Sikorsky X2 coaxial heli developments.
Joined: Mar 2005
Posts: 1,289
Likes: 289
From: Poplar Grove, IL, USA
Joined: Nov 2007
Posts: 11
Likes: 3
From: US
SAD
Lone Wolf 50 totally agree definitely there is a need for a new Hawk transmission with the 901 and the ITEP. Common sense but it’s the Army. Just like inlet barrier filters. Still the Army hasn’t come to their senses to install IBFs. AeroMetals design and fielded IBFs to the S70 FireHawks are awesome and viable. Yet the Army still flies without filters without addressing the fleet engine issues deployed.
As for X2 Y it was very doable within 10 years after of X2 now here we are fingers crossed for the future and common sense from corporate leadership and then the Army. Just like the AH66 Comanche what a phenomenal aircraft and it went to the grave yard because of a paper chase and Army requirements ever changing with every Program Manager. Again another SAD history of something viable and doable.
As for X2 Y it was very doable within 10 years after of X2 now here we are fingers crossed for the future and common sense from corporate leadership and then the Army. Just like the AH66 Comanche what a phenomenal aircraft and it went to the grave yard because of a paper chase and Army requirements ever changing with every Program Manager. Again another SAD history of something viable and doable.
Joined: Feb 2015
Posts: 258
Likes: 58
From: USA
...
The X2 team wanted to after those 9 close out flights put a new design set of rotor blades on the X2, install a real AFCS system, an active tail and active collective to truely close out the X2 design model. The Y version the X2 team envisioned was a two engine S76 sized aircraft with a gross weight ~ 13 to 14000 lbs. But good things end when good things happen due to so called self proclaimed experts and leaders that have self in mind instead of promoting and supporting the real experts to move forward to get it done and accomplished.
...
S97 out of the gate was the wrong aircraft, one engine and no power or payload and capability for true over 200 kt speed or margin. Power to weight to drag basic computations didn’t add up and the aircraft structurally was under designed so it couldn’t do the maneuvers planned for such a capable concept. Then SB1 Defiant came along to scale up a design which we all knew wasn’t a viable path for the concept. So in the end what was good and had potential to change the way the helicopter could fly ended back with Raider and with the triad of Lockheed, Boeing and then the Sikorsky tag alongs chasing stupid Army requirements instead of letting the original X2 team follow thru on the concept and a Y platform aircraft so when it was time we could of offered a viable awesome finished product sooner than later.
...
[size=13px]
The X2 team wanted to after those 9 close out flights put a new design set of rotor blades on the X2, install a real AFCS system, an active tail and active collective to truely close out the X2 design model. The Y version the X2 team envisioned was a two engine S76 sized aircraft with a gross weight ~ 13 to 14000 lbs. But good things end when good things happen due to so called self proclaimed experts and leaders that have self in mind instead of promoting and supporting the real experts to move forward to get it done and accomplished.
...
S97 out of the gate was the wrong aircraft, one engine and no power or payload and capability for true over 200 kt speed or margin. Power to weight to drag basic computations didn’t add up and the aircraft structurally was under designed so it couldn’t do the maneuvers planned for such a capable concept. Then SB1 Defiant came along to scale up a design which we all knew wasn’t a viable path for the concept. So in the end what was good and had potential to change the way the helicopter could fly ended back with Raider and with the triad of Lockheed, Boeing and then the Sikorsky tag alongs chasing stupid Army requirements instead of letting the original X2 team follow thru on the concept and a Y platform aircraft so when it was time we could of offered a viable awesome finished product sooner than later.
...
