Junkers Ju 287

The Junkers Ju 287 was a Nazi Germany aerodynamic testbed built to develop the technology required for a multi-engine jet bomber. It was powered by four Junkers Jumo 004 engines, featured a revolutionary forward-swept wing, and apart from said wing was assembled largely from components scavenged from other aircraft.

The unfinished second and third prototypes, which far more accurately reflected the design of the eventual production bomber, were captured by the Red Army in the closing stages of World War II and the design was further developed in the Soviet Union after the end of the war.

Development
The Ju 287 was intended to provide the Luftwaffe with a bomber that could avoid interception by outrunning enemy fighters. The swept-forward wing was suggested by the project's head designer, Dr. Hans Wocke as a way of providing extra lift at low airspeeds - necessary because of the poor responsiveness of early turbojets at the vulnerable times of take-off and landing. A further structural advantage of the forward-swept wing was that it would allow for a single massive weapons bay forward of the main wing-spar. Prior to the assembly of the first Ju 287, an He 177 A-5 (designated as a 177 prototype, V38) was modified at the Letov plant in Prague to examine the technical characteristics of this single large bomb bay design.

The first prototype was intended to evaluate the concept, and was cobbled together from the fuselage of an He 177 A-5, the tail of a Ju 388, main undercarriage from a Ju 352, and nosewheels taken from crashed B-24 Liberators. Two of the Jumo 004 engines were hung under the wings, with the other two mounted in nacelles added to the sides of the forward fuselage.

Flight tests began on 16 August 1944 (pilot: Siegfried Holzbaur ), with the aircraft displaying extremely good handling characteristics, as well as revealing some of the problems of the forward-swept wing under some flight conditions. The most notable of these drawbacks was 'wing warping', or excessive in-flight flexing of the main-spar and wing assembly. Tests suggested that the warping problem would be eliminated by concentrating greater engine mass under the wings. This technical improvement would be incorporated in the subsequent prototypes. The 287 was intended to be powered by four Heinkel-Hirth HeS 011 engines, but because of the development problems experienced with that motor, the BMW 003 was selected in its place. The second and third prototypes, V2 and V3, were to have employed six of these engines, in a triple cluster under each wing. Both were to feature the all-new fuselage and tail design intended for the production bomber, the Ju 287A-1. V3 was to have served as the pre-production template, carrying defensive armament, a pressurised cockpit and full operational equipment.

Work on the Ju 287 programme, along with all other pending German bomber projects (including Junkers' other ongoing heavy bomber design, the piston-engined Ju 488) came to a halt in July 1944, but Junkers was allowed to go forward with the flight testing regime on the V1 prototype. The wing section for the V2 had been completed by that time. Seventeen test flights were undertaken in total, which passed without notable incident. Minor problems, however, did arise with the turbojet engines and the RATO booster units, which proved to be unreliable over sustained periods. This initial test phase was designed purely to assess the low-speed handling qualities of the forward-swept wing, but despite this the V1 was dived at full jet power on at least one occasion, attaining a speed in the medium dive-angle employed of 660kph. To gain data on airflow patterns, small woolen tufts were glued to the airframe and the "behavior" of these tufts during flight was captured by a cine camera mounted on a sturdy tripod directly ahead of the plane's tailfin. After the seventeenth and last flight in the late autumn of 1944, the V1 was placed in storage and the Ju 287 programme came to what was then believed to be its end. However, in March 1945, for reasons that are not entirely clear, the 287 programme was restarted, with the RLM issuing a requirement for mass production of the jet bomber (100 airframes a month) as soon as possible. The V1 prototype was taken out of storage and transferred to the Luftwaffe evaluation centre at Rechlin, but was destroyed in an Allied bombing raid before it could take to the air again. Construction on the V2 and V3 prototypes was resumed at the Junkers factory near Leipzig, and intended future variant designs (meant for service in 1946) were dusted off. These included the Ju 287B-1, seeing a return to the original powerplant choice of four 2866-lb thrust HeS 011 turbojets; and the B-2, which was to have employed two 7700-lb thrust BMW 018 turbofans. While the Heinkel turbojet was in the pre-production phase at wars' end, work on BMW's radical and massively powerful turbine engine never proceeded past the blueprint stage. The final Ju 287 variant design to be mooted was a Mistel combination-plane ground attack version, comprising an unmanned explosives-packed "drone" 287 and a manned Me 262 fighter attached to the top of the bomber by a strut assembly. The cockpit of the 287 would be replaced by a massive impact-fused warhead. Take-off and flight control of the combination would be under the direction of the 262's pilot. The 262 would disengage from the 287 drone as the Mistel neared its target, the pilot of the fighter remotely steering the 287 for the terminal phase of its strike mission.

The Junkers factory building the V2 and V3 was overrun by the Red Army in late April 1945; at that time, the V2 was 80% complete, and construction of the V3 had just begun. Wocke and his staff, along with the two incomplete prototypes, were taken to the Soviet Union. There, the third prototype (returned to its original Junkers in-house designation, EF 131) was eventually finished and flown on 23 May 1947, but by that time, jet development had already overtaken the Ju 287. A final much-enlarged derivative, the EF 140, was tested in prototype form in 1949 but soon abandoned.