Concorde question
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quote:I remember at Fairford in mid 1974, a CAA test pilot (I honestly forget the gentleman's name) was taking the British pre-production A/C 101 (G-AXDN) for a special test flight.unquote
It was almost certainly Gordon Corps, possibly the finest 'engineering' test pilot I have ever worked with. After Concorde certification Gordon went to work at Toulouse wher he did most of the development flying that led to the A320 FBW system. BZ was the public 'face' of the design, but knowing the two men I have a very shrewd idea as to who did the original thinking! Perhaps Andy could confirm?
Tragically Gordon died young whilst trekking to an A300 crash site somewhere in the Himalayas
ClivL
It was almost certainly Gordon Corps, possibly the finest 'engineering' test pilot I have ever worked with. After Concorde certification Gordon went to work at Toulouse wher he did most of the development flying that led to the A320 FBW system. BZ was the public 'face' of the design, but knowing the two men I have a very shrewd idea as to who did the original thinking! Perhaps Andy could confirm?
Tragically Gordon died young whilst trekking to an A300 crash site somewhere in the Himalayas
ClivL
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quote:Rolls Royce did some analysis on the flight, and were amazed at how well the propulsion systems coped with some of the temperature sheers that we encountered, sometimes 4 to 5 deg's/second. They said that the prototype AFCS had been defeated by rises of only 0.25 deg's/second ).unquote
Just for the record, the intake control system was designed to cope with a temperature shear of 21 deg C in one mile (about 3 seconds)
quote:Not meaning to go off onto a (yet another) tangent; Negative temperature shears, very common at lower lattidudes, always plagued the development aircraft; you would suddenly accelerate, and in the case of a severe shear, would accelerate and accelerate!! (Your Mach number, quite naturaly, suddenly increased with the falling temperature of course, but because of the powerplant suddenly hitting an area of hyper-efficiencey, the A/C would physically accelerate rapidly, way beyond Mmo). Many modifications were tried to mitigate the effects of severe shears, in the end a clever change to the intake control unit software fixed it. (Thanks to this change the production series A/C would not be capable of level flight Mach numbers of any more than Mach 2.13, remembering that Mmo was set at 2.04).unquote
Not temperature shears, and not AICU modifications (which I see has been discussed in a later posting). But back to the 'shears':
Most of Concorde's flight testing was, naturally, done out of Toulouse and Fairford, i.e. into moderate latitude atmospheres where the tropopause is normally around 36,000 ft so that the supersonic flight testing was done in atmosphers where the temperature doesn't vary with altitude. The autopilot working in Mach hold would see an increase in Mach and apply up elevator to reduce IAS and recover the macg setting. But at the lower latitudes around the equator the atmosphere is different in its large scale characteristics. In particular the tropopause is much, much higher and can get as high as 55,000 ft. Nobody had been up there to see what it was like! Now when the A/P applied up elevator to reduce IAS it went into a region of colder air. But the speed of sound is proportional to air temperature, so as the aircraft ascended the IAS dropped alright but since the ballistic (true) velocity of the aircraft takes a while to change and since the speed of sound had dropped the Mach number was increased, so the A/P seeing this applied more up elevator and the aircraft went up and the speed of sound dropped and ........
Like solving crossword clues, the answer is obvious once you have spent some time finding it!
This phenomenon rather than temperature shears (encountered mainly over the tops of Cb clouds) was the reason for the autopilot modifications which included that clever use of autothrottle (I can use that adjective since it was my French colleagues that devised it)
And before anyone asks; yes, the same problem would relate to subsonic aircraft operating in Mach hold driven by the elevators and flying below the tropopause, but:
a) Subsonic aircraft are old ladies by comparison with Concorde in that they fly at only half the speed. At Concorde velocities even modest changes in pitch attitude can generate some pretty impressive rates of climb or dive!
b) Subsonic aircraft are normally constrained by ATC to fly at fixed flight levels - the use of elevator to control Mach number is not really an option - you have to use an autothrottle.
There was that other problem, also described in later postings, where the aircraft regularly 'rang the bell' when passing through the Vmo/Mmo corner in the lower latitudes, but this was simply due to the additional performance one got in these ISA minus conditions in comparison to the temperatures encountered around the same corner in higher temperatures.
Anyway, the flight test campaign got me my first sight of sunrise over the Arabian desert and my first trip to Asia, so it goes into my Concorde memory bank.
