Rate of closure, or closure rate, refers to the rate at which the distance between two aircraft is decreasing or increasing.[1] The rate is typically indicated as VC, is a foundational parameter in aerial combat and is the parameter always present on the TID besides the antenna elevation angle and height. More specifically it is
Sum of the components of fighter and bandit velocities that contribute to downrange travel. CNATRA P-825/17, 5-2
The rate is determined as the difference of the two velocities:
Back to Basics: Rate of Closure (Vc) by KARON, Fly and Wire, 14/08/2021 https://flyandwire.com/2021/08/14/back-to-basics-rate-of-closure-vc/
VC = VC(F14) – VC(TGT)
Where velocity is calculated as:
VC(F14) = VF14 * cos (BRG – HDGF14)
VC(TGT) = VF14 * cos (BRG – HDGF14)
Resulting in:
VC = VF14 * cos (ATA – HDGF14) - VTGT * cos (ATA – HDGTGT)
- ↑ "Back to Basics: Rate of Closure," Karon, Fly and Wire, 14/08/2021