BFM Plotter
← Home

BFM Plotter

Set the start, log each snapshot off the tape, and the board draws itself. Nose angle counts as down unless you tick Up.

Start disposition

Range is the plan distance between the jets at snapshot A. Bearing is measured from #1's nose, clockwise: 90 is #2 at 3 o'clock, 270 is 9 o'clock.

Settings and how it works
  • Distance = average Mach × speed of sound × time. 660 kt suits a warm day at 5,000–15,000 ft; use about 640 kt on a standard day.
  • Board length = distance × cos(average nose angle). Nose angle means flight path, not pitch attitude.
  • Each segment becomes 4 legs (6 if it turns over 180°), each pointing at the middle heading of its chunk. Later legs shrink as the jet slows, assuming steady G.
  • Altitude is optional after snapshot A. Left blank, the plotter predicts it from the nose angle. Filled in, it flags a mismatch over 500 ft, which usually means pitch attitude was read instead of flight path, or Up was missed.
  • Wind is ignored. Both jets drift together, so the picture between them is unchanged.
  • Board ft per cm: 240 matches 12.5 cm = 3,000 ft.

Board

t —

#1 #2 Each line ends in an arrowhead at the next snapshot. Turn on Time links to join the jets at the same moment.
Drag a snapshot to adjust it. A moved snapshot shows a prime mark, such as B′.

3D view

Drag to rotate, scroll or use + and − to zoom. Height is true scale by default. A higher vertical setting makes climbs and dives easier to see, but steeper than they were. Dashed drop lines and floor shadows show where each jet is over the ground. Altitude runs evenly between snapshots; * marks a predicted altitude.

At each snapshot

Geometry

ATA: angle from a jet's flight path to the other jet, with the side it lies on. Aspect: how far off the other jet's tail you sit, 0° tail-on, 180° nose-on, and which side of it you see. HCA: angle between the two headings. Closure is positive when closing. Angles use flight path, not nose position, so at high AOA the real nose leads by up to the AOA. During playback the top row follows the slider.

Legs for the board

Lay each leg with the ruler at its heading, for its length, then smooth through the corners.