|
We never got beyond the test bench stage. No technology issues. Just cost and weight impacts were unacceptable. So you don’t know if Brinelling would be an issue as bench test would never yield the aircraft vibratory environment (the whole bolted to Mother Earth thing). |
Nige wrote: Talk about an armchair expert... Words fail me... |
Originally Posted by The Sultan
(Post 10639224)
Nite wrote: Even the S-97 had the tail running on initial tests. So after 9 months Sikorsky would have the tail prop turning if they could. The fact they don’t proves my point. https://m.youtube.com/watch?v=jX3flLU9Wac The S-97 has never not had a spinning prop shown during any kind of operation... could have a different clutch type (wet vs dry) and thus not be a direct comparison to SB>1. Given the close proximity of the prop to the exhaust, a wet clutch that always had some viscous drag and thus some prop rotation on Raider makes some sense. |
Spline, Maybe someone who knows can clarify. Until then, as the S-97 is a prototype for the following designs you would expect a similar layout. Also we have seen no evidence that confirms the SB-1’s pusher is even connected to the drive system. If not connected after a year+ of running it points to a major problem they are having to address. |
Originally Posted by The Sultan
(Post 10639216)
CTR, So you don’t know if Brinelling would be an issue as bench test would never yield the aircraft vibratory environment (the whole bolted to Mother Earth thing). As you probably are aware, rolling element bearing Brinelling is caused by excessive static load and fretting is caused by oscillating motion less than a full bearing rotation from vibration (even under no load). So if the rotor can freewheel even a couple degrees in flight and the loads are low, both fretting and Brinelling are addressed. Having designed large pitch trim actuators including the C-17, I am intimately familiar with these bearing concerns. |
CTR, In none of the videos of the SB-1 have I seen the tail prop rotate even a few degrees. You may or may not know that in ground shake tests of helicopters/tilt rotors the gearboxes are routinely replaced with non-flight components prior to start of the tests to insure the bearings on flight hardware are not damaged. The vibration levels components are exposed to during these tests are, in most cases, less than or equal to those exhibited on the basic aircraft during operations. |
Originally Posted by The Sultan
(Post 10639644)
In none of the videos of the SB-1 have I seen the tail prop rotate even a few degrees. You may or may not know that in ground shake tests of helicopters/tilt rotors the gearboxes are routinely replaced with non-flight components prior to start of the tests to insure the bearings on flight hardware are not damaged. As far as ground shake testing on helicopters and Tiltrotors, I have supported both. The key differences in shake testing performed on the ground versus flight is that the rotors are intentionally locked for ground testing, and the gearboxes are not designed for this environmental condition. Additionally, gearboxes used for ground testing are almost always not acceptable for flight before any testing is conducted due to design and manufacturing deviations. Finally, remember that the pylon conversion actuators on Tiltrotors are gearbox driven ball screws. They spend long periods stationary, under load, and in a high vibration environment. The key difference is they are designed from the beginning to operate in this environment. So the question is not if gearboxes can survive this environment, it is if they were designed to survive this environment. |
CTR One thing you missed on actuators is they don’t rotate continuously at 600 to 24000 rpm under load like gearbox components and associated bearings and therefore not relevant to the discussion of gearboxes not operating for extended periods in high vibratory environments. |
IFMU Some of the highest vibration in helicopters occurs in the rotor transverse flow range which is the 20 to 40 knot range. These vibration levels often exceed cruise flight levels and do seem to be the speeds the SB-1 is still trying to achieve. Additionally, as you know, the X-2 relied on an active vibration suppression system to make the vibration in the cockpit tolerable. Unlike rotor or transmission mounted devices this system has only an affect on the area in proximity of the device and can significantly increase the vibration in other areas of the fuselage. A cockpit mounted AVS could easily double tail vibration over a not having one. |
Environment
Originally Posted by The Sultan
(Post 10640480)
CTR One thing you missed on actuators is they don’t rotate continuously at 600 to 24000 rpm under load like gearbox components and associated bearings and therefore not relevant to the discussion of gearboxes not operating for extended periods in high vibratory environments. This is not to say the X-2 gearboxes are properly designed to deal with the environment. Only that the technology to design gearboxes to withstand the environment is not new or unique. |
Originally Posted by The Sultan
(Post 10640492)