Just for the record, the intake control system was designed to cope with a temperature shear of 21 deg C in one mile (about 3 seconds)
quote:Not meaning to go off onto a (yet another) tangent; Negative temperature shears, very common at lower lattidudes, always plagued the development aircraft; you would suddenly accelerate, and in the case of a severe shear, would accelerate and accelerate!! (Your Mach number, quite naturaly, suddenly increased with the falling temperature of course, but because of the powerplant suddenly hitting an area of hyper-efficiencey, the A/C would physically accelerate rapidly, way beyond Mmo). Many modifications were tried to mitigate the effects of severe shears, in the end a clever change to the intake control unit software fixed it. (Thanks to this change the production series A/C would not be capable of level flight Mach numbers of any more than Mach 2.13, remembering that Mmo was set at 2.04).unquote
Not temperature shears, and not AICU modifications (which I see has been discussed in a later posting). But back to the 'shears':
Most of Concorde's flight testing was, naturally, done out of Toulouse and Fairford, i.e. into moderate latitude atmospheres where the tropopause is normally around 36,000 ft so that the supersonic flight testing was done in atmosphers where the temperature doesn't vary with altitude. The autopilot working in Mach hold would see an increase in Mach and apply up elevator to reduce IAS and recover the macg setting. But at the lower latitudes around the equator the atmosphere is different in its large scale characteristics. In particular the tropopause is much, much higher and can get as high as 55,000 ft. Nobody had been up there to see what it was like! Now when the A/P applied up elevator to reduce IAS it went into a region of colder air. But the speed of sound is proportional to air temperature, so as the aircraft ascended the IAS dropped alright but since the ballistic (true) velocity of the aircraft takes a while to change and since the speed of sound had dropped the Mach number was increased, so the A/P seeing this applied more up elevator and the aircraft went up and the speed of sound dropped and ........
Like solving crossword clues, the answer is obvious once you have spent some time finding it!
This phenomenon rather than temperature shears (encountered mainly over the tops of Cb clouds) was the reason for the autopilot modifications which included that clever use of autothrottle (I can use that adjective since it was my French colleagues that devised it)
And before anyone asks; yes, the same problem would relate to subsonic aircraft operating in Mach hold driven by the elevators and flying below the tropopause, but:
a) Subsonic aircraft are old ladies by comparison with Concorde in that they fly at only half the speed. At Concorde velocities even modest changes in pitch attitude can generate some pretty impressive rates of climb or dive!
b) Subsonic aircraft are normally constrained by ATC to fly at fixed flight levels - the use of elevator to control Mach number is not really an option - you have to use an autothrottle.
There was that other problem, also described in later postings, where the aircraft regularly 'rang the bell' when passing through the Vmo/Mmo corner in the lower latitudes, but this was simply due to the additional performance one got in these ISA minus conditions in comparison to the temperatures encountered around the same corner in higher temperatures.
Anyway, the flight test campaign got me my first sight of sunrise over the Arabian desert and my first trip to Asia, so it goes into my Concorde memory bank.
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My first post here, many thanks to each contributors (either the questionning or answering ones), this is a brilliant thread ! 
CliveL, thanks for joining, Sir. Please let me try to help with forum issues :
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Hope this helps, and sorry for the drift regarding the topic. Let's get back to the Lady
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CliveL, thanks for joining, Sir. Please let me try to help with forum issues :
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Hope this helps, and sorry for the drift regarding the topic. Let's get back to the Lady
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quote:d putting further Concorde's achievements in terms of stability; the world's only previous large delta winged Mach 2 aircraft, the B58 Hustler, had the slightly awkward feature in the case of an outer engine failure at Mach 2, in that the yaw forces were sufficient to tear the fin off. This happened on more than one occasion during service life of the Hustler, but engine failure (or far more likely a deliberate precautionary shut-down) although hardly a non-event in the case of Concorde, it was routinely dealt with without drama or danger.unquote
To rub it in, a typical double engine surge - they were nearly always double surges as the first surge expelled the ramp shock waves and turned the flow into a pitot with a large standing shock ahead of the intake that screwed up the flow into its neighbour - would produce about 1 degree sideslip and 2 deg bank. There would be a +/- 0.2g variation in normal acceleration and that was it! Through Christiaan's kind offices I am posting the records of such an event.
Hustler pilots eat your heart out!
CliveL
To rub it in, a typical double engine surge - they were nearly always double surges as the first surge expelled the ramp shock waves and turned the flow into a pitot with a large standing shock ahead of the intake that screwed up the flow into its neighbour - would produce about 1 degree sideslip and 2 deg bank. There would be a +/- 0.2g variation in normal acceleration and that was it! Through Christiaan's kind offices I am posting the records of such an event.
