Instrumentation: Air Data and Gyros
Instrumentations
Instrumentations
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Flashcards
Altimeters: Instrumentation Error
Manufacturing imperfections, including friction of the linkage, causes error
Altimeters: Position Error or STatic Source Error
error increases at high altitudes and high Mach numbers. Different flap settings, gear down or up, different bank altitudes
Indicated Altitude
affected by the instrument error, hysteresis error, temperature error
Definition ELEV
Elevation; true vertical distance between MSL and a defined point at the airport.
QNE
1013,25 => Vertical Distance between the reference pressure of 1013 hPa and the airport
T.Alt
True Altitude; is the general geometric vertical distance to MSL
T HGT
True Height; is the general geometric vertical distance to the ground ; USA: Absolute Altitude
Air density is directly related to
Air Temperature, Air pressure, Humidity
When an aircraft reached the absolute ceiling, further climing is impossible due
to lack of power
Wie rechnet man die Density Altitude aus?
DA = PA (Pressure altitude = QNH korrigiert) + 120 * Delta ISA (Abweichung der Temperatur zu ISA = 2K/1000ft zur PA)
Which pressure is measured inside the altimeter
static pressure
Which device is used to measure the pressure inside a mechanical altimeter ?
aneroid Capsule
How is it possible to prevent temperature influences in altimeters?
a Bimetal device ensures that the altimeter indicated static pressure rather than the movement of the mechanical parts.
Impact pressure
Impact pressure equals total pressure minus static pressure
In Case of a imcompressible airflow, the impact pressure is euqal to the
dynamic pressure q q= 1/2 *p*TAS^2
Indicator speed: normally nonlinear
the cake would be narrowly spaced for low speeds and widely spaced for higher speeds ==> Calibration screws
Calibration screws
They handicap the expanding differential capsule
impact pressure is?
Totaler Druck - statischer Druck ==> Measured by using a differential pressure capsule
Compressibility Error
erst Mach above 0.3 or 20'000 ft or over 200 kt
EAS
Equivalent Airspeed; speed after compressibility correction
DAS
Density Airspeed; If the density effect is taken int account before correction the CAS for the compressibility effect
Reihenfolge Speeds
1. IAS => Posoition Error
2. CAS => Compressibility
3. EAS => Desnity
4. TAS
Under sea level conditions the IAS is the same like
TAS
For a given IAS, the TAS xy with altitude
For a given IAS, the TAS increases with altitude
Which device is used to measure impact pressure or differential pressure?
Differential Pressure: can be measured by using a differential pressure capsule
Total pressure: is fed isnide the capsule and static pressure outside the capsule
When flying in Fl 100 and ISA conditions
An aircraft is flying in Fl 120 at constant IAS. What is the correct order of the speeds, starting from teh smallest?
Vertical seppd formel
VVert = delta h / delta t
==> based on change of static pressure over time
2 Unterschiedliche Vertical Speed Indicators Typen
1. Capsule Typ (Flugzeug) 2. Dynamic Vane Typ (Glider)
function of a vertical Speed Indicator
static pressure is supplied directly to a different pressure capsule. The surrounding are of the capsule is connected to the static pressure line via a capillary tube
==> The capillary tube delays the pressure change inside the case and allows the differential pressure capsuale to transform the velocity to the static pressure
==> Um das Loch haben wir statischen Druck, welcher durch das calibrated Leak kommt => Nur solange sensitive, wie wir differential Druck haben
=> IM Cockpit haben wir geringeren Statischen Druck als in der Umgebung, weil Druck aus dem Cockpit rausgesogen wird
Capsule Type> why is vertical speed hintenrein?
indicators needs approximately 4 seconds at lower speed => delayed static pressure is compared with actual static pressure
Dynamic Vane Typ: whats that ? wo kommt es vor?
transmits changes between static air pressure measured outside the aircraft to that inside the aircraft by means of a vane => possible by pressure inside an equalizing bottle => More sensitive to small pressure changes => kommt in Glider zur Anwendung
Variometer Beheviour in higher altitude
pressure difference between inside and outside is slower because of the air's lower density =>longer the time between the actual altitude change and the reliable indication
Zero adjustment screw
Nur von Mechaniker => uses to adjust the instrument in case of a wrong indication ==> Mind. 2 hours warten, bis alle Instrumente die gleiche Temp haben
Vertical Speed Indicator: Instrument Error
Changes in ambient temperature correspond to pressure changes inside the housing => Provided with good thermal insulation
Vertical Speed Indicator: Static source errors
are not relevant => Vertical Speed Indicator are based on a pressure difference and not the total pressure
Vertical Speed Indicator: Time Lag
a few seconds to steady itself because a certain amount of time is necessary to build up a steady pressure difference during climb or descent
what is teh need of capillary tube inside teh Variometer
teh capillary tube delays the pressure change inside the case and allows the differential pressure capsule to transform the velocity of the static pressure change into a mechanical movement
Compare the pressure difference of a climb from 2000 ft to 10'000 ft with a climb from 22'000 ft to 30'000 ft
Pressure difference by a climb from 2000 ft to10'000 ft is significant higher than the difference in pressure at a climb from 22'000 to 3'0'000 ft
Why is it necessary for the air inside a variometer to pass a second capillary at hight atitudes
due to the low air density, the connected static pressure passes easily through the capillary tube; Consequently the displayed vertical speed would be below the actual speed. second tube delays the stream and the indication is more accurate due to the higher resistance
