AIRCRAFT SYSTEMS - MIXTURE CONTROL

Carburetors are normally calibrated at sea-level pressure, where the correct fuel-to-air mixture ratio is established with the mixture control set in the FULL RICH position. However, as altitude increases, the density of air entering the carburetor decreases, while the density of the fuel remains the same.

AIRCRAFT SYSTEMS - CARBURETOR SYSTEMS

Carburetors are classified as either float-type or pressure-type. Pressure carburetors are usually not found on small airplanes. The basic difference between a pressure carburetor and a float-type is the pressure carburetor delivers fuel under pressure by a fuel pump.

AIRCRAFT SYSTEMS - INDUCTION SYSTEMS

The induction system brings in air from the outside, mixes it with fuel, and delivers the fuel/air mixture to the cylinder where combustion occurs.

AIRCRAFT SYSTEMS - ADJUSTABLE-PITCH PROPELLER

Although some older adjustable-pitch propellers could only be adjusted on the ground, most modern adjustable-pitch propellers are designed so that you can change the propeller pitch in flight.

AIRCRAFT SYSTEMS - FIXED-PITCH PROPELLER

The pitch of this propeller is set by the manufacturer, and cannot be changed. With this type of propeller, the best efficiency is achieved only at a given combination of airspeed and r.p.m.

AIRCRAFT SYSTEMS - PROPELLER

The propeller is a rotating airfoil, subject to induced drag, stalls, and other aerodynamic principles that apply to any airfoil. It provides the necessary thrust to pull, or in some cases push, the airplane through the air.

AIRCRAFT SYSTEMS - RECIPROCATING ENGINES

Most small airplanes are designed with reciprocating engines. The name is derived from the back-and-forth, or reciprocating, movement of the pistons. It is this motion that produces the mechanical energy needed to accomplish work. Two common means of classifying reciprocating engines are:

AIRCRAFT SYSTEMS - POWERPLANT

This section covers the main systems found on small airplanes. These include the engine, propeller, and induction systems, as well as the ignition, fuel, lubrication, cooling, electrical, landing gear, autopilot, and environmental control systems. A comprehensive introduction to gas turbine engines is included at the end of this section.

SECONDARY FLIGHT CONTROLS - ADJUSTABLE STABILIZER

Rather than using a movable tab on the trailing edge of the elevator, some airplanes have an adjustable stabilizer. With this arrangement, linkages pivot the horizontal stabilizer about its rear spar. This is accomplished by use of a jackscrew mounted on the leading edge of the stabilator.

SECONDARY FLIGHT CONTROLS - GROUND ADJUSTABLE TABS

Many small airplanes have a non-moveable metal trim tab on the rudder. This tab is bent in one direction or the other while on the ground to apply a trim force to the rudder.

SECONDARY FLIGHT CONTROLS - ANTISERVO TABS

In addition to decreasing the sensitivity of the stabilator, an antiservo tab also functions as a trim device to relieve control pressure and maintain the stabilator in the desired position.

SECONDARY FLIGHT CONTROLS - BALANCE TABS

The control forces may be excessively high in some airplanes, and in order to decrease them, the manufacturer may use balance tabs. They look like trim tabs and are hinged in approximately the same places as trim tabs.

SECONDARY FLIGHT CONTROLS - TRIM TABS

The most common installation on small airplanes is a single trim tab attached to the trailing edge of the elevator. A small, vertically mounted control wheel manually operates most trim tabs. However, a trim crank may be found in some airplanes.

SECONDARY FLIGHT CONTROLS - TRIM SYSTEMS

Although the airplane can be operated throughout a wide range of attitudes, airspeeds, and power settings, it can only be designed to fly hands off within a very limited combination of these variables.

SECONDARY FLIGHT CONTROLS - SPOILERS

On some airplanes, high-drag devices called spoilers are deployed from the wings to spoil the smooth airflow, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft, one of the advantages being the elimination of adverse yaw.

SECONDARY FLIGHT CONTROLS - LEADING EDGE DEVICES

High-lift devices also can be applied to the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps.

FLIGHT CONTROLS - CANARD

The term canard refers to a control surface with functions as a horizontal stabilizer but is located in front of the main wings. The term also is used to describe an airplane equipped with a canard. In effect, it is an airfoil similar to the horizontal surface on a conventional aft-tail design.

SECONDARY FLIGHT CONTROLS - FLAPS

Secondary flight control systems may consist of the flaps, leading edge devices, spoilers, and trim devices.
Flaps are the most common high-lift devices used on practically all airplanes.

