Performance and Limitations

Question 1

What are the four dynamic forces that act on an airplane during all maneuvers?

Answer 1

lift - the upward force acting force
gravity - or weight, the downward acting force
thrust - the forward acting force
drag - the backward acting force

Question 2

What flight condition will result in the sum of the opposing forces being equal?

Answer 2

In steady state, straight and level, unaccelerated flight, the sum of the opposing forces is equal to zero. There can be no unbalanced forces in steady, straight flight (newton’s third law). This is true whether flying level or when climbing or descending. It does not mean the four forces are equal. It means the opposing forces are equal to, and thereby cancel the effects of each other.

Question 3

What is an airfoil? State some examples.

Answer 3

An airfoil is a device which gets a useful reaction from air moving over its surface, namely LIFT. Wings, horizontal tail surfaces, vertical tail surfaces, and propellers are examples of airfoils.

Question 4

What is the angle of incidence?

Answer 4

The angle of incidence is the angle formed by the longitudinal axis of the airplane and the chord of the wing. It is measured by the angle at which the wing is attached to the fuselage. The angle of incidence is fixed and cannot be changed by the pilot?

Question 5

What is relative wind?

Answer 5

The relative wind is the direction of the airflow with respect to the wing. When a wing is moving forward and downward the relative wind moves backward and upward. The flight path and relative wind are always parallel but travel in opposite directions

Question 6

What is the angle of attack?

Answer 6

The angle of attack is the angle between the wing chord line and the direction of the relative wind; it can be changed by the pilot

Question 7

What is bernoulli’s principle?

Answer 7

The pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases. In the case of airflow, high speed flow is associated with low pressure and low speed flow with high pressure. The airfoil of an aircraft is designed to increase the velocity of the airflow above its surface, thereby decreasing pressure above the airfoil. Simultaneously, the impact of the air on the lower surface of the airfoil increases the pressure below. This combination of pressure decrease above and increase below produces lift.

Question 8

What are several factors which will affect both lift and drag?

Answer 8

wing area - lift and drag acting on a wing are roughly proportional to the wing area. A pilot can change wing area by using certain types of flaps
shape of the airfoil - as the upper curvature of an airfoil is increased (up to a certain point) the lift produced increases. Lowering an aileron or flap device can accomplish this. Also, ice or frost on a wing can disturb normal airflow, changing its camber, and disrupting its lifting capability.
angle of attack - as angle of attack is increased, both lift and drag are increased, up to a certain point
velocity of the air - an increase in velocity of air passing over the wing increases lift and drag
air density - lift and drag vary directly with the density of the air. As air density increases, lift and drag increase. As air density decreases, lift and drag decrease. Air density is affected by these factors: pressure, temperature, and humidity

Question 9

What is torque effect?

Answer 9

Torque effect involves newton’s third law of physics - for every action, there is an equal and opposite reaction. Applied to the airplane, this means that as the internal engine parts and the propeller are revolving in one direction, an equal force is trying to rotate the airplane in the opposite direction. It is greatest when at low airspeeds with high power settings and a high angle of attack

Question 10

What effect does torque reaction have on an airplane on the ground and in flight?

Answer 10

In flight - torque reaction is acting around the longitudinal axis, tending to make the airplane roll. To compensate, some of the older airplanes are rigged in a manner to create more lift on the wing that is being forced downward. The more modern airplanes are designed with the engine offset to counteract this effect of torque.
On the ground - during the takeoff roll, an additional turning moment around the vertical axis is induced by torque reaction. As the left side of the airplane is being forced down by torque reaction, more weight is being placed on the left main landing gear. This results in more ground friction, or drag, on the left tire than on the right, causing a further turning moment to the left.

Question 11

What are the four factors that contribute to torque effect?

Answer 11

Torque reaction of engine and propeller - equal and opposite reaction

Gyroscopic precession: the resultant action or deflection of a spinning object when a force is applied to the outer rim of its rotational mass. If the axis of the propeller is tilted, the resulting force will be exerted 90° ahead in the direction of rotation and in the same direction as the applied force. Most noticeable in taildraggers when the tail is raised.

