hile continuing his education as a civil engineer,
Cierva designed a large
tri-motor biplane bomber
in 1918 for a military
competition. On its first
flight, it stalled in a low-level turn and crashed. The pilot walked
away from the wreck, but Cierva decided to turn his efforts to
solving the problem of the stall.
And the concept of the Autogiro was born.
While many inventors at the time were trying to develop a
helicopter, Cierva hit upon the idea of the unpowered rotor
as a source of lift, using the concept of autorotation. Take four long
skinny wings, anchor them at a common point, and you have a
rotor that spins itself when subjected to airflow and will not stall,
eliminating the stall/spin problem of fixed-wing aircraft.
It’s a great concept, but in practice there’s a lot more to it, as
Cierva discovered in his first experiments in the early 1920s. With
forward motion of the aircraft, the advancing blade creates more lift,
which with a rigid rotor head causes the machine to roll toward the
retreating blade. This was solved by adding “flapping” hinges, allowing
the advancing blade to rise and effectively decrease its angle of attack
to match its lift to the retreating (and descending) blade. Due to minor
changes in the speed of each rotor blade during flight, fore-and-aft or
lead-and-lag hinges were required (See illustration on pg. 25).
By the middle 1920s the design was considered a success,
and soon a number of “windmill planes” were built by licensees
of Cierva and flying around Europe under the trademarked
Enter Harold Pitcairn, American builder of airmail aircraft
and a man interested in the development of the helicopter.
Recognizing the potential of the Autogiro,
Pitcairn persuaded Cierva to let him become
the American representative and went on to
build dozens of ’giros of varying types at his
factory in Willow Grove, Pennsylvania. They
were expensive, costing from $5,000 to $8,000
during the Depression when the average
annual income was less than $1,000, but they
found use as advertising vehicles for many
companies like Coca-Cola, Beech-Nut (whose
Autogiro was flown by Amelia Earhart), and
the Champion Spark Plug Company, whose
Pitcairn PCA- 2 Miss Champion is now in the
EAA AirVenture Museum.
Both Pitcairn and Cierva continued to
advance the design, Pitcairn coming up with
the rotor spin-up drive using a unit on the back
of the engine, and both contributed to
advancements such as cyclic control to vary the
angle of each blade individually, eliminating
the need for flapping hinges, and the collective,
which could vary the angle of all blades at once
and which was used for jump takeoffs. These
concepts were crucial to the development of
the helicopter in the late 1930s. Ironically, with
its ability to hover, the helicopter then drove
the Autogiro into obscurity.
NC12678/ The year 1932, however, was the
height of Autogiro popularity, and in March
of that year the Pitcairn Autogiro Company
THE HISTORY OF PITCAIRN PA- 18, N12678
Pitcairn PA- 18, Serial No.
G- 65, is manufactured by
the Pitcairn Autogiro Co. of
Willow Grove, Penn.
NC1267B is used as the personal aircraft of company
president Harold Pitcairn.
Miss Anne West Strawbridge dies at the age of
58, willing her PA- 18 to
relative John Strawbridge.
Firestone Aircraft buys
the Autogiro for $228 after
the PA- 18 changes hands
Sky Voice Inc. purchases
the Autogiro for banner
use along the New Jersey
Joseph Budjinski acquires
the ship, but soon goes
out of business.