Rocket Interceptors and the SR53.
The idea of the rocket interceptor came from the Air Ministry at the start of the 50s. It was almost certainly triggered by the explosion of the first Russian atomic bomb. The Air Ministry then realised the threat from the high flying jet bomber carrying nuclear weapons. Defence of cities such as London was well nigh impossible, but defence of UK airfields, and V bomber bases, might have been more practical.
In 1945 the R.A.F. and U.S.A.F. had indisputably the world's most powerful strategic bomber fleets. Yet they were on the point of becoming obsolete, and the factor that was driving them obsolete was the jet fighter. The increase in performance that the jet engine gave rendered the likes of the Lancaster and its derivatives hopelessly vulnerable. If airborne radar and guided weapons are added to that balance, it tilts even further away from the bomber.
One answer, of course, was to build jet powered bombers. The Air Ministry had been aware of this for some time, and before the war had ended, had issued the Operational Requirements that would lead to the V bombers. Similarly, the Americans, while having pushed their propellor driven designs as far as feasible, were also busy designing jet bombers, culminating in the B52, still in service.
In post war Europe, the strategic focus for the Western Allies switched very rapidly from Germany to Soviet Russia. The Soviet Air Force was also a formidable fighting machine, although it had evolved along lines more tactical than strategic. It had, though, on the drawing board, some impressive interceptor aircraft such as the Mig 15.
And the whole strategic equation was rewritten in 1945 with the advent of the atomic bomb. Now it became infintely more urgent to intercept a bomber before it reached its target. And the further problem was that any jet atomic bomber would be flying very high, very fast. The problem was to get an interceptor to that height quickly enough, and to give it sufficient speed differential to be able to manoeuvre into a position in order to be able to attack. It was further realised that such attack would probably be by guided weapons of some form - either infrared, heat seeking, or radar controlled.
Up until the 60s, the bomber's best defence had always been height. The higher the aircraft, the more difficult it is to spot and the more difficult it is to hit with conventional antiaircraft shells. Fir interceptor fighters, the choice was either to loiter at high altitudes, which, given their limited endurance, was not usually a feasible option, or to reach these heights as quickly as possible. In 1950, the performance of the jet engine was not sufficient to do this. The Germans had had some considerable success with their rocket propelled interceptor, the Me163, even though it came into service very late in the war, and was, to put it politely, of idiosyncratic design.
Hence the Air Ministry issued Operational Requirement 301 (see appendix A), and invited several firms - Blackburn, Westland, Fairey Aviation, Saunders Roe and Bristol to submit designs. The main points of the designs was that they should be relatively simple, use rockets for the main propulsion, but a turbojet to get home and land. Not all the designs featured the Spectre: the Avro design, which the R.A.F. preferred, used an engine called Screamer, using liquid oxygen and kerosine as fuels. This lost it some points on the technical side: handling liquid oxygen would not be as convenient as HTP, although LOX could be prepared from portable compressors if need be. However, if I were a pilot, I would not be that keen on flying with several hundred pounds of liquid oxygen behind me.
Most of the designs were reasonably conventional in appearance, although there were one or two oddities. The designs were submitted to the R.A.E., who then 'scored' them on various criteria. In the end, at the Tender Design Conference in July 1952, they chose the Saunders Roe design as being the most suitable. The Avro was the runner up, and both firms were told to go ahead with the idea of providing at least three prototypes. The philosophy at this time was to have prototypes from two competing designs , so that if one proved to be a turkey, then there was a back up. Accordingly, specification F137D was issued to AVRoe and F138D to Sanders Roe.
But the whole project fell foul of defence cuts in 1952, with the whole project under the axe at one stage. However, the SR design was revived, but with the number of prototypes cut from three to two. A preliminary mock up was produced at Cowes, with a conference in September 1953 to evaluate the design. The first prototype SR53, serial number XD145, was first flown on 16 May 1957, and went supersonic on 15 May 1958.
