Kevin, these are some of the practical issues of FAI NLF design that I hope you can address. The design has to not only perform every aspect of it's mission, but be producible as well. One could imagine rear ejection through a 10mm motor hole, but that is not practical for most events, and a more traditional separation line and ejection is needed. This separation line could cause the flow to transition from laminar to turbulent, so it's location and mitigation is important. Furthermore, low airframe mass is also important. The structural efficiency of cones and cylinders is higher that that of constant curvature structures, so one might have to accept higher mass in a NLF design, or adopt more extreme construction methods. I know that you have adopted a somewhat traditional composite hand layup in a female mold using a bladder. You have validated an overall performance increase of 30%, so you are obviously doing something right. I had been considering winding fiber over a male mandrel, which may have to be sacrificial, and would also require a bit of surface finishing. Placing the separation line at the maximum body diameter would certainly make removal from the mandrel easier. The logical place to put the separation line is at the the laminar to turbulent flow transition ramp, although this places the separation line pretty far aft, but with a large aperture. I noticed that placed your separation line forward, where a more traditional nosecone cylinder separation line would be. Did you find transition at that line to be a non-issue, or did you have to induce a favorable pressure gradient at that point to avoid transition?
I found your "crazy flow interactions at the fins" most distressing. I had hoped that that would just be a non-issue. The boundary layer flow should already be turbulent, so transition is not the issue, but flow separation is. A related concern is if the motor jet could have an adverse effect on the flow, or even if acoustic and vibration noise could cause the boundary layer to transition. More generally, how did you address robustness in your NLF design? How mush angle of attack can you tolerate before the flow transitions?
I abandoned my research in 1990 before reaching the flying stage. It is great to see that this technology finally got off the ground, and also sad that I could have advanced the state of the art by 30? years. I still find NLF sport rocketry a fascinating subject and I hope that you will continue to discus it.
Alan