Heinkel He 100
Encyclopedia
The Heinkel He 100 was a German
pre-World War II
fighter aircraft
design from Heinkel
. Although it proved to be one of the fastest fighter aircraft in the world at the time of its development, the design was not ordered into series production. Approximately 19 prototype
s and pre-production machines were built. The reason for the failure of the He 100 to reach production status is subject to debate. None are known to have survived the war.
Officially, the Luftwaffe
rejected the He 100 to concentrate single-seat fighter development on the Messerschmitt Bf 109
. Following the adoption of the Bf 109 and Bf 110 as the Luftwaffes standard fighter types, the RLM announced a "rationalization" policy that placed fighter development at Messerschmitt and bomber
development at Heinkel.
Because there are no surviving examples, and since many factory documents - including all blueprints for the He 100 - were destroyed during a bombing raid, there is limited specific information about the design and its unique systems.
of the Bf 109 as its next single-seat fighter over the He 112
, Ernst Heinkel became interested in a new fighter that would leap beyond the performance of the Bf 109 as much as the Bf 109 had over the biplane
s it replaced. Other German designers had similar ambitions, including Kurt Tank
at Focke-Wulf. There was never an official project on the part of the RLM, but Rudolf Lucht felt that new designs were important enough to fund the projects from both companies to provide "super-pursuit" designs for evaluation. This would result in the single-engined He 100 fighter, and the promising twin-engine Fw 187 Falke
Zerstörer-style heavy fighter
, both reaching the flight stage of development.
Walter Günter, one half of the famous Günter brothers, looked at the existing He 112, which had already been heavily revised into the He 112B version and decided it had reached the end of its evolution. He started over with a completely new design, Projekt 1035. Learning from past mistakes on the 112 project, the design was to be as easy to build as possible yet 700 km/h (440 mph) was a design goal. To ease production, the new design had considerably fewer parts than the 112 and those that remained contained fewer compound curves. In comparison, the 112 had 2,885 parts and 26,864 rivets, while the P.1035 was made of 969 unique parts with 11,543 rivets. The new straight-edged wing was a source of much of the savings; after building the first wings, Otto Butter reported that the reduction in complexity and rivet count (along with the Butter brothers' own explosive rivet system) saved an astonishing 1,150 man hours per wing.
The super-pursuit type was not a secret, but Ernst Heinkel preferred to work in private and publicly display his products only after they were developed sufficiently to make a stunning first impression. As an example of this, the mock-up for the extremely modern-looking He 100 was the subject of company Memo No.3657 on 31 January that stated: The mock-up is to be completed by us... as of the beginning of May... and be ready to present to the RLM... and prior to that no one at the RLM is to know of the existence of the mock-up.
Walter was killed in a car accident on 25 May 1937, and the design work was taken over by his twin brother Siegfried, who finished the final draft of the design later that year. Heinrich Hertel, a specialist an aircraft structures, also played a prominent role in the design. At the end of October the design was submitted to the RLM, complete with details on prototype
s, delivery dates and prices for three aircraft delivered to the Rechlin
test center. At this point, the aircraft was referred to as the He 113, but the "13"
in the name was apparently enough to prompt Ernst Heinkel to ask for it to be changed to the He 100. It is reported that Ernst Heinkel lobbied for this "round" number in hopes it would improve the design's chances for production.
, the absence of struts and other drag-inducing supports on the tail. The landing gear
(including the tailwheel) was retractable and completely enclosed in flight.
There was also a serious shortage of advanced aero engines in Germany during the late 1930s. The He 100 used the same Daimler-Benz DB 601
engine as the Messerschmitt Bf 109 and Bf 110, and there was insufficient capacity to support another aircraft using the same engine. The only available alternate engine was the Junkers Jumo 211
, and Heinkel was encouraged to consider its use in the He 100. However, the early Jumo 211 then available did not use a pressurized cooling system, and it was therefore not suitable for the He 100's evaporative cooling system. Furthermore, a Jumo 211-powered He 100 would not have been able to outperform the contemporary DB 601-powered Bf 109 because the supercharger
on the early Jumo 211 was not fully shrouded. In order to reduce weight and frontal area, the engine was mounted directly to the forward fuselage
, which was strengthened and literally tailored to the DB 601, as opposed to conventional mounting on engine bearers. The cowling
was very tight-fitting, and as a result the aircraft has something of a slab-sided appearance.
In order to provide as much power as possible from the DB 601, the 100 used exhaust ejectors for a small amount of additional thrust. The supercharger inlet was moved from the normal position on the side of the cowling to a location in the leading edge
of the left wing, which was also a feature of the earlier He 119
. Although cleaner-looking, the long, curved induction pipe most likely negated any benefit.
For the rest of the designed performance increase, Walter turned to the somewhat risky and still experimental method of cooling the engine via evaporative cooling. Such systems had been in vogue in several countries at the time. Heinkel and the Günter brothers were avid proponents of the technology, and had previously used it on the He 119 with promising results. Evaporative or "steam" cooling promised a completely drag-free cooling system. The DB 601 was a pressure-cooled engine in that the water/glycol coolant was kept in liquid form by pressure, even though its temperature was allowed to exceed the normal boiling point. Heinkel's system took advantage of that fact and the cooling energy loss associated with the phase change of the coolant as it boils. Following is a description of what is known about the cooling system used in the final version of Heinkel's system. It is based entirely on careful study of surviving photographs of the He 100, since no detail plans survive. The earlier prototypes varied, but they were all eventually modified to something close to the final standard before they were exported to the Soviet Union
.
Coolant exits the DB 601 at two points located at the front of the engine and at the base of each cylinder block casting immediately adjacent to the crank case. In the Heinkel system, an "S"-shaped steel pipe took the coolant from each side of the engine to one of two steam separators mounted alongside the engine's reduction gear and immediately behind the propeller spinner. The separators, designed by engineers Jahn and Jahnke, accepted the water at about 110 °C (230 °F) and 1.4 bar (20.3 psi) of pressure. The vertically-mounted, tube-shaped separators contained a centrifugal impeller at the top connected to an impeller-type scavenge pump at the bottom. The coolant was expanded through the upper impeller where it lost pressure, boiled and cooled. The by product was mostly very hot coolant and some steam. The liquid coolant was slung by the centrifugal impeller to the sides of the separator where it fell by gravity to the bottom of the unit. There, it was pumped to header tanks located in the leading edges of both wings by the scavenge pump. The presence of the scavenge pump was necessary to ensure the entire separator did not simply fill up with high-pressure coolant coming from the engine.
Existing photographs of the engine bay of the final pre-production version of this system clearly show the liquid coolant from both separators was piped along the bottom left side of the engine compartment and into the right wing. The header tanks were located in the outer wing panels ahead of the main spar
and immediately outboard of the main landing gear bays. The tanks extended over the same portion of the outer panel's span as the outer flap
s. Coolant from the right wing header tank was pumped by a separate, electrical pump to the left wing header tank. Along the way from the right to left wing, the coolant passed through a conventional radiator
mounted on the bottom of the fuselage. That radiator was retractable and intended for use only during ground-running or low-speed flight. Nevertheless, coolant passed through it whenever the engine was running and regardless of whether it was extended or retracted. In the retracted position, the radiator offered little cooling, but some heat was exchanged into the aft fuselage. Finally, a return tube connected the left wing's header tank to that on the right. This allowed the coolant to equalize between the two header tanks and circulate through the retractable radiator. The engine drew coolant directly from both header tanks through two separate pipes that ran through the main landing gear bays, up the firewall
at the back of the engine compartment, and into the usual coolant intakes located at the top rear of the engine.
