Posts about: "Auto-stabilisation" [Posts: 28 Pages: 2]

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\xb0 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\xb0

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\xb0.

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.

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\xb0 nose down.

2) With Vc < 140 KTS and alpha/alpha rate greater than 19.5\xb0 (this itself would generate the 'wobbler' or 'unmistakable warning') a 4\xb0 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

I'm sure Christiaan or Dude will have better explanations, but in brief :




In mechanical back-up control demands were fed to relay jacks which acted as force amplifiers so the pilot was unaware of control run friction. The autopilot also fed into these relay jacks. This meant that the control precision and ability to harmonise control forces given by the electrical control system was not degraded by mechanical system shortcomings.
In electrical signalling there was a dead space at the Powered Flying Control Units (PFCU) to allow for the difference between mechanical and electrical commands produced by autostabiliser activity. Variation of this dead space with flight condition gave the autostabiliser authority limits. Autostab. was not available in mechanical signalling when the PFCU servo valve was locked to the mechanical control system.
So the control column movements were never 'ignored' by either system, but the mechanical system never 'saw' the autostabiliser commands.

Cheers

Clive

Dude - that really brings back pain form the past! I remember knowing (just) enough about the flying controls to pass the ARB, but a diagram similar to that one was presented at one "Technical Refresher" day (remember those?) by one of our more chatty training EOs (could have been you?!) together with a coloured plastic overhead projector schematic complete with slidey moving jacks and PFCUs and things and it worked! I completely understood the system right up until the first pint of Brains that night...

Flying in mechanical signalling was a different experience - losing the autostabs was bad enough (and proved how good that system was). A mate on the fleet once described it as like trying to fly around on a supersonic dustbin lid. I think that description was too kind - the thing was barely controllable in that configuration. One of our skippers described an airtest when he was on the JS where the crew were trying a decel in MS: as the phugoids were diverging he thought he was about to lose his life so leant forward to restore things. Sadly the switches had been left in MS, so he had to move the switches up to "Blue" as well as then pressing the reset tits - a procedure which he described as almost impossible due to the ever more extreme manoeuvres. Recovery, fotunately, was instant. Resetting electrical signalling and autostabilisation always felt like slotting into a groove on the Concorde.

For that reason, I believe, flight in mechanical signalling was removed from transonic flight on airtests and altogether from Base Training. The simulator was the only sensible way of trying to fly like that...

And that flying control pre-flight check! Learning it was a conversion course rite of passage: one of the sadder parts of reading this thread was realising I'd forgotten it. Great times, great aircraft, great people. Nostalgia isn't necessarily a thing of the past... see you in March?

NW1
Ahhh the Tech refresher days. Not being an EO it would not have been me, no. But the 'trainers' often used to come seek me out in the hangar and (over coffee, not beer I'm afraid) confer about various system quirks and nasties to use on you guys during the tech' refreshers. (So I guess can be blamed for a few of the 'stinkers', sorry ). And I definately know who you mean by describing him as a 'chatty' EO.... a truly great guy though.
Mech' signalling during decel'??, OUCH!! I would have thought that the 'supersonic dustbin lid' description would have been quite an accurate description of what must have been a very uncomfortable experience indeed. It was quite a vivid and scary description, I can just imagine trying to move the 3 switches up to BLUE from MECH and stabbing the reset buttons while your seat and the selector panel are seemingly going backwards and forwards, up and down in different directions!! . On the C of A renewal test flights I seem to remember that MECH was only tried fairly briefly at a very subsonic 300 KTS during the early stages of the flights, but even then it felt like the aeroplane was riding a sea of different sized golf balls and the outer wing sections seemed to flap about quite enegetically in a world of their own; it was pure bliss when we reset into BLUE. It really shows us all just how good the FBW and autostab really was, the fact that the aeroplane handled so beautifully throughout such an enormous envelope. Well done CliveL and ChristiaanJ and all you designer chaps. .
Now NW1, I bet you can still really do the flying control check in your sleep ( ), but 'Great times, great aircraft, great people' is certainly a marvelous way to sum up such an amazing time of our lives. I still feel honoured and very lucky to have been a small part of it all for so many years.
And as for March... Yes I will be there; see you on the 4th.
Best regards

Dude

I personally doubt very much if the Emergency Pilot would be the 'way in' for the sidestick input. EFC ROLL commands were inputed from the SFC computer to the Autostab computers as 'stab demands' and therefore drove the MIDDLE and OUTER elevons only for roll. To make matters worse, if your test flight was really 'exciting' and you found yourself at any time at Vmo + 20 KTS, roll control would be through the middle elevons ONLY. I'm with CliveL in that the most likely scenario would be for the demand would feed via a D/A converter somehow. (It would be great to find out though).
I would have thought that the whole venture was a proof of concept by SFENA for future implementation in the Airbus family. This excersise would have been both costly and highly complex at system level, any other reason would really have been quite daft.

Best Regards
Dude

As I recall, they referred to this research project as a CCV (Controlled Configured Vehicle) design study. It would be great if we could get this confirmed, but they talked about subsonic drag reductions of 10 to 15% by flying (not taking off!!) with a far more aft CG than the norm. The 'system' I seem to remember, as a result naturally commanded some down elevon, which increased lift. As the aircraft could then fly with less alpha, I guess this is where the drag reduction comes from. (Clive, I wonder if you could find out through one of your contacts if this was true?).
I'd still personally like to know how the sidestick was integrated into the flying control system, I've been thinking and can not now believe that sidestick inputs could be simply input to the flying control system 'at resolver level'. Remember that the concept of the FBW system on Concorde was that resolvers were utilised as simple 4 wire synchros, and the pitch and roll axis utilised a CX/CDX/CT chain, which produced the error signal to the ESA's in the Autostab computers. Using a sidestick completely breaks up the chain, and my guess is that a seperate digital unit contained the flight rules which were summed against PFCU CT position and sidestick input would have been necessary. It is possible then that an analog output from this 'box' could be fed to the Autostab Computer ESAs and hence drive the elevons. I'm probably completely wrong, but I'd surely still love to know the truth. As you say Clive, ideal stuff for Concorde 2.

Best regards
Dude