The grain
A block of magnesium, Teflon and Viton, burning from every face.
An MJU-7 class flare is a 1 × 2 × 8 inch cartridge, the one most western fighters carry. Chemring publishes its drop-in, the CM 218, as 253 g of MTV in a 51.8 × 24.6 mm case. The grain fills the case less its walls, a millimetre each side.
MTV1, the baseline composition, is half magnesium, 45 % Teflon and 5 % Viton by mass. Pressed to its theoretical density, the mass over the sum of each ingredient's volume, it is 1906 kg/m³, so 253 g is a grain about 12 cm long.
It burns from every face at once, each receding at the composition's linear burn rate: 3.86 mm/s for MTV1, as Debnath et al. measure it (CEJEM 22(2), 2025). A block a × b × c is (a − 2rt) × (b − 2rt) × (c − 2rt) at t, and is gone when its thinnest side is: 22.6 mm over twice 3.86 mm/s, 2.9 s.
What it burns a second is its density times the rate times its burning surface. It burns fastest as it lights, and less as it shrinks.
Left out
- The burn rate's pressure: an MTV grain burns a little slower in thin air. It is the measured rate at every altitude.
- Ignition: the grain lights as it leaves the dispenser, where a real one's igniter takes a fraction of a second.