The steam collected in the separators was vented separately from the liquid coolant. The steam did not require mechanical pumping to do this, and the build up of pressure inside the separator was sufficient. The steam was piped down the lower right side of the engine bay and led into the open spaces between the upper and lower wing skins of the outer wing panels. There, it further expanded and condensed by cooling through the skins. The entire outer wing, both ahead of and behind the main spar, was used for this purpose covering that portion of the span containing the aileron
s (the fuel was also carried entirely in the wings and occupied the areas behind the main spar in the center section and immediately ahead of the outboard flaps). The condensate was scavenged by electrically-driven centrifugal pumps and fed to the header tanks. Sources indicate as many as 22 separate pumps were used for this, each with their own attendant pilot light on the instrument panel, but it is not clear whether that number includes all of the pumps in the entire water- and oil-cooling
systems or merely the number of pumps in the outer wing panels. The former is generally accepted.
Some sources state the outer wing panels used double skins top and bottom with the steam being ducted into a thin space between the outer and inner skins for cooling. A double-skinned panel was used in the oil
cooling system, but surviving photographs of the wings demonstrate they were conventionally single-skinned, and the coolant was simply piped into the open spaces of the structure. Double skinning over such an extensive area would have made the aircraft unacceptably heavy. Furthermore, there was no access to the inner structure to repair damage, such as a bullet hole, from the inside as would be needed if the system used a double skin. A similar system was used by the earlier Supermarine Type 224. Contrary to assertions in some references, all of the He 100s that were built used the evaporative cooling system described above. A derivative of this system was also intended for a late-war project based on the He 100, designated P.1076.
Unlike the cooling fluid, oil cannot be allowed to boil. This presented a particular problem with DB 601-series engines, because oil is sprayed against the bottom of the pistons, resulting in a considerable amount of heat being transferred to the oil as opposed to the coolant. The He 100's oil cooling system was conceptually similar to the water cooling system in that vapor was generated using the heat of the oil and condensed back to liquid by surface cooling through the skins of the airframe. A heat exchanger was used to cool the oil by boiling ethyl alcohol. The oil itself was simply piped to and from this exchanger, which was apparently located in the aft fuselage. The alcohol vapor was piped into the fixed portions of the horizontal and vertical stabilizer
s and into a double-skinned portion of the upper-aft fuselage behind the cockpit. This fuselage "turtle deck" panel was the only double-skinned portion of the aircraft's cooling system. The use of a double-skinned panel was possible here because the inside of panel was accessible in the event of repair. Condensed alcohol was collected by a series of bellows pumps and returned to a single header tank that fed the heat exchanger. Some sources speculate that a small air intake located at the bottom front of the engine cowl was used for an auxiliary oil cooler. No such cooler was fitted, nor was there room for one at that point. This small inlet served simply to admit cool air into what was a very hot portion of the engine bay. Immediately above this vent were the two steam separators, and immediately behind it were the hot coolant pipes coming from the separators.
. The third prototype crashed during testing. The record flight was made using a special version of the DB 601 engine that offered 2010 kW and had a service life of just 30 minutes. Prior to setting this absolute speed record over a short, measured course, Ernst Udet flew the second prototype to a 100 km (62.1 mi) closed course record of 634.32 km/h (394.1 mph) on 5 June 1938. Udet's record was apparently set using a standard DB 601a engine.
There is a debate regarding the correct designation of the He 100 aircraft actually built. One group holds that all of the machines were either "Versuchs" or "trials" prototypes and pre-production "A-0" series machines. This is consistent with the RLM's normal practice of changing an aircraft's sub-designation only with a significant redesign, such as an engine change. All of the He 100s built were essentially the same, and even the prototypes were later updated to the production standard before they were exported to the Soviet Union. The second group holds that the Heinkel factory intended "A," "B," "C" and "D" series aircraft, and the final version was the "D." This camp also holds that there were separate "D-0" and "D-1" production runs, although in extremely limited numbers. Most literature follows the latter school of thought, Since the He 100 was never accepted for operational use by the Luftwaffe, it is unlikely there was ever an official resolution of this issue. The separate letter designations "A" through "D" appear to have come from internal Heinkel documents.
, which resulted in landing speeds so great that they often had to use brakes right up to the last 100 m (328.1 ft) of the runway. The ground crews also disliked the design, complaining about the tight cowling which made servicing the engine difficult. But the big problem turned out to be the cooling system, largely to no one's surprise. After a series of test flights V1 was sent to Rechlin in March.
The second prototype addressed the stability problems by changing the vertical stabilizer from a triangular form to a larger and more rectangular form. The oil-cooling system continued to be problematic, so it was removed and replaced with a small semi retractable radiator below the wing. It also received the still-experimental DB 601M engine which the aircraft was originally designed for. The M version was modified to run on "C3" fuel at 100 octane, which would allow it to run at higher power ratings in the future.
V2 was completed in March, but instead of moving to Rechlin it was kept at the factory for an attempt on the 100 km (62 mi) closed circuit speed record. A course was marked out on the Baltic coast between Wustrow and Müritz, 50 km (30 mi) apart, and the attempt was to be made at the aircraft's best altitude of 5500 m (18,044.6 ft). After some time cleaning out the bugs the record attempt was set to be flown by Captain Herting, who had previously flown the aircraft several times.
At this point Ernst Udet showed up and asked to fly V2, after pointing out he had flown the V1 at Rechlin. He took over from Herting and flew the V2 to a new world 100 km (62.1 mi) closed circuit record on 5 June 1938, at 634.73 km/h (394.4 mph). Several of the cooling pumps failed on this flight as well, but Udet wasn't sure what the lights meant and simply ignored them.
The record was heavily publicized, but in the press the aircraft was referred to as the "He 112U". Apparently, the "U" stood for "Udet". At the time the 112 was still in production and looking for customers, so this was one way to boost sales of the older design. V2 was then moved to Rechlin for continued testing. Later in October, the aircraft was damaged on landing when the tail wheel didn't extend, and it is unclear if the damage was repaired.
The V3 prototype received the clipped racing wings, which reduced span and area from 30 inch and 14.4 square metres (17.2 sq yd), to 24 inch and 11 m² (13.2 sq yd). The canopy was replaced with a much smaller and more rounded version, and all of the bumps and joints were puttied over and sanded down. The aircraft was equipped with the 601M and flown at the factory.
In August, the DB 601R engine arrived from Daimler-Benz and was installed. This version increased the maximum rpm from 2,200 to 3,000, and added methyl alcohol to the fuel mixture to improve cooling in the supercharger and thus increase boost. As a result, the output was boosted to 1324 kW, although it required constant maintenance and the fuel had to be drained completely after every flight. The aircraft was then moved to Warnemünde for the record attempt in September.
On one of the pre-record test flights by the Heinkel chief pilot, Gerhard Nitschke, the main gear failed to extend and ended up stuck half open. Since the aircraft could not be safely landed it was decided to have Nitschke bail out and let the aircraft crash in a safe spot on the airfield. Gerhard was injured when he hit the tail on the way out, and made no further record attempts.
V4 was to have been the only "production" prototype and was referred to as the "100B" model (V1 through V3 being "A" models). It was completed in the summer and delivered to Rechlin, so it wasn't available for modification into racing trim when V3 crashed. Although the aircraft was unarmed it was otherwise a service model with the 601M, and in testing over the summer it proved to be considerably faster than the Bf 109. At sea level, the aircraft could reach 560 km/h (348 mph), faster than the Bf 109E's speed at its best altitude. At 6560 ft (1,999.5 m), it improved to 610 km/h (379 mph), topping out at 669 km/h (415.7 mph) at 5000 m (16,404.2 ft) before falling again to 641 km/h (398.3 mph) at 8000 m (26,246.7 ft). The aircraft had flown a number of times before its landing gear collapsed while standing on the pad on 22 October. The aircraft was later rebuilt and was flying by March 1939.
