1:72 Bell XP-68A „Airagator“ (a.k.a. “Barrelcobra”), second prototype; USAAF s/n 42-228878; Muroc Dry Lake during flight test and evaluation, April 1944 (Whif/kitbashing)
+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based historical facts. BEWARE!
The Bell XP-68A owed its existence to the manufacturer’s rather disappointing outcome of its first jet fighter design, the XP-59A Airacomet. The Airacomet was a twin jet-engined fighter aircraft, designed and built during World War II after Major General Henry H. "Hap" Arnold became aware of the United Kingdom's jet program when he attended a demonstration of the Gloster E.28/39 in April 1941. He requested, and was given, the plans for the aircraft's powerplant, the Power Jets W.1, which he took back to the U.S. He also arranged for an example of the engine, the Whittle W.1X turbojet, to be flown to the U.S., along with drawings for the more powerful W.2B/23 engine and a small team of Power Jets engineers. On 4 September 1941, he offered the U.S. company General Electric a contract to produce an American version of the engine, which subsequently became the General Electric I-A. On the following day, he approached Lawrence Dale Bell, head of Bell Aircraft Corporation, to build a fighter to utilize it. As a disinformation tactic, the USAAF gave the project the designation "P-59A", to suggest it was a development of the unrelated, canceled Bell XP-59 fighter project. The P-59A was the first design fighter to have its turbojet engine and air inlet nacelles integrated within the main fuselage. The jet aircraft’s design was finalized on 9 January 1942 and the first prototype flew in October of the same year.
The following 13 service test YP-59As had a more powerful engine than their predecessor, the General Electric J31, but the improvement in performance was negligible, with top speed increased by only 5 mph and a slight reduction in the time they could be used before an overhaul was needed. One of these aircraft, the third YP-59A, was supplied to the Royal Air Force, in exchange for the first production Gloster Meteor I for evaluation and flight-offs with domestic alternatives.
British pilots found that the YP-59A compared very unfavorably with the jets that they were already flying. The United States Army Air Forces were not impressed by its performance either and cancelled the contract when fewer than half of the originally ordered aircraft had been produced. No P-59s entered combat, but the type paved the way for the next design generation of U.S. turbojet-powered aircraft and helped to develop appropriate maintenance structures and procedures.
In the meantime, a new, more powerful jet engine had been developed in Great Britain, the Halford H-1, which became later better known as the De Havilland Goblin. It was another centrifugal compressor design, but it produced almost twice as much thrust as the XP-59A’s J31 engines. Impressed by the British Gloster Meteor during the USAAF tests at Muroc Dry Lake - performance-wise as well as by the aircraft’s simplicity and ruggedness - Bell reacted promptly and proposed an alternative fighter with wing-mounted engine nacelles, since the XP-59A’s layout had proven to be aerodynamically sub-optimal and unsuited for the installation of H-1 engines. In order to save development time and because the aircraft was rather regarded as a proof-of-concept demonstrator instead of a true fighter prototype, the new aircraft was structurally based on Bell’s current piston-engine P-63 “Kingcobra”. The proposal was accepted and, in order to maintain secrecy, the new jet aircraft inherited once more a designation of a recently cancelled project, this time from the Vultee XP-68 “Tornado” fighter. Similar to the Airacomet two years before, just a simple “A” suffix was added.
Bell’s development contract covered only three XP-68A aircraft. The H-1 units were directly imported from Great Britain in secrecy, suspended in the bomb bays of B-24 Liberator bombers. A pair of these engines was mounted in mid-wing nacelles, very similar to the Gloster Meteor’s arrangement. The tailplane was given a 5° dihedral to move it out of the engine exhaust. In order to bear the new engines and their power, the wing main spars were strengthened and the main landing gear wells were moved towards the aircraft’s centerline, effectively narrowing track width. The landing gear wells now occupied the space of the former radiator ducts for the P-63’s omitted Allison V-1710 liquid-cooled V12 engine. Its former compartment behind the cockpit was used for a new fuel tank and test equipment. Having lost the propeller and its long drive shaft, the nose section was also redesigned: the front fuselage became deeper and the additional space there was used for another fuel tank in front of the cockpit and a bigger weapon bay. Different armament arrangements were envisioned, one of each was to be tested on the three prototypes: one machine would be armed with six 0.5” machine guns, another with four 20mm Hispano M2 cannon, and the third with two 37mm M10 cannon and two 0.5” machine guns. Provisions for a ventral hardpoint for a single drop tank or a 1.000 lb (550 kg) bomb were made, but this was never fitted on any of the prototypes. Additional hardpoints under the outer wings for smaller bombs or unguided missiles followed the same fate.
