Vertical Speed Indicator (VSI) - Purpose, Operation, and Information Provided

Warm-Up – 3/27 – 10 minutes Utilizing your notes and past knowledge answer the following questions: • Describe the purpose of the VSI. • Describe the differential pressure used within the VSI. • Describe the two types of information the VSI provides. • What happens to the VSI when the pilot pulls back on the yoke/stick? • What is the time period from the initial change in the rate of climb to the indication of the new rate indicated on the VSI?

Questions / Comments

Vertical Speed Indicator (VSI) • The VSI indicates whether the aircraft is climbing, descending, or in level flight. • The rate of climb or descent is indicated in feet per minute (fpm). • If properly calibrated, the VSI indicates zero in level flight.

Principle of Operation • This causes a pressure differential that is indicated on the instrument needle as a climb or descent.

Principle of Operation • The VSI displays two different types of information: • • Trend information shows an immediate indication of an increase or decrease in the aircraft’s rate of climb or descent. • • Rate information shows a stabilized rate of change in altitude.

Principle of Operation • If an aircraft is maintaining level flight and the pilot pulls back on the control yoke causing the nose of the aircraft to pitch up, the VSI needle moves upward to indicate a climb.

Principle of Operation • If the pitch attitude is held constant, the needle stabilizes after a short period (6–9 seconds) and indicates the rate of climb in hundreds of fpm. • The time period from the initial change in the rate of climb, until the VSI displays an accurate indication of the new rate, is called the lag.

THIS DAY IN AVIATION • March 27 • 1907 — Romanian Trajan Vuia begins tests of his airplane, newly fitted with steering surfaces. • He makes a short flight of 33 feet in Paris, France.

THIS DAY IN AVIATION • March 27 • 1927 — Young American airmail pilot Charles A. Lindbergh registers his entry in the Raymond Orteig challenge for the first man to cross the Atlantic Ocean solo. • The challenge and a $25,000 prize, has been issued in 1920, but no one has so far been successful in making the flight.

THIS DAY IN AVIATION • March 27 • 1945 — 105 Boeing B-29 “Superfortresses” mined Shimonoseki Strait in a move to halt Japanese shipping.

THIS DAY IN AVIATION • March 27 • 1946 — An air agreement is signed by France and the United States giving Air France the right to serve the cities of Boston, New York, Washington, D.C., and Chicago.

THIS DAY IN AVIATION • March 27 • 1968 — Yuri Gagarin, in April 1961 first man in space, is killed in the crash of a Mikoyan-Gurevich MiG-15UTI “Midget” trainer near the Soviet capital Moscow.

THIS DAY IN AVIATION • March 27 • 1984 — British Airways inaugurates a “Concorde” service from London to Miami twice weekly. • The service operates through Washington-Dulles, necessitating a 50-minute stopover. • The overall trip lasts 6 hours 35 minutes, a saving approximately 2.5 hours over the direct flight by subsonic airliners. • The round-trip fare is quoted as £2,509.

March 2014

Chapter 7 – Flight Instruments FAA – Pilot’s Handbook of Aeronautical Knowledge

Today’s Mission Requirements • Mission: • Identify in writing how to interpret and operate flight instruments. • Describe the pilot’s ability to recognize errors and malfunctions with flight instruments. • Describe the pitot-static system and associated instruments. • Describe the vacuum system and related instruments. • Describe the gyroscopic instruments and the magnetic compass. • EQ: Describe the importance of Aeronautical Knowledge for the student pilot learning to fly.

AirSpeed Indicator (ASI) • The ASI is a sensitive, differential pressure gauge which measures and promptly indicates the difference between pitot (impact/dynamic pressure) and static pressure. • These two pressures are equal when the aircraft is parked on the ground in calm air.

AirSpeed Indicator (ASI) • When the aircraft moves through the air, the pressure on the pitot line becomes greater than the pressure in the static lines. • This difference in pressure is registered by the airspeed pointer on the face of the instrument, which is calibrated in miles per hour, knots (nautical miles per hour), or both.

