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31 Cards in this Set
- Front
- Back
Lift equation |
Lift = 1/2p × V2 x S x Cl p = air density V = true airspeed S = size of wing (surface area) Cl = lift coefficient i) shape of wing ii) AoA |
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Cambered aerofoil |
- produce more lift than symmetrical aerofoil - will produce lift at zero AoA - stall at lower AoA than uncambered Flaps inc camber |
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Parasite drag |
a) Skin friction - friction over surface b) Form drag - air over shape c) Interference - of flow as 2 objects joined
Proportional to: 1. Air density 2. Surface area 3. Velocity squared *unchanged w/ weight & AoA |
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Induced drag |
- pressure difference (top/bottom of wing) = downward force = reaction (lift) = reduction in horiz velocity
Inc w/ factors that inc leakage around wing tip (& AoA): 1. Weight 2. Dec air density (inc AoA) 3. Dec TAS (inc AoA) - *inv proportional to V2
Design features that reduce: 1. High aspect ration 2. Winglets (inc effective aspect ratio) - most effective t/o, climb, hight alt cruise - *inc form drag |
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Total drag |
Acts in same direction as relative airflow - induced drag high at low speeds - parasite drag high at high speeds Min drag speed - lift/drag ratio max |
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Range |
TW - slow down to reduce fuel consumption HW - speed up to minimize time exposed
Range inc: - Red weight (= less induced drag) - Inc alt (up to Vmd or slightly ab for jet a/c) - better fuel economy
To achieve - Max velocity / fuel flow **to maint, as weight reduced, 1. a/s must be reduced 2. red thrust to maint AoA |
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Speed for max range |
Speed where ratio of power/thrust to TAS is lowest- 1.32 x Vmd - not stable & difficult to maintain - LRC higher but reduces trip duration |
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Stall |
AoA at which Cl starts to dec
Design features: 1. Washout - root higher AoI to ensure it stalls 1st 2. Higher camber at root 3. Stall strips at root create early separation of airflow 4. Vortex generators - reenergize boundary layer delaying separation |
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Surface contamination and stall |
Reduce critical AoA Thin layer: -Dec lift up to 30% -Inc drag up to 40% |
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Mach number |
= TAS / LSS |
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Speed of sound |
= 39 x (sq rt temp K) Temp in K = C + 273 |
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Sub/Trans/Supersonic |
Subsonic: airflow over entire airframe < LSS (~ <M0.75) Transonic: airflow over some of a/c lower/higher than LSS (M0.75~1.2) Supersonic: airflow over entire airframe > LSS |
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Shockwave formation |
- As speed of a/c app LSS disturbance of airfoil not communicated forward - collision of air molecules on LE causes rise of pressure, density, and temp & dec in velocity = turbulence/separation aft of shockwave |
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Mmo |
Max operating mach number mach number- indicated by barber pole Beyond will = control and stability problems - caused by shockwaves (mach buffet) - lower altitudes more limiting Limiting mach number - max operating speed in relation to speed of sound |
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Mcrit |
- speed at which shockwave 1st appears on wing - separation not yet occured - airflow at speed of sound but not exceed Where speed > Mcrit - as air passes through shockwave - temp inc, press inc, density inc, speed dec (= drag rise/diversion) |
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Mach tuck |
If speed > Mmo Shockwave also caused rearward movement of CofL = less total lift = nose down pitch Also, disturbed airflow dec horizontal stab (TDF) effectiveness
Design: - pitch trim compensator - stick puller |
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Design to delay shockwave formation |
1. Supercritical aerofoil; - thin flat topped wing - reduce acceleration of airflow 2. Vortex generators - mix airflow ab wing w/ boundary layer, reducing speed, delay boundary layer separation 3. Sweepback - longer effective chord to oncoming airflow, wing thinner reducing acceleration of air *inc Mcrit - shockwave 1st form at root |
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Sweepback |
*Secondary advantage of yaw/directional stability - less sweep = more drag on upwind wing - corecting yaw
Disadvantage: - dec thickness/lower camber = dec lift & higher TO/landing speeds - dutch roll ( combined roll & yaw) - correct w/ rate gyro + yaw damp |
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Angle of bank for rate one turn |
= (TAS kts / 10) + 7 = (TAS mph / 10) + 5 360° in 2mins OR 3° / sec |
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Stall speed in a turn |
= normal stall speed x sq rt load factor in turn 45° AoB = 1.41 LF 60° AoB = 2 LF |
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Longitudinal stability improved |
Moving CoG forward of CoP |
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Laminar flow wing vs conventional wing |
Laminar flow max thickness - 40% chord Conventional wing max thickness - 30% chord |
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*Canards |
- reduce main wing loading - better controls main wing AoA & airflow - inc maneuverability at high AoA - reduces stall speed |
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Buffet boundary |
Factors that affect AoA - g loading - AoB- weight - pressure/density alt Narrow margin of protection btwn low and high speed buffet |
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Buffet boundary |
Buffeting (due airflow separation) Low speed - conventional stall (AoA) High speed - shock wave (AoA & TAS) - choose buffet margin to account for inc 'g' loading (ex due turn or CAT) |
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Coffin corner |
Push down - descend Lower altitude will give wider safety margin |
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Dihedral |
Lateral stability - in bank, low wing flying higher AoA, produces more lift, tendency to return wings level - desirable response to small disturbances - ac must first develop a sideslip towards the 'dropped' wing before can return wings level |
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Low energy regime during landing |
A/c not certified to successfully complete go around (w/out ground contact) once entered 1. Flaps/gear landing config 2. A/c in descent 3. Thrust stabilized in idle range 4. A/s dec 5. A/c close to ground (50' in some cases) |
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State of equilibrium - forces opposing weight/drag in climb |
Resultant of 1. Thrust 2. Lift |
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State of equilibrium - forces opposing weight in descent |
Resultant of lift and drag |
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Critical engine on 4-engine a/c |
#1 or #4 depending on prop rotation |