DURING World War Two, the lack of a long-range bomber force was one of the major deficiencies suffered by the Luftwaffe. Popular myth has it that German air planners had, foolishly, ignored this weapon during the years immediately prior to the war. But this was not so. Indeed, they had been as alive to the possibilities of the heavy bomber as anybody else; within three months of the outbreak of war the first prototype of the four-motor bomber intended to equip the German heavy bomber arm, the Heinkel He 177, was flying. Thus in chronology the first flight of the German bomber was after the British Short Stirling but before the Handley Page Halifax; after the American Boeing Flying Fortress but before the Consolidated Liberator. However, the Heinkel-conceived bomber was to become operational long after its contemporaries—and then only in small numbers. That this was so was because the German air staff, far from being unambitious in its requirements for a long-range bomber, had asked for too much in the specification. As a result, the Heinkel company was forced to introduce many untried features into its design. In retrospect, it is clear that there were too many.
If historians are agreed on one thing regarding the He 177, it is that this aircraft had no effect at all on the course of World War Two. Well over 1,000 of these bombers were built, but it is doubtful whether more than 200 of them were ever used on operations. During the latter part of the conflict, Allied aircraft often brought back reconnaissance photographs of parks in Germany littered with He 177s; the subsequent interpretation reports often stated that ". . . absence of track activity suggests that these aircraft are not being worked on."
When the war ended, the 900 or so He 177s remaining—most of them brand-new and unused—were carted off to the scrapyards. It was an ignominious ending to the saga of the He 177. But, in fact, the notion of a German strategic bomber force—to rival those of the Western Allies—had been killed stone dead nearly a year before the end of the conflict.
DEVELOPMENT
In 1936 the company of Ernst Heinkel AG received details of the new Bomber A requirement from the Reichsluftfahrtministerium (RLM—German Air Ministry). This specification called for an aircraft with a maximum speed of 335 m.p.h., able to carry 4,400 pounds of bombs out to a radius of 1,000 miles or, alternatively, 2,200 lb. out to 1,800 miles. All-in-all, this was a formidable specification, calling as it did for an aircraft able to outrun any fighter and outperform, by a considerable margin, any bomber then in service. In order to meet it Heinkel's chief designer, Siegfried Guenther, had to employ several hitherto untried features.
For example, to power his new bomber Guenther needed a pair of 2,000 h.p. aero-motors. But, at the time, the Germans possessed no aero-engine which developed such power. To overcome this problem—without resorting to four smaller motors and their attendant drag penalty—the Heinkel designer decided to employ the new Daimler Benz DB 606 double engine. This comprised a pair of DB 601 liquid-cooled 12-cylinder inverted-vee inline motors—mounted side-by-side in a single nacelle—driving a single propeller through a connecting gear train and clutch arrangement. Two of the new DB 606s, each of which
developed 2,600 h.p. for take-off, were to power the He 177.
In order to refine the aerodynamic cleanliness of his design even further, Guenther decided to dispense with the usual system of drag-producing radiators for the engine coolant. Instead, he planned to employ evaporative-cooling. The DB 601 had been designed to run very hot. In the evaporative-cooling system—pioneered by the Heinkel company—the coolant water was pressurized; thus, it was possible to heat it to about 110° C before steam began to form in the engine. The super-heated water was then ducted away and depressurized, at which point steam formed. Then, the water was separated and returned to the motor. At the same time, the residual steam was fed through pipes in the wing and cooled by the airflow. After resultant condensation had taken place, the water from the wing pipes was also returned to the engine. During flight tests, this evaporative-cooling system worked quite well on a modified Heinkel He 100 single-seat fighter. However, even before the design of the He 177 was finalized, it was clear that such a system would be incapable of dealing with the vast amount of heat generated by the DB 606. So Guenther had to abandon this cooling system for his bomber and revert to the more conventional radiator and its attendant drag.
In his quest for an aerodynamically "clean" design, Guenther's original intention had been to defend his new bomber with three remotely-controlled gun barbettes and a conventionally-manned tail turret. Compared with the usual form of manned turret, the remotely-controlled barbette traded technical complexity for reduction of size and drag.
Further, it held the advantage that the gunner could be installed in a position where he would have the
best possible view, and where he would be less likely to
be blinded by the flash from his own guns. But, like the evaporative cooling system, the remotely-con-
trolled gun barbette was not sufficiently developed in 1939. So the designer had to revert to the heavier manned turret and accept the resultant drag penalty.
