Chapter 10: Cabin Pressurisation Flashcards
pressure at sea level
14.7 psi
what is cabin altitude?
pressure at set altitude (8k ft)
what is cabin differential pressure?
cabin pressure - ambient pressure = cabin differential pressure (psid or Δd)
what is cabin rate of climb?
rate of change of air pressure inside cabin, in ft per min
what is the normal rate of climb?
1000ft per minute
what are the common effects on human body when rate of change in pressure is large?
1) sickness
2) expansion of gases in abdomen & ear
what does a cabin pressurisation system accomplish?
1) adequate passenger comfort & safety
2) maintain cabin pressure at 8k feet or lower regardless of altitude
3) designed to prevent rapid changes of cabin pressure
4) circulate air from inside of cabin to outside at a rate that quickly removes odor and stale air
5) cabin air must be heated or cooled
how to have positive differential pressure?
contain air at pressure higher than outside atmospheric pressure
making air tight vessel (seals, grommets, sealants)
how does negative differential pressure occur?
when outside atm pressure is higher than cabin pressure (from diving to low altitude)
how can negative differential pressure be solved?
using inward relief valve (opens at negative differential pressure of 0.5 psi)
what is the secondary safeguard to control normal positive differential?
safety valve
sources of air to pressurise reciprocating aircraft
1) supercharger
2) turbocharger
3) engine driven compressor
where must the supercharger be located to be used for pressurisation?
upstream of fuel delivery
ways to control cabin pressure
1) isobaric mode
2) constant differential mode
what is isobaric mode?
cabin pressure is always maintained at set level regardless of change in altitude (e.g. 8k ft)
what is constant differential mode?
controls cabin pressure to maintain constant pressure difference between air and cabin pressure (to prevent airframe limit)
what does the cabin pressure controller do?
control:
- cabin air pressure
- cabin rate of climb
- barometric pressure setting
what does the cabin pressure regulator do?
control position of outflow valves to determine pressure level in cabin
what does a cabin air safety valve do?
pressure relief valve set to open at certain pressure differential > prevent internal pressure from exceeding design limitations
3 indicators for pressurisation
altimeter, vert. speed indicator, cabin psid indicator
at what cabin pressure altitude will warning be made?
10000 ft
