Oct 19 2010

Rotorcraft Pioneers - The Autogiro Posted 13 years 192 days ago ago by Admin

By Brad McNally - In the 1920’s the Autogiro was the cutting edge of aviation technology.  A Spanish engineer by the name of Juan de la Cierva got the Autogiro into the air by solving several fundamental rotary wing flight problems.  An American businessman by the name of Harold Pitcairn partnered with Cierva to bring the Autogiro to the United States and further developed it.  Their work was sometimes collaboration and sometimes competition but it directly led to the development and rapid advance of the helicopter in the late 1930’s and 1940’s.

Juan de la Cierva was born in Murcia, Spain on September 21, 1895.  Cierva came from an upper-class family due to the fact that his father was a successful lawyer and politician.  The flight of the Wright brothers caused considerable interest in aviation across Europe and attracted Cierva’s attention while growing up in Madrid.  At the time there were no aeronautical engineering colleges, so in 1911 Cierva entered the Civil Engineering College of Madrid.  He graduated with the title of Engineer of Roads, Canals and Ports and would later be awarded an honorary degree in aeronautical engineering when such a program was established (Charnov, 2003).  While attending college, Cierva and several of his friends purchased the wreckage of a crashed Sommer biplane.  Despite their very limited funds and experience, they were able to restore the plane thanks in large part to Cierva’s ability to carve a new propeller.  Drawing on the group members’ initials, the plane was dubbed the BCD-1.  The BCD-1 was the first airplane constructed in Spain earning Cierva the title of “Father of Spanish Aviation.”  An improved racing version, the BCD-2 followed.  In 1918, the Spanish government wanted to expand its military aviation capability and created an aircraft design contest with a prize of about $9,600.  Cierva designed and built a bomber, the C-3 which had several innovative features.  The aircraft had three 225 horsepower engines, an 82.5 foot wingspan and a gross weight of 11,000 pounds (Brooks, 1988).  Unfortunately, during test flights the pilot stalled the plane and crashed, ending any hope of winning the competition.

Juan de la Cierva entered politics in 1919 and became a member of the Spanish Parliament.  Despite his busy schedule he never lost interest in aviation.  Due to the crash of the C-3, Cierva became particularly interested in designing an aircraft that would not lose lift at slow speeds.  Cierva correctly reasoned that if the wings of an airplane could be rotated to generate lift, the speed of the airplane would not matter and it would not stall.  The basis for this idea was autorotation.  There are documented discussions of autorotation before Cierva but no one before him had been able to successfully implement it.  In 1919, Cierva began developing autorotational models which later progressed to full scale prototypes.  Various configurations including a coaxial rotor system and three, four and five bladed rotor heads were tried.  All of the designs encountered the same problem; they were not stable and rolled over.  Cierva had experienced success with several of his models.  While trying to reconcile why the models flew but the full scale prototypes did not, he realized the problem was due to dissymmetry of lift.  This fundamental problem in rotary-wing flight is caused by the advancing rotor blades creating more lift than the retreating blades.  The unequal amount of lift in the rotor disk had caused Cierva’s full scale prototypes to role over.  The rotor blades of the models were made out of a very flexible palm wood.  This flexibility allowed the blades to bend and equalize the lift as the blades rotated around, balancing the lift in the rotor disc.  From this revelation Cierva developed and patented the flapping rotor blade which was allowed to move up and down by means of a hinge in the rotor head.  This solved dissymmetry of lift.  A freely flapping blade had been developed and patented in France and Germany prior to Cierva.  However, there is no evidence that Cierva knew of this prior work and he is widely considered to have reached his discoveries independently (Charnov, 2003).  Cierva’s fourth full scale design, the C.4, was the first aircraft to successfully incorporate the flapping hinge.  The body of the C.4 was a Hanriot scout biplane from World War I powered by a Le Rhone rotary engine.  The rotor head incorporated flapping hinges on four blades.  The aircraft was controlled by control surfaces on a set of wings and a tail rudder, similar to a fixed wing aircraft (Gablehouse, 1967).  The first successful Autogiro flight was achieved on January 9, 1293 at the Getafe Airdrome outside of Madrid.

