Source: Flying Review international November 1965
Zdenek Titzand JaroslavZazvonil tell the little-known story of the short-lived .Skoda-Kauba Flugzeugbau and the highly unusual aircraft evolved by its director and chief designer, Ing Otto Kauba
One spring day in 1942, an inconspicuous name plate bearing the legend "Skoda-Kauba Flugzeugbau" appeared outside an equally inconspicuous house in the suburbs of Prague, No 13 Na Florenci Street. The name plate held no significance for any but the few members of a design bureau led by an Austrian engineer from Vienna, a certain Otto Kauba, a few officials in the Reichsluftfahrtministerium in Berlin, and Hermann Goering. This small group knew that behind the windows of the house in Na Florenci Street design work was proceeding on a pilotless flying bomb.
Kauba had succeeded in interesting the Reichsmarshal in his ideas for a flying bomb, and Goering had, in turn, recommended his ideas to the RLM under whose auspices the Skoda-Kauba Flugzeugbau had been formed. The Austrian designer had chosen Prague as a centre for his activities, and it was decided that his prototypes would be built by the nearby Avia works, a part of the Skoda Werke Trust of Pilsen. Otto Kauba's design was, to say the least, unorthodox. Featuring an abbreviated fuselage and elevons attached to supports well aft of the wing, the flying bomb was intended to be powered by an Argus pulsating athodyd or ramjet in its definitive form. However, Kauba's first task was to determine the flying characteristics of the unusual configuration that he proposed, and he accordingly designed a weird low-wing cantilever monoplane powered by a 105 hp Hirth HM 504A-2 air-cooled inline engine driving a two-blade tractor airscrew, and featuring all-metal construction, a fixed nosewheel undercarriage, and the unique trailing elevons. In its initial form, the aircraft was to have an orthodox cockpit for a pilot, the intention being to replace this with an explosive charge after proving the flying characteristics of the machine. Guidance would then be by means of an autopilot and height and range-setting controls, the servo mechanisms controlling the elevons which were the only aerodynamic controls. The wing span and overall length were 19 ft 8 in (6 m) and 14 ft 9 in (4,5 m) respectively, loaded weight was 1,323 lb (600 kg), and anticipated maximum speed exceeded 155 mph (250 km/h).
The RLM instructed Kauba to proceed with the construction of four prototypes, and the first of these, designated SK VIA, was duly completed and transported by road to the Prague-Gbely airfield from which one of Messerschmitt's test pilots was intended to conduct initial flight trials. After a cursory inspection of the SK V I A, the German pilot refused to fly the "strange contraption". Another German pilot, an instructor from the Luftwaffe's flying training school at Vyskov in Moravia, was asked to undertake the flight testing, but he too refused, and in desperation, Kauba approached the management of the Skoda Works to find him a pilot. Accordingly, Petr Siroky, Avia's chief test pilot and a well-known Czech aerobatic pilot, was ordered to undertake the initial flight trials.
Having discovered the eventual purpose of the aircraft, Siroky, too, refused the task, but veiled threats and suggestions of Gestapo interest in himself and his family resulted in what appeared to be a change of heart. In fact, Siroky, with Avia director Cajthamel, was already planning the deliberate destruction of the aircraft, and after a few taxying trials across the Prague-Gbely airfield, Siroky did actually take-off, but as soon as he was airborne he began to switch the ignition on and off so that onlookers would think that the engine was behaving erratically. Then, finally cutting the power completely and with the airscrew windmilling, he put the nose down and bounced the aircraft on its nosewheel. The aircraft somersaulted several times and finally came to rest on its belly, the undercarriage having been wiped off. Siroky was carried unconscious from the wrecked aircraft, but Kauba was suspicious and immediately accused the pilot of sabotage. Fortunately for Siroky, Cajthamel intervened and Kauba dropped his charges.
