TSR2
Page 9
Directional stability at high speeds and high angles of attack had proved to be a problem with many supersonic designs, and at the time the brochure was submitted English Electric was in the middle of dealing with this on the P.17A. While most of the drawings in the brochure showed a clear rear fuselage, a few showed ventral fins, which contributed to yaw stability at high incidences and Mach numbers. With a low-mounted tailplane similar to that of the P.1, the tailplane root fairing could be usefully combined with the ventral fin mounts, and two small ventral fins were preferable to a single larger ventral fin for ground clearance. As it was, the undercarriage would have to be made a little longer than ideal, to allow sufficient ground clearance if the fins were to be required.
As English Electric had put such a lot of effort into the P.17A already (over 100,000 man-hours) it believed it was virtually at the end of the project stage and could get the first prototype aircraft into the air by the end of 1961, achieving CA release by September 1963.
P.17B STOL variant
The second volume of the brochure moved on to alternative solutions, and as English Electric had been asked to consider a smaller airframe, some work was carried out in this direction. English Electric considered that the only real way to produce a smaller and lighter aircraft would be to go with a single-engine design, but was unwilling to carry out further work on such a type, citing the safety case of engine failure on a supersonic design (not famed for gliding ability). The other alternative was to relax the requirements. Shrinking the airframe was not a straightforward process: the cockpit, bomb bay, engines and so on could not be reduced in size. Equipment density was difficult to change also, and a smaller fuselage still had to have enough room for all of these items. Reducing the P.17A to a 50,000lb (23,000kg)-class airframe was impossible, as the only suitable engine would have been the proposed scaled-down version of the Rolls-Royce RB.141, which had been cancelled (though the RB.141 itself was still continuing). Even getting down to 60,000lb (23,000kg) would have needed something like a developed Avon, with fuel consumption reducing combat radius significantly as well as reducing takeoff performance. It seemed that the only engine that would be available and suitable would be the Gyron Junior, as used in the NA.39, which would mean a 50 per cent reduction in the combat radius. Correcting the reduced take-off performance in all cases was possible only with the addition of three 6,300lb (2,860kg)-thrust RB.108 lift engines forward of the c.g., and this brought the weight back up to P.17A levels despite the resulting airframe being smaller.
Leading particulars: English Electric P.17B
Length
86.25ft (26.29m)
Height
23.5ft (7.16m)
Wing span
35ft (10.67m)
Wing area
610sq ft (56.67sq m)
Wing aspect ratio
2
Wing anhedral
10°
Tailplane span
22.7ft (6.91m)
Tailplane area
185.8sq ft (17.26sq m)
Tailplane aspect ratio
2.77
Fin area
187sq ft (17.37sq m)
Fin aspect ratio
0.97
Engines
2 × RB.133R & 3 × 6,300lb
(2,860kg) RB.108
Max speed
750kt (860mph; 1,390km/h)/Mach 2.0 at altitude
Empty weight
38,800lb (17,600kg)
AUW
72,130lb (32,740kg)
A general-arrangement drawing of the English Electric P.17B. Damien Burke
It did, however, raise the interesting possibility of a variant of the P.17 that, while not being reduced in size, could save some time and cost by using an existing less-powerful engine, and use lift-jets to compensate for the losses in take-off performance. This, then, was the P.17B, dimensionally similar to the P.17A but using RB.133R engines along with RB.108 lift jets. Rough calculations showed that it would have a 15 per cent reduction in range, but would benefit from a 25 per cent reduction in take-off roll.
