Aeronautic and Aerospace Flight
Summary
The aero-thermodynamic properties of the atmosphere change markedly with the altitude from ground level. These properties are: temperature, pressure, density, speed of sound, dynamic and kinematic viscosity. These changes must be taken into account for any realistic analysis of aeronautic/aerospace flight. Data are available for all altitudes.
Fig.1 and Fig. 2
show the variation of the Reynolds and Mach number with the flight altitude. For a
given speed the Reynolds number decreases with the increasing altitude, while the
Mach number increases. There is a region in the flight envelope where the flow is
dominated by viscous effects at high Mach numbers.
The speed-altitude band where flight sustained by aerodynamic forces is technically
possible is called flight corridor. The aeronautic vehicle flight regime is
indicated in Fig. 3. These boundaries have been computed by
assuming a minimum and maximum wing loading of W=0.5÷5.0 kPa (10÷100
pounds/ft²), with extreme lift coefficients of CL=0.2 and CL=1.0. to the
square root of W/CL.
The area enclosed in Fig. 3 by the limiting curves indicate the technological
boundaries of atmospheric flight. The figure also shows the operation point of some
vehicles, based on service ceiling and cruise speed: the subsonic Boeing 747, the
supersonic Concorde, and the high-altitude solar powered Centurion that has an
extremely low wing loading (0.66 lb/ft²=0.028 kg/m²), and a very low speed
(about 30 Km/h). This astounding achievement places Centurion beyond the conventional
boundaries.
The aerospace vehicle flight regime is the upper limit, and includes the range of
operation of re-entry space vehicles (Space Shuttle) and ballistic missiles. Fig. 4
below shows the flight path of the space craft Columbia (STS-2, flight data from
Shinn-Simmonds, 1982), and the typical path of a ICBM (intercontinental ballistic
missile.)
For every aircraft a flight envelope is a closed area in the u-z diagram
that specifies the operating conditions. An example is shown in Fig. 5
below.
All the envelopes are estimated from available data.
The graphic shows the following characteristics:
Aeronautic Flight Corridor
Aerospace Flight Corridor
Flight Envelope
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