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HEINKEL HE 5   Heinkel aircraft make history

The Heinkel He 5 seaplane was a successful type in a family of monoplane aircraft that ranged from the W 29 to the He 9 (including the individual models He 31, the mail plane He 12, and its successor He 58) and at a time when seaplane aviation had undergone around 15 years of development and was slowly outgrowing its beginnings. After all, aircraft manufacturers now had engines such as the BMW IV, Bristol Jupiter, Junkers L5, Napier Lion, Rolls-Royce, and other types with 300 to 500 hp at their disposal, which were soon followed by more powerful successors such as the BMW VI.
Nevertheless, sufficiently durable and safe designs had still not been developed, which became apparent at the German Seaplane Competition in Warnemünde in 1926. For Ernst Heinkel (1888-1958), the fortunate participation ended with a great success and a winner's check of 247,125 marks for 1st place and 14,925 marks for 3rd place. Among the 18 registered and 12 participating aircraft, there were five Heinkel aircraft types, including the HE 57 (HE 1) borrowed from Sweden. A maximum of only two aircraft of one type were allowed to participate. In the end, the competition claimed two lives and only three aircraft survived, including the HE 5a (D 937, serial number 247) in first place, piloted by Wolfgang von Gronau, who, incidentally, completed an Atlantic crossing in 1930, taking off from List on Sylt, and a circumnavigation of the globe in 1932 in a Dornier Wal. Another Heinkel, a biplane HD 24 (D 935, serial number 250), achieved third place. The D-1313 "Tsingtau," an HD24W (serial number 271), became world-famous as Gunther Plushow's "Silver Condor," with which he explored Tierra del Fuego from the air.
With the HE 12 (D-1717) in 1929, the era of mail planes launched from ocean-going ships by catapults began, then called catapult flight.
In the autumn of 1926, HE 5s set several records, from which Heinkel aircraft manufacturing benefited. The Swedish Navy, which had already had good experiences with the predecessor models, built the Heinkel HE 5 under license as the S5-Hansa in various modifications from 1927 to 1937, and Denmark later bought and built the HE 8 under license as the H.M.II. Both countries used it as a floatplane for air reconnaissance. From the HE 5a onwards, the monoplane types exhibit the same design solutions and already from the HE 1, slight external differences  de, which are reflected primarily in various tail assembly modifications and the engine cowlings adapted to the respective engine types.
Variations can also be observed in the floats, sometimes with a smooth bottom or keel at the front, with a straight or angled tail section. Water rudders on the floats were not yet
[ present on the Heinkel monoplanes at this time. The design scheme of the monoplanes had already been used by Heinkel in the Hansa- Brandenburg W 29 as the earliest ancestor of the HE 5 and was retained after the First World War until the 1930s.
Requirements for Seaplanes
Seaplanes must meet additional requirements compared to land-based aircraft. Their constructions are intended to be seaworthy
and buoyant, requiring seawater-resistant materials. Initially, these were wood and fabric, but further material development led from aluminum-magnesium wrought alloys such as Hydronalium, Duranalium, and Peraluman to Hydronalium-clad duralumin, the so-called Duralplat, or, more recently, to the use of titanium and fiber-reinforced plastics. The hard duralumin (or simply dural) with steel-like high tensile strength and hardness was developed by Wilm in 1906 and manufactured by the Duren Metal Works from 1909 onwards. Molybdenum steels were used for the steel materials, and corrosion protection coatings were employed. To this day, the issue of protection against fouling remains unresolved, and landing and rinsing with fresh water is still the best protective measure against corrosion.
Technical Specifications and Modifications of the Heinkel HE 5
While its predecessors had a wooden fuselage, the HE 5, thanks to advances in welding technology, was the first to feature a welded steel tube fuselage covered with celluloid canvas. A segmented arched fuselage spine covered the rectangular cross-section. The forward fuselage was covered with aluminum sheeting up to the third seat, which also formed the engine cowling. The rear fuselage was raised to protect the tail assembly from sea shock. The constant-chord wings were a fabric-covered wooden structure with two box spars made of spruce straps and plywood webs, as well as steel tube bracing between the spars. The leading edge was covered with 4 mm plywood.
The wing's angle of incidence is zero degrees, the dihedral angle is shown in the drawing as 3.2 degrees on the underside, and 2.5 degrees in the Heinkel data sheet. Fuel tanks with a capacity of 630 liters were mounted in the wings. The braced horizontal stabilizer had a horn balance, as did the vertical stabilizer, which was designed as a pendulum rudder with a cantilevered keel. Both stabilizers had a fabric-covered steel tube construction.The plywood-clad floats with plywood frames and planking had a flat bottom at the front with four keel strips and a keeled bottom at the rear with aluminum sheeting, as well as a vertical tail section. The elaborate float bracing system made of seamless, precision-drawn steel tubes created a semi-cantilevered structure for the wing. Both construction methods, in wood and steel tubing, can be found in Heinkel biplanes, for example, in the standard HD 60 (later He 60) carrier aircraft, which was built in large numbers.
