Performance and Limitations Flashcards
(45 cards)
What are the four dynamic forces that act on an airplane during all maneuvers?
lift - the upward force 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 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.
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 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?
What is relative wind?
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?
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?
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
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
What is torque effect?
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
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 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?
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.
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 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).
For what 2 reasons in load factor important to pilots?
Danger of overstressing the airframe
Danger of increased stall speed - makes stalls possible at seemingly safe flight speeds.
What situations may result in load factors reaching or exceeding the maximum?
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.
What are the different operational categories for aircraft and within which category does your aircraft fall?
Normal +3.8 to -1.52
Utility +4.4 to -1.76
Aerobatic +6.0 to -3.00
What effect does an increase in load factor have on stalling speed?
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.
Define the term Maneuvering Speed.
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.
Discuss the effect on maneuvering speed of an increase or decrease of weight.
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.
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 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.
What causes an airplane to stall?
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.
What is a spin?
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.
What causes a spin?
Exceeding the critical AOA while applying excessive or insufficient rudder, and to a lesser extent, aileron.
When are spins most likely to occur?
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.
