F-35 accident Fort Worth 15/12/22 - pilot ejected ok
Correct! Thrust is equally distributed between front and rear (cold and hot) nozzles in the Harrier. Donk stops and you go straight (and level!) down +/-. A failure of one reaction control can give a hard-over in pitch or roll, with fatal results but has only (to my knowledge) happened once.
All 4 nozzles are connected by very large bicycle chains which lock them in sync, so that differing nozzle angles are not possible. Simple but very effective system. No effin great intake doors, whizzing fans or bendy rear ends sight.
Mog
All 4 nozzles are connected by very large bicycle chains which lock them in sync, so that differing nozzle angles are not possible. Simple but very effective system. No effin great intake doors, whizzing fans or bendy rear ends sight.
Mog
The Harrier has certainly suffered from nozzle failures in the past, although not sure if it was whilst in the hover. I believe initially the front nozzles were fibreglass before being redesigned. The Harrier’s nozzles are also much nearer to the CofG, so any change of moment from an individual nozzle failure is likely to be less than the F35; however, the loss of a 1/4 of the summed lift vector is probably still going to result in an accident!
All 4 nozzles are connected by very large bicycle chains which lock them in sync, so that differing nozzle angles are not possible. Simple but very effective system. No effin great intake doors, whizzing fans or bendy rear ends sigh
I also noted the C of G element but tired eyes tapping an iPhone drove me to brevity.
I may be wrong, but IIRC the GRP front nozzles were only used on the P1127/Kestral; one came off while exploring supersonic dives so they were replaced with metal nozzles from the Harrier GR1.
PDR
PDR
Salute!
All of the Harrier technology and procedures and such are not relevant to the F-35 when it is landing in one of the modes where the fan is running and all those doors are open and the engine nozzle has swiveled to provide upward thrust.
Great to hear a revue of all the Harrier stuff, but the F-35 is in another universe. I personally know a Harrier pilot, and have been briefed about landing the beast, so not a pure armchair commentator.
Go to the F-35 forums on F-16 dot net and others to get a good understanding of how the thing is supposed to work.
Gums sends...
All of the Harrier technology and procedures and such are not relevant to the F-35 when it is landing in one of the modes where the fan is running and all those doors are open and the engine nozzle has swiveled to provide upward thrust.
Great to hear a revue of all the Harrier stuff, but the F-35 is in another universe. I personally know a Harrier pilot, and have been briefed about landing the beast, so not a pure armchair commentator.
Go to the F-35 forums on F-16 dot net and others to get a good understanding of how the thing is supposed to work.
Gums sends...
I haven't been able to read up on the F-35's systems, but doesn't it use some convoluted control laws that have the stick controlling altitude in hover mode or something like that? In that particular mode... what can you actually do with the throttle to influence a situation such as this? Can you shut the engine down quickly if needed? The only relevant Harrier is the VAAC one I guess...
I haven't been able to read up on the F-35's systems, but doesn't it use some convoluted control laws that have the stick controlling altitude in hover mode or something like that? In that particular mode... what can you actually do with the throttle to influence a situation such as this? Can you shut the engine down quickly if needed? The only relevant Harrier is the VAAC one I guess...
Not relevant to this F-35B incident, in which it isn't really possible to say from the video what happened except that something went wrong. It's fun reading all the (wrong) theories though.
Salute!
PLEASE, go to the f-16 net I referenced and read two or three descriptions of the flight control laws once the pilot hits the landing mode button.
In short, the throttle doofer does not have a cutoff...engine shuts off with a switch.
Second, in the vertical landing mode the throttle thing, aka cow pie, works like this: push forward to move plane forward, move back to slow or go in reverse. The side stick commands up and down and left right movement of the plane.
Please go read all the details at the other forum.
Gums sends...
PLEASE, go to the f-16 net I referenced and read two or three descriptions of the flight control laws once the pilot hits the landing mode button.
In short, the throttle doofer does not have a cutoff...engine shuts off with a switch.
Second, in the vertical landing mode the throttle thing, aka cow pie, works like this: push forward to move plane forward, move back to slow or go in reverse. The side stick commands up and down and left right movement of the plane.
Please go read all the details at the other forum.
Gums sends...
Thanks, that refreshed my memory on the unified control concept. Getting into speculation about what the computer or the stick actuator did or did not do will not get us anywhere but I wonder what will emerge from the investigation in due course.
