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Martin XB-51

history

Unveiled in 1949, the Martin XB-51 was hailed by the US influential magazine, ‘Aviation Week’ as the most unconventional jet designed yet produced in the United States. In spite of all it was never to enter production. Designed as a close support aircraft it fell victim to the demands of the conflict in Korea and the need to rapidly reverse the decline of US tactical Air Power in the aftermath of WWII. The XB-51 design prepared by Martin for the first prototype/serial number 46-685 was built at the Martin factory in Middle River, Maryland and officially rolled out on the 4th September 1949.

A mid-wing all-metal monoplane with swept wings and a ‘T’ tail having an overall length of 85’1” and a span of 52’1” with an empty weight of 29,584 lbs. One of the most striking features of the XB-51 was the employment of a variable incidence system. The incidence of the wings could be varied from +2 degrees to +7 degrees 30 minutes for normal flight and +7 degrees for take off and landing. The wings were mounted on bearings at the rear of the front-mounted irreversible hydraulic jackscrews to move the front of the wing through the incidence range. This enabled the XB-51 to adopt a horizontal landing profile more suited to the aircraft’s bicycle undercarriage.

To keep the wings as aerodynamically clean as possible, many of additional elements as fuel, engine, undercarriage system, these were all placed or attached to the comparatively large fuselage. Two of the three engines were being hanged on pods each side of the lower fuselage forward of wing, the third was buried in tail where it was fed by a gently curving direct leading from an intake on top of fuselage. Tail plane was placed atop the fin served to boost the effect of the fin itself, thereby permitting it to be reduced in size.

The bullet shaped fairing added between the fin and tail plane, this eliminated aircraft vibration and roughness at high speeds. The tail operated a brake parachute ejected from a door on the right side at the base of the rudder. A door type air brake was fitted to the underside of rear fuselage, primarily used to change glide path angle.

The XB-51 carried a single pilot and a radio/SHORAN operator. The pilot sat in the centreline of the aircraft under a fighter type jettisonable canopy. The operator sat on a right hand side of rear cockpit, his exterior view being restricted to a small window on the starboard side of the airframe. Ejection seat was provided for both crew members.

The XB-51 provided a formidable punch carrying an internal bomb storage provided via a detachable rotating bomb bay door. By itself this was an innovation solving the buffet problems created by conventional bomb bay doors. The design forward way on to the B-57 Canberra and was also adapted to the Royal Navy Buccaneer strike aircraft.

The XB-51 could also carry extra bombs fixed externally on the bomb bay door itself. The maximum bomb load was 10,400 lbs. Alternatively eight 5” HVAR rockets could be carried in bomb bay. Eight 20mm canon grouped in the nose. An oblique strike camera was carried in the nose. Vertical reconnaissance cameras were also carried in the fuselage. The aircraft had a range of 8-900 miles at 15-20,000 ft. The service ceiling was 40,000 ft but 30,000 ft was the tactical ceiling limited by manoeuvrability. Wind tunnel tests predicted tail surface flutter if speeds exceeded 620 mph at sea level. Mach 0.9 had been achieved at 20,000 ft. Touch down speed could be 140 mph at normal weight but a run of 2,400 ft was required to become airborne at maximum weight.

In October 1951, English Electric Canberra WD940 was one of two patterns/later serialled 51-17352 supplied to Martin for use in the B-57 engineering programme. The availability of the Canberra marked the demise of the XB-51. Production of the type was cancelled in November 1951.In January 1952 the first prototype also joined the USAF. Its service career was temporally curtailed on 28th February that year when it was damaged in an overshoot landing at Wright Patterson AFB. Other misfortune struck the XB-51 programme less than three months later. During a test flight on 9th May 1952 46-686 disintegrated in mid-air when Major Neil H.Lathrop USAF, head of flight test branch at Edwards was killed.

The Kit

Make: Hobby-Time Kit No.285

Scale: 1/72

Type: a model with 13 major components made in wood, a clear part for the cockpit canopy, two sets of wheels and detail instructions, decals included.

Cost: $6

When one thinks of early jet bomber design, whether it is a US, Russian or British make of all the designs that may come to mind, the XB-51 image will stand out owing to its unique appearance. Two jet engines slung under the forward fuselage and another embedded in the rear fuselage. From early years, Hobby-Time served justice to a type ever neglected by injection moulding manufacturers when it released the scale model made in Balsa wood. The kit comes with reasonably good scale plans and very accurate profile on the pre marked wood parts.