P.17C VTOL variant
English Electric was aware that its P.17A design on its own did not really address the aspect of the GOR that asked for the minimizing of permanent base requirements and operation from dispersed sites, with investigation of unconventional means of improving take-off and landing performance. The most extreme interpretation of this was VTOL, and the P.17C was the result of incorporating this within an enlarged version of the P.17A airframe, ensuring that no take-off roll would ever exceed 1,650yd (1,500m) while giving complete VTOL capability for lighter loads or shorter sorties. No fewer than twenty-eight RB.108 lift engines were incorporated in two bays within the fuselage, one between the cockpit and wing, and the other between the wing and tailplane. This took up a huge amount of space that was thus no longer available for fuel, so the airframe had to be enlarged to compensate. Unlike the P.17A, the two main thrust engines were mounted ahead of the c.g., with a long jet pipe leading to the reheat units and a shorter pipe leading directly down. A deflector would direct the engine’s thrust down either of these pipes (an all-or-nothing affair; not variable) so that the main engines could be used during a vertical take-off. The lift jets would have a small range of tilt so that they could be used to aid transition between vertical and horizontal flight. Bleed air from the engines would power puffer jets at each end of the fuselage and the wingtips, and the wing would have no control surfaces whatsoever. Roll and pitch control would be exclusively via the tailplane, with the puffer jets coming into use at slow speeds.
Leading Particulars: English Electric P.17C
Length
101ft (30.78m)
Height
25.75ft (7.85m)
Wing span
41.3ft (12.59m)
Wing area
850sq ft (78.97sq m)
Wing aspect ratio
2.01
Wing anhedral
10 degrees
Tailplane span
26ft (7.92m)
Tailplane area
158sq ft (14.68sq m)
Tailplane aspect ratio
2.77
Fin area
187sq ft (17.37sq m)
Fin aspect ratio
0.97
Engines
2 × 14,000lb (6,350kg)
RB.142R & 28 × 6,300lb (2,860kg) RB.108
Max speed
Mach 1.7 at 30,000ft
(9,000m)
Empty weight
Not stated
AUW
112,900lb (51,250kg)
The added weight and loss of fuel capacity had a crippling effect. Vertical take-off would only be available up to an overall weight of 83,300lb (37,800kg). Subsonic combat radius would be a mere 390nm (450 miles; 720km) in these cases (the brochure neglecting to mention that, in tropical conditions, VTOL would only be possible with no weapons and a nearly zero fuel load). The 600nm sortie could only be carried out with a short take-off roll, rather than a vertical take-off. To manage the 1,000nm sortie the aircraft would have to be overloaded and use a thick concrete runway to perform a normal rolling (albeit fairly short) take-off. With the aircraft weighing in at 112,900lb (51,250kg) for that sortie, it was clear that this would be a self-defeating design even if it did not suffer development problems, being unable to satisfy the most basic range requirements of the GOR and also being unable to operate from a dispersed site for longer missions.
A general-arrangement drawing of the English Electric P.17C. Damien Burke
P.17D Lifting Platform
Both the P.17B and P.17C were really a lessthan-subtle method of demonstrating that the extreme STOL/VTOL concept would merely produce an aircraft burdened by huge limitations and saddled with developmental problems from birth. They made an alternative solution look a lot more attractive than would otherwise be the case. That alternative was the Shorts ‘lifting platform’.
The Shorts PD.17 (P.17D in English Electric parlance) was, to
modern eyes at least, a rather bizarre and impractical proposal to provide VTOL performance and operational support at dispersed sites by separating the VTOL component into a separate aircraft. (The idea bore some similarity to the Short-Mayo composite seaplane and flying-boat of 1937.) The concept had been dreamed up by Dr Alan Griffith of Rolls-Royce, and Shorts adapted and developed it to propose an operational vehicle for military use. Shorts described this as a ‘direct extrapolation of SC.1 experience’. The platform itself was a cropped delta flying wing with two endplate fins and a fixed tricycle undercarriage terminating in large flat plates rather than wheels, to enable operation from a variety of surfaces. The huge array of fifty-six lift jet engines was split into three groups. The fixed group was thirty-six strong and exhausted vertically downwards; the tilting group comprised twelve engines, exhausting downwards but capable of being tilted ±30 degrees, and the final propulsive group consisted of eight engines exhausting aft for forward thrust; these could be tilted down by up to 70 degrees. English Electric/ Shorts admitted that such a large number of engines was an unattractive concept, and the brochure also suggested various combinations of much larger and more powerful engines that could be used to reduce the number required drastically. However, there would still need to be a generous number so that an engine failure, or failure of a small number, would not result in loss of control or loss of the ability to land at a safe descent rate.
