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Sikorsky SB-1 flies for first time

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Sikorsky SB-1 flies for first time

Old 13th Dec 2019, 18:43
  #121 (permalink)  
 
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We never got beyond the test bench stage. No technology issues. Just cost and weight impacts were unacceptable.
CTR,

So you donít know if Brinelling would be an issue as bench test would never yield the aircraft vibratory environment (the whole bolted to Mother Earth thing).
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Old 13th Dec 2019, 18:54
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Nige wrote:

Talk about an armchair expert...
Words fail me...
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.




Last edited by The Sultan; 15th Dec 2019 at 13:44.
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Old 13th Dec 2019, 20:27
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Originally Posted by The Sultan
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 donít 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.
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Old 14th Dec 2019, 03:56
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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-1ís 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.
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Old 14th Dec 2019, 05:32
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Originally Posted by The Sultan


CTR,

So you donít know if Brinelling would be an issue as bench test would never yield the aircraft vibratory environment (the whole bolted to Mother Earth thing).
Sultan,

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.

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Old 14th Dec 2019, 10:11
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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.


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Old 15th Dec 2019, 07:14
  #127 (permalink)  
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Originally Posted by The Sultan
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 one question I cannot answer is if the SB>1 of the S-97 have a dedicated brake for their tail rotor. I am curious to know.

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.
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Old 15th Dec 2019, 13:42
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CTR

One thing you missed on actuators is they donít 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.
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Old 15th Dec 2019, 14:10
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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.
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Old 15th Dec 2019, 16:56
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Environment

Originally Posted by The Sultan
CTR

One thing you missed on actuators is they donít 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.
Actually, as one example the V-22 conversion actuator gearbox input speed is approximately 6,000 RPM, an output of approximately 600 RPM, and continuous bearing contact stresses higher than in high speed gearboxes (which I have also designed parts for). Actuator gears and bearings on the V-22 actuators also experience full load reversal and impact loads from emergency stop braking. With the exception of high temperature run dry requirements, the V-22 conversion actuators are subjected to a more severe environment than a typical tail rotor gearbox.

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.

Last edited by CTR; 15th Dec 2019 at 17:48.
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Old 16th Dec 2019, 15:01
  #131 (permalink)  
 
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Originally Posted by The Sultan
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.
The translational airspeed region was not as challenging as high speed flight in the X2. In fact for most of the lower speed region the X2 vibes could be managed without AVC using only classical methods to balance the rotors.
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!
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Old 14th Jan 2020, 07:43
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SB-1ís 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.
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/
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Old 14th Jan 2020, 08:30
  #133 (permalink)  
 
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Originally Posted by The Sultan
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/
That isn't what the article says.
There will ďalways be a disparity between where particular vendors are, but that does not mean theyíre not ready to compete,Ē
Nice try though...
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Old 14th Jan 2020, 12:58
  #134 (permalink)  
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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.
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Old 14th Jan 2020, 13:50
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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.
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Old 14th Jan 2020, 15:33
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Nige wrote:

That isn't what the article says.
The purpose of 280 and Defiant programs was to demonstrate the concepts which could meet the anticipated FLRAA requirements. Data from these programs would be used to refine the final spec ahead of a development competition and fly-off. Now that the JMR-TD phase has not been extended and the Army will soon be releasing the requirements for the production FLRAA effort the SB-1 is irrelevant with respect to the next phase (except for further demonstrating that the ABC is not a viable contender). So the Army statements are basically that they have seen enough and are moving on.

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.

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Old 14th Jan 2020, 16:24
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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.
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Old 14th Jan 2020, 18:02
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Originally Posted by CTR
In the meantime, as a program becomes delayed by over a decade, Sikorsky will continue to make money on Blackhawks.
https://www.pprune.org/rotorheads/619699-sikorsky-sb-1-flies-first-time.html#post10492312

I expect this effort will soon begin in earnest.
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Old 14th Jan 2020, 21:48
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Originally Posted by SansAnhedral
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.
Got some savage comments here, lol.
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Old 14th Jan 2020, 23:11
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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.
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