Sikorsky SB-1 flies for first time
US Patent Application showing what looks like SB>1 main rotor system
High resolution first flight image showing bare rotor system
Since you have experience in the Huey, you’ll appreciate the evolution of rotor head technology from greased steel bearings to... steel bearings and TT straps. All metal construction, highly loaded oscillating steel bearings, and even the blade lugs look like they have doublers bolted on. Speaks to the load magnitudes involved on a rigid rotor head of this size. Doesn’t look light or prone to long bearing lives.
Below the Glidepath - not correcting
That MR head is mighty complicated. It all undoubtedly works, but what is the real % gain over a conventional helicopter in terms of cost/maintenance/operational benefit? It seems a lot like an idea looking for a requirement at the moment, I was at West Palm Beach when the Comanche was canned...
Until they achieve and demonstrate a single promised performance metric, or even allow a non-company pilot in the thing to objectively assess the vibration, I would say the jury is still firmly out on that one.
Unbelievable that the US Army can be so patient.
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That MR head is mighty complicated. It all undoubtedly works, but what is the real % gain over a conventional helicopter in terms of cost/maintenance/operational benefit? It seems a lot like an idea looking for a requirement at the moment, I was at West Palm Beach when the Comanche was canned...
As for the coaxial design, the obvious gain is no tail rotor and assorted systems and penalties. Whether that outweighs the complexity of 2 rotor heads I have no idea, but the Russians have been using them for years.
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but what is the real % gain over a conventional helicopter
Sure, in a one-disk system, the advancing blade can generate a lot of lift, but it has to throw most of it away, because it can only provide the dismal amount of lift that the struggling, half-stalled retreating blade provides. Otherwise, the sides are not balanced. The advancing side, at top speed, could provide around 7 times more lift than it is allowed to generate. But use a coaxial system, and there is an advancing blade on both sides, forget the retreating blade, and now because all that lift can be used, the diameter can be smaller. Simples. Tccchhhk.
The advantage is not having to rely on getting any lift from the retreating side of the disks.
Sure, in a one-disk system, the advancing blade can generate a lot of lift, but it has to throw most of it away, because it can only provide the dismal amount of lift that the struggling, half-stalled retreating blade provides. Otherwise, the sides are not balanced. The advancing side, at top speed, could provide around 7 times more lift than it is allowed to generate. But use a coaxial system, and there is an advancing blade on both sides, forget the retreating blade, and now because all that lift can be used, the diameter can be smaller. Simples. Tccchhhk.
Sure, in a one-disk system, the advancing blade can generate a lot of lift, but it has to throw most of it away, because it can only provide the dismal amount of lift that the struggling, half-stalled retreating blade provides. Otherwise, the sides are not balanced. The advancing side, at top speed, could provide around 7 times more lift than it is allowed to generate. But use a coaxial system, and there is an advancing blade on both sides, forget the retreating blade, and now because all that lift can be used, the diameter can be smaller. Simples. Tccchhhk.
Maybe Sikorsky finally gets a really excellent anti-vibration control system working for all flight conditions. Maybe they lose both FVL contracts. We’ll see.
A 4 bladed rotor will interact with 3/4/5P harmonic blade loads. Those harmonic blade loads WILL end up as vibratory hub loads that must be mitigated somehow. Studying a helicopter dynamics textbook will show that. It’s not just a matter of “poor blade tuning” these aircraft struggle with, it’s the intersection of concept and physics.
That MR head is mighty complicated. It all undoubtedly works, but what is the real % gain over a conventional helicopter in terms of cost/maintenance/operational benefit? It seems a lot like an idea looking for a requirement at the moment, I was at West Palm Beach when the Comanche was canned...
Pretty sure I have the above general statements correct since they would apply to any 4 bladed rotor (and ignoring higher harmonics). The X-2D, S-97 Raider, and SB>1 all have different hub and blade configurations. It’s not a given that the tuning and harmonic airloads across all three ships are identical, despite being 4 blades each. In fact, looking at the respective hub designs in patent art, I’m pretty sure they’re not identical. So the X-2D experience might not entirely translate to the larger ships.
