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S97 Raider

Old 15th Oct 2018, 15:58
  #401 (permalink)  
 
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Originally Posted by IFMU View Post
I've never heard the Raider in person. I've spent a lot of time with the X2. The first time Kevin pulled pitch it got very quiet in the TM trailer. All of us looked up from our screens to see what happened. All the data said it was running but the noise went away. Those blades are magic. During the early no prop flights all you could hear outside was the S76 chase. I do not believe that video is doctored.
Excellent job S97 team!
There's nothing "magic" about the rotors. I've been very near an H-53E on takeoff and "heard" it make almost no sound, yet on other days during rotor engagement one would have a difficult time speaking to a person right next to them. The effect of relative wind on the acoustic signature is far more likely the factor in rotor noise. Also, at least when X2 was flying, the -76 was generally positioned closer to the TM van than the test article (to the best of my recollection).
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Old 15th Oct 2018, 21:10
  #402 (permalink)  
 
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Originally Posted by KqQNr View Post
There's nothing "magic" about the rotors. I've been very near an H-53E on takeoff and "heard" it make almost no sound, yet on other days during rotor engagement one would have a difficult time speaking to a person right next to them. The effect of relative wind on the acoustic signature is far more likely the factor in rotor noise. Also, at least when X2 was flying, the -76 was generally positioned closer to the TM van than the test article (to the best of my recollection).
A 53E making no sound? That I've never seen! Or heard I should say.
When they flew the X2 in Elmira, you cannot say the S76 was closer to the X2 trailer. I was there!
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Old 15th Oct 2018, 22:42
  #403 (permalink)  
 
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Fair enough, I was speaking about WPB - and I was there. Re: H-53Es, my point is that if the winds are right, the sound is substantially reduced (but not eliminated). I am sure if you ask the Kilo guys, they will tell you the same thing.
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Old 18th Oct 2018, 17:26
  #404 (permalink)  
 
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Latest V-280 video compilation shows why the 97’s videos are not that impressive.
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Old 19th Oct 2018, 00:45
  #405 (permalink)  
 
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Show some confidence and post that in the 280 thread!
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Old 1st May 2019, 14:31
  #406 (permalink)  
 
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Looks like the full factual NTSB report was released on the S97 "hard landing" back in 2017.

5 seconds of roll oscillations up to 60 degrees (!) followed by rotor intermeshing and destruction. Could have been a far worse outcome. The whole incident reminds of the control issues experienced on XH-59 back in the 70s causing the loss of the first airframe (intermeshing blades in that incident as well) with the 2nd getting airworthy 2 years later.

https://www.verticalmag.com/news/nts...ider-accident/

Actual report:

https://dms.ntsb.gov/public/62000-62...323/624201.pdf
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Old 1st May 2019, 17:34
  #407 (permalink)  
 
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Thank you for the link. The two accidents are very dissimilar. I found the Raider accident troubling as the flight controls were my job on X2. They should have done a better job in test.

I truly believe anybody who designs FBW helicopter control systems should be a helicopter pilot, regardless of what company they work for.
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Old 1st May 2019, 19:54
  #408 (permalink)  
 
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Originally Posted by IFMU View Post
Thank you for the link. The two accidents are very dissimilar. I found the Raider accident troubling as the flight controls were my job on X2. They should have done a better job in test.
True, they were somewhat opposite in respect (too low gains in XH-59 vs 2.5x cyclic oversensitivity in S-97 in transition), but still overall the same general issue - cyclic flight control.
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Old 2nd May 2019, 02:25
  #409 (permalink)  
 
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Sans, it wasn’t low gain on the 59 ( in the sense of control sensitivity ), but rather low blade range, i.e., total moment capability longitudinally. The hell of that issue was that they’d been up against the forward stop previously.
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Old 2nd May 2019, 12:03
  #410 (permalink)  
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CLAW Rate Limits for Envelope Protection?

Reading the accident report I was surprised to discover that the blades contacted each other while still in flight from rapid roll reversals. I had expected to read they contacted each other when the aircraft landed hard. I would’ve expected some level of envelope CLAW protection to prevent actuator commands that could result in upper and lower rotor blade contact from pilot inputs. Even if the cyclic gain was too high, shouldn’t the actuator commands to the rotor have been limited?
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Old 2nd May 2019, 14:54
  #411 (permalink)  
 
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Originally Posted by JohnDixson View Post
Sans, it wasn’t low gain on the 59 ( in the sense of control sensitivity ), but rather low blade range, i.e., total moment capability longitudinally. The hell of that issue was that they’d been up against the forward stop previously.
Ah I see. Thanks for the correction John, I got the "low gain" quote from the Sikorsky Archives article.