After this setback RLM interest in Kauba's proposals began to wane, but in 1943, as a result of representations made by a Nazi director of the Skoda Works, work was resumed and the second prototype, designated SK V1, was finished. Essentially similar to its predecessor apart from having a rudder, the SK V1 was flown successfully by Rudolph Opitz who had been flight testing the radical Messerschmitt Me 163 at Peenemunde (see FLYING REVIEW INTERNATIONAL September 1965). Trials were conducted from the Prague-Ruzyn airfield, and the aircraft was found to be somewhat nose heavy. In an attempt to move the cg further aft, the third prototype, the SK V2, featured appreciable wing sweep with the trailing elevons mounted closer to the wing trailing edges, but the aircraft was still nose heavy, and the lack of premise evinced during flight trials coupled with the more advanced work on pilotless flying bombs by that time being undertaken by other designers decided Kauba to turn his attention to other projects, and all further work on his flying bomb was finally abandoned. In the meantime, salvaged components of the original SK VIA were used in the construction of a light sporting single-seater, the SK V3, with a fixed tailwheel undercarriage and an orthodox configuration, but Kauba's next serious design, the SK V4, was a single-seat fighter trainer powered by a 240 hp Argus As 10C-3 eight-cylinder inverted-Vee air-cooled engine. Featuring exceptionally clean lines, the SK V4 was a low-wing cantilever monoplane with a tailwheel undercarriage, the wide-track main members of which retracted inwards. Provision was made for the mounting of a single 7,9-mm MG 17 machine gun, an electrically-actuated variable-incidence tailplane was provided, and the structure comprised a one-piece wooden wing built around a single box spar, and a welded steel-tube fuselage with plywood skinning. Performance included maximum speeds of 261 mph (420 km/h) at altitude and 240 mph (385 km/h) at sea level, an initial climb rate of 2,008 ft/min (10,2 m/sec), a service ceiling of 24,600 ft (7 500 m), a range of 578 miles (930 km) cruising at 195 mph (314 km/h), and an endurance of 2.94 hr. Empty and loaded weights were 2,249 lb (1 020 kg) and 2,756 Ib (1 250 kg) respectively, and overall dimensions were: span, 24 ft 11} in (7,6m), length, 18 ft 41 in (5,6 m), and wing area, 90.42 sq ft (8,4 m°).
A PRODOCTION CONTRACT
So successful were flying trials with the SK V4 that the RLM awarded Skoda-Kauba a contract for the development of a more powerful fighter trainer of generally similar configuration and construction. Designated SK 257, the new aircraft was powered by a 485 hp Argus As 410 twelve-cylinder inverted-Vee air-cooled engine, and four prototypes were completed. Again, the aircraft displayed exceptional handling qualities and performance, and the SK 257 trainer was ordered into quantity production for the Luftwaffe at a factory at Trencin on the Biskupice airfield in Slovakia. Achieving a maximum speed of 217 mph (350 km/h), the SK 257 had a loaded weight of 2,270 Ib (1030 kg) and had a wing span and overall length of 24 ft 1141 in (7,6 m) and 23 ft 3J in (7,1 m) respectively. In the event, only five production SK 257 trainers were completed at Trencin, and the manufacturing standard of these was so low that they failed to pass the Luftwaffe quality control inspectors.
By this time, Kauba had several more ambitious projects on the drawing boards, one of which was the SK V5 single-seat fighter which, essentially a scaled-up SK V4 and intended to out-perform the Focke-Wulf Fw 190 in every respect, was intended to be powered by a 1,750 hp Daimler-Benz DB 603 liquidcooled engine. A maximum speed of 475 mph (765 km/h) was anticipated for the SK V5 which employed an unusual form of wing construction, this being known as the Skoda-KaubaBanweise tubular-spar structure and comprising normal ribs built up on a single tubular-type spar which stretched from wing-tip to wing-tip, the forward bulkhead and engine firewall to which the engine bearers were attached forming an integral part of the spar. This method of construction was claimed to offer both an increase in structural strength and a reduction in structural weight, and the Focke-Wulf organisation evinced interest at a late stage in the war, considering the introduction of the tubular spar in the Fw 190D and Ta 152 fighters. Unfortunately, although highly promising, the SK V5 progressed no further than a series of wind tunnel models and a full-scale mock-up as the RLM felt the development of an entirely new piston-engined fighter to be wasted effort at a time when emphasis was being placed on jet fighters.
The next experimental Skoda-Kauba design was the SK V6, a small single-seat twin-boom monoplane employing some of the structural components of the SK V1. The 105 hp Hirth HM 504A engine was installed as a pusher and drove a two-blade, fixed-pitch wooden airscrew between the tail booms, and after a series of flight trials the prototype was modified under the designation SK SL6 at the request of Blohm and Voss to flight test the so-called "Arrow Wing" arrangement evolved by Dr Richard Vogt and his chief aerodynamicist, George Haag. This arrangement called for the provision of short booms which, attached to the tips of a moderately swept wing, each carried a half tailplane and an elevator. This highly unorthodox layout was featured by several projected Blohm and Voss fighters, including the P 208, P '-)'M, P 210, P 212 and P 215, and during 1944 the SK SL6 undertook a number of test flights to prove the feasibility of the control surface arrangement.
