Dive Bomber That Misplaced Out to the Celebrated Stuka
The Blohm & Voss Ha-137 is a forgotten also-ran within the dive bomber competitors gained by the well-known Junkers Ju-87 Stuka.
A handful of World Struggle II plane took generic names and made them their very own. For instance, the sobriquet “Flying Fortress,” coined for quite a few massive bombers bristling with armament, in the end grew to become the official identify of the Boeing B-17. In Russia, Shturmovik merely means “floor assault airplane,” however the phrase got here to be related to the Ilyushin Il-2. Likewise, Stuka—a reputation derived from the time period Sturzkampfflugzeug, or “dive bomber”—is universally accepted because the identify of 1 German airplane, the Junkers Ju-87.
The Ju-87 could be mentioned to have had the monopoly on its identify from the second its blueprints have been drawn up as a part of the clandestine revival of Germany’s army air arm, the Luftwaffe. Nonetheless, the Germans did undergo the pretense of holding a contest and invited Arado and Heinkel to submit their very own dive-bomber designs. There was additionally an unsolicited fourth contender, from a brand new agency, that had its share of fascinating options, regardless that its probabilities of success have been hopelessly distant.
Other than being a single-seater design with an open cockpit—as in contrast with the cover that sheltered the Ju-87’s two crew members—that fourth competitor, the Blohm & Voss Ha-137, bore a outstanding similarity to the Junkers design. The resemblance was strictly coincidental, nevertheless. In one other coincidence, the Ju-87’s designer, Hermann Pohlmann, joined Blohm & Voss later, in 1940, however the Ha-137’s origin could be traced to a different German designer’s work—on a Japanese fighter.
In June 1933, the Japanese military instructed the Kobe-based Kawasaki Plane Engineering Firm Ltd. to design a radical new low-wing monoplane battleer. Work was initiated by Kawasaki’s chief designer, Takeo Doi, and a visiting German engineer, Dr. Richard Vogt. Vogt’s strategy to the mission was to include an inverted gull wing to offer higher downward visibility to the pilot and likewise enable a shorter, sturdier undercarriage.
In the meantime, on July 4, 1933, Germany’s largest shipbuilding agency, the Blohm & Voss Schiffwerft of Hamburg, established an aviation subsidiary, the Hamburger Flugzeugbau (plane producer). After producing its first airplane, the Ha-135 coach, chief designer Reinhold Mewes left the agency to work for the Fieseler Flugzeugbau. Vogt was then requested to return to Germany to turn out to be chief designer, common supervisor and half proprietor of the Hamburger Flugzeugbau.
Whereas he was on his approach house aboard SS Europa, Vogt conceived the thought for a novel structural refinement to the inverted gull wing—a single, fundamental load-carrying, tubular spar, situated on the thickest level of the wing part and sealed to type a gasoline tank.
In Vogt’s absence, Kawasaki accomplished 4 prototypes of its experimental Ki.5 fighter. In the midst of testing and modification between February and September 1934, the Ki.5 failed to provide the all-around visibility that Vogt predicted and likewise suffered from poor lateral stability at low speeds. Prudently reverting to a extra conservative various, Kawasaki went on to mass-produce the Ki.10 biplane fighter in 1935.
Vogt’s first design for the Hamburger Flugzeugbau was the Ha-136, an all-metal superior coach, of which two prototypes have been inbuilt 1934. Vogt, nevertheless, had extra formidable design plans. He had realized that the C-Amt (technical workplace) of the air journey fee had begun a two-stage mission to develop dive bombers for the Luftwaffe, whose existence, in violation of the Versailles Treaty of 1919, was nonetheless being saved secret. The primary stage of this Sturzbomber-Programm referred to as for the design of a standard all-metal biplane and resulted within the development of the Fieseler Fi.98 and Henschel Hs-123; the latter was chosen for manufacturing within the late summer of 1935. The second section envisioned the event of a complicated, state-of-the-art dive bomber, and the Arado, Heinkel and Junkers corporations have been requested to develop prototypes.