At the same time, work was proceeding on another interceptor fighter, although one of more conventional design. This was the English Electric F23/49, later to be named the Lightning, and in November 1954 there arose a project to fit it with 2 rocket motors each of 2250 pound thrust, using HTP and kerosene, with a burn time of 2.5 minutes. Napier were to provide the motors. Development continued for some years, with test flights of the rocket motors in Canberras, but this rocket augmentation was cancelled in 1958.
But whilst development had gone on with the SR53, the R.A.F. realised its limitations. The main of these was endurance and turbojet performance - it would be better to have something that would do more than just "get you home". Hence a improved design, the F177, was proposed, which replaced the Viper jet of the SR53 with the Gyron Junior. But other events were catching up with the SR53.
When the Air Ministry were considering the project initially, it was only seven years on from the first British jet flight by Whittle, and the jet's performance was not up to requirements. The Ministry were aiming for a development period of around another seven years, and in that time the performance of the jet engine would increase considerably. Indeed, in February 1955, a paper was prepared comparing various configurations of the SR53, the F177 and the F23/49. The latter was a conventional jet aircraft, and although its climb rate was not up to that of the rocket powered aircraft, it was not that far behind.
The second event was the development of guided weapons. In 1950, there was no other way of intercepting high flying bombers. But by the mid 50s, guided weapons such as Bloodhound, radar guided and with a range of fifty miles, were appearing on the scene. Their role was exactly that of the SR53, at a good deal lost cost. Indeed, the threat of guided missiles removed the bomber's previous safety of height, as the downing of Gary Power's U2, which wrecked the summit between Krushchev, Eisenhower and Macmillan. Doing the same with a manned interceptor was still much more difficult, as the Russians were to experience in their interception of Korean Airlines Flight 007 in 1987 - and that target was a Boeing 747 taking no evasive action whatsoever.
The third event was the advent of the ballistic missile. In 1950, the only feasible method of delivering nuclear warheads was by bomber. By 1957, Sputnik had been launched, and ballistic missiles were entering service in the USA and USSR. There was no defence against these weapons.
In other words, the SR53 was obsolete. First the F177 was cancelled, then the SR53, as a result of the 1957 and 1958 Defence White Papers. The Lightning was the only interceptor left to the R.A.F.. This policy was much vilified at the time, but in retrospect, was almost certainly correct.
The two prototypes, now flying, were then kept on for research and development. XD 151, the second prototype, crashed on take off on 6th June, 1958, the pilot being killed. Despite investigation by the Aircraft Investigation Board, the cause was never discovered. The take off was aborted just as the aircraft was leaving the ground, and the rocket and jet engines were cut. The investigation was unable to determine whether this was done by the pilot, or whether they had cut out through accident or failure. But the aircraft was going too fast to stop in the space left, and it hit obstructions at high speed and burst into flame.
After the accident, test flying was continued with XD 145. Sanders Roe put forward quite an
ambitious programme for the craft, talking about airlaunching it, and using it with uprated
motors, almost as an equivalent to the X-15. But R.A.E. and the Americans, who were
providing some of the funds, were less impressed, feeling that the aircraft, although
interesting and unique, was not suitable for such a programme. Indeed, Saunders Roe at one
stage were talking of it in terms of doing research for re entry studies for a manned satellite,
and for this, the SR53 with its aluminium airframe, would definitely have been unsuitable.
Eventually in June 1960, the further flying programme was cancelled, and the machine
handed over to the R.A.E. Fortunately it has been perserved, and can be seen in the Aviation
Museum at R.A.F. Cosford.
The other SR53 pages:
Here is the original Operational Requirement for the project as issued by the Air Ministry:
Air Staff Requirement No O.R. 301 (Issue 2) Rocket Propelled Interceptor.
Introduction.
1. Current day interceptor projects are expected to be adequate in performance to match the
enemy threat in normal circumstances, but may be unable to destroy enemy aircraft carrying
out special operations at exceptional heights.
2. An aircraft to fulfil this requirement must have a outstanding ceiling and altitude
performance. So far as is known at present, the characteristics can only be provided by rocket
propulsion, and, although aware of the probable operating limitations of this method, the Air
Staff consider that the promise of tactical advantage more than outweighs other
considerations.
Requirements.
