Airspeed indicator

As airspeed indicator (English airspeed indicator; ASI) are in aviation instruments for measuring the velocity of the aircraft relative to the surrounding air (travel, English air speed. ) Respectively. The ride of the aircraft is also referred to as airspeed.

The barometric airspeed indicator is the standard design today. The instrument consists of a pressure-tight housing to which the static pressure is connected. Inside the housing is a barometer can ( diaphragm cell ), which is subjected to the total pressure of static and dynamic pressure.

The difference between the total pressure and the static pressure corresponds to by the Bernoulli equation, the speed-dependent dynamic pressure. This pressure difference is shown on a scale as the velocity.

In sailing and ultralights to show your speed usually in km / h is done in most aircraft, however, in knots, at some smaller schools and touring aircraft, mostly American manufacturer, in miles per hour. There are also airspeed indicator with multiple scales available.

Single engine

The scale of the airspeed for single-engine aircraft carrying color sheets for marking individual speed ranges:

• No bow = outside safe operating limits (relative to 1g)
• White bow = operating range for extended flaps, limited by VS0 (based on 1g) and VFO or VFE.
• Green bow = normal operating range ( flaps retracted), limited by VS1 ( stall speed in clean 1g) and VNO (normal operational speed)
• Yellow sheet = caution, only allowed in calm air. In this speed range, the structure can be overloaded by strong turbulence. This speed range is limited by VNO and VNE ( Often confused with the maneuvering speed at which full rudder deflections are still allowed. The maneuvering speed is not shown on the airspeed indicator. )
• Red line = maximum speed ( VNE Velocity never Exceed )

The arches serve as a reminder aid, the exact speeds, procedures and limitations are included in the flight manual for the affected aircraft, in any case. There are to be found among other information on in-flight performance as a function of weight, center of gravity and altitude.

Zweimots and Mehrmots

The markings on the airspeed indicator of two- engine and multi-engine airplanes are identical to those on the airspeed indicator of Einmotorflugzeugen. However, There is also the blue line for Vyse, which symbolizes the best rate of climb in the event of an engine failure.

Commercial aircraft often have so-called Speedbugs which ( a reminder equaling ) in preparation for landing, for example, the VREF and / or VTGT be pushed.

There are many aircraft still more speed ranges but they are not of permanent maximum interest, simply must be memorized by the pilot variably behave with the flight or weight ( and thus are not shown as a colored area on the airspeed indicator ). This would include the:

( for translations and further explanation of the abbreviations see: Abbreviations / Aeronautics)

• V1 (critical engine failure speed decision )
• V2 ( climb out speed)
• VA ( maneuvering speed )
• VB, VC, VD ( speeds from the vn diagram)
• VLE ( Max Landing Gear Extended Speed)
• VLO ( Max Landing Gear Operation Speed)
• VMBE (Maximum Brake Energy Speed)
• VMCA (minimum control speed Air)
• VMCG (Minimum Control Speed ​​Ground )
• VMU (Minimum Unstick Speed)
• VX (best angle of climb speed)
• VXSE ( single engine best angle of climb speed)
• VY (best rate of climb speed)

If a drive Mach - knife used in place of a, we replace (if appropriate) in oa Abbreviations against the V M - follow it eg: MNO, etc.

There are other speed ranges of aircraft that may be of interest in certain situations and often in Betr. POH ( flight manual ) are listed. However, you also do not occur on the airspeed indicator as a marker on AND do not have a fixed abbreviation in the style of VREF, VMU, etc.

Examples:

Gliders

Gliders have in addition to the markings that (see above) are also present in the single engine, still a yellow triangle. This refers to the manufacturer's recommended approach speed at maximum weight without ballast with no wind.

Motor gliders have usually still a blue line at the speed of best climb (VY ).

Technology of the airspeed indicator and pressure decrease

The static pressure is used in many types of aircraft to about 1 mm openings ( engl. static ports) on both sides of the hull removed and passed over hose lines to the instruments. The two-sided arrangement of the pressure gage is designed to reduce false alarms, eg by shifting flight conditions as well as problems caused by clogged pressure gage. At the static pressure system and altimeter and variometer are connected next to the airspeed indicator.

The total pressure is taken at the airspeed indicator described here on the pitot tube (English pitot tube ) and also directed by hose to the instruments. The pitot tube is located at the most aircraft on the fuselage top or near the wing leading edge and extends into a largely undisturbed air flow into it. The pitot tube can to protect against icing with a heater ( pitot heat, usually electrical) be equipped.

Since nowadays there are airplanes that have a black box, the speed of the airspeed indicator must be recorded electronically. One possibility is the signaling by means of a variable capacitor that is integrated in the instrument.

Frequently the pitot tube when parking the aircraft with a protective sheath covered (eg protection against blockage by insects ) is. The pressure gage static pressure get less chance to protection as the pitot tube. In the pre-flight check is to examine, among other things, that the protective coatings were removed and the pressure take-off points in a perfect condition ( no constipation, etc.).

Common is the use of Prandtl tubes simultaneously with those of the dynamic pressure and the static pressure can be removed. These are to be distinguished from the outside only after closer inspection of the normal pitot tube.

Many transport aircraft more pressure tapping points (for both static as well as for total pressure), often separated for captain and co-pilot, rarely with switchover ( eg in the case of malfunction). During the takeoff run is to check that the indicated speed is continuously growing. When crews of civil aircraft of both captain and co-pilot should confirm the passage of the 80 - node display in her airspeed indicator with the exclamation eighty ( engl eighty). If this bid is not the same or are there other signs of a false indication is in the procedure carried out for the take-off.

Airspeed indicator are partly equipped with electrical signal generators can be powered via the eg autopilot or transponder with information about the speed, provided that they do not have their own pressure ports or evaluation instruments. For the autopilot mode-selector to be used signal source is present in some aircraft types. Glass cockpit ( EFIS ) can be supplied also with the speed signal. In this case, however, an analog instrument is available as a backup.

For slow aircraft Venturi tubes are used to the pressure tapping occasionally instead of the pitot tube. These provide a vacuum instead of a positive pressure as the Pitot tube. The difference in pressure per velocity difference can be influenced by the shape of the venturi within wide limits, consistently is a three- fold improvement in sensitivity compared with Pitot tubes.

Trivia

" Speedometer " means in English not speedometer, but tachometer.