Sikorsky SB-1 flies for first time
Noneo wrote:
You are correct in identifying one of the few performance points the 97/SB-1 programs demonstrated which was the ability of the rotors to collide in moderate roll reversals. You are, however, naive in thinking the SB team will admit this concept flaw. They will instead hide behind a claim that a simple tweak to the fly-by-wire control laws has eliminated the chance of this flaw reoccurring. Only after the loss of a couple more aircraft will they propose changing rotor separation.
I have to believe Sikorsky has already told the Army that their demonstrators can't pull high g maneuvers. But that they will increase rotor spacing for production. Which will make a slow, tall Defiant even slower and taller.
Noneo wrote:
You are correct in identifying one of the few performance points the 97/SB-1 programs demonstrated which was the ability of the rotors to collide in moderate roll reversals. You are, however, naive in thinking the SB team will admit this concept flaw. They will instead hide behind a claim that a simple tweak to the fly-by-wire control laws has eliminated the chance of this flaw reoccurring. Only after the loss of a couple more aircraft will they propose changing rotor separation.
You are correct in identifying one of the few performance points the 97/SB-1 programs demonstrated which was the ability of the rotors to collide in moderate roll reversals. You are, however, naive in thinking the SB team will admit this concept flaw. They will instead hide behind a claim that a simple tweak to the fly-by-wire control laws has eliminated the chance of this flaw reoccurring. Only after the loss of a couple more aircraft will they propose changing rotor separation.
FLRAA RFP
Article in Defense News:
https://www.defensenews.com/land/202...t-competition/
Finally new stuff to talk about.
Recently read an article on the Bradley replacement where they had to cancel the original program because only one vendor responded. They then dumbed down the requirements and went out for new responses. Apparently it is unfair to have requirements that only the best can meet. This explains the FLRAA changes.
As to the issue discussed most: \ the speed requirement is as follows:
So the min acceptable speed was reduced from 250 kts to 230 kts to keep SB in the competition to avoid the Bradley replacement problem. Much to SB's despair the objective speed was defined as 280 kts which the V-280 easily meets and the ABC concept can never meet. Additionally, the 280 kt objective matches nicely with the Marine new medium lift minimum speed requirement.
I think everyone knows how this plays out. No vendor team will get both the FLRAA and FARA. Even if Bell's Invictus equals the Sikorsky Raider in every way, Sikorsky will be given the program. FARA will only go to Bell if the ABC's concept deficiencies are overwhelming so Bell gets the FLRAA without years of protest from the losers.
Once the two programs are awarded, the emphasis on Pacific operations will keep FLRAA safe while the FARA can be terminated for cause when Sikorsky stumbles (face it what program have they recently executed flawlessly?) with minimum impact to the US's warfighting capabilities.
https://www.defensenews.com/land/202...t-competition/
Finally new stuff to talk about.
Recently read an article on the Bradley replacement where they had to cancel the original program because only one vendor responded. They then dumbed down the requirements and went out for new responses. Apparently it is unfair to have requirements that only the best can meet. This explains the FLRAA changes.
As to the issue discussed most: \ the speed requirement is as follows:
The Army has set its threshold speed requirement for the aircraft at 230 knots, with an objective requirement of 280 knots, according to the RFP. The contract would set up an incentive to reach the objective speed requirement as well.
I think everyone knows how this plays out. No vendor team will get both the FLRAA and FARA. Even if Bell's Invictus equals the Sikorsky Raider in every way, Sikorsky will be given the program. FARA will only go to Bell if the ABC's concept deficiencies are overwhelming so Bell gets the FLRAA without years of protest from the losers.
Once the two programs are awarded, the emphasis on Pacific operations will keep FLRAA safe while the FARA can be terminated for cause when Sikorsky stumbles (face it what program have they recently executed flawlessly?) with minimum impact to the US's warfighting capabilities.
What maneuverability?
From "Spyclip":
https://www.secretprojects.co.uk/thr....13812/page-46
"I can confidently say that there have been a total of zero published flight demonstrations where level 1 handling qualities were demonstrated with requisite rates in pitch, roll, or (particularly) yaw on any ABC aircraft historically.
