1937 Junkers EF61 - High Altitude Experimental Aircraft.
In 1934, the Junkers Flugzeugwerke sent a proposal to the Technical Department of the Air Commissariat for a pressurized bomber capable of operating at heights inaccessible to fighters. This radical proposal aroused keen interest, and after Junkers proposed the EF-61 project in early 1935, an order was issued for two prototype aircraft.
Meanwhile, flight tests of the Ju-49 continued, but after reaching an altitude of 12500m in September 1935, the engine stalled and the aircraft was wrecked.
The first of two experienced high-altitude bombers EF-61-V1 was ready in the fall of 1936.
It was equipped with two Daimler-Benz DB-600A engines with a take-off power of 950hp with frontal radiators. The first flight took place at the end of the year.
The aircraft had a two-spar wing of high elongation, with a span of 27m. The fuselage had an oval section with a corrugated working skin covered with fabric.
The nose was formed by a round section of a pressurized cabin for two crew members. The view of the crew was provided by a large round panel in the bow of the cabin. Glazing was double with a layer of dried air. The glazing material was the so-called "reilite". A small round panel on the lower, right side of the cockpit provided a downward view of the pilot during landing.
A transparent panel was also in the floor on the left for aiming the scorer, who acted as a navigator and shooter. In the latter case, he could use the MG-15 machine gun in the rear of the cockpit. The cabin was accessed through a round hatch on its right side.
Delays in the readiness of pressurized cabin forced to start flying without it. However, the plane never received it. On September 19, 1937, it hit a flutter and crashed, killing both pilots. While the plane was flying around, the pressurized cabin was also tested for pressure. As a result, it turned out that the plastic was too fragile for glazing a large round panel and could not withstand pressure at an altitude above 12000m.
Thus, work on the second experimental EF-61-V2 was also delayed: its first flight took place only in October 1937.
The new pressurized cabin without large area glazing and portholes received only one transparent blister, shifted to the starboard side. The pilot's seat was raised and moved to the very end of the cockpit. Above the pilot's seat was a metal dome with two plexiglass portholes, providing a view forward and to the left. At the end of the blister, a MG-15 machine gun was installed. Behind the cockpit was equipped with a small bomb bay for four 250kg bombs.
Unfortunately, even before the start of high-altitude flights, the second plane crashed in December 1937. There were no plans to build a new aircraft. Thus, work on the first high-altitude bomber with a pressurized cabin was discontinued.