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Is a vertical touch & go even possible in the aircraft?
I'm struggling to see another video of an F35B hitting the deck & then becoming airborne again, everything I see follows the same sequence of touchdown & throttle down, the process seems so consistent that it may be automated after WOW. Sensor, processing or software glitch possibly "Fan - start the shutdown sequence" & "Engine - give it plenty"?
I'm struggling to see another video of an F35B hitting the deck & then becoming airborne again, everything I see follows the same sequence of touchdown & throttle down, the process seems so consistent that it may be automated after WOW. Sensor, processing or software glitch possibly "Fan - start the shutdown sequence" & "Engine - give it plenty"?
But was it a vertical landing? It looked to me as if it had some forward in it leading to a bit of a rolling landing which I presume is slightly different for the software sequences.
How far away is an ejection seat which can activate at angles close to horizontal at low level and then steer itself to a safe parachute deployment altitude?
Salute!
Yeah, Okie, those Russian seats have shown in more than one airshow how good they are. I also felt very comfortable in the ACES2 seat in the Viper.
Gums sends...
Yeah, Okie, those Russian seats have shown in more than one airshow how good they are. I also felt very comfortable in the ACES2 seat in the Viper.
Gums sends...
I remember John Farley discussing the differences between the Harrier and the F35B, he seemed impressed with the pilot friendliness and simplicity of the vertical landing system in the latter but concerned about the mechanical complexity of the system and it’s vulnerability to failure
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Did the magnificent John Farley fly the F-35B? He flew the VAAC Harrier version? Anyhoo this is how it goes ashore. Complexity is the job of the computer flight controls while the pilot positions the F-35B accurately according to F-35B pilot reports with failure modes in STOVL flight also taken into account but what caused the accident under discussion - I have no idea. F-35B Vertical Landings FCLP USMC
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A V/STOL FLIGHT CONTROL JOURNEY ENABLED BY RAE SCIENTISTS John Farley 2006
"...it was clear to me [John Farley] that the eventual aim of the scientists was to hand over control of the aircraft to a computer leaving the pilot just to tell that computer what manoeuvre he wanted it to fly. If this happened it would mean the Harrier pilot’s nozzle lever would no longer be needed because control of the nozzle angle – as well as everything else that the pilot hitherto controlled – would be left to the computer...."
&
“…UNIFIED. Unified was the most radical mode. Here the pilot pulls back on the stick to go up and pushes to go down, regardless of airspeed. At all speeds above 40 kt ground speed the stick commands flight path rate and so relaxing it to the centre position when the aircraft is flying level maintains height. If the aircraft is in a climb or a dive, relaxing the stick maintains the existing climb or dive flight path angle. As the aircraft decelerates through 40 kt the stick response blends to become a height rate control by 30 kt ground speed so, in the hover, with stick centre commanding zero height rate, it appears to the pilot as a height hold.
When flying up and away lateral stick commands roll rate. This blends between 130 and 100 kt to become a closed loop roll attitude control, so that relaxing the stick to centre below 100 kt commands wings level. Above 40 kt ground speed the rudder pedals command sideslip. Decelerating below this speed the pedals blend to a yaw rate command by 30 kt, providing a heading hold in the hover with feet central. A throttle-type left hand inceptor, incorporating two detents, commands longitudinal acceleration.
Putting the inceptor in the centre detent holds the current speed. Acceleration or deceleration is selected by moving the lever forward or aft of the detent, with full travel demanding maximum available performance. Decelerating through 35 kt ground speed starts a blend and below 25 kt the aft detent commands zero ground speed. Either side of the aft detent gives the pilot a closed loop control of ground speed up to 30 kt forwards or backwards. In summary, if the pilot centres both the stick and throttle when flying on the wings, the aircraft holds the existing speed, bank attitude and climb or dive angle. In the hover, centralising everything maintains the existing hover height, position and heading. Such hover characteristics are the stuff of dreams for every Harrier pilot at the start of their conversion.…”
http://www.rafmuseum.org.uk.nyud.net...AF-Historical- Society-Journals/Journal-35A-Seminar-the-RAF-Harrier-Story.pdf
______________
VERTICAL LEAP Richard Scott Feb 2020 "...JOHN FARLEY AND VAAC...
