Two apparently unrelated events early in 1931, one in Europé and one in the USA, were destined to influence the development little more than a year later of one of the most elegant aeroplanes ever to come from a German drawing board and one that was to be of particular importance to Heinkels designer twins, Walter and Siegfried Giinter. The airraft in question, the Heinkel He 70, was not an unqualified success in all its röles, but it provided HeinkePs designers and engineers with their first practical experience of such features as a cantilever low wing layout, retractable undercarriage, split trailing edge flaps and flush-riveted metal fuselage construction all features that were to find their way into subsequent Heinkel designs, some of which were to help provide the backbone of the oftensive strength of the Luftwaffe when it went to war latcr in the same decade. war still seemed far distant when the 'thirties dawned, however, and it was the development of air transport that occupied the attention of many aircraft manufacturers around the world. Among them was the struggling Lockheed Aircraft Company of Burbank, California, which evolved the Orion as a high speed transport combining a low wing and retractable undercarriage of the smaller Altair with the enclosed cabin accomodation of the high-wing Vega. First flown in 1931, the Orion quickly established a reputation for speed, service and luxury albeit the cabin seated only four passengers. about the same time that Lockheed began testing the Orion, well-established Swiss airlines — Ad Astra Aero AG and Balair AG merged to form Swissair, and when that airline went shopping for its first new equipment, early in 1932, it was the Lockheed Orion that attracted the attention of the founding directors Balz Zimmerman and Walter Mittelholzer.
Two Orions were imported by Swissair and were used to open an express service, in May 1932, linking Zurich with Munich and Vienna. With a maximum speed of 224 mph (360 km/h) and cruising at 180 mph (290 km/h), the Orions created a sensation on the European airline scenc. They were, incidentally, the first US airliners purchased by any European airline, thus opening the door to what was eventually to become a fiood of US transport aircraft, with which the European manufacturers, pre-occupied with the production of military aircraft, would in the end prove unable to compete eflectively. In 1932, however, there were plenty of designers willing to learn
the lessons of the Orion and to attempt to produce comparablc, competitive, aeroplanes, and Siegfried and Walter Gunter were among them. The opportunity to translate ideas into achievement was provided by Deutsche Lufthansa, which, early in 1932, invited both Heinkel and Junkers to investigate the design of a high-speed. small-capacity transport aeroplane for use on express routes in Europé, with a performance comparable to that of the Orion. Projects quickly took shapeon the drawing boards at Warnemiindeand Dessau, respectively as the Heinkel He 65 and the Junkers Ju 60; both were clean, low-wing monoplanes powered by the 575 hp BMW-built Pratt & Whitney Hornet radial, with passengers in a cabin within the fuselage and a separate cockpit for the two-man crew.
Neither Heinkel nor Junkers intended to use a retractable undercarriage, believing that properly faired main units were preferable to the complication of retraction mcchanisms, still a relative unknown quantity in Europe. However, Lufthansa had not expected the Orion to appear on European routes for some years when it had drawn up its requirements at the beginning of 1932, and the arrival of Swissair's pair of Orions in May was something of a bombshell. With the competition already on the doorstep, as it were, rather than being some 3,500 mls (5 633 km) away on the other side of the Atlantic, DLH and the manufacturers realised that they had not simply to match the Orion's performance but to better it.
introduction of retractable main undercarriage members, substitution of a 637 hp BMW VI 5,5 Z 12-cylinder Vee engine with liquid (glycol) cooling, and a reduction of about 2,200 Ib (1 000 kgLjn the gross weight. To minimize drag, the engine cooling radiator was made retractable, being located in the fuselage just forward of the wing. Built in the Heinkel works at Warnemiinde, near Rostock, the prototype He 70a emerged on 1 December 1932, making its first flight the same day after a series of taxi runs in the hands of the company's chief test pilot, Flugkapitän Werner Junck; the aircraft being ferried, with main wheels locked down, to Travemiinde for continuation of flight testing. Carrying no markings, the He 70 was seen to be an elegant monoplane, the wing, tailplane and fin-and-rudder assembly all being of assthetically-pleasing elliptical form. Viewed head-on, the wing was of “inverted gull” form, having marked anhedral on the inner sections, this transforming to dihedral on the outer panels; the arrangement, which was to be emulated by several subsequent Heinkel designs, had several advantages it simplified the structural joint between wing and fuselage, it shortened the undercarriage main members and it helped keep the tailplane clear of disturbed airflow bchind the wing. Wing construction was of wood, with two box spars, closely-spaced ribs and plywood covering, and the fuselage was all-metal. Each main undercarriage unit comprised an oleo leg and two other members, one of which served to raise the whecl outwards to lie flush in the wing well when it was drawn inwards towards the fuselage. Wheelbrakes were fitted and the tail skid was also retractable in the prototype, although this latter feature was later abandoned. Anothcr unusual feature of the He 70 was that the cockpit, elcgantly faired into the fuselage lines, was offset to port, although the instrument panel, below the windscreen line, occupied the full width of the fuselage. A radio operator was seated to the right of, and slightly behind and below the pilot, having no dircct view out of the cockpit.
