Re: Concorde Question?

From:         Pete Mellor <pm@csr.city.ac.uk>
Date:         20 May 94 01:58:40 
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In article <airliners.1994.1233@ohare.Chicago.COM>, tristar500@aol.com 
(TriStar500) writes:- 

> MD-11 does have fuel in the tail. Also, A-310-300.

The following is a translation of part of an article in "Der Spiegel" 
(1st or 2nd week in April) about the crash in Siberia of an A310:- 

   The fateful flight condition was favoured by a design feature of modern 
   long-haul aircraft, which was introduced on the Airbus A310 ER as the 
   first type; the aircraft has an additional tank in the high tail-fins, 
   whose fuel content (4.92 tonnes) after reaching level flight (?) is 
   balanced with the remaining tanks by computer-controlled circulation 
   pumps (see diagram). 

   [According to the diagram, the outer wing tanks contain 2960 kg and 
    the inner wing tanks 11,160 kg, on each side, the main tank 15,710 kg, 
    and the "trim tank" in the tail-fins 4,920 kg.] 

   Disadvantage: With heavy rear-loading at high altitude, the aircraft is, 
   as one Lufthansa pilot explained "manually controllable only with great 
   difficulty; one should never take out the precisely-controlling autopilot." 
   [OK - I've sacrificed style to accuracy! :-) ] 
   Manoeuvring in that case would be about as difficult as steering a car 
   "on smooth ice" or with "five sacks of potatoes in the boot". 

   The potential safety problem was offset against an economic requirement: 
   Through technically-sophisticated balancing between the tanks complementing 
   traditional trim, the aircraft uses around one percent less fuel - 
   a not insignificant saving on long-haul flights. 

   [End of translation.] 

Two things are worth noting here:- 

a) The balancing act with the fuel is computer-controlled. 

b) The aircraft is only marginally stable with this system in operation. 
   (The article implied that it could have been a contributory factor in 
   the crash.) 

Concorde uses fuel-pumping to the rear tanks to alter its CG, too, but 
(I *believe*) this is done to counter the change in CL as it goes 
supersonic, and is controlled by the flight engineer rather than being 
automatic. 

Peter Mellor, Centre for Software Reliability, 
City University, Northampton Square, London EC1V 0HB 
Tel: +44 (71) 477-8422, Fax.: +44 (71) 477-8585, 
E-mail (JANET): p.mellor@csr.city.ac.uk 
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