The MR-1 Diversion Ruler/Plotter was developed to assist both student and experienced pilots in Visual Flight Rules (VFR) conditions. It’s a perfect tool for those undertaking their Private Pilot Licence (PPL), or Commercial Pilot Licence (CPL). Especially if you’re getting towards the end of your navigation experience.
But recently we’ve been asked: “How exactly does the Fly GA MR-1 Diversion Ruler work?”
Well, it’s actually very simple. I’ll explain…
Step 1: Use the Compass Rose to establish True Baring
The Diversion Ruler’s transparent 50mm Compass Rose includes 5 and 10 degree markers.
Simply place the Compass Rose over the adjoining lines of the marked-out route in order to determine the baring. Be sure to correctly direct the ruler in the North direction.
In the below example, the baring is 045 degrees.
Note: this doesn't account for wind. You'd need to adjust accordingly.
Step 2: Measure the Length of the Route (In NM)
The Diversion Rulers are scaled at 1:500,000. You can measure up to 40 NM.
For this step you simple need to measure the length of the straight line route for which you’ve established true baring.
The route in our example is 34 NM.
Step 3: Use the Speed/Time Conversion Table to Estimate Journey Time
The Diversion Ruler’s speed/time conversion table (in the centre) takes away the need for mental calculations during the planning and diversion segments of the PPL syllabus. The table works for speeds from 70kts to 160kts up to a distance of 40nm. Importantly, this tells us the time, in minutes, that it takes to complete the journey.
All you have to do is look at the table and read-off whatever minutes figure aligns to the length (in NM) you measured in Step 2. Be sure to read from the row with the Knotts that are applicable to the plane you’re flying (e.g. 90 Kts for a Cessna).
In our example, the Diversion Ruler calculates that we’ll take approximately 26 minutes to fly 34 NM, using a Cessna (90 Kts).
Note: for longer routes you'd usually check the time it took to travel 1/2 the distance, and then update the remainder of the journey accordingly.