Early in 1943, a
Junkers design team lead by Hans Wocke was assigned the task of
developing a high-speed heavy bomber which could outrun any
contemporary Allied fighter. They first looked at a turbojet-powered
swept-back wing design. The swept-back wing offered advantages at the
upper end of the performance envelope, but they were accompanied by
disadvantages at low speeds. As a sweptback-winged aircraft slows down,
its wingtip stalls first, causing a loss of roll control just when you
need it the most. The Junkers team proposed a unique solution to this
problem, a forward-swept wing. It was hoped that this wing would
transfer the stability problems to the high-speed end of the
performance envelope, where they could more easily be handled. In
theory, the swept-forward wing would have its highest lift coefficient
at the root, decreasing towards the tip. Consequently, the tip would be
the last to stall as the aircraft slowed down, aileron control being
available beyond the main centre-section flow breakaway.
The downside of the
swept-forward wing design is in its elastic behaviour, specifically the
phenomenon of "aero-elastic divergence". As an airplane flies through
the air, its wing is subjected to a more-or-less random twisting moment
exerted by variable aerodynamic forces caused by rapid changes in wind
currents or by rapid manoeuvres. If the wing is swept forward, a small
increase in the angle of attack at the tip will increase the lift,
causing a twisting moment at the tip, which in turn will cause an
increased angle of attack, which will cause still more lift, etc. This
causes the aircraft to become seriously unstable. In the worst case,
the wing can undergo a catastrophic structural failure. This can make
for a real bad day.
The
Reichsluftfahrtministerium (State Ministry of Aviation, better known as
the RLM) gave the project the go-ahead and assigned it the designation
Ju 287. The first prototype, the Ju 287 V1, was to be a flying testbed
to check out the low-speed characteristics of the swept-forward wing.
In order to get something in the air as soon as possible, parts were
scavenged from existing aircraft to the extent feasible. The Ju 287 V1
used a fuselage from a He 177A bomber, a tail assembly from a Ju 388,
and a massive fixed undercarriage consisting of Ju 352 mainwheels
enclosed by large fairings and a pair of nosewheels scavenged from a
B-24 Liberator. Virtually only the swept-forward wing was new. The wing
used a Junkers reverse-camber, high speed airfoil section with a
two-spar all-metal structure. The inner leading edges were fitted with
fixed slats to delay the initial root stall, and large slotted flaps
were fitted which extended down to 40 degrees. The ailerons were
arranged to droop 23 degrees to provide a completely cambered wing for
maximum lift coefficients. Power was provided by four 1984 lb. st.
Junkers Jumo 004B turbojets, two mounted on the sides of the forward
fuselage and two slung under the rear edges of the wings.
The Ju 287 V1 flew for
the first time on August 16, 1944. Flight testing proceeded without any
serious incidents, and the aircraft turned out to have rather pleasant
flying characteristics. There were virtually no trim changes with flap
operation, and landings were fairly easy. Lateral control was good
except when yaw was applied, a pronounced wing drop then being
experienced. The aircraft reached speeds as high as 404 mph in a dive,
and confirmed the aero-elastic problems inherent in the swept-forward
wing, with decreasing elevator forces during tight turns and pull outs
from shallow dives.
Testing revealed that
it would be a good idea to mount the engines on the forward edges of
the wings in order to provide a mass balance, and this was to be done
for the high-speed second prototype, the Ju 287 V2. The Ju 287 V3 was
to be the production prototype with full military equipment being
provided.
The wing of the Ju 287
V2 was similar to that of the V1, but the fuselage was entirely
different, being quite similar to that of the propeller-driven Ju 388.
A fully-retractable undercarriage was to be fitted, all members being
stowed inside the fuselage. Originally, the plane was to be powered by
four 2866 lb. st. Heinkel-Hirth 011A turbojets mounted in pairs and
projecting ahead of the wing leading edges. However, owing to delays in
the availability of this power plant, Junkers decided to power both the
V2 and the V3 with six 1760 lb. st. BMW 003A-1 turbojets. Two different
arrangements were to be tried, one with a cluster of three engines
under each wing and the other with two engines underneath each wing and
one on each side of the fuselage nose a la Ju 287 V1. The former engine
arrangement was to power the V2, whereas the V3 and the pre-production
Ju 287A-0 were to be powered by the second engine arrangement.
The V3 was to be the
first prototype to carry armament: a tail barbette containing a pair of
MG 131 machine guns operated remotely by a periscopic sight from the
crew compartment. The cockpit was fully pressurized. A maximum bombload
of 8800 lbs was envisaged. It was anticipated that the V3 could achieve
a maximum speed of 509 mph at sea level and 537 mph at 16,400 feet.
Range was expected to be 985 miles with an 8800 lb bombload. The V3 was
expected to be able to attain an altitude of 19,700 feet in 10.5
minutes. Weights were estimated to be 26,278 lbs empty, and 47,398 lbs
fully loaded.
The Ju 287 V2 was
undergoing final assembly when the Junkers factory was overrun by
Soviet forces in 1945. The incomplete prototype, Wocke, plus his design
team, were all carted off to the Soviet Union. The Junkers team
continued to work on the project in the Soviet Union, and the Ju 287 V2
was flown for the first time in 1947.
Specifications
Year deployed
Wing span, m
Length, m
Height, m
Wings area, m2
Weight, kg
empty aircraft
normal take-off
Engine
Thrust, kgs
Maximum speed, km/h
at
sea level
at altitude
Cruising speed, km/h
at sea level
at altitude
Range, km
Rate of climb, m/min
Service ceiling, m
Crew
Armament:
|
20.10
18.60
61.00
11930
21500
6 TJE блW-003ю-1 Shturm
6 У 800
815
860
715
790
2100
575
10000
3
2 13-mm machine-guns лG-131 up to 4000 kg bombs
|
|