Pressure instruments Flashcards
3 categories of aircraft instruments
- Pressure instruments
- Gyroscopic instruments
- Magnetic instruments
Static pressure is measured on the surface of the aeroplane by
static vent
Dynamic pressure is related to
- Speed of the body traveling through the air
- Air density (lower -> lower pressure)
Dynamic pressure formula
1/2 * rho * V^2
The pitot-static system is for the following insturments
Altitude indicator, VSI, ASI
Vs0
Stalling peed with landing gear down, flaps lowered, poweroff
Vs1
Stalling speed with landing gear up, flaps up, poweroff
Vfe
maximum speed for flaps extended
Vno
Maximum structual operatin speed
Vne
Never-exceed speed
TAS can be brain-calculated by
5000ft is 8% more of IAS
2% of CAS per 1000ft
If static vent is blocked, the ASI in a climb will
under-read will show a less value
If static vent is blocked, the ASI in a descent wil
over-read
PUDSOD
Pitot blocked, asi will Under read in Descent
Static blocked, asi will Over read in a Descent
QNE
ISA pressure
How VSI works
There’s a delay when a new static pressure enters, therefore a comparison can be made
The alternate static source feeds from
the cockpit
Using the alternate static, the altimeter and IAS
altimeter will be higher than actual (since static pressure is a bit less in the cockpit)
VSI will over-read
Altimeter errors
- Pressure (static is not accurately measured due to slip or skid)
- Intrument errors
- Time lag
- Temparature
- Orographic
Two static vents help
reduce errors, if one vent is having distrubed airflow, the other one can compensate
