PPL Guide Ch. 6 - Performance and Limitations Flashcards
What are the four dynamic forces that act on an airplane during all maneuvers? (FAA-H-8083-25)
- Lift - the upward acting force.
- Gravity (or weight) - the downward acting force.
- Thrust - the forward acting force.
- Drag - the backward acting force.
What flight condition will result in the sum of the opposing forces being equal? (FAA-H-8083-25)
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.
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.
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 AOI is fixed and cannot be changed by the pilot.
What is 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.
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.
What is Bernoulli’s Principle? (FAA-H-8083-25)
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.
What are several factors which will affect both lift and drag?
– 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 (e.g. 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 AOA 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.
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, and 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 AOA.
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 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.
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. j
- 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 taildraggers when a tail is raised.
- Corkscrewing effect of the propeller slipstream - Highspeed 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 AOA, 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 AOA 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.
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.
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, e.g., to refer to a load factor of three as 3 G’s. 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 G’s.
For what two reasons is load factor important to pilots? (FAA-H-8083-25)
- Because of the obviously dangerous overload that it is possible for a pilot to impose on the aircraft structure.
- Because an increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds.
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*.
- Turbulence - Severe vertical gusts cause a sudden increase in AOA, 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.
