Pressure Instruments Flashcards
What are the three major categories of flight instruments?
Pressure
Gyroscopic
Magnetic
What are the three (major) pressure instruments in an aircraft?
ASI
Altimeter
VSI
What measures static pressure on an aircraft?
Static vent
Static pressure is exerted…
Equally in all directions
What pressure is exerted equally in all directions?
Static pressure
What two factors influence the strength of dynamic pressure?
Speed of body relative to air
Density of air
Dynamic pressure equation
1/2 Rho V-squared
1/2 Rho V-squared = ?
Dynamic pressure
Dynamic pressure varies directly with what?
V-squared
What is ram pressure?
Total pressure
How does an ASI scale indicate speed (simply)?
Instead of indicating pressure, it is calibrated to read in knots
An ASI is essentially a recalibrated…?
Altimeter
What two instruments rely only on static pressure?
Altimeter and VSI
What instruments relies on both static and dynamic pressure?
ASI
If using an alternate static source, what can be said of the pressure readings?
Cabin pressure is slightly less than atmospheric pressure
What component sits within an ASI’s system?
Diaphragm
The caution range on an ASI is given what colour?
Yellow
What kind of speed is most related to dynamic pressure?
IAS
What speed do aerodynamic qualities of an aircraft depend on?
IAS
What speed do navigational purposes depend on?
TAS
In a lift/drag equation, what kind of speed is ‘V’ in V-squared?
TAS
If TAS is V in the lift/drag equation, how is IAS involved in the equation also?
In rho as a function of dynamic pressure
Why must TAS increase in a climb at constant IAS?
Constant IAS means 1/2 rho v-squared must remain constant
Rho decreases in a climb so V (TAS) must increase
At 5000ft, TAS exceeds IAS by approximately what percentage?
8%
If a pitot/static vent becomes blocked, what can be said of the pressure at the time?
It will remain constant
A block static vent has what effect on an ASI in a climb?
ASI will under-read
A block static vent has what effect on an ASI in a descent?
ASI will over-read
Pneumonic for remembering block static vent/pitot in a descent?
PUDSOD
Describe the pressure relationships in an ASI when a static vent is blocked in a climb?
Trapped pressure is greater than outside pressure
Total - Static Pressure = lower dynamic pressure than actual
Describe the pressure relationships in an ASI when a static vent is blocked in a descent?
Trapped pressure is lesser than outside pressure
Total - Static Pressure = greater dynamic pressure than actual
In an ASI, a higher dynamic pressure equates to what?
Higher IAS
A blocked pitot on take-off will have what effect on the ASI?
Only static pressure will be fed to ASI
ASI will read 0
