Rocket Pictures #7

Computational Fluid Dynamics (CFD) is a method to calculate fluid flow in, or around objects. It is like running a virtual wind tunnel. I recently attended a class to learn how to use a package at work. The instructor told us to bring a project to practice hands-on. Silly me, I brought something fun to work on! (Come to think of it, I may be earning a reputation with our instructors, when I bring in home projects to play with!). I modeled an Estes Alpha, to see what effect launch lugs have on the drag. This has fascinated me since the 70s when I read about the influence of launch lug drag in the Estes report "Aerodynamic Drag of Model Rockets" TR-11.

According to RockSim, an Alpha on a C6-5 has a top speed of 522 ft/sec. I ran three cases:

1. No launch lug.
2. Launch lug mounted at the CG (stock, per instructions).
3. Split launch lugs, one at the base of the nose, and the other between the fins.

The results are inconclusive, since I left the bottom of the rocket flat, there is a large low pressure area behind the rocket, giving a false drag reading. I need to add a tail cone and rerun the analysis. The plots below show some initial results.

Since this was a training class, I didn't have time to complete the analysis. We were running on really old PCs, and each run took about an hour. There are a bunch of settings I could tweak to get better resolution, but that will have to wait until I am back on my "home" monster machine. I also got one shot to create the graphics, and I failed to make the color scale legends the same for all cases. Once we get the software installed, I plan to work on this to see if I can determine an optimum launch lug size and placement.

For more information on CFD analysis, go to CFD Online