# How to Model the Aerodynamics of Landing a Falcon 9

I'm currently working on a landing simulation for the Falcon 9. One of my primary tasks is to model both the environment and the rocket. In a previous rough simulation, aerodynamics were mostly ignored. Now, I'm trying to improve on that, aiming to incorporate aspects like the effects of restorative torque. However, I'm running into some challenges and am seeking insights.

1. Coefficient of Drag: I've gone through a few papers on the topic of landing a rocket. Most of them either use a constant Coefficient of Drag (which seems like a very rough approximation) or a lookup table, based on the Mach number and angle of attack. However, they don't detail how they determined the values within these tables. Can someone guide me on how to approximate these more accurately? Is it reasonable to think of a rocket as a flat base cylinder and source some experimental data, or is that oversimplifying things? Should I, instead, use the coefficient from another rocket during launch (since those seem to be more available) and tweak them slightly? Additionally, I'm curious about the angle of attack's influence on the coefficient of drag. Is it primarily about the cross-sectional area, or is there more nuance to it?

2. Center of Pressure: I've been trying to figure out how to determine the center of pressure. All I was able to find were either very complicated calcultions, or methods for uniform pressure scenarios. I'm uncertain about calculating it during atmospheric descent. Are there any straightforward approximations for this situation?

3. Grid Fins: Given their importance, I'm keen on understanding how their effects can be implemented as well. Does it make sense to simulate the grid fins' effects distinctly? Or are they generally bundled with the overall net force acting on the rocket's center of pressure? To me, implementing them separately seems to be more simple to implement.

4. I've come across the idea that the gases expelled during the entry burn might act as a shield for the engine nozzles against drag, resulting in a different coefficient. That sounds interesting, but is it accurate?

Any guidance would be greatly appreciated!

• Have you considered exploring the Kerbal Space Program? A quick search shows that there are "shareables" for the Falcon 9 booster available online. I've not tinkered much with KSP, but the amount of information available within the program is substantial and may be useful to your quest. Commented Aug 12, 2023 at 18:13
• I looked into KSP. Wasn't able to get a lot of "detailed" information. Most explanations how the physics behind it worked was to focus on how to exploit it within the game. Commented Aug 12, 2023 at 23:10
• "resulting in a more favorable coefficient" -- what's a more favorable coefficient of drag during re-entry? Commented Aug 13, 2023 at 0:29
• @RussellBorogove That's a good point. Favorable isn't the correct term here, I'll edit it. Commented Aug 13, 2023 at 0:43
• " However, they don't detail how they determined the values within these tables." In my day, wind tunnels. Now, probably CFD. Commented Aug 13, 2023 at 1:04