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Weapons & Countermeasures Modeling in Falcon 4.0:
Interview with Realism Patch Group's "Hoola"
by Paul Stewart[Paul] I see. When you modeled the kinematic properties for the missiles in F4, what variables did you take into account when designing them?
[Hoola] I took into account the engagement scenario when determining the missile kinematics. F4 is hardwired to have a simple 6-degree of freedom model for the missile. Some variable like motor thrust is fixed, and invariable with atmospheric pressure. These should be variable, but should not matter that much. The kinematics were tuned under approximately 100-150 different firing scenarios, such as head-on, tail-on, beam, snap-up, snap-down, against various target maneuvers, and what I did was to examine the missile energy bleed rate and tracking performance (such as how much lead it pulls, how much it compensates for the LOS rate, etc).
[Paul] I distinctly remember that, when you looked at things like range, etc, you used your knowledge of things as minute as the shape of the "ogival" dome of the AA10B to factor in. Could you go into how your knowledge of the missiles factored in....it seem you used your knowledge about the physical characteristics of the missile themselves...
[Hoola] What I did was to use my knowledge of aeronautics to do the missiles. Many aspects of missiles are similar to airplanes, such as usage of reference lengths, reference areas, force coefficients, etc.
The reference lengths/areas and force coefficients are engineering forms of representing the forces that will act on a missile (put in simple terms). These forms the basis of missile kinematics, i.e., to solve the 6 degree of freedom equations embedded in the F4 .exe for each missile motion.
[Paul] I'd like to discuss the missile modeling process a bit more in detail. One of the missiles that was most changed was the AA10C. It used to be a 50nm missile with incredible lethality. Now it has a variable range anywhere between 8 and 25nm depending on the engagement geometry. How did you arrive at its rocket propulsion times, its thrust? How its kinematic range gets determined? Why cant a user just go into the "dat" files and just "decrease the burn time" to get the same effect?
AA-10C “ALAMO” SARH Missile
[Hoola] The rocket propulsion times are all based on the layout and geometry of each missile. What I did was to examine the drawings of the missiles, as well as the photographs, to determine the component location and approximate size (such as GCS location, warhead size, servo locations, etc). Based on this, the burn time is modeled, and the thrust profile tailored in repeated ballistic firings to determine the acceleration rate. This was how the boost-sustain profile was done.
Of course there is a certain amount of educated estimation about the thrust profile and burn times, but this comes with some experience and knowledge. There are quite some data on generic rocket motors available to the public, but these are usually hidden somewhere in obscure trade publications and technical journals.
As for range estimation, we considered the published specifications, and then modeled the possible aerodynamic coefficients. There are ways to do this, such as using simplified ogive bodies etc. This gives the ballpark numbers to start with. Then, energy bleed rate is tested by firing at different altitudes, etc., both ballistically and against targets of various profiles.
A lot of what we did on the AA-10C stemmed from interpreting the published specifications carefully, tempered with some of my experience in the field of knowing what numbers are sensible to use and what aren't.
An important thing that many people do not understand, is that the kinematic models in F4 are inter-related, and you cannot achieve an accurate model by fiddling with one coefficient and not another. Simply reducing the drag may not be good enough, ditto changing the burn times. There are occasions where specific problems crop up at a combination of dynamic pressure and Mach, and I had to look specifically into a specific Mach number to correct an energy retention problem. These are needed as problems can be very specific, and making gross changes to one aspect will usually throw the entire model off, such as playing with burn time, Some understanding of aeronautics, flight dynamics and control/guidance systems will be very helpful.
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