Contents

RULES OF THUMB
Before thermometers were invented, brewers would dip a thumb or finger into the mix to find the right temperature for adding yeast. Too cold, and the yeast wouldn't grow. Too hot, and the yeast would die. This thumb in the beer is where we get the phrase "rule of thumb."

Basic Rule of Thumb:
You won't remember a rule of thumb unless you use it.

The Flying Rule of Three
If three things go wrong on the ground before departure…don't depart.
If three things go wrong in the air…get on the ground.

TEMPERATURE
Double the degrees Celsius, subtract 10% (round up), then add 32
15deg;C = 15 + 30 -3 = 27 + 32 =59

Rule of thumb:
To find standard temperature Celsius for a given altitude you should double the altitude, subtract 15 and place a - sign in front.

DEW POINT
Subtracting the dew point from the surface temperature, dividing the difference by 4.4 and then moving the decimal point three places to the right can approximate the base of a cumulus cloud. Surface dewpoint and temperature is commonly part of every ATIS.

LANDING PERFORMANCE
Actual touchdown speed answer x itself (squared)
Proper touchdown speed
Use the number greater than 1 as a % . This is the % greater the landing distance will be.
--Use of this formula is a good reason to believe in the importance of precise speed control in landing.
--Standard distance between runway lights is 200'
--Have passenger count lights to determine your aircraft performance.
--Takeoff and landing distances in the book are of maximum performance type. For normal operations double the book figures.
--Ground speed at which hydroplaning will occur is seven times the square root of the tire pressure.

DESCENT
1. Multiply your present altitude times three and the product is the distance from your destination altitude which you should start down.

2. The rate of descent is based on indicated airspeed. Divide ias by two and add a zero. This is the rate of descent required for the distance to be covered.

(150kt range of ground speeds)
3. Distance to Descend
Two times the ground speed in miles-per-minute times the altitude to lose in thousands of feet.
Example:
Ground speed in descent 120 kts (2 miles per minute). To lose 5000' from 8000 to 3000 you must start your descent 20 miles out from your 3000' mark. 2 x 2 = 4 x 5 = 20 miles out

4. --Take three times your height above destination to the nearest 1000'. Multiply by four. Gives descent distance in miles to begin 3-degree descent.
5. --To get a 3 degree descent profile multiply your ground speed by 5 to get a fpm descent.
6. -- Take 1/3 of altitude-to-lose to get distance, descent at 1/2 ground speed.
7. --Take half of ground speed and add a zero for descent rate.
8. Ground speed times 5 to get VSI rate of descent giving 3degree slope.
9. -- For establishing a 3 degree slope descent is to multiply your ground speed by 5 and add 50. Not exact but good enough

Engine Failure Descent
You have a minute in the air for every 1000' of altitude
You can expect to glide one mile for every 1000' of altitude.
A 360 will lose 1000' of altitude
Land into the wind with the rows.

Distance to Initiate Descent
Distant to descend divided by 1000 (knock off zeros) and multiply by three will give distance.

Distance for 500 fpm Descent
Altitude to lose expressed in thousands of feet times groundspeed in miles per minute x 2
5000' to lose at 120 knots gives 5 X 2 X 2 = 20 as the miles needed at 500 fpm descent.

Using ground speed to get rate of descent
Divide ground speed by two and add a zero.

Navigation Error
The "1 in 60 rule" may come in handy too. The 1 in 60 rule says that for every 1 degree off course you are, you are 1 mile off course at 60 miles.

WEIGHT
Rule of Thumb:
--Figure weight and balance when seating is over half filled or luggage carried.
--A 2% increase in weight will cause a 1% change in stall speed.

RECIPROCALS
Rule of Thumb
The 22 rule for Reciprocals
Take any heading and the first digit, 0, 1, 2, or 3. Add or subtract 2 to the first digit to get a 0, 1, 2, or 3 for an answer. If you add then subtract 2 from the second digit, if you subtract then add 2 to the second digit. Third digit remains the same.

COMPASS TURNS
Rules of Thumb compass turns:
--Compass turns can be made by time with a standard rate of 3-degrees per second.
--For recovery from a bank to a given heading is to lead by half the angle of bank + any other requirement below.
--When turning Northerly, undershoot the heading by the latitude in degrees plus half of the bank angle.
--When turning Southerly, overshoot the heading by the latitude minus half the bank angle.
--When turning East or West from the South roll out 5 degrees early.
--When turning East or West from the North roll out 10 degrees early.

KNOTS TO MILES PER HOUR
The conversion from Knots to MPH is about 1.15. This means that MPH are Knots with a 15 percent tip. If you aren't a big tipper the conversion can be done by whatever method you use to figure how much to leave with a 15 percent tip.

Simple way:
Take 10% and then add half that.

The method I use is to mentally drop a zero off of the number to divide by ten, then take half what I get, add those two figures and add them to the original amount.
120 Knots 10% = 12 and half that = 6
12 + 6 = 18 and 120 + 18 = 138 MPH

Even going with 150 Knots 10% = 15 and half that = 7.5
15 +7.5 = 22.5 and 150 + 22.5 = 172.5 and I doubt it's necessary to get down to that point five. So round up or down and it either comes out as 172 or 173.

Miles to knots and back.
A quick and dirty technique that seems to work
The difference between knots and MPH is about fifteen percent.

Move the decimal point one place to the left. That divides by ten. Add half of that to get fifteen percent. Going from knots to mph, add it. Going from mph to knots, subtract it.

Continue To Next Page