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