AirSpeed Indicator (ASI) • The ASI is the one instrument that utilizes both the pitot, as well as the static system. • The ASI introduces the static pressure into the airspeed case while the pitot pressure (dynamic) is introduced into the diaphragm.

AirSpeed Indicator (ASI) • The dynamic pressure expands or contracts one side of the diaphragm, which is attached to an indicating system. • The system drives the mechanical linkage and the airspeed needle.

AirSpeed Indicator (ASI) • Multiple types of airspeeds. • Indicated airspeed (IAS)—the direct instrument reading obtained from the ASI • Calibrated airspeed (CAS)—IAS corrected for installation error and instrument error.

AirSpeed Indicator (ASI) • True airspeed (TAS)—Becauseair density decreases with an increase in altitude, an aircraft has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure. • TAS increases as altitude increases.

AirSpeed Indicator (ASI) • Groundspeed (GS)—the actual speed of the airplane over the ground. • It is TAS adjusted for wind. • GS decreases with a headwind, and increases with a tailwind.

AirSpeed Indicator Markings • This system of color-coded markings enables a pilot to determine at a glance certain airspeed limitations that are important to the safe operation of the aircraft.

AirSpeed Indicator Markings • Standard color-coded markings: • White arc — commonly referred to as the flap operating range since its lower limit represents the full flap stall speed and its upper limit provides the maximum flap speed. • Approaches and landings are usually flown at speeds within the white arc.

AirSpeed Indicator Markings • Lower limit of white arc (VS0)—the stalling speed or the minimum steady flight speed in the landing configuration. • Maximum landing weight in the landing configuration (gear and flaps down). • Upper limit of the white arc (VFE)—the maximum speed with the flaps extended.

AirSpeed Indicator Markings • • Green arc—the normal operating range of the aircraft. • Most flying occurs within this range.

AirSpeed Indicator Markings • Lower limit of green arc (VS1)—the stalling speed or the minimum steady flight speed obtained in a specified configuration. • Maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up).

AirSpeed Indicator Markings • Upper limit of green arc (VNO)—the maximum structural cruising speed. • Do not exceed this speed except in smooth air. • Yellow arc—caution range. Fly within this range only in smooth air, and then, only with caution.

AirSpeed Indicator Markings • Red line (VNE)—never exceed speed. • Operating above this speed is prohibited since it may result in damage or structural failure.

Other AirSpeed Limitations • Maneuvering speed (VA)—the maximum speed at which the structural design’s limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage.

Other AirSpeed Limitations • Best angle-of-climb speed (VX)—the airspeed at which an aircraft gains the greatest amount of altitude in a given distance. • It is used during a short-field takeoff to clear an obstacle. • Best rate-of-climb speed (VY)—the airspeed that provides the most altitude gain in a given period of time.

Instrument Check • When beginning the takeoff, make sure the airspeed is increasing at an appropriate rate.

Blockage of the Pitot-Static System • Blockage may be caused by moisture (including ice), dirt, or even insects • A blocked pitot tube affects the accuracy of the ASI, but, a blockage of the static port not only affects the ASI, but also causes errors in the altimeter and VSI.

Blockage of the Pitot-Static System • If both the pitot tube opening and the drain hole should become clogged simultaneously, no change is noted on the airspeed indication should the airspeed increase or decrease.

Blockage of the Pitot-Static System • If the static port is unblocked and the aircraft should change altitude, then a change is noted on the ASI. • The change is not related to a change in airspeed but a change in static pressure.

Blocked Static System • If the static system becomes blocked but the pitot tube remains clear, the ASI continues to operate; however, it is inaccurate. • The airspeed indicates lower than the actual airspeed.

Blocked Static System • A blockage of the static system also affects the altimeter and VSI. • Trapped static pressure causes the altimeter to freeze at the altitude where the blockage occurred.

Blocked Static System • In the case of the VSI, a blocked static system produces a continuous zero indication.

Blocked Static System • Alternate static source in the flight deck. • Alternate static source introduces static pressure from the flight deck back into the system.

Vertical Speed Indicator (VSI) - Purpose, Operation, and Information Provided