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Old 22nd Aug 2010, 12:18
  #66 (permalink)  
Join Date: Dec 2000
Location: UK
Posts: 257

...The altitude flown was due to temperature and weight of the areoplane. This is true of all aeroplanes...

Sadly, it isn’t, as subsonic aircraft are allocated a specific cruising flight level and often - for example on the North Atlantic Track system - a specific cruising Mach number as well, and no deviation from that clearance is permitted without specific permission from ATC. Obviously everyone flight plans at the most economic heights and speeds for their aircraft type, but in busy airspace not everyone gets what they want!

Think of your flight plan as being Angelina Jolie, and your ATC clearance as being your wife. Your flight plan is what you’d really like to have, but your ATC clearance is what you’re going to have to live with!

... altitude flown was due to temperature and weight of the areoplane...this was more true of Concorde?...

Subsonic aircraft could equally benefit from using cruise-climb techniques (early long range aircraft crews knew all about cruise-climb techniques and used them when able) but with the large number of subsonic aircraft now using the world’s airways it is impractical for ATC to allow them to drift up and down at will, and so they are assigned specific cruising altitudes.

Few other aircraft got up to Concorde’s cruising levels, and so ATC were able to issue much more flexible clearances to her.

A typical Concorde ATC clearance would have allowed her to accelerate to M2.00 whilst operating within a "block" of altitude, rather than at a specific flight level. Typically this block clearance would have been to operate anywhere between FL450 up to FL600 without restriction.

So, unlike subsonic aircraft assigned a fixed cruising altitude such as FL350, Concorde could, and did, drift up or down, and was thus able to remain at the optimum altitude for the prevailing conditions throughout most of the flight.

... I remember reading the BA Concorde flew with 2 Captain Pilots (and of course the most important Flight Engineer)...

Concorde operated, as did all 3 crew aircraft in BA, with a standard crew of a Captain, F/O and F/E.

A small number of trips had two Captains on board (or two F/Es for that matter) when training or checking was going on, or an extra crew member was carried for PR purposes, but otherwise, the vast majority of occasions, just the standard crew was on board. Everyone preferred it that way, especially the F/O and F/E!

... The subsonics have issues with Coffin Corner (I think I read that one Airbus model had somehting like 7kts between the high and low end of the envelope when up high); did Concorde have this "problem"?...

Have a look at this picture of G-BOAE, cruising at her maximum certificated altitude of FL600, en-route to Barbados on 16 August 2003:

The available IAS speed range is shown on the ASI, and lies between the yellow and black Barbers Pole, currently indicating 440kts, and the white bug set to 300kts, the VLA (Lowest Authorised speed) at this altitude.

The available Mach speed range is shown on the Mach meter, and lies between the yellow and black Barbers Pole, currently indicating M2.05, and the yellow bug which indicates the lowest Mach number allowed for the current aircraft CG position (the AFT limit) currently showing M1.35.

So, given that at her maximum altitude she had a speed range of 140kts IAS and a Mach range of M0.7, we can see that coffin corner was not a problem!


...I too would like to ask what her idle thrust glide ratio was...

By my calculations, the figures quoted for a straight in approach, give an average glide ratio of around 20:1, however these were for a standard decel/descent, and on Concorde the early part of the decel/descent was not flown at idle power.

A considerable amount of power was left on initially, around 94% N2, for various reasons, and only below M1.0 were the throttles usually selected to idle.

I hadn’t noticed it until now but there does not appear to have been a chart giving glide distance at idle thrust!

However, since the speeds to be flown during the “4 Eng Flame Out” procedure were not too far from the normal decel/descent speeds, I’ll hazard a guess (and that is all it is) that the glide distance from FL600, with no thrust, would have been about 150nm, giving a glide ratio of around 15:1.
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