Performance and Limitations

Question 1

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

Answer 1

• lift: upward acting force
• gravity: weight, downward acting force
• thrust: forward acting force
• drag: backward acting force

Question 2

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

Answer 2

steady-state, straight-and-level, unaccelerated flight, sum of opposing forces is equal to zero

Question 3

What is an airfoil?

Answer 3

device which gets a useful reaction from air moving over its surface, namely LIFT. (Ex: wings, horizontal tail surfaces, vertical tail surfaces, propellers)

Question 4

What is the “angle of incidence”?

Answer 4

• angle formed by the longitudinal axis of the airplane and the chord of the wing
• measured by angle at which wing is attached to fuselage;
• fixed and cannot be change by pilot

Question 5

What is “relative wind”?

Answer 5

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

Question 6

What is the “angle of attack”?

Answer 6

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

• pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases
• airflow, high speed flow is associated with low pressure and low speed flow with high pressure
• airfoil designed to increase velocity of airflow above its surface, decreasing pressure above the airfoil; impact of air on lower surface of the airfoil increases the pressure below; this combination of pressure decrease above and increase below produces lift

Question 8

What is “torque effect”?

Answer 8

as 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 high angle of attack

Question 9

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

Answer 9

• in flight: acting around the longitudinal axis, tending to make the airplane roll; modern airplanes designed with the engine offset to counteract this effect of torque.
• on the ground: during takeoff roll, an additional turning moment around the vertical axis is induced by torque reaction; as left side of the airplane is being forced down, more weight is being placed on the left main landing gear; results in more ground friction, or drag, on the left tire than on the right, causing a further turning moment to the left

Question 10

What are the four factors that contribute to torque effect?

Answer 10

• torque reaction of the engine and propeller: rotation of propeller (from the cockpit) to the right, tends to roll or bank the airplane to the left
• gyroscopic effect of the propeller: if axis of a propeller is tilted, the resulting force will extend 90 degrees ahead in the direction of rotation and in the same direction as the applied force; most noticeable on takeoffs in taildraggers when the tail is raise.
• corkscrewing effect of the propeller slipstream: high speed rotation of an airplane propeller results in a corkscrewing rotation to the slipstream as it moves rearward; at high propeller speeds and low forward speeds (as in takeoff), the 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 angle of attack, the bite of the downward moving propeller blade is greater than the bite of the upward moving blade; greater thrust on the downward moving blade on the right side, and this forces the airplane to yaw to the left

Question 11

What is “centrifugal force”?

Answer 11

“equal and opposite reaction” of the airplane to the change in direction and it acts “equal and opposite” in the horizontal component of lift

Question 12

What is “load factor”?

Answer 12

ratio of the total load supported by the airplane wing to the actual weight of the airplane and its contents; actual load supported by the wings divided by the total weight of the airplane; ratio of a given load to the pull of gravity

Question 13

For what two reasons is load factor important to pilots?

Answer 13

• dangerous overload that is possible for a pilot to impose on the aircraft structure
• increase load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds

Question 14

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

Answer 14

as load factor increases, stalling speed increases