Leading particulars: Shorts PD.17
Length
77ft (23.47m)
Height (normal)
11.6ft (3.53m)
Wing span
47ft (14.32m)
Wing area
1,838sq ft (170.75sq m)
Wing aspect ratio
1.2
Fin area (each)
150sq ft (13.93sq m)
Fin aspect ratio
0.48
Engines
56 × 2,500lb (1,135kg) RB.108
Empty weight (P.17A carrier version)
46,550lb (21,130kg)
AUW (with P.17A at overload weight)
129,300lb (58,690kg)
AUW (freighter version, 21,000lb (9,525kg) load)
110,000lb (49,930kg)
A general-arrangement drawing of the Shorts PD.17 Lifting Platform. Damien Burke
The P.17A would start each mission parked on top of the P.17D, with a hydraulically powered hook on the P.17D engaging an attachment point on the P.17A. The P.17D would lift off vertically using the fixed engine group, and accelerate to a suitable forward speed using the propulsive group with assistance from the tilting group during the transition from vertical to forward flight, at which point the fixed and tilting groups could be shut down. Once a suitable flying speed was reached the P.17A would be released and fly off on its own to carry out its sortie. The P.17A could then either land in the conventional manner on a normal runway, or rendezvous with the P.17D in mid-air, match speeds and dock back on the platform. The platform would then slow down, the fixed and tilting groups would be restarted, and the combination would transition to the hover and land vertically. It was claimed that the platform would be relatively cheap and simple to produce, as it had no need of complex navigation systems, no attack system and no weapons.
The retrieval sequence. With IR seekers looking for a bright IR beacon on the underside of the P.17A, the mid-air docking would have been semi-automatic, with manual control only for initial rendezvous and final link-up. BAE Systems via Warton Heritage Group
With the P.17D, every cargo ship with a sufficiently large area of clear deck could be an aircraft carrier. BAE Systems via Warton Heritage Group
The leading edge of the P.17D’s wing would contain a long slit-type intake. Most of the length of this intake would feed the fixed engine group via a plenum chamber, also fed by spring-loaded doors in the upper surface of the wing. The intake section nearest the wingtip/fins would direct air to the propulsive group. The tilting group would be fed by spring-loaded doors and retractable ram scoops on the wing’s upper surface. Attitude control in the hover would be effected by means of puffer jets using bleed air from the entire engine complement (as on the SC.1), and puffer jets would continue in use during conventional flight, though roll control would be augmented by spoilers on the upper wingtip surfaces.
Operation from dispersed sites introduced huge problems, in that all such sites needed to be supplied with fuel, weapons and support equipment. The lifting platform could double as a freighter and fuel tanker to keep these sites supplied, with an internal cargo bay in a central position and an underslung cargo pannier (which could contain fuel, ground equipment, weapons, etc) able to be delivered to dispersed sites (not just P.17A dispersals; supplies could be delivered to ground forces, too). As a tactical freighter it would able to carry a payload of up to 40,000lb (18,100kg) over a range of 300nm (345 miles; 555km) or up to 20,000lb (9,000kg) over 740nm (850 miles; 1,370km). Carrying a full 8,500gal (38,640L) of fuel, the P.17D could also act as an in-flight refuelling tanker and support P.17As during ferrying operations. One of the major problems of VTOL operation of such a platform was ground erosion. This was barely mentioned in the brochure, which limits remarks on the subject to the prospect of ‘messy’ ground operations and the need for mesh guards over intakes to stop ingestion of foreign objects.
