Boeing B-29 Superfortress EB-29

When the Second World War ended, the United States Army Air Forces found themselves with hundreds of B-29s without a combat role and with a new generation of experimental projects — rocket aircraft, parasite fighters, in-flight coupling trials — that needed exactly what the Superfortress could offer: a cavernous bomb bay, a high ceiling and generous endurance. That combination produced the EB-29 designation. The "E" did not stand for "experimental" in the usual sense but for "exempt": because each conversion was unique, the airframe was excused from the standard modification orders applied to the rest of the fleet. The conversions were carried out in the years immediately after the war and consisted essentially of rebuilding the bomb bay to accept, carry and drop experimental aircraft in flight. No two EB-29s were alike; every airframe was adapted to the machine it had to carry.

Compared with the production bomber, the EB-29 gave up its bomb load and much of its defensive armament, receiving instead a mounting and release mechanism in the bay together with the instrumentation needed to monitor each trial. In the case of the X-1 carrier, the rocket plane rode slung in the bomb bay and was dropped from it in flight. The bomber supplied what the X-1 could not afford on its own: the aircraft had originally been intended to take off from the ground, but the end of the war made the Superfortress available and with it the option of beginning every flight already at altitude, saving the rocket engine's fuel for the useful part of the test.

The XS-1 programme, later the X-1, opened with glide flights over Pinecastle in Florida. On 19 January 1946 Jack Woolams, Bell's chief test pilot, made the first of them; in all he flew ten unpowered sorties in which the B-29 released the X-1 at 29,000 feet (8,800 m) and the rocket plane touched down about twelve minutes later at around 110 miles per hour (180 km/h). After the first prototype went back to Buffalo to be readied for powered flight, testing moved to Muroc in California, where on 9 December 1946 the engine was lit in flight for the first time with Chalmers "Slick" Goodlin at the controls, reaching Mach 0.795 after a drop from the B-29.

The climax came on 14 October 1947 over the Mojave Desert. Captain Charles "Chuck" Yeager, flying X-1 number 46-062, named "Glamorous Glennis" after his wife, was dropped from the B-29's bomb bay and reached Mach 1.06 — about 700 miles per hour, or 1,100 km/h — on the programme's 50th flight, the first manned supersonic flight in history. The programme's three leading figures — Larry Bell, Yeager himself and John Stack of NACA — received the 1948 Collier Trophy at the White House. Throughout that campaign the B-29 mothership was the quiet link in the chain: it hauled the X-1 to release height, let it go and returned to base while the rocket plane glided down to the dry lake bed. In time the EB-29 was replaced in the role by a B-50, the more powerful derivative of the same bomber, which went on to carry the second-generation X-1s.

Another EB-29 was assigned to trials of the McDonnell XF-85 Goblin, a tiny parasite fighter meant to ride inside the Convair B-36 and emerge to defend it against Soviet fighters on long-range missions. The EB-29 acted as the carrier for the release-and-recovery trials, but the experiment proved a failure. Even so, the Air Force did not abandon the idea of a bomber-borne fighter and redirected it towards the FICON programme with the B-36.

The EB-29's third life was its boldest. The idea of extending an aircraft's range by adding floating panels at the wingtips — which would behave like the long, narrow wing of a glider — is traced to German experiments in 1944 and 1945 and to Richard Vogt, who developed it further in the United States after the war. It was tested at Wright Field in the late 1940s with a Douglas C-47A and a Culver Q-14B, with promising results, and Republic Aviation was awarded the contract to pursue it. Thus began Project MX-1016, "Tip Tow": giving piston-engined bombers jet fighter escort by hooking the fighters to the bomber's wingtips, with provision for attaching and detaching in flight.

The set-up comprised a specially modified ETB-29A, serial 44-62093, and two EF-84Ds, serials 48-641 and 48-661. The F-84 pilots kept manual control while coupled and managed roll with elevator rather than aileron; the jets shut down their engines to save fuel while being "towed" and in-flight restarts were achieved successfully. Trials began with a single fighter and progressed to two: the first simultaneous hook-up of both F-84s came on the tenth flight, on 15 September 1950, and the longest flight with all three joined, on 20 October 1950, lasted two hours and forty minutes. The flexibility of the B-29's wing and the wingtip vortices were a concern from the outset and forced changes to the coupling mechanisms.

Republic received a further contract to fit the system with automatic flight control. Testing continued while the modifications were made, including night flights, and in March 1953 the automatic system was ready to try. Several hook-ups were made with one or other F-84 while persistent electrical faults were chased. On 24 April 1953, over Peconic Bay in New York State, the left-hand F-84 coupled and the automatic system was engaged: the fighter instantly flipped over onto the B-29's wing and both aircraft crashed, killing the bomber's five crew and the jet's pilot. The pilot of the right-hand F-84D, Major Clarence E. "Bud" Anderson, survived and later described the experiments in a paper for the Society of Experimental Test Pilots.

The concept was pursued in parallel with a B-36 and two RF-84Fs under Project Tom-Tom, itself cancelled in 1956 after a fighter was torn from the bomber's wingtip; in-flight refuelling by then promised a far safer way of extending fighter range. The EB-29s' mark is nonetheless indelible: from the bay of one of them the sound barrier was broken for the first time, and 44-62093 stands as a reminder of the price of post-war aviation's most daring ideas.