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Additional Information from
Internet 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 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 leap beyond the performance of the Bf 109 as much as the
Bf 109 had over 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 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
(380 kn; 430 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.[1] 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 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 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.
He 100 should have been designated He 113, but since the number
"13" was unlucky, this had been dropped. 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
Heinkel He 100
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 cockpit, 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 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, which was also a
feature of the earlier and larger He 119 experimental high-speed reconnaissance
aircraft. 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 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 final version of Heinkel's cooling
system. It is based entirely on careful study of surviving photographs of the
He 100, since no detailed 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 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
flaps. 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 buildup 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 ailerons (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 indicate that they were
conventionally single-skinned, and that 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
stabilizers 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 (463.919 mph) on 30 March 1939. 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 offered 2,010 kW (2,700 hp)
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 mi) closed course record of 634.32 km/h (394.15 mph) 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.[by whom?] One group[who?] 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[who?] 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
Heinkel He 100 V1
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 100 m
(330 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 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 5,500 m (18,000 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 mi) closed-circuit record on 5 June
1938, at 634.73 km/h (394.40 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 9.40 m (30 ft 10 in) and 14.4 square metres (155 sq
ft), to 7.59 m (24 ft 11 in) and 11 m2 (120 sq ft). 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
1,800 PS; 1,776 hp (1,324 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 (300
kn; 350 mph), faster than the Bf 109E's speed at its best altitude. At 2,000 m
(6,560 ft), it improved to 610 km/h (330 kn; 380 mph), topping out at 669 km/h
(416 mph) at 5,000 m (16,000 ft) before falling again to 641 km/h (398 mph) at
8,000 m (26,000 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 (403.1 kn; 463.9
mph). Once again the aircraft was referred to as the He 112U in the press. It
is unclear what 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 millimetres (0.79 in) MG FF cannon in the wings and four 7.92 mm (0.312
in) MG 17 machine guns 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 started 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 take-offs 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 Heinkel up on their offer
although the company 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", resulting 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 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 (0.79 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
AXHei.
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 being to enlarge the
horizontal stabilizer.
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 (430 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 mph) range. A low
drag airframe is good for both speed and range, and as a result the He 100 had
a combat range of 900 to 1,000 km (560 to 620 mi) compared to the Bf 109's 600
km (370 mi). While not in the same league as the later escort fighters, this
was at the time a superb range, which suggests that a production Heinkel 100
might have offset the need for the Bf 110 to some degree.
By this point, the war was under way, and as the
Luftwaffe would not purchase the aircraft in its current form, the production
line was shut down. There were allegations that politics played a role in
killing the He 100.
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. 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 used for a
propaganda spoof, as the supposed Heinkel He 113.
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 by the
design.[4] The Soviets were particularly interested in the surface cooling
system, having built the experimental Ilyushin I-21 with evaporative cooling
and to gain experience with it they purchased the six surviving prototypes (V1,
V2, V4, V5, V6 and V7).[4] After arriving in the USSR they were passed onto the
TsAGI institute for study.
The Japanese were also looking for new designs, notably
those using inline engines, where they had little experience and 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 renamed AXHei, for "Experimental Heinkel
Fighter".[4] 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 latter
name.
The prototypes were accompanied by Heinkel test pilot
Gerhard Nitschke, who worked with Lieutenant Mitsugi Kofukuda during the tesing
and evaluation.[5] The Navy was so impressed by tests 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
Japanese 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 European war on, the jigs and plans never
arrived.
Further developments
In late 1944, the RLM went to manufacturers for a new
high-altitude fighter with excellent performance; the Ta 152H (an inline
engined version of the Focke-Wulf Fw 190) was in limited production but Heinkel
was contracted to design an aircraft and Siegfried Günter was placed in charge
of the new Projekt 1076. The new design was similar to the He 100 but 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 inverted 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 cannons.
Three engine types were planned, the DB 603M with 1,361
kW (1,825 hp), the DB 603N with 2,051 kW (2,750 hp) or the Jumo 213E, designed
from the start to have the same fluid service locations as the DB 603, with
1,287 kW (1,726 hp). The 603M and 213E both supplied 1,545 kW (2,072 hp) using
MW-50 water injection. Performance with the 603N was projected to be 880 km/h
(550 mph), in the same class as the Messerschmitt Me 262 pioneering jet fighter
then entering service testing, which would have stood as a record for many
years, even against specialist racing machines. Performance would still be
excellent even with the far more likely 1,500 kW (2,000 hp)-output and above
class aviation piston engines, which eventually proved to be a severe
technological barrier for the German aero-engine industry during the war years.
The 603M was projected to give it the high speed of 855 km/h (531 mph).
These figures are somewhat suspect and are likely to be
optimistic guesses that could not have been realised, 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. The only remaining gain of thrust would come from the piston
engine exhausts. The advanced counter-rotating Vereinigte Deutsche Metallwerke
(VDM)-origin propeller design is unlikely to have been able to counteract this
problem. The design apparently received low priority and it was not complete by
the end of the war. Siegfried Günter later provided detailed drawings and plans
for the Americans in mid-1945.
Legacy
In 1939, it was reputedly one of the world's most
advanced fighter designs, even faster than the later Fw 190, with performance
unrivalled until the introduction of the Vought F4U Corsair in 1943, with the
similarly-powered Republic XP-47J hitting 505 mph (813 km/h) in early August
1944.[6] Nevertheless, the aircraft was not ordered into production. The reason
why the He 100 was not 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 were 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 could not 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 engine 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 that it was not worth the effort, considering that 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.