If any of these had been accomplished over the Jupiter swamps with Raider I would eat my shoe if Sikorsky would decline to publicize such footage.
The fact that the V-280 was able to perform these maneuvers at double the gross weight of S-97 makes the ongoing ad nauseum Sikorsky marketing of mythical extreme rigid rotor agility that much more egregious.
All of this is to say absolutely nothing of SB1's lack of demonstrating anything of note whatsoever."
____________________________________________________________ _________
A "feature" of the Kamov is that the rotors occasionally hit each other:
https://www.bbc.com/russian/russia/2...licopter_crash
The Raider and Defiant are more complex than the Kamov Alligator. They have a very large pusher prop, some say the largest prop ever produced in the US for Defiant. In a fast maneuver, there will be large 1-P moments input to the airframe. The control system must account for this, which may be ?impossible?. Note the AVX proposal had two ducted fans, so would not have this problem.
https://www.secretprojects.co.uk/thr....13812/page-46
"I can confidently say that there have been a total of zero published flight demonstrations where level 1 handling qualities were demonstrated with requisite rates in pitch, roll, or (particularly) yaw on any ABC aircraft historically.
If any of these had been accomplished over the Jupiter swamps with Raider I would eat my shoe if Sikorsky would decline to publicize such footage.
The fact that the V-280 was able to perform these maneuvers at double the gross weight of S-97 makes the ongoing ad nauseum Sikorsky marketing of mythical extreme rigid rotor agility that much more egregious.
All of this is to say absolutely nothing of SB1's lack of demonstrating anything of note whatsoever."
____________________________________________________________ _________
A "feature" of the Kamov is that the rotors occasionally hit each other:
https://www.bbc.com/russian/russia/2...licopter_crash
The Raider and Defiant are more complex than the Kamov Alligator. They have a very large pusher prop, some say the largest prop ever produced in the US for Defiant. In a fast maneuver, there will be large 1-P moments input to the airframe. The control system must account for this, which may be ?impossible?. Note the AVX proposal had two ducted fans, so would not have this problem.
Last edited by noneofyourbusiness; 20th Jul 2021 at 20:37.
The massive diameter prop on Defiant will have a massive roll torque input to the airframe. When a conventional helicopter loses tail rotor authority, the helicopter spins about its axis. Large gear reduction, large torque, transmitted through the ring gear to the airframe. Normally the only roll torque in a conventional helicopter is from the much lower torque from the engines. The Defiant has to have a substantial gear reduction from the engine to the prop. Large gear reduction, large torque. The AVX design was better.
The massive diameter prop on Defiant will have a massive roll torque input to the airframe. When a conventional helicopter loses tail rotor authority, the helicopter spins about its axis. Large gear reduction, large torque, transmitted through the ring gear to the airframe. Normally the only roll torque in a conventional helicopter is from the much lower torque from the engines. The Defiant has to have a substantial gear reduction from the engine to the prop. Large gear reduction, large torque. The AVX design was better.
Did I say Raider/Defiant couldn't fly because of it? No. Is it better not to have a large reaction torque? Yes.
To create a roll moment with the cyclics, the rotors are tilted with respect to each other, reducing clearance between the rotors, compared to the AVX design. There is a structural weight penalty. Flying with the rotors tilted with respect to each other reduces efficiency.
Edit -If cyclic control is lost, the helicopter could flip. AVX is just more proof, the better design does not always win.
Care to discuss Raider/Defiant lack of demonstrated maneuverability?
Last edited by noneofyourbusiness; 21st Jul 2021 at 14:37. Reason: another one
From "Spyclip":
https://www.secretprojects.co.uk/thr....13812/page-46
"I can confidently say that there have been a total of zero published flight demonstrations where level 1 handling qualities were demonstrated with requisite rates in pitch, roll, or (particularly) yaw on any ABC aircraft historically.
If any of these had been accomplished over the Jupiter swamps with Raider I would eat my shoe if Sikorsky would decline to publicize such footage.
The fact that the V-280 was able to perform these maneuvers at double the gross weight of S-97 makes the ongoing ad nauseum Sikorsky marketing of mythical extreme rigid rotor agility that much more egregious.
