approach to various principles and operating practices with formulas and examples using equations, it is more important that the reader understand WHY a principle of flight theory is discussed and how that subject matter intertwines with other materials presented; thus a qualitative approach is used throughout this textbook.
Perhaps your goal is to be a pilot, who will “slip the surly bonds of earth,” as John Gillespie Magee wrote in his classic poem “High Flight.” Or you may wish to build or maintain aircraft as a skilled technician. Or possibly you wish to serve in another vital role in the aviation industry, such as manager, dispatcher, meteorologist, engineer, teacher, or another capacity. Whichever area you might be considering, this textbook will build on what you already know and will help prepare you for a successful aviation career.
INTRODUCTION
This chapter begins with a review of the basic principles of physics and concludes with a summary of linear motion, mechanical energy, and power. A working knowledge of these areas, and how they relate to basic aerodynamics, is vital as we move past the rudimentary “four forces of flight” and introduce thrust and power‐producing aircraft, lift and drag curves, stability and control, maneuvering performance, slow‐speed flight, and other topics.
You may already have been introduced to the four basic forces acting on an aircraft in flight: lift, weight, thrust, and drag. Now, we must understand how these forces change as an aircraft accelerates down the runway, or descends on final approach to a runway and gently touches down even when traveling twice the speed of a car on the highway. Once an aircraft has safely made it into the air, what effect does weight have on its ability to climb, and should the aircraft climb up to the flight levels or stay lower and take “advantage” of the denser air closer to the ground?
By developing an understanding of the aerodynamics of flight, and of the ways in which design, weight, load factors, and gravity affect an aircraft during flight maneuvers from stalls to high‐speed flight, the pilot learns how to control the balance between these forces. This textbook will help clarify these concepts among others, leaving you with a better understanding of the flight environment.
BASIC QUANTITIES
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) |
EXAMPLES
Convert 110 kts. to fps: 110 kts. × 1.69 = 185.9 fps
Convert 50 kts. to fpm: 50 kts. × 101.3 = 5,065 fpm
Convert 450 fps to kts. = 450 fps × 0.5925 = 267 kts.
Convert 25 sm to nm: 25 sm × 0.869 = 21.7 nm
Application 1.1
An airplane flight manual (AFM) states a given aircraft should be rotated at 65 kts. indicated airspeed (IAS), yet the pilot misinterprets the airspeed indicator and rotates at 65 mph (IAS).
Does the aircraft rotate at a faster or slower airspeed than the manufacturer recommends? What are the implications?
FORCES
A force is a push or a pull tending to change the state of motion of a body. A resolution of the typical forces acting on an aircraft in steady flight is shown in Figure 1.1, while Figure 1.2 shows the four separate components of aerodynamic forces during straight‐and‐level, unaccelerated flight. The component that is 90° to the flight path and acts toward the top of the airplane is called lift. The component that is parallel to the flight path and acts toward the rear of the airplane is called drag; while the opposing forward force is thrust and is usually created by the engine. Weight opposes lift and as we will see is a function of the mass of the aircraft and gravity.
The