This new aircraft quickly gained attention in Europe. Cierva even trademarked the term Autogiro, which is still used worldwide to describe any autorotational aircraft made by Cierva or under license.  Several new Autogiro models were designed, built and demonstrated in Spain, France and England.  In 1925, an early English pilot named James Weir saw an Autogiro demonstration flight.  Weir was so impressed with the aircraft that he brought it to the attention of his brother, an English Lord and several English financiers.  On March 24, 1926, this group reached an agreement with Juan de la Cierva to establish the Cierva Autogiro Company Limited (Charnov, 2003).  The purpose of the new company was to develop the Autogiro through licensing and selling Cierva’s designs and patents.  Juan de la Cierva became the technical director of the company and subsequent work was relocated to England.

Around the same time that the Cierva Autogiro Company was starting up, the Autogiro caught the attention of an American businessman and aviation pioneer named Harold Pitcairn.  Pitcairn was born in 1897 outside of Philadelphia, PA.  Harold’s father John was a Scottish immigrant who became a wealthy industrialist after co-founding the Pittsburgh Plate Glass Company (Smith, 1981).  Pitcairn became interested in aviation at an early age.  In 1914, Harold’s father arranged for his son to have an internship at Glenn Curtiss’s airplane factory.  Harold not only got experience building airplanes but also saw first hand the legal battles that Curtiss faced for patent infringement accusations from the Wright Brothers.  Similar legal issues would come to play a major role in Harold Pitcairn’s life many years later.  After graduating from preparatory school, Pitcairn’s father paid for him to attend flight training and he eventually earned a pilot’s license signed by Orville Wright (Charnov, 2003).  Pitcairn later volunteered to become an air cadet in the US military during World War I and completed military flight training.  He never saw combat because the war ended before he reported to an operational assignment.

After being honorably discharged from the military, Pitcairn’s ingenuity and determination helped to make him a successful businessman.  Despite his success in the business world, he was never able to shake his fascination with aviation.  In 1924, Pitcairn left his job and founded two companies, Pitcairn Aircraft and Pitcairn Aviation.  Pitcairn Aircraft designed several new fixed wing aircraft including the Mailwing series and also dabbled in rotary wing aircraft design.  Pitcairn Aviation established a very valuable network of airfields and airmail routes.  Upon hearing about the Autogiro in 1925 Pitcairn immediately became interested in the aircraft and met personally with Cierva in Madrid later that year.   Pitcairn kept a close eye on Autogiro developments and two more meetings occurred in 1928.  The outcome of these meetings was that Pitcairn secured the American licensing and manufacturing rights to the Autogiro and all of Cierva’s patents for $300,000.  The Cierva Autogiro Company would get reciprocal rights to any patents that Pitcairn would later obtain.  The Pitcairn-Cierva Autogiro Company was set up in the United States to do research and development and license Autogiro patents for US manufacturing (Charnov, 2003).  Pitcairn became a director of the Cierva Autogiro Company and Juan de la Cierva became a director of the Pitcairn-Cierva Autogiro Company.  Harold Pitcairn also received a Cierva C.8 Autogiro which he brought back to America.  The C.8W (W because a Wright engine had been put into this Autogiro) became the first Autogiro to fly in the United States on December 18, 1928.

In order to finance the Pitcairn-Cierva Autogiro Company, Harold Pitcairn sold all of Pitcairn Aviation’s valuable airmail routes.  This gave Pitcairn the necessary capital and the first licensee of the Pitcairn-Cierva Autogiro Company was Pitcairn Aviation.  Autogiro development and demonstration was pushing ahead on both sides of the Atlantic.  Prior to the Pitcairn-Cierva negotiations, Cierva incorporated lead and lag hinges to the Autogiro rotor head.  These hinges allowed the blades to move fore and aft relieving pressure at the blade root.  Cierva received his pilot’s license in 1927 and flew from London to Paris in 1928.  This flight was the first rotary-wing crossing of the English Channel and the first international Autogiro flight (Charnov, 2003).  For accomplishing this flight, Cierva received the 1928 Lahm Prize from the Aero Club of France.  In 1929, the first Pitcairn Autogiro, the PCA-1 flew.  The PCA-1 was followed by the PCA-1A and the PCA-1B, both experimental models based on Pitcairn’s fixed-wing Mailwing designs.  An improved version, the PCA-2 followed in 1930.  The PCA-2 was the first original American Autogiro design and featured a prerotator.  The prerotator used a clutch to rotate the rotor head with the engine while on the ground.  This was a major advancement that eliminated the need for ground taxiing to get the head up to speed for takeoff.  Cierva promptly incorporated a similar feature in his later designs.  In 1931, flying in a Pitcairn PCA-2, Amelia Earhart set a world altitude record.  Earhart flew from Pitcairn Field in Willow Grove, PA and ascended to an altitude of 18,415 feet.  This flight brought significant attention to Pitcairn and the Autogiro.  Earhart would later fly a cross county Autogiro flight in a Pitcairn Autogiro sponsored by the Beech-Nut Packing Company.  For developing the Autogiro, Harold Pitcairn and his associates received the Collier Trophy from President Hoover in 1931.  The trophy was awarded for the most significant aviation contribution in the preceding year.  The ceremony took place on the White House lawn where a PCA-2 was landed for the event.  This was the first rotary-wing aircraft to land at the White House (Charnov, 2003).