Seats were provided in the cabin for four or five passengers. The second He 70 was completed in February 1933, as the He 70b, with the marking D-3 for comparative flight trials with the Ju 60 (D-5) and a Ju W34 (D-4). It originally had a BMW VI 6,0 Z engine and was generally similar to the He 70a. The latter, now registered D-2537, had mcanwhile also been fitted with a BMW VI 6,0 Z engine — later replaced by a BMW VI
6,3 Z. The He 70a was also tested with various trailing-edge flaps plain, slottcd and split and plain flaps were adoptcd for the produetion aircraft, although not at first fitted to the first three He 70s completed. A larger tailplane was also introduced from the third aircraft.
Before entcring airline service, the He 70 demonstrated its potential in a number of record-breaking flights made in March and April 1933 by the second aircraft. Piloted by Flugkapitän Untucht of Lufthansa, it achieved an average speed of 222 mph (357,4 km/h) over a 100-km (62-ml) closed circuit with a 1 000-kg(2 200-ib) payload, 221 mph (355.3 km/h) over a 500-km (310-ml) circuit with the same payload, and 214 mph (345,3 km/h) over a 2.000-km (1,242-ml) circuit with no payload. Also during 1933, the DVL confirmed the maximum speed of the prototype at 234,3 mph (377 km/h). This compared with the 227 mph (365 km/h) of the first Orion. although a couple of later special models were faster. More significantly perhaps, the top speed of the He 70 was substantially in advance of the best performance achieved by the (biplane) fighters still forming the front-line equipment of almost every European air force — the RAF and the clandcstine Luftwaffe included. Moreover.theHe70wasfarfrom havingdemonstrated its maximum performance. which was limited in 1933 only by engine power and propeller efliciency, not by aerodynamic considerations; six years latcr, an He 70 powered by a Rolls-Royce Peregrine for development flying (as described later in this account) was to attain a top speed of 299 mph (481 km/h) a remarkable achievemcnt for an aeroplane conceived in 1932 and a tribute to the efficiency of the Gunter brothers’ design of which they themselves probably remained unaware. For its record flights, the He 70b had a BMW VI 7,5 Z engine driving a VDM three-bladed variable-pitch propeller in place of the original ground-adjustable two-bladed unit, and some modifications to the cockpit fairing. After reconversion to passenger configuration, D-3 was delivered to Lufthansa, which called it the Hy 70A and retained HeinkeFs original name of Blitz (Lightning), although bird names were used for the remainder of the fleet.
The next aircraft to reach Lufthansa was the third prototype, similar to the He 70A apart from having a BMW VI 7,3 Z engine. Known to Heinkel as the He 70c and to Lufthansa as the He 70B, it was originally flown as D-3114 and later became D-UBAF Sperber. A pre-production batch of three He 70Bs was put in hand, with registrations D-UBYL, D-UZUH and D-UPFT, but because of military interest now being shown, these were completed as high-speed reconnaissance aircraft, one as the prototype He 70F-1 and two as part of a batch of 12 He 70Cs for the Luftwaffe. In their place, Lufthansa received three He 70D-0s from a batch of 12 built primarily for military use, these being identified as D-UBIN Falke, D-UDAS Habicht and D-UGOR Schwalbe.
