Posts about: "Depressurisation" [Posts: 8 Pages: 1]

Re the questions about depressurisation, this may be useful.



It shows the emergency descent profile (solid line, 'Avion'), and the resulting effect on the cabin altitude (dotted lines) in the cases of one window ('hublot') blowing out with either three or four air conditioning packs ('groupes') operating.

As the graph shows, in the worst case the cabin altitude rises to about 40,000ft for about two minutes before starting to drop again, which is survivable when breathing oxygen.

It was studies like this, that lead to the small windows on Concorde. Keen spotters may actually notice that the windows on the prototypes are bigger than on all the other aircraft

The diagram is taken from "The Concorde Story" by Chris Orlebar, but the original was so pale that it was uncopyable, so I did redraw it, in answer to a question by a French friend (hence the legends in French).

Hi everyone
Earlier in this thread there was an interesting discussion on emergency depressurisation. During the rapid descent I would guess that the FE would be very busy find out "what was what" etc.

So I have been wondering if there were any special procedures for managing the CofG in a rapid descent especially as there could also be many other factors needing the crews attention?

BTW it only seems like yesterday when I was sat in front of my parents TV watching Concorde take off for the first time from Filton and in fact it's now nearly 42 years ago. I like most people watched the event in black and white which just goes to prove how far ahead of her time she was.
Regards
Nick

Well never having done this set of drills for real, I can only give the experience from the sim, which is never the same as the real aircraft, however with this set of problems there is a big difference between sim and aircraft and that is if for real on the aircraft you might have to cope with pressure breathing, whereas on the sim the mask was just on demand.

Pressure breathing we had to practise on a special little rig at the training base at Heathrow under medical supervision every two years {I think}. Even on this rig we did not get full pressure breathing but sufficient for us to experience what it would be like. Whilst we were on this rig they would ask us to read from a checklist, and it was then you realised how hard it would be in real life.

Normal breathing means you have to use muscle power to inhale and you relaxe to exhale, and luckily for most of us we do not have to think about doing it. However on pressure breathing you are blown up by the pressure and you have to concentrate to stop the pressure air coming in. To exhale you had to use muscle power to push the air out and whilst you were doing this you could speak. Normally a couple of you did it at a time so you could see the affect it had on your buddy who normally went red in the face and the veins started to show up.

All in all I found it quite a tiring experience

So, if the crew were in an emergency descent due to pressurization failure there would be the Depressurization drill, the emergency descent drill and the normal checklist to fit in, while trying to control your breathing and speak as you were trying to force the air out of your lungs. Along with this trying despaeratly to keep switching your intercom off so the pilots could use the R/T otherwise the sound of your breathing deafened everything

As checklist work was carried out by the F/E he could initially be quite busy so the pilots would start the fuel fwd transfer with a switch on the over head panel. However this was quite a rough and ready system so as soon as the F/E could find time he would use his panel switches to transfer the fuel. These switches allowed more flexibility as to where the fuel would go.

That is why it was mandatory for F/E to have two legs as if he only had one there would have been no where to rest all the checklist he might be running at the same time

Sorry about the length, and her in doors is now demanding my attention ,
{just to do some work or other } so I will come back to the subject of the course later

Just wondering was that the maximum speed "in" the design ? I understand that "the higher & the colder = the faster" was the key to the performance and that the Mach +/- 2.0 cruise was implied by limiting altitude to FL 600 in order to mitigate cabin depressurization consequences. I guess there where also thermal issues but was, say, Mach 2.2 @ FL700 "warmer" than Mach 2.0 @ FL600 ?

Also wondering what was the max altitude ? Was high altitude stall (for the lack of a better word) ever experimented during tests or training ?

atakacs

Quote:

Just wondering was that the maximum speed "in" the design ? I understand that "the higher & the colder = the faster" was the key to the performance and that the Mach +/- 2.0 cruise was implied by limiting altitude to FL 600 in order to mitigate cabin depressurization consequences. I guess there where also thermal issues but was, say, Mach 2.2 @ FL700 "warmer" than Mach 2.0 @ FL600 ?