Given its full lack of expertise in fight plane, the brand new Hamburger Flugzeugbau had not been invited to take part within the Sturzbomber-Programm in any respect, however Vogt noticed it as a golden alternative to exhibit the deserves of his tubular-spar wing, which he felt was ideally suited to face as much as the stresses of dive bombing. Vogt subsequently submitted his personal design research, designated Undertaking 6, to the C-Amt as a non-public enterprise.
Primarily, Vogt’s dive bomber was an aerodynamically improved and considerably scaled-up model of the Kawasaki Ki.5. The wing used Vogt’s tubular spar, of which the middle portion was product of welded chrome-molybdenum metal and the outer sections of riveted duralumin, sealed to comprise 59.4 imperial gallons of gasoline. Hydraulically operated trailing-edge flaps have been put in within the heart part and on the inboard parts of the outer wing panels. Every wheel was mounted between two vertical pneumatic shock absorbers and enclosed below streamlined fairings. The oblong-section fuselage was a semimonocoque construction, with the pilot seated in an open cockpit over the wing’s trailing edge. Two mounted, synchronized 7.9mm MG17 machine weapons have been mounted within the higher decking of the ahead fuselage. The same weapon was put in in every undercarriage fairing, however there was sufficient area to accommodate 20mm MG FF cannons rather than the MG17s if the C-Amt’s specification referred to as for better firepower.
Undertaking 6 was designed to make use of the Kind XV engine that was then being developed by the Bayerische Motoren Werke. When the way forward for the BMW XV fell into doubt, the C-Amt requested Vogt to change his design to take the BMW 132A-3, a license-built model of the 650-hp Pratt & Whitney Hornet 9-cylinder radial engine. Vogt obliged by resubmitting his design as Undertaking 6a and added another model, Undertaking 6b, utilizing a Rolls-Royce Kestrel engine. Hedging his bets even additional, Vogt ready a backup design, Undertaking 7, utilizing a biplane wing construction and a Wright Cyclone engine, however the C-Amt was sufficiently impressed with Undertaking 6a to award the Hamburger Flugzeugbau a contract for 3 prototypes, below the designation Ha-137.
The primary prototype, Ha-137V-1 (given the civil registration D-IXAX), was accomplished and flown at Hamburg in April 1935. It was shortly adopted by a second prototype, the Ha-137V-2 (D-IGBI). Implywhereas, nevertheless, the State Ministry of Aviation (Reichsluftfahrtministerium, or RLM) had issued its definitive specification for the second-phase Sturzbomber in January 1935, stipulating that it have a rear gunner. Vogt had identified that the two-seat requirement was coming, however a second crew place would have necessitated a considerably bigger plane than he had in thoughts, with an opposed impact on efficiency. He subsequently continued work on the Ha-137 as a single-seater, playing that it would nonetheless win over the RLM.
What Vogt didn’t know was that the deck had been stacked not solely in opposition to his Ha-137 but additionally in opposition to the 2 official Sturzbomber-Programm contenders. Though the specification was issued concurrently to Arado, Heinkel and Junkers, it had, the truth is, been drawn up across the design that the RLM had favored from the very starting—the Junkers Ju-87.
Arado’s Ar-81V-3 biplane managed to provide an general efficiency superior to that of the Ju-87V-2, however it was rejected by the RLM on precept as a retrogressive design. Heinkel designer Walter Günter produced the He-118, which was a bigger however extra highly effective and aerodynamically refined monoplane than the Ju-87 and featured retractable touchdown gear. Chief of Plane Procurement and Provide Ernst Udet was sufficiently impressed to test-fly the He-118V-3 prototype himself on June 27, 1936. When Udet failed to regulate the propeller pitch as he went right into a dive, nevertheless, the propeller “ran away” into excessively excessive rpm and floor up the discount gears, on high of which the tail broke away. Udet bailed out safely, however the incident dashed the He-118’s final slim hope of breaking the Ju-87’s preordained maintain on a manufacturing contract.
