Oral Exam Preparation Questions and Answers
|DETERMINING PERFORMANCE AND LIMITATIONS
A. Aerodynamics 1. What are the four dynamic forces that act on an airplane during all maneuvers? (FAA-H-8083-25)
Lift – the upward acting force
2. What flight condition will result in the sum of the opposing forces being equal? (FAA-H-8083-25)
In steady-state, straight-an-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. This simply means that the opposing forces are equal to, and thereby cancel the effects of, each other.
3. What is an airfoil? State some examples. (FAA-H-8083-25)
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.
4. What is the “angle of incidence”? (FAA-H-8083-25)
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.
5. What is a “relative wind”? (FAA-H-8083-25)
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.
6. What is the “angle of attack”? (FAA-H-8083-25)
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.
7. What is “Bernoulli’s Principle”? (FAA-H-8083-25)
Bernoulli’s Principle – 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.
8. What are several factors which will affect both lift and drag?
Wind area – Lift and drag acting on a wing are roughly proportional to the wind area. A pilot can change wing area by using certain types of flaps (i.e., Fowler 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.
9. What is “Torque effect”? (FAA-H-8083-25)
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 air speeds with high power settings and a high angle of attack.
10. What effect does torque reaction have on an airplane on the ground and in flight? (FAA-H-8083-25)
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 in 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 take off 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 let main landing gear. This results in more ground friction, or drag, on the let tire than on the right, causing a further turning moment to the left.
11. What are the four factors that contribute to torque effect? (FAA-H-8083-25)
Torque reaction of the engine and propeller. For every action there is an equal and opposite reaction. The rotation of the propeller (from the cockpit) to the right, tends to roll or bank the airplane to the left.
Gyroscopic effect of the propeller. Gyroscopic precession applies here: 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 a 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. It is most noticeable on takeoffs in tail draggers when the tail is raised.
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 a 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). When an airplane is flying with a high angle of attack, the bite of the downward moving propeller blade is greater than the bite of the upward moving blade. This is due to the downward moving blade meeting the oncoming relative wind at a greater angle of attack than the upward moving blade. Consequently there is greater thrust on the downward moving blade on the right side, and this forces the airplane to yaw to the left.
12. What is “centrifugal force”? (FAA-H-8083-25)
Centrifugal force is 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.
13. What is “load factor”? (FAA-H-8083-25)
Load factor is the ratio of the total load supported by the airplane’s wing to the actual weight of the airplane and its contents. In other words, it is the actual load supported by the wings divided by the total weight of the airplane. It can also be expressed as the ratio of a given load to the pull of gravity; i.e., to refer to a load factor of three as “3 Gs.” In this case the weight of the airplane is equal to 1 G, and if a load of three times the actual weight of the airplane were imposed upon the wing due to curved flight, the load factor would be equal to 3 Gs.
14. For what two reasons is load factor important to pilots? (FAA-H-8083-25)
a. Because of the obviously dangerous overload that it is possible for pilot to impose on aircraft structure.
15. What situations may result in load factors reaching the maximum or being exceeded? (FAA-H-8083-25)
Level Turns – The load factor increases at a terrific rate after a bank has reached 45° or 50°. The load factor in a 60° – bank turn is 2 Gs. The load factor in a 80° – bank turn is 5.76 Gs. The wing must produce lift equal to these load factors if altitude is to be maintained.
Turbulence – Severe vertical gusts cause a sudden increase in angle of attack, resulting in large loads which are resisted by the inertia of the airplane.
Speed – The amount of excess load that can be imposed upon the wing depends on how fast the airplane is flying. At speeds below maneuvering speed, the airplane will stall before the load factor can become excessive. At speeds above maneuvering speed, 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.
16. What are the different operational categories for aircraft and within which category does your aircraft fall? (FAA-H-8083-25)
The maximum safe load factors (limit load factors) specified for airplanes in the various categories are as follows:
17. What effect does an increase in load factor have on stalling speed? (FAA-H-8083-25)
As load factor increases, stalling speed increases. Any airplane can be stalled at any airspeed within the limits of its structure and the strength of the pilot. At a given airspeed the load factor increases as angle has been increased to a certain angle. Therefore, there is a direct relationship between the load factor imposed upon the wing and its stalling characteristics. A rule 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.
