Max Performance Short Range Flight

[Andrew Marshall]

Hi, I've always been curious about what a max performance short range flight for Concorde would look like. So the general scenario would be:

1. Still air distance between fields of 300 NM
2. No weather, standard atmosphere conditions
3. No noise restrictions
4. Light load, say 50 passengers
5. Complete disregard for passenger comfort:)

The questions that come to mind are:

1. With no noise restrictions, are there any other restrictions on the use of reheat? As in, can you go full reheat from brake release until top of descent?
2. What is the climb and descent profile to minimize time? Do you climb at max speed following the pole on the way up? Or gain some speed, then rapidly climb, and level off and accelerate?
3. If I recall, there are restrictions on the use of the "speed brakes", sub-sonic and max continuous use for two minutes? Are there other strategies that can be employed to rapidly descend and decelerate to a stable approach?
4. What is the minimum distance to be on a stable approach from the destination field?

Look forward to your comments!

[Fraser Gale]

1. Yes, there was a “reheat envelope” outside of which you weren’t supposed to use them - it was a graph like the flight envelope so difficult to quote here but generally up to FL100 you could use them at any airspeed but above FL100 there was a minimum airspeed of around 300kts and the maximum speed is M1.7.  Max altitude around FL450.

You were only allowed to use them for 15 mins per flight with the engines in “flight” rating, though on one flight they were having trouble accelerating due to high temperatures and they had to contact Rolls Royce to ask what would happen if they left the reheat on for longer and they gave permission. 
I should say I was told first hand by a captain of a flight on a light weight charter where they did leave the reheat in to FL600 and in fact exceeded it slightly to avoid negative g’s at the top. 
 

2. Minimum time to an altitude is an interesting question.  I don’t think you can really do much to get to FL600 quicker other than be as empty/light as possible and get up to VMO as quickly as possible, which you need to be at to get through the high drag from M0.96 to M1.5, but this is normal procedure anyway.  Having said that, you could do a zoom climb while subsonic where you aim for a lower speed and use all the energy to climb.  One captain did attempt a supersonic zoom climb but all that happened was when the reheat was taken out, speed dropped to the point they had to descend back down again and they ended up back where they started almost! 
A departure from a country I won’t name for reasons of tact was once performed in a hurry because of a security issue, so they left the reheat in and did a zoom to an initial subsonic altitude. 
 

3. I assume by speed brakes you mean in flight reverse in which case yes, there were such limits including a minimum altitude to give you time to shut the engine down if you couldn’t get reverse to cancel.  There wasn’t really any other ways to descend quicker other than slowing to minimum speed to add drag, but you have to be careful how far you go with that one and stay in limits.  Remember that in an emergency situation, closing the throttles to idle was enough drag to send people down the isle! 
 

4. There were formal “stable approach criteria” but I’d need to look it up.  In our simulated world my advice would be to have everything sorted by the 1000ft call.

I hope I’ve understood your questions correctly and given reasonable answers…

[Andrew Marshall]

Yes, very helpful! Curious if you know the IAS for best rate of climb? Not sure if this is something mentioned in the pilot's hand book or similar? Some university coursework here (https://engineering.purdue.edu/~andrisan/Courses/AAE190 Fall 2000/Concorde/Concorde_Performance.pdf) suggest approximately 320 knots.

Your comment on in flight reverse also makes me wonder if it is faster (i.e. shortest possible total journey time) to go for a max drag descent (through out the anchors, slow to min speed) or alternatively, go for a VMO descent?

[Andrew Wilson]

Some crews flew a ‘spill door descent’ whilst supersonic. If you reduced the throttles further than 18TLA, the spill doors would open which increased drag. Got the thing subsonic pretty quickly apparently!

[Fraser Gale]

3 hours ago, Andrew Wilson said:

Some crews flew a ‘spill door descent’ whilst supersonic. If you reduced the throttles further than 18TLA, the spill doors would open which increased drag. Got the thing subsonic pretty quickly apparently!

Yes, it was also used for low ISA situations like going into Bahrain.  The only trouble with this was if you for whatever reason needed to re-apply the power it would have most likely caused engine surge.  
The more official way to rush your descent was to engage the autopilot in MACH HOLD on reaching M1.3 and close the throttles.  You plummeted rather quickly and capture FL410 flying level with no power which reduced you to subsonic very quickly.  If VMO was reached select IAS hold.  You would really need to warn the passengers and strap them in for this though. 

[Fraser Gale]

6 hours ago, Andrew Marshall said:

Yes, very helpful! Curious if you know the IAS for best rate of climb? Not sure if this is something mentioned in the pilot's hand book or similar? Some university coursework here (https://engineering.purdue.edu/~andrisan/Courses/AAE190 Fall 2000/Concorde/Concorde_Performance.pdf) suggest approximately 320 knots.

Your comment on in flight reverse also makes me wonder if it is faster (i.e. shortest possible total journey time) to go for a max drag descent (through out the anchors, slow to min speed) or alternatively, go for a VMO descent?

Things like best rate of climb speed aren’t really mentioned in the flying manual as the airlines want every crew member to fly the thing the same way, so it’s about standardisation.  I may have a figure for that somewhere in an obscure place but generally with Concorde the faster you flew, the less drag she produced so better performance.  Whenever incidence (angle of attack) was greater than about 7 degrees, she was using the vortices for lift which gave great lift but a lot of drag, which is why flying subsonic was not economical. It also produced a small buffet making the whole aircraft shake like in constant light turbulence so any speed below 250-260kts wouldn’t give good performance.  The more I think about it, I think VMO could be considered as best everything…
 

If you wanted to break the Atlantic crossing record you would want to stay as fast as possible, even when subsonic, then use in-flight reverse to get down as quickly as possible, yes.  The current (and forever) record flight crew planned to do this but tried to do it at the upper speed limit for using them, causing the speed switch (that they weren’t aware of) to activate on one of them and stopped deployment.  They still broke the record though! 
Remember it was an airliner though, and using in-flight reverse could be uncomfortable for the passengers who had spent most of the flight climbing, suddenly they were dropping like a stone…. I think there was a general feeling that on charters you could get away with more things like this because folk just wanted the experience but that’s just an assumption after a few conversations I’ve had with former crews. 

Reverse could also be handy for slowing you down on reaching an altitude after a high energy descent.

Basically, anything goes!