Although V4 was to have been the last of the prototypes in the original plans, production was allowed to continue with a new series of six aircraft. One of the airframes was selected to replace V3, and as luck would have it V8 was at the "right point" in its construction and was completed out of turn. It first flew on 1 December but this was with a standard DB 601Aa engine. The 601R was then put in the aircraft on 8 January 1939, and moved to a new course at Oranienberg. After several shakedown flights, Hans Dieterle flew to a new record on 30 March 1939, at 746.6 km/h (463.9 mph). Once again the aircraft was referred to as the He 112U in the press. It is unclear when happened to V8 in the end; it may have been used for crash testing.
V5 was completed like V4, and first flew on 16 November. It was later used in a film about V8's record attempt, in order to protect the record breaking aircraft. At this point, a number of changes were made to the design resulting in the "100C" model, and with the exception of V8 the rest of the prototypes were all delivered as the C standard.
V6 was first flown in February 1939, and after some test flights at the factory it was flown to Rechlin on 25 April. There it spent most of its time as an engine testbed. On 9 June, the gear failed inflight, but the pilot managed to land the aircraft with little damage, and it was returned to flying condition in six days.
V7 was completed on 24 May with a change to the oil cooling system. It was the first to be delivered with armament, consisting of two 20 millimetre (0.78740157480315 in) MG FF cannon
s in the wings and four 7.92 mm (.30-caliber) MG 17 machine gun
s arranged around the engine cowling. This made the He 100 the most heavily armed fighter of its day. V7 was then flown to Rechlin where the armament was removed and the aircraft was used for a series of high speed test flights.
V9 was also completed and armed, but was used solely for crash testing and was "tested to destruction". V10 was originally to suffer a similar fate, but instead ended up being given the racing wings and canopy of the V8 and displayed in the German Museum in Munich as the record-setting "He 112U". It was later destroyed in a bombing attack.
Overheating problems and general failures with the cooling system motors continued to be a problem. Throughout the testing period, failures of the pumps ended flights early, although some of the test pilots simply starting ignoring them. In March, Kleinemeyer wrote a memo to Ernst Heinkel about the continuing problems, stating that Schwärzler had asked to be put on the problem.
Another problem that was never cured during the prototype stage was a rash of landing gear problems. Although the wide-set gear should have eliminated the collapse of landing gears that plagued the Bf 109, especially in the difficult takeoffs and landings, the He 100's landing gear was not built to withstand heavy use, and as a result they were no improvement over the Bf 109. V2, 3, 4 and 6 were all damaged to various degrees due to various gear failures, a full half of the prototypes.
The D-0 was similar to the earlier C models, with a few notable changes. Primary among these was a larger vertical tail in order to finally solve the stability issues. In addition, the cockpit
and canopy were slightly redesigned, with the pilot sitting high in a large canopy with excellent vision in all directions. The armament was reduced from the C model to one 20 mm (0.78740157480315 in) MG FF/M in the engine V firing through the propeller spinner, and two 7.92 mm (.30-caliber) MG 17s in the wings close to the fuselage.
The three D-0 aircraft were completed by the summer of 1939 and stayed at the Heinkel Marienehe plant for testing. They were later sold to the Japanese Imperial Navy to serve as pattern aircraft for a production line, and were shipped there in 1940. They received the designation AXHe.
.
But the big change was the eventual abandonment of the surface cooling system, which proved to be too complex and failure prone. Instead an even larger version of the retractable radiator was installed, and this appeared to completely cure the problems. The radiator was inserted in a "plug" below the cockpit, and as a result the wings were widened slightly.
While the aircraft didn't match its design goal of 700 km/h (435 mph) once it was loaded down with weapons, the larger canopy and the radiator, it was still capable of speeds in the 644 km/h (400.2 mph) range. A low drag airframe is good for both speed and range, and as a result the He 100 had a combat radius between 900 kilometre compared to the Bf 109's 600 km (372.8 mi). While not in the same league as the later escort fighters, this was at the time a superb range and may have offset the need for the Bf 110 to some degree. Finally, there were allegations that politics played a role in killing the He 100.
By this point, the war was underway, and as the Luftwaffe would not purchase the aircraft in its current form, the production line was shut down.
The remaining 12 He 100 D-1 fighters were used to form Heinkel's Marienehe factory defense unit, flown by factory test pilots. They replaced the earlier He 112s that were used for the same purpose, and the 112s were later sold off. At this early stage in the war, there were no bombers venturing that far into Germany, and it appears that the unit never saw action. The eventual fate of the D-1s remains unknown. The aircraft were also put to an interesting propaganda
/disinformation
role, as the supposed Heinkel He 113
.
The Soviets were particularly interested in the surface cooling system, having built the experimental Ilyushin I-21
with evaporative cooling, and in order to gain experience with it they purchased the six surviving prototypes (V1, V2, V4, V5, V6 and V7). After arriving in the USSR they were passed onto the TsAGI
institute for study; there they were analyzed with He 100 features influencing a number of Soviet designs, notably the LaGG-3 and MiG-1
. Although the surface cooling system wasn't copied, the addition of larger Soviet engines made up for the difference and the LaGG-3 was a reasonably good performer. It's perhaps ironic that German aircraft would later be shot down by German inspired aircraft.
The Japanese were also looking for new designs, notably those using inline engines where they had little experience. They purchased the three D-0s for 1.2 million RM, as well as a license for production and a set of jigs for another 1.6 million RM. The three D-0s arrived in Japan in May 1940 and were re-assembled at Kasumigaura. They were then delivered to the Japanese Naval Air Force where they were re-named AXHei, for "Experimental Heinkel Fighter". When referring to the German design the aircraft is called both the He 100 and He 113, with at least one set of plans bearing the later name.
In tests, the Navy was so impressed that they planned to put the aircraft into production as soon as possible as their land-based interceptor
; unlike every other armed forces organization in the world, the Army and Navy both fielded complete land-based air forces. Hitachi won the contract for the aircraft and started construction of a factory in Chiba for its production. With the war in full swing in Europe, however, the jigs and plans never arrived. Why this wasn't sorted out is something of a mystery, and it appears there isn't enough information in the common sources to say for sure what happened.
(a version of the Focke-Wulf Fw 190
) was currently in limited production for just this task but Heinkel was contracted to design an aircraft, and Siegfried Günter was placed in charge of the new Projekt 1076.
The resulting design was similar to the He 100, but the many detail changes resulted in an aircraft that looked all new. It sported a new and longer wing for high-altitude work, which lost the gull wing bend and was swept
forward slightly at 8°. Flaps or ailerons spanned the entire trailing edge
of the wing giving it a rather modern appearance. The cockpit was pressurized
for high-altitude flying, and covered with a small bubble canopy
that was hinged to the side instead of sliding to the rear. Other changes that seem odd in retrospect is that the gear now retracted outward like the original Bf 109, and the surface cooling system was re-introduced. Planned armament was one 30 mm (1.2 in) MK 103 cannon
firing through the propeller hub, and two wing mounted 30mm MK 108 cannon
s.
The use of one of three different engines was planned: the DB 603M with 1361 kW, the DB 603N with 2051 kW, or the Jumo 213E
, designed from the start to have the same fluid service locations as the DB 603, with 1287 kW. The 603M and 213E both supplied 1545 kW using MW-50 water injection. Performance with the 603N was projected to be 880 km/h (546.8 mph), in the same class as the Messerschmitt Me 262
pioneering jet fighter then entering evaluationary service, which would have stood as a record for many years even when faced with dedicated racing machines. Performance would still be excellent even with the far more likely 1500 kW class engines, the 603M was projected to give it the high speed of 855 km/h (531.3 mph).
