This is an area of higher pressure induced by the flow of air around the leading edge of the wing. For example, a static source co-located with the pitot head positioned just ahead of the wing but too close to its under surface could be in an area of slightly higher pressure than that of the surrounding air. Conversely, a static source producing lower than true static pressure will cause the altimeter to indicate higher than it should.Ī poor static source also affects the airspeed indicator's readings. If the static source is located in an area producing higher than true (surrounding atmosphere) static pressure, your altimeter will read lower than it should. Even though the fuselage sides may seem to be uniform in the area selected for the static vents, a future relocation of the vents could become necessary because of erratic or unreliable instrument readings. The remoted static pressure vents, when installed, should be located in an area of air flow unaffected by wing junctures or fuselage bumps and irregularities. and this is worthy of your consideration. One advantage of a separate static source remoted from the pitot tube is the theoretical assurance that your altimeter and vertical speed indicator will continue to function even though the pitot tube may become blocked by mud daubers, ice, dirt or a forgotten pitot tube cover. Brief transgressions from coordinated flight will affect your instrument readings only momentarily unless you habitually fly the airplane in a constant skid.īoth static vents, when located on opposite sides of the fuselage, must be manifolded (connected together by a "T" or a "Y" fitting). Actually, static ports are ordinarily installed on both sides of the fuselage to minimize the effects of slipping or skidding flight resulting from sloppy or unintentional rudder inputs. There you will often find one to three small vent holes, in a flush-mounted fitting of sorts, serving as a static air inlet. somewhere in the side of the fuselage, that is. On the other hand, one fairly reliable source location for a static pressure vent, remote though it might be from the pitot tube area, is the fuselage. It could assure a higher degree of accuracy in instrument performance than might a static air pressure source remotely located. In such installations the pitot-static tube is a dual-function unit providing both ram (P) air and static (S) air for the instruments connected to it.Īlthough the static pressure is not always obtained at the pitot tube head assembly, it would seem that such an arrangement where both ram air and static air are taken from the same source area is a good one. These pitot tubes are, therefore, more correctly identified as "Pitot-Static" tubes. Some pitot tubes contain both an inlet for the pitot or ram pressure, and another for the static pressure. However, you can make your own installation of the pitot-static system into a big deal or keep it on a modest minimum effort level. These two air pressure sources, and the interconnecting plastic tubing, constitute the aircraft's pitot-static system.Ĭalling it a "system" when little more than a bent aluminum tube and some plastic tubing embody the main elements may be a bit grandiose. In addition, the airspeed indicator requires a source of ram air (pitot) pressure. Nevertheless, the three instruments do have something in common - each must be vented to a source of atmospheric (static) pressure for proper operation. While a small number of builders might think a rate of climb (vertical speed) indicator is essential, it is not one of the mandatory VFR instruments. AMONG THE MINIMUM instrumentation required for VFR (Visual Flight Rules) flying are two flight instruments - the airspeed indicator and the altimeter.
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