18. Define the term “maneuvering speed”. (FAA-H-8083-25)
Maneuvering speed 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. When operating below this speed, a damaging positive flight load should not be produced because the airplane should stall before the load becomes excessive.
19. Discuss the effect on maneuvering speed of an increase or decrease in weight. (FAA-H-8083-25)
Maneuvering speed increases with an increase in weight and decreases with a decrease in weight. An aircraft operating at a reduced weight is more vulnerable to rapid accelerations encountered during flight through turbulence or gusts. Design limit load factors could be exceeded if a reduction in maneuvering speed is not accomplished. An aircraft operating at or near gross weight in turbulent air is much less likely to exceed design limit load factors and may be operated at the published maneuvering speed for gross weight if necessary.
20. What causes an airplane to stall? ((FAA-H-8083-25)
An airplane stalls when the critical angle of attack has been exceeded. When the angle of attack increases to approximately 18° to 20°, the air can no longer flow smoothly over the top wing surface. Because the airflow cannot make such a great change in direction so quickly, it becomes impossible for the air to follow the contour of the wing. This is the stalling or critical angle of attack. This can occur at any airspeed, in any attitude, with any power setting.
21. What is a “spin”? (AC-61-67C)
A spin in a small airplane or glider is a controlled (recoverable) or uncontrolled (possibly unrecoverable) maneuver in which the airplane or glider descends in a helical path while flying at an angle of attack greater than the critical angle of attack. Spins result from aggravated stalls in either a slip of a skid. If a stall does not occur, a spin cannot occur.
22. What causes a spin? (AC 61-67C)
The primary cause of an inadvertent spin is exceeding the critical angle of attack while applying excessive or insufficient rudder, and to a lesser extent, aileron.
23. When are spins most likely to occur? (AC 61-67C)
A stall/spin situation can occur in any phase of flight but is most likely to occur in the following situations:
a. Engine failure on takeoff during climb out – pilot tries to stretch glide to landing area by increasing back pressure or makes an uncoordinated turn back to departure runway at a relatively low airspeed.
24. What procedures should be used to recover from an inadvertent spin? (AC 61-67C)
a. Close the throttle (if not already accomplished).
25. What causes “adverse yaw”? (FAA-H-8083-25)
When turning an airplane to the left for example, the downward deflected aileron on the right produces more lift on the right wing. Since the downward deflected right aileron produces more lift, it also produces more drag, while the opposite left aileron has less left and less drag. This added drag attempts to pull or veer the airplane’s nose in the direction of the raised wing (right); that is, it tries to turn the airplane in the direction opposite to that desired. This undesired veering is referred to as adverse yaw.
26. What is “ground effect”? (FAA-H-8083-3)
Ground effect is a 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 up wash, downwash, and wingtip vortices. In order for ground effect to be of a significant magnitude, the wing must be quite close to the ground.
27. What major problems can be caused by ground effect? (FAA-H-8083-3)
During landing, at a height of approximately one-tenth of a wing span above the surface, drag may be 40 percent less than when the airplane is operating out of ground effect. Therefore, any excess speed during the landing phase may result in a significant float distance. In such cases, if care is not exercised by the pilot, he/she may run out of runway and options at the same time.
During takeoff, due to the reduced drag in ground effect, the aircraft may seem capable of takeoff well below the recommended speed. However, as the airplane rises out of ground effect with a deficiency of speed, the greater induced drag may result in very marginal climb performance, or the inability of the airplane to fly at all. In extreme conditions, such as high temperature, high gross weight, and high-density altitude, the airplane may become airborne initially with a deficiency of speed and then settle back to the runway.
B. Weight and Balance
1. Define the following : (FAA-H-8023-25)
Empty weight – The airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft. Includes hydraulic fluid, unusable fuel, and undrainable oil.
Gross weight – The maximum allowable weight of both the airplane and its contents.
Useful load – The weight of the pilot, copilot, passengers, baggage, usable fuel and drainable oil.
Arm – The horizontal distance in inches from the reference datum line to the center of gravity of the item.
Moment – The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches.
Center of gravity – The point about which an aircraft would balance if it were possible to suspend it at that point. Expressed in inches from datum.
