Aerodynamics Flashcards
Define chord line…
The straight line connecting the leading and trailing edge of an airfoil.
Vmu
Minimum Unstick Speed, slower speed to get airborne, etc.
What causes the phenomena referred to as “much tuck”?
The movement of the shock wave aft forces the wing’s center of pressure aft, causing the aircraft a tendency to pitch nose down without enough tail down force.
What is the effect of winglets?
Winglets are method of creating an artificial aspect ratio. Wingtip vortices increase drag by downwash induction. Winglets are small wings places at an AOA with respect to the resultant flow of the free airstream and the vortex flow. The lift vector of the winglet points in the forward direction. The forward component of this vector therefore gives a force in the direction of flight that is actually negative drag or thrust.
What is the Subsonic regime?
Aircraft mach speed where all the local air flow is less than the speed of sound. The mach range is below .75 Mach.
What does the term “power” imply?
Power implies work rate.
What is P-factor?
P-factor is the yaw effect that is experienced on propellor driven airplanes. At low airspeeds and high angles of attack, the descending blade produces more thrust than the ascending blade
How does the wake turbulence vortex circulate around each wingtip?
Outward, upward and around each tip. Since the pressure differential is caused by a lower pressure above the wing and a higher pressure below the wing, the air from the bottom moves out, up and around.
How does frost affect stall speed?
It increases stall speed and lowers the angle of attack at which the aircraft will stall. Ice, frost and snow.
What three conditions are required to cause dynamic hydroplaning?
The conditions required to cause dynamic hydroplaning are high speed, standing water and poor surface macro texture.
What is viscous hydroplaning?
Viscous hydroplaning occurs when there is a thin film of water covering a smooth surface such as a painted or rubber coated portion of the runway. Viscous hydroplaning can occur at much lower speeds than dynamic hydroplaning.
You are on a heading of 180 @ 20NM. You want to be at a heading of 270@ 10NM. The winds are 240@30 kts. What is your heading to the fix and what is your timing outbound?
2 formulas to accurately determine this. The first is the pythagorean theorem, or a^2 + b^2 = c^2. Using this you determine the heading to fly is 333°, to get 333°. With the angle now known, using an E6B to convert for Wind Correction Angle.
How can turbulent air cause an increase in the stall speed of an airplane?
When the aircraft is flying at a high speed with the wings at a low angle of attack, a sudden current of air moving upward changes the relative wind direction as it meets the airfoil. This increases the angle of attack.
Why is humid air worse for performance than dry air?
Water vapor is lighter than air; consequently, moist air is lighter than dry air. Therefore, as the water content of the air increases, the air becomes less dense, increasing density altitude and decreasing performance.
How does a yaw damper work?
By deflecting the rudder slightly in flight as needed to control yawing in turbulence and to eliminate the coupled roll/yaw dynamic condition known as Dutch roll. It also works automatically to keep all turns properly coordinated between the roll and yaw modes.
What are the pros and cons of a swept wing?
Pro : Only a component of the forward velocity will hit the wing chordwise. This allows the airplane to fly at a higher Mach number. Con: The wing tips have a tendency to stall first. To counteract this, the outer portion of the wing is designed with a smaller angle of attach than the thicker inner portion near the root. There is also a predisposition towards dutch roll, which is when an aircraft tends to roll whenever it yaws.
Which laws relate to the development of thrust in any power-plant?
Newton’s laws of motion. More specifically, the second law; a body of mass “m” subject to a net force “F” undergoes an acceleration “a” that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F=ma. The third law; for every action there is an equal and opposite action.
Why does an aircraft lose speed in a turn?
An increase in AOA is required to hold an aircraft at a steady altitude (due to a loss in the vertical component of lift). Since the AOA is increased, there is a corresponding increase in induced drag. This causes a loss of airspeed in proportion to the angle of bank.
Vr
Rotation Speed
V1
Decision Speed
How does Vmc change with altitude?
At sea level Vmc increases. At high altitudes Vmc decreases. Remember, parameters which are good for Vmc are not necessarily good for engine performance.
If the left engine is inoperative and the runway choices are 18/36 and 12/30 and the winds are 210 at 30 knots, what runway should you use?
A crosswind coming on the side of the operating engine is most favorable; in the air, it requires less rudder to keep the aircraft aligned with the runway (‘into’ the wind counteracts weathervane). Therefore, with the winds out of 210, runway 18 would be the best choice for the above scenario as it keeps the wind off the right side of the aircraft and thus, into the good engine.
What factors affect V1?
V1 is calculated for gross weight, flap setting, pressure altitude and temperature. Runway contaminates, inoperative anti-skid or anything that reduces stopping performance will also lower V1 as an abort would have to occur at a lower speed.
