Heinkel He 70 Blitz

Heinkel Flugzeugwerke
Industry	Aerospace, Aircraft manufacturing
Founded	1922
Headquarters	Rostock, Germany

Template:Infobox aircraft

The Heinkel He 70 Blitz ("lightning") was a swift monoplane developed and manufactured by the German firm Heinkel Flugzeugwerke. It was the Luftwaffe's inaugural Schnellbomber.

Initiated in the early 1930s, the He 70 was conceived following a request from Deutsche Lufthansa for a rapid mail plane. Heinkel engineered a low-wing cantilever monoplane featuring multiple drag-reducing innovations, such as an aerodynamically optimized elliptical wing, a sleek exterior surface, and retractable landing gear. A single BMW VI 7.3 Z engine powered the aircraft, cooled by a compact retractable radiator, further minimizing drag. The prototype's first flight occurred on 1 December 1932, after which it established eight distinct world speed records within months.

Deutsche Lufthansa incorporated the He 70 into its fleet in 1934; however, its commercial tenure was relatively short-lived before being superseded by larger, more advanced models. Beyond civilian applications, the He 70 was modified for military roles as a light bomber and reconnaissance platform. These militarized variants served with the Royal Hungarian Air Force and the Ejército del Aire. By the onset of the Second World War, the type had been largely reassigned to secondary duties such as training. The He 70 is notably recognized as a predecessor to the Heinkel He 111, sharing a similar elliptical wing design.

Design and development

Created during the early 1930s, the Heinkel He 70 Blitz (Lightning) was developed as a mailplane for Deutsche Lufthansa, responding to their demand for an aircraft surpassing the speed of the Lockheed Model 9 Orion (operated by Swissair) on short routes. Initially, German authorities specified a target maximum speed of 250 kilometres per hour (160 mph) in 1931, which was later revised upward to 320 km/h (200 mph).^[1] At that time, Germany was actively pursuing high-speed mailplanes capable of competing with American models; it was widely acknowledged that superior speed offered a significant edge over other transport methods.^[2] Achieving this performance required more than just powerful engines; aerodynamic refinement of the airframe was essential.^[3]

On 12 February 1932, an official contract was issued for an aircraft designated He 65, promising a top speed of 285 kilometres per hour (177 mph).^[1] However, by July that year, it was decided to enhance the design to reach higher speeds; this updated version became known as the He 70. The revised model guaranteed a maximum velocity of 312 km/h (194 mph), while retaining identical cabin size, wing loading, and landing speeds compared to its American counterparts.^[1] Speed performance took precedence in this redesign.^[1]

To minimize aerodynamic resistance while providing sufficient fuselage cross-section for two crew members plus five passengers with luggage,^[1] a low-wing cantilever monoplane layout was chosen. This arrangement differed from rival manufacturer Junkers, offering superior aerodynamic efficiency relative to usable cabin volume. Initially, wing flaps were omitted to reduce weight and complexity and maximize top speed; despite acceptable landing behavior without flaps, compact flaps were later introduced to enable operations from shorter runways after testing various configurations.^[4]

The design team evaluated multiple wing shapes to balance aerodynamic efficiency with factors such as roll damping, structural weight, and accommodation of retractable landing gear.^[5] Particular attention focused on ensuring torsional rigidity and sufficient resistance to oscillations—a critical challenge for cantilever wings. The selected wing featured a profile thickness that tapered significantly toward the tips; its camber corresponded directly with thickness based on mathematical calculations.^[6] Constructed primarily from wood with a twin-spar framework extending into two box-shaped recesses within the fuselage secured by bolts to main frames, the ribs consisted of spruce, webs were made from laminated birch, and plywood skin covered the exterior,^[7] enhancing torsional stiffness.^[8]