The three XP-68As were built at Bell’s Atlanta plant in the course of early 1944 and semi-officially christened “Airagator”. After their clandestine transfer to Muroc Dry Lake for flight tests and evaluations, the machines were quickly nicknamed “Barrelcobra” by the test staff – not only because of the characteristic shape of the engine nacelles, but also due to the sheer weight of the machines and their resulting sluggish handling on the ground and in the air. “Cadillac” was another nickname, due to the very soft acceleration through the new jet engines and the lack of vibrations that were typical for piston-engine- and propeller-driven aircraft.
Due to the structural reinforcements and modifications, the XP-68A had become a heavy aircraft with an empty weight of 4 tons and a MTOW of almost 8 tons – the same as the big P-47 Thunderbolt piston fighter, while the P-63 had an MTOW of only 10,700 lb (4,900 kg). The result was, among other flaws, a very long take-off distance, especially in the hot desert climate of the Mojave Desert (which precluded any external ordnance) and an inherent unwillingness to change direction, its turning radius was immense. More than once the brakes overheated during landing, so that extra water cooling for the main landing gear was retrofitted.
Once in the air, the aircraft proved to be quite fast – as long as it was flying in a straight line, though. Only the roll characteristics were acceptable, but flying the XP-68A remained hazardous, esp. after the loss of one of the H-1s engines: This resulted in heavily asymmetrical propulsion, making the XP-68A hard to control at all and prone to spin in level flight.
After trials and direct comparison, the XP-68A turned out not to be as fast and, even worse, much less agile than the Meteor Mk III (the RAF’s then current, operational fighter version), which even had weaker Derwent engines. The operational range was insufficient, too, esp. in regard of the planned Pacific theatre of operations, and the high overall weight precluded any considerable external load like drop tanks.
However, compared with the XP-59A, the XP-68A was a considerable step forward, but it had become quickly clear that the XP-68A and its outfit-a-propeller-design-with jet-engines approach did not bear the potential for any service fighter development: it was already outdated when the prototypes were starting their test program. No further XP-68A was ordered or built, and the three prototypes fulfilled their test and evaluation program until May 1945. During these tests, the first prototype was lost on the ground due to an engine fire. After the program’s completion, the two remaining machines were handed over to the US Navy and used for research at the NATC Patuxent River Test Centre, where they were operated until 1949 and finally scrapped.
Length: 33 ft 9 in (10.36 m)
Wingspan: 38 ft 4 in (11.7 m)
Height: 13 ft (3.96 m)
Wing area: 248 sq ft (23 m²)
Empty weight: 8,799 lb (3,995 kg)
Loaded weight: 15,138 lb (6,873 kg)
Max. take-off weight: 17,246 lb (7,830 kg)
2× Halford H-1 (De Havilland Goblin) turbojets, rated at 3,500 lbf (15.6 kN) each
Maximum speed: 559 mph (900 km/h)
Range: 500 mi (444 nmi, 805 km)
Service ceiling: 37,565 ft (11,450 m)
Rate of climb: 3.930 ft/min (20 m/s)
Wing loading: 44.9 lb/ft² (218.97 kg/m²)
Time to altitude: 5.0 min to 30,000 ft (9,145 m)
4× Hispano M2 20 mm cannon with 150 rounds
One ventral hardpoint for a single drop tank or a 1.000 lb (550 kg) bomb
6× 60 lb (30 kg) rockets or 2× 500 lb (227 kg) bombs under the outer wings
The kit and its assembly:
This whiffy Kingcobra conversion was spawned by a post by fellow user nighthunter in January 2019 at whatifmodelers.com about a potential jet-powered variant. In found the idea charming, since the XP-59 had turned out to be a dud and the Gloster Meteor had been tested by the USAAF. Why not combine both into a fictional, late WWII Bell prototype?
The basic idea was simple: take a P-63 and add a Meteor’s engine nacelles, while keeping the Kingcobra’s original proportions. This sounds pretty easy but was more challenging than the first look at the outcome might suggest.