As a parcel of air rises, what is the affect on its Pressure? Density? Temperature?
When a parcel of air is forced to rise it expands because its pressure decreases. As pressure decreases so, too, does density. The temperature decreases with altitude for this parcel of air.
Define chord…
This is the precise distance of the width of the wing from the leading to the trailing edge along the chord line.
What is negative static stability?
When an aircraft continues to diverge from an equilibrium after it has been disturbed about one of its axis.
They decide to move the cargo more aft of the original position. What does this do?
Yoke pressure during rotation decreases and takeoff distance decreases.
With regard to the jet airplane, what two values are plotted on a thrust curve chart?
Thrust available (T) versus thrust required, or drag (D). for a given speed, altitude and configuration. Generally, the jet airplane will require consideration of the thrust required and the propeller airplane will require consideration of the power required.
What is the difference between thrust and power?
Thrust is ‘force’. Force is what accelerates an object to either change its speed or its direction (or both). The amount of work you do (energy you use) in a given period of time, is Power. Thrust is what pulls or pushes the airplane through the air, power is what produces the thrust.
What affect does altitude have on mach number?
Mach number is the ration of TAS to the speed of sound. The speed of sound in the atmosphere varies only with temperature. As the temperature increases, so too does the speed of sound, and vice versa. Assuming a climb to altitude is achieved at a constant TAS, mach will increase with altitude
V2
Best Climb Gradient
What is the mean chamber line?
It is the location, or the set of points forming a curve, halfway between the upper and lower surfaces as measured perpendicular to the mean camber line itself.
Can you name 3 components of parasitic drag?
Form drag, skin friction and interference
Is the stall speed for an aircraft the same at different altitudes?
The stalling speed of a particular aircraft is not a fixed value for all flight situations, but a given aircraft always stalls at the same AOA regardless of airspeed, weight, load factor, or density altitude.
What is Air Density?
The air’s thickness determined by pressure, temperature and humidity.
What sequence of events would stop a turbine aircraft the quickest?
A firm touchdown at the target touchdown point, followed by the deployment of ground spoilers, the timely selection of thrust reverse (if installed), and the smooth application of maximum braking will result in the shortest landing distance ground roll, particularly on wet or contaminated runway surfaces.
How does an aircraft stall?
An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wings surface brought on by exceeding the critical AOA
What is the definition of V2?
Takeoff Safety Speed. V2 ensures that the airplane can maintain an acceptable climb gradient with the critical engine inoperative.
Why does a tailwind increase takeoff roll?
The effect of a tailwind is to require the airplane to achieve a greater ground speed to attain the lift-off speed. A tailwind which is 10 percent of the takeoff airspeed will increase the takeoff distance approximately 21 percent.
You are flying at 250 KIAS in 1G flight. You nose the aircraft over to 0G flight, which of the following is true? A.) Induced drag is decreased B.) Parasite drag is decreased C.) Both are decreased D.) Total drag is zero
Drag caused by the development of lift is induced drag, if the aircraft is in a zero G condition lift must be equal to zero (Load = Lift/Weight). If load = 0 and weight is unchanged, lift must equal 0, therefore induced drag is decreased. A wing surface, even at zero lift, will have “profile” drag due to skin friction and form.
What effect does CG have on range and stability?
With an aft CG, an airplane will be less stable but have an increased range (due to slightly higher cruise speed).
With an inoperative engine, what technique should a pilot use to choose the most suitable runway?
A crosswind coming on the operating engine side is most favorable; on the ground it lowers the minimum control speed; in the air. it requires less rudder to keep the aircraft aligned with the runway (‘into’ the wind counteracts weathervane). Counteracting the yaw of the dead engine requires some amount of rudder, a crosswind on top of the asymmetrical thrust lowers the remaining available rudder authority for excess crosswind.
You are descending through moderate icing conditions, and your pitot-static system ices up. What does your airspeed indicator show?
A decrease in airspeed.
How does center of gravity affect range and stability?
An aft CG will be less stable and will cruise faster for a given power setting, thus increasing the range. A forward CG will be more stable in pitch and roll but will have a slower cruise speed and thus, a decreased range.
Define Accelerate-go distance…
Accelerate-go distance is the horizontal distance required to continue the takeoff and climb to 35 feet, assuming an engine failure at V1
Can you cruise further on one engine or two engines in a twin turbojet aircraft?
If an engine fails during optimum cruise of a turbojet airplane, the airplane must descend and will experience a loss in range. However, the turbojet airplane is generally overpowered at LDmax, and a loss of a power-plant will not cause a significant change in maximum endurance.
When is wake turbulence generated?
Wake turbulence is generated from the moment an aircraft leaves the ground until it touches down, since trailing vortices are a byproduct of wing lift. Prior to takeoff or touchdown pilots should note the rotation or touchdown point of the preceding aircraft.