These figures are somewhat suspect though, and are likely just optimistic guesses that could not have been met - something Heinkel was famous for. Propellers lose efficiency as they approach the speed of sound, and eventually they no longer provide an increase in thrust for an increase in engine power. Even the advanced counter-rotating VDM design is unlikely to have been able to effect this problem too much.
The design apparently received low priority, and it was not completed by the end of the war. Siegfried Günter later completed the detailed drawings and plans for the Americans in mid-1945.
in 1943. Nevertheless the aircraft was not ordered into production. The reasons the He 100 wasn't put into service seems to vary depending on the person telling the story, and picking any one version results in a firestorm of protest.
Some say it was politics that killed the He 100. However, this seems to stem primarily from Heinkel's own telling of the story, which in turn seems to be based on some general malaise over the He 112 debacle. The fact is that Heinkel was well respected within the establishment regardless of Messerschmitt's success with the Bf 109 and Bf 110, and this argument seems particularly weak.
Others blame the bizarre production line philosophy of the RLM, which valued huge numbers of single designs over a mix of different aircraft. This too seems somewhat suspect considering that the Fw 190 was purchased shortly after this story ends.
For these reasons, it seems safe to accept the RLM version of the story largely at face value; that the production problems with the DB series of engines was so acute that all other designs based on the engine were canceled. At the time the DB 601 engines were being used in both the Bf 109 and Bf 110 aircraft, and Daimler couldn't keep up with those demands alone. The RLM eventually forbade anyone but Messerschmitt from receiving any DB 601s, leading to the shelving of many designs from a number of vendors. Furthermore, the Bf 109 and Bf 110 were perceived as superior to their likely opponents, which made the requirement for an even more powerful aircraft less imperative.
The only option open to Heinkel was a switch to another engine, and the RLM expressed some interest in purchasing such a version of the He 100. At the time the only other useful inline was the Junkers Jumo 211
, and even that was in short supply. However, the design of the He 100 made adaptation to the 211 difficult; both the cooling system and the engine mounts were designed for the 601, and a switch to the 211 would have required a redesign. Heinkel felt it wasn't worth the effort considering the aircraft would end up with inferior performance, and so the He 100 production ends on that sour note.
For this reason more than any other the Focke-Wulf Fw 190
became the next great aircraft of the Luftwaffe, as it was based around the otherwise unused Bramo 139 (and later BMW 801
) radial engine. Although production of these engines was only starting, the lines for the airframes and aircraft could be geared up in parallel without interrupting production of any existing design, which was exactly what happened.
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...
pre-World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
design from Heinkel
Heinkel
Heinkel Flugzeugwerke was a German aircraft manufacturing company founded by and named after Ernst Heinkel. It is noted for producing bomber aircraft for the Luftwaffe in World War II and for important contributions to high-speed flight.-History:...
. Although it proved to be one of the fastest fighter aircraft in the world at the time of its development, the design was not ordered into series production. Approximately 19 prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
s and pre-production machines were built. The reason for the failure of the He 100 to reach production status is subject to debate. None are known to have survived the war.
Officially, the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
rejected the He 100 to concentrate single-seat fighter development on the Messerschmitt Bf 109
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...
. Following the adoption of the Bf 109 and Bf 110 as the Luftwaffes standard fighter types, the RLM announced a "rationalization" policy that placed fighter development at Messerschmitt and bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
development at Heinkel.
Because there are no surviving examples, and since many factory documents - including all blueprints for the He 100 - were destroyed during a bombing raid, there is limited specific information about the design and its unique systems.
Development
Following the selection by the RLMReich Air Ministry
thumb|300px|The Ministry of Aviation, December 1938The Ministry of Aviation was a government department during the period of Nazi Germany...
of the Bf 109 as its next single-seat fighter over the He 112
Heinkel He 112
The Heinkel He 112 was a fighter aircraft designed by Walter and Siegfried Günter. It was one of four aircraft designed to compete for the Luftwaffes 1933 fighter contract, which was eventually won by the Messerschmitt Bf 109...
, Ernst Heinkel became interested in a new fighter that would leap beyond the performance of the Bf 109 as much as the Bf 109 had over the biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
s it replaced. Other German designers had similar ambitions, including Kurt Tank
Kurt Tank
Kurt Waldemar Tank was a German aeronautical engineer and test pilot, heading the design department at Focke-Wulf from 1931-45. He designed several important aircraft of World War II, including the Focke-Wulf Fw 190 fighter aircraft.-Early life:Tank was born in Bromberg , Province of Posen...
at Focke-Wulf. There was never an official project on the part of the RLM, but Rudolf Lucht felt that new designs were important enough to fund the projects from both companies to provide "super-pursuit" designs for evaluation. This would result in the single-engined He 100 fighter, and the promising twin-engine Fw 187 Falke
Focke-Wulf Fw 187
The Focke-Wulf Fw 187 Falke was a German aircraft developed in the late 1930s. It was created by Kurt Tank as a twin-engine, high-performance fighter, but the Luftwaffe never saw a need for the design, which fitted "between" the Messerschmitt Bf 109 and Bf 110...
Zerstörer-style heavy fighter
Heavy fighter
A heavy fighter is a fighter aircraft designed to carry heavier weapons or operate at longer ranges. To achieve acceptable performance, most heavy fighters were twin-engined, and many had multi-place crews....
, both reaching the flight stage of development.
Walter Günter, one half of the famous Günter brothers, looked at the existing He 112, which had already been heavily revised into the He 112B version and decided it had reached the end of its evolution. He started over with a completely new design, Projekt 1035. Learning from past mistakes on the 112 project, the design was to be as easy to build as possible yet 700 km/h (440 mph) was a design goal. To ease production, the new design had considerably fewer parts than the 112 and those that remained contained fewer compound curves. In comparison, the 112 had 2,885 parts and 26,864 rivets, while the P.1035 was made of 969 unique parts with 11,543 rivets. The new straight-edged wing was a source of much of the savings; after building the first wings, Otto Butter reported that the reduction in complexity and rivet count (along with the Butter brothers' own explosive rivet system) saved an astonishing 1,150 man hours per wing.
The super-pursuit type was not a secret, but Ernst Heinkel preferred to work in private and publicly display his products only after they were developed sufficiently to make a stunning first impression. As an example of this, the mock-up for the extremely modern-looking He 100 was the subject of company Memo No.3657 on 31 January that stated: The mock-up is to be completed by us... as of the beginning of May... and be ready to present to the RLM... and prior to that no one at the RLM is to know of the existence of the mock-up.
Walter was killed in a car accident on 25 May 1937, and the design work was taken over by his twin brother Siegfried, who finished the final draft of the design later that year. Heinrich Hertel, a specialist an aircraft structures, also played a prominent role in the design. At the end of October the design was submitted to the RLM, complete with details on prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
s, delivery dates and prices for three aircraft delivered to the Rechlin
Rechlin-Lärz Airfield
Rechlin-Lärz Airfield is an airfield in the village of Rechlin, Mecklenburg-Western Pomerania, Germany, which is certified for aviation equipment up to 14 tons weight...
test center. At this point, the aircraft was referred to as the He 113, but the "13"
Triskaidekaphobia
Triskaidekaphobia is fear of the number ; it is a superstition and related to a specific fear of Friday the 13th, called paraskevidekatriaphobia or friggatriskaidekaphobia.The term was first used by Isador Coriat in Abnormal...
in the name was apparently enough to prompt Ernst Heinkel to ask for it to be changed to the He 100. It is reported that Ernst Heinkel lobbied for this "round" number in hopes it would improve the design's chances for production.
Design
In order to get the promised performance out of the aircraft, the design included a number of drag-reducing features. On the simple end was a well-faired cockpitCockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
, the absence of struts and other drag-inducing supports on the tail. The landing gear
Undercarriage
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...
(including the tailwheel) was retractable and completely enclosed in flight.
