This reply is talking about the in game footage of Tomcat launching Aim-54 I posted above: The AIM-54 Phoenix missile - Technology, History and Performance - #1106 by SE_8749236
TL;DR: The Aim-54 in game is estimated to have a drag coefficient of ~4.25, a typical amateur rocket IRL has drag coefficient of 1 or less.
Using in game footage and kinematics, we can estimate the drag force that the Aim54 is receiving.
With aircraft as reference frame, Aim-54 starts at 0m/s and displacement of 0.
After launch and it starts fall behind, when ignition, it was displaced backwards by ~10 meters.
I’ll calculate 5 meters displacement as well in case I’m over estimating the distance it moved backwards.
10m:
Using d = v1t + 0.5at^2, you get:
10m = 00.5s + 0.5*(a*(0.5s)^2
10m = 0.5*(a*(0.25s^2)
a = 10m / 0.5 / 0.25s^2 = 10 * 2 * 4
a = 80m/s^2
F=ma, and let’s use the lighter Aim54A, m=443kg.
F = 443 * 80 = 35440N of force.
This is clearly an overestimation, since this is more than twice the thrust of Aim-54.
5m:
Using d = v1t + 0.5at^2, you get:
5m = 00.5s + 0.5*(a*(0.5s)^2
5m = 0.5*(a*(0.25s^2)
a = 5m / 0.5 / 0.25s^2 = 5 * 2 * 4
a = 40m/s^2
F=ma, and let’s use the lighter Aim54A, m=443kg.
F = 443 * 40 = 17720N of force.
This is still more than the thrust of rocket motor.
Perhaps base drag reduction is already implemented.
I did calculation wth 4m, since it can’t possibly have displacement less than 4 meters since the missile clearly moved at least its body length after launch but before ignition.
4m:
Using d = v1t + 0.5at^2, you get:
4m = 00.5s + 0.5*(a*(0.5s)^2
4m = 0.5*(a*(0.25s^2)
a = 4m / 0.5 / 0.25s^2 = 4 * 2 * 4
a = 32m/s^2
F=ma, and let’s use the lighter Aim54A, m=443kg.
F = 443 * 32 = 14176N of force.
For comparison, Aim54’s rocket motor in game has 14350N of force.
This yield a net force of 174N, which translates to ~0.4m/s^2 of acceleration, or 1.44km/h per second.
If base drag reduction is not modeled b=ub gane, Aim-54 in game shouldn’t accelerate noticeably at all. Thus base drag reduction is likely modeled.
However, the drag is still way too big and it significantly negatively affects Aim-54 after its burn ends.
If we use drag equation we can estimate the drag coefficient of Aim-54:
Launch speed = 337 knots = ~624km/h = ~173m/s
Launch altitude = 31841ft = ~9705m ==> air density = less than 0.4671.
Missile cross section area when nose first (using 0.39m diameter to compensate for fins): ~0.477m^2
Equation: drag = CA0.5pv^2, C = drag coefficient
Assuming drag = 14176N
14176 = C * 0.477 * 0.5 * 0.4671 * 173^2
C = 14176 / (0.477 * 0.5 * 0.4671 * 173^2) = 14176 / 3334
C = ~4.25
That’s a drag coefficient of whopping 4.25, even worse than a bowl with concave side facing towards the air stream.
This doesn’t make sense for a streamlined missile.
Even if you play with the number and get the estimated drag coefficient down to 2, it is still way worse than IRL. Since typical amateur rockets has drag coefficient of 1 or less when not burning.
This means either CxK is not drag coefficient for missiles and it needs to be lowered, or CxK is drag coefficient but War Thunder has bug where missile’s drag coefficient is 4 times (or more) than it was supposed to be.
