 of the group's Sporting Code for rotorcraft, available on the NAA website, says a helicopter is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."
By the FAI's own definition, Sikorsky's X2 seems to fit. It generates lift from its main rotors — the ones on top — which spin on an axis perpendicular to the lengthwise axis of the aircraft's body.
While the axis of the pusher prop is horizontal, like the aircraft's lengthwise axis, the pusher prop does not generate lift — only thrust, Sikorsky said. The X2 does not rely on wings for lift, or anything else; it has none.
"The X2 demonstrator is considered a pure helicopter because all of its lift is derived from its rotor system rather than being augmented by wings," Steve Weiner, Sikorsky's director of engineering sciences and head engineer for the X2, said in a statement. "No other helicopter meeting these criteria has cruised at 250 knots to date."
Other helicopter-like aircraft have traveled at 250 knots and faster, such as the V-22 Osprey, a high-speed aircraft made by a partnership of Bell Helicopter and The Boeing Co. But it has large wings and two dramatically adjustable rotors. The experimental Bell 533, which traveled at more than 270 knots, had stub wings and jet engines.
Whatever the squabbles among helicopter purists, advances in aircraft technology are blurring the lines between long-recognized types of flying machines — even for people who have been flying them for decades.
"It's actually a good question," said Jay Brown, a former Army helicopter pilot in Vietnam who is the executive director of the Combat Helicopter Pilots Association. "It's come up before when we talk about people who are eligible for membership in our organization."
Brown said his group has concluded that the V-22, for example, a so-called tilt-rotor helicopter, should not count as a helicopter, because its rotors swivel from a horizontal to a vertical orientation for forward travel.
"The V22 is not a helicopter," he said in an interview. "When it shifts from hovering flight to forward flight, it becomes an airplane." (Boeing, one of the V-22's producers, agrees, describing it as a tiltrotor aircraft that takes off and lands like a helicopter, but converts into a turboprop airplane.)
Brown says the X2, despite the pusher propeller at its rear, meets his concept of a helicopter, because its top-mounted rotor system "stays where you expect a helicopter rotor system to be."
"If you were in theory to remove the rotor system, it would stop flying," Brown said of the X2. "It has to have the rotor system spinning in order to maintain flight. I think it's still a helicopter."
The American Helicopter Museum and Education Center, near Philadelphia, keeps things simple by opting for a flexible definition.
Said president Sean Saunders, "It changes with every new invention."
Geoff Russell, a spokesman for AgustaWestland, a Sikorsky competitor in Europe, also said the X2 does not qualify as a "pure helicopter" because it generates power from a device other than the main rotor atop the aircraft.
On the subject of [other] power (lift/thrust), many conventional helicopters with in-line gas turbine engines (including Lynx) derive some of their forward thrust from the ejection of the engine exhaust gas stream in a rearwards direction, so that’s Lynx discounted is it not Geoff?
And what about lift/thrust derived from a canted tail rotor assembly (BlackHawk/CH-53 etc). With application of forward cyclic, does not the resultant lift/thrust moment generated by the tail rotor assembly - now angled slightly forward – contribute to overall forward thrust, thereby producing some additional force from a device [other] than the main rotor atop the aircraft?
Does this mean that any helicopter with an canted tail rotor does not qualify as a “pure helicopter?”
And so the debate goes on..........
Hilife is absolutely right.The canted tail rotor produces lift and thrust ,as does the main rotor.This qualifies it as a helicopter.The X2 prop only produces thrust and becomes the driving force in forward flight,not the rotor system which is actually slowed to produce less power in forward flight.
The Lynx got away with it because the power was all through the rotor system and the aft facing engine exhausts produced only the residual thrust as is common on many helicopters, such as Bell 212,Hughes OH-6 .Some others redirected to one side ,to counterct torque and others up into the rotor system.
The Lynx got away with it because the power was all through the rotor system and the aft facing engine exhausts produced only the residual thrust as is common on many helicopters, such as Bell 212,Hughes OH-6 .Some others redirected to one side ,to counterct torque and others up into the rotor system.
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235 knots! Congratulations test pilot, test team and design team.
