Ch. 11 Aircraft Performance Flashcards
Standard Atmosphere
15 degrees Celsius (59 degrees Fahrenheit)
29.92 in Hg (1013.2 mb)
Standard lapse rate
Temperature decreases at the rate of approximately 3.5 degrees Fahrenheit or 2 degrees Celsius per thousand feet up to 36,000 ft MSL.
Above what altitude is temperature considered constant up to 80,000 feet MSL?
36,000 feet MSL.
Standard pressure lapse rate
Pressure decreases at a rate of 1”Hg per thousand feet of altitude gain to 10,000 feet.
Any temperature or pressure that differs from the standard lapse rate is considered:
Nonstandard temperature and/or pressure.
Height above the standard datum plane.
Pressure altitude
What is the standard datum plane?
A theoretical level at which the pressure of the atmosphere is 29.92”Hg.
What are two reasons pressure altitude is important?
- Basis for determining aircraft performance
2. Assigning flight levels to aircraft operating at or above 18,000 feet MSL.
What are the three ways of calculating the pressure altitude?
- Setting altimeter to 29.92”Hg and reading output.
- By applying a correction factor to the indicated altitude according to the reported altimeter setting.
- Using a flight computer.
The altitude in the standard atmosphere corresponding to a particular value of air density.
Density altitude
Pressure altitude corrected for nonstandard temperature.
Density altitude
As the density of the air increases (lower density altitude), aircraft performance:
Increases.
As air density decreases (higher density altitude), aircraft performance:
Decreases.
Under standard conditions, pressure altitude and density altitude identify:
The same level.
Air density is affected by changes in:
Altitude, temperature, and humidity.
How does density of air vary with temperature?
Inversely. As temperature goes up, density goes down and vice versa.
How does density of air vary with pressure?
Directly. As pressure increases so does density and vice versa.
In the atmosphere, both temperature and pressure decrease with altitude and have conflicting effects upon density. So for us pilots should we expect the density of air to increase or decrease with altitude? Why?
Expect the density to decrease with altitude. The fairly rapid drop in pressure as altitude is increased usually has the dominant effect on density.
Refers to the amount of water vapor contained in the atmosphere and is expressed as a percentage of the maximum amount of water vapor the air can hold.
Humidity or relative humidity.
The amount of water vapor that air can hold is based upon:
Temperature of the air.
The density of air increases or decreases with more humidity?
Decreases.
The ability of an aircraft to accomplish certain things that make it useful for certain purposes.
Performance
The various items of aircraft performance result from the combo of:
Aircraft and power plant characteristics.
The unaccelerated condition of flight is achieved with the aircraft trimmed and powerplant set for:
Lift equal to weight and thrust equal to drag.
Thrust is a:
Force
Power is a:
Measurement of the rate of performing work or transferring energy. (How much work, how fast)
Maximum angle of climb (AOC)
Maximum amount of altitude gain per horizontal distance traveled.
Max angle of climb occurs at the airspeed and AOA combination which allows the maximum excess:
Thrust.
Maximum rate of climb (ROC)
Maximum gain in altitude over a given period of time.
Maximum rate of climb occurs at an airspeed and AOA combination that produces the maximum excess:
Power.
As altitude is increased the max ROC, max AOC, maximum and minimum level flight airspeeds converge at what point?
The absolute ceiling of the aircraft.
Absolute ceiling
Altitude which produces zero ROC.
Service ceiling
Altitude which aircraft is unable to climb at rate greater than 100 fpm.
Total weight of aircraft divided by rated horsepower of engine. Expressed in pounds per horsepower.
Power loading
Total weight divided by wing area. Expressed as pounds per square foot.
Wing loading.
Why is power loading significant?
It is a significant factor in aircraft’s takeoff and climb capabilities.
Why is wing loading significant?
Determines landing speed.