Does a forward CG require an aircraft to fly at a higher or lower angle of attack for a given weight/configuration?
Moving an airplane CG more forward necessitates an increase in the wing-body lift force which can only be accomplished by increasing the airplane angle of attack. Alternatively, you could say that for any given angle of attack, the lift coefficient is greater at the more aft CG position.
What factors should be considered when landing in conditions conducive to hydroplaning?
The approach should be flown: on speed, on centerline and on glide path.
What does the term ‘faired’ mean with regard to aileron, rudder and elevator position?
Faired, i.e. not deflected from its neutral position, the aileron is aligned with the wing, the rudder is aligned with the vertical tail, the elevator is aligned with the stabilizer.
What are the characteristics of an aircraft loaded at the aft limit?
There’s a benefit to loading a plane toward, but within aft CG limits: faster cruise. This is a result of tail-down force, while only an aerodynamic load, must be carried by the airplane. When the aircraft is loaded aft, less tail-down force is required to achieve aircraft balance. Therefore, an aft-loaded airplane requires less lift than one that is loaded forward. This translates to faster cruise and better climb rate.
What are 4 effects of an aircraft climbing out of ground effect?
The aircraft will require a higher AoA to maintain the same coefficient of lift.
An increase in induced drag will require an increase in thrust.
Decreased stability and a nose-up change in moment.
A reduction in static pressure and an increase in indicated speed.
What is the difference between stalls at high altitude and low altitude?
Not as much thrust at higher altitude for recovery is available.
What influences the turn-radius the most? Altitude, Weight, Load Factor, Airspeed?
Airspeed. The radius of turn (R) can be computed using a simple formula. The radius of turn is equal to the velocity squared (V^2) divided by 11.26 times the tangent of the bank angle. Since velocity is squared, a higher airspeed will affect the radius of the turn greater than any other factor.
What is the definition of drag?
Drag is a force produced by the flow of a viscous fluid over a body, acting in a direction parallel to the free stream direction of the flow.
A swept-wing airplane with weak static directional stability and increased dihedral causes an increase in ____?
Dutch roll tendency. A swept wing airplane has an increase in dihedral effect. When an airplane’s dihedral effect is large in comparison with its static directional stability its Dutch roll tendencies will increase.
What is the Transonic regime?
Aircraft mach speed where some but not all local air flow velocities are Mach 1.0 or above. The mach range is Mach numbers from .75 to 1.20.
What is aerodynamic pressure ?
It is force per unit area exerted on a surface. If you hold your hand out of a moving car with the palm into the wind, it is the force exerted on your palm. It exist because air molecules are striking the surface of your hand and transferring some of their momentum to the surface.
Define region of reverse command?
It is the region of flight speeds below maximum endurance airspeed (L/Dmax) where a decrease in speed requires an increase in power.
The rudder controls yaw around the _____ axis and exhibits which type of stability?
(Vertical, Directional) The rudder controls yaw around the vertical axis and exhibits directional stability.
As an aircraft’s CG moves rearward, what are some of the affects?
An increased aft CG will cause an aircraft to be less stable in both pitch and roll. However, reduced aerodynamic loading of the horizontal tail will slightly lower stall speed and increase cruise speed for a given power setting.
Which of the following factors affect Vmc more; gross weight at its maximum or a CG in the most critical position?
The location of the weight with respect to CG is more critical than the weight of the aircraft.
Negative camber
mean camber line is below chord line.
Why does drag increase in a climb?
When the flightpath is inclined upward, a component of the airplane’s weight acts in the same direction as, and parallel to, the total drag of the airplane, thereby increasing the total effective drag.
What is induced drag?
Induced drag results from the production of lift. The pressure differential between upper and lower surfaces of the wing induces a vortex at each tip, causing a down push on the air leaving the trailing edge, This downwash causes the stream to depart down from incoming air. The lift vector, perpendicular to the actual airflow tilts back, resulting in lift in the streamwise direction. Induced drag is greatest at low airspeeds.
In a straight wind aircraft which portion of the wing stalls first?
In most straight-wing aircraft, the wing is designed to stall the wing root first. The wing root reaches its critical AoA first making the stall progress outward toward the wingtip. By having the wing root stall first, aileron effectiveness is maintained at the wingtips, maintaining controllability of the aircraft.
What is a servo tab?
An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite of the primary control
What is service ceiling?
Service Ceiling is the altitude where the rate of climb is only 100 feet per minute.
Define Accelerate-stop distance….
Accelerate-stop distance is the runway length required to accelerate to a specified speed (either VR or VLOF, as specified by the manufacturer), experience an engine failure, and bring the airplane to a complete stop.
