P.Grosz, G.Haddow, P.Shiemer Austro-Hungarian Army Aircraft of World War One (Flying Machines)

Austro-Hungarian Helicopter Development

  The concept of a vertical aircraft or helicopter (Hubschrauber) began to challenge the imagination of Austro-Hungarian scientists toward the end of the 19th century. Noteworthy are the investigations of Josef Popper-Lynkeus, Anton Jarolimek, Professor Georg Wellner, and Wilhelm Kress. In 1894, Wellner experimented with a rotating-wing model that achieved a lift coefficient of 15 kg per horsepower. Kress built a small 33 kg model with counter-rotating propellers powered by an electric motor. In 1895 his associate, Dr. Waechter, successfully demonstrated the model indoors and out to the Technical Military Committee. Subsequently, Kress proposed a man-carrying helicopter weighing 325 kg driven by a 20 hp engine. From these rough beginnings, ideas were generated that would find their realization in time of war.
  Major Stephan Petroczy von Petrocz, the commander of the Lehr Bataillon in Wiener-Neustadt, conceived the idea of replacing the hydrogen-filled observation balloon by a motor-driven helicopter. To this end, in April 1916, he met with Austro-Daimler director and chief engineer Ferdinand Porsche, several of his assistants, and Oeffag director Karl Ockermuller and Diplom-Ingenieur Karl Balaban to discuss the feasibility of building such an aircraft. The result was that Petroczy submitted a proposal to the LFT command on 28 April 1916, calling for development of a captive (tethered) helicopter for use as a static observation platform. The advantages cited were: less danger of fire, less conspicuous and smaller target while aloft, increased operational readiness, elimination of expensive hydrogen generating equipment, and fewer ground-handling personnel required. The belief that, compared to a balloon, the tethered helicopter was more resistant to wind shear was an optimistic dream.
  Power was to be supplied by a 300 hp electro-motor that Daimler was developing for aircraft use. The war ministry approved the project on 5 May 1916. Oeffag was funded to build several experimental, rotating test rigs and to investigate the operating parameters of large-diameter airscrews or rotors. It soon became apparent that the key to success lay in developing a high-efficiency airscrew. The best available had an efficiency of 61 percent, whereas 90 percent or better was required. Balaban moved to Fischamend to work with Leutnant Oskar von Asboth in Professor Knoller's propeller test facility. The result was the perfection of large helicopter rotors up to 8 meters (26.2 ft) in diameter using the highest quality mahogany and yielding a 90-95 percent efficiency.
  Eager to proceed, the Fliegerarsenal (Flars) issued specifications calling for a tethered helicopter carrying one observer and a large parachute for the entire aircraft. An operating altitude of 500 to 1000 meters (1,640-3,281 ft) in wind conditions up to 14 knots was required. The empty weight was estimated at 580 kg, plus the weight of the tethering cable (1000 meters at 150 kg) and the vertical wind component on the cable (230 kg) brought the total weight to 960 kg. With an estimated lifting force of 1200 kg, the reserve lift of 240 kg was deemed sufficient for one machine gun, camera, and telephone. Writing in 1922, Balaban felt that such rigid specifications hampered development. It would have been wiser to complete the propeller-rotor development and experiment with flying models first and then write the specification based on experienced! At the time the helicopter work was beginning to bear fruit, Petroczy was promoted to command Flars (mid-1917), enabling him to divert additional funds into his pet project. He proposed building two manned, and two smaller, unmanned helicopters of different configuration.


PKZ 1 Helicopter

  Oberleutnant Dr. Theodor von Karman (later of Cal Tech fame) and Ingenieurleutnant Wilhelm Zurovec, both attached to Flars, were assigned the task of constructing a prototype helicopter applying the latest information from the propeller laboratory. Eschewing endless theoretical calculations, Karman and Zurovec proceeded with empirical trials. As first envisaged, the tethered helicopter had 10 to 12 lifting rotors arranged in a circle, but the problem of weight and complexity reduced the final choice to a four-rotor design. After testing rubber-band powered models without success, Zurovec conceived a unique compressed air motor (weighing 4 kg and developing 6 hp at 2400 rpm) which enabled him to construct a 35 kg flying model. Starting in June 1917, flight tests explored various stabilizing surfaces, center of gravity shift, and rotor configurations. Unable to achieve dynamic stability with one or two tethering cables, Karman and Zurovec found that a three-cable system gave the best results. A further 50 flights, ranging in height from 10 to 15 meters, were performed in the great balloon hangar at Fischamend between July 1917 and March 1918.
  Meanwhile, on 21 August 1917, the MAG company in Matyasfold had been given the task of building a full-scale, manned helicopter based on the Karman-Zurovec model work. Having little financial incentive and directed by the military bureaucracy, MAG progress was slow, to some degree due to late delivery of the Daimler electro-motor. Completion, scheduled for October, did not occur until February 1918. The aircraft, called a Schraubenfesselflieger (SFF - rotor-driven tethered aircraft) was identified in post-war literature as the Petroczy-Karman-Zurovec PKZ 1. The design was patented jointly by Karman and Zurovec (German patent 346,425, dated 28 June 1917). Karman remained as project director, but it appears that Zurovec began work on his own PKZ 2 helicopter project in November 1917. The PKZ 1 motor weighed 195 kg and produced 190 hp at 6000 rpm - 60 hp less than projected because the winding insulation was of inferior quality. In flight, power would have been transferred by an aluminum cable 800 meters long. On the first test in Fischamend (date unknown), the PKZ 1 (empty weight 650 kg) took off with surprising abruptness at a rotor speed of 700 rpm and rose to the maximum tethered height of 50 cm. Next, three men climbed aboard and the helicopter easily hovered at the limit of the restraining cables. After 15 minutes into the fourth flight, the over-burdened motor burned through. With high-grade electrical copper and quality insulation impossible to obtain, Daimler was unable to repair the motor. Since the private initiative of Liptak had sped the PKZ 2 to completion, the PKZ 1 was transferred to the Liptak factory but, lacking a motor, nothing was done. Nevertheless, the PKZ 1 had demonstrated the feasibility of an electric-powered helicopter as predicted by the model tests in Fischamend.