6th Sep 2010, 09:17
permalink Post: 222
Coffin Corner
Nick Thomas
Just like Christiaanj I'm trying to dig up an accurate flight envelope diagram. (A lot of my Concorde 'technical library' is out on long term loan), but I would suggest that anywhere within Concorde's published flight envelope you never hit any equivilant to Coffin Corner, a la' U2. The whole issue is really one of air DENSITY, rather that pressure, where as you climb at a given Mach Number, your Indicated airspeed (IAS) falls away with altitude. (Velocity of sound being primarily tied to static air temperature). Now if you are climbing in the stratosphere, where temperature is more or less constant up to around 65,000', you can say that your TRUE Airspeed (TAS) is also constant with climb at a given Mach number. But lift and drag are functions of IAS (the equivalent airspeed that the aircraft would 'feel' at sea level) and not TAS. Because the U2 had a very low Maximum allowable Mach number (Mmo) as IAS fell away with altitude, it would get to the point where it's lowest permitted airspeed (we called this VLA) got to within a few knots of Mmo and severe aerodynamic buffering. i.e. you were screwed with nowhere to go but down
.
In the case of Concorde, Mach 2 at FL500 was 530KTS, falling to 430KTS at FL600. Although we have less lift due to 100KTS lower IAS, the aircraft is now much lighter (this is the whole principal of cruise/climb) which keeps the universe in balance, but drag is now significantly lower too, getting us better MPG
.
On the ASI, the only limitation displayed was Vmo; however the Machmeter did display fwd and aft CG limits at a given Mach number. The ONLY time that Concorde would experience relatively low speeds at altitude was at Top of Descent. I'm a little fuzzy here how it all worked exactly (it's an age thing you know), I'm sure one of the pilots can correct me, but I seem to remember that the autothrottle was disconnected, ALTITUDE HOLD was selected on the AFCS, and the throttles slowly retarded. (If you pulled back too far you'd often get a gentle 'pop surge' from the engines, and you had also to be wary of equipment cooling airflow too). The aircraft was then allowed to gently decelerate, still at TOD altitude, until Mach 1.6, when power was tweaked to give 350KTS IAS and IAS HOLD was selected. The aircraft was now free to carry out her loooong descent to 'normal' altitudes. VLA on Concorde was not directly displayed as you never flew anywhere near it, and also every pilot knew his VLA
. (Stray into this and you'd get a 'stick' shaker warning.
I hope this blurb helps Nick
Dude
Just like Christiaanj I'm trying to dig up an accurate flight envelope diagram. (A lot of my Concorde 'technical library' is out on long term loan), but I would suggest that anywhere within Concorde's published flight envelope you never hit any equivilant to Coffin Corner, a la' U2. The whole issue is really one of air DENSITY, rather that pressure, where as you climb at a given Mach Number, your Indicated airspeed (IAS) falls away with altitude. (Velocity of sound being primarily tied to static air temperature). Now if you are climbing in the stratosphere, where temperature is more or less constant up to around 65,000', you can say that your TRUE Airspeed (TAS) is also constant with climb at a given Mach number. But lift and drag are functions of IAS (the equivalent airspeed that the aircraft would 'feel' at sea level) and not TAS. Because the U2 had a very low Maximum allowable Mach number (Mmo) as IAS fell away with altitude, it would get to the point where it's lowest permitted airspeed (we called this VLA) got to within a few knots of Mmo and severe aerodynamic buffering. i.e. you were screwed with nowhere to go but down
.
In the case of Concorde, Mach 2 at FL500 was 530KTS, falling to 430KTS at FL600. Although we have less lift due to 100KTS lower IAS, the aircraft is now much lighter (this is the whole principal of cruise/climb) which keeps the universe in balance, but drag is now significantly lower too, getting us better MPG
.
