Pitot Static System Flashcards
Pitot Static System
THE TWO MOST CRITICAL FACTORS IN AVIATION PERFORMANCE ARE TEMPERATURE AND PRESSURE; with temperature the most critical, everything in the atmosphere chases temperature.
Atmospheric Conditions: High pressure = high density = low density altitude (favorable flight); Low pressure = low density = high density altitude (unfavorable flight)
Standard atmosphere
Pressures
Altimeter
Airspeed indicator
Vertical speed indicator
Malfunctions
Standard atmosphere
29.92 inches of mercury (Hg) displaced in a near-airless vacuum tube
50% of the weight of the atmosphere is contained within 18,000ft of the ground
90% of the weight of the atmosphere is contained within 53,000ft of the ground
MSL - Mean Sea Level: 29.92Hg 15C (or 1013.2mb/Hp, 59C)
1000’: 28.92Hg 13C
2000’: 27.92Hg 11C
3000’: 26.92Hg 9C
4000’: 25.92Hg 7C
5000’: 24.92Hg 5C (standard lapse rate: up to here, -1” Hg and -2C per 1000’)
7500’: 22.42Hg 0*C
Air density
- The three components of atmospheric density are TEMPERATURE, PRESSURE, and HUMIDITY
- higher density is favorable for flight, and equates to low density altitude
Pressure increase = higher density
Pressure decrease = lower density
Temperature rise = lower density
Temperature fall = higher density
Humidity rise = lower density
Humidity fall = higher density
Mean sea level standard
29.92Hg at 15*C (no *F or mb standard)
Static vs Dynamic Pressure
The two pressures associated with the atmosphere are STATIC and DYNAMIC.
Static/ambient pressure is pressure that is not moving (no winds - static ports)
Dynamic pressure is pressure that is caused by motion; a helicopter moves through this (Pitot tube)
Impact pressure
Static + Dynamic pressure (only two pressures related to atm, EFFECT THE PITOT STATIC SYSTEM)
Static Atm Pressure: relates to a perfect atm day, molecule of air just “sitting” in the atmosphere
Dynamic Atm Pressure: what a helicopter “flys through”
The 5 names of the pressures related to the PITOT STATIC SYSTEM ARE:
1) Static Pressure:
(The pressures below are dynamic pressure hitting the pitot tube as 4 different names)
2) Impact Pressure: Dynamic pressure that “impacts” the Pitot Tube
3) Ram Pressure: same
4) Total Pressure: same
5) Pitot Pressure: same
Construction of the Pitot/Static System
Pitot/Static system consists of: Pitot system and Static system
Static vents: (Static) Altimeter gauge, Vertical Speed gauge, and Airspeed gauge use static pressure. Altimeter and Vertical Speed use static ports only
Pitot tube: (Dynamic) Airspeed indicator gauge only - uses static and dynamic pressure to get a differential for speed indication.
Altimeter
Base altitude - thinnest line that indicates 10’s of thousands of feet
“Fat bob” line - indicates thousands of feet
Thinnest line - indicates hundreds of feet
- Kollsman Window:* “corrects for atm pressure changes”
- corrects for atmospheric pressure changes (28.00Hg high to 31.00Hg low)
- ADJUSTMENTS – for current field elevation as published by an FAA facility, OR a current altimeter setting AS BROADCAST by an FAA facility (legally)
1” Hg change for 1000ft alt. change
.1” Hg change for 100ft alt. change
.01” Hg change for 10ft alt. change
max altimeter mechanical error (army) for Kollsman Window adjustment is 75ft.
“Indicated” - read off the face of an instrument
Indicated altitude
Read from the instrument with correctly set (current) Kollsman window setting (SLP sea level pressure)
True altitude
The actual altitude above MSL (mean sea level)
We want true and indicated to match
Absolute altitude
Absolute altitude is the altitude above ground level (not necessarily the same as MSL)
Altimeter Pressure Altitude
Altitude above the Standard Datum Plane (the 29.92Hg altitude, not necessarily MSL)
Density Altitude
Density corresponding to a given altitude in a standard atmosphere
Can be determined by correcting pressure altitude for non-standard temperature
Max torque avail, max gross weight, and performance are all affected by density altitude
*If temperatures are Colder than standard, Density Altitude (DA) and True
Altitude (TA) will always be lower than Pressure Altitude (PA). If temperatures are WARMER than standard, DA AND TA will always be higher than PA
you will attempt to get a current altimeter setting every 50-80 nautical miles along your departure route, not to exceed 100 nautical miles
Maximum mechanical altimeter error
Maximum mechanical FAA (and Army) altimeter error is +/-75ft: cannot fly
Refer to operator or maintenance manual for aircraft specific altimeter error, not to exceed FAA/Army maximum error
High to Low chart write on back of test
(Known) Indicated alt. IALT —— TALT True alt. (Unknown)
Pressure Alt. H. ——. L. Density Alt.
Altimeter L. ——. H. True Alt.
H - higher pressure, warmer than standard temps, or higher altimeter setting
L - lower pressure, coder than standard temp, or lower altimeter setting
Rule - always enter chart from known side, and only stay on the line entered… answer will be on that line underneath the I or the T
Flying “toward”, arrow points “toward where you WILL BE (you depart with knowns)
FLING “in”, you got to the place you where going
