KDR: AB 2

22.4.4 describe the normal changes in pressure, temperature and density with increased altitude in the atmosphere

temperature decreases at 2 degrees C per 1,000ft (ISA lapse rate=1.98 degrees C/1,000ft) in the troposphere

density decreases with altitude as both pressure and temperature decreases

the tropopause is at approximately 36,090ft (11km) in the ISA model

above the tropopause, ISA temp remains constant at -56.5 degrees C

• increase in altitude: pressure, temperature and density decrease

22.6.22 describe how TR varies with increasing angle of attack (alpha)

TR direction tilts increasingly rearward (more drag relative to lift) as alpha grows

at the stall, TR drops sharply and changes direction significantly

the ratio of lift to drag component (L/D) peaks at a moderate alpha

beyond the stall, the drag component dominates the diminished TR

22.8.2 identify the factors affecting lift (low-subsonic speed airflow)

density (rho)

velocity (v²)

wing area

CL

• speed is squared, so it has the dominant effect on wing

22.8.18 define aspect ratio (AR) and describe the effect on AR on CL

AR is span over chord

decrease AR equates to decrease CL and increase in geometric stalling angle

• high AR=steeper CL curve slope, less induced drag, better glide performance

• low AR=shallower CL curve slop, more induced drag

22.10.28 explain a typical graph for lift/drag (L/D) ratio versus alpha

decrease AOA L/D falls off rapidly meaning the a/c is least efficient aerodynamically

increase L/D also reduces but less rapidly until the stalling angle (not efficient)

• most efficient AOA or the max L/D ratio is at 4 degrees

22.20.6 state what the vx and vy speeds are and differentiate between these speeds and the normal climb speed

vy: best rate of climb, maximum higher per unit time

vx: is normally slower than vy below the absolute ceiling

• for obstacle clearance after take-off

normal climb speed is selected for practical operation, cooling, visibility, and handling

22.20.8 define absolute ceiling and service ceiling

absolute ceiling: at an altitude the power required to keep the aircraft in straight and level and the power available are equal and the aircraft cannot climb

• theoretical; takes infinite time to reach

service ceiling: rate of climb = 100fpm (piston) or 500fpm

• both ceiling decrease with increased weight, height, temperature, and lower pressure

• at the ceiling, vx=vy=only possible level flight speed

22.20.16(a) weight on glide angle and best glide speed

a/c weight does not affect the glide angle

a/c weight increases best glide speed (square root of weight ratio) and descent rate

• heavier=same distance, faster arrival

22.28.6 define critical engine

the engine with the smallest moment arm is therefore the worst to have failed

22.30.2 define specific air range (SAR) and specific fuel consumption(SFC)

specific air range (SAR): distance covered per unit of fuel consumed

• higher SAR=more efficient range performance

specific fuel consumption (SFC): fuel consumed per unit of power out put per unit of time

• lower SFC = more efficient engine

• best range requires optimising both airframe efficiency (L/D) and engine efficiency (SFC)