There was also a serious shortage of advanced aero engines in Germany during the late 1930s. The He 100 used the same Daimler-Benz DB 601
Daimler-Benz DB 601
|-See also:-Bibliography:* Mankau, Heinz and Peter Petrick. Messerschmitt Bf 110, Me 210, Me 410. Raumfahrt, Germany: Aviatic Verlag, 2001. ISBN 3-92550-562-8.* Neil Gregor Daimler-Benz in the Third Reich. Yale University Press, 1998-External links:...
engine as the Messerschmitt Bf 109 and Bf 110, and there was insufficient capacity to support another aircraft using the same engine. The only available alternate engine was the Junkers Jumo 211
Junkers Jumo 211
|-See also:-References:* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
, and Heinkel was encouraged to consider its use in the He 100. However, the early Jumo 211 then available did not use a pressurized cooling system, and it was therefore not suitable for the He 100's evaporative cooling system. Furthermore, a Jumo 211-powered He 100 would not have been able to outperform the contemporary DB 601-powered Bf 109 because the supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
on the early Jumo 211 was not fully shrouded. In order to reduce weight and frontal area, the engine was mounted directly to the forward fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
, which was strengthened and literally tailored to the DB 601, as opposed to conventional mounting on engine bearers. The cowling
Cowling
A cowling is the covering of a vehicle's engine, most often found on automobiles and aircraft.A cowling may be used:* for drag reduction* for engine cooling by directing airflow* as an air intake for jet engines* for decorative purposes...
was very tight-fitting, and as a result the aircraft has something of a slab-sided appearance.
In order to provide as much power as possible from the DB 601, the 100 used exhaust ejectors for a small amount of additional thrust. The supercharger inlet was moved from the normal position on the side of the cowling to a location in the leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
of the left wing, which was also a feature of the earlier He 119
Heinkel He 119
|-See also:-References:*Donald, David, "An Industry of Prototypes - Heinkel He 119", Wings of Fame, Volume 12. Aerospace Publishing Ltd., London, UK/AIRtime Publishing Inc., Westport, Connecticut, 1998, ISBN 1-86184-021-7 / 1-880588-23-4, pp. 30–34....
. Although cleaner-looking, the long, curved induction pipe most likely negated any benefit.
For the rest of the designed performance increase, Walter turned to the somewhat risky and still experimental method of cooling the engine via evaporative cooling. Such systems had been in vogue in several countries at the time. Heinkel and the Günter brothers were avid proponents of the technology, and had previously used it on the He 119 with promising results. Evaporative or "steam" cooling promised a completely drag-free cooling system. The DB 601 was a pressure-cooled engine in that the water/glycol coolant was kept in liquid form by pressure, even though its temperature was allowed to exceed the normal boiling point. Heinkel's system took advantage of that fact and the cooling energy loss associated with the phase change of the coolant as it boils. Following is a description of what is known about the cooling system used in the final version of Heinkel's system. It is based entirely on careful study of surviving photographs of the He 100, since no detail plans survive. The earlier prototypes varied, but they were all eventually modified to something close to the final standard before they were exported to the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
.
Coolant exits the DB 601 at two points located at the front of the engine and at the base of each cylinder block casting immediately adjacent to the crank case. In the Heinkel system, an "S"-shaped steel pipe took the coolant from each side of the engine to one of two steam separators mounted alongside the engine's reduction gear and immediately behind the propeller spinner. The separators, designed by engineers Jahn and Jahnke, accepted the water at about 110 °C (230 °F) and 1.4 bar (20.3 psi) of pressure. The vertically-mounted, tube-shaped separators contained a centrifugal impeller at the top connected to an impeller-type scavenge pump at the bottom. The coolant was expanded through the upper impeller where it lost pressure, boiled and cooled. The by product was mostly very hot coolant and some steam. The liquid coolant was slung by the centrifugal impeller to the sides of the separator where it fell by gravity to the bottom of the unit. There, it was pumped to header tanks located in the leading edges of both wings by the scavenge pump. The presence of the scavenge pump was necessary to ensure the entire separator did not simply fill up with high-pressure coolant coming from the engine.
Existing photographs of the engine bay of the final pre-production version of this system clearly show the liquid coolant from both separators was piped along the bottom left side of the engine compartment and into the right wing. The header tanks were located in the outer wing panels ahead of the main spar
Spar (aviation)
In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings whilst on the ground...
and immediately outboard of the main landing gear bays. The tanks extended over the same portion of the outer panel's span as the outer flap
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
s. Coolant from the right wing header tank was pumped by a separate, electrical pump to the left wing header tank. Along the way from the right to left wing, the coolant passed through a conventional radiator
Radiator (engine cooling)
Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine....
mounted on the bottom of the fuselage. That radiator was retractable and intended for use only during ground-running or low-speed flight. Nevertheless, coolant passed through it whenever the engine was running and regardless of whether it was extended or retracted. In the retracted position, the radiator offered little cooling, but some heat was exchanged into the aft fuselage. Finally, a return tube connected the left wing's header tank to that on the right. This allowed the coolant to equalize between the two header tanks and circulate through the retractable radiator. The engine drew coolant directly from both header tanks through two separate pipes that ran through the main landing gear bays, up the firewall
Firewall (construction)
A firewall is a fireproof barrier used to prevent the spread of fire between or through buildings, structures, electrical substation transformers, or within an aircraft or vehicle.- Applications :...
at the back of the engine compartment, and into the usual coolant intakes located at the top rear of the engine.
The steam collected in the separators was vented separately from the liquid coolant. The steam did not require mechanical pumping to do this, and the build up of pressure inside the separator was sufficient. The steam was piped down the lower right side of the engine bay and led into the open spaces between the upper and lower wing skins of the outer wing panels. There, it further expanded and condensed by cooling through the skins. The entire outer wing, both ahead of and behind the main spar, was used for this purpose covering that portion of the span containing the aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s (the fuel was also carried entirely in the wings and occupied the areas behind the main spar in the center section and immediately ahead of the outboard flaps). The condensate was scavenged by electrically-driven centrifugal pumps and fed to the header tanks. Sources indicate as many as 22 separate pumps were used for this, each with their own attendant pilot light on the instrument panel, but it is not clear whether that number includes all of the pumps in the entire water- and oil-cooling
Oil cooling
Oil cooling refers to a process whereby heat is displaced from a 'hotter' object, into a cooler oil and is the principle behind oil cooler devices. The oil carrying the displaced heat usually passes through a cooling unit such as a radiator or less commonly a gas decompresser...
systems or merely the number of pumps in the outer wing panels. The former is generally accepted.
Some sources state the outer wing panels used double skins top and bottom with the steam being ducted into a thin space between the outer and inner skins for cooling. A double-skinned panel was used in the oil
Motor oil
Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
cooling system, but surviving photographs of the wings demonstrate they were conventionally single-skinned, and the coolant was simply piped into the open spaces of the structure. Double skinning over such an extensive area would have made the aircraft unacceptably heavy. Furthermore, there was no access to the inner structure to repair damage, such as a bullet hole, from the inside as would be needed if the system used a double skin. A similar system was used by the earlier Supermarine Type 224. Contrary to assertions in some references, all of the He 100s that were built used the evaporative cooling system described above. A derivative of this system was also intended for a late-war project based on the He 100, designated P.1076.