Corkscrewing effect of the propeller slipstream strikes the vertical tail surface on the left side pushing the tail to the right and yawing the airplane to the left.

Asymmetrical loading of the propeller (P-Factor) @ high angles of attack the bite of the downward moving propeller blade is greater than the bite of the upward moving blade. The downward moving blade is meeting the relative wind at a greater angle of attack than the upward moving blade causing greater thrust on the downward moving side forcing the airplane to the left.

Question 12

What is centrifugal force?

Answer 12

The equal and opposite reaction of the airplane to the change in direction, and it acts equal and opposite to the horizontal component of lift.

Question 13

What is load factor?

Answer 13

The ration of the total load supported by the airplanes wing to the actual weight of the airplane and its contents. Also expressed as the ratio of given load to the pull of gravity (3 Gs is 3X the weight of the airplane imposed upon the wings due to curved flight).

Question 14

For what 2 reasons in load factor important to pilots?

Answer 14

Danger of overstressing the airframe

Danger of increased stall speed - makes stalls possible at seemingly safe flight speeds.

Question 15

What situations may result in load factors reaching or exceeding the maximum?

Answer 15

Level Turns - increases at a terrific rate after bank has reached 45° or 50°. Load factor in 60° bank is 2Gs, 80° bank is 5.76Gs.

Turbulence - Severe vertical gusts cause a sudden increas in angle of attack, resulting in large loads which are resisted by the inertia of the airplane.

Speed - Amount of excess load that can be imposed upon a wing depends on how fast the airplane is flying. Below maneuvering speed, the airplane will stall before the load factor can become excessive. Above, the limit load factor for which an airplane is stressed can be exceeded by abrupt or excessive application of the controls or by strong turbulence.

Question 16

What are the different operational categories for aircraft and within which category does your aircraft fall?

Answer 16

Normal +3.8 to -1.52
Utility +4.4 to -1.76
Aerobatic +6.0 to -3.00

Question 17

What effect does an increase in load factor have on stalling speed?

Answer 17

Stalling speed will increase. An airplane can be stalled at any airspeed within limits of its structure and the strength of the pilot. The formula for determining the speed at which a wing will stall is that the stalling speed increases in proportion to the square root of the load factor.

Question 18

Define the term Maneuvering Speed.

Answer 18

Va is the maximum speed at which abrupt control movement can be applied or at which the airplane could be flown in turbulence without exceeding design load factor limits. Below this speed the aircraft should stall before the load becomes excessive.

Question 19

Discuss the effect on maneuvering speed of an increase or decrease of weight.

Answer 19

Maneuvering speed increases with and increase in weight and decreases with a decrease in weight. An aircraft operating at a reduced weight is more vulnerable to rapid acceleration encountered during flight through turbulence or gusts.

Question 20

Define loss of control inflight (LOC-I) and describe several situations that might increase the risk of an LOC-I accident occurring.

Answer 20

LOC-I is defined as a significant deviation of an aircraft from the intended flight path and it often results from an airplane upset. Maneuvering is the most common phase of flight for LOC-I accidents to occur; however, LOC-I accidents occur in all phases of flight. Situations that increase the risk of this include uncoordinated flight, equipment malfunctions, pilot complacency, distraction, turbulence, and poor risk management, such as attempting to fly in IMC when the pilot is not qualified or proficient in it.

Question 21

What causes an airplane to stall?

Answer 21

When the critical angle of attack has been exceeded. When the AOA increases to approx 18°-20°, the air can no longer flow smoothly over the top wing surface. This can occur at any airspeed, in any attitude, with any power setting.

Question 22

What is a spin?

Answer 22

When the aircraft descends in a helical path while flying at an AOA greater than the critical angle of attack. Spins result from aggravated stalls in either a slip or a skid. No stall = no spin.

Question 23

What causes a spin?

Answer 23

Exceeding the critical AOA while applying excessive or insufficient rudder, and to a lesser extent, aileron.