Autogiro development and manufacturing in the United States was gaining momentum.  In 1931, Pitcairn changed the name of the Pitcairn-Cierva Autogiro Company to the Autogiro Company of America or ACA (Charnov, 2003).  The ACA issued Autogiro manufacturing licenses to the Buhl Aircraft Company and the Kellett Aircraft Corporation; the later would build several Autogiros for the US Army.  In 1932, Pitcairn and Cierva shared the John Scott Award, presented by the directors of City Trusts of the City of Philadelphia for “the invention of the Autogiro, its improvement and development as a propelling and stabilizing force for heavier than air craft, and its introduction into America.”  Pitcairn and Cierva began to work closely on Autogiro development, both traveling across the Atlantic to see the other.  Cierva devised a control system that would eliminate the need for the fixed wing control surfaces that were being used on the original indirect control Autogiros.  Although the Autogiro was able to still generate lift at slow speeds, the control surfaces did not function well and loss of control had led to several highly publicized accidents.  Cierva correctly reasoned that if he could make the rotor head directly control the aircraft the fixed wing control surfaces would not be needed and control would not be degraded at slow speeds.  Cierva was proposing the cyclic control that is found in modern helicopters.  The new type of Autogiro would be called a direct control Autogiro.  Cierva also realized that through the use of Pitcairn’s prerotator system the rotor head could be over spun to store energy that could be used to affect a jump takeoff.  In order to convert this energy to lift, the pitch of the rotor blades needed to be collectively increased.  This would cause the Autogiro to lift vertically into the air.  De-clutching the rotor head and engaging the propeller would allow the Autogiro to fly forward, in affect performing a vertical takeoff.  This revelation significantly contributed to the collective control found in modern helicopters.  Cierva shared his ideas with Pitcairn and the two worked to turn these ideas into reality.  Despite their relationship as personal friends and joint business partners their companies soon began to work separately.  Information and developments did not flow easily between the two, especially coming out of England.  Both firms were wary of the other and wanted to be the first to develop direct control and jump takeoff ability.                

Juan de la Cierva had perhaps his finest hour at the 1933 Chicago World’s Fair.  On June 28, 1933, Cierva received the Daniel Guggenheim Medal at Soldier’s Field in front of thousands of spectators.  The medal was for the “World’s most notable Achievement in Aviation” and had only been previously awarded three times.  The future of the Autogiro was drastically altered three years later.  On December 9, 1936, Juan de la Cierva perished when the KLM DC-2 that he was flying in from London to Amsterdam crashed while taking off in low visibility conditions.  Cierva was posthumously awarded the Royal Aeronautical Society’s prestigious Gold Medal.  Fortune Magazine went as far as to proclaim Cierva’s Autogiro as “the only basic contribution to the art of flight since the Wright brothers rode a biplane into the air in 1903.”  Harold Pitcairn wrote that “Juan Cierva will be known to enduring fame as the outstanding pioneer in the field of rotary-wing aircraft…All helicopters and similar types of craft that have shown promise of practical performance  incorporate some of the principles and inventions developed by Cierva (Charnov, 2003).”  With Cierva no longer able to facilitate communication between the companies, Harold Pitcairn found it increasingly harder to get information on what was happening in England at the Cierva Autogiro Company.  This was despite the fact that Pitcairn was a board member of the English company.  A confrontation between Pitcairn and the other board members ensued.  Pitcairn was shocked to learn that the Cierva Autogiro Company had licensed its cyclic and collective control systems to Germany’s Focke Achgelis Company.  Focke Achgelis subsequently used these licenses to build what is considered to be the first successful helicopter, the Fa-61.   The Cierva Autogiro Company later received a license to build Fa-61 helicopter derivatives.  This venture into helicopter manufacturing effectively ended Autogiro development at the Cierva Autogiro Company.  Pitcairn returned to the United States undeterred and continued forging ahead with the Autogyro. 

