POWERED-LIFT AIRCRAFT TECHNOLOGY
 
 
INTRODUCTION
 
     Powered-lift aircraft have the capability to vary, in
flight, the direction of the force produced by the
propulsion system.  Propulsive force is a vector, not a
scalar quantity.  The magnitude and the direction of the
propulsive force is varied to produce thrust, lift, or
various thrust/lift components.  The propulsion system and
airframe are integrated, or closely coupled, so that in all
or some flight modes, propulsion-system exhaust flows
influence the external aerodynamics about the airframe.
Frequently, but not always, powered-lift aircraft have
aircraft flight control systems augmented by propulsion
systems.
 
     For over 30 years, powered-lift research and technology
(R&T) has been perceived in the context of enabling an
aircraft to operate from short or reduced-length runways, or
from minimum-sized terminal sites.  Powered-lift aircraft
have been categorized by such acronyms as STOL (for short
takeoff and landing) and VTOL (for vertical takeoff and
landing).  These acronyms correspond to the aircraft's
operational capabilities at the terminal site.
 
     Operation from small sites or reduced runway lengths is
an important attribute of an aircraft, as evidenced by
rotorcraft, the Harrier aircraft, and powered-lift
transports such as the C-17.  The powered-lift
technologywhich enables STOL or VTOL also provides enhanced
in-flight performance, such as steep-gradient flight for
noise abatement and improved combat maneuverability.  For
these reasons, powered-lift R&T will continue to address
STOL and VTOL aircraft and their associated in-flight
advantages.
 
     Today, powered-lift technolgy is on the threshold of
expansion.  Powered-lift technology may be applicable to
many types of aircraft (including those without STOL or
VTOL), such as subsonic transports and business jets that
operate from today's long runways.  For many types of
aircraft, a desired set of the aircraft's parameters of
merit (e.g., useful load, gross weight, noise,
maneuverability) can be enhanced by applying powered-lift
technology.  For mission requirements that do not include
STOL or VTOL, a question to address is, "What is better, the
optimally designed powered-lift aircraft or the optimally
designed nonpowered-lift aircraft?"  For mission
requirements that do include STOL or VTOL, that question is
already answered.
 
     This report presents an overview of four categories of
powered-lift aircraft:
 
     1.  Subsonic STOL aircraft
     2.  Subsonic V/STOL aircraft
     3.  Supersonic STOL aircraft
     4.  Supersonic STOVL aircraft
 
     Examples of research are discussed which indicate that
powered-lift technology may also yield the best design for
some conventional takeoff and landing (CTOL) aircraft that
operate from long runways only.
 
     Overall aircraft configurational aspects and flight
controls are discussed as are aerodynamics.  Propulsion
systems and aircraft structures, particularly for aircraft
capable of vertical flight, are of critical importance.
 
     Structures technology applies to all aircraft.
Powered-lift aircraft become increasingly competitive with
nonpowered-lift aircraft as structures are strengthened and
are manufactured of lightweight materials.  Excellent
articles are available on advanced lightweight structures,
but we have not searched the literature for such references
dealing with lightweight structures specifically for
powered-lift aircraft.