From the lefthand seat

The minimum drag speed for take-off or landing is between 250 and 300 knots (depending on the aircraft’s weight), and every decrease in speed during approach calls for more thrust. Therefore, if – during approach – Concorde is disturbed from its descent pattern, it will not automatically regain the original speed but will require an in­ crease in thrust to achieve it. This is one significant difference between the supersonic airliner and its subsonic counter­ parts.

On take-off, Concorde becomes airborne at a speed about 100 knots below its minimum drag speed, but its high thrust-to-weight ratio enables it to climb at a much steeper angle than a subsonic aircraft. Nonetheless, particular atten­tion is needed during noise abatement procedures, when the required reduction of thrust reduces the angle of climb to three degrees.

One specific point about delta-winged aircraft is that, for a given thrust, a decrease in air speed eventually results in lower and lower climb rates until zero and then negative rates are reached. But a zero rate of climb in Concorde does not present an aerodynamic barrier.

Another characteristic particularly evident at low speed is induced drag which, in this speed regime, is much higher with a delta than with a “conventional” wing. This means that, during turning manoeuvres, the pilot needs to increase engine power to maintain a constant speed. To help him, however, Concorde has a mass of automatic aids, including duplicated automatic throttles. To combat the loss of control effectiveness in the transonic regime, Concorde’s controls are deliberately over-powered and are therefore very effective indeed. Their response is instantaneous – so much so that, at high subsonic speeds where their efficiency is greatest, built­ in artificial feel has been incorporated to guard against any tendency towards too abrupt control movements. Stability correctors, working through electric trim systems, restore positive longitudinal stability and damp down any transonic phenomena – especially the “reversal” well known to fighter pilots who fly close to the “sound barrier”. But the Concorde pilot is aware of this “barrier” only by his instruments and the slight oscillation in static pressure registered on the altimeter.

This series of controls and mechanisms, acting together, protect the aircraft against deviations in attitude at low speeds and against excessive speeds at the upper end of. the scale. They also provide excellent “anti-zoom” protection, preven­ting Concorde from climbing too high in cruising flight; this is important because, at Mach 2, Concorde has a total potential energy which could theoretically take it up to a height of 36km (nearly 23 miles).

Other piloting aids, such as autostabilisers in roll, yaw and pitch, provide excellent dynamic damping in the three axes over the whole speed range. Automatic yaw/roll control compensation means that even the failure of an engine at Mach 2 need cause no alarm, and there are further refinements to ensure – in combination with those already mentioned – that the pilot has a very “manageable” aircraft at all speeds, with built-in control forces graduated over the whole of the speed range from low speeds up to Mach 2. Cruise at Mach 2, for example, is a very relaxed and precise operation for the pilot compared with flying a subsonic air­ liner at its cruise speed.

A pilot sitting for the first time in a Concorde flight deck might not immediately notice the ways in which it differs from a subsonic airliner’s flight deck. Certainly, he will be im­pressed by the mass of instruments, and he will note the visor and droop nose, but he could easily overlook one small in­strument which is peculiar to the SST: the centre of gravity indicator.

In piloting Concorde, this instrument, with its vertical scale, plays an essential part throughout the whole flight envelope, and centre of gravity limits are directly related to Mach number and speed. By means of fuel transfer, the cen­tre of gravity of the aircraft can be adjusted throughout the flight as the centre of pressure changes. In this way, the flight engineer can balance the quantities of fuel in the forward and aft tanks to maintain optimum performance throughout, and it is the little centre of gravity indicator which monitors this.

The most important operational feature of Concorde is that it flies much faster – that, after all, is its whole raison d’etre! Even so, there is no difficulty in integrating it with subsonic traffic because speed separation is quite naturally achieved through height separation – Concorde does not fly at Mach 2 at low level, nor does a Piper Cub fly at 60,000 feet! What is more, the SST’s high rate of climb also leads to rapid separation of the aircraft.

Supersonic acceleration begins when cleared by Air Traf­fic Control – usually, around 28,000-29,000 feet – and the speed at 40,000 feet (the operating ceiling for most subsonic airliners) is Mach 1. 4. This phase of flight lasts about. five minutes and covers a distance of some 80 nautical miles. The only operational requirement is that this acceleration should not be checked since this would cause a speed performance penalty as a result of the aircraft having to operate in a speed regime which is uneconomical because of higher drag.

At 50,000 feet, Concorde reaches Mach 2. The “cruise climb” means that – with speed and thrust constant, and air­ craft weight reducing as fuel is consumed – the aircraft climbs gently to around 60,000 feet. This type of cruise has the advantage of being the most economical in terms of fuel con­sumed and hence distance travelled. On the descent, Con­corde decelerates to subsonic speed at 40,000 feet.

From the moment that Concorde rejoins subsonic traffic, its speed can be varied and differs little from other aircraft. In the approach circuit, it performs just like any other airliner.

Regarding Concorde’s North Atlantic range, a_ great deal has been talked about its range capability, especially as the original specification called for Paris-New York. But ex­perienced professionals will not have forgotten the introduc­tion of the Boeing 707 on the North Atlantic in 1958. Briefly, the situation was that in plenty of instances a Boeing 707 could not file a flight plan for a flight direct from Paris to New York! And what is one to make of the Athens-New York and London-Los Angeles flights carried out by some airliners? Do they have the 35 minutes’ holding on arrival now being demanded of Concorde?

The range margins of an airliner are an operational problem governed by very strict rules, and Concorde neither asks for nor gets any special dispensation.

Without going into details here, let’s say that Concord does not exactly have “short legs”. Indeed, on May 22, 1976, it flew the President of France from Pointe a Pitre to Paris, which is 300 nautical miles farther than the distance from Washington to Paris. It carried a payload of five tons and on arrival could have diverted 500nm with statutory reserves. Concordes have flown non-stop from Caracas to Paris and from Puerto Rico to London.

In any case, fuel reserves on arrival are a matter for in­dividual airlines to decide. An airliner which desires a high degree of regularity over a critical sector will limit the payload or accept a percentage of re-routing when carrying large payloads. Between these two extremes, the pilot carries out his mission in collaboration with ATC, his judgment and the aircraft’s safety being always the decisive factors.

One of Concorde’s greatest advantages is its ability to land in conditions of low cloud and low visibility. At this mo­ment of time, landings can be made when the ceiling is as low as 30 metres.

In fact Concorde can already make zero-visibility lan­dings, although it may be some time before this becomes accepted practice. This is because, to meet certification re­quirements, a specified number of landings must be made to provide a statistical basis for assessment.

There is something completely idiosyncratic about Concorde at landing: during approach, it seems to rear up like a spirited horse! As it nears the ground, the curve of its descent flattens out but the altitude does not change. “Ground effect” reduces the vertical speed until, at touchdown, it is effectively zero. But, of course, that doesn’t mean that the pilot can sit back in a blissful trance while his charge lands itself!

In fact, just as the aircraft encounters the “ground effect” the nose tends to dip, making it necessary for the pilot to apply a little back pressure on the stick. Pilot skill, “ground effect” and Concorde’s longitudinal balance combine to bring the aircraft down on to the runway with a smoothness which gives the man at the controls a feeling of satisfaction that compensates for any less happy moments.

To pilot Concorde, therefore, it is necessary to have not only skill but also knowledge of the aircraft, its systems and its environment.

Article written by Pierre Dudal, Commandant de Bord, Air France