The next problem came when the Technical Office at the German Air Ministry decided that it required the He 177 to be able to dive-bomb. Certainly there were great advantages to be gained if it could because the contemporary German horizontal bombsight in service gave poor results. Dive-bombing was much more accurate, but the manoeuvre and subsequent pull-out placed a great strain on the airframe. Inevitably, the airframe had to be strengthened to meet the new loads dive-bombing would impose—with a resultant weight penalty.
All these moves combined to push the He 177 design round a vicious circle. In each case the extra weight or drag meant that the bomber flew slower for the same power setting. Consequently, it would use more fuel in covering a given distance and would require more to be carried if the He 177 were to meet its original range specification. So, additional fuel tanks had to be fitted into the wings and the wings had to be further strengthened to take this extra weight. Thus, each move provided a further twist to the weight-drag-speed-range-more weight spiral. In the end, the increase in weight reached such proportions that Guenther had to redesign the main undercarriage. Instead of the originally projected single wheel leg under each engine nacelle, he had to
incorporate a double leg system—the outer leg retracted into the wing outboard of the nacelle and, similarly, the inner leg retracted into the wing inboard of the nacelle.
On November 19, 1939, Dipl. Ing. Franke, chief of the RLM Rechlin flight test centre, lifted the prototype He 177 into the air for the first time—being airborne for only twelve minutes. This brief beginning was forced on Franke. He had to return with engines overheating. Also, the test pilot complained of the bomber's poor stability and tendency to aileron flutter.
The second prototype—generally similar to the first—made its first flight Soon™ afterwards. Following Franke's initial flight, the first prototype's tail surfaces were increased in size. But this modification had not been incorporated in the second before it began initial flight trials. During subsequent diving tests, the aircraft developed severe control flutter and broke-up in the air. Test pilot Rickert failed to bale out and was killed. Following this incident, the tail surfaces of the third, fourth and fifth prototypes—which were now nearing completion—also were increased in size.
When the diving trials were resumed, the fourth prototype failed to pull out of a dive and crashed into the Baltic; the cause was put down to a malfunction of the propeller-pitch mechanism. Shortly afterwards, and early in 1941, the fifth prototype suffered a double engine fire while simulating a low-level attack; it crashed into the ground and exploded.
This was an inauspicious start for the new German heavy bomber. Three out of the first five prototypes had crashed during the early test programme. The Heinkel company put in hand a number of design changes to overcome the various failings in their product.
Even so, one problem was to attend the bomber almost throughout its service—that of engine overheating and resultant fires. The causes of this were many and varied. At first, the lubrication to the DB 606 engines was poor; as a result, all-too-often the connecting rod bearings would seize-up, causing the
rods to smash through the crank case which in turn allowed the lubricating oil to spill over the red-hot engine exhausts. Moreover, if the throttles were handled roughly, the fuel-injectors would leak and allow neat Benzin (gasoline or petrol) to run down into the bottom of the engine bay. If the aircraft was flying in a high angle-of-attack attitude—for example, when landing or flying at high altitude—sometimes the fuel would drip down onto the engine exhaust pipes. In either case the outcome was the same—fire.
During the flight test programme other, but less lethal, problems arose. Soon™, it became clear that whatever the wishes of RLM Technical Office, the He 177 was much too big for a dive-bomber. To dive the He 177, the pilot had to cut his speed right back before he could force the nose down. Almost as Soon™ as he had established the dive, it was time to initiate the pull out. And in spite of the specially strengthened airframe, it was still all too easy to overstress the bomber during the dive-attack manoeuvre. Fortunately, by the time this deficiency became clear, the need for the He 177 to dive had passed. The new Lotfe Bombenvisier (tachometric bombsight) now
about to enter service promised accuracies in horizontal-bombing of the same order of those obtained during dive-bombing attacks. As a result, the dive-brakes were omitted from all aircraft built after the initial pre-production batch.
The initial pre-production run totalled 35 aircraft; and these He 177 A-0-series, in almost every case, were used to explore various aspects of both the "performance envelope" and the bomber's technical features. Then came the first production version, the He 177 A-1. A total of 130 examples of this series left the production line at Warnemunde between March 1942 and June 1943. But, with its teething troubles still uncured, the He 177 was still a long way from being suitable for operational use as a bomber. In the event, almost all the A-ls were relegated to second-line duties; even after 34 had been delivered to the First Gruppe of K.G.40 at Bordeaux/Merignac in the summer of 1942—in a premature attempt to introduce the type into operational service—they were withdrawn shortly afterwards.