First flight occurred in June, 1973. One month later the first XH-59A aircraft experienced a low speed accident on the flight field. The design team had never dealt with a rotor system as stiff as this before. There was much concern about the extremely high control power that the rotor could develop. As a result, the control system was designed with a very low gain to prevent the controls from being too sensitive. This seemed to work out fine in the initial hover tests. However, when the pilots moved out of hover to transition to forward flight, the aircraft tended to nose up. The pilot inputted more and more forward cyclic to counter this, until the stick was on the forward stop and the aircraft was still nosing up. The pilot reduced the collective to get it back on the ground. The tail contacted the ground first and the aircraft rolled over until the blades struck the ground. The rotor system was destroyed. Both pilots were uninjured.

This set the program back for over a year while the cause of the accident was determined. The conclusion was that the control system gains were too low to cover all flight modes. Aircraft #1 was rebuilt for wind tunnel testing, but was not returned to flight status
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Old 3rd May 2019, 03:13
  #412 (permalink)  
 
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The transition to forward flight resulted in the main rotor downwash impacting the low horizontal tail, which is what of course drove the tail down and nose up.
( About a year later, we were to engage that sort of problem in a major way with the original UTTAS tail which if I recall was 60 sq ft. ).
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Old 25th Jun 2019, 23:41
  #413 (permalink)  
 
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From R&W:

The compound helicopter, one of two Sikorsky built initially to satisfy the Army’s need for an armed scout helicopter to replace the OH-58D Kiowa Warrior, now has 55 total flight hours. It has flown to 207 knots in level cruise flight, performed 60-degree banks and risen to 8,000 feet.


Raider is flying almost weekly and at up to 180 knots — well past the sprint speed of a conventional helicopter — on almost every outings, said Chief Test Pilot Bill Fell. The goal was to fly at 220 knots, but the aircraft might not make that benchmark in its current configuration, Fell said.
Sent from my iPad
The above from R&W. Knowing the goals of the program this has to be considered a major setback to both the program and a failure of the ABC concept to produce a leap forward in rotorcraft. Taken with the lack of progress on the SB-1 one has to wonder if Sikorsky would have been better off not building hardware and hope a paper proposal based on empty promises could yield a development contact. Now that they have generated real data it will be hard to put the failure Genie back in the bottle.
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Old 26th Jun 2019, 12:07
  #414 (permalink)  
 
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Originally Posted by The Sultan View Post
From R&W:



The above from R&W. Knowing the goals of the program this has to be considered a major setback to both the program and a failure of the ABC concept to produce a leap forward in rotorcraft. Taken with the lack of progress on the SB-1 one has to wonder if Sikorsky would have been better off not building hardware and hope a paper proposal based on empty promises could yield a development contact. Now that they have generated real data it will be hard to put the failure Genie back in the bottle.
An article a while back had the comment from the Army stating something to the effect of “the Army knows quite a bit about the rigid coaxial configuration”... that may not be a good thing for Sikorsky and Sikorsky-Boeing.
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Old 26th Jun 2019, 15:01
  #415 (permalink)  
 
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The compound helicopter, one of two Sikorsky built initially to satisfy the Army’s need for an armed scout helicopter to replace the OH-58D Kiowa Warrior, now has 55 total flight hours. It has flown to 207 knots in level cruise flight, performed 60-degree banks and risen to 8,000 feet.
Wait, 55 flight hours in 4 years of flight testing?
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Old 26th Jun 2019, 16:36
  #416 (permalink)  
 
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55 hours is the total for the one that hasn’t crashed.
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Old 26th Jun 2019, 20:17
  #417 (permalink)  
 
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Article and video about 97’s “agility.” Looks lumbering at best, must be concerned about getting another upper/lower rotor collision. Not so sure why they spend so much time on fuselage attitude when tilt rotors are superior in every way whether you want a +/- pitch attitude or acceling or deceling with a level fuselage.

https://breakingdefense.com/2019/06/...for-army-fara/
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Old 24th Jul 2019, 11:11
  #418 (permalink)  
 
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Just think...this is the best Sikorsky can say about the S-97.

http://digitaledition.rotorandwing.c...707.1544675409

Having to use rotor aero to increase rotor separation to allow “safe” flight thereby resulting in so much drag they can not meet even their new lowered high speed goals does not bode well for this program or the SB-1.
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Old 24th Jul 2019, 13:23
  #419 (permalink)  
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So Which Story is Correct?