Ifmu Wrote:
The X-2 was a tiny concept demonstrator with an occupied area of around 5 feet on the center line. It is simplistic to get that small of an area smooth in only one direction and at one frequency such as N/rev. The problem becomes significantly harder trying to suppress vibration over a large three dimensional space, which the last S-97 pilot report I saw says they have failed at. In fact the pilot quotes indicated the vibration (and loads?) were so bad that the crew were reluctant (note I didn’t say scared) to go above 180 knots once it became obvious the latest cure for vibration being tested did not meet expectations. As the 97 still appears to be restricted to 180 knots for even high profile demos they apparently failed to overcome the issue.
I have no knowledge of Raider or Defiant, but they got it working for X2. I personally don't see any reason why it wouldn't work for the new aircraft. They have excellent dynamics people, not just in theory but supporting the aircraft in the field and in the air.
But when will an Army pilot fly the Defiant
When I first saw the article, I was expecting that a customer pilot was finally flying the SB>1 Defiant. I can’t quite understand all the hype for an Army customer Pilot flying the S 97. I would’ve expected this to have already occurred years ago.
The article did note that an Army customer Pilot flew the V-280 back in February 2018. Would have enjoyed reading an article comparing the handling qualities of the two aircraft by the same pilot.
The article did note that an Army customer Pilot flew the V-280 back in February 2018. Would have enjoyed reading an article comparing the handling qualities of the two aircraft by the same pilot.
Taking Lowering the Bar to Extremes
From Sans earlier:
[QUOTESeems Sikorsky's own demonstration flights have implied that. After reaching barely over 200 kt in Sept 2018, they subsequently have flown progressively slower in their big-to-do demo flights - only reaching 190 kt in July 2019 and then 180 kt in Feb 2020. And of course, nothing since then at all.
][/QUOTE]
From above article:
Unless I missed a revision, the FARA min max speed was 180 knots. In what fuzzy world is 187 knots (+4%) considered well in excess of that requirement? In my world that difference is considered barely outside allowed measurement error. I know the commercial requirement is to demonstrate 10% margin to an never exceed airspeed limit, so they are (in their world) grossly short of the 198 knots required to get credit for being able to do 180 knots.
Sikorsky really needs better PR people. The speed thing is bad enough, the I not letting the Army sit at the real controls (paraphrasing) is worse. Implies that the 97 is not the easiest thing to fly. Wonder if their scared the Army pilot be slightly aggressive on the controls ending up in another collision between the rotors.
[QUOTESeems Sikorsky's own demonstration flights have implied that. After reaching barely over 200 kt in Sept 2018, they subsequently have flown progressively slower in their big-to-do demo flights - only reaching 190 kt in July 2019 and then 180 kt in Feb 2020. And of course, nothing since then at all.
][/QUOTE]
From above article:
Raider achieved 187 knots, well in excess of the Army’s threshold speed for FARA.
Sikorsky really needs better PR people. The speed thing is bad enough, the I not letting the Army sit at the real controls (paraphrasing) is worse. Implies that the 97 is not the easiest thing to fly. Wonder if their scared the Army pilot be slightly aggressive on the controls ending up in another collision between the rotors.
When I first saw the article, I was expecting that a customer pilot was finally flying the SB>1 Defiant. I can’t quite understand all the hype for an Army customer Pilot flying the S 97. I would’ve expected this to have already occurred years ago.
The article did note that an Army customer Pilot flew the V-280 back in February 2018. Would have enjoyed reading an article comparing the handling qualities of the two aircraft by the same pilot.
The article did note that an Army customer Pilot flew the V-280 back in February 2018. Would have enjoyed reading an article comparing the handling qualities of the two aircraft by the same pilot.
Firstly, that was not a flight of (an actual FVL aircraft) Defiant. Secondly, I must have missed the part in there where Charlie was permitted to make a single comment about the Raider flight (specifically the vibration). The fact it was explicitly mentioned that he was muzzled about the experience is telling.
It's definitely eyebrow raising that it took over 5 years for a pilot to set foot into the S-97. The V-280 had the Army XP flight 2 months after first flight!
It's definitely eyebrow raising that it took over 5 years for a pilot to set foot into the S-97. The V-280 had the Army XP flight 2 months after first flight!
Bell Tiltrotor Guest Pilots
Before it was sent to the Smithsonian Air and Space Museum, the actor Harrison Ford flew the XV-15. Maybe he will be the next V-280 guest pilot ;-)
