adrian
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- Jan 19, 2009
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... or Simulation Vs. Swing Test.
This is Green Cheese, a proposed but never built British nuclear anti-ship missile:
https://www.skomer.u-net.com/projects/greencheese.htm
The appearance is not all that inspiring, but with that name it had to be done. The problem is obvious - the fins are very low span. With a model based on BT-60 tubing and a hollow hemispherical nose working out at 10.75" long, VCP and Rocksim with its various calculation methods put the CP somewhere between 4 and 5" from the tip of the nose.
Building the model during International Rocket Week in Scotland, I stuffed what clay (actually Play-Doh) I had into the nose, and the CG ended up right in the middle of the various CP estimates. Nevertheless I put a C6-5 in the back and swing-tested the model, which "flew" perfectly. And it's never going to get a C6-5 in actual flight - C6-3 tops.
The next thing to try was a real launch. I marked the flight card "Rocksim says it's unstable, swing test OK, now we find out which is right". Not surprisingly it was announced as a heads up flight. In fact it was a straight up flight, albeit on a B6-2 for this test.
The lighter motor didn't move the CG much. Besides, now I'm back home from IRW I can put a bit more nose weight in to account for the difference between a B6-2 and C6-3 before the model goes up on full power...
This is Green Cheese, a proposed but never built British nuclear anti-ship missile:
https://www.skomer.u-net.com/projects/greencheese.htm
The appearance is not all that inspiring, but with that name it had to be done. The problem is obvious - the fins are very low span. With a model based on BT-60 tubing and a hollow hemispherical nose working out at 10.75" long, VCP and Rocksim with its various calculation methods put the CP somewhere between 4 and 5" from the tip of the nose.
Building the model during International Rocket Week in Scotland, I stuffed what clay (actually Play-Doh) I had into the nose, and the CG ended up right in the middle of the various CP estimates. Nevertheless I put a C6-5 in the back and swing-tested the model, which "flew" perfectly. And it's never going to get a C6-5 in actual flight - C6-3 tops.
The next thing to try was a real launch. I marked the flight card "Rocksim says it's unstable, swing test OK, now we find out which is right". Not surprisingly it was announced as a heads up flight. In fact it was a straight up flight, albeit on a B6-2 for this test.
The lighter motor didn't move the CG much. Besides, now I'm back home from IRW I can put a bit more nose weight in to account for the difference between a B6-2 and C6-3 before the model goes up on full power...