FLIGHT CONTROLS - STABILIZER

As mentioned earlier, a stabilizer is essentially a one-piece horizontal stabilizer with the same type of control system. Because stabilizers pivot around a central hinge point, they are extremely sensitive to control inputs and aerodynamic loads.

FLIGHT CONTROLS - V-TAIL

The V-tail design utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers.

FLIGHT CONTROLS - T-TAIL

In a T-tail configuration, the elevator is above most of the effects of downwash from the propeller as well as airflow around the fuselage and/or wings during normal flight conditions.

FLIGHT CONTROLS - RUDDER

The rudder controls movement of the airplane about its vertical axis. This motion is called yaw. Like the other primary control surfaces, the rudder is a movable surface hinged to a fixed surface, in this case, to the vertical stabilizer, or fin.

FLIGHT CONTROLS - ELEVATOR

The elevator controls pitch about the lateral axis. Like the ailerons on small airplanes, the elevator is connected to the control column in the cockpit by a series of mechanical linkages. Aft movement of the control column deflects the trailing edge of the elevator surface up.

FLIGHT CONTROLS - COUPLED AILERONS AND RUDDER

Coupled ailerons and rudder means these controls are linked. This is accomplished with rudder-aileron interconnect springs, which help correct for aileron drag by automatically deflecting the rudder at the same time the ailerons are deflected.

FLIGHT CONTROLS - FRISE-TYPE AILERONS

With a Frise-type aileron, when pressure is applied to the control wheel, the aileron that is being raised pivots on an offset hinge. This projects the leading edge of the aileron into the airflow and creates drag.

FLIGHT CONTROLS - DIFFERENTIAL AILERONS

With differential ailerons, one aileron is raised a greater distance than the other aileron is lowered for a given movement of the control wheel. This produces an increase in drag on the descending wing.

FLIGHT CONTROLS - ADVERSE YAW

Since the downward deflected aileron produces more lift, it also produces more drag. This added drag attempts to yaws the airplane's nose in the direction of the raised wing. This is called adverse yaw.

FLIGHT CONTROLS - AILERONS

Ailerons control roll about the longitudinal axis. The ailerons are attached to the outboard trailing edge of each wing and move in the opposite direction from each other.

FLIGHT CONTROLS - PRIMARY FLIGHT CONTROLS

Aircraft flight control systems are classified as primary and secondary. The primary control systems consist of those that are required to safely control an airplane during flight. These include the ailerons, elevator (or stabilizer), and rudder.

HIGH-SPEED FLIGHT- FLIGHT CONTROLS

On high-speed airplanes, flight controls are divided into primary flight controls and secondary or auxiliary flight controls. The primary flight controls maneuver the airplane about the pitch, roll, and yaw axes. They include the ailerons, elevator, and rudder.

HIGH-SPEED FLIGHT- MACH BUFFET BOUNDARIES

Thus far, only the Mach buffet that results from excessive speed has been addressed. It must be remembered that Mach buffet is a function of the speed of the airflow over the wing—not necessarily the speed of the airplane.

HIGH-SPEED FLIGHT- SWEEPBACK

Most of the difficulties of transonic flight are associated with shock wave induced flow separation. Therefore, any means of delaying or alleviating the shock-induced separation will improve aerodynamic performance.

HIGH-SPEED FLIGHT- SHOCK WAVES

When an airplane flies at subsonic speeds, the air ahead is "warned" of the airplane's coming by a pressure change transmitted ahead of the airplane at the speed of sound.

HIGH-SPEED FLIGHT- BOUNDARY LAYER

Air has viscosity, and will encounter resistance to flow over a surface. The viscous nature of airflow reduces the local velocity's on a surface and is responsible for skin friction drag.

HIGH-SPEED FLIGHT- MACH NUMBER VS AIRSPEED

Speeds such as Mach Crit and MMO for a specific airplane occur at a given Mach number. The true airspeed (TAS), however, varies with outside air temperature. Therefore, true airspeeds corresponding to a specific Mach number can vary considerably (as much as 75 – 100 knots).

HIGH-SPEED FLIGHT- SPEED RANGES

The speed of sound varies with temperature. Under standard temperature conditions of 15°C, the speed of sound at sea level is 661 knots.

HIGH-SPEED FLIGHT-SUPERSONIC VS SUBSONIC FLOW

In subsonic aerodynamics, the theory of lift is based upon the forces generated on a body and a moving gas (air) in which it is immersed. At speeds below about 260 knots, air can be considered incompressible, in that at a fixed altitude, its density remains nearly constant while its pressure varies.

