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Introduction to the Flight Environment

CHAPTER OBJECTIVES

After completing this chapter, you should be able to:

• Define basic units of measurement used in the introduction to aerodynamics in flight and convert from one unit of measurement to another.
• Identify the four forces on an airplane in constant altitude, unaccelerated flight.
• Calculate the mass of an aircraft.
• Define vector addition and apply to an aircraft in a climb.
• Describe Newton's laws of motion and recognize how they apply to an introduction to aerodynamics.
• Define the purpose of linear motion in relation to constant acceleration, and then calculate aircraft acceleration, takeoff distance, and takeoff time.
• Describe the difference between energy and work and calculate the potential and kinetic energy of an aircraft in flight.
• Calculate the equivalent horsepower of an aircraft from a known thrust and speed.
• Define friction as it applies to an aircraft.

A basic understanding of the physical laws of nature that affect aircraft in flight and on the ground is a prerequisite for the study of aerodynamics. Modern aircraft have become more sophisticated, and more automated, using advanced materials in their construction requiring pilots to renew their understanding of the natural forces encountered during flight. Understanding how pilots control and counteract these forces better prepares pilots and engineers for the art of flying for harnessing the fundamental physical laws that guide them. Though at times this textbook will provide a quantitative 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

From the fundamental units, other quantities can be derived:

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:

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 sum of the opposing forces is always zero in steady flight, but this does not mean the four forces are equal. In future chapters of this textbook, we will further demonstrate the following statement regarding forces acting on an airplane in steady flight: The sum of all upward component of forces equals the sum of all downward components of forces, and the sum of all forward components of forces equals the sum of all backward components of forces.

Figure 1.1 Forces on an airplane in steady flight.

Figure 1.2 Resolved forces on an airplane in steady flight.

Source: U.S. Department of Transportation Federal Aviation Administration (2008a).

MASS

Mass is a measure of the amount of material contained in a body, usually measured in kilograms; we will use slugs as the unit in this textbook. Weight, on the other hand, is a force caused by the gravitational attraction of the earth (g = 32.2?ft/s2), moon, sun, or other heavenly bodies. Weight will vary depending on where the body is located in space (specifically, how far from the source of gravitational attraction), but mass will not vary with position.

Rearranging gives

This mass unit is called the slug.

EXAMPLE

Calculate the mass of an aircraft that weighs 2576?lb.

SCALAR...