Conversions

1 MPH = 0.87 Knot

1 Knot = 1.15 MPH

1 MPH = 1.61 Kilometer Per Hour (KPH)

1 KPH = 0.62 MPH

1 Knot = 0.51 Meters Per Second (MPS)

1 MPS = 2 Knots

1 Knot = 1.85 KPH

1 KPH = 0.54 Knots

Calculating Speed

Ground Speed = KTAS - Headwind or KTAS + Tailwind

Groundspeed = Distance / Time

Example:

Distance = 50 NM

Time = 25 minutes

Groundspeed = 50 / 25 = 2 NM per minute

2 NM per minute x 60 minutes = 120 NM per hour

NM / Minute = True Airspeed (TAS) / 60

Example:

TAS = 120 knots

120 / 60 = 2 NM per minute

Rule of Thumb

Note the time required to fly a certain distance, then form a fraction by placing the distance over the flight time. Multiply the denominator by a number that will yield approximately 60, then multiply the numerator by the same number to get the groundspeed.

Example:

12 minutes is required to fly 27 NM (27/12)

12 x 5 = 60

27 x 5 = 135

Groundspeed is 135 knots

Rule of Thumb

36 seconds is 1/100 of an hour. Determine your ground distance flown in 36 seconds, and multiply by 100 to get your groundspeed.

Rule of Thumb

To estimate the approximate TAS increase the IAS shown on the airspeed indicator by a percentage equal to double the number of thousands of feet.

Example:

At 5000 ft MSL, increase IAS by 10% to obtain the TAS.

At 10,000 ft MSL, increase the IAS by 20% to obtain the TAS.