Datum – An imaginary vertical plane or line from which all measurements of arm are taken. Established by the manufacturer.
2. 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? (FAA-H-8083-25)
Weight * Arm = Moment
By rearrangement of this equation to the forms:
Weight = Moment / Arm
Arm (CG) = (Total Moment / (Total) Weight
With any two known values, the third value can be found.
Remember : W A M
(Weight * Arm = Moment)
3. What performance characteristics will be adversely affected when an aircraft has been overloaded? (FAA-H-8083-1)
a. Higher takeoff speed
4. What effect does a forward center of gravity have on an aircraft’s flight characteristics? (FAA-H-8083-1)
Higher stall speed – stalling angle of attack is reached at a higher speed due to increased wing loading.
Slower cruise speed – increased drag; greater angle of attack 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.
5. What effect does a rearward center of gravity have on an aircraft’s flight characteristics? (FAA-H-8083-1)
Lower stall speed – less wing loading.
Higher cruise speed – reduce drag; smaller angle of attack is 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.
6. What are the standard weights assumed for the following when calculating weight and balance problems? (FAA-H-8083-25)
Crew and passengers …………………….170 lbs each
C. Aircraft Performance
1. What are some of the main elements of aircraft performance? (FAA-H-8083-25)
a. Takeoff and landing distance
2. What factors affect the performance of an aircraft during takeoffs and landings? (FAA-H-8083-25)
a. Air density (density altitude)
3. What effect does wind have on aircraft performance? (FAA-H-8083-25)
Takeoff – a headwind will increase the airplane performance by shortening the takeoff distance and increasing the angle of climb. However, a tailwind will decrease performance by increasing the takeoff distance and reducing the angle of climb. The decrease in airplane performance must be carefully considered by the pilot before a downwind takeoff is attempted.
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. Again, the pilot must take the wind into consideration prior to landing.
Cruise flight – winds aloft have somewhat an opposite effect on airplane performance. A headwind will decrease performance by reducing ground speed, which in turn increases the fuel requirement for the flight. A tailwind will increase the fuel requirement for the flight. A tailwind will increase performance by increasing the ground speed, which in turn reduces the fuel requirement for the flight.
4. How does weight affect takeoff and landing performance? (FAA-H-8083-25)
Increased gross weight can have a significant effect on takeoff performance.
a. Higher liftoff speed;
The effect of gross weight on landing distance is that the airplane will require a greater speed to support the airplane at the landing angle of attack and lift coefficient resulting in an increased landing distance.
An increase in density altitude results in :
a. Increased takeoff distance (greater takeoff TAS required).
6. Define the term “ density altitude “. (FAA-H-8083-25)
Density altitude is pressure altitude corrected for nonstandard temperature. Under standard atmospheric condition, air at each level in the atmosphere has a specific density, and under standard conditions, pressure altitude and density altitude identify the same level. Therefore, density altitude is the vertical distance above sea level in the standard atmosphere at which a given density is found.
7. How does air density affect aircraft performance? (FAA-H-8083-25)
The density of the air has a direct effect on :
a. Lift produced by the wings;
8. What factors affect air density? (FAA-P-8740-2)
Altitude – the higher the altitude, the less dense the air.
9. How does temperature, altitude, and humidity affect density altitude? (FAA-P-8740-2)
a. Density altitude will increase ( low air density ) when one or more of the following occurs:
10. Know the following speeds for your airplane!
Vso – Stall speed in landing configuration; the calibrated power-off stalling speed or the minimum steady flight speed at which the airplane is controllable in the landing configuration.
11. What information can you obtain from the following charts? (FAA-H-8083-25)
Takeoff Performance Charts
a. Normal takeoff ground run in feet
Climb Performance Charts
12. Define the term “Pressure altitude”, and state why it is important. (FAA-H-8083-25)
Pressure Altitude – the altitude indicated when the altimeter setting window (barometric scale) is adjusted to 29.92. This is the altitude above the standard datum plane, a theoretical plane where air pressure (corrected to 15°C) equals 29.92 in Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.
13. The following questions are designed to provide pilots with a general review of the basic information they should know about their specific airplane before taking a flight check or review.
What is the normal climb-out speed?