Airspeed indicator Flashcards
airspeed units
Kts= 1.151Mph
or =1.852Km/h
airspeed
TAS=actual speed
use IAS fro controlling aircraft
1/2pV2 = dynamic pressure
ASI operation
pitot pressure fed into pressure capsule
static fed into case
any movement of capsule therefore due to dynamic pressure
calibration
calibrated to ISA sea level conditions
IAS & TAS only same when ISA applies
ASI, IAS and TAS at altitude
ASI under-reads TAS at alt due to density error
TAS has to be faster at alt to keep same IAS reading
ASI coloured arcs
white- flaps operating arc, between VSO & VFE
green- normal operating arc , between VS1 & VNO
yellow- caution arc, between VNO & VNE
red line- VNE
Light twin ASI
second red line- VMCA - min control speed in air ( sing eng below vmca you’re committed to land)
blue line- VYSE- best rate of climb speed one engine out
both in lower speed range
Aerodynamic performance
depends on mass flow over wings and speed of air
1/2pV2 = dynamic pressure
describes energy of airflow and determine critical conditions such as stall
ASI will only read accurately in ISA conditions because…
density varies with altitude and temperature
ASI decelerating
PITOT press decreases
press capsule contract
needle decreases
ASI errors
IMP
compressibility error- when above 300kts
density error- error due to altitude and temperature variations from ISA
PUD SOD
Pitot blocked Under reads Descending Static blocked Over reads Descending
ASI pitot leak
leak within line
reduces pitot pressure
ASI under reads
ASI static leak
Pressurised- in hull high press opposes pitot and ASI under read
outside hull or associated with unpresurised cabin the cabin press/leak point press < ambient due to aerodynamic suction so ASI over read