Really an answer for CliveL, but I'll have a go. The short answer to your question is 'oh yeah, big time'. Total temperature varies with the SQUARE of Mach number and static temperature. Depending on the height of the tropopause itself as well as other local factors, there can be little or no significant variation of static temperature between FL600 and FL700. The 400\xb0K (127\xb0C) Tmo limit was imposed for reasons of thermal fatigue life, and equates to Mach 2.0 at ISA +5. (Most of the time the lower than ISA +5 static air temperatures kept us well away from Tmo). In a nutshell, flying higher in the stratosphere gains you very little as far as temperature goes. (Even taking into account the very small positive lapse above FL 650 in a standard atmosphere). As far as the MAX SPEED bit goes, Concorde was as we know flown to a maximum of Mach 2.23 on A/C 101, but with the production intake and 'final' AICU N1 limiter law, the maximum achievable Mach number in level flight is about Mach 2.13. (Also theoretically, somewhere between Mach 2.2 and 2.3, the front few intake shocks would be 'pushed' back beyond the lower lip, the resulting flow distortion causing multiple severe and surges).
On C of A renewal test flights (what I always called the 'fun flights') we DID used to do a 'flat' acceleration to Mach 2.1 quite regularly, as part of the test regime, and the aircraft used to take things in her stride beautifully. (And the intakes themselves were totally un-phased by the zero G pushover that we did at FL630). This to me was an absolute TESTAMENT to the designers achievement with this totally astounding aeroplane , and always made me feel quite in awe of chaps such as CliveL.

Quote:

Also wondering what was the max altitude ? Was high altitude stall (for the lack of a better word) ever experimented during tests or training ?

Well the maximum altitude EVER achieved in testing was I believe by aircraft 102 which achieved 68,000'. As far as the second part of your question goes, not to my knowledge (gulp!!) but perhaps CliveL can confirm.

Shaggy Sheep Driver
So glad you are enjoying the thread, and absolutely loved the description of your flight in OAD and your photo is superb. I don't think it is possible to name a single other arcraft in the world that could be happily flown hands off like this, in a turn with 20\xb0 of bank at Mach 2. (One for you ChristiaanJ; The more observant will notice that we are in MAX CLIMB/MAX CRUISE with the autothrottle cutting in in MACH HOLD. Oh, we are in HDG HOLD too ).
Now for your question A very good question. The anti-skid system used a fixed simulated nose wheel rolling speed Vo signal as soon as the undercarriage was down and locked, this was confirmed by the illumination of the 8 'R' lights on the anti-skid panel. The illumination of these lights confirmed that there was full ant-skid release from the relevant wheel, due to there being of course zero output initially from the main gear tachos but this simulated Vo output from the nose gear tacho. The Vo signal therefore ensured that the aircraft could not be landed 'brakes on' (all the main wheels think they are on full skid) and that there was anti-skid control pending lowering of the nose-wheel. As the main wheels spin up on landing, their tacho outputs now start to back off the Vo signal, and braking can commence. As the nose leg compresses, the Vo signal is removed and the Nose-wheel tachos(their were 2 wired in parallel) spin up, their output will now replace the Vo signal, and full precise anti skid operates.
As far as your air conditioning question goes, you needed an external air conditioning truck to supply cabin air on the ground. Not needed in the hangars of course, but come departure time if these trucks were not working, then the cabin could become very warm/hot place indeed (depending on the time of year). Oh for an APU
Best regards

Dude

It\xb4s a privilege to read so much knowledge. Thanks for taking the time to post it all.

Am just curious about the Emergency Descent/Rapid Depressurization profile that was used by Concorde.

TUC is so small at 60,000ft...I reckon that masks were not used at all times during cruise, so, what procedure was used?

How fast could the descent be completed to a safe altitude?

I don\xb4t think that any explosive decompression really puts the cabin altitude at 60,000ft instantaneously, but am just curious about this aspect of the Concorde.

Thanks for your time.

SEQU

Curious to know what drills were followed with a rapid depressurization at it's normal cruising levels between FL500-600.



Was it possible to go to idle power prior to starting a descent, and with no spoilers would reverse have been used to achieve a higher rate ?

Thanks Exwk, is it accurate that FL600 was the Concorde's regulated ceiling due to the time required to descend in the event of a depressurization or were there other factors involved ?


It sounds like you could get down pretty quickly when needed. I believe it was capable of higher altitudes and sometimes reached FL600 in cruise, I forget the highest achieved during flight test although that is probably in this thread !


Incidentally what was the envelope for using reverse ? Your description of it's operation makes it sound less than practical ?


Why was that ?


Best wishes.