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 three methods of determining pressure altitude?

Answer 6

1.) Set your altimeter to 29.92, and read indicated altitude.
2.) Apply correction factor to indicated altitude according to local altimeter setting.
3.) Use a flight computer. Field elv - (altim-29.92 x 1000) = 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 factors affect the performance of an aircraft during takeoffs and landings?

Answer 19

• density altitude
• wind
• runway surface (clean, contaminated)
• runway slope
• weight
• engine thrust

Question 20

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

Answer 20

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 21

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

Answer 21

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 22

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

Answer 22

• Angle of Attack
• Airspeed
• Flaps

Question 23

What effect does a forward center of gravity have on an aircraft’s flight characteristics?

Answer 23

Higher stall speed—Stalling angle of attack reached at a higher speed due to increased wing loading.

Slower cruise speed—Increased drag, greater angle of attack required to maintain altitude.

More stable—The center of gravity is further forward from the center of pressure, which increases longitudinal stability.

Greater back elevator pressure required—Longer takeoff roll, higher approach speeds and problems with the landing flare.

Question 24

What effect does an aft center of gravity have on an aircraft’s flight characteristics?

Answer 24

Lower stall speed—Less wing loading.

Higher cruise speed—Reduced drag, smaller angle of attack required to maintain altitude.

Less stable—Stall and spin recovery more difficult; when angle of attack is increased it tends to result in additional increased angle of attack.

Question 25

Will the center of gravity be forward or aft of the center of pressure?

Answer 25

Forward.
An aircraft’s weight is concentrated at the CG and the aerodynamic forces of lift occur at the CP.

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

How will an INCREASE or DECREASE in weight affect MANEUVERING SPEED?

Answer 28

As weight of the aircraft INCREASES, maneuvering speed will also INCREASE.

A heavier aircraft will need more lift to counteract the increased weight.