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Equations of motion
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
Speed and its measurement have a significant position in aircraft performance analysis. Although the Global Positioning System (GPS) is a powerful tool in the measurement of several flight variables including speed, but, due to safety reasons and FAA regulations, all aircraft use a device called Pitot tube to measure the aircraft speed. In addition, the GPS only measures the ground speed; not the airspeed. Airspeed is measured by comparing the difference between the pitot and static pressures (Figure 2.18) and, through mechanical linkages, displaying the resultant on an airspeed indicator. A static port (tube) measures only the static pressure, since the hole is perpendicular to the air flow, so the flow must turn 90° to enter into the tube. In contrast, a pitot tube measures the dynamic pressure, since the hole faces the airflow. When a pitot tube has a static port, it is often referred to as the pitot-static tube.
A socio-technical analysis of functional properties in a joint cognitive system: a case study in an aircraft cockpit
Published in Ergonomics, 2019
Arie Adriaensen, Riccardo Patriarca, Anthony Smoker, Johan Bergström
The performance data is derived from different sources and in different forms: for example, the GW is calculated from the ZFW, in our case study pre-computed or written in the flight plan by flight dispatch, while the remaining fuel weight is derived from fuel gauges. The net result is a semantic number for the projected gross weight as expected at touchdown. This must be transformed into the landing speed for a certain weight, because landing speed, i.e. the approximate moment when lift is lost, varies with weight. On the DC-9 and on many other aircraft, the conversion from weight into speed is accomplished by a simple, but very effective artefact, i.e. a booklet of speed cards (Hutchins 1995a): ‘The booklet contains a page for each weight interval (usually in 2,000 pound increments) with the appropriate speeds permanently printed on the card’. Turning the booklet to the correct page automatically displays the correct landing speeds, which are then positioned on a prominent place in the cockpit to serve as a memory aid for the approach and landing phase. The speeds from the booklet subsequently serve to set several speed bugs, which can be positioned relative to the airspeed indicator. This is another simple-effective memory aid, which physically stores the speeds until touchdown.