As an instrument pilot, you must understand the relationship and differences between the aircraft's flight path, angle of attack, and pitch attitude. Also, it is crucial to understand how the aircraft will react to various controls and power changes because the environment in which instrument pilots fly has inherent hazards not found in visual flying. The basis for this understanding is found in the four forces and Newton's laws.


The Four Forces
The four basic forces acting upon an aircraft in flight are lift, weight, thrust, and drag. The aerodynamic forces produced by the wing create lift. A by-product of lift is induced drag. Induced drag combined with parasite drag (which is the sum of form drag, skin friction, and interference drag) produce the total drag on the aircraft. Thrust must equal total drag in order to maintain speed.

Lift must overcome the total weight of the aircraft, which is comprised of the actual weight of the aircraft plus the tail down force used to control the aircraft's pitch attitude. Understanding how the aircraft's thrust/drag and lift/weight relationships affect its flight path and airspeed is essential to proper interpretation of the aircraft's instruments, and to making proper control inputs.

Tag: Flying instrument, instrument flight, aviation, piloting, instrument rating, instrument flying training, instrument flight rating, instrument rating requirement, instrument rating regulation, aircraft, aero plane, airplane, and aeronautical knowledge.

Newton's First Law
Newton's First Law of Motion is the Law of Inertia, which states that a body in motion will remain in motion, in a straight line, unless acted upon by an outside force. Two outside forces are always present on an aircraft in flight: gravity and drag. Pilots use pitch and thrust controls to counter these forces to maintain the desired flight path. If a pilot reduces power while in straight-and-level flight, the aircraft will slow. A reduction of lift will cause the aircraft to begin a descent. [Figure 2-1: Newton's first law of motion]

Newton's Second Law
Newton's Second Law of Motion is the Law of Momentum, which states that a body will accelerate in the same direction as the force acting upon that body, and the acceleration will be directly proportional to the net force and inversely proportional to the mass of the body. This law governs the aircraft's ability to change flight path and speed, which are controlled by attitude (both pitch and bank) and thrust inputs. Speeding up, slowing down, entering climbs or descents, and turning are examples of acceleration that pilots control in everyday flight. [Figure 2-2: Newton's second law of motion]

Newton's Third Law
Newton's Third Law of Motion is the Law of Reaction, which states that for every action there is an equal and opposite reaction. As shown in figure 2-3: Newton's third law of motion, the action of the jet engine's thrust or the pull of the propeller led to the reaction of the aircraft's forward motion. This law is also responsible for a portion of the lift that is produced by a wing, by the downward deflection of the airflow around it. This downward force of the relative wind results in an equal but opposite (upward) lifting force created by the airflow over the wing.

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Flight path: The line, course, or track along which an aircraft is flying or is intended to be flow.

Angle of attack: The acute angle formed between the chord line of an airfoil and the direction of the air that strikes the airfoil.

Induced drag: Caused by the same factors that produce lift, its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, and this increases induced drag.

Parasite drag: Caused by the friction of air moving over the structure, its amount varies directly with the airspeed. The higher the airspeed, the greater the parasites drag.

Relative wind: The direction from which the wind meets an airfoil....read more

The rate of turn, normally measured in degrees per second, is based upon a set bank angle at a set speed. If either one of these elements changes, then the rate of turn will change. If the aircraft increases its speed without changing the bank angle, then the rate of turn will decrease. Likewise, if the speed decreases without changing the bank angle, the rate of turn will increase.

Changing the bank angle without changing speed will also cause the rate of turn to change. Increasing the bank angle without changing speed will increase the rate of turn, while decreasing the bank angle will reduce the rate of turn.

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The standard rate of turn, 3 °� per second, is used as the main reference for bank angle. Therefore, you must understand how the angle of bank will vary with speed changes, such as slowing down for holding or an instrument approach. Figure 2-9: "Turns" shows the turn relationship with reference to a constant bank angle or a constant airspeed, and the effects on rate of turn and radius of turn....read more

This maneuver may produce extreme disorientation. While in straight-and-level flight, the pilot should sit normally, either with eyes closed or gaze lowered to the floor. The instructor pilot starts a positive, coordinated roll toward a 30° or 40° angle of bank. As this is in progress, the pilot should tilt the head forward, look to the right or left, then immediately return the head to an upright position. The instructor pilot should time the maneuver so the roll is stopped just as the pilot returns his/her head upright. An intense disorientation is usually produced by this maneuver, with the pilot experiencing the sensation of falling downwards into the direction of the roll.

Tag: Flying instrument, instrument flight, aviation, piloting, instrument rating, instrument flying training, instrument flight rating, instrument rating requirement, instrument rating regulation, aircraft, aero plane, airplane, and aeronautical knowledge.

In the descriptions of these maneuvers, the instructor pilot is doing the flying, but having the pilot do the flying can also make a very effective demonstration. The pilot should close his/her eyes and tilt the head to one side. The instructor pilot tells the pilot what control inputs to perform. The pilot then attempts to establish the correct attitude or control input with eyes still closed and head still tilted. While it is clear the pilot has no idea of the actual attitude, he/she will react to what the senses are saying. After a short time, the pilot will become disoriented and the instructor pilot then tells the pilot to look up and recover. The benefit of this exercise is the pilot actually experiences the disorientation while flying the aircraft.

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Proper power control results from the ability to smoothly establish or maintain desired airspeeds in coordination with attitude changes. Power changes are made by throttle adjustments and reference to the power indicators. Power indicators are not affected by such factors as turbulence, improper trim, or inadvertent control pressures. Therefore, in most aircraft little attention is required to ensure the power setting remains constant.Tag: Flying instrument, instrument flight, aviation, piloting, instrument rating, instrument flying training, instrument flight rating, instrument rating requirement, instrument rating regulation, aircraft, aero plane, airplane, and aeronautical knowledge.

From experience in an aircraft, you know approximately how far to move the throttles to change the power a given amount. Therefore, you can make power changes primarily by throttle movement and then crosscheck the indicators to establish a more precise setting. The key is to avoid fixating on the indicators while setting the power. Knowledge of approximate power settings for various flight configurations will help you avoid over-controlling power....read more

It is not sufficient in the airspace system for only the pilot to have an indication of the aircraft's altitude; the air traffic controller on the ground must also know the altitude of the aircraft. To provide this information, the aircraft may be equipped with an encoding altimeter.

When the ATC transponder is set to Mode C, the encoding altimeter supplies the transponder with a series of pulses identifying the flight level (in increments of 100 feet) at which the aircraft is flying. This series of pulses is transmitted to the ground radar where they appear on the controller's scope as an alphanumeric display around the return for the aircraft. The transponder allows the ground controller to identify the aircraft under his/her control and to know the pressure altitude at which each is flying.

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A computer inside the encoding altimeter measures the pressure referenced from 29.92" Hg and delivers this data to the transponder. When the pilot adjusts the barometric scale to the local altimeter setting, the data sent to the transponder is not affected. 14 CFR part 91 requires the altitude transmitted by the transponder to be within 125 feet of the altitude indicated on the instrument used to maintain flight altitude.

Encoding altimeter: A sensitive altimeter that sends signals to the ATC transponder, showing the pressure altitude the aircraft is flying....read more