VI. Performance and Limitations Flashcards
What happens to aircraft performance as air becomes less dense?
As air becomes less dense, you will see reduced performance in:
- Thrust (prop has less air to push)
- Power (less air intake)
- Lift (airfoils have less air)
What is the standard atmosphere at sea level?
Temperature of 59°F or 15°C
Pressure of 29.92 inHg or 1013.2 millibars.
What are standard atmosphere temperature and pressure lapse rates?
- Temperature: decreases of 2°C per 1,000 feet up to 36,000 feet. Considered constant up to 80,000 feet.
- Pressure decreases aprx 1 inHg per 1,000 feet of altitude gain to 10,000 feet.
Define the term “Pressure Altitude”
Height above the standard datum plane (theoretical reference point). If you set the altimeter to 29.92, it would indicate the pressure altitude.
Why is pressure altitude important?
- Serves as a basis for determining aircraft performance.
- Needed for operating in the “flight levels” (above 18,000ft MSL.)
What are the 2 methods of determining pressure altitude?
1.) Set your altimeter to 29.92, and read indicated altitude.
2.) Use a flight computer.
(29.92- Current Pressure) x 1000 + field elevation = Pressure Alt
Defined “Density Altitude”
Pressure altitude corrected for nonstandard temperature.
“Altitude the airplane feels like it’s flying at.”
How does air density affect aircraft performance?
Lower density altitude = Higher aircraft performance
Higher density altitude = Lower aircraft performance
What are the main three factors that affect air density?
Altitude, temperature, humidity.
Define “relative humidity.”
Refers to the amount of water vapor in the atmosphere, expressed as a percentage of the maximum amount of water vapor that air can hold.
Performing a preflight inspection, you notice frost on top of both wings. How will this affect the aircraft on departure?
- Increased weight
- Increased drag
- Reduced lift
- Altered center of gravity
- Impaired control
- Frost could turn into ice.
What are the two types of drag?
Induced - Created as a result of lift.
Parasite - Drag from everything but the wings.
With a decrease in airspeed, what happens to induced drag?
It increases. The lower the airspeed, the greater the angle of attack required to produce lift.
What causes parasite drag?
The friction of air moving over the aircraft surface.
Form drag, interference, and skin friction.
Define the term “Service Ceiling”.
The maximum density altitude where the best rate of climb airspeed will produce a 100fpm climb (max weight, max power, clean config)
Will an aircraft always be capable of climbing to and maintaining its service ceiling?
No. Depends on density altitude.
What is the difference between:
“Power Loading” and “Wing Loading”?
Power Loading: Expressed in pounds per horsepower. Total weight of the airplane divided by the rated horse power.
Wing Loading: Expressed in pounds per square foot. Total weight of the airplane divided by the wing area (in sq/ft)
What is flight in the region of reverse command?
The region of reverse command is a flight regime where more power is required to maintain a specific airspeed as an aircraft slows down.
It’s also known as the back of the power curve.
Think of landing:
Pitch - Airspeed
Power - Altitude
What effect does an increase in density altitude have on takeoff and landing performance?
a. Increased takeoff distance
b. Reduced rate of climb (decreased thrust)
c. Increased true airspeed on approach and landing (same IAS).
d. Increased landing roll distance.
Explain the difference between the best glide speed and minimum sink speed.
Best glide — provides the greatest forward distance for a given loss of altitude. Roughly halfway between VX and VY.
Minimum sink—Used to maximize the time that the airplane remains in flight, losing altitude at the lowest rate. Not an often published airspeed but is generally a few knots less than best glide speed.
What are three ways a pilot can control lift during flight?
- Angle of Attack
- Airspeed
- Flaps
What effect does a forward CG have on an aircraft’s stability, cruise speed, and stall speed?
More Stable — center gravity is further from the center of pressure.
Slower cruise speed—Increased drag, greater angle of attack required to maintain altitude.
Higher stall speed — did the increased wing loading. Our critical angle of attack has reached at a higher speed.
What effect does an aft CG have on an aircraft’s stability, cruise speed and stall speed?
Less stable— CG is closer to center of pressure. Stall and spin recovery more difficult.
Higher cruise speed—Reduced drag, smaller angle of attack required to maintain altitude.
Lower stall speed—Less wing loading.
What SIMPLE weight check can be made by pilots before flight?
Useful load check.
Does my payload+fuel fit within my useful load?
If ACTUAL weights for w/b are unknown, what ASSUMED weights can be used for computations? (FAA)
Crew/Passengers = 190lbs Each
AvGas = 6lbs/Gal
Oil = 7.5lb/Gal
Water = 8.35lb/Gal
What is angle of attack?
It is the angle between the cord line of the wing, and direction of the wind that strikes the wing (relative wind).
What factors affects stall speed?
Weight and center of gravity.
What is P-factor?
Also known as asymmetric blade effect. Caused by moving propeller, moving counterclockwise at a higher angle of attack.
The down going blade has a greater angle of attack than the upgoing one. The down going blade is on the right side, and so it tends to pull the nose of the airplane to the left.
Define maneuvering speed?
Maximum speed where the pilot can make abrupt control changes without damaging the airplane
Aircraft will stall before exceeding maximum G loading.
What is the relationship between maneuvering speed and weight?
VA will decrease as the weight of the aircraft decreases
What is adverse yaw?
The natural and undesirable tendency for an aircraft to yaw in the opposite direction of a roll.
It is caused by the drag, created by the down deflection of the aileron in a turn.
Define standard empty weight?
The weight of the air frame and engine with all the standard equipment installed in the aircraft. Unusable fuel and oil are included in this weight.
Define basic empty weight (BEW).
This is the weight of the airplane with all optional equipment that has been added. The manufacturer includes the full oil weight in BEW.
Define useful load.
It is the difference between gross takeoff, weight, and basic empty weight.
Is the low that is not a permanent part of the plane. Eg- fuel, pilot, passengers, baggage.
Define maximum gross weight.
This is the maximum permissible weight that the aircraft can be to fly.
