機師考試小知識— 常用航空單位換算

 (以下僅供簡略快速換算,實際換算請依照Pilot Operating Handbook 或 Airplane Flight Manual)

Rules of Thumb.

Listed below are some tried and tested aviation rules of thumb that can help you become a safer, more competent pilot. These is just a sampling of the many that exist. If you have any that you’d like to add, please leave a comment. Unless otherwise specified they are intended for light aircraft. Never, at any time should they be substituted for figures found in your specific aircraft Pilot’s Operating Handbook (POH) or Airplane Flight Manual (AFM). Nor should they be used as a substitute for any Federal Aviation Regulation (FAR), or just plain old common sense. How’s that for fine print?

AIRSPEED/ALTITUDE/TEMPERATURE

  • Standard Temperature (ISA): 15°C (59°F) at sea level. ISA decreases 2°C (3.5°F) per 1,000 foot increase in altitude
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  • True Airpseed (TAS): Add 2% to indicated airspeed (IAS) for every 1,000  foot increase in altitude
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  • Density Altitude: For every variation of ±15°F or ±8°C from standard temperature at a given pressure altitude, density altitude increases/decreases 1,000 feet
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  • Air Density/Humidity: For every 20°F temperature increase air density decreases 2-3% (moisture holding capacity doubles)
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  • Relative Humidity: Dew point/Temperature =  Percentage [Example: (9°C/19°C) = 47%]
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  • Density Altitude: Increases or decreases 120 feet for each 1 degree Celsius that the temperature varies from standard temperature
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  • Density Altitude: Outside temperature minus standard temperature multiplied by 120 plus pressure altitude [Example: (OAT-ISA) x 120 + PA = DA]
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  • Calculating standard temperature at altitude: [Example of 12,000 feet: (12 x 2) -15=9. Convert to a negative. -9°C at 12,000 feet]
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  • Celsius to Fahrenheit (15°C, for example): (15 x 2) + 30 = 60°F (59°F)
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  • Fahrenheit to Celsius (59°F, for example): (59 – 30) ÷ 2 = 14.5°C (15°C)
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  • Maneuvering Speed (Va): Reduce Va by one-half the percentage of weight reduction. [Example: Va at 3,000 lbs = 100kts.; 2,400 lbs = 20% reduction on weight. Reduce Va by 10 kts.]
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  • Maneuering Speed Formula: Va2 = Va√(W2 ÷ W1); whereas Va2 is calculated maneuvering speed, Va is maneuvering speed at gross weight, W2 is reduced weight, and W1 is gross weight
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  • Manuevering Speed (Va): Subtract 1 knot for each 100 pounds under gross landing weight
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  • Stall speed: As weight doubles, stall speed increases by √2, or 1.414
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AIRCRAFT LOADING

  • Weight of 100LL: 6.0 lbs/gal
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  • Weight of Jet A: 6.75 lbs/gal
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  • Weight of 50W Oil: 7.5 lbs/gal (1.875 lbs/qt)
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  • Jet A lbs. to gallons: Divide pounds required by 10, add 50% [Example: (2,000 lbs. ÷ 10) x 1.5 = 300 gallons) OR drop the zero then add 50%]
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  • Weight x Arm = Moment
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  • Total Moment ÷ Total Weight = CG (inches)
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  • CG Distance Aft of LEMAC ÷ MAC = CG in % MAC
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  • Weight Shift Formula: (Weight shifted/Total weight) = (Distance CG shifted/Distance weight shifted)

TAKEOFF/LANDING PERFORMANCE

  • General: Add at least a 20% safety margin to all POH/AFM performance figures, as insurance
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  • Takeoff distance: Increase by 10% for each 1,000 foot density altitude above sea level
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  • Ground roll: Increases or decreases by 10% for every 10°C change in temperature from ISA
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  • Ground roll: For every 10% change in weight, ground roll changes 20%
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  • Abort distance: Abort the takeoff if the aircraft has not achieved 70% of its flying speed by the time it has used 50% of the runway
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  • Rotate speed (Vr): Generally equal to 1.15 Vs
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  • Obstacle clearance: The distance/time to clear an obstacle is reduced by 5% for every 100 lbs. below max gross weight
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  • Runway gradient: A 1% airport grade will affect the aircraft by 10% over what is stated in the POH/AFM
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  • Tailwind: A tailwind of 10% of your approach speed will increase landing distance by 20%
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  • Headwind: A headwind of 10% or your approach speed will decrease landing distance by 20%

CLIMB/ENROUTE/DESCENT

  • Climb Gradient (Feet per NM to Feet per min.): Groundspeed x feet per NM/60. [Example: (140 kts x 200 ft/nm) ÷ 60 = 466 ft/min]
  • To reduce effects of headwind in climb: Climb at cruise climb
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  • To take advantage of tailwind in climb: Climb at Vy
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  • Angle of Bank for Standard Rate Turn: 10% of TAS + 5 [example: (120 x .10) + 5 = 17°]
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  • Pivotal Altitude: (TAS)²/11.3 (knots) OR  (TAS)²/15 (MPH)
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  • Time to Station: (60 x Time between bearings)/bearing change = time [Example: (60 x 6 min)/10° = 36 min. to station]
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  • Distance to Station: (TAS x Min. flown)/degree of bearing change = distance [Example: (160 x 6 min/10° = 96 miles)]
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  • Time to Descend: (Altitude to Lose/Rate of Descent) = Time to Descend
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  • Miles to Descend: (Flight Level/3) = NM [Example: (120/3) = 40 NM]
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  • 3° Glideslope: Half your ground speed and add a zero [Example: (90 ÷ 2 = 45) x 10 = 450 fpm]
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  • Calculating Visual Descent Point (VDP) Distance Method: HAT (height above touchdown)/300 [Example: (480/300) = 1.6 NM from threshold]
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  • Calculating Visual Descent Point (VDP) Time Method: HAT x 10% [Example: 480 x 10% = 48 seconds to subtract from MAP timing]

reference: http://axenty.com/blog/tips/rules-of-thumb/


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