EFFECT OF LOAD DISTRIBUTION

The effect of the position of the center of gravity on the load imposed on an airplane's wing in flight is not generally realized, although it may be very significant to climb and cruising performance.

EFFECTS OF WEIGHT ON STABILITY AND CONTROL ABILITY

The effects that overloading has on stability also are not generally recognized. An airplane, which is observed to be quite stable and controllable when loaded normally, may be discovered to have very different flight characteristics when it is overloaded.

EFFECT OF WEIGHT ON AIRPLANE STRUCTURE

The effect of additional weight on the wing structure of an airplane is not readily apparent. Airworthiness requirements prescribe that the structure of an airplane certificate in the normal category (in which acrobatics are prohibited) must be strong enough to withstand a load factor of 3.8 to take care of dynamic loads caused by maneuvering and gusts.

EFFECTS OF WEIGHT ON FLIGHT PERFORMANCE

The takeoff/climb and landing performance of an airplane are determined on the basis of its maximum allowable takeoff and landing weights. A heavier gross weight will result in a longer takeoff run and shallower climb, and a faster touchdown speed and longer landing roll.

WEIGHT AND BALANCE

Often a pilot regards the airplane's weight and balance data as information of interest only to engineers, dispatchers, and operators of scheduled and nonscheduled air carriers.

LOAD FACTORS AND FLIGHT MANEUVERS - VG DIAGRAM

The flight operating strength of an airplane is presented on a graph whose horizontal scale is based on load factor. The diagram is called a Vg diagram—velocity versus "g" loads or load factor.

LOAD FACTORS AND FLIGHT MANEUVERS - ROUGH AIR

All certificate airplanes are designed to withstand loads imposed by gusts of considerable intensity. Gust load factors increase with increasing airspeed and the strength used for design purposes usually corresponds to the highest-level flight speed.

LOAD FACTORS AND FLIGHT MANEUVERS - CHANDELLES AND LAZY EIGHTS

It would be difficult to make a definite statement concerning load factors in these maneuvers as both involve smooth, shallow dives and pull-ups.

LOAD FACTORS AND FLIGHT MANEUVERS - HIGH-SPEED STALLS

The average light plane is not built to withstand the repeated application of load factors common to high-speed stalls.

LOAD FACTORS AND FLIGHT MANEUVERS - SPINS

Since a stabilized spin is not essentially different from a stall in any element other than rotation, the same load factor considerations apply as those that apply to stall recovery.

LOAD FACTORS AND FLIGHT MANEUVERS - STALLS

The normal stall entered from straight level flight, or an unaccelerated straight climb, will not produce added load factors beyond the 1-G of straight-and-level flight.

LOAD FACTORS AND FLIGHT MANEUVERS - TURNS

Increased load factors are a characteristic of all banked turns. Load factors become significant both to flight performance and to the load on wing structure as the bank increases beyond approximately 45°.

LOAD FACTORS AND FLIGHT MANEUVERS

Critical load factors apply to all flight maneuvers except unaccelerated straight flight where a load factor of 1 G is always present. Certain maneuvers considered in this section are known to involve relatively high load factors.

LOAD FACTORS AND STALLING SPEEDS

Any airplane, within the limits of its structure, may be stalled at any airspeed. When a sufficiently high angle of attack is imposed, the smooth flow of air over an airfoil breaks up and separates, producing an abrupt change of flight characteristics and a sudden loss of lift, which results in a stall.

LOAD FACTORS IN AIRPLANE DESIGN

The answer to the question "how strong should an airplane be" is determined largely by the use to which the airplane will be subjected.

LOAD FACTORS

The preceding sections only briefly considered some of the practical points of the principles of flight.

BASIC PROPELLER PRINCIPLES - ASYMMETRIC LOADING (P FACTOR)

When an airplane is flying with a high angle of attack, the "bite" of the downward moving blade is greater than the "bite" of the upward moving blade.

BASIC PROPELLER PRINCIPLES - CORKSCREW EFFECT

The high-speed rotation of an airplane propeller gives a corkscrew or spiraling rotation to the slipstream.

BASIC PROPELLER PRINCIPLES - TORQUE REACTION

Torque reaction involves Newton's Third Law of Physics—for every action, there is an equal and opposite reaction.

BASIC PROPELLER PRINCIPLES - TORQUE AND P FACTOR

To the pilot, "torque" (the left turning tendency of the airplane) is made up of four elements

AERODYNAMICS OF FLIGHT- BASIC PROPELLER PRINCIPLES

The airplane propeller consists of two or more blades and a central hub to which the blades are attached. Each blade of an airplane propeller is essentially a rotating wing. As a result of their construction, the propeller blades are like airfoils and produce forces that create the thrust to pull, or push, the airplane through the air.

