VI. Performance and Limitations

Question 1

What happens to aircraft performance as air becomes less dense?

Answer 1

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)

Question 2

What is the standard atmosphere at sea level?

Answer 2

Temperature of 59°F or 15°C

Pressure of 29.92 inHg or 1013.2 millibars.

Question 3

What are standard atmosphere temperature and pressure lapse rates?

Answer 3

• 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.

Question 4

Define the term “Pressure Altitude”

Answer 4

Height above the standard datum plane (theoretical reference point). If you set the altimeter to 29.92, it would indicate the pressure altitude.

Question 5

Why is pressure altitude important?

Answer 5

• Serves as a basis for determining aircraft performance.
• Needed for operating in the “flight levels” (above 18,000ft MSL.)

Question 6

What are the 2 methods of determining pressure altitude?

Answer 6

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

Question 7

Defined “Density Altitude”

Answer 7

Pressure altitude corrected for nonstandard temperature.
“Altitude the airplane feels like it’s flying at.”

Question 8

How does air density affect aircraft performance?

Answer 8

Lower density altitude = Higher aircraft performance

Higher density altitude = Lower aircraft performance

Question 9

What are the main three factors that affect air density?

Answer 9

Altitude, temperature, humidity.

Question 10

Define “relative humidity.”

Answer 10

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.

Question 11

Performing a preflight inspection, you notice frost on top of both wings. How will this affect the aircraft on departure?

Answer 11

• Increased weight
• Increased drag
• Reduced lift
• Altered center of gravity
• Impaired control
• Frost could turn into ice.

Question 12

What are the two types of drag?

Answer 12

Induced - Created as a result of lift.

Parasite - Drag from everything but the wings.

Question 13

With a decrease in airspeed, what happens to induced drag?

Answer 13

It increases. The lower the airspeed, the greater the angle of attack required to produce lift.

Question 14

What causes parasite drag?

Answer 14

The friction of air moving over the aircraft surface.
Form drag, interference, and skin friction.

Question 15

Define the term “Service Ceiling”.

Answer 15

The maximum density altitude where the best rate of climb airspeed will produce a 100fpm climb (max weight, max power, clean config)

Question 16

Will an aircraft always be capable of climbing to and maintaining its service ceiling?

Answer 16

No. Depends on density altitude.

Question 17

What is the difference between:
“Power Loading” and “Wing Loading”?

Answer 17

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)

Question 18

What is flight in the region of reverse command?

Answer 18

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

Question 19

What effect does an increase in density altitude have on takeoff and landing performance?

Answer 19

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.

Question 20

Explain the difference between the best glide speed and minimum sink speed.

Answer 20

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.

Question 21

What are three ways a pilot can control lift during flight?

Answer 21

• Angle of Attack
• Airspeed
• Flaps

Question 22

What effect does a forward CG have on an aircraft’s stability, cruise speed, and stall speed?

Answer 22

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.

Question 23

What effect does an aft CG have on an aircraft’s stability, cruise speed and stall speed?

Answer 23

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.

Question 24

What SIMPLE weight check can be made by pilots before flight?

Answer 24

Useful load check.
Does my payload+fuel fit within my useful load?

Question 25

If ACTUAL weights for w/b are unknown, what ASSUMED weights can be used for computations? (FAA)

Answer 25

Crew/Passengers = 190lbs Each
AvGas = 6lbs/Gal
Oil = 7.5lb/Gal
Water = 8.35lb/Gal

Question 26

What is angle of attack?

Answer 26

It is the angle between the cord line of the wing, and direction of the wind that strikes the wing (relative wind).

Question 27

What factors affects stall speed?

Answer 27

Weight and center of gravity.

Question 28

What is P-factor?

Answer 28

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.

Question 29

Define maneuvering speed?

Answer 29

Maximum speed where the pilot can make abrupt control changes without damaging the airplane

Aircraft will stall before exceeding maximum G loading.

Question 30

What is the relationship between maneuvering speed and weight?

Answer 30

VA will decrease as the weight of the aircraft decreases

Question 31

What is adverse yaw?

Answer 31

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.

Question 32

Define standard empty weight?

Answer 32

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.

Question 33

Define basic empty weight (BEW).

Answer 33

This is the weight of the airplane with all optional equipment that has been added. The manufacturer includes the full oil weight in BEW.

Question 34

Define useful load.

Answer 34

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.

Question 35

Define maximum gross weight.

Answer 35

This is the maximum permissible weight that the aircraft can be to fly.