The four engine dive bomber

GenLt. Walther Weaver, the Luftwaffe’s first chief of staff, was an advocate of a long-range strategic bomber.

After  his demand for the development of the previously discussed Ural bombers, he followed with a more ambitious requirement, the Bomber A, for an even faster and more modern long-range bomber.

In 1936, the Heinkel Company set to work on Bomber A, but before a prototype was built, Weaver was killed in a place crash and his successor instead changed the focus to dive bombers and twin-engine medium bombers.

Heinkel was allowed to continue with the project but on Nov. 5, 1937, Ernst Udet, chief of the Luftwaffe’s development wing and the major proponent of the dive bomber, told Heinkel the bomber, now designated the He-177 “Grief” (Griffin), had to be able to perform 45 degree dive bombing attacks.

Heinkel knew a normal aircraft of this size would require 4,000 horsepower to meet its performance goals, and this meant – given the engines of the time – four engines. But it would be impossible to build a wing strong enough to support four engines in the high G pull out from a 45 degree dive bombing attack.

Heinkel’s chief designer, Siegfried Gunter, thought he knew a way out. He had designed the Heinkel He-119 high-speed racer, which had a pair of Daimler Benz engines mechanically coupled together and mounted in a slim fuselage and driving a single propeller, making it look like a single engine aircraft.

Gunter modified the He-177 to have each nacelle carry two engines.

To avoid heavy and drag producing cooling radiators, he added an evaporative cooling system that ducted away hot water from the engines and fed it through pipes in the wing where it was cooled by the airflow then returned.

But the evaporative cooling system was quickly seen as inadequate and dropped in favor of conventional radiators in each nacelle, which added significantly to the weight and drag.

On Nov. 9, 1939, the first prototype He-177 V1 made its first flight, and the first tests showed the four engine/two nacelle combination provided a substantial reduction in drag, making it possible to dive bomb as well as making the aircraft quite maneuverable.

However, the initial flight was terminated abruptly after only 12 minutes as a result of overheating engines, foreshadowing the problems that were to make the He-177 one of the worst aircraft of World War II.

To reduce drag, the engine nacelles had to have a small diameter, partially achieved by having a single central exhaust manifold between the two inner cylinder banks of the engines. Not surprisingly, this manifold became very hot and regularly caused the normal accumulation of oil in the nacelle to ignite. Adding to the problem was another concession to the small diameter nacelle – no firewall.

The crammed nacelle also had insufficient space for the fuel and oil lines, which resulted in kinks and leaky connections, and a poorly designed fuel pump that delivered extra fuel when the pilot throttled back, creating another fire hazard. The oil pump did not provide adequate lubrication and resulted in the disintegration of rod bearings, which then punctured the oil tanks and poured oil on to the hot exhaust pipe.

As if this was not enough, the design weight skyrocketed. The large wing flaps cracked from the stress of dive bombing and need extensive strengthening, adding more weight, which required a redesign of the landing gear. The new design was so poor it took two hours to change just a tire.

The first Grief squadron was sent to the Eastern Front, but on the He-177s first 13 missions, seven crashed in flames without any action attributable to the enemy. They were later withdrawn and informally dubbed “Luftwaffenfeuerzeug,” or Luftwaffe’s petrol lighter.

Other He-177s were sent to the west and suffered a similar fate.

On one of their first missions – a raid on London on the night of Feb. 13, 1944 – 13 He-177s took off but eight had to return to base because of overheating or burning engines.

By late 1944, modifications had been made to eliminate the engine fires and the He-177 performed some useful service as carriers of anti-ship missiles. However, it was too late to have an impact on the war.

(For questions or comments, contact Dr. Michel at arshall.michel@ramstein.af.mil.)