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GENERAL AVIATION RULES OF THUMB
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Standard Pressure, Temperature, and Lapse Rate
Sea level standard pressure = 29.92" hg
Standard lapse rate = -1" hg. for each 1000' increase in altitude
Sea level standard temperature = 15°C / 59°F
Standard Lapse Rate = -2°C / -3.5°F for each 1000’ increase in altitude
Take Off
T/O distance increases 15% for each 1000' DA above sea level
A 10% change in A/C weight will result in a 20% change in T/O distance
Available engine HP decreases 3% for each 1000' of altitude above sea level
Fixed pitch, non-turbo A/C climb performance decreases 8% for each 1000' DA above sea level
Variable pitch, non-turbo A/C climb performance decreases 7% for each 1000' DA above sea level
During each 1000' of climb, expect to see a loss of approximately 1” of manifold pressure
During each 1000' of climb, expect TAS to increase 2%
If you don't have 70% of your take off speed by runway midpoint, abort the take off
Level Off – Lead your level off by 10% of airplane’s rate of climb. e.g. – 500'/minute rate of climb; lead level off by 50'
Pressure Altitude – Set A/C altimeter to 29.92 and read PA from the altimeter
DA increases or decreases 120' for each 10°C the temperature varies from standard temperature
Standard temperature (ISA) decreases 2°C Per 1000' increase in altitude
TAS increases 2% over IAS for each 1000' above sea level
MANEUVERING
Maneuvering speed Va = ~1.7 x Vs1
Va decreases 1% for each 2% reduction in gross weight
Vy decreases ~1/2 to 1 knot for each 1000' DA
Vy, Vx and Vg (best glide) decreases ~1/2 Knot for Each 100 pounds Under MGW
Vr = ~1.15 x Vs
Cruise
The width of one finger = ~5NM on a sectional chart (average person)
Tip of the thumb to the knuckle = ~10NM on a sectional chart (average person)
Cruise fuel consumption of a non-turbocharged A/C engine = ~1/2 the rated HP/10
Cruise climb airspeed should be reduced by 1% for each 1000' of climb
To determine a relatively proficient cruise climb speed, take the difference between Vx and Vy and add that sum to Vy. For example, if Vx = 65 and Vy = 75, the difference is 10KTS. Add 10KTS to Vy (75KTS) and you have a cruise climb of 85KTS
Landing
Final Approach Speed = 1.3 x Vso. Also known as Vref
A tailwind of 10% of your final approach speed increases your landing distance by 20%; A headwind of 10% decreases landing distance by 20%
A 10% change in airspeed will cause a 20% change in stopping distance
A slippery or wet runway may increase your landing distance by 50%
For each knot above Vref over the numbers, the touchdown point will be 100' further down the runway
For each 1000' increase in field elevation, stopping distance increases 4%
A 10 Reduction in Approach Angle Will Increase Landing Distance 13%
10° – 25° of flaps add more lift than drag; 25° – 40° flaps add more drag than lift
Maximum Glide
Weight has no effect on max. glide range or ratio
Weight does have an effect on max. glide airspeed
Reduce glide speed 5% for each 10% decrease in gross weight
Tailwinds increase glide range; headwinds reduce glide range
With a 10, 20 or 30 KT tailwind, reduce glide speed by 4, 6 or 8 KT, respectively
With a headwind, increase glide speed by 50% of the headwind component
Maximum Glide = Minimum Drag. Low on fuel? Fly an airspeed equal to maximum glide to achieve maximum endurance
Other
Rollout from a turn – Lead your rollout by an amount equal to _ your bank angle. e.g. – 30° angle of bank; lead rollout by 15° prior to new heading
The radius of a standard rate turn in meters = TAS x 10
Most structural icing occurs between 0°C to –10°C
Deviate 10-20 miles upwind around thunderstorms; Don’t fly under anvil
Hail may be found 10 miles or more underneath the anvil
Dew point of 10°C or 53°F = Enough moisture present for severe thunderstorms
Compiled by Jim Van Namee. Jim is a CFII at Taos Regional Airport. He is a retired Naval Aviator and owner of Silver Eagle Aviation. Jim can be reached at 505-377-6786 or jimvn@aol.com.
Editor’s note: These “rules of thumb” are meant as general observations. Pilots should consult official materials, such as approved charts and aircraft manufacturers operating handbooks, for information specific to their aircraft or flight.
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| The material in this publication is for advisory information only and should not be relied upon for navigation, maintenance or flight techniques. SW Regional Publications and the staff neither assume any responsibility for the accuracy of this publication's content nor any liability arising fom it |
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