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.
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 (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.
What procedure should be used to recover from an inadvertent spin?
1) Close the throttle
2) Neutralize the ailerons
3) Apply full opposite rudder
4) Briskly move the elevator control forward to approximately the neutral position
5) Once the stall is broken the spinning will stop. Neutralize the rudder when the spinning stops.
6) When the rudder is neutralized, gradually apply enough aft elevator pressure to return to level flight.
Remember PARE
Power - reduce to idle
Ailerons - position to neutral
Rudder - apply full opposite against rotation
Elevator - apply positive, forward of neutral, movement to break stall
Once the spin rotation stops, neutralize the rudder and begin applying back pressure to return to level flight.
What causes adverse yaw?
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 lift and less drag. This added drag attempts to pull or veer the airplane’s nose in the direction of the raised wing; that is, it tries to turn the plane in the direction opposite to that desired. This undesired veering is referred to as adverse yaw.
What is ground effect?
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 wing’s upwash, downwash, and wingtip vortices. In order for ground effect to be of a significant magnitude, the wing must be quite close to the ground.
When the plane is close to the ground (one wing length above or closer) wingtip vortices get cut off by the ground, so they can’t fully develop and instead dissipate against the ground. The reduction in vortices causes a reduction in downwash (when wind comes off the wing, it angles down to the ground). The reduction in vortices and downwash cause a reduction in induced drag, which causes improved performance.
What major problems can be caused by ground effect?
During landing: At a height of approximately one-tenth of a wing span above the surface, drag may be 40% 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 this case, the pilot may run out of runway and options for landing.
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.
Define empty weight.
The weight of the airframe, engines, all permanently installed equipment, and unusable fuel. Depending on the FARs under which the aircraft was certificated, either the undrainable oil or full reservoir of oil is included.
Define gross weight.
The maximum allowable weight of both the airplane and its contents.
Define useful load.
The weight of the pilot, copilot, passengers, baggage, usable fuel and drainable oil.
Define arm.
The horizontal distance, in inches, from the reference datum line to the center of gravity of the item.
Define moment.
The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches.
Define 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.
Define datum.
An imaginary vertical plane or line from which all measurements of arm are taken. Established by the manufacturer.
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?
Weight x Arm = Moment
Weight = Moment/Arm
Arm (CG) = Total Moment/Total Weight
Remember WAM (Weight x Arm = Moment)
What performance characteristics will be adversely affected when an aircraft has been overloaded?
1) Higher takeoff speed
2) Longer takeoff run
3) Reduced rate and angle of climb
4) Lower maximum altitude
5) Shorter range
6) Reduced cruising speed
7) Reduced maneuverability
8) Higher stalling speed
9) Higher landing speed
10) Longer landing roll
11) Excessive weight on the nosewheel
What effect does a forward center of gravity have on an aircraft’s flight characteristics?
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, problems with landing flare, possible to land on nose wheel, possible to prop strike, possible to porpoise down the runway.
Higher induced drag.
What effect does a rearward center of gravity have on an aircraft’s flight characteristics?
Lower stall speed - Less wing loading.
Higher cruise speed - Reduced 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.
Possible to balloon out of ground effect when landing. Landing on back wheels. Could float more when landing.
Easier rollout on takeoff.
What are the standard weights assumed for the following when calculating weight and balance?
Gas
Oil
Water
Gas - 6 pounds/gallon
Oil - 7.5 pounds/gallon
Water - 8.35 pounds/gallon
