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

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.

My first post here, many thanks to each contributors (either the questionning or answering ones), this is a brilliant thread ! :D

CliveL, thanks for joining, Sir. Please let me try to help with forum issues :
To get the "quote box", you'll want to add "tags" before and afther the quoted text, as follows :

Type this : [quote]Here is the quoted text[/quote]

To get this : Or type this : [quote=OriginalPosterName]Here is the quoted text[/quote]

To get this : More informations are available, for example, on Wikipedia : here.

Hope this helps, and sorry for the drift regarding the topic. Let's get back to the Lady :)

Cheers
AZR

CliveL, check your PMs (private messages).
CJ

OK Christiaan willdo

CliveL

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

quote:On 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 questionshttp://images.ibsrv.net/ibsrv/res/sr...lies/wink2.gif

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

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

quote:During 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 whilehttp://images.ibsrv.net/ibsrv/res/sr...lies/smile.gif

CliveL

Hi Clive
dont do that you're very interesting
cheers
rod

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 .

Both CliveL and EXWOK are of course right about the pitch-down into ground effect... I think I apologised for my bludner in a later post.

CJ

Here are the graphs that CliveL was referring to.

The Mach trim control law

http://img.photobucket.com/albums/v3...J/Machtrim.gif


The aircraft response to a double engine surge
Split into two halves (longitudinal and lateral response)

http://img.photobucket.com/albums/v3...ublesurge1.gif

http://img.photobucket.com/albums/v3...ublesurge2.gif


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

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

Thumbs Up for CJ, CliveL, M2Dude and other guys.:ok:

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

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 :D).
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 :O

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 :sad:(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 :O

Firstly; Thanks AZR!

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

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?

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).

Allow me to nitpick a moment.....

Pilot demands in manual flight produced electrical signals corresponding to the control position, which were sent to the 'servo control amplifiers' (eight in all, one per control surface) which in turn commanded the PFCUs (power flying control units) that hydraulically moved the control surfaces.

Autopilot demands directly moved the pilot's controls (stick and rudder) via hydraulic cylinders (the 'relay jacks') so that the same signals as in manual flight then went to the servo control amplifiers.

The purpose of the autostab was to provide proper dynamic stability over the full flight envelope. The aircraft could be flown without autostab, but over some of the speed range it was only marginally stable.
The electrical signals from the autostab computing were fed directly into the servo control amplifiers, so there was no feedback to the pilot's controls, unlike the autopilot demands.

There was occasional confusion about exactly what did what and how and where.... because the servo control amplifiers - although a function independent of the autostab as such - were housed... in the autostab computers.

To complete the tale, this is what those servo control amplifiers look like.
The one of the left is from prototype 002, the one on the right from a production aircraft. To give them scale, the one on the right is about the size of a box of large kitchen/fireplace matches.

http://img.photobucket.com/albums/v3...J/0107001a.jpg

CJ

Re TURB mode
That reminds me.....

We spent a lot of time, and did a lot of flights, to get the VOR (capture and hold) autopilot mode to work satisfactorily.

It was not until years later, and on another type, that a pilot told me "VOR mode? We never use it. We use TRK or HDG mode, and monitor on the HSI that we're on the VOR radial."

IIRC, in service it was the same on Concorde, but maybe EXWOK or one of the other pilots here can confirm it?

CJ

Not sure what you mean here. The production aircraft outer wing was significantly revised with different camber to give a better cruise drag, and the aircraft was built to a 'jig' shape which differed from the desired cruise shape to allow for aeroelastic distortion under 1g flight loads, but I don't recall any specific tailoring of structural flexibility to reduce CP shift. Could you mean the process I have just described?

http://i1080.photobucket.com/albums/...l1/Image49.jpg

CliveL

Thanks for yours reply. :O

BTW, what about the super-stabilization? Does it only function when the
aircraft was lift on for 10 minute or for a whole flight regime? Also, what is
the stalling AoA of the Concorde?

Finally, What does the function of the Thrust recuperator and how does it work?

Edit: According to the CliveL picture, why Concorde wing LE has to droop down?
Is it use to produce the "negative drag" by the vortex?
Also, does the tip of the wing always has a negative AoA at all flight regime
or does it gonna bend up as the airspeed increase?

