performance factors Flashcards
what is air density?
the mass in an object divided by its volume. the more dense it is the heavier it is
what is air pressure
the force exerted by the air on anything in contact with it. measured with a barometer in hectopascals
what happens to air pressure as altitude increases?
air pressure decreases, because air has mass and therefore gravity acts on it and with higher air pressure their is a higher number of air molecules in a given volume or parcel of air.
what is the ISA pressure? and what is the pressure lapse rate
1013.2hPa, 1hPa per 30ft
what is the temperature lapse rate? and what is the mean sea level ISA temperature?
1.98 degrees per 1000ft
15 degrees
what is pressure altitude?
the difference between the air pressure existing at any altitude and the values associated with ISA.
e.g if pressure is 993 hPa
difference of 20 hPa from ISA value of 1013
20 x 30 = 600 ft so pressure altitude = 600ft
pa is the altitude at which we would expect to find the prevailing air pressure
in isa, we would expect to find a pressure of 993hPa at 600ft AMSL
for pressure altitude if QNH is less than ISA what should you do and if it’s more what should you do?
less than ISA, add variation to the aerodrome altitude
more than ISA, subtract.
how can you determine pressure altitude by using an altimeter?
setting the altimeter to 1013
what does temperature do on performance?
if temperature alone is considered, a high temperature is indicative of poorer performance and conversely, low temperatures provide better performance conditions.
must also take air pressure into account.
what is density altitude?
the pressure altitude and the affects of temperature.
how is density altitude calculated?
find pressure altitude then adjust that for the temperature difference from what we would expect to find at that pressure altitude.
what is the adjustment for temperature?
a rate of 1-degree celsius per 120ft
what is the difference between high air density and high-density altitude?
a high air density is a great thing for aircraft performance
a high density altitude is a bad thing
how does air density affect performance?
high-density day, more air molecules in the same parcel of air allowing greater engine performance and aerodynamic efficiency.
low-density day, less air molecules per same volume of air meaning the opposite.
how is ISA temperature found at an altitude?
ISA temp at MSL = 15 degrees with a lapse rate of 2 degrees per 1000ft
e.g pressure altitude of 2000ft at 2000ft is 11 degrees
( 2000ft x 2 C per 1000ft = 4 degrees) 15 - 4 = 11
how is ISA temperature deviation found?
by finding the ISA temperature at an altitude and by adding or subtracting it relative to the ISA
ISA temp at pressure altitude of 2000ft is 11 degrees
(2000ft x 2degrees per 1000ft = 4 degrees) 15 - 4 = 11 or ISA - 4
how is density altitude calculated?
multiplying the ISA temperature deviation with the adjustment for temperature (120 ft per 1 degree) then adding it onto the pressure altitude
e. g PA = 4000 ft ISA temp = ISA - 4
- 4 x 120 = -480ft
4000ft - 480ft = 3520 ft
what is the difference between TODR and TODA?
TODR is the actual distance that an aircraft requires from a standing start, with full power, to get to 50 feet above the runway at takeoff safety speed.
TODA is the length of the take off run available plus the length of any clearway ( a portion of ground or water that an aircraft may climb over)
what is the difference between LDR and LDA?
LDR - horizontal distance from a point 50ft above the threshold, to the point that the aircraft can be brought to a complete stop with max braking.
LDA - length of the runway that’s declared by the airfield operator as available and suitable for the ground run of an aircraft.
where is TODR, TODA, LDR and LDA found?
in the NZAIP VOL 4 containing all the info. may have stuff like circles on the runway meaning you cannot land in the first ___ metres of that runway which is known as a displaced threshold.
how does weight affect takeoff performance?
heavier aircraft require greater takeoff distance. due to slower acceleration on the runway and the requirement for increased flying speed to provide the required safety margin (20%) above the increased stall speed.
how does density affect takeoff performance?
low air density results in a greator TODR because of poorer performance of the engine and airframe.
occurs on hot days, low-pressure days, high elevation aerodromes
how does humidity affect takeoff performance?
high humidity reduces air density meaning poorer performance
how does temperature affect takeoff performance?
causes poor performance
