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Update: Whatu has developed an offline/standalone calculator. You can download it here: RODv1 (54.55 kB).This version is specially useful when no Internet connection is available. Thanks Whatu for sharing.

Have you ever faced the following situation while flying in Flight Simulator?

I am 7nm from the airport at 3000ft. What descent rate ft/min should I use to get to the airport?

I have faced this situation many times, specially when executing non precision approaches. Decided to do some math and created a Descent Rate Calculator. 

Given the desired approach speed, the heading for the final approach, the initial altitude, distance to the runway, runway elevation and winds information, the calculator finds out the head and cross wind components, ground speed, estimated time of arrival and descent rate. The following is a description for each parameter:

Approach Speed: The desired Indicated Airspeed (KIAS) for the final approach. Example: 120 knots

Runway Heading: This is the heading to fly for the final approach.

Altitude Leaving: Is the altitude at which you expect to start the descent.

Distance to Runway: Is the distance from the start of the descent to the runway Touch Down Zone. 

Runway Elevation: Terrain elevation at the runway.

Wind Direction: Heading from where the wind is blowing. Obtained from METAR or wind checks.

Wind Speed: Speed at which the wind is blowing. Obtained from METAR or wind checks.

The calculator provide default parameters. These parameters can be modified according to your situation. Just delete the default and enter the desired value. When all the parameters are populated, press the "Calculate" button. The calculator will provide the following output:

Head Wind Component: The equivalent wind speed blowing in front (head) of your plane. If the result is negative, then the wind is blowing from your tail.

Cross Wind Component: The equivalent wind speed blowing from the sides of your plane. If negative, the wind is blowing from your left. If positive, from your right.

Wind Correction Angle: The amount of crab angle required to achieve the Runway Heading in degrees. Positive (+) value means a crab to the right A negative (-) means a crab to the left.

Final Heading: The heading required to correct (crab) deviation due to wind.

Ground Speed: The speed of your ground track.

ETA: Estimated Time of Arrival. The amount of time it will take from the start of the descent to the landing.

Descent Rate: The rate of descent required to avoid overshoot or undershoot the runway.

Formulas: 

The tool implements Ed William's Wind Triangle Formulas with minor modifications to tailor to my conventions. However, the tool does not check for "impossible" situations like flying an approach speed slower than head wind component.  

 

Head Wind = Wind Speed * COS (Runway Heading - Wind Direction)

Cross Wind = Wind Speed * SIN (Runway Heading - Wind Direction)

SWC=(Wind Speed/Approach Speed) * SIN(Wind Direction-Runway Heading)

Ground Speed = Approach Speed * SQUAREROOT (1-SWC^2) - Head Wind 

Estimated Time of Arrival = Distance to Runway * (60 / Ground Speed)

Descent Rate =  (Altitude Leaving - Runway Elevation) / Estimated Time of Arrival

Wind Correction Angle=ASIN((Wind Speed/Ground Speed)*sin(Wind Direction-Runway Heading))

Final Heading =  Runway Heading + Wind Correction Angle

 

Final Comments:

Comments, corrections and suggestions are encouraged. Finally, the calculator is for flight simulation use only. Use it at your own risk and discretion.