Thanks for all of yours reply.:ok:

Best regards

VOR tracking on Conc
 

You're right Christiaan - memories of the exact details are growing misty now, but I do remember trying to get the autoflight VOR tracking facility to work and not getting anything sensible. I (and everyone else I ever flew with) invariably used the INS to track to a VOR - or just tuned the station and flew it like an aeroplane using controls and needles. The Concorde aeroplane encouraged the latter technique because it was so rewarding (but occasionally deeply frustrating) to fly. Good days were phenominal. Bad days were... bad (Mike Riley put this well in his "Concorde - Stick and Rudder" book).

NW1 - amen..........

Clive L - the whole aeroflexing of the 'A' tanks thing was something mentioned during ground school on my conversion course; I may have misunderstood or it may have been less than accurate info.

Mr Vortex - the superstab was always available, though clearly it wasn't a regime one could get into during many phases of flight. As for the 'stalling' alpha - it doesn't have any meaning on a delta. By normal standards Concorde lifted off and landed in what would be called a 'stalled' condition on a conventional aircraft; in Concorde this was 'vortex lift' and was the secret to having an 1100kt speed range on one wing section. (We've talked about this much earlier in the thread).

The limiting factors for max alpha are pitch-down control and drag. IIRC the ability to stop pitching up ended at about 21-22degs alpha (CliveL will know exact numbers I guess!).

Stick shake went off at 16.5degs and stick 'nudger' (badly named - nearly tore my arms out when we tried it on the conversion course) at 19.5 degs, although this could go off sooner under phase advance if the rate of increase was high. (NB - all the above from memory; flt crew with manuals or development men with proper knowledge feel free to correct)

Lastly - the thrust recuperator was explained by M2dude much earlier in the thread, I'll have a look for it. Short answer - clever gizmo on the port(?) fwd outflow valve to recover thrust from outflow air.

"Superstab" ?

CJ

Superstab
 

Hazy recollection - effectively an additional autostabilisation input in the nosedown sense active at high alpha/low CAS.

Ultimately applied a further nose down elevon input (4 degrees????) if CAS was less than (140kts???? That's a VERY low speed). (Colloquially known as 'super-duper stab' on my course)

It's many years now since my course, and that's the last time I saw this so I think I'm going to need help from a grown-up to come up with a decent answer.

High Level Incremental Fuel (HLI)
 

Hi,

Can someone please explain to me the purpose of High Level Incremental Fuel (HLI)?

Was it just a case of squeezing a bit more fuel in all the tanks above their normal refuelling levels to increase the fuel load for maximum range, possibly something like LHR - BGI with unfavourable weather conditions?

How often was it used and were there any special operating procedures in place when it was used?

Many thanks,

Steve.

The AFCS included an incidence term in the auto-trim system (additional to Mach trim, but (I think) in the same 'box') which gave conventional stick force stability by applying effective down elevator as AoA increased above 11 deg. This was a non-linear relationship that catered for the gentle 'pitch-up' present in the low speed pitching moment curve. However this system had to be limited in its rate of application to guard against trim runaway. This made it incapable of providing full stability at the maximum rate of change of incidence that the aircraft could acheive.

To cover this case the 'superautostabiliser'was developed. It effectively restricts the rate of variation of incidence so that, if the pilot entered into an avoidance manoeuvre of sufficient magnitude to trigger the stick wobbler, i.e. about 1.5g, he would be able to recover easily without exceeding the maximum incidence demonstrated in flight (which was in fact slightly greater than the maximum steady incidence limit). This superautostab had gain scheduled against AoA and also included phase advanced pitch rate and speed terms. Finally, there was a 'yaw superautostabiliser which applied rudder as a function of lateral acceleration to restrict sideslip which (see below) could affect the maximum lift attainable. [Note that because of the dynamics of slender aircraft operating at high AoA it was readily possible to develop sideslip in a turn]

Hope that is clear.

Whilst talking about maximum lift etc. can I confirm the numbers quoted in an earlier posting for the start of vortex lift - about 6 or 7 deg AoA at low speed, and for the AoA at maximum lift - about 23 deg. This is where the pitching momemt curve vs AoA 'breaks'. It is not a stall in the conventional sense because of course the flow over the leading edge has been separated long ago. Instead it is the AoA at which the LE vortices become 'too big for their boots' and go unstable and 'burst'. This AoA is sensitive to sideslip and the leading wing half will go first.

CliveL

Before adding my own little bit to Clive's earlier reply about the autotrim, I will try to explain, for those not fully familiar with the subtleties of automatic flight control, the difference between "closed loop" and "open loop".

