Performance & Limitations Flashcards
What are the four dynamic forces that act on an airplane during all maneuvers?
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?
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 stead, 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?
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?
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.
What is a relative wind?
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?
The angle between the wing chord line and the direction of the relative wind. This can be changed by the pilot.
What is 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.
What are several factors that 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 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 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.
What is torque effect?
(One of the left turning tendencies.)
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.
What effect does torque reaction have on an airplane on the ground and in flight?
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 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 turning tendencies?
Torque reaction to 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 degrees ahead in the direction of rotation and in the same direction as the applied force. It is most noticeable on takeoffs in taildraggers when the tail is raised.
Spiraling 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 (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.
What is centrifugal force?
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?
The ratio of the total load supported by the airplane’s wing to the actual weight of the airplane and its contents. The actual load supported by the wings divided by the total weight of the airplane. It can also be expressed as the ration 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 1G, 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.
For what two reasons is load factor important to pilots?
1) Because of the dangerous overload that it is possible for a pilot to impose on the aircraft structure.
2) 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?
Level turns: The load factor increases at a terrific rate after a bank has reached 45 or 50 degrees. The load factor in a 60 degree bank turn is 2 Gs. The load factor in a 80 degree 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.
What are the different operational categories for aircraft and within which category does your aircraft fall?
The maximum safe load factors (limit load factors) specified for airplanes are as follows:
1) Normal - +3.8 to -1.52
2) Utility (mild aerobatics including spins) - +4.4 to -1.76
3) Aerobatic - +6.0 to -3.00
The 172 falls in the normal category
What effect does an increase in load factor have on stalling speed?
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 of attack increases, and the wing stalls because the angle of attack 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.
Define the term maneuvering speed.
The maximum speed at which the limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage.
The speed at which abrupt control changes can be made and the plane will stall before it breaks.
It is the speed below which you can, in smooth air, move a single flight control one time, to its full deflection, for one axis of airplane rotation only (pitch, roll, or yaw) without risk of damage to the airplane. Speeds up to, but not exceeding the maneuvering speed allow an aircraft to stall prior to experiencing an increase in load factor that would exceed the limit load of the aircraft.
Discuss the effect on maneuvering speed of an increase or decrease in weight.
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.
Define loss-of-control-inflight (LOC-I) and describe several situations that might increase the risk of an LOC-I accident occurring.
LOC-I is 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.
What causes an airplane to stall?
Exceeding the critical angle of attack. Every airplane has a specific angle of attack where the airflow separates from the upper surface of the wing and the stall occurs. Each airplane has only one specific angle of attack where the stall occurs, regardless of airspeed, weight, load factor, or density altitude.
What is a spin?
A controlled (recoverable) or uncontrolled (possibly unrecoverable) maneuver in which the airplane 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 or a skid. If a stall does not occur, a spin cannot occur.
What causes a spin?
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.
When are spins most likely to occur?
A stall or spin can occur in any phase of flight, but is most likely to occur in the following situations:
1) Engine failure on takeoff during climbout: The 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.
2) Crossed-control turn from base to final (slipping or skidding turn): The pilot overshoots final and makes uncoordinated turn at a low airspeed.
3) Engine failure on approach to landing: The pilot tries to stretch glide to runway by increasing back pressure.
4) Go-around with full nose-up trim: The pilot applies power with full flaps and nose-up trim combined with uncoordinated use of rudder.
5) Go-around with improper flap retraction: The pilot applies power and retracts flaps rapidly resulting in a rapid sink rate followed by an instinctive increase in back pressure.