Question 24

When are spins most likely to occur?

Answer 24

Can occur in any phase of flight but are most likely to occur:

Engine failure on takeoff during climbout - pilot tries to stretch glide to landing area by increasing back pressure or makes an uncoordinated turn back to departure runway at low airspeed.

Crossed-control turn from base to final - pilot overshoots final (crosswind?) and makes uncoordinated turn at a low airspeed.

Engine failure on approach to landing - pilot tries to stretch glide to runway by increasing back pressure.

Go-around with full nose up trip - pilot applies power with full flaps and nose up trim compined with uncoordinated use of rudder.

Go-around with improper flap retraction - pilot applies power and retracts flaps rapidly resulting in a rapid sink rate followed by and instinctive increase in back pressure.

Question 25

What procedure should be used to recover from an inadvertent spin?

Answer 25

Close the throttle

Neutralize the ailerons

Apply full opposite rudder

Briskly move the elevator control forward to the neutral position (varies by a/c)

Once stall is broken the spinning will stop. Neutralize the rudder when spinning stops.

When the rudder is neutralized, gradually apply enough aft elevator pressure to return to level flight.

Question 26

What causes adverse yaw?

Answer 26

When turning an airplane the downward deflected aileron produces more lift and more drag. While the opposite aileron has less lift and less drag. This added drag attempts to pull or veer the airplanes nose in the direction of the raised wing; the opposite to that desired.

Question 27

What is ground effect?

Answer 27

Condition of improved performance the airplane experiences when it is operating near the ground. A change occurs in the three dimensional flow pattern around the airplane because the airflow around the wing is restricted by the ground surface. This reduces the wings upwash, downwash, and wingtip vortices. Must be close to the ground.

Question 28

What major problems can be caused by ground effect?

Answer 28

During landing - @ height of approx 1/10 of a wing span above the surface, drag may be 40% less than when the airplane is operating out of ground effect. Any excess speed during landing may result in significant floating.

During Takeoff - the reduced drag may allow the aircraft to takeoff below recommended speed. As airplane rises out of ground effect speed deficient the greater induced drag may result in marginal climb performance, or may settle back to the runway in extreme conditions.

Question 29

Define the following.

Answer 29

Empty weight - Airframe, engines, and all items of operating equipment that have fixed location and are permanently installed in the aircraft. Includes hydraulic fluid, unusable fuel, and undrainable oil.
Gross weight - Maximum allowable weight of both the airplane and its contents.
Useful load - Weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil.
Arm - Horizontal distance in inches from the reference datum line to the center of gravity of the item.
Moment - Product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches.
Center of gravity - Point about which an aircraft would balance if it were possible to suspend it at that point. Expressed in inches from datum.
Datum - Imaginary vertical plane or line from which all measurements of arm are taken. Set by manufacturer.

Question 30

What basic equation is used in all weight and balance problems to find the center of gravity location of an airplane and/or its components?

Answer 30

W.A.M.

Weight X Arm = Moment

Weight = Moment/Arm

(Total) Moment
Arm (CG) = ————
(Total) Weight

Question 31

What performance characteristics will be adversely affected when an aircraft has been overloaded?

Answer 31

Higher takeoff speed
Longer takeoff run
Reduced rate & angle of climb
Lower maximum altitude
Shorter range
Reduced Cruising speed
Reduced maneuverability
Higher stalling speed
Higher landing speed
Longer landing roll
Excessive weight on the nosewheel

Question 32

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

Answer 32

Higher stall speed - stalling angle of attack is reached at a higher speed due to increased wing loading.

Slower cruise speed - increased drag; greater AOA is required to maintain altitude.

More stable - the center of gravity is farther forward from the center of pressure which increases longitudinal stability.

Greater back elevator pressure required - longer takeoff roll: higher approach speeds and problems with landing flare.

Question 33

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

Answer 33

Lower stall speed - less wing loading.

Higher cruise speed - reduced drag; smaller AOA required to maintain altitude.