The donor kits are a vintage Airfix 1:72 Gloster Meteor Mk.III, since it has the proper, small nacelles, and an Eastern Express P-63 Kingcobra. The latter looked promising, since this kit comes with very good surface and cockpit details (even with a clear dashboard) as well as parts for several P-63 variants, including the A, C and even the exotic “pinball” manned target version. However, anything comes at a price, and the kit’s low price point is compensated by soft plastic (which turned out to be hard to sand), some flash and mediocre fit of any of the major components like fuselage halves, the wings or the clear parts. It feels a lot like a typical short-run kit. Nevertheless, I feel inclined to build another one in a more conventional fashion some day.
Work started with the H-1 nacelles, which had to be cut out from the Meteor wings. Since they come OOB only with a well-visible vertical plate and a main wing spar dummy in the air intake, I added some fine mesh to the plate – normally, you can see directly onto the engine behind the wing spar. Another issue was the fact that the Meteor’s wings are much thicker and deeper than the P-63s, so that lots of PSR work was necessary.
Simply cutting the P-63 OOB wings up and inserting the Meteor nacelles was also not possible: the P-63 has a very wide main landing gear, due to the ventral radiators and oil coolers, which were originally buried in the wing roots and under the piston engine. The only solution: move the complete landing gear (including the wells) inward, so that the nacelles could be placed as close as possible to the fuselage in a mid-span position. Furthermore, the - now useless - radiator openings had to disappear, resulting in a major redesign of the wing root sections. All of this became a major surgery task, followed by similarly messy work on the outer wings during the integration of the Meteor nacelles. LOTS of PSR, even though the outcome looks surprisingly plausible and balanced.
Work on the fuselage started in parallel. It was built mainly OOB, using the optional ventral fin for a P-63C. The exhaust stubs as well as the dorsal carburetor intake had to disappear (the latter made easy thanks to suitable optional parts for the manned target version). Since the P-63 had a conventional low stabilizer arrangement (unlike the Meteor with its cruciform tail), I gave them a slight dihedral to move them out of the engine efflux, a trick Sukhoi engineers did on the Su-11 prototype with afterburner engines in 1947, too.
Furthermore, the whole nose ahead of the cockpit was heavily re-designed, because I wanted the “new” aircraft to lose its propeller heritage and the P-63’s round and rather pointed nose. Somewhat inspired by the P-59 and the P-80, I omitted the propeller parts altogether and re-sculpted the nose with 2C putty, creating a deeper shape with a tall, oval diameter, so that the lower fuselage line was horizontally extended forward. In a profile view the aircraft now looks much more massive and P-80esque. The front landing gear was retained, just its side walls were extended downwards with the help of 0.5mm styrene sheet material, so that the original stance could be kept. Lots of lead in the nose ensured that the model would properly stand on its three wheels.
Once the rhinoplasty was done I drilled four holes into the nose and used hollow steel needles as gun barrels, with a look reminiscent of the Douglas A-20G.
Adding the (perfectly) clear parts of the canopy as a final assembly step also turned out to be a major fight against the elements.
Painting and markings:
With an USAAF WWII prototype in mind, there were only two options: either an NMF machine, or a camouflage in Olive Drab and Neutral Grey. I went for the latter and used Tamiya XF-62 for the upper surfaces and Humbrol 156 (Dark Camouflage Grey) underneath. The kit received a light black ink wash and some post shading in order to emphasize panels. A little dry-brushing with silver around the leading edges and the cockpit was done, too.
The cockpit interior became chromate green (I used Humbrol 150, Forest Green) while the landing gear wells were painted with zinc chromate yellow (Humbrol 81). The landing gear itself was painted in aluminum (Humbrol 56).
Markings/decals became minimal, puzzled together from various sources – only some “Stars and Bars” insignia and the serial number.
Somehow this conversion ended up looking a lot like the contemporary Soviet Sukhoi Su-9 and -11 (Samolyet K and LK) jet fighter prototype – unintentionally, though. But I am happy with the outcome – the P-63 ancestry is there, and the Meteor engines are recognizable, too. But everything blends into each other well, the whole affair looks very balanced and believable. This is IMHO furthermore emphasized by the simple paint scheme. A jet-powered Kingcobra? Why not…?