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Helicopter missing in the Med

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Helicopter missing in the Med

Old 15th Jun 2020, 00:13
  #101 (permalink)  
 
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Originally Posted by The Sultan View Post
Real flight tests of a higher harmonic control was conducted by Hughes on a OH-6 in the early 80”s. Lot of pre-flight press and zero coverage post test flights. Those in the know indicated that the mechanical components between actuators and blade beat themselves to death in a very short period of operational time. Concept shelved as impractical.

Even with moving the entire thing to the rotating system, who thinks individual independent blade control is a good idea? There are so many failure modes the system safety assessment would be a nightmare (except for Boeing who doesn’t bother with such trivia). Any failure due to mechanical, wiring, electronic, or environmental (lighting) which results in the loss of pitch control to one blade is a catastrophic event which requires 1 in a billion level of reliability. So everything has to be independently triple redundant and impervious to common mode failure (lighting again). Concept impractical at the the most casual analysis.
The OH-6 wasn't the only HHC testbed, either. Several manufacturers tried this vibration or L/De improving approach 40 years ago and there are exactly zero fielded aircraft with HHC rotor control today. I think the primary reason it (and all of the downsides Sultan mentioned) are being investigated again is that HHC is seen as a solution to the even larger problems with rigid rotors.
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Old 17th Jun 2020, 08:05
  #102 (permalink)  
 
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https://www.ctvnews.ca/canada/cyclon...-dnd-1.4985880
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Old 17th Jun 2020, 09:22
  #103 (permalink)  
 
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So there’s a potential issue with the AP conflicting with pilot inputs that has caused this and they are just adding a note to the Flight Manual and resuming operations? Is that not a little close to Boeing’s 737 Max initial solution?
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Old 17th Jun 2020, 12:43
  #104 (permalink)  
 
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So what is different with the design of the Cyclone AP/FD (other than it being FBW) - every other AP has the ability to 'fly through' so the pilot can always override the FD. Any military pilot worth his salt encountering a possible control malfunction would disengage at least the FD and probably the AP if in any doubt.
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Old 17th Jun 2020, 14:28
  #105 (permalink)  
CTR
 
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Originally Posted by [email protected] View Post
So what is different with the design of the Cyclone AP/FD (other than it being FBW).....
The Cyclone cyclic control side stick is a unique trim configuration, similar to what is used on an F-16 and Airbus FBW commercial airliner. So basically, it is a simple spring to center joystick with zero position relationship with AP inputs. All other production FBW rotorcraft I am aware of (NH90, V-22, CH-53K) simulate conventional mechanical flight control AP system operation with stick movements.

Note, the Leonardo 609 and Bell 525 also incorporate AP systems that simulate cyclic stick motion, following encouragement of certification authorities.


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Old 17th Jun 2020, 15:48
  #106 (permalink)  
 
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Originally Posted by drugsdontwork View Post
So there’s a potential issue with the AP conflicting with pilot inputs that has caused this and they are just adding a note to the Flight Manual and resuming operations? Is that not a little close to Boeing’s 737 Max initial solution?
Noting close to the 737 Max!

The pilot attempted to make a number of manoeuvres while the Cyclone's "flight director," or auto-pilot, was still engaged
That's the misuse of automation '101'! Any aircraft will do what it's been told to in that situation - FBW or not.
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Old 17th Jun 2020, 16:40
  #107 (permalink)  
 
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...... suggested the problem was the result of a "series of events" and only occurred within a "very narrow band" of flight activities that had not been previously identified or tested.
Does this mean it was flown outside it’s envelope?
or not necessarily so?
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Old 17th Jun 2020, 19:06
  #108 (permalink)  
 
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Like everyone else here I have flown on lots of fly by wire aircraft and we have built up enough confidence to accept them as an every day low risk means of transport. However this accident, if we take the RCAF statement at face value, appears to be the very scenario that we all worried about when FBW was first installed. According to the statement the aircraft did not respond as expected to the pilot's control input and the RCAF bland assurances about resumption of operations seem disingenuous at best.

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Old 18th Jun 2020, 08:19
  #109 (permalink)  
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https://nationalpost.com/news/canada...s-to-fly-again

Deadly Cyclone crash caused by 'conflict' between pilot, helicopter: Canadian military says
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Old 18th Jun 2020, 11:50
  #110 (permalink)  
 
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Originally Posted by ChrisVJ View Post
Like everyone else here I have flown on lots of fly by wire aircraft and we have built up enough confidence to accept them as an every day low risk means of transport. However this accident, if we take the RCAF statement at face value, appears to be the very scenario that we all worried about when FBW was first installed. According to the statement the aircraft did not respond as expected to the pilot's control input and the RCAF bland assurances about resumption of operations seem disingenuous at best.
We don't know how the RCAF know that the aircraft did not behave as the crew expected - unless there is something recorded in the voice data (like "woah, what's it doing??" recoding ends). Regardless, what the crew expected it to do and what the aircraft was actually being commanded to do may be totally different things, given that the later statement says it was being hand flown with the FD engaged. Maybe they decelerated with aft cyclic then released the pressure and the aircraft tried to regain the original IAS datum, maybe they reduced power using the collective trim and the rad-alt datum reduced too. There could be all sorts of answers that are nothing to do with FBW and there are a number of serious S92 incidents out there, resulting from mishandling of its Flight Director, that testify to that.
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Old 18th Jun 2020, 16:30
  #111 (permalink)  
 
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ISTR the Mk 6 Chinook that was sold to the RAF by Boeing suddenly showed interesting handling characteristics when flown in a more aggressive fashion than it had been tested and declared airworthy in.
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Old 24th Jun 2020, 14:32
  #112 (permalink)  
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Latest News Report from CBC

Latest. https://www.cbc.ca/news/politics/cyc...rash-1.5624242

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Old 24th Jun 2020, 15:05
  #113 (permalink)  
 
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From article:

The investigation into the crash is still ongoing, but flight safety investigators and the senior commander in charge of joint flying operations said last week a combination of a software "bias" and the crew's inability to react to the unexpected moves of the flight control computer likely contributed to the tragedy on April 29.