Early in 1934, using one of these aircraft, Lufthansa made a proving flight from Berlin to Seville and Las Palmas, a distance of 2,610 mls (4 200 km) being covered in 13 hr 25 min, and thereafter the He 70s were used to carry mail as far as Seville on the airline’s fortnightly service to South America. Inauguration of the Blitz-Strecken (Lightning Routes) followed on 15 June 1934,.linking Berlin, Hamburg, Cologne and Frankfurt, with the first service being operated by Habicht. The Lufthansa fleet was completed during 1935, with delivery of ten He 70G-ls, these being commercial versions based on the military He 70F. Powered by the BMW VI 7.3 Z engine, these had a further increase in all-up weight, accommodated five passengers and had a retractablc tailskid. Like the military
versions. they had the cockpit on the centreline. and were part of a production batch of 25. the remainder being used by the Luftwaffe in the liaison role. With delivery of these. Lufthansa elinquished ils two prototypes. and for the next couple of years He 70Gs saw constant service on domestic routes in Germany. They were finally withdrawn in 1938. by which time capacity was too small. and the Heinkel He 111 ls took over the Blitz-Strecken. The nine Ile 70G-1s for Lufthansa were D-UBOX Geier. D-UJUZ Bussard. D-UKEK Amsel, D-UMIM Albatros. D-UNEH Condor. D-UPYF Adter. D-UQIP Rabe. D-USAZ Buntspechl. D-UXUV Drossel and D-UVOR Kormoran.
Among the other He 70G-1s were D-UFAZ and D-USOR,armed personncl transports for the Lu/twaffe with accomdatton for three passcngcrs. Six He 70G-2s, with tailwheel in place of skid. were specially-equippcd personnel transports for General Staff use. registered D-UPET. D-UGEX. D- UHYQ. D-UHAF. D-UXUL and D-UFAL. of the other civil-registered He 70s. most were prototypes
or development models. They included the first He 70C-0, D-UHYS; the He 70d military prototype D-UKOL, the military He 70E prototype D-UFIL and various He 70Fs. D-UXER and D-UPUY were He 70F-2 prototypes, and D-UKAF, D-UJEZ, D-UVYR and D-UVYP were He 70F-2s for use by the Chancellor’s flight. He 70F-2s D-URAF and D-UMAL- carried radar for special missions. D-UFAL was the prototype He 70F-3 and other aircraft of this subtype carried the markngs D-OMER, D-OFYT, D-OSOL, D-OTYS and D-OZ1X.
The Rolls-Royce saga
Of the Heinkel He 70’s varied achievements in both the commercial and the military fields, one of its most unexpected must surely have been the röle it played in developing Rolls- Royce engines power plants that were destined to figure prominently in RAF aircraft committed to the defence of the UK against the Luftwaffe. The Rolls-Royce company had taken in 1934 the unusual step, for an engine manufadturer. of setting up its own flight test department. Initially, this Experimental Flight Test Establishment, based at Hucknall, near Derby, relied upon an assortment of biplanes as test vehicles, but it was soon realised that a more specialised aircraft would be valuable — one that was large enough to permit easy installation of various engines and different engine/exhaust/ radiator/oil cooler combinations, could accommodate test instrumentation and an observer as well as the pilot, was free of unnecessary drag-producing excrescences and had a high performance. Few aeroplanes, in 1935, appeared capable of meeting this requirement, and none better than the Heinkel He 70. A contract was signed between Rolls-Royce and Heinkel —
there being, at that time, no political or commercial impediments to such a deal whereby the latter agreed to undertake installation of a 675 hp Kestrel V water-cooled 12-cylinder Vee engine, conduct initial flight tests and deliver the completed aircraft to Hucknall, all for the sum of £13,000. The Kestrel was supplied to Rostock towards the end of 1935 where, there is little doubt, it was subjected to close technical scrutiny and perhaps bench-testing before being fitted in the He 70G D-UBOF. Re-registered G-ADZF, the test aircraft flew for the first time with the Rolls-Royce engine on 16 January 1936, piloted by Heinkefs new chief test pilot Otto Cuno. Somewhat surprisingly, Heinkel found it necessary to make 12 more flights, with a total airborne time of 6 hr 15 min, before delivering 'DZF to Hucknall on 27 March 1936, Otto Cuno making the flight from Rostock in 3 hr 40 min. If nothing else, the flight testing in Germany allowed Heinkel to compile comprehensive comparative data for the He 70G with BMW VI 7,3 Z and Kestrel V engine. Figures published later showed that the Kestrel installation was 17} in (0,45 m) shorter and the gross weight was 220 Ib (100 kg) lower. The maximum speed increased from 224 mph (360 km/h) to 255 mph (410 km/h) at sea level; the time to reach 13.123 ft (4 000 m) was reduced from 15 min to 11.8 min and the initial rate of climb improved from 1,025 ft/ min (5,2 m/sec) to 1,340 ft/min (6,8 m/sec). Rolls-Royce sub- sequently established a top speed of 258 mph (415 km/h) at 15,000 ft (4 572 m) for the aircraft as delivered.