Closed loop

As an example, let's look (very simplified) at how the autopilot maintains a selected altitude.

http://img.photobucket.com/albums/v3...Closedloop.gif

On the one hand we have the desired altitude as selected on the autopilot controller (here 40,000 ft).
On the other hand we have the true altitude, as measured by the altimeter (let's say 39,000 ft).
We subtract the two to obtain the altitude error (in this case 39,000-40,000=-1,000 ft).
We 'multiply' the altitude error by a factor, the gain (for the discussion, let's assume this gain is 1 degree elevon per 1000 ft altitude error), and send the resulting elevon position command to the elevon.

So, the elevon moves 1° nose-up, the aircraft starts to climb, the altitude increases and the altitude error decreases until it becomes zero, by which time the elevon position has also returned to zero.

What we have now is a "closed loop" : any deviation from the selected altitude results in an elevon command in the opposite direction, until the deviation is again reduced to zero.
Another commonly used term is "feedback" : any error is fed back in the opposite sense until it's reduced to zero.

The significant figure here is the 'gain'.
If the gain is too small, the autopilot response to a disturbance (say turbulence) will be sluggish ; the aircraft takes too long to return to the desired altitude.
If the gain is too high, a small disturbance will cause the aircraft to start climbing too rapidly, and to overshoot the desired altitude, then descend to correct the new error, etc.
In other terms, the control loop is no longer stable, but starts to oscillate.

Both theory and practice show that the exact value of the gain is not all that critical, a few percent more or less do not markedly change the response of the loop.

Note: a "closed control loop" as described above can be implemented in just about any way you like.
It can be done purely mechanically, with a few clever clockwork mechanisms 'computing' the altitude error and controlling the elevator pneumatically or hydraulically. It's how the earliest autopilots worked.
After that came electromechanical systems, analogue computers and then digital computers... but the principle has remained unchanged.


Open loop

As already described in earlier posts, the situation with the automatic trim is the opposite.

http://img.photobucket.com/albums/v3...enlooptrim.gif

We now need to compute a neutral elevon position from several data, such as Mach number or airspeed, but without any feedback as to whether our computations are correct.

We're now working in "open loop".
To complicate matters... that neutral elevon position is not a simple linear function of Mach and airspeed, but far more complex (see the earlier posted graphs).
And because of the large response of the aircraft to small changes in trim, in particular in the transonic regions, those computations have to be far more accurate : a one degree error is simply not acceptable.


In the end.....

The AICS (air intake control system) also uses several "open loop" functions.
The early development aircraft still had an analogue system, which proved all too soon to be inadequate, so, at a very late stage, it was replaced by a digital system (one of the rare digital systems on Concorde).

The "open loop" functions of the autotrim system initially had the typical "a few" percent" accuracy of the other flight control systems, which, for the autotrim, also proved inadequate.
We managed to "save the furniture" (as they say in French) by using 0.1% components in all the critical computing paths, so the autotrim computers remained analogue until the end.

But, a slide rule is not accurate to 0.1%... So that's when I had to buy my very first pocket calculator.
£42 at 1972 prices... just as well the firm paid.

CJ

I've noticed that several postings refer to the production AICU as a 'digital' control system. Strictly speaking it wasn't; it was a hybrid digital/analogue system where the inner dynamic control loops (the closed loop part) were analogue systems operating to maintain limits defined by the digital arithmetic processors. This allowed us to have quite sophisticated control 'laws' which would have been next to impossible with a pure analogue system.

CliveL

HLI
 

For spfoster:

You've pretty much worked HLI out. No particular special requirements, it was normally associated with 54% CG departures, since that was the norm with high fuel loads.

Contacts were bridged which allowed some of the tanks to operate at a higher level before shut-off. Sounds simple, doesn't it? But it was a pain in the a***.

The tanks were first filled to normal level (this got tank 11 filled) then a metered amount was uplifted with the bridges in place to those tanks with HLI (M2dude will remind me which they were.....I'm guessing 5,6,7,8 and maybe 9&10?????). It could take ages.

It was invariably followed by a taxy with a Pre Take Off Burn Off to get the CG to its correct position, so you now had the problem that you had to burn enough fuel from tanks 1-4 to allow them to be topped up by tanks 5 & 7 to the extent that 5 & 7 could accept fuel from tank 11 to bring the CG fwd to 54%. Because they were so full it could take ages to get 5 & 7 to accept fuel and then any bump or turn would shut them off. So overall you've filled the tanks, presumably because you need the fuel, but because you've done this you have to burn loads of fuel taxying while you get the CG sorted out.