3. The Air Staff require a single rocket propelled interceptor built to satisfy the broad
requirement that follows.
General design considerations.
4. In order to facilitate ease and speed of production, the aircraft and its equipment are to be
as simple as possible.
5. In the first instance, operation in temperate climates only is envisaged. Should world wide
operation be required later, a separate requirement will be stated.
6. Although the Air Staff would consider any proposal for unconventional methods of take off
if great advantages were gained thereby, conventional operation with a normal undercarriage
would be preferred, since this would not only reduce the amount of auxiliary equipment
required but was facilitate ground handling and assist turnaround.
7. Should unconventional take offs have to be accepted in order to get the necessary
performance, any specialist equipment involved, such as catapults, launching ramps or
trolleys must be designed concurrently with the aircraft and must feature ease of transport and
assembly.
8. For conventional operation the aircraft will normally be used from 2000 yd standard fighter
runways , but it is desirable that it should be able to operate from runways or prepared strips
1500yds or less.
9. Because it is not intended to land the aircraft under rocket power, and because all available
rocket fuel is likely to be consumed in climb and flight at altitude, a small auxiliary turbine
engine is to be provided which will enable the aircraft to return to base and land under its own
power. The maximum thrust of the auxiliary engine is to be sufficient to recover from a
baulked landing by climbing away with wheels and flaps down, with armament fitted, but
with all rocket fuel consumed.
10. Neither the aircraft nor its rocket motor are to be regarded as expendable in any way.
Performance.
General.
11. Justification for this project depends mainly on this aircraft's ability to reach an
exceptionally high altitude very quickly and there develop sufficient speed for long enough to
intercept and destroy a fast flying enemy. Height, rate of climb, speed (and acceleration) are
therefore of prime importance, and it is essential that the first should be considerably better
than that expected in contemporary conventional fighter projects.
Ceiling.
12. A subsonic ceiling of at least 75 000 ft is required.
Rate of Climb.
13. The aircraft should be able to reach 60 000 ft from rest at sea level in 2 to 3 minutes
using maximum power.
Speed.
14. Because this aircraft is required for high altitude interception, and all possible weight
saving is essential, the Air Staff is prepared to accept a design limitation of M=0.95 below 20
000 ft. Above 20 000 ft, however, the design limitation is to increase progressively so that at
42 000 ft the limitation has risen to M=2.0 and remains constant at M=2.0 above 42 000 ft.
The aim is that an aircraft of this type should be capable of supersonic speed at all heights
above 30 000 ft while carrying its armament. The greatest practicable degree of thrust control
by throttling is required.
Endurance.
15. The endurance should be sufficient to provide a sortie as follows:
(a) take off and climb to 60 000 ft
(b) 7 minutes cruise at 60 000 ft at not less than M=0.8 in steady level flight.
(c)2 minutes combat at 60 000 ft at M=0.95 in steady level flight.
(d) Descent from altitude followed by cruise on the auxiliary power at for 10 minutes.
(e) Approach and landing followed by recovery from a baulked landing and a second circuit
and landing.
16. Provision should be made for extra fuel to increase the cruise time of paragraph 15(b)
above by 3 minutes.
17. It s accepted that if maximum thrust is used in obtaining supersonic flight for combat, or
if the aircraft is used above 60 000 ft, the above endurance figures will be reduced.
Manoeuvrability.
18. A high degree of manoeuvrability is required at all heights, particularly above 50,000ft. A
rate of roll of 200 degrees a second is to be the aim.
Take-off
19. If conventional take off methods are employed, the distance to under I.CA.N. conditions
at maximum A.U.W. is not to exceed 2000yds. The aim is to have the shortest take-off run
compatible with the other characteristics required.
Landing.
20. It must be possible to use normal powered approach and landing technique under
auxiliary power. Under I.C.A.N. conditions, and with all rocket fuel consumed, but with full
weapon load, the landing distance over 50ft is not to exceed 1500yds. The aim is to have the
shortest landing run compatible with the other characteristics required.
Air Brakes.