Hustler pilots eat your heart out!
CliveL
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quote
n boarding Concorde, I gave my business card to the purser, asking that she pass it forward. A few minutes later as the door was closing she came back to pass along an invitation from the skipper to join them in the cockpit.
For the balance of the climb I plied the guys with questions and received courteous and detailed answers to every one, I stayed through the supersonic acceleration until I thought I'd worn out my welcome at cruise climb, returning to my seat in the mid cabin area for lunch. They invited me back for the descent and approach, which was very well appreciated.unquote
When I retired I flew to Wsahington and back with BA and when the crew found I was on board I also got invited to view TO and approach from the jump seat. The main difference was that it was me that was plied with questions
My main memory is that it is one thing to argue with the airworthiness authorities about 'pilot delay times' when calculating balanced field lengths, but when you are sitting at the sharp end and getting towards V1 the end of the runway is approaching at a helluva lick which puts a degree of realsim into one's thoughts!
The other memory is the sheer beauty of London when approached sitting in the front of a Concorde on a clear winter's evening when the lights are on.
CliveL
n boarding Concorde, I gave my business card to the purser, asking that she pass it forward. A few minutes later as the door was closing she came back to pass along an invitation from the skipper to join them in the cockpit. For the balance of the climb I plied the guys with questions and received courteous and detailed answers to every one, I stayed through the supersonic acceleration until I thought I'd worn out my welcome at cruise climb, returning to my seat in the mid cabin area for lunch. They invited me back for the descent and approach, which was very well appreciated.unquote
When I retired I flew to Wsahington and back with BA and when the crew found I was on board I also got invited to view TO and approach from the jump seat. The main difference was that it was me that was plied with questions
My main memory is that it is one thing to argue with the airworthiness authorities about 'pilot delay times' when calculating balanced field lengths, but when you are sitting at the sharp end and getting towards V1 the end of the runway is approaching at a helluva lick which puts a degree of realsim into one's thoughts!
The other memory is the sheer beauty of London when approached sitting in the front of a Concorde on a clear winter's evening when the lights are on.
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quote:Interestingly, all the supersonic transport designs of the era (Concorde,Tu-144, B2707, L2000) can trace their ancestry back to NASA (NACA?) public-domain studies of the late fifties, that demonstrated the advantages of a slender delta for a supersonic transport aircraft.unquote
You guys are making me look out all the books/reports on Concorde that I had filed long ago!
I think there are a lot of guys who used to work at Farnborough that wouldn't agree with you here Christian. UK work on the possibility of designing a supersonic transport kicked off in November 1956 and that certainly included studies involving slender delta wings based on work that had already been started by the RAE at Farnborough. I was reading a lot of NACA material at that time and I don't remember anything demonstrating the advantages of a slender delta for supersonic transports. Do you have any references?
CliveL
You guys are making me look out all the books/reports on Concorde that I had filed long ago!
I think there are a lot of guys who used to work at Farnborough that wouldn't agree with you here Christian. UK work on the possibility of designing a supersonic transport kicked off in November 1956 and that certainly included studies involving slender delta wings based on work that had already been started by the RAE at Farnborough. I was reading a lot of NACA material at that time and I don't remember anything demonstrating the advantages of a slender delta for supersonic transports. Do you have any references?
CliveL
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quoteuring landing, Concorde isn't flared at all, it is flown onto the ground at a constant pitch attitude.
What does happen is that the ground effect over the last 50 ft or so of height considerably flattens the trajectory, so you do not touch down with the same vertical speed as during the final approach !
What also happens is that the ground effect produces a pitch-up moment, so the pilot has to push forward on the stick to maintain the same pitch attitude.
Putting the nosewheel down after touchdown is enough to completely “ruin” the lift, so that there is no need for “lift-dumpers” or spoilers.unquote
Sorry Christan, but I did the original pre first flight work on this one, so I know you are mistaken here. You are abolutely correct in saying that the ground effect cushions the aircraft beautifully so that all the pilot needs to do is to hold constant attitude, but the ground effect also produces a nose DOWN moment, so the pilot must exert a steadily increasing pull on the stick to maintain the correct attitude.
So far as lift on the ground is concerned, the aircraft attitude (and therefore the AoA) is substantially zero. without any flaps then the lift is also zero so, as you say, leif dumpers would be useless. They could of course act as airbrakes but you wouldn't add their weight and complexity just for that.
