On January 1, 1928, brothers I. and J. Stiller, both of whom were engineers living in Radom, Poland, filed a patent in Warsaw for a peculiar helicopter design featuring two small propellers fitted on the upper end of swiveling shafts arranged in parallel. These propellers were driven by an internal combustion engine located between the shafts. Means were provided for shifting the direction of the line of thrust of the propellers in the fore and aft planes. The propellers could then be used for sustentation (hovering) or propulsion, or both, in varying proportions. The engine and gearing were enclosed in a compact, streamlined fuselage within which was also carried the passenger. A vertical rudder was fitted at the stern without an elevator. From a modern perspective, the design is more of a convertiplane or tiltrotor than a conventional helicopter, but then the formula for the latter had not yet been set as of 1928. The technical description in the patent is in German, perhaps reflecting the strong influence of that country on Poland’s educational/patent systems.
The Stiller brothers received the endorsement of an H.V. Appen of Ulen & Company, a company with offices in both Warsaw and New York. Appen had studied at MIT and sent the Stiller proposal to a Professor Warner, the Assistant Secretary – Charge of Aviation at the Department of Commerce on February 11. He hoped that Warner might know someone who could help out the Stiller brothers, who lacked capital and were unable to raise any in their native Poland. The Stiller brothers also wrote a letter to the Professor, wherein they mention also sending a copy of the proposal to the Ford Motor Company in Detroit.
The proposal eventually made its way to NACA, which evaluated the design on behalf of the Aeronautical Patents and Design Board in Washington, D.C. In the memo, G.W. Lewis, Director of Aeronautical Research, was highly skeptical of the design. Very similar arrangements had been proposed before; as submitted, the propellers were of small diameter. He believed that a successful helicopter propeller should be of large diameter and of slow speed instead of as proposed. The most serious criticism was the lack of means for controlling altitude, attitude, and position. Once an aircraft of any kind left the ground, it moved with the air currents; these could move in an erratic manner and the pilot had to be able to control it against them. Up till that time, no one had been successful in devising a method for obtaining this control (for a helicopter) and the Stillers had not provided for such control in their design. He considered the device impracticable and advised against awarding money for further development of the project.
No further documentation concerning the Stiller helicopter has been found in NACA files; if any Polish aviation experts know more about the project or the subsequent activities of the Stiller brothers, feel free to comment below or contact the editor. To view the primary documents concerning the Stiller helicopter in depth, please click through the image gallery above.
All images from NARA Archives II, College Park, MD, RG 255