Concorde Main Landing Gear

 

.

Concorde’s development phase raise another issue concerning her landing gear. Its large delta-wing requires a high angle of attack, which leads to a pitch angle on touchdown of 11 degrees. This requires the landing gear to be unusually strong due to the unusual loadings which it would have to cope with. This angle of attack caused another problem, it put the rearmost part of the engines nearest to the ground, this required the legs to be long enough to stop them touching. So the increased weight loading and length required a major redesign of the landing gear for Concorde.

As part of the 2001 modification following the 2000 Paris crash. The original standard aviation design nylon bias ply tyres on all eight main wheels were replaced with a new puncture resistant lighter weight tyre, the NZG Near Zero Growth tyre developed by Michelin Aviation Products. The Michelin tyres are rim-to-rim reinforced radial tyres that are resistant to incision. If severe damage should occur to the tyre it is designed to fragment into very small pieces too small to result in rupturing a tank. Expansion of the tyre under pressure and consequential elongation of the rubber tread is minimised by reinforced belts and sidewalls. The electrical wiring in the undercarriage was encased in steel braiding as part of the modifications carried out during 2001.

Concorde is equipped with a hydraulically operated retractable tricycle landing gear layout, with a nose gear consisting of two wheels and 2 main gears consisting of 4 wheels each. Separate from this configuration is a tail bumper gear consisting of 2 wheels, that is fitted to prevent any damage to the fuselage and engine nacelles, should the aircraft suffer too high an angle of attack during take-off or landing.

One interesting note about the main landing gear is that if both were to just swing up to be stowed away they would hit each other and jam. The combined length of both undercarriages is greater than the distance between both undercarriage roots. This problem required that the undercarriage be first retracted vertically and then swung inwards to be tucked in the wing and fuselage belly.

Concorde maximum permissible weight for the start of any ground manoeuvre is 186,880kgs and for the start of take-off 185,070kgs. At the point of rotation, the main landing gear, which is literally the centre of rotation, is loaded up at 195kts as the rear end squats and the frontend is hauled off the runway. The maximum landing weight is 111,130kgs, though in 1981 landing at up to 130,000kgs was authorised. Normal approach speed (Vref) varies with the aircraft weight from 150kts to 162kts at maximum landing weight, however a Vref+7kts became the standard in 1979. At 130,000kgs, Vref was up to 175kts while on the day something quite unpleasant could happen and Concorde had to make an immediate return landing, the maximum weight Vfef would be 207kts and 238mph. These are just some of the numbers that the French landing gear manufactures had to contend with.

The landing gear is a spring/damper unit providing suspension and damping by an oil/gas medium (oleo/pneumatic). The oil is of the hydraulic system, the familiar pink DTD 585, while the gas has been changed from compressed air to nitrogen. First and foremost, the landing gear is a shock absorber, its job, to absorb the dissipate kinetic energy at landing.

 


 

Main Landing Gear

Concorde’s main landing gear comprises of two sets of four-wheel bogies.  The main landing gear was designed by Messier-Dowty and has to shorten during the retraction process, as it would otherwise not be able to fit into the bays in the wing roots after take-off. It is also fitted with a spray guard to prevent water from wet runways being flung-up and sucked into the engine air intakes and also fitted with Oleo-pneumatic shock-absorbers.

During the development phase of Concorde’s life, the main landing gear location was a real headache. At the only logical position, the legs would have collided as they were retracted upwards and inwards, they were basically too long.  So they were shortened, so whenever the gear was down and locked they were at their full length, but during the retraction process, a mechanical linkage gradually and completely pulled the  oleo inside the barrel, a simple, yet effective and trouble-free solution.

Main landing gear facts

Number of wheels on each bogie – 4

Direction of retraction -Inwards

Tyre size – 47X15.75-22

Tyre type – Michelin NZG

Tyre pressure – 232PSI

Brakes – 4 X Dunlop Carbon Fibre with SNECMA (Hispano) SPAD anti-skid units

The manufacturer – Messier-Dowty

The emergency Operation of the main landing gear – A, Hydraulically lowered by standby system. B, Mechanical release and freefall to lock

Normal operation – Hydraulic system (Green)

1, Cross beam:

2, Upper brace truss rod:

3, Trunnion:

4, Lower brace truss rod:

5, Hydraulic sequence valve:

6, Leg:

7, Torque links:

8, Shock absorber:

9, Wheels:

10, Brakes:

11, Bogie-beam:

12, Brake torque link:

13, Pitch damper:

14, Axle:

15, Telescopic brace strut:

16, Actuating cylinder:

17, Actuating rod