IFMU Some of the highest vibration in helicopters occurs in the rotor transverse flow range which is the 20 to 40 knot range. These vibration levels often exceed cruise flight levels and do seem to be the speeds the SB-1 is still trying to achieve. Additionally, as you know, the X-2 relied on an active vibration suppression system to make the vibration in the cockpit tolerable. Unlike rotor or transmission mounted devices this system has only an affect on the area in proximity of the device and can significantly increase the vibration in other areas of the fuselage. A cockpit mounted AVS could easily double tail vibration over a not having one. When I was a younger man I also thought AVC would make vibes better in some areas but worse in others. Makes sense from what we learned in freshman level physics. On an S92 with cabin mounted force generators (FGs) surveys showed that vibe levels pretty much decreased everywhere though pilot and passenger were the focus. So reality and theory diverge here. The X2 FGs were not cabin mounted but were on the structure as close to the dynamic system as possible. This reduced the vibes before it got to the cabin. The result was not merely tolerable, but the IPS at 250kts was lower than a UH60 at cruise. That is exceptional! |
SB-1’s Time Has Expired
Comments made by senior govt officials indicate that the SB-1 has run out of time without doing much more than hover. Quote from Defense News:
While the SB-1 logged much less in flight time than the V-280, the Army has determined it has enough data to move forward on its FLRAA program rather than extend the JMR TD to wait for the Sikorsky-Boeing team to log equivalent hours to its competitor Bell. Full Article: https://www.defensenews.com/land/202...ive-down-risk/ |
Originally Posted by The Sultan
(Post 10662408)
Comments made by senior govt officials indicate that the SB-1 has run out of time without doing much more than hover. Quote from Defense News:
As there have been no reports that the SB-1 has exceeded even 20 kts at the end of the JMR-TD the data the Army has gathered supports a conclusion that the tilt rotor can meet or exceed all program goals while the ABC concept is plagued with multiple limitations that will keep it from being a viable platform. Full Article: https://www.defensenews.com/land/202...ive-down-risk/ There will “always be a disparity between where particular vendors are, but that does not mean they’re not ready to compete,” |
Politics Motives versus Technological Reality
Sultan has yet to realize that in the US Army and DOD in general, political motives almost always trump technological realities.
Sikorsky from the start of the FVL technology demonstrator selection was favored by the US Army to be the ultimate supplier for the UH-60 replacement. With all the resources of Sikorsky and Boeing combined, how could they fail? Then Bell all alone, using advanced design tools and proven tilt rotor technology, screwed that all up and succeeded beyond expectations. Does anyone think that if the situation was reversed, and Bell was two years behind schedule, that the US Army would select Bell to proceed to the next stage and build a prototype? Of course not. If Bell had failed as badly in producing a demonstrator aircraft as Sikorsky and Boeing have done, the competition would be over and the SB>1 Defiant would be moving forward in development all alone. Sultan, what is just, fair and technically correct has no place in the administration of the FVL contracts. |
Its downright laughable how much tapdancing the defense media does when it comes to reporting on SB1 in order not to potentially upset LockMart.
I've now read I think 4 different articles regarding the comments by the Army on the FLRAA timeline, and not a single one of them gives any attention to the fact that SB1 only managed to fly for less than 5 hours in almost a full calendar year, nor the fact it hasn't demonstrated anything appreciably more than daylight under its wheels. They seem to be more focused on the BS excuses about rotor blade manufacturing....something that had zero to do with it staying on the ground after the blades were delivered (presumably....unless the blades are actually not holding up in PTSB runs, which would be even more of a disaster). Similarly, all the same reporters have displayed some considerable collective amnesia on the craft that was intended to serve as risk reduction to Defiant - the S97. With 5 full years since first flight under its belt, why hasn't there been any Army pilots in that thing? Why has it not even approached its target max speeds, or displayed any of the fancy maneuverability Sikorsky loves to show off in their computer generated movies? Literally nobody is calling out the elephant in the room on this tech, Many people in the industry have been saying for years the ABC concept is flawed, doesn't scale, and has immense fundamental issues. If the abject failure of the SB1 demonstrator program and the lack of any real progress with the S97 over half a decade doesn't make that case, its hard to imagine what would. The silence on this outside of aviation forums and defense article comment sections is deafening. |
Nige wrote:
That isn't what the article says. If the final spec comes out with a max speed range of 20 to 300 kts, max altitude of 10 feet to 20k feet, and a range of 100 feet to 700+ miles I will concede that I was wrong and the SB-1 is not a failure. Moving forward it will be interesting to see what Boeing proposes as I do not see them not trying to compete for FLRAA. |
In a Just World
Sultan,
In a fair and just world he would be correct. But I believe the US Army will give Sikorsky as many bites of the apple as possible to try to get it right. In the meantime, as a program becomes delayed by over a decade, Sikorsky will continue to make money on Blackhawks. |
Originally Posted by CTR
(Post 10662863)
In the meantime, as a program becomes delayed by over a decade, Sikorsky will continue to make money on Blackhawks.
I expect this effort will soon begin in earnest. |
Originally Posted by SansAnhedral
(Post 10662731)
Its downright laughable how much tapdancing the defense media does when it comes to reporting on SB1 in order not to potentially upset LockMart.