The SK V7 was a small research aircraft of canard or tail-first arrangement employing some of the structure of the SK V2 and powered by a 60 hp Walter Mikron 11 engine installed as a pusher. Spanning 20 ft (6,1 m) and having a loaded weight of 1,102 Ib (500 kg), the SK V7 was never completed, but the SK V8 light side-by-side two-seat primary training and sporting monoplane was completed and flown in the winter of 1944, flying with both ski and wheel fixed undercarriages. The SK V8 was powered by a 105 hp Hirth HM 504A-2 engine and had a wing span of 26 ft 1 in (7,95 m), but although the aircraft survived the war, no further details were recorded.
There was a profusion of other Skoda-Kauba projects, for this small company comprising only eighty Czech and forty German employees was nothing if not prolific. These projects included
the tiny SK V9, a miniature aircraft which was to have been powered by an engine of only 15 hp; the SK V10 trainer powered by two Argus As 411 engines; the SK VI I advanced trainer with a single Argus As 411, and the SK V12 aerodynamic research aircraft embodying forward wing sweep and powered by a 70 hp engine. It was perhaps- fitting that Kauba's last project should be his most spectacular-the SK P14 ramjet-driven interceptor.
The SK P14 fighter was designed around a 31 ft 2 in (9,5 m) ramjet developed by Eugen Saenger and intended to operate on diesel oil or powdered coal! Saenger had been working on ramjets for a number of years and in 1944, with some RLM support, Kauba began to evince interest in the possible application of this revolutionary power plant as the prime mover of a fighter. The sheer size of the ramjet rendered its installation in a small fighter difficult, and Kauba elected to build the power plant as an integral part of the aircraft, housing the pilot, armament and all fuel in a superstructure built above the ramjet. The pilot lay prone above the narrow neck of the ramjet, a single 30-mm MK 103 cannon being mounted above the pilot with a single large fuel tank of 297 Imp gal (1 3501) capacity immediately aft and conforming
in shape to the contour of the diffuser portion of the power plant. The intake was carried forward slightly beyond the nose, and the diffuser gradually tapered to the parallel-sided combustion chamber which possessed a diameter of 4 ft 1 I in (1,5 m), conventional wings spanning 25 ft I lin. (7,9 m) and having an area of 134 sq ft (12,5 m') were fitted, and the diminutive tail surfaces were also conventional. For take-off it was intended that a three-wheel bogie would be used, this being jettisoned as soon as the SK P14 was airborne and the landing being effected on an extensible skid.
It was estimated that the Sänger ramjet would provide 9,680 Ib thrust (4 390 kgp) at sea level at 630 mph (1010 km/h) and 2,970 Ib thrust (l 350 kgp) at 33,000 ft (10 060 m) at- 545 mph (880 km/h), loaded weight being 6,270-6,820 Ib (2 845-3 090 kg). Estimated performance included the ability to reach a service ceiling of 59,880 ft (18 250 m), initial climb rate being 26,500 ft/min (134,6 m/sec) and altitudes of 19,685 ft (6000m) and 32,810 ft (10 000 m) being attained in 1.7 and 6.3 min respectively. Maximum endurance was expected to range from 28 min at 230 mph (370 km/h) at sea level to 43 min at 355 mph (570 km/h) at 32,810 ft (10000 m).
Unfortunately, the ramjet enjoyed little popularity at the RLM as a potential power plant for manned aircraft, and with the demise of the research programme late in 1944 also came the demise of Kauba's ambitious fighter, and during the final months of the war, the Skoda-Kauba facilities were occupied in adapting a number of Fw 190 fighters and Horten Vill flying wings to take the Skoda-Kauba-Banweise tubular spar. Shortly before the termination of hostilities, Otto Kauba fled Prague. On April 30, 1945 at the offices in No 13 Na Florenci Street, all documentation and project drawings were carefully burned and three years after its appearance, the Skoda-Kauba Flugzeugbau nameplate was finally removed.