I see I have covered about 10 pages out of the 45 or so, but I don't want to hog this thread so I had better shut up for a while
CliveL
uring landing, Concorde isn't flared at all, it is flown onto the ground at a constant pitch attitude.What does happen is that the ground effect over the last 50 ft or so of height considerably flattens the trajectory, so you do not touch down with the same vertical speed as during the final approach !
What also happens is that the ground effect produces a pitch-up moment, so the pilot has to push forward on the stick to maintain the same pitch attitude.
Putting the nosewheel down after touchdown is enough to completely “ruin” the lift, so that there is no need for “lift-dumpers” or spoilers.unquote
Sorry Christan, but I did the original pre first flight work on this one, so I know you are mistaken here. You are abolutely correct in saying that the ground effect cushions the aircraft beautifully so that all the pilot needs to do is to hold constant attitude, but the ground effect also produces a nose DOWN moment, so the pilot must exert a steadily increasing pull on the stick to maintain the correct attitude.
So far as lift on the ground is concerned, the aircraft attitude (and therefore the AoA) is substantially zero. without any flaps then the lift is also zero so, as you say, leif dumpers would be useless. They could of course act as airbrakes but you wouldn't add their weight and complexity just for that.
I see I have covered about 10 pages out of the 45 or so, but I don't want to hog this thread so I had better shut up for a while
CliveL
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Ref the landing manoeuvre: CliveL is quite correct - there was a distinct nosedown pitch generated by descent into gnd effect.
The machine was very light in pitch on approach (spring feel only and not much positive stability, especially with the A/T active owing to its destabilising effect) so minimal pitch input was the order of the day. Then you descended into gnd effect and a steadily increasing pull was reqd to hold the desired attitude (any nose down change at this stage was a prelude to disaster!).
The overall effect was not unnatural, since it was similar to a flare and hold off in a conventional aircraft (although more Stearman than 747).
AFTER touchdown, selection of reverse caused a distinct pitch up, and if this was allowed to get hold it was a real problem to get the nose back down. As explained pages earlier this deprived you of braking ability.....for this reason both pilots pushed the control column firmly forward after nosewheel touchdown, and I'm guessing that's what ChristiaanJ meant .
The machine was very light in pitch on approach (spring feel only and not much positive stability, especially with the A/T active owing to its destabilising effect) so minimal pitch input was the order of the day. Then you descended into gnd effect and a steadily increasing pull was reqd to hold the desired attitude (any nose down change at this stage was a prelude to disaster!).
The overall effect was not unnatural, since it was similar to a flare and hold off in a conventional aircraft (although more Stearman than 747).
AFTER touchdown, selection of reverse caused a distinct pitch up, and if this was allowed to get hold it was a real problem to get the nose back down. As explained pages earlier this deprived you of braking ability.....for this reason both pilots pushed the control column firmly forward after nosewheel touchdown, and I'm guessing that's what ChristiaanJ meant .
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Here are the graphs that CliveL was referring to.
The Mach trim control law
The aircraft response to a double engine surge
Split into two halves (longitudinal and lateral response)
Note the almost immediate rudder response, long before the engine N2 rpm starts to wind down. I'll have something to say about that in a separate post....
CJ
The Mach trim control law
The aircraft response to a double engine surge
Split into two halves (longitudinal and lateral response)
Note the almost immediate rudder response, long before the engine N2 rpm starts to wind down. I'll have something to say about that in a separate post....
CJ
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A double engine failure, or even a double engine surge, could lead to a very nasty yaw, faster than the pilot, not necessarily instantly aware of exactly what was happening, could counter.
The designers were, right from the start, aware of this problem.
Hence, the prototypes were equipped with specific "contre automatique" (auto-rudder) computers, that would "kick in" a given rudder deflection as soon as they detected an engine failure (and twice as much in the case of a double failure).
Unfortunately... the manner of detecting an engine failure was based on pressure sensors in the engine, which proved to be notoriously unreliable.
Since the whole system was "fail-passive", in the case of a pressure sensor failure nothing happened, other than that I got the "suspect" computer dumped in my lap every time, since it was easier to swap a computer than test and swap pressure sensors....
In the end, it was always "no fault found", and the engineers had to go and test the sensors to find the failed one.
Already on the pre-production aircraft, this Rube Goldberg system was replaced by a single circuit board 'buried' in the autostab computer.
It used a lateral accelerometer to detect the abrupt yaw of a sudden engine failure or surge, and applied appropriate rudder. Look at the sudden rudder deflection 'peak' on the lateral response graph in the previous post.
