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IMPROVEMENTS WITH THE SPEY
The Spey A-4 is based on the proposed CA-4E airframe which
was a single-seat development of the TA-4E, incorporating many
of the latter's improvements plus new features of its own. Like
the TA-4E, the CA-4E has a 9,300 lb st (4220 kgp) Pratt &
Whitney J52-P-8A turbojet, lift dumpers, steerable nose-wheel,
zero-zero ejection seat and modernized electronics. In addition.
the wing and fuselage store positions have been strengthened, to
permit maximum loads of 4,600 lb (2086 kg) on the fuselage,
2,600 Ib (1180 kg) on each inner wing position and 1,000 Ib
(454 kg) loads on the outer pylons. The maximum weight is
increased by 2,920 lb (1325 kg) to 27,420 lb (12440 kg), and low
pressure tyres are introduced for operations from unprepared
fields.
All these features are offered in the Spey A-4, but use of the
Rolls-Royce turbofan offers 41 per cent more thrust and 17-24
per cent lower cruising sfc compared with the J52-P-6A in the
standard Navy A-4E, with consequent performance improvement.
The Spey version in the Skyhawk is the RB.168-20, rated
at 12,000 lb st (5443 kgp) and specified also for the HS 801
(maritime Comet); it is essentially an unreheated version of the
RB. 168-25R specified for the F-4K Phantom II and is a military
version of the RB.163-25 in the later Tridents and One-Elevens.
The Spey weighs some 470 lb (213 kg) more than the J52 and
has a frame diameter 3.5 in (8.9 cm) greater. To accommodate
this larger engine, the fuselage of the Skyhawk is deepened by
5 in (12.7 cm) aft of the self-sealing fuel tank behind the cockpit,
and is lengthened by a 10 in (25.4 cm) section just aft of the
cockpit. The engine air intakes are enlarged to match the greater
air mass flow requirement, the minimum cross-section of the
inlet duct being increased from 3.3 sq ft to 5 sq ft (0.31 to 0.46
m'). The changes to the fuselage involve a small increase in fin
area by increasing the chord and the overall height of the fin.
Approximately one-third of the bare airframe (less engine) by
weight is modified for the Spey installation. Materials and
construction methods are unchanged, but the changes in the
fuselage shape require some re-arrangement of the equipment in
the centre and rear fuselage and some re-routing of control
cables. Other items needing modification in the Spey installation
include the cockpit environment control system (for compatibility
with the higher pressures and temperatures of bleed air
from the 152; the pneumatic system which pressurizes the fuel
system; and the hydraulic system (because of larger-displacement,
lower-speed pumps used on the Spey).
The Spey A-4 has an empty weight of 10,739 lb (4871 kg),
compared with 9,853 lb (4470 kg) for the standard A-4E. As
already noted, there is a 2,920 Ib (1325 kg) difference in maximum
weights and the maximum ordnance load is increased to 12,000 lb
(5443 kg). Key points of the Spey A-4's performance are its
ability to take-off in 3,840 ft (1170 m) at max weight: its 2,750
naut mile (5 095 km) ferry range without refuelling and its Mach
0.92 max speed (590 knots-1093 km/h) at 35,000 ft (10670 m).
Douglas estimate that there is currently a market for about
2,000 low-cost ground attack aircraft, to replace F-84s, F-86s and
other obsolescent aircraft. The competition for this market is
growing, not only from other US manufacturers (primarily
Northrop with the F-5A and Ling-Temco-Vought with the A-7A)
but also from the European industry, primarily with the BAC/
Breguet Jaguar (see Vol 21 No 6 p 371). At $764,000 (£272,000)
complete with all-weather navigation equipment. the Spey A-4 is
among the lowest priced of the available types, and is offered in
quantity in less than two years from go-ahead.
Flying Review March 1966