The armament of the pre-production He 177 A-0 had comprised a single power-operated gun turret to the rear of the cabin, three flexible mountings in the nose and one at the extreme tail. The He 177 A-1 carried one of the newly-developed remotely-controlled barbettes above the centre fuselage in place of the earlier powered gun turret; the latter mounted a single 13-mm MG 131 machine-gun was aimed from a sighting position to the rear of the cabin. The flexible gun positions remained unchanged, as did the rear mounting.
The next production version of the A-series—the He 177 A-3—featured an additional powered manned gun position. The new dorsal turret, amidships, mounted a single 13-mm MG 131. Also, the barbette
was enlarged to house two instead of one 13-mm machine-guns. Structurally, the A-3 featured a fuselage extended by 5 feet 3 inches aft of the wing in order to improve stability, and engine nacelles were some 8 inches longer and redesigned to reduce the possible causes of fire.
Late in 1942, I. Gruppe of Ergtinzungs Kampfgeschwader (Replacement or Reserve Training Bomber Geschwader) K.G. 50, based at Brandenburg/ Briest, received the first examples of the A-3. During the all-out German effort to supply troops cut-off in the Stalingrad pocket from the air, the He 177s of K.G. 50 were pressed into use in the transport role. But with only makeshift servicing arrangements—and subjected to the full rigours of the Russian winter—the unit was able to achieve little. There was little room for stowing supplies in the bomb-bay, and the He 177 made an inefficient transport aircraft. After a few resupply sorties, the He 177s reverted to the bomber role—but with hardly greater success. The old problem of engine fires still had not been solved completely and Several bombers were lost to this cause. When, in February 1943, the Stalingrad defenders finally surrendered, the surviving He 177s returned to Germany.
One hundred and seventy He 177 A-3s were built before production of the sub-series was phased-out in favour of the A-5. The A-4 was a high-altitude project with four separate engines; it did not go into production.
The first He 177 A-5 left the Heinkel factory in February 1943. This sub-type was powered by two DB 610 motors, each comprising a coupled pair of DB 605s. The combination developed a maximum output of 3,100 h.p. at 7,000 feet; an increase which went some way to overcoming the general lack of
power of earlier versions of the He 177. However, many of the problems associated with the earlier coupled engine arrangement remained. During 1943 the plants at Orienburg and Warnemunde turned out a total of 261 examples of the A-5.
That the He 177 still had its faults, the German% Air Ministry admitted ; but the need was such that at last the bomber was to be issued to front-line units for operations.
If historians are agreed on one thing regarding the He 177, it is that this aircraft had no effect at all on the course of World War Two. Well over 1,000 of these bombers were built, but it is doubtful whether more than 200 of them were ever used on operations. During the latter part of the conflict, Allied aircraft often brought back reconnaissance photographs of parks in Germany littered with He 177s; the subsequent interpretation reports often stated that ". . . absence of track activity suggests that these aircraft are not being worked on."
When the war ended, the 900 or so He 177s remaining—most of them brand-new and unused—were carted off to the scrapyards. It was an ignominious ending to the saga of the He 177. But, in fact, the notion of a German strategic bomber force—to rival those of the Western Allies—had been killed stone dead nearly a year before the end of the conflict.
DEVELOPMENT
In 1936 the company of Ernst Heinkel AG received details of the new Bomber A requirement from the Reichsluftfahrtministerium (RLM—German Air Ministry). This specification called for an aircraft with a maximum speed of 335 m.p.h., able to carry 4,400 pounds of bombs out to a radius of 1,000 miles or, alternatively, 2,200 lb. out to 1,800 miles. All-in-all, this was a formidable specification, calling as it did for an aircraft able to outrun any fighter and outperform, by a considerable margin, any bomber then in service. In order to meet it Heinkel's chief designer, Siegfried Guenther, had to employ several hitherto untried features.
For example, to power his new bomber Guenther needed a pair of 2,000 h.p. aero-motors. But, at the time, the Germans possessed no aero-engine which developed such power. To overcome this problem—without resorting to four smaller motors and their attendant drag penalty—the Heinkel designer decided to employ the new Daimler Benz DB 606 double engine. This comprised a pair of DB 601 liquid-cooled 12-cylinder inverted-vee inline motors—mounted side-by-side in a single nacelle—driving a single propeller through a connecting gear train and clutch arrangement. Two of the new DB 606s, each of which
developed 2,600 h.p. for take-off, were to power the He 177.