Since there was no separate 'auto-rudder engage' control switch (the function was permanently active), and it was only mentioned very much in passing during training, some pilots were not even aware it existed.......
CJ
The designers were, right from the start, aware of this problem.
Hence, the prototypes were equipped with specific "contre automatique" (auto-rudder) computers, that would "kick in" a given rudder deflection as soon as they detected an engine failure (and twice as much in the case of a double failure).
Unfortunately... the manner of detecting an engine failure was based on pressure sensors in the engine, which proved to be notoriously unreliable.
Since the whole system was "fail-passive", in the case of a pressure sensor failure nothing happened, other than that I got the "suspect" computer dumped in my lap every time, since it was easier to swap a computer than test and swap pressure sensors....
In the end, it was always "no fault found", and the engineers had to go and test the sensors to find the failed one.
Already on the pre-production aircraft, this Rube Goldberg system was replaced by a single circuit board 'buried' in the autostab computer.
It used a lateral accelerometer to detect the abrupt yaw of a sudden engine failure or surge, and applied appropriate rudder. Look at the sudden rudder deflection 'peak' on the lateral response graph in the previous post.
Since there was no separate 'auto-rudder engage' control switch (the function was permanently active), and it was only mentioned very much in passing during training, some pilots were not even aware it existed.......
CJ
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Thumbs Up for CJ, CliveL, M2Dude and other guys.
I'm wondering that does the auto-stab function in yaw axis does apply some
rudder when pilot fly the aircraft by his hand to prevent the sideslip or
dutchroll or not?
Also, does the auto stab does "modify" some pilot input to minimize the effect
of the turbulence all the time when airplane encounter the turbulence or only
when the AP are in the "TURB" mode? Does it help to reduce the stress on the
aircraft like the "load alleviation" on the moder aircraft like A380?
And final the final question, how the camber help to reduce the shifting
position of the center of pressure on the Concorde and if possible where is it
on the wing?
Thanks for all of yours reply.
Best regards
I'm wondering that does the auto-stab function in yaw axis does apply some
rudder when pilot fly the aircraft by his hand to prevent the sideslip or
dutchroll or not?
Also, does the auto stab does "modify" some pilot input to minimize the effect
of the turbulence all the time when airplane encounter the turbulence or only
when the AP are in the "TURB" mode? Does it help to reduce the stress on the
aircraft like the "load alleviation" on the moder aircraft like A380?
And final the final question, how the camber help to reduce the shifting
position of the center of pressure on the Concorde and if possible where is it
on the wing?
Thanks for all of yours reply.
Best regards
Last edited by Mr.Vortex; 22nd Dec 2010 at 06:21. Reason: Forgot something...
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ChristiaanJ
But this was the beauty of Concorde, there was so much in the way of automatic protections and enhancements 'built in' that one could quite quite reasonably take it all for granted. That was definately true for most of the AFCS computation. (It's all your fault ChristiaanJ for helping to design such a great system ).
And now we have CliveL joining this thread, one of the true 'fathers of Concorde', it can only become even more fascinating with his inputs here.
(BTW, this thread has now passed 100,000 viewings in just four short months).
Best regards
Dude
Since there was no separate 'auto-rudder engage' control switch (the function was permanently active), and it was only mentioned very much in passing during training, some pilots were not even aware it existed.......
).And now we have CliveL joining this thread, one of the true 'fathers of Concorde', it can only become even more fascinating with his inputs here.
(BTW, this thread has now passed 100,000 viewings in just four short months
).Best regards
Dude
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MrVortex
Concorde had triple-axis auto stabilisation, where pilot demands were routed via an AUTOSTAB COMPUTER and summed with any stabilisation demands. There was automatc roll/yaw crossfeed, where for a given roll demand there was a coresponding amount of rudder applied, the amount of which was a function of Mach number. As far as 'dutch roll' etc the autostab system employed rate gyros in the same way as a conventional 'yaw damper' would operate in an inferior 
(oops, my bad.. I mean SLOWER) aircraft.
The AUTOSTAB operated full time, irrespective of AFCS mode. (Perhaps EXWOK, NW1 or one of the other boys will confirm that TURB mode was seldom EVER used in airline service. It was a (if I remember correctly) a Pitch/HDG hold autopilot mode with reduced gain).
Best regards
Dude
I'm wondering that does the auto-stab function in yaw axis does apply some rudder when pilot fly the aircraft by his hand to prevent the sideslip or dutchroll or not?
(oops, my bad.. I mean SLOWER) aircraft.