[size=13px]
S-97 Raider was certainly underpowered for a "true X2". Never came close to hitting the optimistic speed targets (nor did Defiant) and in the end, when it flew without the propellor (another story), it could cruise at 180+ knots... which is great for a helicopter it's size. So you're right... not enough power installed to really make the propellor a good addition relative to the weight/cost/complexity it adds. The airframe was undersized but really wasn't tunable away from 4P, just the nature of the geometry and open cabin. It could have been a little better but when you contract someone else to do your work, you get what you get :-/
The X2D was a cool program but don't over-romanticize it. The blade construction was poor, the rotor head was extremely heavy with short life, the gearbox was troublesome, the rotor required retracking all the time, and ended up having to treat multiple frequencies of vibrations with a large AVCS scheme for that sized aircraft, etc. A "S-76 sized" Y model would have been much larger than 14,000 lb... the weight parametrics of X2 aircraft were all underpredicted. Rotor weight scales faster than the aircraft does, the impact of yaw control and MR loads on MRGB sizing was underpredicted, yaw control was insufficient, oscillatory loads were wildly underpredicted, AVCS sizing was underpredicted, impact of AVCS flight criticality wasn't appreciated, and the list goes on. By the time those are addressed, part lives pumped up to acceptable levels, and ride quality made commercially acceptable, weight would have ballooned. Then you add on Part 29 requirements like damage tolerance and bird strike, etc. Strikes at 250 knots are far heavier to design for than 150 knots... if the FAA doesn't make you use an airplane-level 4 lb bird if you want to cruise at higher altitudes. I think that S-76 sized "Y" model would have been a ~20,000 lb aircraft if it was to be FAA certified and if it wasn't certifiable and marketable, then why build it?
The physics are the physics, though. An edgewise flow, stiff out of plane rigid rotor is a bad idea. Draggy, heavy, huge loads and horrific vibrations unless you pump the blade count up so high the blades are too slender to keep separated for a coaxial. The integrated propellor propulsor is better than slapping jets on the side like XH-59A but results in low ground clearance, a high power clutch, and high mass in the wrong spot for a coaxial helicopter. There is a 1980's memo floating around SAC listing out the problems of the ABC vs what the claims and goals of the program were. The X2 configuration addressed some of those, but not all, and the unaddressed issues bit the X2 aircraft as well.
X2 wasn't the future of Sikorsky, it was a bold bet on a dubious idea. Right now, X2 Technology is headed where it belongs: in a museum.
Joined: Aug 2009
Aviation Qualifications: Military
Posts: 9,336
Likes: 2,184
From: Texas
Joined: Dec 2010
Posts: 290
Likes: 38
From: USA
These will never be. They were nice marketing concepts that predate the X2 demonstrator. Since these and similar were published, it's become apparent that in the real world the mast and transmission of an X2 take up so much internal space that any cabin or cargo space has to be forward of the mast, as can be seen in every ABC/X2 that has flown, and Raider-X and Defiant-X
Joined: Feb 2015
Posts: 258
Likes: 58
From: USA
These will never be. They were nice marketing concepts that predate the X2 demonstrator. Since these and similar were published, it's become apparent that in the real world the mast and transmission of an X2 take up so much internal space that any cabin or cargo space has to be forward of the mast, as can be seen in every ABC/X2 that has flown, and Raider-X and Defiant-X
Joined: Aug 2023
Aviation Qualifications: Spotter
Posts: 74
Likes: 46
From: Texas
Defiant to a Museum?
https://www.twz.com/air/sb1-defiant-...st-in-a-museum
WTF! Why would they put this miserable failure in a museum?
WTF! Why would they put this miserable failure in a museum?
Joined: Oct 2007
Posts: 300
Likes: 42
From: Texas
https://www.twz.com/air/sb1-defiant-...st-in-a-museum
WTF! Why would they put this miserable failure in a museum?
WTF! Why would they put this miserable failure in a museum?
Joined: Nov 2006
Posts: 803
Likes: 52
From: Pensacola, Florida
Joined: Mar 2005
Posts: 1,289
Likes: 289
From: Poplar Grove, IL, USA
Joined: Feb 2015
Posts: 258
Likes: 58
From: USA
No kidding. Europe already has indigenous "normal" helicopters, compounded helicopters, and tiltrotors (with an assist from Bell)... so where does the X2 fit in given the transatlantic tension and the lack of program wins for the X2 concept? Even an Augusta/Bell tiltrotor based on FLRAA is probably a political stretch, even if it made the most sense (not saying it does).