In order to refine the aerodynamic cleanliness of his design even further, Guenther decided to dispense with the usual system of drag-producing radiators for the engine coolant. Instead, he planned to employ evaporative-cooling. The DB 601 had been designed to run very hot. In the evaporative-cooling system—pioneered by the Heinkel company—the coolant water was pressurized; thus, it was possible to heat it to about 110° C before steam began to form in the engine. The super-heated water was then ducted away and depressurized, at which point steam formed. Then, the water was separated and returned to the motor. At the same time, the residual steam was fed through pipes in the wing and cooled by the airflow. After resultant condensation had taken place, the water from the wing pipes was also returned to the engine. During flight tests, this evaporative-cooling system worked quite well on a modified Heinkel He 100 single-seat fighter. However, even before the design of the He 177 was finalized, it was clear that such a system would be incapable of dealing with the vast amount of heat generated by the DB 606. So Guenther had to abandon this cooling system for his bomber and revert to the more conventional radiator and its attendant drag.
In his quest for an aerodynamically "clean" design, Guenther's original intention had been to defend his new bomber with three remotely-controlled gun barbettes and a conventionally-manned tail turret. Compared with the usual form of manned turret, the remotely-controlled barbette traded technical complexity for reduction of size and drag.
Further, it held the advantage that the gunner could be installed in a position where he would have the
best possible view, and where he would be less likely to
be blinded by the flash from his own guns. But, like the evaporative cooling system, the remotely-con-
trolled gun barbette was not sufficiently developed in 1939. So the designer had to revert to the heavier manned turret and accept the resultant drag penalty.
The next problem came when the Technical Office at the German Air Ministry decided that it required the He 177 to be able to dive-bomb. Certainly there were great advantages to be gained if it could because the contemporary German horizontal bombsight in service gave poor results. Dive-bombing was much more accurate, but the manoeuvre and subsequent pull-out placed a great strain on the airframe. Inevitably, the airframe had to be strengthened to meet the new loads dive-bombing would impose—with a resultant weight penalty.
All these moves combined to push the He 177 design round a vicious circle. In each case the extra weight or drag meant that the bomber flew slower for the same power setting. Consequently, it would use more fuel in covering a given distance and would require more to be carried if the He 177 were to meet its original range specification. So, additional fuel tanks had to be fitted into the wings and the wings had to be further strengthened to take this extra weight. Thus, each move provided a further twist to the weight-drag-speed-range-more weight spiral. In the end, the increase in weight reached such proportions that Guenther had to redesign the main undercarriage. Instead of the originally projected single wheel leg under each engine nacelle, he had to
incorporate a double leg system—the outer leg retracted into the wing outboard of the nacelle and, similarly, the inner leg retracted into the wing inboard of the nacelle.
On November 19, 1939, Dipl. Ing. Franke, chief of the RLM Rechlin flight test centre, lifted the prototype He 177 into the air for the first time—being airborne for only twelve minutes. This brief beginning was forced on Franke. He had to return with engines overheating. Also, the test pilot complained of the bomber's poor stability and tendency to aileron flutter.
The second prototype—generally similar to the first—made its first flight Soon™ afterwards. Following Franke's initial flight, the first prototype's tail surfaces were increased in size. But this modification had not been incorporated in the second before it began initial flight trials. During subsequent diving tests, the aircraft developed severe control flutter and broke-up in the air. Test pilot Rickert failed to bale out and was killed. Following this incident, the tail surfaces of the third, fourth and fifth prototypes—which were now nearing completion—also were increased in size.
When the diving trials were resumed, the fourth prototype failed to pull out of a dive and crashed into the Baltic; the cause was put down to a malfunction of the propeller-pitch mechanism. Shortly afterwards, and early in 1941, the fifth prototype suffered a double engine fire while simulating a low-level attack; it crashed into the ground and exploded.
This was an inauspicious start for the new German heavy bomber. Three out of the first five prototypes had crashed during the early test programme. The Heinkel company put in hand a number of design changes to overcome the various failings in their product.