X2 hovers like a helicopter, transitions like a helicopter, cruises like a helicopter, and has the ability to autorotate like a helicopter.
When the ABC technology is handed down to commercially available machines i have no doubt what the machines will be called.
X2 hovers like a helicopter, transitions like a helicopter, cruises like a helicopter, and has the ability to autorotate like a helicopter.
When the ABC technology is handed down to commercially available machines i have no doubt what the machines will be called.
Because it looks like a duck, waddles like a duck, and swims like a duck doesn't meant it is a duck Graviman !
Could X2 stay aloft at high speed on slowed down main rotor lift alone......that is the question.
Could X2 stay aloft at high speed on slowed down main rotor lift alone......that is the question.
Could X2 stay aloft at high speed on slowed down main rotor lift alone......that is the question.
I guess I am in the camp that thinks the X2 fits this definition exactly:
Section 9 of the group's Sporting Code for rotorcraft, available on the NAA website, says a helicopter is a "rotorcraft which, in flight, derives substantially the whole of its lift from a power-driven rotor system whose axis (axes) is (are) fixed and substantially perpendicular to the longitudinal axis of the rotorcraft."
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This all reminds me of the recent astronomical debate to decide upon the fate of Pluto. Planet or planetoid, i'm sure Pluto really wasn't overly concerned.
Whatever definition is selected to accurately describe X2, it is a significant step in pioneering aviation. This makes Kevin Bredenbeck a pioneering aviator. These flights have demonstrated that a machine with low disk loading can achieve high speed flight without significant compromise to its low speed performance. Ultimately this means that ABC technology can filter out to EMS and other arenas where the ability to get to destination is as important as the ability to hover over or land at destination. I doubt the beneficiaries of such a service will concern themselves with how the machine is defined...
Whatever definition is selected to accurately describe X2, it is a significant step in pioneering aviation. This makes Kevin Bredenbeck a pioneering aviator. These flights have demonstrated that a machine with low disk loading can achieve high speed flight without significant compromise to its low speed performance. Ultimately this means that ABC technology can filter out to EMS and other arenas where the ability to get to destination is as important as the ability to hover over or land at destination. I doubt the beneficiaries of such a service will concern themselves with how the machine is defined...
Graviman...Absolutely agree with you so why do Sikorsky muddy the waters by claiming X2 is something it plainly isn't?
The FAI clearly agrees if the statemnent attributed to their president is true,to whit the only way it can be a true helicopter is for all the dynamic lift and power to go through the rotor sytem (apart from engine exhaust Cfoskey).Otherwise it is clearly a compound...or even a gyrodyne as some of the autogyros also used a powered rotor sytem to jump/take off before switching to prop power for forward flight and the rotor to provide just lift.
Reminds me of Sikorsky's long ago argument about being the first to fly the (practical)helicopter when Igor actually had to rely on Cierva patents to make the VS300 work and even then was beaten by the French,Belgians ,Brits and Germans!!
The FAI clearly agrees if the statemnent attributed to their president is true,to whit the only way it can be a true helicopter is for all the dynamic lift and power to go through the rotor sytem (apart from engine exhaust Cfoskey).Otherwise it is clearly a compound...or even a gyrodyne as some of the autogyros also used a powered rotor sytem to jump/take off before switching to prop power for forward flight and the rotor to provide just lift.
Reminds me of Sikorsky's long ago argument about being the first to fly the (practical)helicopter when Igor actually had to rely on Cierva patents to make the VS300 work and even then was beaten by the French,Belgians ,Brits and Germans!!
The FAI clearly agrees if the statemnent attributed to their president is true,to whit the only way it can be a true helicopter is for all the dynamic lift and power to go through the rotor sytem (apart from engine exhaust Cfoskey).
power-driven rotor system
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Heli1:
The record-setting Lynx had the engine exhausts very specifically modified to generate quite a lot of thrust. Westland never released any photos of the modified exhaust, but it contributed significantly to the forward thrust.
The record-setting Lynx had the engine exhausts very specifically modified to generate quite a lot of thrust. Westland never released any photos of the modified exhaust, but it contributed significantly to the forward thrust.