Mockingly, the single-seat configuration that disqualified the Ha-137 from the Sturzbomber-Programm virtually acquired it accepted in a unique class. On the advice of Colonel Wolfram von Richthofen, the RLM agreed to sanction the continued growth of the Ha-137, each as a backup for the Ju-87 and as a potential close-support plane, or Schlacht-flugzeug. Consequently, three extra prototypes have been ordered with the brand new Junkers Jumo 210 liquid-cooled engine. Whereas the radial-engine-powered first and second plane have been thought to be prototypes for the Ha-137A, the third prototype, designated Ha-137V-3 (D-IZIQ), was accomplished with a supercharged 640-hp Rolls-Royce Kestrel 12-cylinder, liquid-cooled engine, because the prototype for a potential manufacturing mannequin to be designated Ha-137B. Whereas the sooner radial-engine fashions used a three-bladed, adjustable-pitch steel propeller, the Ha-137V-3 used a two-bladed fixed-pitch picket propeller.
Testing of the primary two prototypes started at Travemünde in the summertime of 1935. In distinction to the disappointing Kawasaki Ki.5, the Ha-137 was praised for its good efficiency and nice dealing with traits, in addition to its exceptionally sturdy construction. As with the Ki.5, nevertheless, the gull wings did nothing to enhance visibility for the pilot throughout takeoff and touchdown.
The Ha-137V-1 was broken in October when ammunition exploded within the starboard aspect of the wing heart part throughout armament trials. The Ha-137V-3 participated in dive-bombing trials on the Rechlin check heart in June 1936, however throughout that very same month Ernst Udet changed Richthofen as chief of the event part of the RLM’s Technischen Amt (which changed the C-Amt). Though Udet was an ardent supporter of the dive bomber, he connected little significance to Schlachtflugzeug and promptly knowledgeable Vogt that no manufacturing contract can be awarded for the Ha-137. When World Struggle II started on September 1, 1939, the close-support activity was primarily relegated to the Ju-87’s obsolescent biplane predecessor, the Henschel Hs-123.
In the meantime, Vogt’s design group realized that an plane provider mission was included within the 1936 funds, and work started on Undertaking 11, a naval model of the Ha-137A, in addition to a floatplane referred to as Undertaking 11a. The Ha-137’s single-seat configuration and restricted tactical radius, nevertheless, precluded any critical curiosity by the German navy.
Regardless of the succession of setbacks its design had suffered, the Hamburger Flugzeugbau produced three further Ha-137 prototypes, powered by 610-hp Junkers Jumo 210Aa engines and utilizing three-bladed, adjustable-pitch steel propellers. These have been the Ha-137V-4 (D-IFOE), the V-5 (D-IUXU) and the V-6 (D-IDTE). The Ha-137V-4 had a wing-span of 36 toes 7 inches, a wing space of 252.952 sq. toes, a size of 31 toes 3⁄4 inch and a peak of 9 toes 21⁄4 inches. Its most pace was 205 mph at 6,560 toes. Cruising pace was 180 mph, and vary was 360 miles. The speed of climb with out an exterior load was 4 minutes to six,560 toes and 9 minutes to 13,120 toes. The plane’s service ceiling was 22,965 toes. Along with machine weapons or cannons, the Ha-137V-4 was designed to hold 4 110-pound SC50 bombs on under-wing racks.
The Ha-137V-6 was truly accomplished earlier than the V-5, however it crashed in July 1937 and was destroyed. The Ha-137V-5 was delivered on October 26, 1937. The 2 surviving Jumo-engine prototypes subsequently served in numerous experimental trials. One of many prototypes carried out a few of the first firing exams with the Rheinmetall-Borsig 65mm Rauchzylinder RZ65 rocket missiles.
Though his Ha-137 appears to have been doomed from the begin to one disappointment after one other, the aviation world had not seen the final of Dr. Richard Vogt. In the summertime of 1937, he unveiled the prototype of the Ha-138, a twin-boom flying boat that later entered service because the Bv-138 Fliegende Holzschuh (“Flying Clog”)—the one Blohm & Voss product to attain any measure of mass manufacturing. A number of of Vogt’s different designs, although much less profitable, would however achieve him a distinct segment in aviation historical past for sheer originality, starting from the tiny Bv-40 glider fighter, to the large Bv-238 flying boat (its most loaded weight, at 220,460 kilos, made it the heaviest plane on the planet in 1945). In between have been such weird ideas because the asymmetrical Bv-141 reconnaissance airplane.
This text initially appeared within the July 1997 difficulty of Aviation Historical past. To subscribe right now, click on right here!