The HE 5 was designed for engine outputs of 420 to 800 hp and was equipped with various engines, such as the HE 5a with the 450 hp Napier-Lion twelve-cylinder W engine, whose design consisted of three rows of four cylinders each, or from HE 5c to f with the BMW VI twelve-cylinder V engine. Following the technical developments in aircraft engine construction, the Swedish S5 aircraft were predominantly equipped with nine-cylinder radial engines; the 55/55A types, for example, with the 450 hp Bristol-Jupiter, which was also built under license by Siemens & Halske as the Siemens-Jupiter. Further engine modifications followed. Thus, the S5D variant, the last one built by Sweden, received a more powerful Mercury My VII-A engine with 675 hp, which drove a three-bladed metal propeller.
The Soviet Union at that time had an interest in modernizing its outdated aircraft fleet and attempted to procure modern technology abroad. Soviet military officials considered the BMW VI to be the most modern engine and chose it for their He 5. According to Russian sources, the aircraft had rigid wooden twin-blade Heine propellers (Hugo Heine Propellerwerk Berlin) and were designated He 5c. The Soviet side was not satisfied with the results of the practical trials on the Black Sea, especially with the range of approximately 500 km, which they considered too short. Heinkel's hopes for orders from the Soviet Union were not fulfilled with this aircraft, but were in 1930 with an initial order of 20 HD 55 flying boats in conjunction with the delivery of the K3 aircraft catapult. This larger order helped Heinkel survive the crisis years of that time.
The HE 5e
Of the HE 5s built by Heinkel, the HE 5e reached the highest production number with eight aircraft. The aircraft were used by the DVS for seaplane training. Although historians assume two-seat trainers (D 1164, D-1386), the photograph of the HE 5 in List on Sylt proves these aircraft to be three-seaters. In its armed version, the aircraft delivered to the USSR carried a Vickers 7.7 mm machine gun permanently mounted on the left side of the fuselage above the engine and a 7.7 mm Lewis twin machine gun on the rear seat, both manufactured in 1924. In addition, there were four bomb locks for light bombs (32/50/82 kg) up to a total load of 160 kg, a bombsight, photographic equipment, and a radio. The antenna was a retractable trailing antenna housed in an antenna tube. A wind generator was mounted on the fuselage for power supply. Russian sources describe this aircraft as a two-seater. An interesting aspect of the HE 5e (serial number 302, registration D-1511) under consideration here—Caspar called this aircraft the "bread fly" because it provided supplementary income for accompanying administrative staff—is the conversion to the HE 5eVF version (VF for experimental wing) carried out in 1930. The owner of this machine was the E-Stelle See in Travemünde (RDL test center; RDL for Reich Association of the German Aviation Industry). While the previous machines had a high-lift airfoil approximately 15 percent thick with a slightly concave underside, the VF version featured a somewhat thinner, semi-symmetrical airfoil of approximately 12 percent with a convexly curved underside. Heinkel's airfoil code was a long series of numbers.with the special feature that the x-value starts at the trailing edge and ends at the nose at 100 percent. The 1/f tail assembly, with its triangular fins and elliptical rudders, also represented the transition to the Heinkel successor types, but its shape was continuously modified in these. In Germany, one HE 5a, one HE 5b, two HE 5c, one HE 5d, and eight HE 5e aircraft were built, one of which was converted to VE. In Bremen, four HE 5f aircraft were built under license by Focke-Wulf. In Sweden, 40 examples were produced, including four 55s, 22 S5As, one 55B, nine 55Cs, and four 55Ds. These Heinkel maritime patrol aircraft are said to have remained in service in the Scandinavian countries until 1945. Anyone who would like to see the fuselage structure of an original HE 5f (formerly D-2231/OMIP, serial number 117, built by Focke-Wulf in Bremen) has the opportunity to do so at the Polish Aviation Museum in Krakow.
Paintwork of the seaplanes
The Heinkel aircraft, which were built using mixed construction methods, had protective coatings For several materials, painting was required, such as for the steel tubes of the fuselage, wing, and tail assembly structures, for the wing timbers, for the aluminum skins, for the light alloy engine casings, and for the fabric covering. Painting was generally carried out, even on the inside before skinning; only in later prototypes are unpainted cases known.