Even so, one problem was to attend the bomber almost throughout its service—that of engine overheating and resultant fires. The causes of this were many and varied. At first, the lubrication to the DB 606 engines was poor; as a result, all-too-often the connecting rod bearings would seize-up, causing the
rods to smash through the crank case which in turn allowed the lubricating oil to spill over the red-hot engine exhausts. Moreover, if the throttles were handled roughly, the fuel-injectors would leak and allow neat Benzin (gasoline or petrol) to run down into the bottom of the engine bay. If the aircraft was flying in a high angle-of-attack attitude—for example, when landing or flying at high altitude—sometimes the fuel would drip down onto the engine exhaust pipes. In either case the outcome was the same—fire.
During the flight test programme other, but less lethal, problems arose. Soon™, it became clear that whatever the wishes of RLM Technical Office, the He 177 was much too big for a dive-bomber. To dive the He 177, the pilot had to cut his speed right back before he could force the nose down. Almost as Soon™ as he had established the dive, it was time to initiate the pull out. And in spite of the specially strengthened airframe, it was still all too easy to overstress the bomber during the dive-attack manoeuvre. Fortunately, by the time this deficiency became clear, the need for the He 177 to dive had passed. The new Lotfe Bombenvisier (tachometric bombsight) now
about to enter service promised accuracies in horizontal-bombing of the same order of those obtained during dive-bombing attacks. As a result, the dive-brakes were omitted from all aircraft built after the initial pre-production batch.
The initial pre-production run totalled 35 aircraft; and these He 177 A-0-series, in almost every case, were used to explore various aspects of both the "performance envelope" and the bomber's technical features. Then came the first production version, the He 177 A-1. A total of 130 examples of this series left the production line at Warnemunde between March 1942 and June 1943. But, with its teething troubles still uncured, the He 177 was still a long way from being suitable for operational use as a bomber. In the event, almost all the A-ls were relegated to second-line duties; even after 34 had been delivered to the First Gruppe of K.G.40 at Bordeaux/Merignac in the summer of 1942—in a premature attempt to introduce the type into operational service—they were withdrawn shortly afterwards.
The armament of the pre-production He 177 A-0 had comprised a single power-operated gun turret to the rear of the cabin, three flexible mountings in the nose and one at the extreme tail. The He 177 A-1 carried one of the newly-developed remotely-controlled barbettes above the centre fuselage in place of the earlier powered gun turret; the latter mounted a single 13-mm MG 131 machine-gun was aimed from a sighting position to the rear of the cabin. The flexible gun positions remained unchanged, as did the rear mounting.
The next production version of the A-series—the He 177 A-3—featured an additional powered manned gun position. The new dorsal turret, amidships, mounted a single 13-mm MG 131. Also, the barbette
was enlarged to house two instead of one 13-mm machine-guns. Structurally, the A-3 featured a fuselage extended by 5 feet 3 inches aft of the wing in order to improve stability, and engine nacelles were some 8 inches longer and redesigned to reduce the possible causes of fire.
Late in 1942, I. Gruppe of Ergtinzungs Kampfgeschwader (Replacement or Reserve Training Bomber Geschwader) K.G. 50, based at Brandenburg/ Briest, received the first examples of the A-3. During the all-out German effort to supply troops cut-off in the Stalingrad pocket from the air, the He 177s of K.G. 50 were pressed into use in the transport role. But with only makeshift servicing arrangements—and subjected to the full rigours of the Russian winter—the unit was able to achieve little. There was little room for stowing supplies in the bomb-bay, and the He 177 made an inefficient transport aircraft. After a few resupply sorties, the He 177s reverted to the bomber role—but with hardly greater success. The old problem of engine fires still had not been solved completely and Several bombers were lost to this cause. When, in February 1943, the Stalingrad defenders finally surrendered, the surviving He 177s returned to Germany.
One hundred and seventy He 177 A-3s were built before production of the sub-series was phased-out in favour of the A-5. The A-4 was a high-altitude project with four separate engines; it did not go into production.
The first He 177 A-5 left the Heinkel factory in February 1943. This sub-type was powered by two DB 610 motors, each comprising a coupled pair of DB 605s. The combination developed a maximum output of 3,100 h.p. at 7,000 feet; an increase which went some way to overcoming the general lack of
power of earlier versions of the He 177. However, many of the problems associated with the earlier coupled engine arrangement remained. During 1943 the plants at Orienburg and Warnemunde turned out a total of 261 examples of the A-5.
That the He 177 still had its faults, the German% Air Ministry admitted ; but the need was such that at last the bomber was to be issued to front-line units for operations.