Armstrong Whitworth A.W.52

https://en.wikipedia.org/wiki/Armstr...itworth_A.W.52

The Armstrong Whitworth A.W.52 was a British flying wing aircraft design of the
late 1940s for research into a proposed flying wing jet airliner. Three
aircraft, the A.W.52G glider and two jet-powered research aircraft, were built
for the programme. The airliner was cancelled but research flying continued
until 1954.

Armstrong Whitworth Aircraft proposed a jet-powered six or four-engine flying
wing airliner design, using a laminar flow wing, during the Second World War.
This had to be a large aircraft in order to provide passenger head-room within
the wing. The low-speed characteristics of the design were tested on a 53 ft 10
in (16.41 m) span wooden glider known as the A.W.52G; the glider was designed to
be roughly half the size of the powered A.W.52, which in turn would be about
half the size of the airliner. Construction of the AW.52G began in March 1943,
with the glider making its maiden flight, towed by an Armstrong Whitworth
Whitley bomber, on 2 March 1945. Flight testing, with tug releases from 20,000
ft (6,096 m) giving flights of around 30 min continued, mostly satisfactorily
until 1947. In 1944, Armstrong Whitworth received a contract that would allow
them to produce two A.W.52 prototypes for evaluation, nominally as mail carrying
aircraft.

The A.W.52 was intended for high speeds and was an all-metal turbojet-powered
aircraft, with a retractable undercarriage; aerodynamically it had much in
common with the glider. Both aircraft were moderately-swept flying wings with a
centre section having a straight trailing edge. The wing tips carried small (not
full chord) end-plate fin and rudders, which operated differentially, with a
greater angle on the outer one. Roll and pitch were controlled with elevons that
extended inward from the wing tips over most (in the case of the A.W.52 about
three-quarters) of the outer, swept part of the trailing edge. The elevons moved
together as elevators and differentially as ailerons. They were quite
complicated surfaces – which included trim tabs – and hinged not from the wing
but from "correctors", which were wing-mounted; the correctors provided pitch
trim. To delay tip stall, air was sucked out of a slot just in front of the
elevons, by pumps powered by undercarriage-mounted fans on the glider and
directly from the engine in the A.W.52. The inner centre section wing carried
Fowler flaps and the upper surface of the outer section carried spoilers.

Maintenance of laminar flow over the wings was vital to the design and so they
were built with great attention to surface flatness. Rather than the usual
approach, where skinning is added to a structure defined by ribs, the A.W.52's
wings were built in two halves (upper and lower) from the outside in, starting
from pre-formed surfaces, adding stringers and ribs then joining the two halves
together. The result was a surface smooth to better than 2/1000 of an inch (50
µm).

The crew sat in tandem in a nacelle so that the pilot was just forward of the
wing leading edge, providing a better view than in the glider. The pressurised
cockpit was slightly off-set to port. The engines were mounted in the wing
centre section, close to the centre line and so not disturbing the upper wing
surface.


Role
Experimental flying wing

Manufacturer
Armstrong Whitworth Aircraft

Designer
John Lloyd

First flight
13 November 1947

Retired
1954

Primary user
Royal Aircraft Establishment

Number built
2

The first prototype flew on 13 November 1947 powered by two Rolls-Royce Nene
engines of 5,000 lbf (22.2 kN) thrust each. This was followed by the second
prototype on 1 September 1948 with the lower-powered (3,500 lbf/15.5 kN) Rolls
Royce Derwent. Trials were disappointing: laminar flow could not be maintained,
so maximum speeds, though respectable, were less than expected. As in any
tail-less aircraft, take-off and landing runs were longer than for a
conventional aircraft (at similar wing loadings) because at high angles of
attack, downward elevon forces were much greater than those of elevators with
their large moment.

The first prototype crashed without loss of life on 30 May 1949, making it the
first occasion of an emergency ejection by a British pilot. Despite the
termination of development, the second prototype remained flying with the Royal
Aircraft Establishment until 1954.

The accident

On 30 May 1949, while diving the first prototype at 320 mph (515 km/h), test
pilot J.O. Lancaster encountered a pitch oscillation believed to be caused by
elevon flutter. Starting at two cycles per second, it rapidly increased to
incapacitating levels. With structural failure seemingly imminent, Lancaster
ejected from the aircraft using its Martin-Baker Mk.1 ejection seat, becoming
the first British pilot to use the apparatus in a "live" emergency. It was
fortunate that he was alone in the aircraft as the second crew member was not
provided with an ejection seat.

As luck would have it, the aircraft, left to its own devices, stopped fluttering
and glided down to land itself in open country with relatively little damage.
Following this incident, and in view of the disappointing results obtained, no
further development of the flying-wing formula was undertaken by Armstrong
Whitworth, who had now turned their attention to the more conventional A.W. 55
propeller-turbine airliner. The second A.W. 52 was handed over to the Royal
Aircraft Establishment at Farnborough, where it was used for experimental flying
until it was finally disposed of in June 1954.

Specifications (TS 363, Nene powered)

General characteristics
Crew: 2, pilot and navigator-wireless operator / flight test observer
Capacity: 4,000 lb (1,800 kg) / 300 cu ft (8.5 m3)
Length: 37 ft 5 in (11.4 m)
Wingspan: 89 ft 11 in (27.4 m)
Height: 14 ft 5 in (4.4 m)
Wing area: 1,314 sq ft (122.1 m2)
Airfoil: NPL.655-3-218 at root, tapering to NPL.655-3-118 at extremity of the
centre section and to NPL.654-3-015 at the tips
Empty weight: 19,660 lb (8,918 kg)
Gross weight: 34,150 lb (15,490 kg)
Powerplant: 2 × Rolls-Royce Nene centrifugal-flow turbojet, 5,000 lbf (22 kN)
thrust each

Performance
Maximum speed: 500 mph (805 km/h; 434 kn) at sea level
Range: 1,500 mi (1,303 nmi; 2,414 km)
Service ceiling: 36,000 ft (11,000 m)
Rate of climb: 4,800 ft/min (24 m/s) at sea level
Wing loading: 24.8 lb/sq ft (121 kg/m2)
Max lift coefficient: 1.6




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