Performance And Limitations Flashcards
How is aircraft performance significantly affected as air becomes less dense?
As air becomes less dense…
- power reduces (less air intake)
- prop is less efficient
- lift reduces (air exerts less force)
What is standard atmosphere at seal level?
15C or 59F and 29.92Hg
Standard temp and pressure lapse rate.
Temp decreases at 3.5F or 2C per 1,000 ft up to 36,000, constant temp up to 80,000
Pressure decreases at 1in Hg per 1,000ft to 10,000 ft
Define pressure altitude
Height above standard datum plane. Altimeter set to 29.92Hg
Why is pressure altitude important?
Basis for determining airplane performance and assigning flight levels above 18,000
2 methods of determining pressure altitude?
Set altimeter to 29.92
Apply correction factor to reported altimeter setting
Define density altitude.
Pressure altitude corrected for non standard temperature
How does air density affect aircraft performance?
Performance increases as density increases. Performance decreases and density decreases.
An increase in air density means a lower density altitude
How is density altitude determined?
Find pressure altitude and correct for non standard temperature
What factors affect air density?
Conditions that result in high/low density altitude?
Air density is affected by changes in altitude, temperature, and humidity.
High density altitude refers to thin air while low density altitude refers to dense air
High density altitude- high elevation, low pressure, high temps, high humidity
Low density altitude- lower elevation, high pressure, low temps, low humidity
What effect does pressure have on air density?
Directly proportional
If pressure doubles, density doubles
This is only true at constant temperature
What effect does temperature have on density.
Inversely proportional
Increase in temp means decrease in density.
Only true with constant pressure
Since temperature and pressure decrease with altitude, how will air density be overall affected?
Density is likely to decrease with altitude gain. The fairly rapid drop in pressure with increasing altitude is usually the dominating factor.
What effect does humidity have on air density?
Water vapor is lighter than air. So moist air is lighter than dry air. As water content of air increases, air becomes less dense. Which increases density altitude and decreases performance. Humidity alone is not considered an important factor in calculating density altitude but it does contribute
Define relative humidity
Amount of water vapor in atmosphere
Varies with temp
Warm air holds more water vapor than cold
What effect does landing at high elevation airports have on ground speed
True airspeed is faster resulting in faster ground speed throughout approach, touchdown, and landing roll.
Which means greater distance to clear obstacles, longer ground roll therefore longer runway.
What are some main elements of aircraft performance?
Take off/landing distance Rate of climb Ceiling Payload Range Speed Maneuverability Stability Fuel economy
Relationship of lift, weight, thrust, drag in steady, unaccelerated flight?
Equal
