Largely remembered for its contribution to bomber design and production for the German Luftwaffe during World War 2, the aero-concern of Heinkel also plied its trade as a fighter designer and developer. Notable entries went on to include the "He 112" and "He 280" (both detailed elsewhere on this site), the latter a jet-powered fighter prototype. In the pre-war years, the company worked to develop a new, all-modern frontline fighter that became the "He 100". The aircraft was a promising, high-performance solution but ultimately passed over due to the existing Luftwaffe commitment to the Messerschmitt Bf 109. Compounding its issues was the general wartime availability of the famous Daimler-Benz DB601 series inline engine which powered the Bf 109 as well as the Messerschmitt Bf 110 heavy fighter form.
Nevertheless, the He 100 project was pursued by Heinkel, partly a private venture though with limited support from the German Air Ministry (the "RLM"). In all, the He 100's development program yielded nineteen aircraft and as many as six pre-production forms may have followed - though none of the airframes survived the war. It did see value as a propaganda tool and was featured in the lead-up to the fighting of World War 2 as the "He 113".
The He 100 began life as "Projekt 1035" and arrived after Heinkel engineers had pushed the He 112 product to its evolutionary end - 103 examples of this fighter were produced serving (limited) the Luftwaffe as well as the Spanish, Hungarian, and Romanian air services. With this experience in hand, the design team began a "clean sheet" fighter design to develop yet-another single-seat, single-engine monoplane fighter - one of enhanced performance and simplified construction - to interest Luftwaffe authorities as it geared up for war in Europe. The design was ready for review by the RLM in October 1937 and prototype He 100 V1 achieved its first-flight on January 22nd, 1938. In March 1939, the He 100 managed to capture an absolute speed record of 463.92 miles-per-hour.
The He 100 design was wholly-modern for its time: the rounded, streamlined fuselage seated the engine at its traditional place in the nose, the cockpit set over midships, and a tapered empennage terminating at the single, low-profile vertical fin. Horizontal tailplanes were positioned low along the fin. The wing mainplanes were mounted slightly ahead of midships and had straight leading edges and tapered trailing edges with rounded wing tips. Ground running was accomplished via a traditional "tail-dragger" undercarriage approach involving a pair of main legs and a tail wheel - all retracting into the aircraft when in flight. The pilot sat under a framed canopy with raised dorsal spine behind, restricting views to the rear but offering greater internal volume for fuel and other equipment.
Dimensions included a length of 26.10 feet, a span of 30.9 feet, and a height of 11.9 feet. Empty weight was 4,000lb against an MTOW of 5,515lb. Up to 660lb of fuel could be carried aloft.
As designed, the aircraft carried a single 20mm MG FF automatic cannon buried in the engine block and firing through the propeller hub. In addition to this there were a pair of 7.92mm MG 17 series machine guns, one gun in each wing root. For its time, this gave the fighter a considerable punch against enemy aircraft including bomber types and rivaled that of the competing Bf 109.
Power was from a Daimler-Benz DB601M liquid-cooled V12 inline piston engine developing 1,175 horsepower at take-off and providing the aircraft with a maximum speed of 420 miles-per-hour, a cruising speed near 345 mph, a range out to 630 miles, and a service ceiling up to 36,000 feet. Time to 20,000 feet was 7.8 minutes.
As He 100 V1 became the first prototype in the series, the follow-up form was He 100 V2 which intended to address stability problems featured in its predecessor (as well as the He 112). He 100 V3 was given "clipped" wing tips for increased performance (a quality also given to later-generation Supermarine Spitfires by the British). These three aircraft were collectively showcased under the "He 100A" designation.
He 100 V4 was built to a greater production standard and classified under the "He 100B" designation. This model carried the DB601M but lacked all armament and reached 416 mph in tested (at 16,000 feet of altitude). It later suffered undercarriage damage and had to be rebuilt.
He 100 V5 was built closely to the He 100 V4 specification and flew for the first time in November of 1938 but changes enacted led to the overarching "He 100C" branch. He 100 V6 followed into the air during February 1939 but was used more as an engine testbed. He 100 V7 saw its cooling system modified and arrived in May 1939 with, base on sources, its complete armament suite installed. Being the closest specimen to a full-working fighter, the aircraft nonetheless was stripped of its combat value and entered into high-speed testing for the remainder of its life. He 100 V9 models were used in crash testing.
At the time of its inception, the He 100 was one of the highest-performing military fighters anywhere in the world, capable of exceptional speed with enough inherent firepower to boot. However, the crippling issue to the He 100 program appears to be the availability of the Daimler-Benz DB601 series inline engine as it was also being featured, not only in the competing Bf 109 fighter, but in the Messerschmitt Bf 110 heavy fighter (a twin-engined design to make matters worse). As such, the German Air Ministry pushed along with the war effort relying heavily on these two aircraft designs (the upcoming Focke-Wulf Fw 190 fighter instead relied on an air-cooled radial engine for its part in the story).
Beyond engine availability, the design also suffered through cooling issues and undercarriage collapses that were never ironed out in testing.
For a brief period, Heinkel entertained the prospect of a re-engined its He 100 with the Junkers Jumo 211 series inline. However, this avenue was fraught with all sorts of challenges that made the switch prohibitive, especially for a fighter specifically designed around the Daimler-Benz installation. Additionally, the Juno 211 also soon faced availability issues all its own.
As mentioned, the He 100 fighter was featured under the "He 113" propaganda program by the Third Reich in the run-up to World War 2 and appeared in "action" photography while also being touted in three-view and perspective drawings intended to showcase German ingenuity using the latest in military fighter development. The He 113 was, in fact, nothing more than the He 100D-1 reconstituted for propaganda purposes. Its success in this role was limited though British intelligence did, in fact, classify it and attempted to assigned various performance and structural values to the unproven design.
The He 100 design was sold to ally Japan, which were impressed by the type, but the war in Europe nixed any plans to ship the needed equipment for serial production. The Soviets bought six of the He 100 airframes for further study.