The Heinkel He 70 Blitz (Lightning) was designed in the early 1930s as a mail plane for Deutsche Lufthansa in response to a request for an aircraft to service short routes.
It had a cantilever low-wing monoplane, with an aerodynamically efficient elliptical wing and retractable undercarriage, and a single nose-mounted engine.
In order to meet the demanding speed requirements, care was taken to minimize drag, with flush rivets giving a smooth surface, and fully retractable main landing gear.
The tail wheel was not retractable.
It was powered by a 470 kW (630 hp) BMW VI V-12 engine cooled with ethylene glycol rather than water.
This allowed a smaller radiator to be used, which also retracted at high speed to further reduce drag.
The pilot and radio operator were seated in tandem, followed by a cabin seating four passengers in pairs facing each other, and proved to have excellent performance, setting eight world records for speed over distance, and reaching a maximum speed of 377 km/h (234 mph).
The Luftwaffe operated He 70s from 1935, initially as a light bomber and reconnaissance aircraft.
As soon as purpose-built designs became available, it was relegated to use as a liaison and courier aircraft.
Twenty-eight aircraft were sent in the late 1930s to Spain with the German-manned Legion Condor, where they were used during the Spanish Civil War as fast reconnaissance aircraft.
There they were known as the Rayo, Spanish for “lightning”.
The He 70K (later given the RLM number: He 170) was a fast reconnaissance airplane export variant used by the Hungarian air force.
Powered by a Gnome-Rhône Mistral Major radial engine, the engines were built under license in Hungary as the WM-K-14, but the air frame and final assembly were in Germany.
The new engines raised the top speed of the aircraft from 360 to 435 km/h (224 to 270 mph).
18 were used by the Royal Hungarian Air Force from 1937 to 1942.
A major weakness of the He 70 in military use was the fire risk.
Parts of the airframe were made out of an extremely flammable magnesium alloy called “Elektron”, though the majority of the monocoque fuselage was Duralumin.
Elektron is very light yet strong but burns readily when ignited and is difficult to extinguish.
Moreover, each wing contained a non-self-sealing 210-litre (47-imperial-gallon) fuel tank, which may have further added to the aircraft’s reputation for catching fire.
Other problems included poor defensive armament, short range and poor view from the cabin, all of which led to the Hungarian He 170A fleet being prematurely retired and replaced with obsolescent Heinkel He 46 parasol-wing monoplanes, until Focke-Wulf Fw 189 “Uhu” medium altitude observation aircraft could be introduced.
Variants
He 70a
First prototype.
He 70b
Second prototype with the crew of 2 and 4 seats for passengers.
He 70c
Third prototype armed with machine gun for trials of versions for light bomber, reconnaissance and courier duties.
He 70d
Fourth prototype built in 1934 for Luft Hansa, powered by BMW VI 7,3 engine.
He 70e
Fifth prototype built in 1934 for Luftwaffe as light bomber, powered by BMW VI 7,3 engine.
He 70A
Passenger version for Luft Hansa.
He 70D
Passenger version for Luft Hansa, 12 examples built.
He 70E
Light bomber version for Luftwaffe, later converted to F version.
He 70F
Reconnaissance / courier version for Luftwaffe.
He 70F-1
Long-range reconnaissance version.
He 70F-2
Similar to the He 70F-1
He 70G
Passenger version built for Luft Hansa, after 1937 converted to F version.
He 70G-1
One aircraft fitted with an 810 hp (600 kW) Rolls-Royce Kestrel piston engine.
He 70K
(He 170A)
Military variant equipped with a licence-built 746 kW (1,000 hp) WM-K-14 radial engine.
He 270 V1
(W.Nr. 1973, D-OEHF)
Prototype with DB-601Aa inline engine.
Specifications
Crew
Three
Length
11.7 m (38 ft 5 in)
Wingspan
14.8 m (48 ft 7 in)
Height
3.1 m (10 ft 2 in)
Wing area
36.5 m2 (393 sq ft)
Empty weight
2,360 kg (5,203 lb)
Gross weight
3,386 kg (7,465 lb)
Max take-off weight
3,500 kg (7,716 lb)
Powerplant
1 × BMW VI 7.3 Z,
V-12 liquid-cooled piston engine,
550 kW (740 hp)
Propellers
2-bladed variable-pitch metal propeller
Performance
Maximum speed
360 km/h (220 mph, 190 kn) at sea level
Cruise speed
295 km/h (183 mph, 159 kn)
Range
1,820 km (1,130 mi, 980 nmi)
Service ceiling
6,000 m (20,000 ft)
Time to altitude
1,000 m (3,281 ft) in 2 minutes 30 seconds
4,000 m (13,123 ft) in 15 minutes
Armament
Guns
1 × 7.92 mm (0.312 in) MG 15 machine gun in the rear cockpit
Bombs
6 × 50 kg (110 lb) or 24 x 10 kg (22 lb) bombs internally
