User Guide

Above these are two more gauges, both quite important. On

the left, two pointers show how much fuel remains in the left and

right wing tanks - always nice to know! To the right of the throttle,

two more pointers are controlled by the red fuel mixture knob.

Since airplanes operate over a much wider altitude range than

cars, it’s necessary for the pilot to adjust the ratio of fuel and air

entering the engine. Modern cars do this automatically, with fancy

computers and oxygen sensors...but modern cars can also pull

over to the side of the road if they quit. The 172’s constant-flow

mechanical fuel injection system is stone-age technology by com-

parison...but it requires no electrical power whatsoever and has

only one moving part.

The right needle in this dual gauge shows, in gallons per

hour, how much fuel the engine is using. This is not only useful

information to have in general (“if I have 30 gallons on board and

I’m using ten gallons per hour, it’s gonna get awful quiet around

here in three hours or so”), but can provide a quick way of setting

the mixture (“at 8000 feet and 2300 rpm, I should be burning

about eight and a quarter gallons an hour”).

The left needle provides an even more precise way of setting

mixture. It measures exhaust gas temperature (EGT). For any given

power setting, the highest possible EGT occurs when the fuel/air

ratio is exactly correct. Often, however, operating at peak EGT is

hard on the engine. In many cases, you’ll lean the engine (by slow-

ly and carefully easing back on the mixture control) until EGT

peaks, then enrich by a set number of degrees for best power or

economy.

The vertical row of instruments to the right of the main flight

group, and the stack of radios to the right of them, will come into

play when we start looking at navigation and instrument flight. For

the moment, though, we’ve been on the ground long enough. Let’s

start flying!

Flight Instruction

Fuel Gauges

Cessna Floor Panel

Elevator Trim Indicator

Elevator Trim Knob

Fuel Cutoff

Fuel Tank Selector