In July 1936, a new series of tests began, with a 750 hp Kestrel XVI installed, together with an automatic control system, in which a thermostat operated the radiator flap to maintain the required flow of cooling air. Unlike the original He 70 versions, ’DZF at this stage had a fixed radiator under the front fuselage. With the Kestrel XVI installation, the cooling system was changed from pure water to a 30-70 per cent glycol-water
mixture, and comparative tests were made with the original wooden fixed-pitch propeller and a Hamilton Standard variable- pitch metal unit.
During 1937, three dilTerent nose configurations were tested on the He 70, in each case with a Kestrel XVI. The first trial made use of twin circular radiators, one each side near the front of the engine, producing an installation identical with that in the Miles M.9 Kestrel; various exhaust configurations were tested and a max speed of 280 mph (451 km/h) at 15,850 ft (4 830 m) was recorded. The second configuration, first flown on 16 July, had the radiators in a mid-ventral position and in addition to being flight tested, the He 70 was evaluated in this configuration in the full-scale wind tunnel at Farnborough. In this guise, a top speed of 264 mph (425 km/h) at 16,000 ft (4 877 m) was recorded. The final test configuration in 1937 comprised an annular cowling with the radiators, oil cooler and header tank grouped round the propeller reduction gear assembly in what had the appearance ofa radial engine cowling; first flown in this form on 26 October 1937, the He 70 achieved a speed of 279 mph (449 km/h) at 15,500 ft (4 724 m).
On 21 March 1938, G-ADZF began another series of trials, with a retractable ventral radiator and the original nose cowling restored. By varying the radiator area exposed to the airstream, it was possible to establish just how much was needed for various engine settings; with the radiator fully retracted, a speed of 288 mph (463 km/h) was recorded.
The final phase of the He 70’s useful life at Hucknall began on 8 October 1938, when the first flight was made with a Peregrine I engine replacing the Kestrel. This was the first flight of the Peregrine engine, which was a development of the Kestrel destined to power the Westland Whirlwind, although not with unqualified success (see Whirlwind/July 1973 issue). With the Peregrine rated at 845 hp. the He 70 now achieved 299 mph (481 km/h) at 16,650 ft (5 075 m) helped. perhaps, by a new finish applied during the final conversion, when a high-gloss maroon coat replaced the overall grey in which the He 70 had been delivered.
By August 1939, the Rolls-Royce test bed had completed 176 hrs with the Peregrine engine and 242 hrs with the Kestrel, making a significant contribution to the company’s knowledge of radiator and exhaust design and other matters relevant to subsequent engine development. Because of its visua) similarity to other Heinkel types which it was thought might well make their appearance over the UK, the He 70 was grounded on 31 August 1939, but made two further flights in March 1940. It was subsequently stored at Hucknall until March 1945, when, sadly, this classic and historic aircraft was broken up for scrap.
Military applications
The remarkable speed performance demonstrated by the He 70 prototypes naturally attracted the attention of the various semi-clandestine military organisations that, long before 1932, had been planning and training for the creation of an overt Luftwaffe. Speed was not everything, however; although the He 70 was considerably faster than the He 51 fighter biplanes with which the new Jagdfiieger were to be equipped, it was too large to be an easily-manoeuvred heavy fighter, and interest therefore centred around its possibilities as a light bomber and reconnaissance aircraft.
The first examples of the He 70 delivered for military use differed little from the basic commercial model, but a modified cockpit fairing was gradually evolved, using the He 70Bs and the first He 70C (D-UHYS). The fairing was widened to become symmetrical on the fuselage centreline, and provision was made for an observer or gunner in the dorsal position, occupying the passenger cabin. This same arrangement was used on a new military prototype with uprated BMW VI 7.3 Z engine. the He 70d D-UKOL, and on nine He 70D-0s for the Luftwaffe.