I can see our colonial cousins are never going to be satisfied
IFMU seems to think that a pusher prop is the same as a tail rotor (which has pitch links et al and actually takes power out of the dynamic system).I would argue there is a big difference between this and an airscrew that takes power away from the rotor.
Shawn is correct in part although there are pictures of the aft facing exhausts on G-Lynx,in particular in the book " Putting the Record Straight "by Dave Gibbings ,senior Westland flight engineer at the time.He explains how the engines were boosted in power using water injection to feed the uprated transmission and how the exhausts were turned to face aft to get rid of the 600lbs of residual thrust. The importance here is that it was residual and not the prime means of forward speed.The aircraft was also fitted with additional tail fins because the tailrotor could not counteract the increased torque suppiled to the main rotor.Again evidence that the drive was predomimantly through the rotor system.
IFMU seems to think that a pusher prop is the same as a tail rotor (which has pitch links et al and actually takes power out of the dynamic system).I would argue there is a big difference between this and an airscrew that takes power away from the rotor.
Shawn is correct in part although there are pictures of the aft facing exhausts on G-Lynx,in particular in the book " Putting the Record Straight "by Dave Gibbings ,senior Westland flight engineer at the time.He explains how the engines were boosted in power using water injection to feed the uprated transmission and how the exhausts were turned to face aft to get rid of the 600lbs of residual thrust. The importance here is that it was residual and not the prime means of forward speed.The aircraft was also fitted with additional tail fins because the tailrotor could not counteract the increased torque suppiled to the main rotor.Again evidence that the drive was predomimantly through the rotor system.
Last edited by heli1; 22nd Aug 2010 at 13:20. Reason: update
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This thread is actually turning into an interesting discussion on where the boundaries lie for what folks consider to be a helicopter. Part of me can't help but hear the nostalgic cry for the way things were...
heli1, what i understand you to be saying is that Sikorsky/Schweizer engineers should have compromised the design, maybe by tilting the rotor system to do away with the pusher prop, in order to keep the coveted title of "helicopter"?
Let me turn the problem around by asking what anyone has to gain by denying X2 the title "worlds fastest helicopter"?
Also, regarding tail-rotor/pusher-prop then i wonder how long it will be before the prop becomes teetering to remove any sideslip/climb pitch/yaw cross coupling. Once this happens then how long before a cyclic mechanism is introduced to improve yaw response characteristics (say FBW to vector powered flight and autorotation correctly).
Personally, my interest in X2 is that it promises to bring high speed helicopter flight to the wider fleet which is constrained on landing/hanger space and operational cost. What it is called does not affect my interest in the ship.
heli1, what i understand you to be saying is that Sikorsky/Schweizer engineers should have compromised the design, maybe by tilting the rotor system to do away with the pusher prop, in order to keep the coveted title of "helicopter"?
Let me turn the problem around by asking what anyone has to gain by denying X2 the title "worlds fastest helicopter"?
Also, regarding tail-rotor/pusher-prop then i wonder how long it will be before the prop becomes teetering to remove any sideslip/climb pitch/yaw cross coupling. Once this happens then how long before a cyclic mechanism is introduced to improve yaw response characteristics (say FBW to vector powered flight and autorotation correctly).
Personally, my interest in X2 is that it promises to bring high speed helicopter flight to the wider fleet which is constrained on landing/hanger space and operational cost. What it is called does not affect my interest in the ship.
Last edited by Graviman; 25th Aug 2010 at 11:30. Reason: Typo.
Graviman.....Of course Sikorsky/Schewizer are pursuing a very useful and potentially valuable course and no way would I suggest they should have compromised the design.
What they have is a fine Compound Helicopter ,in the traditions of the Piasecki 16H,Lockheed Cheyenne and similar high speed designs with pusher airscrews ,some of which went faster than contemporary helicopters of the same period but still could not qualify for the absolute title as " The World's Fastest Helicopter" .