Did the S-97 rotors mesh in the air as described in the NTSB report based on the analysis of the video? Or has Rotor & Wing misquoted the pilots description of events by writing that the rotors meshed as a result of the hard landing?

From Rotor &Wing Article:
A glitch in the code caused the flight control system to miscue during the transition from takeoff to forward flight, and the aircraft began to wobble as the computer lost control of the separation between the counter-spinning rotors. The aircraft responded to pilot inputs more powerfully than it should have, causing the aircraft to slam into the ground. The force of the impact flexed the rotors enough that they made contact and shattered, Fell (Sikorsky Senior Test Pilot Bill Fell) explained.

From NTSB Accident Report:
3.0 VIDEO SUMMARY. Video of the accident sequence of events was reviewed. The video was filmed from the right rear quadrant of the helicopter. It showed the helicopter slowly taxing forward with all 3 landing gear wheels in contact with the ground. As the helicopter approaches the edge of the runway, the tail wheel lifts off the ground followed by the main landing gear lifting off the taxiway simultaneously. As the helicopter gets airborne, the nose pitched upward slightly with a slight right roll. The helicopter then rolls to the left about 20° angle of bank and the left landing gear contacts the ground. A right roll followed that went slightly past horizontal. The roll reversed to the left, exceeding 30° angle of bank, then reversed to the right, and as the helicopter rolled through the vertical plane, the upper and lower rotors intermeshed about the 1 o’clock position (as viewed from the cockpit), creating a cloud of blade fragments and gray dust. The right roll continued, exceeding 60° angle of bank, then reversed to the left, and then landed hard as the helicopter passed through the vertical plane. The rotors continued to turn, decelerating until they come to a stop 43 seconds later.

Last edited by T28B; 24th Jul 2019 at 13:57. Reason: formatting of degree symbol
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Old 24th Jul 2019, 16:00
  #420 (permalink)  
 
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Originally Posted by CTR View Post
Did the S-97 rotors mesh in the air as described in the NTSB report based on the analysis of the video? Or has Rotor & Wing misquoted the pilots description of events by writing that the rotors meshed as a result of the hard landing?

From Rotor &Wing Article:
A glitch in the code caused the flight control system to miscue during the transition from takeoff to forward flight, and the aircraft began to wobble as the computer lost control of the separation between the counter-spinning rotors. The aircraft responded to pilot inputs more powerfully than it should have, causing the aircraft to slam into the ground. The force of the impact flexed the rotors enough that they made contact and shattered, Fell (Sikorsky Senior Test Pilot Bill Fell) explained.

From NTSB Accident Report:
3.0 VIDEO SUMMARY. Video of the accident sequence of events was reviewed. The video was filmed from the right rear quadrant of the helicopter. It showed the helicopter slowly taxing forward with all 3 landing gear wheels in contact with the ground. As the helicopter approaches the edge of the runway, the tail wheel lifts off the ground followed by the main landing gear lifting off the taxiway simultaneously. As the helicopter gets airborne, the nose pitched upward slightly with a slight right roll. The helicopter then rolls to the left about 20° angle of bank and the left landing gear contacts the ground. A right roll followed that went slightly past horizontal. The roll reversed to the left, exceeding 30° angle of bank, then reversed to the right, and as the helicopter rolled through the vertical plane, the upper and lower rotors intermeshed about the 1 o’clock position (as viewed from the cockpit), creating a cloud of blade fragments and gray dust. The right roll continued, exceeding 60° angle of bank, then reversed to the left, and then landed hard as the helicopter passed through the vertical plane. The rotors continued to turn, decelerating until they come to a stop 43 seconds later.
It seems abundantly clear that in Bill's and Sikorsky repeated attempts to downplay the incident with the media, numerous reporters are understandably interpreting the blade contact as being a result of the hard landing, and not vice versa - a la the old XH-59 incident. This was certainly not the case.

I am sure Sikorsky was ruing the day of the NTSB report release. In my previous post I had posited that based on the long-range helicopter news footage of the aftermath they could have been looking for possibly thrown components...little did I know they were searching for the outboard few feet of all the blades!
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