Aircraft technical Basics: Introduction to Airplanes - Navy Training Courses Edition of 1944: Chapter 4 Instruments

CHAPTER 4 INSTRUMENTS

A LOOK AT THE COCKPIT

To some folks, the inside of an airplane cockpit is as mysterious and complicated as the Einstein theory. The cockpit, it's true, does have a lot if equipment packed in a small space. But when you think of all the things a pilot must know and DO to fly an airplane, you realize the necessity for so many instruments and controls. They provide extra sets of "hands" and "eyes" without which flying a modern airplane would be impossible.

There are two ways of grouping airplane instruments for the purpose of learning about them. One way is according to the jobs they do. From this point of view they fall into three classes. You have FLIGHT instruments, NAVIGATION instruments, and ENGINE instruments. Another method of classifying airplane instruments is according to the principles on which they work. Some operate as the result of changes in TEMPERATURE or PRESSURE. Some are HYDRAULIC - that is, they operate by fluid pressure. Others are put in action by MAGNETISM and ELECTRICITY. Some use GYROSCOPES. You'll find this second method of classifying a big help if you go on to specialize in instrument work.

FLIGHT INSTRUMENTS

Flight instruments keep you posted on the positions assumed by the airplane in flight, and make it possible for you to control them intelligently.

The main flight instruments appear in figure 14. The CONTROL STICK (or, in some airplanes, the "wheel" control) operates the ailerons and elevators. Move the stick forward and you lower the elevators, so the airplane noses down. Pull it back and the nose rises. Move the stick from side to side and you operate the ailerons, causing the air-plane to bank to right or left, according to the direction in which you're leaning.

Figure 14.-Flight and navigation instruments.

To STEER the airplane to left or right you use the RUDDER PEDALS. Most airplanes also have BRAKE PEDALS attached to the forward ends of the rudder pedals. The brakes work independently - that is, you can apply them to either landing wheel separately, or to both at the same time.

The ALTIMETER shows you how high above the point of take-off the airplane is flying. It can also be adjusted to indicate height above sea level, if that's preferable under the circumstances. The AIRSPEED INDICATOR tells how rapidly the airplane is moving in relation to the air.

The BANK AND TURN INDICATOR is another one of those combination instruments. The turn indicator part of it shows whether the airplane is flying in a straight line or turning. The bank indicator is a little ball in a curved groove. If the airplane is skidding or slipping, the ball rolls to one side like the "tilt" on a pinball machine.

The RATE OF CLIMB INDICATOR - not to be confused with the altimeter - indicates how fast you're climbing or gliding. During level flight it registers zero.

When you're flying blind, it's mighty hard to tell whether the airplane is flying on an even keel, nosing down or up, banking, or whatever. It's absolutely foolhardy to rely on your sense of balance or the feel on the seat of your pants, for airplanes have a habit of playing tricks on human machinery under such circumstances. The rate of climb indicator, bank and turn indicator, and ARTIFICIAL HORIZON instrument are a mighty fine threesome to rely upon instead - when you're in a tight spot with "ceiling zero."

The AUTOMATIC PILOT is a fairly recent development, but it has become an important factor in safe aviation. It allows the pilot to set the controls for steady, straightaway flight while he attends to the other important chores that must take part of his time and attention.

NAVIGATION INSTRUMENTS

Navigation instruments help you to arrive at your destination without getting lost. The main one used are shown in figure 14.

The COMPASS (there are several types) shows you the direction in which the airplane is heading with respect to magnetic north. The DRIFT INDICATOR tells you how the wind is trying to blow you off your course. The OCTANT or SEXTANT is used to get directional bearings from the sun and stars. The CHRONOMETER - or just plain CLOCK - is an instrument without which celestial bearings and other reckoning of position would be meaningless. The RADIO, which often provides information of great value, might also be listed as a navigation instrument.

ENGINE INSTRUMENTS

Engine instruments tell you about operating conditions in the engine and other parts of the power plant, and provide you with means of regulating engine operation.

It's almost impossible to put too much emphasis on the importance of knowing what the power plant of your airplane is doing. It's true that a person who is thoroughly familiar with airplane engines can sometimes identify irregularities in operation merely by listening to the sound of the engine. But that's guesswork, at best. Only the engine instruments, like those in figure 15, can do a really reliable job.

The TACHOMETER is an instrument that tells you how many times a minute the engine crankshaft is turning. It's a valuable indicator of engine performance, because almost any sort of engine trouble results in a slow-down of the power plant's revolutions per minute (rpm).

Many airplanes are equipped with a combination instrument called the ENGINE GAGE UNIT, which shows the temperature of the engine oil, the oil pressure, and the fuel pressure - all on a single dial. In other airplanes, the three instruments may have separate dials, but they will function in the same way.

There are quite a few types of FUEL QUANTITY GAGES to tell you how much gas is in the fuel tanks. HYDROSTATIC gages give correct gasoline-level readings only after you pull and release a pump handle that's connected with the fuel system. ELECTRICAL gages and ordinary FLOAT gages are also used in airplanes for the purpose of determining gasoline levels.

Figure 15.-Engine instruments.

Then there are THERMOMETERS. They keep you posted on the temperature of various parts of the engine, how hot or cold the air is outside the cock-pit, and similar things.

The MAGNETO SWITCH turns the engine ignition on and off. This switch generally has three ON positions, labeled "right" and "left" and "both," since almost all modern airplane engines have dual ignition systems.

The CARBURETOR AIR HEATER CONTROL adjusts the supply of heat to the carburetor air intake - important in preventing ice formation in this part of the fuel system when you're flying high.

Almost all airplanes are equipped with PRIMERS to make engine starting easier. A primer is usually hand operated from the cockpit and pumps a charge of liquid gasoline into the intake manifold.

The WOBBLE PUMP is used to build up the fuel pressure during starting so that gasoline can reach the carburetor, even though the engine-driven fuel pump is not operating. The wobble pump is likewise valuable as an emergency pump if the engine-driven pump breaks down. To shut off the whole fuel supply to the engine, you can close a FUEL SHUT-OFF COCK.

The mixture of gasoline and air reaching the engine cylinders can be regulated by adjusting the MIXTURE CONTROL. In an airplane the THROTTLE serves the same purpose as the gas pedal in an automobile - it controls the amount of fuel fed to the engine.