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B.126T / OR.314 / OR.324 Low Altitude Bomber Designs

JFC Fuller

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CNH has posted large images of three of the contenders put forward for the RAF Low Altitude Bomber requirement of 1952-4, I hope he doesn't mind me consolidating them in this thread along with some other bits and pieces. The four designs usually associated with this requirement are as follows:

Handley Page HP.99
Avro 721
Short P.D.9
Bristol Type 186

In 1952 Vickers also drew a Low Level Valiant design that, given the timing and proposed performance, must have had this requirement in mind. Someone has drawn an artists impression at the Military Factory website.

As an observation, all these designs appear to pre-date the application of area rule by British aircraft designers. However, by mid 1954 the Buccaneer was acquiring area rule bulges and the concept was applied retrospectively to the Vulcan B.2 tail. HP produced an area ruled Victor design, the Phase 4, in about 1956. It seems reasonable to assume, given the date at which the OR.324 study came to an end it, had it proceeded the proposed aircraft would have acquired area ruling. My aerodynamic knowledge is limited but the HP.99 looks like the easiest to area rule, it would probably involve wasting around the mid section at the wing joint and over the upper fuselage and a Buccaneer style rear upper fuselage bulge below the vertical tail. Overall, the HP.99 seems like the aircraft that would have been closest to meeting the requirement but the fuselage arrangement looks structurally challenging, perhaps further refinement would have seen it adopt a bicycle and outrigger arrangement like the Shorts P.D.9, Avro 730 and the Boeing B-47?
 

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CNH

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The proposal from Shorts shot itself in the foot. It envisages the aircraft carrying a Blue Danube bomb, and releasing it by means of a toss manoeuvre during which time the aircraft would have to ascend to a height of 5000 feet. This entirely negates the concept of the low altitude aircraft.

The Avro proposal is equally bizarre, in that the stand-off missile proposed would be housed in the very tail of the aircraft, and released in a somewhat cloacal manner. What this would do to the centre of gravity of the aircraft can be left to the imagination.

The Bristol proposal comes from a slightly bizarre RAE proposal to carry the bomb not in a conventional bomb bay, but on the top of the aircraft, being cantilevered up before launch – hence the requirement for a V tail. This also seems somewhat impracticable.
 

JFC Fuller

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The Avro 721's weapons carriage has conceptual similarity to the linear bomb tunnel used on the North American A-5 Vigilante. In the case of the Avro 721 I wonder whether it was to allow a long store to be carried without interrupting the cross fuselage structure associated with the low mounted wing. The HP.99 looks to have overcome this by having a mid-wing configuration allowing the bomb bay to run beneath it, creating its own challenge with undercarriage arrangement.

It is interesting to note that the original GOR.339 specification for TSR-2, from March 1957, called for a 1,000nm radius at an average cruising altitude of 1,500ft. OR.324 was calling for 2,500nm (5,000nm range) at 1,500 ft, albeit without the supersonic dash capability asked for in OR.339, in October 1953. The OR.3567 Navigation and Bombing System and OR.941 integrated control system seem to have been evolving into something very similar to that pursued for TSR-2 too. The OR.1125 Red Cat stand-off missile adds a Blue Steel scale programme for good measure.

The complexity aside, as a concept, OR.324 seems far more logical than the OR.336 concept that succeeded it as a V-Bomber replacement. It would have been survivable for far longer than the OR.336 concept and would have made for a better conventional delivery platform. The proposed timeline, probably impossible, would have had it arrive about the time that the V-Bombers were all ordered to penetrate at low level though that is with the benefit of hindsight.
 
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CNH

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I hope you will see what I mean from these two diagrams. First of all, Avro estimated the weight of the missile – that is the missile plus the warhead – at 4000 lbs, which is fairly unrealistic.

Secondly, you can see how the missile is mounted in the aircraft – basically it forms part of the structure of the fuselage at the tail. Now imagine the effect on the centre of gravity of the aircraft once this missile is released. On release of the weapon, the C of G of the aircraft moves forward by 14%!

From the brochure, it appears that the bomb is not a stand-off missile, as specified in the requirement, but some sort of glide bomb. In order for the aircraft to escape the blast, the missile has to be released at a height of 11,000 feet. Again, this is totally against the philosophy of a low altitude bomber. You either use a stand-off missile, or a bomb which is capable of being released at very low level (in other words, WE177).

720 1.png
720 2.png
 
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Hood

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I think that the OR.324 contenders have tended to be overlooked, partly because they were overshadowed and sandwiched by the V-bombers and TSR.2 and perhaps partly because of their bizarre layouts that looked more like doodles than serious bombers.

Yet the specification was quite remarkable in its ambition and scope and recognition of the low altitude penetration role. The downfall was perhaps the emphasis on launching a single nuclear bomb, this was no Canberra replacement but with some foresight it might have proved a good alternative to GOR.339.

The radical layouts show that the aircraft designers were not really sure of the weapon to be carried or the best method of delivery. It makes me wonder how much advice they got from the MoS and the RAE on the subject? As CNH has pointed out, there are some naive if not impactical and dangerous features. These must have stemmed from unfamilarity with the weapons side and how to best integrate them. Were they left to their own devices? It would seem so since they had to come up with the aircraft and happy. Not an idea state of affairs.
 

JFC Fuller

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The impracticality of the known designs seems to come from the evolution of the Operational Requirement. OR.314 was very loose, almost a fishing expedition if you will. OR.324, by late 1953, is much more refined and outlines specific dimensions and weights for the stand-off bomb but none of the known designs were specifically designed against this. The known designs were developed against the early requirement and it looks like the only one that came close to being adaptable to the later requirement was the HP.99, the 4,000lb weapon shown by Avro being far short of even the smallest (7,500lb) option included in OR.324 by late 1953.

OR.324 required 2.5x the combat radius and over twice the payload of GOR.339, it was a true Bomber Command strategic bomber. I find it particularly fascinating because it appears just as rapid change in aerodynamics (area rule) and engines is accelerating, the takeoff thrust of the Olympus almost doubling between the first production Vulcans (Olympus 101) and the 22R TSR-2 engine, opening up interesting possibilities for what could have been submitted against OR.324 if it had been issued to industry in 1954/5.
 
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LowObservable

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Good grief, I swear that the Eagle comic was turning out better PD than much of the British aircraft industry in the 1950s. Gerry Anderson would have tossed out some of these designs as too fanciful.
 
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