21 Air brakes are required. As they will be used as an aid to combat, it must be possible to
use them through the entire speed range of the aircraft without affecting stability or otherwise
impairing its aiming and weapon firing qualities.
Particular Design Features.
Accommodation
22. A pressure cabin is required. The pressure differential should not be more than 4 psi and
not less than 3psi. This will provide adequate cockpit pressure whilst avoiding the dangers
of explosive decompression.
Emergency Escape.
23. Because there may be many new operating hazards to be faced for the first time in this
aircraft, particular attention must be paid to ensure the best possible emergency escape
facilities for the pilot. A dinghy and personal survival pack are required.
View.
24. The best possible view is required particularly in the forward hemisphere. Special
attention is to be paid to de-icing and demisting the windscreen and canopy, using a method
which imposes no restriction on the pilot's view through the transparency.
Hood and Windscreen strength
25. Particular attention is to be paid to the strength of the hood and windscreen in order to
reduce the risk of failure under the extreme operating conditions of temperature and pressure.
Armament.
Guided weapons.
26. The armament is to consist of at least two Blue Jay air to air missiles.
Radar ranging.
27 Although adequate range information is necessary for the use of Blue Jay, the present
radar ranging equipment is likely to impose an intolerable weight and performance penalty on
the aircraft. Radar ranging is not therefore to be fitted. The possibilities of obtaining the
necessary range information by other lighter and less complicated means are to be examined.
Sight.
28. The normal reflector gunsight is required when BlueJay weapons are carried.
Camera.
29. AG45 camera installation is required.
Aircraft Equipment.
General.
30. Because of the limited range and endurance, and also to preserve the essential
requirement for ease and speed of prediction, there is no intention an elaborate standard of
equipment for this aircraft or of regarding it as in any way capable of all weather operation.
The standard to be aimed at is that n the hands of a pilot of average wartime skill and
experience the aircraft should be capable of taking off, climbing, and of delivering its attack,
and returning safely to base by day in weather conditions down to 8/8th cloud, with base
about 2000ft, and visibility about 3 miles. Operation in conditions somewhat worse than this
is expected to be practicable but it is accepted that it may involve an appreciable problem due
to numbers of aircraft landing away from their own bases.
For Information Only.
Guidance to target.
31. It was originally intended to develop concurrently with the aircraft some special system of
radio or radar guidance. However, after closer examination of the guidance system, it has now
been decided to operate the aircraft under normal close control.
Flight Instruments.
32. Flight instruments are required to supply all the information at present provided by the
standard panel, in all conditions of flight of which the aircraft is capable. In particular, a
means of presenting the pilot with information and pitch attitude and heading during near
vertical climb.
Radio and Communications.
33. The following equipment is required:-
(a)VHF providing 10 channels.
(b) single channel stand by VHF
(c) telescramble.
(d) IFFMark 10
Personal equipment.
34. Connections are required for a pressure suit, an anti-g suit, and an air ventilated suit. If
available the Universal coupling now being developed will be required. It should be possible
to operate the aircraft whilst wearing an inflated pressure suit.
35. Oxygen is required for a climb to 60 000 ft., 15 minutes at this altitude, including 5
minutes after a cabin pressure failure and with the pressure suit inflated and a descent to
below 10 000 ft in these conditions.
Electrical power.
36. A source of electrical power is required which will provide electricity for the operation of
essential equipment during the descent with the rocket motor off.
General.
37. It is essential that every effort is made to design this aircraft to facilitate servicing.
Accessibility of components is to be adequate to allow servicing by change of major
components in the field by squadron personnel. The aircraft is to have a reliable performance
with q minimum requirement for servicing and inspection, other than the need to replenish
consumable stores, over any period of 100 hours flying or four moths elapsed time, which
ever is the less. Provision is to be made for simple and rapid refuelling, re-arming and
replenishment servicing to facilitate turn-round of the aircraft within the shortest possible
time.
Transportation
38. It will be necessary for adequate lifting or supporting points to be provided to facilitate transportation of aircraft if necessary, such as after a forced landing.
Target Date.
39. The Air Staff require this aircraft in service by 1957.
Air Ministry 18th August 1953.
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