Also, does the auto stab does "modify" some pilot input to minimize the effect of the turbulence all the time when airplane encounter the turbulence or only when the AP are in the "TURB" mode? Does it help to reduce the stress on the aircraft like the "load alleviation" on the moder aircraft like A380?
Best regards
Dude
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Originally Posted by Mr Vortex
I'm wondering that does the auto-stab function in yaw axis does apply some
rudder when pilot fly the aircraft by his hand to prevent the sideslip or
dutchroll or not?
Also, does the auto stab does "modify" some pilot input to minimize the effect
of the turbulence all the time when airplane encounter the turbulence or only
when the AP are in the "TURB" mode? Does it help to reduce the stress on the
aircraft like the "load alleviation" on the moder aircraft like A380?
And final the final question, how the camber help to reduce the shifting
position of the center of pressure on the Concorde and if possible where is it
on the wing?
rudder when pilot fly the aircraft by his hand to prevent the sideslip or
dutchroll or not?
Also, does the auto stab does "modify" some pilot input to minimize the effect
of the turbulence all the time when airplane encounter the turbulence or only
when the AP are in the "TURB" mode? Does it help to reduce the stress on the
aircraft like the "load alleviation" on the moder aircraft like A380?
And final the final question, how the camber help to reduce the shifting
position of the center of pressure on the Concorde and if possible where is it
on the wing?
Then, yes the autostabiliser does provide yaw damping to control the Dutch roll, but there was also (from memory) some roll damping.
No, there is no load alleviation function. Concorde had a very low aspect ratio wing which gives in turn a very low lift curve slope, so the loads coming from hitting gusts are quite modest and load alleviation was not needed. The autostabiliser was working all the time, not just when A/P was engaged. Since the span was also low the manoeuvre bending moment was also small so again load alleviation was not required. BTW, I believe that the A380 load alleviation is just this manoeuvre case not gust loads. The A320 had gust load alleviation on early models, but it proved to be a pain in the neck and was gratefully dropped when the MTOW went up and made manoeuvre loads the critical design case.
Finally, the camber is spread all over the wing. In cross section it looks like a banana with the bent bit like a shallow 'U' and the leading edge drooped downwards, so the whole thing lookss like a distorted 'S'
CliveL
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Was just just the prototypes, or also the production aircraft, where the outer part of the wings ('A' tanks) was designed to flex a little to create some reflex in the cruise, in order to reduce the aft movement of the CP?
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Turb mode
'Dude -
I didn't ever use this mode, and never saw anybody else use it.
Significant turbulence was almost unheard of in supercruise - light to mod was the worst I ever had. Subsonic one would be subject to the same air as the blunties, but in an aircraft which had a high wing loading and good controls. Once you got down into the low-level turbulence on a windy day (say 2000' and below) you were in vortex lift and this seemed even better.
I flew this machine through some vicious conditions and it was - by a country mile - the best aeroplane I've ever flown in bad air, better even than the 747. I could bore you with war stories, but will illustrate the point with the time we asked Tower to advise the aircraft following us that it was pretty wild below 2000', only to hear that everyone else had cleared off owing to the wind conditions.......
The only people that really got a rough ride were the flt crew, who were at the front of a long extension ahead of the really stiff part of the hull, which tended to whip around long before it got bumpy in the cabin.
It wasn't like flying a transport aircraft at all in rough conditions, and this was a real help in keeping a prestige operation in the air when bad wx appeared. (Of course it wouldn't have helped in the present BAA-induced debacle).
I didn't ever use this mode, and never saw anybody else use it.
Significant turbulence was almost unheard of in supercruise - light to mod was the worst I ever had. Subsonic one would be subject to the same air as the blunties, but in an aircraft which had a high wing loading and good controls. Once you got down into the low-level turbulence on a windy day (say 2000' and below) you were in vortex lift and this seemed even better.
I flew this machine through some vicious conditions and it was - by a country mile - the best aeroplane I've ever flown in bad air, better even than the 747. I could bore you with war stories, but will illustrate the point with the time we asked Tower to advise the aircraft following us that it was pretty wild below 2000', only to hear that everyone else had cleared off owing to the wind conditions.......
The only people that really got a rough ride were the flt crew, who were at the front of a long extension ahead of the really stiff part of the hull, which tended to whip around long before it got bumpy in the cabin.
It wasn't like flying a transport aircraft at all in rough conditions, and this was a real help in keeping a prestige operation in the air when bad wx appeared. (Of course it wouldn't have helped in the present BAA-induced debacle).