That tricky rendezvous with the P.17A in mid-air had had some thought devoted to it, too. Ideally, the P.17A would be able to find the P.17D using its own FLR, or by homing on a UHF transmission from the platform, but if both of these were out of action the P.17D could take on the task using a small radar of its own. A rendezvous circuit would be flown at 2,000ft (6,000m) and 250kt (290mph/470km/h) until the two aircraft found each other, and then a recovery course would be flown at 200kt (230mph/370km/h). The P.17D’s cockpit housed two crew, who had a good view both up and down (through windows in the floor in the latter case), and infra-red (IR) seeker heads on the wingtips (based on those of the Blue Jay missile) would be used to lock on to an IR lamp mounted on the P.17A’s rear fuselage underside. Once the P.17A had taken up position ahead and above the platform, with undercarriage down, and an IR lock-on was in place, the platform’s pilot would be in charge of the hooking-up procedure. The autopilot, linked to the IR seekers, could control engine thrust to make the platform climb and close the distance between it and the P.17A, with the platform’s pilot manually controlling the last few feet of the engagement.
There would, of course, be plenty of occasions when a P.17D platform would need to be loaded with a P.17A on the ground; if the P.17A had landed conventionally, for example. For this purpose there would be a winch to pull the P.17A up ramps on to the platform. The nose leg of the platform could be depressed, allowing the platform to ‘kneel’, and the ramp sections could be stored in the underslung pannier for transport. Ferry flights of the platform would rely on a basic navigation system similar to that of the P.1B, with a master reference gyro, UHF homer and radio altimeter. While the primary purpose of the platform was to allow tactical operation from dispersed sites on a European battlefield, it also opened up the possibilities of surprise attacks on an enemy unprepared to deal with a sudden attack from close range. On the day of such an attack, P.17As could be fuelled and depart from their normal bases, rendezvousing with P.17Ds which had been pre-positioned closer to the intended target. A final refuelling and rearming here would enable the P.17As to strike at a target much further away from home base than would otherwise be the case, and either return to a platform rendezvous or go straight home.
The P.17D lifting off (or perhaps landing) with a P.17A on board. The ground erosion problem from P.17D operations would have been considerable, and in this illustration the groundcrew with their support equipment have clearly retired to a safe distance! BAE Systems via Warton Heritage Group
The P.17D’s real advantage was that it would leave English Electric free to develop the aircraft it really wanted, while being able to offer VTOL as a bolt-on solution at a later date. Shorts ha
d high hopes for the lifting platform and foresaw the possible development of several versions, increasing its own utility and also that of any aircraft linked to it. The most basic development would be the addition of ducted fans to give additional ferry range, but you could then also delete the undercarriage and other items associated with low-speed flight from the strike aircraft, making it entirely dependent on the platform but with a consequent increase in range and performance. A platform developed for higher launching speeds could even act as a booster to launch a ramjet aircraft or missile. (Indeed, a year later Rolls-Royce enquired about just such a use to transport Blue Streak missiles to dispersed sites, rather than housing them in underground silos.)
While the P.17D was a simpler aircraft than the P.17A, similar design effort would be needed due to its larger size and the additional investigations required into stability and control in the hover and transition to/from forward flight (which were already under way with the SC.1 programme). By the time of brochure submission there had not been an opportunity to carry out windtunnel tests of a combined P.17A & D model, but these were going to be given high priority. English Electric suggested that an additional year might be necessary compared with P.17A development, leading to a first flight of the platform by the end of 1962, the first composite P.17A/P.17D flight by the end of 1963 and CA release for the combination in mid-1965. If the P.17A was not ready in time, early testing could be carried out using a P.1B as the test vehicle, which would have the bonus of demonstrating if it was feasible to marry the lifting platform to P.1B operations and thereby achieve operational improvements in P.1B range and take-off distance.