Less stable - stall and spin recovery more difficult; the center of gravity is closer to the center of pressure, causing longitudinal instability.

Question 34

What are the standard weights assumed for the following when calculating weight and balance problems?

Answer 34

Crew and passengers = 170 lbs
Gasoline = 6 lbs/ gal
Oil = 7.5 lbs/ gal
Water = 8.35 lbs/ gal

Question 35

What are some of the main elements of aircraft performance?

Answer 35

Takeoff and landing distance
Rate of Climb
Ceiling
Payload
Range
Speed
Fuel Economy

Question 36

What factors affect the performance of an aircraft during takeoffs and landings?

Answer 36

Air Density (density altitude)
Surface Wind
Runway Surface
Upslope or Downslope of runway
Weight

Question 37

What effect does wind have on aircraft performance?

Answer 37

Takeoff - a headwind will increase the airplane performance by shortening the takeoff distance and increasing the angle of climb. A tailwind will decrease performance by increasing the takeoff distance and reducing the angle of climb.

Landing - a headwind will increase airplane performance by steepening the approach angle and reducing the landing distance. A tailwind will decrease performance by decreasing the approach angle and increasing the landing distance.

Cruise flight - winds aloft have somewhat the opposite effect on performance. Headwind will decrease performance by reducing ground speed, which in turn increases fuel requirements. Tailwind will increase performance by increasing the ground speed, which in turn reduces the fuel requirement for the flight.

Question 38

How does weight affect takeoff and landing performance?

Answer 38

Increased weight can have a significant effect on takeoff performance:
Higher liftoff speed
Greater mass to accelerate
Increased retarding force (drag and ground friction)
Longer takeoff distance

The effect of gross weight on landing distance is that the airplane will require a greater speed to support the airplane at the landing AOA and lift coefficient resulting in and increased landing distance.

Question 39

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

Answer 39

Increased takeoff distance (greater takeoff TAS req)
Reduced rate of climb (decreased thrust and reduced acceleration)
Increased true airspeed on approach and landing (same IAS)
Increased landing roll distance.

Question 40

Define the term density altitude.

Answer 40

Pressure altitude corrected for nonstandard temperature.

Question 41

How does air density affect aircraft performance?

Answer 41

Direct effect on:
Lift produced by the wings
Power output of the engine
Propeller efficiency
Drag forces

Question 42

What factors affect air density?

Answer 42

Altitude - higher = less dense
Temperature - warmer = less
Humidity - more = less dense

Question 43

How does temperature, altitude, and humidity affect density altitude?

Answer 43

Density altitude will increase when Hot, High, Humid

Density altitude will decrease when cold, low, dry.

Question 44

What information can you obtain from the following charts?

Answer 44

a. Takeoff charts - These allow you to compute the takeoff distance of the airplane with no flaps or with a specific flap configuration. You can also compute distances for a no flap takeoff over a 50 foot obstacle scenario as well as with flaps over a 50 foot obstacle.
The takeoff distance chart provides for various airplane weights, altitudes, temperatures, winds, and obstacle heights.
b. Fuel, time, and distance to climb chart - This chart will give the fuel amount used during the climb, the time it will take to accomplish the climb, and the ground distance that will be covered during the climb. To use this chart, obtain the information for the departing airport and for the cruise altitude.
c. Cruise and range performance chart - This is designed to give true airspeed, fuel consumption, endurance in hours, and range in miles at specific cruise configurations
d. Crosswind and headwind component chart - This allows for figuring the headwind and crosswind component for any given wind direction and velocity
e. Landing charts - provide normal landing distance as well as landing distance over a 50 foot obstacle
f. Stall speed performance charts - These are designed to give an understanding of the speed at which the airplane will stall in a given configuration.

Question 45

Define the term pressure altitude and state why it is important.

Answer 45

Pressure altitude - the altitude indicated when the altimeter setting window is adjusted to 29.92. This is the altitude above the standard datum plane, a theoretical plane where air pressure equals 29.92 in Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.