XV-15 litho - NASA's History Office

Figure 7.
Henry Berliner tiltpropeller
helicopter.
(National Air and Space
Museum–NASM–Photo)
6
1920s (figure 7). This design resembled
a fixed-wing biplane of the period,
except that it had a large diameter
fixed-pitch propeller mounted on a
vertical shaft near the tip of each
wing. For forward flight, the shafts
would be tilted forward. Reports indicate
that the Berliner helicopter
achieved forward speeds of about 40
mph. While the propellers were not
designed to convert fully to the conventional
airplane mode, the Berliner
side-by-side helicopter was an early
example of the rotor arrangement used
on current tilt rotor aircraft.
Another design conceived to provide vertical lift and forward flight is the “Flying
Machine” for which George Lehberger was issued a patent in September 1930
(figure 8). His approach contained the basic concept of the tilt rotor aircraft, that
is, the use of a relatively low disc loading thruster (propeller) that can tilt its axis
from the vertical (for vertical lift) to the horizontal (for propulsive thrust). While
the authors are not aware of any attempt by inventor George Lehberger to develop
this vehicle, it would be expected to encounter performance, loads, structural
dynamics, and control deficiencies if built as indicated in the patent illustration.
The vectored thrust low disc loading VTOL aircraft required many technology
advancements before it would be a practical aircraft type.
In the late 1930s, a British patent was issued for the Baynes Heliplane (figure 9)
which resembled the configuration of the current tilt rotor aircraft. Inadequate
financial backing prevented development work, leaving the exploration of tilt
rotor technology to other engineers in the four decades that followed.
In Germany, the Focke-Achgelis FA-269 trail-rotor convertiplane project was initiated
in 1942. This aircraft, illustrated in figure 10, followed the moderately successful
lateral twin-rotor helicopter, the Focke-Wulf Fw-61 flown in 1937. The
FA-269 used pusher propellers that tilted below the wing for takeoff. This project
was discontinued after a full-scale mockup was destroyed during a bombing in
WWII. Years later, variants of the trail-rotor tilt rotor configuration would surface
again in design studies at Bell and McDonnell Douglas.
The accomplishments of the German Focke-Wulf activities did not go unnoticed by
the americans. Two enterprising engineers, Dr. Wynn Laurence LePage and Haviland
Hull Platt of the Platt-LePage Aircraft Company of Eddystone, Pennsylvania,
became intrigued with the success of the German helicopter and decided to pursue
the development of a viable helicopter in the U.S. with the same general arrangement
of the Fw-61. The product of this work was the 1941 Platt-LePage XR-1A lateral