Unlike the cooling fluid, oil cannot be allowed to boil. This presented a particular problem with DB 601-series engines, because oil is sprayed against the bottom of the pistons, resulting in a considerable amount of heat being transferred to the oil as opposed to the coolant. The He 100's oil cooling system was conceptually similar to the water cooling system in that vapor was generated using the heat of the oil and condensed back to liquid by surface cooling through the skins of the airframe. A heat exchanger was used to cool the oil by boiling ethyl alcohol. The oil itself was simply piped to and from this exchanger, which was apparently located in the aft fuselage. The alcohol vapor was piped into the fixed portions of the horizontal and vertical stabilizer
Vertical stabilizer
The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip. It is analogical to a skeg on boats and ships.On aircraft, vertical stabilizers generally point upwards...
s and into a double-skinned portion of the upper-aft fuselage behind the cockpit. This fuselage "turtle deck" panel was the only double-skinned portion of the aircraft's cooling system. The use of a double-skinned panel was possible here because the inside of panel was accessible in the event of repair. Condensed alcohol was collected by a series of bellows pumps and returned to a single header tank that fed the heat exchanger. Some sources speculate that a small air intake located at the bottom front of the engine cowl was used for an auxiliary oil cooler. No such cooler was fitted, nor was there room for one at that point. This small inlet served simply to admit cool air into what was a very hot portion of the engine bay. Immediately above this vent were the two steam separators, and immediately behind it were the hot coolant pipes coming from the separators.
World speed record
One aspect of the original Projekt 1035 was the intent to capture the absolute speed record for Heinkel and Germany. Both Messerschmitt and Heinkel vied for this record before the war. Messerschmitt ultimately won that battle with the first prototype of the Me 209, but the He 100 briefly held the record when Heinkel test pilot Hans Dieterle flew the eighth prototype to 746.606 km/h (463.9 mph) on 30 March 1939. The third and eighth prototypes were specially modified for speed with unique outer wing panels of reduced spanWingspan
The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...
. The third prototype crashed during testing. The record flight was made using a special version of the DB 601 engine that offered 2010 kW and had a service life of just 30 minutes. Prior to setting this absolute speed record over a short, measured course, Ernst Udet flew the second prototype to a 100 km (62.1 mi) closed course record of 634.32 km/h (394.1 mph) on 5 June 1938. Udet's record was apparently set using a standard DB 601a engine.
There is a debate regarding the correct designation of the He 100 aircraft actually built. One group holds that all of the machines were either "Versuchs" or "trials" prototypes and pre-production "A-0" series machines. This is consistent with the RLM's normal practice of changing an aircraft's sub-designation only with a significant redesign, such as an engine change. All of the He 100s built were essentially the same, and even the prototypes were later updated to the production standard before they were exported to the Soviet Union. The second group holds that the Heinkel factory intended "A," "B," "C" and "D" series aircraft, and the final version was the "D." This camp also holds that there were separate "D-0" and "D-1" production runs, although in extremely limited numbers. Most literature follows the latter school of thought, Since the He 100 was never accepted for operational use by the Luftwaffe, it is unlikely there was ever an official resolution of this issue. The separate letter designations "A" through "D" appear to have come from internal Heinkel documents.
Prototypes
The first prototype He 100 V1 flew on 22 January 1938, only a week after its promised delivery date. The aircraft proved to be outstandingly fast. However, it continued to share a number of problems with the earlier He 112, notably a lack of directional stability. In addition, the Luftwaffe test pilots disliked the high wing loadingWing loading
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly,...
, which resulted in landing speeds so great that they often had to use brakes right up to the last 100 m (328.1 ft) of the runway. The ground crews also disliked the design, complaining about the tight cowling which made servicing the engine difficult. But the big problem turned out to be the cooling system, largely to no one's surprise. After a series of test flights V1 was sent to Rechlin in March.
The second prototype addressed the stability problems by changing the vertical stabilizer from a triangular form to a larger and more rectangular form. The oil-cooling system continued to be problematic, so it was removed and replaced with a small semi retractable radiator below the wing. It also received the still-experimental DB 601M engine which the aircraft was originally designed for. The M version was modified to run on "C3" fuel at 100 octane, which would allow it to run at higher power ratings in the future.
V2 was completed in March, but instead of moving to Rechlin it was kept at the factory for an attempt on the 100 km (62 mi) closed circuit speed record. A course was marked out on the Baltic coast between Wustrow and Müritz, 50 km (30 mi) apart, and the attempt was to be made at the aircraft's best altitude of 5500 m (18,044.6 ft). After some time cleaning out the bugs the record attempt was set to be flown by Captain Herting, who had previously flown the aircraft several times.
At this point Ernst Udet showed up and asked to fly V2, after pointing out he had flown the V1 at Rechlin. He took over from Herting and flew the V2 to a new world 100 km (62.1 mi) closed circuit record on 5 June 1938, at 634.73 km/h (394.4 mph). Several of the cooling pumps failed on this flight as well, but Udet wasn't sure what the lights meant and simply ignored them.
The record was heavily publicized, but in the press the aircraft was referred to as the "He 112U". Apparently, the "U" stood for "Udet". At the time the 112 was still in production and looking for customers, so this was one way to boost sales of the older design. V2 was then moved to Rechlin for continued testing. Later in October, the aircraft was damaged on landing when the tail wheel didn't extend, and it is unclear if the damage was repaired.
The V3 prototype received the clipped racing wings, which reduced span and area from 30 inch and 14.4 square metres (17.2 sq yd), to 24 inch and 11 m² (13.2 sq yd). The canopy was replaced with a much smaller and more rounded version, and all of the bumps and joints were puttied over and sanded down. The aircraft was equipped with the 601M and flown at the factory.
In August, the DB 601R engine arrived from Daimler-Benz and was installed. This version increased the maximum rpm from 2,200 to 3,000, and added methyl alcohol to the fuel mixture to improve cooling in the supercharger and thus increase boost. As a result, the output was boosted to 1324 kW, although it required constant maintenance and the fuel had to be drained completely after every flight. The aircraft was then moved to Warnemünde for the record attempt in September.
On one of the pre-record test flights by the Heinkel chief pilot, Gerhard Nitschke, the main gear failed to extend and ended up stuck half open. Since the aircraft could not be safely landed it was decided to have Nitschke bail out and let the aircraft crash in a safe spot on the airfield. Gerhard was injured when he hit the tail on the way out, and made no further record attempts.
V4 was to have been the only "production" prototype and was referred to as the "100B" model (V1 through V3 being "A" models). It was completed in the summer and delivered to Rechlin, so it wasn't available for modification into racing trim when V3 crashed. Although the aircraft was unarmed it was otherwise a service model with the 601M, and in testing over the summer it proved to be considerably faster than the Bf 109. At sea level, the aircraft could reach 560 km/h (348 mph), faster than the Bf 109E's speed at its best altitude. At 6560 ft (1,999.5 m), it improved to 610 km/h (379 mph), topping out at 669 km/h (415.7 mph) at 5000 m (16,404.2 ft) before falling again to 641 km/h (398.3 mph) at 8000 m (26,246.7 ft). The aircraft had flown a number of times before its landing gear collapsed while standing on the pad on 22 October. The aircraft was later rebuilt and was flying by March 1939.
Although V4 was to have been the last of the prototypes in the original plans, production was allowed to continue with a new series of six aircraft. One of the airframes was selected to replace V3, and as luck would have it V8 was at the "right point" in its construction and was completed out of turn. It first flew on 1 December but this was with a standard DB 601Aa engine. The 601R was then put in the aircraft on 8 January 1939, and moved to a new course at Oranienberg. After several shakedown flights, Hans Dieterle flew to a new record on 30 March 1939, at 746.6 km/h (463.9 mph). Once again the aircraft was referred to as the He 112U in the press. It is unclear when happened to V8 in the end; it may have been used for crash testing.
V5 was completed like V4, and first flew on 16 November. It was later used in a film about V8's record attempt, in order to protect the record breaking aircraft. At this point, a number of changes were made to the design resulting in the "100C" model, and with the exception of V8 the rest of the prototypes were all delivered as the C standard.