... Literally nobody is calling out the elephant in the room on this tech, Many people in the industry have been saying for years the ABC concept is flawed, doesn't scale, and has immense fundamental issues. If the abject failure of the SB1 demonstrator program and the lack of any real progress with the S97 over half a decade doesn't make that case, its hard to imagine what would. The silence on this outside of aviation forums and defense article comment sections is deafening. |
CTR,
From the reported govt comments the general impression I got was the FLRAA will be accelerated to pick two to continue soon with down select in 2022/23 rather than 2025. If this ends up being the case I don’t see how anyone but Bell can get something in the air and demoed with the required flight spectrum (if a flight evaluation is even still going to be a requirement). If this is the case I expect to see Boeing banging on Bell’s door asking/demanding to be a partner and LM saying doing the avionics is good enough. |
Originally Posted by CTR
(Post 10662700)
Sultan has yet to realize that in the US Army and DOD in general, political motives almost always trump technological realities.
Sikorsky from the start of the FVL technology demonstrator selection was favored by the US Army to be the ultimate supplier for the UH-60 replacement. With all the resources of Sikorsky and Boeing combined, how could they fail? Then Bell all alone, using advanced design tools and proven tilt rotor technology, screwed that all up and succeeded beyond expectations. Does anyone think that if the situation was reversed, and Bell was two years behind schedule, that the US Army would select Bell to proceed to the next stage and build a prototype? Of course not. If Bell had failed as badly in producing a demonstrator aircraft as Sikorsky and Boeing have done, the competition would be over and the SB>1 Defiant would be moving forward in development all alone. Sultan, what is just, fair and technically correct has no place in the administration of the FVL contracts. |
Update
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For 100kt, the fuselage angle is noticeably nose-down - what will it look like at 280kt?
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Wow. . . .100 knots. The fuselage angle indicates the tail prop is probably generating little or no thrust which means the fuselage has to tilt to get any non vertical thrust. A shame the program it was developed for completed last month.
|
Good afternoon, folks. I'm a semi-new member. It seems that there is a bit of anti-SB-1 sentiment, and i'll rant my ideas on it. ALot of us want to see Bell Helicop-- er, Bell Flight, prevail in the FVL FLRAA or whatever it's called now. They're kind of an underdog i.e. they've had their machines in various entries over the years, and lost out to the AH-64 and UH-60 i.e. bid programs for Turkey, Taiwan, South Korea, Greece, etc, other countries, and the dominance of the AW139 in civil and militaries, the seeing the dead end of the ARH-70 bid, the Bell 210/412 not being picked over the Lakota UH-72... It would be great to see Bell prevail, especially as the Navy went with the AW-119 for the TH-57 replacement despite the idea of replacing a Bell 206 with a 407 seemed like a sure bet. Seems like Leonardo is winning everything these days!! I also secretly kick my table leg when I see on heli Hub that some other county Air ambulance replaces their Bell 412 with a $&@ Airbus H135/145 or Leo-Agusta Westland-Boeing whatever AW139. If only the Bell 525 had been ready in time for the UH-1N replacement... grrr.
It's good to see the AH-1Z get some foreign interest, like the Czech Republic's order and Bahrain' s pending sale, with Morocco and Romania showing interest. bell was able to make a sale to pakistan - but the AH-1Zs are currently in storage due to political order. I believe the winged and plane-propped V-280 will have the range and speed advantage, and will be agile enough at the X. I simply don't see the SB>1 being as fuel efficient with the twin rotors and pusher prop, but may be nearly as fast as Valor due to raw power, but if Raider S-97 and Raider X are examples, it will be very agile at the X. We have to be aware that Sikorsky has a strong contender in the SB-1. However, I am sure Bell has their cards lined up for the FVL, with the V-280 building on the V-22 to make a strong case for tilt-rotors, and their B360 Invictus has the least complex approach to FARA, which may be a good thing. Go Bell Flight! |
Originally Posted by Ascend Charlie
(Post 10665771)
For 100kt, the fuselage angle is noticeably nose-down - what will it look like at 280kt?
|
Because it is in flight test, they will be doing flights at many different power settings on the rotor, prop, plus horizontal tail position. Each one will give a different attitude for a given airspeed. There is no reason it won't fly level body throughout the envelope once they have it mapped out.
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IFMU: gee, what's with the common sense and rational thought in a post?
Are you sure you are in the right place? :E |
Originally Posted by Copter Appreciator00
(Post 10671499)
if Raider S-97 and Raider X are examples, it will be very agile at the X.
40 years after XH-59, 10 years after X2, and 5 years after first flight on S-97 and the most extreme maneuvering we have seen is footage of Raider plodding around lazy strafing circles played back at 1.5X speed on Sikorsky youtube videos. I simply don't see the SB>1 being as fuel efficient with the twin rotors and pusher prop, but may be nearly as fast as Valor due to raw power |
If the Army specs a high rate roll reversal at high speed (low rotor rpm) to simulate SAM avoidance the ABC concept is finished. The S-97 crash at full rpm showed how even moderate roll rates will cause the rotors to collide.