All of this is to say absolutely nothing of SB1's lack of demonstrating anything of note whatsoever."
____________________________________________________________ _________
A "feature" of the Kamov is that the rotors occasionally hit each other:
https://www.bbc.com/russian/russia/2...licopter_crash
The Raider and Defiant are more complex than the Kamov Alligator. They have a very large pusher prop, some say the largest prop ever produced in the US for Defiant. In a fast maneuver, there will be large 1-P moments input to the airframe. The control system must account for this, which may be ?impossible?. Note the AVX proposal had two ducted fans, so would not have this problem.
https://www.secretprojects.co.uk/thr....13812/page-46
"I can confidently say that there have been a total of zero published flight demonstrations where level 1 handling qualities were demonstrated with requisite rates in pitch, roll, or (particularly) yaw on any ABC aircraft historically.
If any of these had been accomplished over the Jupiter swamps with Raider I would eat my shoe if Sikorsky would decline to publicize such footage.
The fact that the V-280 was able to perform these maneuvers at double the gross weight of S-97 makes the ongoing ad nauseum Sikorsky marketing of mythical extreme rigid rotor agility that much more egregious.
All of this is to say absolutely nothing of SB1's lack of demonstrating anything of note whatsoever."
____________________________________________________________ _________
A "feature" of the Kamov is that the rotors occasionally hit each other:
https://www.bbc.com/russian/russia/2...licopter_crash
The Raider and Defiant are more complex than the Kamov Alligator. They have a very large pusher prop, some say the largest prop ever produced in the US for Defiant. In a fast maneuver, there will be large 1-P moments input to the airframe. The control system must account for this, which may be ?impossible?. Note the AVX proposal had two ducted fans, so would not have this problem.
I think a historical knock on tiltrotor maneuverability was probably based on yaw rate, which is primarily affected by rotor flapping limits. The V-22 has around 10 degrees of flapping cooked into the hub and I do not believe meets level 1 HQ yaw rate (probably exacerbated in crosswinds). The V-280 on the other hand showed some very impressive ADS-33 level 1 yaw maneuvers for its gross weight, thanks wholly to the massive increase to 15 degrees of flapping. When ground taxi turning in their demo footage, the flapping can look pretty wild!
Inherent to tiltrotors, the control power from flapping is applied at the wingtips, creating a solidly effective yaw moment arm.
Now with the compound coaxial pusher prop design, you have the large and heavy static pusher prop assembly, gearbox/bearings, massive stabilizer, and tailwheel assembly - a huge amount of dead weight at the end of a very long moment arm from the mast. The only way to achieve yaw control is by differential torque between the rotors, which have been designed to be as stiff and lightweight as possible. This is a massively different situation from a conventional helicopter where the yaw moment is applied by the tail rotor at that same location perpendicular to the longitudinal axis.
I wonder, at the same medium to large gross weights, is a high flapping tiltrotor going to have substantially better yaw control than a rigid rotor coaxial design with a pusher assembly? I would say almost certainly. It's a real shame that Defiant hasn't even attempted (that we know of) high yaw rate maneuvers that could be compared to the myriad V-280 demos. Perhaps they have and the results were disappointing.
I am going to Ramble on. Even with a clutch, the prop placement of Raider/Defiant is an accident waiting to happen. Unlike a Black Hawk, with a high mounted tail rotor.
Igor Sikorsky, truly an aviation genius, used two jet engines on opposite sides of the helicopter, to provide forward thrust on the ABC demonstrator. Then someone at Sikorsky had a wet dream that they would use a single large pusher prop instead.
Igor Sikorsky, truly an aviation genius, used two jet engines on opposite sides of the helicopter, to provide forward thrust on the ABC demonstrator. Then someone at Sikorsky had a wet dream that they would use a single large pusher prop instead.
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To create a roll moment with the cyclics, the rotors are tilted with respect to each other, reducing clearance between the rotors, compared to the AVX design. There is a structural weight penalty. Flying with the rotors tilted with respect to each other reduces efficiency.
That being said, I think the coaxial rotor idea is not very good. A lot more complexity. a large minimum level of rigidity in order to avoid collision between the rotors (which will lead to a rought ride, even worse than the BO105).