V6 was first flown in February 1939, and after some test flights at the factory it was flown to Rechlin on 25 April. There it spent most of its time as an engine testbed. On 9 June, the gear failed inflight, but the pilot managed to land the aircraft with little damage, and it was returned to flying condition in six days.
V7 was completed on 24 May with a change to the oil cooling system. It was the first to be delivered with armament, consisting of two 20 millimetre (0.78740157480315 in) MG FF cannon
MG FF cannon
The MG FF was a drum-fed, 20 mm aircraft autocannon, developed in 1936 by Ikaria Werke Berlin of Germany. It was a derivative of the Swiss Oerlikon FF F cannon, itself a development of the German World War I Becker 20 mm cannon, and was designed to be used in fixed or flexible mountings, as...
s in the wings and four 7.92 mm (.30-caliber) MG 17 machine gun
MG 17 machine gun
The MG 17 was a 7.92 mm machine gun produced by Rheinmetall-Borsig for use at fixed mountings in many World War II Luftwaffe aircraft.- History :...
s arranged around the engine cowling. This made the He 100 the most heavily armed fighter of its day. V7 was then flown to Rechlin where the armament was removed and the aircraft was used for a series of high speed test flights.
V9 was also completed and armed, but was used solely for crash testing and was "tested to destruction". V10 was originally to suffer a similar fate, but instead ended up being given the racing wings and canopy of the V8 and displayed in the German Museum in Munich as the record-setting "He 112U". It was later destroyed in a bombing attack.
Overheating problems and general failures with the cooling system motors continued to be a problem. Throughout the testing period, failures of the pumps ended flights early, although some of the test pilots simply starting ignoring them. In March, Kleinemeyer wrote a memo to Ernst Heinkel about the continuing problems, stating that Schwärzler had asked to be put on the problem.
Another problem that was never cured during the prototype stage was a rash of landing gear problems. Although the wide-set gear should have eliminated the collapse of landing gears that plagued the Bf 109, especially in the difficult takeoffs and landings, the He 100's landing gear was not built to withstand heavy use, and as a result they were no improvement over the Bf 109. V2, 3, 4 and 6 were all damaged to various degrees due to various gear failures, a full half of the prototypes.
Operational history
He 100 D-0
Throughout the prototype period the various models were given series designations (as noted above), and presented to the RLM as the basis for series production. The Luftwaffe never took them up on the offer. Heinkel had decided to build a total of 25 of the aircraft one way or the other, so with 10 down, there were another 15 of the latest model to go. In keeping with general practice, any series production is started with a limited run of "zero series" machines, and this resulted in the He 100 D-0.The D-0 was similar to the earlier C models, with a few notable changes. Primary among these was a larger vertical tail in order to finally solve the stability issues. In addition, the cockpit
Cockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
and canopy were slightly redesigned, with the pilot sitting high in a large canopy with excellent vision in all directions. The armament was reduced from the C model to one 20 mm (0.78740157480315 in) MG FF/M in the engine V firing through the propeller spinner, and two 7.92 mm (.30-caliber) MG 17s in the wings close to the fuselage.
The three D-0 aircraft were completed by the summer of 1939 and stayed at the Heinkel Marienehe plant for testing. They were later sold to the Japanese Imperial Navy to serve as pattern aircraft for a production line, and were shipped there in 1940. They received the designation AXHe.
He 100 D-1
The final evolution of the short He 100 history is the D-1 model. As the name suggests the design was supposed to be very similar to the pre-production D-0s, the main planned change was to enlarge the horizontal stabilizerTailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
.
But the big change was the eventual abandonment of the surface cooling system, which proved to be too complex and failure prone. Instead an even larger version of the retractable radiator was installed, and this appeared to completely cure the problems. The radiator was inserted in a "plug" below the cockpit, and as a result the wings were widened slightly.
While the aircraft didn't match its design goal of 700 km/h (435 mph) once it was loaded down with weapons, the larger canopy and the radiator, it was still capable of speeds in the 644 km/h (400.2 mph) range. A low drag airframe is good for both speed and range, and as a result the He 100 had a combat radius between 900 kilometre compared to the Bf 109's 600 km (372.8 mi). While not in the same league as the later escort fighters, this was at the time a superb range and may have offset the need for the Bf 110 to some degree. Finally, there were allegations that politics played a role in killing the He 100.
By this point, the war was underway, and as the Luftwaffe would not purchase the aircraft in its current form, the production line was shut down.
The remaining 12 He 100 D-1 fighters were used to form Heinkel's Marienehe factory defense unit, flown by factory test pilots. They replaced the earlier He 112s that were used for the same purpose, and the 112s were later sold off. At this early stage in the war, there were no bombers venturing that far into Germany, and it appears that the unit never saw action. The eventual fate of the D-1s remains unknown. The aircraft were also put to an interesting propaganda
Propaganda
Propaganda is a form of communication that is aimed at influencing the attitude of a community toward some cause or position so as to benefit oneself or one's group....
/disinformation
Disinformation
Disinformation is intentionally false or inaccurate information that is spread deliberately. For this reason, it is synonymous with and sometimes called black propaganda. It is an act of deception and false statements to convince someone of untruth...
role, as the supposed Heinkel He 113
Heinkel He 113
The Heinkel He 113 was a supposed Luftwaffe fighter aircraft of World War II, but which existed only as a propaganda and/or disinformation strategy....
.
Foreign use
When the war opened in 1939 Heinkel was allowed to look for foreign licensees for the design. Japanese and Soviet delegations visited the Marienehe factory on 30 October 1939, and were both impressed with what they saw. Thus it was in foreign hands that the 100 finally saw use, although only in terms of adopted design features. Six He 100s were exported to the Soviet Union and three were exported to Japan. Although any Japanese aircraft that survived the war would have been destroyed by the Allies, there is a possibility that parts of or even a complete He 100 may exist somewhere in storage in Russia. It is also possible the Russians made plans or blueprints of their He 100s while the design was being studied.The Soviets were particularly interested in the surface cooling system, having built the experimental Ilyushin I-21
Ilyushin I-21
|-See also:...
with evaporative cooling, and in order to gain experience with it they purchased the six surviving prototypes (V1, V2, V4, V5, V6 and V7). After arriving in the USSR they were passed onto the TsAGI
TsAGI
TsAGI is a transliteration of the Russian abbreviation for Центра́льный аэрогидродинами́ческий институ́т or "Tsentralniy Aerogidrodinamicheskiy Institut", the Central Aerohydrodynamic Institute....
institute for study; there they were analyzed with He 100 features influencing a number of Soviet designs, notably the LaGG-3 and MiG-1
Mikoyan-Gurevich MiG-1
The Mikoyan-Gurevich MiG-1 was a Soviet fighter aircraft of World War II that was designed to meet a requirement for a high-altitude fighter issued in 1939. To minimize demand on strategic materials such as aluminum, the aircraft was mostly constructed from steel tubing and wood...
. Although the surface cooling system wasn't copied, the addition of larger Soviet engines made up for the difference and the LaGG-3 was a reasonably good performer. It's perhaps ironic that German aircraft would later be shot down by German inspired aircraft.
The Japanese were also looking for new designs, notably those using inline engines where they had little experience. They purchased the three D-0s for 1.2 million RM, as well as a license for production and a set of jigs for another 1.6 million RM. The three D-0s arrived in Japan in May 1940 and were re-assembled at Kasumigaura. They were then delivered to the Japanese Naval Air Force where they were re-named AXHei, for "Experimental Heinkel Fighter". When referring to the German design the aircraft is called both the He 100 and He 113, with at least one set of plans bearing the later name.