...the first thing you have to decide is what you want to put your hands and feet on in a ‘jump-jet’ — and various other changes. What they finished up with, which has now gone into the F-35, is a left-hand inceptor which slides backwards and forwards and looks a bit like a throttle. It isn’t a throttle; it tells the aircraft, ‘I want to go slower or faster’. Put it in the detent in the middle, and it says, ‘Hold the speed I’m at’. Put it in the detent in the middle, and it says, ‘I want you to hover’. The right hand is operating a little sidestick, and with that you’re indicating whether you want to go left, right, up or down”. As Farley concluded admiringly, “It completely deskills the whole operation.”
Ben Dunnell AEROPLANE Magazine February 2020, Issue No 562, Vol 48, No 2
"...it was clear to me [John Farley] that the eventual aim of the scientists was to hand over control of the aircraft to a computer leaving the pilot just to tell that computer what manoeuvre he wanted it to fly. If this happened it would mean the Harrier pilot’s nozzle lever would no longer be needed because control of the nozzle angle – as well as everything else that the pilot hitherto controlled – would be left to the computer...."
&
“…UNIFIED. Unified was the most radical mode. Here the pilot pulls back on the stick to go up and pushes to go down, regardless of airspeed. At all speeds above 40 kt ground speed the stick commands flight path rate and so relaxing it to the centre position when the aircraft is flying level maintains height. If the aircraft is in a climb or a dive, relaxing the stick maintains the existing climb or dive flight path angle. As the aircraft decelerates through 40 kt the stick response blends to become a height rate control by 30 kt ground speed so, in the hover, with stick centre commanding zero height rate, it appears to the pilot as a height hold.
When flying up and away lateral stick commands roll rate. This blends between 130 and 100 kt to become a closed loop roll attitude control, so that relaxing the stick to centre below 100 kt commands wings level. Above 40 kt ground speed the rudder pedals command sideslip. Decelerating below this speed the pedals blend to a yaw rate command by 30 kt, providing a heading hold in the hover with feet central. A throttle-type left hand inceptor, incorporating two detents, commands longitudinal acceleration.
Putting the inceptor in the centre detent holds the current speed. Acceleration or deceleration is selected by moving the lever forward or aft of the detent, with full travel demanding maximum available performance. Decelerating through 35 kt ground speed starts a blend and below 25 kt the aft detent commands zero ground speed. Either side of the aft detent gives the pilot a closed loop control of ground speed up to 30 kt forwards or backwards. In summary, if the pilot centres both the stick and throttle when flying on the wings, the aircraft holds the existing speed, bank attitude and climb or dive angle. In the hover, centralising everything maintains the existing hover height, position and heading. Such hover characteristics are the stuff of dreams for every Harrier pilot at the start of their conversion.…”
http://www.rafmuseum.org.uk.nyud.net...AF-Historical- Society-Journals/Journal-35A-Seminar-the-RAF-Harrier-Story.pdf
______________
VERTICAL LEAP Richard Scott Feb 2020 "...JOHN FARLEY AND VAAC...
...the first thing you have to decide is what you want to put your hands and feet on in a ‘jump-jet’ — and various other changes. What they finished up with, which has now gone into the F-35, is a left-hand inceptor which slides backwards and forwards and looks a bit like a throttle. It isn’t a throttle; it tells the aircraft, ‘I want to go slower or faster’. Put it in the detent in the middle, and it says, ‘Hold the speed I’m at’. Put it in the detent in the middle, and it says, ‘I want you to hover’. The right hand is operating a little sidestick, and with that you’re indicating whether you want to go left, right, up or down”. As Farley concluded admiringly, “It completely deskills the whole operation.”
Ben Dunnell AEROPLANE Magazine February 2020, Issue No 562, Vol 48, No 2
Last edited by SpazSinbad; 23rd Dec 2022 at 08:58. Reason: + quotes
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"The US16E Seat interfaces with Lockheed Martin's auto-eject system (F-358 STOVL) which caters for low-altitude, low-speed and adverse pitch attitude escape conditions" MB PR
Synopsis of Lecture to RAeS Loughborough Branch on 08 Mar 2011 - Martin-Baker: the JSF story so far by Steve Roberts, JSG IPT Lead, Martin-Baker Aircraft Company Ltd http://homepage.ntlworld.com/john.ol...JSF%20seat.pdf
“...The ejection seat was required to be common to all three aircraft variants. It was also required to have superior ejection performance to all previous seats, meet new neck injury criteria and provide an auto-ejection capability when used in the F-35B (STOVL) aircraft. The last requirement demanded early firing of the ejection seat in the event of an aircraft malfunction in a manner similar to that used in the Russian YAK 36, 38 and 141 aircraft....