The fuselage employed a spindle-shaped monocoque structure fabricated from duralumin.^[9] Its longerons, bulkheads, and stiffeners were open channel sections; this combination allowed unobstructed compartments within the frame bulkheads and longitudinal channels riveted near the cabin area.^[8] Bulkheads were not directly attached to the skin but terminated in longitudinal channels resting on circular bulkheads riveted to the skin.^[8] Although not highly resistant to buckling under stress, deformation remained minimal even under heavy loads. Thick shell plates were installed only at critical points such as main wing fittings to manage local stresses.^[10]

To reduce drag further, flush riveting was employed on the fuselage surface; similarly, all external fittings—including foot steps and door handles—were recessed and flush-mounted windows were installed.^[7] The fully retractable main landing gear retracted into spaces between wing spars as another drag-minimizing feature. Ailerons were carefully balanced to prevent flutter.^[11] Flight control surfaces utilized elliptical planforms with cantilever construction. No wind tunnel tests preceded completion of the first prototype due to anticipated discrepancies between models and actual aircraft; however, several tests were conducted post-construction.^[12]

Typically operated by two crew—a pilot and radio operator—seated in tandem centrally but slightly elevated for enhanced visibility,^[13]^[14] visibility was further improved through a transparent movable cabin roof and adjustable seating. A third cockpit seat accommodated either a mechanic or an additional passenger. Behind the flight deck lay a compact cabin accommodating four passengers seated face-to-face in pairs.^[13]^[15] This passenger compartment featured air-based heating and ventilation along with large windows serving as emergency exits; aft of this space was a baggage hold.^[15]

Propulsion came from a single BMW VI V-12 engine delivering up to 630 hp (470 kW) at1,600 rpm.^[16] Uncommonly cooled using ethylene glycol rather than water allowed installation of a smaller radiator beneath the fuselage with only one-third of conventional frontal area; this radiator could be retracted during high-speed flight for additional drag reduction.^[17] The oil tank’s bottom section functioned as part of cooling system aided by a wing pump circulating oil. Both engine and cowling were streamlined wherever feasible.^[18] The aircraft’s speed potential could have increased further if equipped with a more powerful engine.^[19]

The initial prototype completed its maiden flight on December1st,1932,^[20] demonstrating outstanding performance by setting eight world speed records over distances and achieving maximum velocity of 377 km/h (234 mph).^[21]

Civilian operations

Between 1934 and 1937, Luft Hansa utilized He 70 aircraft to provide a rapid air service linking Berlin with Frankfurt, Hamburg, and Cologne, as well as operating routes between Cologne and Hamburg. From 1934 to 1936, these aircraft also flew international flights from Stuttgart to Seville. This route formed part of Luft Hansa's South American mail service, which extended via Bathurst in The Gambia to Natal, Brazil. The service employed Junkers Ju 52/3m and Dornier Wal flying boats for the transatlantic segments.

In 1937, all remaining He 70s were handed over to the Luftwaffe.

Military service

File:Heinkel He-70K típusú távolfelderítő repülőgép. Fortepan 26468.jpg

He 70Ks of the Royal Hungarian Air Force

The Luftwaffe began operating the He 70 in 1935, initially employing it as a light bomber and for aerial reconnaissance missions. Once more advanced specialized aircraft became available, the He 70 was reassigned primarily for use as a liaison and courier platform.Template:Fix/category^{[citation needed]}

In the late 1930s, a total of 28 He 70s were deployed to Spain as part of the German-manned Condor Legion. These planes were active during the Spanish Civil War, mainly fulfilling fast reconnaissance roles. In Spain, they earned the nickname Rayo, meaning "lightning".Template:Fix/category^{[citation needed]}

One unit was acquired by Rolls-Royce to serve as an engine test platform and remained in operation until 1944.^[22]

He 170

The export version designated He 70K, later assigned the RLM code He 170, was a swift reconnaissance model operated by the Hungarian Air Force. It featured a Gnome-Rhône Mistral Major radial engine produced under license in Hungary as the WM-K-14, while assembly and airframe construction were completed in Germany.^[23] This new powerplant increased maximum speed from 360 to 435 km/h (224 to 270 mph).^[24] The Royal Hungarian Air Force operated eighteen of these aircraft from 1937 until 1942.