The lead investigator, Col. John Alexander, said the crash and the software issue were "completely unforeseen."
Sounds like a repeat of the S-97 crash which was the aircraft controls responding in an unexpected manner to a normal input with no recognition time available to adapt to the flight control error. The timeline would indicate that both the 97 and 148 controls were done by the same flight controls team, which points to systemic failures in the development processes used. Does not bode well for CH-53K deployment.
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Old 24th Jun 2020, 20:44
  #114 (permalink)  
 
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It sounds barely feasible as a reason for a crash - what manoeuvre were they performing that was so unusual? They'll be getting Dominic Cummings to give a press conference next!
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Old 25th Jun 2020, 11:33
  #115 (permalink)  
 
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Question

Originally Posted by CTR View Post
The Cyclone cyclic control side stick is a unique trim configuration, similar to what is used on an F-16 and Airbus FBW commercial airliner. So basically, it is a simple spring to center joystick with zero position relationship with AP inputs. All other production FBW rotorcraft I am aware of (NH90, V-22, CH-53K) simulate conventional mechanical flight control AP system operation with stick movements.

Note, the Leonardo 609 and Bell 525 also incorporate AP systems that simulate cyclic stick motion, following encouragement of certification authorities.
CTR - can you please explain the location of this "cyclic control side stick" you mention? It seems apparent a traditional cyclic (while FBW) is used on the CH-148 and no side stick as on F-16 and Airbus FBW airliner.

What are your sources for this information?

Also I assume you are aware of the different characteristics between analoge and digital FBW when you throw all FBW rotorcraft into one bag? (NH90, V-22, CH-53K)


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Old 25th Jun 2020, 16:41
  #116 (permalink)  
 
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Originally Posted by pitchlink1 View Post
Also I assume you are aware of the different characteristics between analoge and digital FBW when you throw all FBW rotorcraft into one bag? (NH90, V-22, CH-53K)
I’d say all of those use digital FBW computers.

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Old 25th Jun 2020, 20:34
  #117 (permalink)  
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Description of S-92 FBW /CH-148 Cyclone Flight Controls

From Aviation Today:

”The principal flight control stick will be in the cyclic position, in front of the pilot, but it will function more like a joystick. Officially called the "right-hand controller," it is comparable to the Comanche's sidearm controller, and it controls pitch, roll and yaw.

The right-hand controller doesn't give the pilot the exact feedback of a conventional cyclic stick, but Mayo believes helicopter pilots will find operating the FBW-equipped S-92 "to be an easy transition because the automatic features simplify the job of flying."

Link to full article below.
https://www.aviationtoday.com/2004/0...-for-the-s-92/


And yes, I am familiar with the differences between analog and digital flight control systems. But in all other FBW production helicopters and Tiltrotors (Comanche does not count) the cyclic is back driven in response to AP inputs. In the CH-148 it does not, unless changes to the architecture have been made late in development I am not aware of.
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Old 27th Jun 2020, 12:39
  #118 (permalink)  
 
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My memory is dim re whether this was pre-Comanche or pre-S-92?MHP, but there were a couple of engineers who pushed the most efficient controller design: build in the capability for the controller to go up and down for collective.
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Old 27th Jun 2020, 15:26
  #119 (permalink)  
 
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Early Sikorsky FBW development

Sikorsky with its SHADOW XS-76 demonstrator helicopter extensively evaluated helicopter FBW controls. At that time we concentrated on the types of controllers and did little evaluating more complex control laws. The Shadow aircraft had an electric side arm controller, electric conventional pedals and an electric back driven collective in the front cockpit. The copilot’s station had an electric sidearm controller. The pilots station had conventional mechanical controls that could override and shut off the FBW control system.

Two sidearm controllers were evaluated. One ridged stick and one with limited compliance similar the F-16. Configurations evaluated included: 4 axis, pitch ,roll, yaw and collective on the side arm controller, 3 plus 1, pitch roll and Yaw on the side arm controller and a conventional collective. The collect was back driven and would move up and down with input from the side arm controller. A lemon squeezed type switch on the collective would disable the collective function on the side arm controller. Lastly we evaluated a conventional configuration, pitch and roll on the side arm controller, yaw pedals and a conventional collective that was moved up and down.

The co-pilots side arm controller was typically a 4 axis controller and was used to assist the front seat pilot through some maneuvers. This was extensively used when military pilots and dignitaries were provided with a front seat demonstration flights.
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Old 27th Jun 2020, 16:38
  #120 (permalink)  
 
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Jack,perhaps you can elaborate and expand on the evaluation in terms of `the good,bad and the ugly` aspects of handling the controls ,or if it`s in the public domain,reference to reports.
Are pilots likely to become`one-armed paper-hangers` in the future with foot and arm-rests...?
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