Designed to a 1936 requirement known as Bomber A, the aircraft was originally intended to be a purely strategic bomber intended to support a long-term bombing campaign against Soviet industry in the Urals. During the design phase, Luftwaffe doctrine came to stress — unrealistically, for a 30-meter (100 ft) wingspan-class bomber airframe — the use of moderate-angle dive bombing in order to improve accuracy, and the design was extensively modified to allow shallow-angle “glide bombing”. This change, along with the demand that it use only two fully nacelled “power system” engines, required to each be of over 1,500 kW (2,000 PS) output levels apiece to allegedly reduce drag for the initially demanded “glide bombing” capability, created numerous problems for the aircraft. Luftwaffe aircrew nicknamed it the Luftwaffenfeuerzeug (“Luftwaffe’s lighter”) or the “Flaming Coffin” due to the serious engine problems on initial versions. Many of these stemmed from the power plants’ inadequately-designed and poorly maintained installation in their wing nacelles,[3] which caused cooling and ventilation problems that were never completely solved.
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The He 177 had Fowler-type extensible trailing edge flaps, which covered the trailing edge of the wing, including those portions covered by ailerons. Each aileron comprised upper and lower portions, the latter arranged to slide rearwards with flap extension, while the upper part retained its function of providing lateral control for take-off and landing. The original wing design did not fully take into account the stresses resulting from the operation of the Fowler flaps. A Rechlin report dated 9 October 1942 stated:
“The examination has shown that the strength of the He 177’s wings is one-third below that estimated by Heinkel. The reason for this is the uneven rigidity of the individual members with consequent deformation under load. This condition was not recognized by Heinkel at the proper time, the failure tests having been undertaken too late in view of the size of the structure.”
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During development, the anticipated weight of the He 177 increased so much that a main undercarriage design sufficient to handle the 32 metric tons (35 short tons) loaded weight, was difficult to achieve. The engine nacelles and wings had little room for the main undercarriage members, which needed to be longer than usual, for ground clearance for the large diameter four-blade propellers. After several extremely complex arrangements had been considered during initial design, a novel system was adopted. Instead of a wheel leg under each engine nacelle, two wheel legs were attached to the main spar at each nacelle, the outboard legs retracting upward and outward into shallow wing wells and the inboard legs swinging upward and inward into similar wells in the wing roots, with all units enclosed by flush fitting wheel and strut doors, which almost met under each engine nacelle when fully extended. During the retraction cycle, the forward-oriented lever-action lower gear strut sections, on which the wheels were mounted onto their axles, pivoted to a 90° angle from 120° when fully extended to the main gear leg, to be able to fit into the wheel wells.
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The initial production version of the Greif, the He 177 A-1, tended to be unstable in the yaw and pitch axes during flight tests in August 1942, which would have led to poor bombing accuracy. Shortly after these tests, the third production A-1 example (factory serial number 15153, with Stammkennzeichen of GI + BN) had its fuselage lengthened by 160 cm (63 in) just aft of the trailing edge of the wing. The modified aircraft, with the longer distance of the “tail moment”, showed a marked degree of improvement in yaw and pitch axis stability, enough to mandate the construction of the He 177 A-3 and all later models of the He 177 with the lengthened fuselage.[30]
In early September 1944, the Royal Aircraft Establishment (RAE) was ordered to supply an aircrew for a He 177 that the French Maquis and Allied units in Vichy France would take control of at the airfield at Blagnac near Toulouse, where elements of both the He 177A-equipped KG 4 and KG 100 Luftwaffe bomber wings were based. A transport and two escort fighters from the RAE flew to the area to leave the Royal Aircraft Establishment Chief Test Pilot Roland Falk and a flight engineer with the commando group. On 10 September, as Operation Dragoon was wrapping up in the southeast of France, the aircraft was seized and flown back to the UK by Wing Commander Roland Falk. Soon afterwards, Capt. Eric Brown, an RN pilot then posted to the RAE as a test pilot, flew the He 177.[31] He wrote that the in-flight handling characteristics of the He 177 A-5 were “… positive about all axes, but the controls were all remarkably light for such a large aircraft. Indeed I had the feeling that the elevator was dangerously light and I was all too aware of the intelligence reports of He 177s breaking up in the air so I decided to treat this control very gently… The aircraft had an automatic pull-out device and an acceleration warning apparatus fitted, but it really was nailbiting to have to treat a giant like this immense Heinkel bomber as if it was made of glass. The stalling characteristics with flaps and undercarriage lowered, the aircraft buffeted violently at 140 km/h (87 mph) before the nose dropped at 135 km/h (84 mph). The buffet experienced was so violent that I had some concerns over structural damage. Somehow the He 177 always conveyed an impression of fragility despite its size.”[32]
He added that it was “one of the very few German aircraft of the period that I tested that I did not enjoy flying”.
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Beset by technical difficulties in development, the He 177 had a troubled history in service. Overly demanding design requirements of long range, high speed, heavy bomb load, and the formerly required dive bombing capability — itself rescinded only in September 1942 by the Reichsmarschall, as previously stated — did not help. Although the He 177 entered service in 1942, it was far from operational. In an assessment of the aircraft on 9 April 1942, the newly activated Erprobungsstaffel 177 reported that the Greif had good flying characteristics, but had unacceptable engine troubles and problems with its airframe strength. As an emergency measure, it was used to supply the encircled 6th Armee at Stalingrad, where it was found to be unsuited for the transport role, carrying a little more cargo than the smaller, more reliable Heinkel He 111, and proving useless for the evacuation of wounded. As a result, the He 177s reverted to bombing and flak-suppression missions near Stalingrad. Only 13 missions were flown, and seven He 177s were lost to fire without any action attributable to the enemy.
As the war progressed, He 177 operations became increasingly desultory. Fuel and personnel shortages presented difficulties, and He 177s were sitting on airfields all over Europe awaiting new engines or engine related modifications. Of the 14 He 177 sent out during Operation Steinbock, one suffered a burst tire, and eight returned with overheating or burning engines. Of the four that reached London, one was lost to night fighters. These aircraft were brand new, delivered a week before the operation and not fully flown in, because the air unit had moved to a new airfield the day before, and lacked sufficient maintenance personnel and material. Constant attacks against Luftwaffe long-range combat units in France made continuous operations difficult.