Editing Heinkel He 100 (section)

== Prototypes ==
[[File:He 100 V1 на аэродроме Росток-Мариенех.JPG|thumb|Heinkel He 100 V1]]

=== 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 {{convert|100|m|ft|abbr=on}} 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.

=== He 100 V2 ===
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&nbsp;km (62&nbsp;mi) closed circuit speed record. A course was marked out on the Baltic coast between Wustrow and Müritz, 50&nbsp;km (30&nbsp;mi) apart, and the attempt was to be made at the aircraft's best altitude of {{convert|5,500|m|ft|abbr=on}}. 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 {{convert|100|km|abbr=on}} closed-circuit record on 5 June 1938, at {{convert|634.73|km/h|abbr=on}}. 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.

=== He 100 V3 ===
The V3 prototype received the clipped racing wings, which reduced span and area from {{convert|30|ft|10|in|order=flip|abbr=on}} and {{convert|14.4|m²}}, to {{convert|24|ft|11|in|order=flip|abbr=on}} and {{convert|11|m²|abbr=on}}. The [[Aircraft canopy|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 {{convert|1324|kW|PS hp|abbr=on|order=flip}}, 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.

=== He 100 V4 ===
V4 was to have been the only "production" prototype (postwar called the He 100B, previous aircraft being the He 100A). 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 {{convert|560|km/h|kn mph|abbr=on}}, faster than the Bf 109E's speed at its best altitude. At {{convert|6560|ft|order=flip|abbr=on}}, it improved to {{convert|610|km/h|kn mph|abbr=on}}, topping out at {{convert|669|km/h|abbr=on}} at {{convert|5000|m|abbr=on}} before falling again to {{convert|641|km/h|abbr=on}} at {{convert|8,000|m|abbr=on}}. 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.

=== He 100 V5 ===
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 what postwar has been referred to as the "He 100C"-model, and with the exception of V8, the rest of the prototypes were all delivered as the V5 standard.

=== He 100 V6 ===
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.

=== He 100 V7 ===
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 {{convert|20|mm}} [[MG FF cannon]] in the wings and four {{convert|7.92|mm|abbr=on|3}} [[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.

=== He 100 V8 ===
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 {{convert|746.6|km/h|kn mph|abbr=on}}. 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.

=== He 100 V9 ===
V9 was also completed and armed, but was used solely for crash testing and was "tested to destruction". 

=== He 100 V10 ===
V10 was originally to suffer a similar fate as the V9, 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.