The He 70E (prototype D-UFIL) was intended as a bomber and the He 70F (prototype D-UBYL) was similar but for reconnaissance duties. The raised decking aft of the pilofs position was more extensively glazed and the gunner’s position was semi-enclosed. A bomb-bay was introduced in the fuselage centre-section to accommodate six 110-lb (50-kg) or 24 22-lb (10-kg) bombs or in the case of the He 70F a 61.5 Imp gal (275-1) auxiliary fuel tank plus a hand-operated camera.
Production versions of the bomber and reconnaissance models were designated He 70E and He 70F respectively and plans were made by the Reichsluftfahrtministerium (Air Ministry) to include 72 reconnaissance versions in the total strength of 4,021 aircraft that the Luftwaffe was expected to achieve by the end of September 1935. The first four He 70F-0s were delivered before the end of 1934, with the F-l, F-2 and F-3 versions following in 1935-36, with small improvements. Carrying three crcw membcrs, the He 70F-1 had a defensive armament of one 7,9-mm MG 15 machine gun on a flexible mounting in the aft cockpit, with six 75-round ammunition drums. The auxiliary fuel tank was carried on shackles in the forward part of the bomb bay, and could be jettisoned when empty; the main fuel capacity comprised two 46-Imp gal (210-1) tanks in the wing centre section. Fully loaded, the He 70F-1 had a top speed of 208 mph (335 km/h) but it did not prove very populär with its crews, who were unaccustomed to aircraft with confined, fully enclosed accommodation, and its service career was to prove relatively short.The He 70Fs were operated primarily by the Fernaujklärungsgruppen. units having responsibility for long-range reconnaissance both for strategic purposes and for target spotting in support of bomber units. Between 1935 and 1937, each of six Aujklärungsgruppen, viz (F)/121 at Neuhausen, (F)/122 at Prenzlau. (F)/123 at Grossenhain, (F)/124 at Kassel, (F)/125 at Wiirzburg and (F)/127 at Goslar, operated examples of the He 70F. In most cases, they equipped one Staffelin each Gruppe. other equipment being He 45 biplanes and. in due course, Dornier Do 17Fs. The latter had a much greater range than the He 70s, and were altogether more suitable for use as camera
platforms, but prior to the twin-engi ned typebecomingavai lable, the Heinkel inonoplanes did undertake some clandestine high- altitude reconnaissance sorties beyond the German national frontiers.
Numerically, the He 70E bomber was less significant than the He 70F in Luftwaffe service, but 27 were in use as fast long- range bombers in 1937 with the first of the Luftwaffe's Sturzkampfflugzeuge (dive bombing aircraft) units formed as the I Gruppe of Stuka Geschwader 152 in 1936 but redesigna- ted IV(Stuka)/LG 1 in 1937, at Barth/Baltic. Three He 70s also served (alongside Henschel Hs 123s) in each Staffel of 11/162 at Luebeck-Blankensee during 1936 and 1937, but the type was unsuited to the dive-bombing röle of these units, and was replaced by Ju 87s as quickly as possible. Of the total of 304 He 70s ol all types built, 262 are believed to have been delivered to the Luftwaffe.
In September 1938, 73 He 70s remained in the Luftwaffe invefitory, of which 49 were scrviccablc, but a year later all had been withdrawn from the Aufklärungsgruppen and had been relegated to service with the AjB Schulen and the Kurrierstaffeln, for training and Communications duties respectively. The type had already received its baptism of fire. however, as a result of 18 He 70F-2s being taken to Spain late in 1936 by Aujklärungsgruppe A/88 as part of the Legion Condor. They achieved little success in German hands and were soon replaced by Do 17F-ls, whereupon, in April 1937, 12 of the Heinkels were transferred to the Nationalist Southern Army, which was having to rely upon ancient Breguet XIX monoplanes for its observation and reconnaissance missions. Under the command of Major Sartorious, the He 70s were used to equip Grupo 7-G-14 in the Bilbao area and thereafter played important bombing and recce röles. In November 1937, the Group was divided into two, participating in the Teruel operations that winter but being transferred to the less important Andalucia and Extremadura fronts in June 1938. Only one He 70 was lost by the Nationalist air arm up to the end of the Civil War in April 1939, and the type served on in Spain until the early fifties for liaison and Communications duties.