AERODYNAMICS OF FLIGHT-STALLS

An airplane will fly as long as the wing is creating sufficient lift to counteract the load imposed on it. When the lift is completely lost the airplane stalls.

AERODYNAMIC FORCES IN FLIGHT MANEUVERS - FORCES IN DESCENTS

As in climbs, the forces acting on the airplane go through definite changes when a descent is entered from straight-and-level flight.

AERODYNAMIC FORCES IN FLIGHT MANEUVERS - FORCES IN CLIMBS

For all practical purposes, the wing's lift in a steady state normal climb is the same as it is in a steady level flight at the same airspeed.

AERODYNAMIC FORCES IN FLIGHT MANEUVERS - FORCES IN TURNS

If an airplane were viewed in straight - and - level flight from the rear and if the forces acting on the airplane actually could be seen, two forces (lift and weight) would be apparent.

Aerodynamics of Flight - SPIRAL INSTABILITY

Spiral instability exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.

Aerodynamics of Flight - FREE DIRECTIONAL OSCILLATIONS (DUTCH ROLL)

Dutch Roll is a coupled lateral/directional oscillation that is usually dynamically stable but is objectionable in an airplane because of the oscillatory nature.

Aerodynamics of Flight - VERTICAL STABILITY (YAWING)

Stability about the airplane's vertical axis (the sideways moment) is called yawing or directional stability. Yawing or directional stability is the more easily achieved stability in airplane design.

Aerodynamics of Flight - LATERAL STABILITY (ROLLING)

Stability about the airplane's longitudinal axis, which extends from nose to tail, is called lateral stability. This helps to stabilize the lateral or rolling effect when one wing gets lower than the wing on the opposite side of the airplane.

Aerodynamics of Flight - LONGITUDINAL STABILITY (PITCHING)

In designing an airplane, a great deal of effort is spent in developing the desired degree of stability around all three axes.

Aerodynamics of Flight - STATIC AND DYNAMIC STABILITY

STATIC STABILITY
Stability of an airplane in flight is slightly more complex than just explained, because the airplane is free to move in any direction and must be controllable in pitch, roll, and direction.

Aerodynamics of Flight - BASIC CONCEPTS OF STABILITY

The flight paths and attitudes in which an airplane can fly are limited only by the aerodynamic characteristics of the airplane, its propulsive system, and its structural strength.

Aerodynamics of Flight - DESIGN CHARACTERISTICS

Every pilot who has flown numerous types of airplanes has noted that each airplane handles somewhat differently—that is, each resists or responds to control pressures in its own way.

Aerodynamics of Flight - MOMENTS AND MOMENT ARM

A study of physics shows that a body that is free to rotate will always turn about its center of gravity. In aerodynamic terms, the mathematical measure of an airplane's tendency to rotate about its center of gravity is called a "moment."

Aerodynamics of Flight - AXES OF AN AIRPLANE

Whenever an airplane changes its flight attitude or position in flight, it rotates about one or more of three axes, which are imaginary-lines, that pass through the airplane's center of gravity.

Aerodynamics of Flight - GROUND EFFECT

It is possible to fly an airplane just clear of the ground (or water) at a slightly slower airspeed than that required to sustain level flight at higher altitudes. This is the result of a phenomenon, which is better known than understood even by some experienced pilots.

Aerodynamics of Flight - WINGTIP VORTICES

The action of the airfoil that gives an airplane lift also causes induced drag. It was determined that when a wing is flown at a positive angle of attack, a pressure differential exists between the upper and lower surfaces of the wing. That is, the pressure above the wing is less than atmospheric pressure and the pressure below the wing is equal to or greater than atmospheric pressure.

Aerodynamics of Flight - LIFT

The pilot can control the lift. Any time the control wheel is more fore or aft, the angle of attack is changed. As angle of attack increases, lift increases (all other factors being equal). When the airplane reaches the maximum angle of attack, lift begins to diminish rapidly. This is the stalling angle of attack, or burble point.

Aerodynamics of Flight - WEIGHT

Gravity is the pulling force that tends to draw all bodies to the center of the earth. The center of gravity (CG) may be considered as a point at which all the weight of the airplane is concentrated. If the airplane were supported at its exact center of gravity, it would balance in any attitude. It will be noted that center of gravity is of major importance in an airplane, for its position has a great bearing upon stability.