TIMELINE
1923 - 1933
History From 1923-1933

Summary
This period was marked by small improvements in helicopter design and performance, but did not witness the development of successful or practical designs.  However, the introduction of the Autogiro by Juan de la Cierva was a critical breakthrough that presented helicopter designers with most of the essential elements of a practical rotorcraft.  The most notable advances in technology occurred in Spain, England, Italy, France and the Soviet Union.

Technology
The Autogiro was aircraft of a category now known as gyroplanes in which the lifting rotor “windmilled” as a propeller pulled the machine through the air.  Its rotor system incorporated numerous innovations necessary for practical helicopter rotor systems, including flapping and lead-lag hinges.  Blade design moved away from the ungainly low-aspect ratio airfoils and highly loaded lifting propellers of the previous two decades to high-aspect, relatively efficient airfoils.  However, rotor control had not advanced much beyond Pescara’s early demonstrations of cyclic and collective control.  Cierva Autogiros were controlled by airplane-type control surfaces in this period.  E. Burke Wilford’s W.R.K Gyroplane successfully employed a cyclically controlled rotor, but was undone by the heavy vibrations of the rigid rotor system.  Pure helicopters showed some limited innovations, such as Von Baumhauer’s 1928 single main rotor design, which featured an anti-torque tailrotor.  In 1930, the Soviet Union introduced the most promising design to date with the Aerodynamic and Hydrodynamic Central Institute’s (TSAGI) 1-EA.  This single-rotor design featured a swashplate and adequate power and lifting rotors.  However, the design lacked adequate dampers and other refinements and progress in refining the design was slow.  Stalin’s purges put an end to the most promising advances outside of the Autogiro industry.

Application and Operations
Cierva developed the Autogiro as a form of stall-proof safety plane that could land in restricted spaces (takeoffs could be another matter entirely).  By 1930 Autogiro production had begun in earnest in the United States in England and the first commercial rotorcraft began to enter service.  With acquisition costs five times as high as comparably sized high-end fixed wing aircraft, the Autogiro was not a success as a general aviation aircraft.  It did enjoy some success as an aerial advertising platform, airshow attraction and status symbol for the wealthy, but these niche markets were rapidly satisfied, and by the end of this period, civil Autogiro production had almost entirely ceased.  Nonetheless, the Autogiro succeeded in conveying to the public that rotorcraft were relatively safe and viable forms of rotorcraft, which made governments and the general public far more accepting of investing in rotorcraft research and development than they might otherwise have been.

Design and Manufacture
Most of the more promising helicopter designs of the period originated from individual inventors operating with the support of private investors.  In the late 1920, the Autogiro marked the rise of dedicated rotorcraft manufacturers in the form of Cierva who then licensed his technologies, most notably to Harold Pitcairn in the United States (who then administered the licenses to other Americans such as Wallace Kellett and Lawrence D. Buhl, but also Henrich Focke in Germany and Fernand Lioré in France.    

Government Involvement
Government investment in rotorcraft during this period increased, but remained haphazard.  In the United States, the U.S. Army showed some limited interest in Autogiros as observation platforms and the National Advisory Committee for Aeronautics took some cursory interest in them, but did not see rotary wing aircraft as particularly promising field.  The U.S. Navy showed the most interest and procured Pitcairn XOP-1 Autogiros for shipboard trials on the USS Langley and the Marine Corps tested them in Nicaragua, but the overall consensus was that the limited payload outweighed any performance advantages held by the Autogiro.  With rapidly rising rates of performance in airplanes, including STOL capabilities as demonstrated by the Curtiss Tanager, Autogiro advocates found themselves in an uphill battle to sell an aircraft whose operating environment was best described as “low and slow” and suffered from the twin perils of high cost and limited payload. 

Representative Designs

  • Cierva C.4
  • Cierva C.8
  • Cierva C.19
  • Pitcairn PCA-2
  • Kellett K-3
  • Oemichen
  • D’Ascanio
  • Florine
  • TSAGI 1-EA
  • Von Baumhauer

Notable Personalities

  • Juan de la Cierva
  • Harold Pitcairn
  • Wallace Kellett
  • E. Burke Wilford
  • Corradine D’Ascanio
  • Etienne Oemichen
  • Boris Yuriev
  • Nicholas Florine
  • Von Baumhaue