Level: Middle School to H. S.
Time involvement: 20 to 30 minutes.
Despite lacking a formal engineering education the Wright Brothers understood the importance of measurement in unlocking the secrets of flight. Their 1903 Flyer contained three instruments: a stopwatch, an engine speed instrument and an anemometer to measure air speed. Today’s modern aircraft have the same three basic ones the Wrights used in addition to precise instruments to measure altitude, attitude relative to the horizon, direction of flight, engine instruments, and, of course, sophisticated GPS based navigational tools. Unfortunately, merely holding an altimeter and gazing at the clock-like face gives little clue about how it works.
Fortunately, this mini-lesson utilizes several cut-away instruments revealing the delicate internal construction that translates air pressure and other inputs into useful information for the pilot about how high am I, how fast am I moving, where am I heading, and, am I turning. In addition, a “G” meter that measures the stresses on the airframe and pilot during abrupt maneuvers is a less common instrument but fun to let students hold and simulate high “G” forces in sharp turns.
Discussion: Although modern instrument panels use computer displays of the older mechanical versions the older instruments provide a more visual and understandable teaching model. The “turn coordinator” (used in the lesson) contains a small gyroscope, which will be powered allowing the instrument to demonstrate actual “live” instrument operation. The magnetic compass is not a cut away due to the fact that it contains a special stabilizing fluid to make the instrument more readable in turbulent air.
The human body is well equipped to function on earth with visual contact to the nearby environment. The sensation of movement is largely tied to the visual effect of viewing stationary nearby objects. Since the lift of the aircraft’s wings is proportional to the speed of the air moving across them it is extremely important to know how fast the aircraft is moving through the air. Failure to maintain critical flying speed at a low altitude will trigger a “stall” of the wing and cause an often fatal crash. Given the fact that air is transparent “air speed” may be significantly different from ground speed. A tail wind will give the illusion of a much higher air speed. Consequently, flight instructors teach students from their earliest lessons to constantly monitor their “airspeed” based on the instrument in front of them.
Internal structures of the human ear give us a keen sense of balance. Even with our eyes closed we can tell when we are standing erect or might lose our balance. Unfortunately, when flying into a cloud our earthbound sense of balance becomes fooled. Sadly, many early aircraft accidents occurred when pilots attempted to fly their craft through clouds.
It took until 1929 until a successful gyroscopically based aircraft instrument was developed. In that year “Lieut. James H. Doolittle took off under a hooded cockpit, (at Mitchell Field, Long Island) circled the field and landed without once seeing outside the airplane. Instrument flying had been born!
Notes: Aircraft instruments are expensive and delicate. Thanks to the generosity of an instrument repair station these instruments have been obtained.