Compound is what it means..a mix of powered rotary wing and aeroplane ,unlike the autogyro which is a mix of unpowered rotary wing and powered aeroplane .Further the FAI has a category for Compounds although I admit it isn't published on their website but ....I recall the Rotodyne set up a closed circuit record for compound helicopters in the late fifties so it must exist.
Finally what we are talking about here is not about anyone gaining anything but accuracy and getting things right instead of dumming down technological and historical progress. .
What they have is a fine Compound Helicopter ,in the traditions of the Piasecki 16H,Lockheed Cheyenne and similar high speed designs with pusher airscrews ,some of which went faster than contemporary helicopters of the same period but still could not qualify for the absolute title as " The World's Fastest Helicopter" .
Compound is what it means..a mix of powered rotary wing and aeroplane ,unlike the autogyro which is a mix of unpowered rotary wing and powered aeroplane .Further the FAI has a category for Compounds although I admit it isn't published on their website but ....I recall the Rotodyne set up a closed circuit record for compound helicopters in the late fifties so it must exist.
Finally what we are talking about here is not about anyone gaining anything but accuracy and getting things right instead of dumming down technological and historical progress. .
Last edited by heli1; 23rd Aug 2010 at 13:49. Reason: addition
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Fairey Rotodyne.
I'm not a chopper pilot, though I wish I was, indeed no kind of a pilot at all - an engineer, who has found this thread to be very interesting indeed. The current question of whether the X2 is a 'proper' helicopter and relative speeds etc., reminded me of the machine I saw at Farnborough all those years ago. It seemed like a good idea at the time, but it obviously wasn't. 
From what I remember, the Rotodyne was an autogyro? I know it used engine bleed gas for the tip 'jets' (?) and I vaguely remember reading something about 'afterburning' the bleed gas in the tip pods to provide something. But that would defeat the autogyro principle would it not?
In any event, does anyone remember how fast the Rotodyne was, what with those big old Dart's pulling it along. I know it was damn noisy!
Roger.
From what I remember, the Rotodyne was an autogyro? I know it used engine bleed gas for the tip 'jets' (?) and I vaguely remember reading something about 'afterburning' the bleed gas in the tip pods to provide something. But that would defeat the autogyro principle would it not?
In any event, does anyone remember how fast the Rotodyne was, what with those big old Dart's pulling it along. I know it was damn noisy!
Roger.
My minimal experience in the X-59 (ABC) lends me to believe that both arguments may be correct. At lift off to a hover the X-2 is a pure coaxial rotor helicopter just like the X-59. Once the X-59 accelerated to more than 200 KIAS under power from the J-60s, the engine torque from the 2 PT6 rotor drive motors dropped to 0%. At that point the helicopter was an auto-gyro. The question is, at 235 KIAS is any of the S-2's engine torque going to the main rotor system.
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At lift off to a hover the X-2 is a pure coaxial rotor helicopter just like the X-59. Once the X-59 accelerated to more than 200 KIAS under power from the J-60s, the engine torque from the 2 PT6 rotor drive motors dropped to 0%. At that point the helicopter was an auto-gyro.
The question is, at 235 KIAS is any of the S-2's engine torque going to the main rotor system.
It is claimed that even the simple gyro-copter will benefit from some mechanically powered rotor-assist.
However, this calls for Reverse Velocity Utilization and Variable Speed Transmission; two features that Sikorsky appears to be unwilling or unable to provide.
Dave J.
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Heli1 has almost got it right... the X2 is almost a compound helicopter because the X2 lacks a wing surface.
"COMPOUND HELICOPTER- rotorcraft with driven rotors, additional means of propulsion, and using aerodynamic lift." (from VTOL by Mike Rogers 1989).
The words aerodynamic lift in this definition refers to a fixed wing.
The X2 is not a "pure helicopter" but it is also not exactly a compound because it lacks a wing.
slowrotor
"COMPOUND HELICOPTER- rotorcraft with driven rotors, additional means of propulsion, and using aerodynamic lift." (from VTOL by Mike Rogers 1989).
The words aerodynamic lift in this definition refers to a fixed wing.
The X2 is not a "pure helicopter" but it is also not exactly a compound because it lacks a wing.
slowrotor