Limitations

A significant drawback of the He 70 in military applications was its propensity to catch fire. Portions of its structure were constructed from an extremely flammable magnesium alloy known as "elektron", although most of the monocoque fuselage consisted of duralumin. While elektron offered a lightweight yet robust solution, it ignited easily and was challenging to extinguish once ablaze. Additionally, each wing housed a non-self-sealing 210-litre (47-imperial-gallon) fuel tank, likely contributing to its vulnerability to fires.Template:Fix/category^{[citation needed]}

Other issues included inadequate defensive weaponry, limited operational range, and restricted visibility from the cockpit. These factors led to the early retirement of Hungary’s He 170A fleet, which was temporarily replaced by outdated Heinkel He 46 parasol-wing monoplanes until more capable observation aircraft like the Focke-Wulf Fw 189 "Uhu" could be introduced.Template:Fix/category^{[citation needed]}

Influence

Although the He 70 was primarily utilized in limited training roles during the Second World War, it holds the distinction of being the Luftwaffe's inaugural Schnellbomber and served as a foundational model for several bombers that participated in the Battle of Britain.

German designs

The He 70 is chiefly recognized as the predecessor to the Heinkel He 111, which featured comparable elliptical wings and a streamlined fuselage in a twin-engine layout. Entering Luftwaffe service in 1936, the He 111 became the most produced bomber type for the Luftwaffe, with over 5,600 units manufactured throughout the war's early years.^[25]Template:Fact

Additionally, a reduced-scale version of the He 70 was developed into the He 112 fighter. Although it was ultimately outperformed by the Messerschmitt Bf 109 in competition, it still saw limited production.

Japanese designs

Japan acquired an He 70 for examination purposes, which influenced the design of the Aichi D3A ("Val"), a carrier-based light bomber.^[26] This aircraft incorporated the He 70's signature low-mounted elliptical wing.

British designs

Beverley Shenstone, who advised R.J. Mitchell on aerodynamics, refuted claims that the Spitfire's wing design was copied from the He 70. Shenstone stated:

Template:Blockquote

Before joining Heinkel, the Günther brothers had already implemented an elliptical wing on the Bäumer Sausewind sports aircraftTemplate:Fix/category^{[citation needed]}.

According to Shenstone, the He 70’s impact on Spitfire development was confined mainly to serving as a standard for aerodynamic refinement.

Variants

He 70a: Initial prototype.^[27]
He 70b: Second prototype featuring two crew members and seating for four passengers.
He 70c: Third prototype equipped with a machine gun for testing variants intended for light bombing, reconnaissance, and courier missions.
He 70d: Fourth prototype constructed in 1934 for Luft Hansa, powered by a BMW VI 7.3 engine.
He 70e: Fifth prototype built in 1934 for use by the Luftwaffe as a light bomber, also powered by BMW VI 7.3 engine.
He 70A: Passenger model designed for Luft Hansa.
He 70D: Luft Hansa passenger version with twelve units produced.
He 70E: Light bomber variant developed for Luftwaffe, later converted into the F model.
He 70F: Reconnaissance and courier variant deployed by Luftwaffe.
He 70F-1: Extended-range reconnaissance configuration.
He 70F-2: Variant similar to He 70F-1.
He 70G: Passenger model manufactured for Luft Hansa and converted to F specification after 1937.
He 70G-1: A single aircraft fitted with an 810 hp (600 kW) Rolls-Royce Kestrel piston engine.
He 70K (He 170A): Military version equipped with license-produced 746 kW (1,000 hp) WM-K-14 radial engine.
He 270 V1 (W.Nr. 1973, D-OEHF): Prototype powered by a DB-601Aa inline engine.