XV-15 litho - NASA's History Office

Introduction
For as long as can be remembered,
humans have always wanted to fly… to
be able to soar into the sky and alight
wherever their fancy takes them. One
such individual was Leonardo da Vinci
(1452-1519), who was the first person
to approach heavier-than-air-flight in a
somewhat scientific manner. Da Vinci
is credited with the design of the first
helicopter, basically a helical air screw
(figure 1), which was conceived to lift
off the ground vertically—no ground
roll required, no runway needed.
However, nearly four centuries later,
when technology advancements
allowed sustained, powered manned
flight, the practical solution demonstrated
by the Wright brothers used a
fixed-surface to provide the lift. This required the aircraft to accelerate along the
ground until a sufficient speed was reached so that the necessary force could be
generated for the vehicle to become airborne. The da Vinci dream of vertical
liftoff was finally achieved with the development of the successful helicopter
more than 30 years after the first fixed-wing flight. 1 While, in the second half of
this century, this remarkable machine has become an essential vehicle for numerous
civil and military applications, because of its vertical lift capabilities, it
remains extremely limited in the speed and range that it can attain. By the middle
of this century, these limitations to the helicopter’s effectiveness and the demonstrated
capabilities of the fixed-wing airplane had fostered a new dream… the
development of an aircraft with the vertical takeoff and hover capability of the
helicopter, and with the speed and range of the fixed-wing aircraft. This is the
story of the quest for a new type of aircraft that would make that dream a reality.
The search for an aircraft type with Vertical Takeoff and Landing (VTOL) capabilities
triggered the imagination of designers and inventors to produce numerous
configurations using a wide variety of lifting and propulsion devices. A summary
of these configurations is shown in the V/STOL (Vertical or Short Takeoff and
Landing) concepts illustration 2 prepared by the McDonnell Aircraft Company in
the 1960s (figure 2). For the various aircraft types considered, one of the key distinguishing
features is associated with the device used for providing the vertical
1 th While several helicopters became airborne during the first three decades of the 20 century, the
Focke-Wulf Fw-61 is generally credited with being the first helicopter to demonstrate performance
and precision control, essential characteristics of a successful helicopter. The first flight
occurred in Germany in 1937 and public flight demonstrations were made in 1938.
2 Seth B. Anderson, “Historic Overview of V/STOL Aircraft Technology,” NASA TM 81280,
March 1981.
Figure 1.
Leonardo da Vinci 15 th
century helical air screw
flying machine.
1