The rotor head on conventional helicopters creates about 30% of the parasitic drag. Parasitic drag is the main reason for power consumption at high speed. The SB-1 has two rotor heads. These may be encased in fairings, but many protoypes with rotor head fairings in the past showed only a small reduction of parasitic drag.
The effect of "advancing blade theory" could have been created just as well with a comparatively small asymmetric wing. This means a conventional configuration with an asymmetric wing and a thrust vectored tail rotor, or tail rotor at an fixed intermediate angle and compensating fin would have much less drag, less complexity, less risk of rotor blade collision, and easier to inspect and mantain main rotor head.
I am going to Ramble on. Even with a clutch, the prop placement of Raider/Defiant is an accident waiting to happen. Unlike a Black Hawk, with a high mounted tail rotor.
Igor Sikorsky, truly an aviation genius, used two jet engines on opposite sides of the helicopter, to provide forward thrust on the ABC demonstrator. Then someone at Sikorsky had a wet dream that they would use a single large pusher prop instead.
Igor Sikorsky, truly an aviation genius, used two jet engines on opposite sides of the helicopter, to provide forward thrust on the ABC demonstrator. Then someone at Sikorsky had a wet dream that they would use a single large pusher prop instead.
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Interestingly, Igor died a year before the XH-59A first flew. He was quoted posthumously by Ben Kocivar in popular science's Sept 1982 piece on the "ABC copter" as having once said:
Having two overhead rotors on a helicopter is like having two cooks in the kitchen. They will not get along.
Genius indeed
A cyclic input will tilt both rotors in the same direction. Therefore the clearance will stay approximately the same.
That being said, I think the coaxial rotor idea is not very good. A lot more complexity. a large minimum level of rigidity in order to avoid collision between the rotors (which will lead to a rought ride, even worse than the BO105).
The rotor head on conventional helicopters creates about 30% of the parasitic drag. Parasitic drag is the main reason for power consumption at high speed. The SB-1 has two rotor heads. These may be encased in fairings, but many protoypes with rotor head fairings in the past showed only a small reduction of parasitic drag.
The effect of "advancing blade theory" could have been created just as well with a comparatively small asymmetric wing. This means a conventional configuration with an asymmetric wing and a thrust vectored tail rotor, or tail rotor at an fixed intermediate angle and compensating fin would have much less drag, less complexity, less risk of rotor blade collision, and easier to inspect and mantain main rotor head.
That being said, I think the coaxial rotor idea is not very good. A lot more complexity. a large minimum level of rigidity in order to avoid collision between the rotors (which will lead to a rought ride, even worse than the BO105).
The rotor head on conventional helicopters creates about 30% of the parasitic drag. Parasitic drag is the main reason for power consumption at high speed. The SB-1 has two rotor heads. These may be encased in fairings, but many protoypes with rotor head fairings in the past showed only a small reduction of parasitic drag.
The effect of "advancing blade theory" could have been created just as well with a comparatively small asymmetric wing. This means a conventional configuration with an asymmetric wing and a thrust vectored tail rotor, or tail rotor at an fixed intermediate angle and compensating fin would have much less drag, less complexity, less risk of rotor blade collision, and easier to inspect and mantain main rotor head.
You make very good points. Interesting, thank-you. Wouldn't the design you propose still have retreating blade stall at high forward speed?
Last edited by noneofyourbusiness; 22nd Jul 2021 at 23:08.
The XH-59B was the intended follow on to the XH-59A, and it had a ducted pusher prop design going all the way back to ca 1980.
Interestingly, Igor died a year before the XH-59A first flew. He was quoted posthumously by Ben Kocivar in popular science's Sept 1982 piece on the "ABC copter" as having once said:
Genius indeed
Interestingly, Igor died a year before the XH-59A first flew. He was quoted posthumously by Ben Kocivar in popular science's Sept 1982 piece on the "ABC copter" as having once said:
Genius indeed
I can't blame Igor for that, or for being frustrated with coaxial designs.
Last edited by noneofyourbusiness; 22nd Jul 2021 at 23:16.
The comment made in that post about yaw is interesting.