Definitely this is a far cry from the type of kit that one expects to pick when buying a scale model these days. For the past two years I have exhausted all my efforts to get an Execuform vac form kit of which I came to know contained accurate scale plans. Following the release of the Anigrand kit the production of this vac kit came to an abrupt end. A resin kit is the last thing I will go for. So my next option was to make a ‘Google search’ to see what was on offer and up came the search with a Hobby-Time kit from Phil Juvet in the US. The kit was with me within a week that I placed the order.

The kit, which contained all the wooden blanks, was still in its original cardboard box and the original titles printed in red. Each blank was accurately outlined and easily snapped so that one will only require to sand down the airfoil section using the piece of sand paper that also comes with the kit. In a small sealed bag there were the two sets of wheels black rubbery plastic and the cockpit canopy that was clear injected plastic. The fuselage of the XB-51, which is in the shape of a moray eel, comes in the form of a wooden block that is cut in outline but required sanding the round corners to conform shape. To simplify matters the comprehensive instruction sheet gives accurate snap gauges that I copied on a cardboard and cut shapes with scissors. These gauges at different fuselage stations served to bring the correct fuselage airfoil. Balsa wood blocks of different shape and sizes were to serve to shape all the kit components.

Construction

All I have used from this kit is basically the fuselage balsa block. The rest of the kit was scratch built from scrap plastic pieces. A gig was also made in cardboard for use when the wings dihedral are to fix at the correct angle. With the fuselage smoothened to shape a coat of dope mixed with little talc powder was applied and this was followed by sanding. The open grain pores were practically all closed bringing a smooth surface finish throughout. The wheel wells were then marked and curved out. The box like interior of each well was then covered with a plastic card cut to fit forming smooth interior walls to which detail was added at a later stage. The third engine space which is embedded at the rear of fuselage was curved out forming a groove and a tube like engine was embedded in it, fixing it in place and fairing smooth using filler to the sides. The other two under fuselage engines were shaped from two belly tanks that came from a Hasegawa Voodoo F-101 kit. These had the ends cut and shaped by filing. A centre bullet shape was added inside the intake of all three engines using rounded plastic sprue of correct diameter.

Wings, tail planes, fin and rudder were made from scrap plastic correctly cut in outline and then shaped to respective airfoil sections. I opted to use plastic for all of these parts, as it was easier to score panel lines and control surfaces than if I was using the wooden parts supplied. Six triangular shaped brackets were then cut and fixed under each of the wing surfaces. These were actuators. Wing tip dolly wheels were also made from scrap plastic and added to the wing tips. A pylon was shaped from a thick plastic piece and fitted to each engine pod. This had dowels at the joining end to secure each of the engines to the fuselage.

The cockpit was then cut out and the pit itself smoothed as best one could. A plastic base plate was added and on top were mounted the ejection seat, control wheel, rudder pedals, instrument panel and side instrument. As for the radio operator compartment, there is very little that could be seen from the starboard side window and there was no scope to add any detail there. Even the round window itself was represented by a circular black decal that had the same effect as seen in photos.

Main wings were superglue in place guided by dowel pins that were carefully fitted to correspond with the inclined wing root. The tail fin bullet shape at top was made from a small fuel tank. A set of wheels of right size replaced the somewhat under scale kit wheels adding a scratch built oleo legs complete with landing light and other visible detail.

Painting and decals

Cockpit interior painted predominantly black with touches of white and silver for the instruments, seat cushions were olive drab, a crew figure added and cockpit canopy fixed in place with Klear {Future} and allowed to set. Wheel wells painted zinc chromate green and wheel legs in silver. The nose legend XB-51 and the fin serial number came from kit decals but other USAF legend were all Scale Master decals picking the correct size as appropriate. The US insignia were picked from Super Scale decal sheet.

The XB-51 was finished in Day Glow Model Master Blaze at the front lower fuselage and the outer half of the wing undersides. The rest of airframe was silver using Hempel paints thinned down for airbrush use. Finally kit was given a brush coat of Klear.

Conclusion

Building a model of the XB-51 brings back memories of a unique aircraft and of the colourful post war era bright colour schemes on aircraft that gave contribution towards the development of early aircraft designs and systems.