...The F-35-B (STOVL) aircraft has additional failure modes associated with Lift Fan, Vane Box, Lift Fan Drive Shaft, Roll Duct and Turbine failures. A typical pilot takes two seconds to react to the ejection klaxon or one second if warned in advance of a likely failure. In the case of a STOVL related failure, ejection must take place within 0.6 seconds. Hence it was necessary to install smart failure sensors on the aircraft to automatically fire the ejection circuit mounted in the back of the seat....”
Synopsis of Lecture to RAeS Loughborough Branch on 08 Mar 2011 - Martin-Baker: the JSF story so far by Steve Roberts, JSG IPT Lead, Martin-Baker Aircraft Company Ltd http://homepage.ntlworld.com/john.ol...JSF%20seat.pdf
“...The ejection seat was required to be common to all three aircraft variants. It was also required to have superior ejection performance to all previous seats, meet new neck injury criteria and provide an auto-ejection capability when used in the F-35B (STOVL) aircraft. The last requirement demanded early firing of the ejection seat in the event of an aircraft malfunction in a manner similar to that used in the Russian YAK 36, 38 and 141 aircraft....
...The F-35-B (STOVL) aircraft has additional failure modes associated with Lift Fan, Vane Box, Lift Fan Drive Shaft, Roll Duct and Turbine failures. A typical pilot takes two seconds to react to the ejection klaxon or one second if warned in advance of a likely failure. In the case of a STOVL related failure, ejection must take place within 0.6 seconds. Hence it was necessary to install smart failure sensors on the aircraft to automatically fire the ejection circuit mounted in the back of the seat....”
For those who wish to read more on VAAC and FBW in general, there is very good book by Gerry Shanks (RAE) - "The Challenges of Fly-By-Wire", the role of the Royal Aircraft Establishment (Bedford and Farnborough).
Starting with the 'Flying Bedstead' though to VAAC leading to the F35.
There is a good description of the principles of the Two-Inceptor control system, Unified and Fusion concepts. It is interesting to note the the final choice was biased by pilots viewpoint, particularly Harrier vs non Harrier. As JF noted above, flying an (old) aircraft, or controlling a computer which flys the aircraft. There were similar debates about VTO aircraft from the SC5 onwards.
There is complementary book by Brian Weller 'The History of the Fly-By-Wire Jaguar'. It's technical views relate to the design of a FBW system without any manual reversion, and thence control of an highly unstable aircraft; including pilot viewpoints.
Wrt the F35 accident it appears that there was a lack of 'up' thrust from the fan.
Seeking more understanding, does the F35 hover control have pitch-attitude stabilisation, if so by what means; can the attitude be adjusted manually (slew / trim) or it is it pre programmed. Thence with a fan thrust malfunction, the stabilisation would attempt to apply more fan thrust to counter the nose down pitch change - maintain attitude, but not necessarily increase nozzle thrust.
and / or;
with perhaps natural pilot reaction, with Unified control - back stick would demand more thrust from both fan and nozzle, but only enough able to raise the rear end.
Starting with the 'Flying Bedstead' though to VAAC leading to the F35.
There is a good description of the principles of the Two-Inceptor control system, Unified and Fusion concepts. It is interesting to note the the final choice was biased by pilots viewpoint, particularly Harrier vs non Harrier. As JF noted above, flying an (old) aircraft, or controlling a computer which flys the aircraft. There were similar debates about VTO aircraft from the SC5 onwards.
There is complementary book by Brian Weller 'The History of the Fly-By-Wire Jaguar'. It's technical views relate to the design of a FBW system without any manual reversion, and thence control of an highly unstable aircraft; including pilot viewpoints.
Wrt the F35 accident it appears that there was a lack of 'up' thrust from the fan.
Seeking more understanding, does the F35 hover control have pitch-attitude stabilisation, if so by what means; can the attitude be adjusted manually (slew / trim) or it is it pre programmed. Thence with a fan thrust malfunction, the stabilisation would attempt to apply more fan thrust to counter the nose down pitch change - maintain attitude, but not necessarily increase nozzle thrust.
and / or;
with perhaps natural pilot reaction, with Unified control - back stick would demand more thrust from both fan and nozzle, but only enough able to raise the rear end.
Last edited by safetypee; 24th Dec 2022 at 07:22.