In tests, the Navy was so impressed that they planned to put the aircraft into production as soon as possible as their land-based interceptor
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
; unlike every other armed forces organization in the world, the Army and Navy both fielded complete land-based air forces. Hitachi won the contract for the aircraft and started construction of a factory in Chiba for its production. With the war in full swing in Europe, however, the jigs and plans never arrived. Why this wasn't sorted out is something of a mystery, and it appears there isn't enough information in the common sources to say for sure what happened.
Further developments
In late 1944, the RLM went to manufacturers for a new high-altitude fighter with excellent performance - the Ta 152HFocke-Wulf Ta 152
The Focke-Wulf Ta 152 was a World War II German high-altitude fighter-interceptor designed by Kurt Tank and produced by Focke-Wulf. The Ta 152 was a development of the Focke-Wulf Fw 190 aircraft...
(a version of the Focke-Wulf Fw 190
Focke-Wulf Fw 190
The Focke-Wulf Fw 190 Würger was a German Second World War single-seat, single-engine fighter aircraft designed by Kurt Tank in the late 1930s. Powered by a radial engine, the 190 had ample power and was able to lift larger loads than its well-known counterpart, the Messerschmitt Bf 109...
) was currently in limited production for just this task but Heinkel was contracted to design an aircraft, and Siegfried Günter was placed in charge of the new Projekt 1076.
The resulting design was similar to the He 100, but the many detail changes resulted in an aircraft that looked all new. It sported a new and longer wing for high-altitude work, which lost the gull wing bend and was swept
Swept wing
A swept wing is a wing planform favored for high subsonic jet speeds first investigated by Germany during the Second World War. Since the introduction of the MiG-15 and North American F-86 which demonstrated a decisive superiority over the slower first generation of straight-wing jet fighters...
forward slightly at 8°. Flaps or ailerons spanned the entire trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
of the wing giving it a rather modern appearance. The cockpit was pressurized
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
for high-altitude flying, and covered with a small bubble canopy
Bubble canopy
A bubble canopy is a canopy made like a soap bubble, which attempts to provide 360° vision to the pilot.-History:Bubble canopies have been in use since World War II. The British had already developed the "Malcolm hood", which was a bulged canopy, but the British Miles M.20 was one of the first...
that was hinged to the side instead of sliding to the rear. Other changes that seem odd in retrospect is that the gear now retracted outward like the original Bf 109, and the surface cooling system was re-introduced. Planned armament was one 30 mm (1.2 in) MK 103 cannon
MK 103 cannon
The Rheinmetall-Borsig MK 103 was a German 30 mm caliber autocannon that was mounted in German combat aircraft during World War II. Intended to be a dual purpose weapon for anti-tank and air-to-air fighting, it was a development of the heavy MK 101. Compared to the MK 101, it was lighter,...
firing through the propeller hub, and two wing mounted 30mm MK 108 cannon
MK 108 cannon
The MK 108 was a 30 mm caliber autocannon manufactured in Germany during World War II by Rheinmetall-Borsig for use in aircraft.-Development:...
s.
The use of one of three different engines was planned: the DB 603M with 1361 kW, the DB 603N with 2051 kW, or the Jumo 213E
Junkers Jumo 213
|-See also:-Bibliography:* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
, designed from the start to have the same fluid service locations as the DB 603, with 1287 kW. The 603M and 213E both supplied 1545 kW using MW-50 water injection. Performance with the 603N was projected to be 880 km/h (546.8 mph), in the same class as the Messerschmitt Me 262
Messerschmitt Me 262
The Messerschmitt Me 262 Schwalbe was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but engine problems prevented the aircraft from attaining operational status with the Luftwaffe until mid-1944...
pioneering jet fighter then entering evaluationary service, which would have stood as a record for many years even when faced with dedicated racing machines. Performance would still be excellent even with the far more likely 1500 kW class engines, the 603M was projected to give it the high speed of 855 km/h (531.3 mph).
These figures are somewhat suspect though, and are likely just optimistic guesses that could not have been met - something Heinkel was famous for. Propellers lose efficiency as they approach the speed of sound, and eventually they no longer provide an increase in thrust for an increase in engine power. Even the advanced counter-rotating VDM design is unlikely to have been able to effect this problem too much.
The design apparently received low priority, and it was not completed by the end of the war. Siegfried Günter later completed the detailed drawings and plans for the Americans in mid-1945.
Legacy
In 1939, it was reputedly one of the most advanced fighter designs, even faster than the later Fw 190, with performance unrivalled until the introduction of the Vought F4U CorsairF4U Corsair
The Vought F4U Corsair was a carrier-capable fighter aircraft that saw service primarily in World War II and the Korean War. Demand for the aircraft soon overwhelmed Vought's manufacturing capability, resulting in production by Goodyear and Brewster: Goodyear-built Corsairs were designated FG and...
in 1943. Nevertheless the aircraft was not ordered into production. The reasons the He 100 wasn't put into service seems to vary depending on the person telling the story, and picking any one version results in a firestorm of protest.
Some say it was politics that killed the He 100. However, this seems to stem primarily from Heinkel's own telling of the story, which in turn seems to be based on some general malaise over the He 112 debacle. The fact is that Heinkel was well respected within the establishment regardless of Messerschmitt's success with the Bf 109 and Bf 110, and this argument seems particularly weak.
Others blame the bizarre production line philosophy of the RLM, which valued huge numbers of single designs over a mix of different aircraft. This too seems somewhat suspect considering that the Fw 190 was purchased shortly after this story ends.
For these reasons, it seems safe to accept the RLM version of the story largely at face value; that the production problems with the DB series of engines was so acute that all other designs based on the engine were canceled. At the time the DB 601 engines were being used in both the Bf 109 and Bf 110 aircraft, and Daimler couldn't keep up with those demands alone. The RLM eventually forbade anyone but Messerschmitt from receiving any DB 601s, leading to the shelving of many designs from a number of vendors. Furthermore, the Bf 109 and Bf 110 were perceived as superior to their likely opponents, which made the requirement for an even more powerful aircraft less imperative.
The only option open to Heinkel was a switch to another engine, and the RLM expressed some interest in purchasing such a version of the He 100. At the time the only other useful inline was the Junkers Jumo 211
Junkers Jumo 211
|-See also:-References:* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
, and even that was in short supply. However, the design of the He 100 made adaptation to the 211 difficult; both the cooling system and the engine mounts were designed for the 601, and a switch to the 211 would have required a redesign. Heinkel felt it wasn't worth the effort considering the aircraft would end up with inferior performance, and so the He 100 production ends on that sour note.
For this reason more than any other the Focke-Wulf Fw 190
Focke-Wulf Fw 190
The Focke-Wulf Fw 190 Würger was a German Second World War single-seat, single-engine fighter aircraft designed by Kurt Tank in the late 1930s. Powered by a radial engine, the 190 had ample power and was able to lift larger loads than its well-known counterpart, the Messerschmitt Bf 109...
became the next great aircraft of the Luftwaffe, as it was based around the otherwise unused Bramo 139 (and later BMW 801
BMW 801
The BMW 801 was a powerful German air-cooled radial aircraft engine built by BMW and used in a number of German military aircraft of World War II. The engine's cylinders were in two rows of seven cylinders each, the bore and stroke were both 156 mm , giving a total capacity of 41.8 litres...
) radial engine. Although production of these engines was only starting, the lines for the airframes and aircraft could be geared up in parallel without interrupting production of any existing design, which was exactly what happened.
Specifications (He 100D-1)
See also
Survivors: there are apparently no confirmed HE-100's in existence, however there is a full scale mock up at the Planes of Fame Museum located at the Chino airport in Chino, CA.External links
- Additional details on the P.1076 from Don Johnson's Luft'46 site
- AIR 40/237
- Luftwaffe Resource Group
- He 100 page contains a three view of the D-1 and some basic information
- This page includes a description similar to that from The Encyclopedia, as well as links to a number of images of the aircraft.