On the ASI, the only limitation displayed was Vmo; however the Machmeter did display fwd and aft CG limits at a given Mach number. The ONLY time that Concorde would experience relatively low speeds at altitude was at Top of Descent. I'm a little fuzzy here how it all worked exactly (it's an age thing you know), I'm sure one of the pilots can correct me, but I seem to remember that the autothrottle was disconnected, ALTITUDE HOLD was selected on the AFCS, and the throttles slowly retarded. (If you pulled back too far you'd often get a gentle 'pop surge' from the engines, and you had also to be wary of equipment cooling airflow too). The aircraft was then allowed to gently decelerate, still at TOD altitude, until Mach 1.6, when power was tweaked to give 350KTS IAS and IAS HOLD was selected. The aircraft was now free to carry out her loooong descent to 'normal' altitudes. VLA on Concorde was not directly displayed as you never flew anywhere near it, and also every pilot knew his VLA
. (Stray into this and you'd get a 'stick' shaker warning.
I hope this blurb helps Nick
Dude
12th Sep 2010, 19:41
permalink Post: 332
BlueConcorde
,
Look at my post #260, second diagram, taken directly from the BA Flying Manual.
There is a "first stage warning" (Mach/CG lights and gong) above Mach 1.6 and below Mach 0.45 for the aft CG limit.
It's only in the "corridor" that there is a "second stage warning" (flashing Mach/CG lights and stick shaker).
CJ
Look at my post #260, second diagram, taken directly from the BA Flying Manual.
There is a "first stage warning" (Mach/CG lights and gong) above Mach 1.6 and below Mach 0.45 for the aft CG limit.
It's only in the "corridor" that there is a "second stage warning" (flashing Mach/CG lights and stick shaker).
CJ
12th Sep 2010, 20:04
permalink Post: 333
Blue Concorde
The logic of the C of G limit warnigs were
1st stage warning then the F/E rectifys it by moving the fuel
2nd stage warning was considered a more dangerous exceedence and would be remedied by the F/E moving fuel and the pilot slowing or speeding up the aircraft depending on which limit had been triggered
The aft limit second stage warning was a flashing light and a stick shaker to which the natural response from the pilot is to speed up Now you can see from your diagram that above M1.6 increasing will not improve the siuation if the aft boundry has been infringed. Therefore to prevent an auto response from the pilot to a stick shaker [ push the nose down and speed up] the 2nd stage aft warning was not available after M1.6
Tanks 5 and 7 were operated as a pair as were tanks 6 and 8
Because of the odd shapes of the tanks when you were transferring from the set 5 and 7 the F/E had to pump fuel across the ship to keep lateral trim.
Once they were empty and 6 and 8 were being used then again due to their shape the F/E had to transfer fuel across the aircraft to keep lateral trim ,but this time in the opposite direction . well it stopped him getting bored
The logic of the C of G limit warnigs were
1st stage warning then the F/E rectifys it by moving the fuel
2nd stage warning was considered a more dangerous exceedence and would be remedied by the F/E moving fuel and the pilot slowing or speeding up the aircraft depending on which limit had been triggered
The aft limit second stage warning was a flashing light and a stick shaker to which the natural response from the pilot is to speed up Now you can see from your diagram that above M1.6 increasing will not improve the siuation if the aft boundry has been infringed. Therefore to prevent an auto response from the pilot to a stick shaker [ push the nose down and speed up] the 2nd stage aft warning was not available after M1.6
Tanks 5 and 7 were operated as a pair as were tanks 6 and 8
Because of the odd shapes of the tanks when you were transferring from the set 5 and 7 the F/E had to pump fuel across the ship to keep lateral trim.
Once they were empty and 6 and 8 were being used then again due to their shape the F/E had to transfer fuel across the aircraft to keep lateral trim ,but this time in the opposite direction . well it stopped him getting bored
23rd Dec 2010, 00:39
permalink Post: 957
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.
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.
23rd Dec 2010, 03:11
permalink Post: 958
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
:
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
A warm welcome to the forum, please keep your most illuminating posts coming!
EXWOK
Quote:
| I'm trying to remember what drove the fixed nose-down elevon input at low EAS/high alpha which I alluded to earlier. Presumably it wasn't superstab but some other element of the autostab system |
- Incidence Trim
- Super Stab
- High Incidence Directional Stability
- Auto Trim Inhibit
- Stick Shaker
- A/P disconnect
- Stick Wobbler
- IAS below 140 kts
- Incidence greater than 19\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