Unfortunately, no color photographs of the aircraft exist from the late 1920s, at most colorful advertising posters or paintings by marine artists, which, however, may not be authentic. For example, a poster for the 1926 seaplane competition shows the aircraft painted yellow. The color information in this documentation also does not claim to be absolutely accurate – and if anyone who might have further Heinkel documents knows more about this, we would be grateful for any information. Therefore, determining the color tones is difficult. Michael Ullmann gives the following color tones for the period before 1933:
a) Light gray for all surfaces, for example, DKH L 40/52 Light Gray or Avionorm Nitrocoat 7375 Matte Gray; and

b) Silver for the floats as DKH L 40/52 Silver or Ikarol 111/5, the later RLM 01 Silver.
When asked, he assumes: "Wing top surface yellow, floats and fabric covering in silver, remaining metal parts matte light gray." Is that certain?
Incidentally, the list already mentions the most important aircraft paints of the time: Avionorm from Ludecke & Co. GmbH in Berlin-Wilmersdorf; DKH from Dr. Kurt Herberts & Co. Lackfabrik in Wuppertal-Barmen; Ikarol from Warnecke & Böhm AG in Berlin-Weissensee; and Tokiool from Zoellner-Werke GmbH in Berlin-Neukirchen. The company Farben-Kiroff- Technik, which also supplies historical RLM paints, uses sources that specify silver and gray for the aluminum parts and light gray for the covering.
According to Dr. Volker Koos, the floats may have had a copper coating in the underwater area or possibly completely, but this is not proven. The floats could also have been yellow, especially since paint systems (paint chains) existed for this color and this is documented later. However, another reflective coating is also possible.
The gray color tone on the wooden base of the floats is similar to that on the fabric covering or the aluminum sheet; or the topcoat has worn away. The floats of the Krakow wreck have a greenish tint; here, the topcoat has probably weathered away, revealing the original green primer.
The color information for the HE 58 (D-1919) is better documented. Jörg-M. Hormann writes about the catapult aircraft launched from the express steamers Bremen and Europa that a striking paint scheme of red and white (fuselage red and markings white, as well as wing white and markings red) was tested on the HE 58 (later on the Ju 46) because the previously silver-gray painted aircraft blended in with the gray sky or sea; yellow is not mentioned here. A clear indication of a Heinkel seaplane paint scheme from this period is given by Gunther Pluschow in his book "Silver Condor over Tierra del Fuego": He speaks of a silver paint scheme for the aircraft HD 24W, the D-1313 "Tsingtau".
Paint scheme, markings, and insignia of the HE 5e I have rendered the colors of the HE 5e in the drawing according to Michael Ullmann, but I leave both variants open for the wing. There is no suitable RLM or RAL equivalent for the light gray. The late RLM 02 is too dark. A possible option would be RAL 7004 Signal Grey, slightly lightened with white. The silver tone can be achieved with RAL 9006 White Aluminum.
For yellow, RAL 1003 Signal Yellow, RAL 1004 Golden Yellow, RAL 1021 Rapeseed Yellow, or Lufthansa Yellow RAL 1028 would be conceivable. I chose red for the fenders at the float tips because that's how it's documented in the Krakow Aviation Museum. On the nose of the D-1511, the RDL-Travemünde coat of arms is affixed to both sides on a cream-white background with semi-matte black lettering. The Heine wooden propeller with a steel-reinforced leading edge features the Heine logo on each half of the blade. This logo was available in various versions; I found four, the one presented here at the German Museum of Technology in Berlin. The propeller may have been protected with a clear coat. It shows the wood tone. The registration number D-1511 (as in the picture with a hyphen) is located on both sides of the fuselage and on the wing in double size on both sides, top and bottom. On the left side of the tail, the usual weight information is found in small print. Above this, the owner's information may be located. The Heinkel logo - although normally located on the vertical stabilizer of Heinkel aircraft - could not be found in the pictures; perhaps it has been retouched. The markings D-1511 are presumably in semi-matte black; later, this became the color RLM 22, which corresponds to RAL 9004 Signal Black.
Finally, regarding the Heinkel type designation – whether HE or He – the following should be said: HE stood for Heinkel monoplane, HD for Heinkel biplane. From 1932 onwards, the standardization of type designations with two letters began, such as Ju, Fw, Me, and thus also He for Heinkel aircraft (regardless of whether monoplane or biplane) – no longer with a factory-specific, but rather a consecutive number, which, however, included all manufacturers. Two spellings can be found for the registration code: without (D 1511) and with a hyphen between the letter and number (D-1511). From October 1930, the hyphen became mandatory.