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Originally Posted by The Sultan
(Post 10673256)
If the Army specs a high rate roll reversal at high speed (low rotor rpm) to simulate SAM avoidance the ABC concept is finished. The S-97 crash at full rpm showed how even moderate roll rates will cause the rotors to collide.
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Originally Posted by The Sultan
(Post 10673256)
If the Army specs a high rate roll reversal at high speed (low rotor rpm) to simulate SAM avoidance the ABC concept is finished. The S-97 crash at full rpm showed how even moderate roll rates will cause the rotors to collide.
high rate roll reversal at high speed (low rotor rpm) to simulate SAM avoidance Missile seeker heads have not gotten worse in the interim. |
Originally Posted by Lonewolf_50
(Post 10673707)
My instructors at Fallon and Nellis, regarding SAM evasion by helicopters, would be laughing pretty hard at your understanding of how slow aircraft deal in modern SAM avoidance.
The FLRAA is a 280+ Kt aircraft and not a 30 yr old 120 kt or slower design. I believe the avoidance technique is still to pop chaff and flares and then be somewhere else when the missile arrives. Kind of defeats the purpose to fly straight and level after deploying countermeasures. From a countermeasures description: Once the presence of a "live" IR missile is indicated, flares are released by the aircraft in an attempt to decoy the missile; some systems are automatic, while others require manual jettisoning of the flares. The aircraft would then pull away at a sharp angle from the flare (and the terminal trajectory of the missile) and reduce engine power in attempt to cool the thermal signature. Optimally, the missile's seeker head is then confused by this change in temperature and flurry of new signatures, and therefore follows the flare(s) rather than the aircraft.=13.33px |
Originally Posted by The Sultan
(Post 10673807)
Lone
The FLRAA is a 280+ Kt aircraft and not a 30 yr old 120 kt or slower design. There is a rate change that takes a lot more speed to make a difference to a seeker head with tech that is two generations older than what is available now. What feels like a radical maneuver in that cockpit looks pathetic to the seeker head. (Granted, I am sure that old OV-10 Bronco hands may have a tew things to say about this). I believe the avoidance technique is still to pop chaff and flares and then be somewhere else when the missile arrives. |
Originally Posted by SplineDrive
(Post 10673272)
The crash was a result of the wrong set of control laws being active, not the rate of input... the crash isn’t representative of how well the aircraft will maneuver. Most rotary wing platforms are capable of blade to “something” strikes if control laws drive the aircraft to a bad state.
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Lone,
To be fair, it was the Army themselves (and Sikorsky over the years with their presumed greater hover maneuverability) who had been touting the value of exceeding ADS-33 requirements and the (preposterous) idea of dodging threats from slow speed/hover. It was always the knock against tiltrotors, hence why the V280 added massive amount of flapping to address the V22's relative sluggishness. Bell always argued the survivability was not from dancing around a seeker, but flying high above the threat, faster, and eliminating the time time on station. The Army should really have recalled the AH-64 fights in Najaf to remember why the doctrine immediately changed from lobbing munitions from a stand off hover to constant high speed strafing attacks. |
Update today. Sikorsky sounds nervous. Go to breakingdefense.com
“We’re flying it before we’re buying it,” McCarthy said this morning. “There’s nothing better than putting hours against the platform and learning.” "The SB>1 Defiant compound helicopter has only 11 hours of flight testing, versus over 160 for Bell’s V-280 Valor""But what has the actual aircraft done in flight? Fell said that Defiant has flown backwards, sideways, banked at a 45-degree angle, and flown forward in level flight as fast as 150 mph (130 knots)."But that’s not halfway to the 322 mph (280 knots) that the Army wants. Even the Army’s minimum requirement for top speed is 265 mph (230 knots). "When will the Defiant fly at its top speed? “A few months,” Fell said. That’s a remarkably short timespan compared to how long it’s taken to get it this point." |
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Another article.
https://www.verticalmag.com/news/sik...er-tail-rotor/ I like this part: If the tail boom, which includes no hydraulics, took a direct hit and literally fell off, the aircraft would still be able to operate as a helicopter. All control surfaces aft of the engine outlet are controlled by electronic actuators. |
Originally Posted by SansAnhedral
(Post 10673878)
The Army should really have recalled the AH-64 fights in Najaf to remember why the doctrine immediately changed from lobbing munitions from a stand off hover to constant high speed strafing attacks.
The Army requirements for Comanche had some very tough to meet lateral movement numbers. I'll offer that "shoot it from a hover" was being been abandoned in the midl to late 90's in at least a part of the Army's recon / attack community. |
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