Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 14

An introduction to aerodynamics must begin with a review of physics, and, in particular, the branch of physics that will be presented here is called mechanics. We will examine the fundamental physical laws governing the forces acting on an aircraft in flight, and what effect these natural laws and forces have on the performance characteristics of aircraft. To control an aircraft, whether it is an airplane, helicopter, glider, or balloon, the pilot must understand the principles involved and learn to use or counteract these natural forces.

We will start with the concepts of work, energy, power, and friction, and then build upon them as we move forward in future chapters.

Because the metric system of measurement has not yet been widely accepted in the United States, the English system of measurement is used in this book. The fundamental units are

Force	Pounds (lb)
Distance	Feet (ft)
Time	Seconds (s)

From the fundamental units, other quantities can be derived:

Velocity (distance/time)	ft/s (fps)
Area (distance squared)	square ft (ft2)
Pressure (force/unit area)	lb/ft2 (psf)
Acceleration (rate of change in velocity)	ft/s/s (fps2)

Aircraft measure airspeed in knots (nautical miles per hour) or in Mach number (the ratio of true airspeed to the speed of sound). Rates of climb and descent are measured in feet per minute, so quantities other than those above are used in some cases. Some useful conversion factors are listed below:

Multiply	by	to get
knots (kts.)	1.69	feet per second (fps)
fps	0.5925	kts.
miles per hour (mph)	1.47	fps
fps	0.6818	mph
mph	0.8690	kts.
kts.	1.15	mph
nautical miles (nm)	6076	feet (ft)
nm	1.15	statute miles (sm)
sm	0.869	nm
kts.	101.3	feet per minute (fpm)