Prototype fighter aircraft, German, WW2
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 prototypes and pre-production examples were built. None are known to have survived the war.
The reason for the He 100 failing to reach production status is mostly unknown. 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 Messerschmitt Bf 110 as the Luftwaffe's standard fighter types, the Ministry of Aviation (the Reichsluftfahrtministerium or 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.
Development.
Following the selection by the RLM of the Bf 109 as its next single-seat fighter over the He 112, Ernst Heinkel became interested in a new fighter that would surpass the performance of the Bf 109 as much as the Bf 109 had surpassed that of the biplanes 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 development and started 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 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 Günter was killed in a car accident on 25 May 1937, and 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 in 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 prototypes, delivery dates and prices for three aircraft delivered to the Rechlin test center.
The He 100 should have been designated He 113, but since the number "13" was unlucky, it was not used. It is reported that Ernst Heinkel lobbied for this "round" number in the hope that it would improve the design's chances for production.
Design.
In order to get the promised performance the design included a number of drag-reducing features. 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 alternative 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, exhaust ejectors were used to provide 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. Although cleaner-looking, the long, curved induction pipe most probably negated any benefit.
Engine coolant and oil cooling systems.
For the rest of the designed performance increase with the DB 601 powerplant, Walter turned to the experimental method of evaporative cooling. 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 and reduced weight. No detailed plans of the installation 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.
World speed record.
One aspect of the original "Projekt" 1035 was intended to capture the absolute speed record. The third and eighth prototypes were specially modified for speed, with unique outer wing panels of reduced span. The third prototype crashed during testing. The record flight was made using a special version of the DB 601 engine that produced 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 closed course record of on 5 June 1938. Udet's record was apparently set using a standard DB 601a engine.
However, although the Me 209 V1 (known erroneously as the "Me 109R", ignoring the July 1938-dated change in prefixes) officially won over the He 100 and held the world speed record for piston engined aircraft for roughly 30 years, some historians such as Erwin Hood, state that the Me 209 V1's flight was 450 meters above sea level due to the topography of where its flight was held (at Augsburg) compared to that the He 100 V8's location of 50 meters above sea level (in Mecklenburg), thus their speed comparisons are not valid as the higher an aircraft goes, the lower the density of the atmosphere is, thus there is less drag. Hood then asserts that, based on his own calculations, if the He 100 V8 had flown at the same altitude of the Me 209 V1, it would have obtained a speed of 757 km/h.
Designation debate.
There is a debate regarding the correct designation of the He 100 aircraft actually built. Green (1970) cited "A", "B", "C" and "D" variants, and that later He 100 prototypes and all pre-production He 100s were called "He 100D-0" and "He 100D-1" production runs. However, Heinkel documents indicate that the pre-production were only designated He 100A-0, and that all of the He 100s built were essentially the same, with even the prototypes later updated to the production standard before they were exported to the Soviet Union. Thus, supposed "He 100B", "He 100C", and "He 100D" designations are fictitious postwar inventions.
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 loading, which resulted in landing speeds so great that they often had to use brakes right up to the last 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 He 100 V2 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 . 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 closed-circuit record on 5 June 1938, at . 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 and , to and . 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 , 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