Although direct control and jump takeoff ability increased the Autogiro’s capabilities, the helicopter soon became reality and interest in the Autogiro faded.  Government funding was funneled into helicopter development effectively cutting out the Autogiro companies.  Pitcairn’s Autogiro Company of America was acquired by Firestone Tire and Rubber in 1942 and renamed G and A Aircraft.  By 1948, after failing to market a successful helicopter, G and A Aircraft was out of business (Charnov, 2003).  At the beginning of World War II, the US government was in need of places to train new pilots for the war effort and was preparing to acquire the inactive Pitcairn Field via eminent domain.  In order to avoid the associated legal proceedings, Harold Pitcairn sold the airfield outside Philadelphia that bore his name to the government for its appraised value.  Pitcairn Field later became US Naval Air Station Willow Grove.  In 1943 in an attempt to help the war effort, Harold Pitcairn offered to reduce the royalties on his 19 personal rotary-wing patents and another 145 patents held by his company from 5% to .85% for any licensee supplying the US government.  This incredibly generous and patriotic offer was accepted by the government for the duration of the war plus six months.  This offered expired in 1946, at which time some of the biggest helicopter manufacturers continued to supply the government while using Pitcairn’s patents without properly compensating him.  In 1951, after failing to reach an industry wide settlement, Pitcairn filed a lawsuit against the United States Government which had indemnified the helicopter manufacturers.  The ensuing litigation became the longest patent suit in American history.  It finally concluded in 1977 after reaching the Supreme Court.  Pitcairn received 14 million dollars in unpaid royalties and 17 million dollars in back compensation (Charnov, 2003).  Unfortunately this settlement came nearly 17 years after Harold Pitcairn passed away.  On July 22, 1960 Harold Pitcairn died in his home as a result of a gun shot.  The events surrounding his death remain unclear and there is still some debate over whether it was an accident or suicide.
 
Autogiro technology advanced rapidly in the 1930’s with work being done in the United States and Europe.  Advances in both control and capability were realized as the direct control and jump takeoff abilities were developed.  However, the Autogiro never reached true vertical flight capability.  By the end of the 1930’s the helicopter had become a reality and the Autogiro began to fade into aviation history.  In the 1950’s there was renewed interest in autogyros.  This resurgence in popularity was largely led by Dr. Igor Bensen and his Gyrocopter designs.  Over the last fifty years many new autogyro models have been developed with varying levels of success.  Today there exists a small but loyal and dedicated international autogyro community somewhat unified by the Popular Rotorcraft Association.  A successful large scale American autogyro manufacturing operation, as envisioned by Harold Pitcairn, never came to be.  However, in many ways the rotary-wing aircraft industry that Pitcairn established in the Philadelphia area is still very much alive.  Currently this area is home to several large helicopter facilities run by Augusta Westland, Boeing, Piasecki and Sikorsky.  The influence of Cierva and Pitcairn’s innovations on the modern helicopter can not be overstated.  The flapping hinges in the rotor head effectively solved the problem of dissymmetry of lift and made rotary-wing flight possible.  The collective and cyclic controls are fundamental helicopter design features.  If the Wright brothers and their historic work made flight possible, then Juan de la Cierva and Harold Pitcairn helped make helicopter flight possible.   Without question the Autogiro occupies a significant place in rotorcraft history making these men true Rotorcraft Pioneers.


References
Brooks, P. (1988). Cierva Autogiros: The Development of Rotary-Wing Flight.
Washington, DC: Smithsonian Institution

Charnov, B. (2003). From Autogiro to Gyroplane: The Amazing Survival of an Aviation
Technology. Westport, CT: Praeger.

Gablehouse, C. (1967). Helicopters and Autogiros: A Chronicle of Rotating-Wing
Aircraft. Philadelphia: J. B. Lippincott Company

Smith, F. (1981). Legacy of Wings: The Story of Harold F. Pitcairn. Lafayette Hill, PA:
T. D. Associates