I think a historical knock on tiltrotor maneuverability was probably based on yaw rate, which is primarily affected by rotor flapping limits. The V-22 has around 10 degrees of flapping cooked into the hub and I do not believe meets level 1 HQ yaw rate (probably exacerbated in crosswinds). The V-280 on the other hand showed some very impressive ADS-33 level 1 yaw maneuvers for its gross weight, thanks wholly to the massive increase to 15 degrees of flapping. When ground taxi turning in their demo footage, the flapping can look pretty wild!
Inherent to tiltrotors, the control power from flapping is applied at the wingtips, creating a solidly effective yaw moment arm.
Now with the compound coaxial pusher prop design, you have the large and heavy static pusher prop assembly, gearbox/bearings, massive stabilizer, and tailwheel assembly - a huge amount of dead weight at the end of a very long moment arm from the mast. The only way to achieve yaw control is by differential torque between the rotors, which have been designed to be as stiff and lightweight as possible. This is a massively different situation from a conventional helicopter where the yaw moment is applied by the tail rotor at that same location perpendicular to the longitudinal axis.
I wonder, at the same medium to large gross weights, is a high flapping tiltrotor going to have substantially better yaw control than a rigid rotor coaxial design with a pusher assembly? I would say almost certainly. It's a real shame that Defiant hasn't even attempted (that we know of) high yaw rate maneuvers that could be compared to the myriad V-280 demos. Perhaps they have and the results were disappointing.
I think a historical knock on tiltrotor maneuverability was probably based on yaw rate, which is primarily affected by rotor flapping limits. The V-22 has around 10 degrees of flapping cooked into the hub and I do not believe meets level 1 HQ yaw rate (probably exacerbated in crosswinds). The V-280 on the other hand showed some very impressive ADS-33 level 1 yaw maneuvers for its gross weight, thanks wholly to the massive increase to 15 degrees of flapping. When ground taxi turning in their demo footage, the flapping can look pretty wild!
Inherent to tiltrotors, the control power from flapping is applied at the wingtips, creating a solidly effective yaw moment arm.
Now with the compound coaxial pusher prop design, you have the large and heavy static pusher prop assembly, gearbox/bearings, massive stabilizer, and tailwheel assembly - a huge amount of dead weight at the end of a very long moment arm from the mast. The only way to achieve yaw control is by differential torque between the rotors, which have been designed to be as stiff and lightweight as possible. This is a massively different situation from a conventional helicopter where the yaw moment is applied by the tail rotor at that same location perpendicular to the longitudinal axis.
I wonder, at the same medium to large gross weights, is a high flapping tiltrotor going to have substantially better yaw control than a rigid rotor coaxial design with a pusher assembly? I would say almost certainly. It's a real shame that Defiant hasn't even attempted (that we know of) high yaw rate maneuvers that could be compared to the myriad V-280 demos. Perhaps they have and the results were disappointing.
Totally wrong. The coax limitation for yaw is in autorotation. They leave room for differential collective on top of collective.
There are two cyclics. Tilting both rotors in the same direction creates a sideways force, the same as a conventional helicopter, but with no tail rotor. So we end up with a sideways push as well as roll. We need to counteract the roll torque from the prop. Tilting the rotors in opposite directions creates a pure couple, force times the distance separating the rotors.
You make very good points. Interesting, thank-you.
You make very good points. Interesting, thank-you.
An X2 rotor system would use lateral cyclic, same direction for both rotors, to react any torque from the prop. Also no big deal.
In the absence of education or experience in these things, you might find it helpful to learn to fly helicopters, or anything.
A conventional helicopter has to react the thrust from the tail rotor with lateral cyclic. It's no big deal.
An X2 rotor system would use lateral cyclic, same direction for both rotors, to react any torque from the prop. Also no big deal.
In the absence of education or experience in these things, you might find it helpful to learn to fly helicopters, or anything.
An X2 rotor system would use lateral cyclic, same direction for both rotors, to react any torque from the prop. Also no big deal.
In the absence of education or experience in these things, you might find it helpful to learn to fly helicopters, or anything.
When you get an answer from your bosses at Sikorsky, I am willing to learn and be educated.