As you guess, it was mainly a LHR-BGI thing, or a JFK with weather problems, and more often than not you gained very little.

superstab
 

CliveL -

Many thanks for the superstab explanation -it makes more sense as a manoeuvre-driven input than as low-speed protection as the conversion course implied.

I'm trying to remember what drove the fixed nose-down elevon input at low CAS/high alpha which I alluded to earlier. Presumably it wasn't superstab but some other element of the autostab system; is NW1, Bellerophon or Brit312 able to help me out here?

Exwok,

Thanks very much for the explanation - you, your friends, colleagues and everyone that has contributed have made this the most interesting thread I have ever read on Concorde.

It's great to keep the memories alive.

A safe and happy Christmas to you all.

Regards,

Steve.

You're more than welcome.

It's nice to stretch the memory a bit - it's supposed to be good for the brain, and may make up for the seasonal synapse bashing that's about to start.....

Superstab
 

Hmm. There was, I think, a raft of high-incidence (alpha) protection fitted.

Digging out the old BAe conversion course notes:

The "Anti-Stall" (SFC) 1&2 sytems offered:

Super Stab: Increased authority of pitch autostab as incidence increased above 13.5 degrees - proportional to pitch rate and incidence angle - and a nose down pitch trim with a Vc (CAS) deceleration with incidence > 13.5

Stick "Wobbler": the "unmistakable warning" - when incidence > 19 and Vc<270kts the control columns took a life of their own and tried to fling you into the forward galley. Served you right.

Some other high incidence stuff was fed from the ADC rather than the SFC, like:

The ">13.5d incidence" feed to the SFC

CAS (Vc) feed to the SFC

Incidence from 16 to 19 degrees (rate dependant) to get the SFC to feed in up to 4 degree nose down pitch command and the sticj wobbler trigger.

Increase of authority of yaw autostab as incidence > 13.5d

Autotrim inhibit > 14.5d incidence

Stick shaker >16.5d incidence

AP/FD disconnect > 17.5d incidence

There was loads of other technical stuff which engineers understood, but we had to learn by writing diagrams which made sense to us enough to pass the written exam. The bottom line was an aeroplane which flew beautifully, but which you had to understand well, and which you could not tease beyond its limits. If you ignored a limit or an SOP then you reached an unpleasant place far quicker than with the blunties - it was a challenge which rewarded as quickly and as deeply as it punished.

CliveL

A warm welcome to the forum, please keep your most illuminating posts coming!


EXWOK

Digging out my old BAeAS notes, if you still have them, the reference is in the Anti High Incidence section at 7.4.82. In addition to the following systems, already mentioned by NW1:

• Incidence Trim
• Super Stab
• High Incidence Directional Stability
• Auto Trim Inhibit
• Stick Shaker
• A/P disconnect
• Stick Wobbler

there was a further protection called the 4° Nose Down Demand, although, like you, I seem to remember it was referred to on the course by other names. The requirements to trigger this were:

• IAS below 140 kts
• Incidence greater than 19°

It operated through the pitch auto-stabs, so at least one of them had to be engaged for the system to operate, as well as the associated anti-stall being on and the ADCs agreeing. There was a high-rate-of-increase of incidence protection incorporated in this system, and it could be activated at an incidence as low as 13°.

Purely in the interests of historical accuracy, may I point out that I did once complete a load sheet on a charter flight, but this occasioned such ribald comments from the starboard side of the flight deck, accompanied by ill-suppressed mirth from the maroon Mafioso in the engine room, that I decided in future to delegate all further such calculations to the F/O. :p

Merry Christmas to all

Bellerophon

SUPERSTAB
To hopefully further clarify, this was controlled from the SFC computer and was a two part mix:
1) With Vc < 270 KTS the AUTOSTAB pitch damping was increased as a function of pitch rate and pitch rate DOT, Vc DOT and corrected (wing) incidence. Maximum possible demand limited to 8° nose down.

2) With Vc < 140 KTS and alpha/alpha rate greater than 19.5° (this itself would generate the 'wobbler' or 'unmistakable warning') a 4° nose down signal is generated over a 1 second time constant.

I hope the enclosed diagram helps to put it all in place.

Best Regards
Dude :O

http://i1237.photobucket.com/albums/.../Superstab.jpg

Flexure and stuff
 

EXWOK
Clive, I think we need your help here. I was also told, both while I was at Fairford and during one of my two ground school courses at Filton in the early 80s, that the lateral stiffeners (underneath the wing just inboard of the Rib 12 area) were added to reduce outer wing flexure and in themselves gave us a performance penalty. Can you shed any light Clive?

Best regards
Dude :O