Final developments
In an efiort to extend the longevity of the He 70, Heinkel studied several alternative power plant installatio'ns during 1936, leading to the use of He 170 and He 270 designations (which were company type numbers rather than RLM-allocated designa-
tions). Among the engines considered was the 910 hp Daimler Benz DB 600G, and at one stage, Heinkel apparently regarded this as the He 170 — actually illustrating the proposal in a company brochure with a photograph of the Kestrel-engined G-ADZF, which presumably possessed fairly similar cowling lines. In the event, however, the DB 600 engine was not used in any He 70 airframe, and the He 170 designation was assigned nstead to a version with the 910 hp Gnöme-Rhöne 14K Mistral-Major 14-cylinder two-row radial.
This variant was developed specifically for use by the clandestine air arm set up in Hungary — where the He 70F demonstrator D-UMAL was displayed during 1936 in order to make use of the Mistral-Major engines being produced in Budapest by Manfred Weiss Flugzeug und Motorenfabrik. A trial installation of a (French-built) Gnöme-Rhöne 14K was made in an He 70F-3 airframe, known as the He 170 VI (D-OASA) and flown before the end of 1936. It was followed by a second prototype, the He 170A-01 (D-OHEW) in which the engine was located farther forward, cg difficulties having been exper- ienced with the shortnosed VI.
Eighteen He 170As were ordered by the H ungarian government. deliveries being made between September 1937 and February 1938,andincludingtheHe 170A-01 already mentioned. They were used to equip two squadrons in the 1st Independent Long-Range Reconnaissance Group, formed at Måtyåsföld. near Budapest, in 1939, and later transferred to Kecskemet, from where the first operational sorties were flown in March 1939 when the Hungarian Army reoccupied Carpatho-Ruthenia
In the summer of 1940, the aircraft were used to make manyhotographic sorties over Transylvania, which Hungary was demanding should be returned to her control by Rumania.
After this transfer had been made in August 1940, the He 170As returned to Budaörs. near Budapest, remaining grounded for most of the winter because of unserviceability.
With the start of the Balkan campaign in April 1941, theHe 170As became active again, flying low-levcl missions for the Hungarian Army when it occupied the Båcska territory that had been ccded to Yugoslavia; and on 26 June 1941, the first sortie over Soviet territory was flown. Fewcr than 30 missions were mounted in this campaign. however, before the type was withdrawn from service by the Hungarian High Command because of operational unsuitability: specifically, it was short on range, the field of vision was strictly limited and the crews disliked the propensity of the wooden wings to burn when hit. In fairness to the He 170 which was always known simply as He 70 to the Hungarians it should be added that only one was shot down (by Soviet fighters) and one other was lost when it ran out of fuel on a reconnaissance mission.
In parallel with the project to instal a DB 600G in an He 70, Heinkel had also studied a DB 601 installation. Rated at 1,175 hp, the DB 601 Aa offered the possibility of a major improvement in performance, and a trial installation was made in a late-production He 70F which flew in the Spring of 1938 as the He 270 VI (D-OEHF). Other changes included an improved installation for the dorsal machine gun, addition of a fixed forward-firing 7,9-mm MG 17 gun, elimination of the cabin Windows and provision for additional fuel tanks. With a gross weight of 9,149 Ib (4 150 kg), the He 270 had a maximum speed of 286 mph (460 km/h) at 6,560 ft (2 000 m) and a maximum range of 994 mls (1 600 km).
Heinkel proposed a scheme to modify the Luftwaffe and Lufthansa He 70s to this new standard, but little interest was aroused by this proposal, for the replacement of the He 70s in front-line Luftwaffe units was already imminent, and only five remained in service with Lufthansa and. in any case, DB 601 s were in short supply and were badly needed for use in more modern types. So came to an end the production and development of a short-lived star in the German firmament an aircraft of great beauty and of considerable technical merit that was, neverthcless, quickly overtaken by types of even greater capability, in both commercial and military röles, that appeared as a result of the technological revolution that the Blitz itself helped to launch.
