I'm collecting some experimental data for calibrating stability calculations. I need a range of airframe shapes with different properties that I can swing test or wind tunnel test, then compare the results with computer simulations.
I figure the easiest way to do this is using cardstock models, because I can design families of parts (different fin shapes, nose lengths, body lengths, etc) and print them out to mix and match. And I can add measurement marks as part of the printed template.
Here's the first one:
The body diameter is 13.2mm, the same size as a BT-5 or T motor rocket. The test jig is built around a plastic T engine hook retainer, with a string and a weight at the far end. The weight keeps everything straight when the jig is hung or swung so the model can be slid to pivot at different points without having to rebalance the center of gravity.
This model is designed so the projected side area of the small fins on the back is exactly the same shape as the nose cone in the front, so using the lateral area method predicts the CP at exactly the center point of the model. I expect the real CP to be behind the center because fin area should be more effective than body tube area for moving the CP, and measuring this thing should act as a sensitive test of how big the difference is.
So it's not a typical cardstock rocketry project, and strictly speaking it's not even a rocket because there's no place to put an engine. But it's a thing I made, and I wanted to talk about it.
It's built from 65# cardstock with a printed SVG template. There are some fit problems; I need to increase the allowances for paper thickness a bit next time.
It looks like the forum won't let me post an SVG file...
I figure the easiest way to do this is using cardstock models, because I can design families of parts (different fin shapes, nose lengths, body lengths, etc) and print them out to mix and match. And I can add measurement marks as part of the printed template.
Here's the first one:
The body diameter is 13.2mm, the same size as a BT-5 or T motor rocket. The test jig is built around a plastic T engine hook retainer, with a string and a weight at the far end. The weight keeps everything straight when the jig is hung or swung so the model can be slid to pivot at different points without having to rebalance the center of gravity.
This model is designed so the projected side area of the small fins on the back is exactly the same shape as the nose cone in the front, so using the lateral area method predicts the CP at exactly the center point of the model. I expect the real CP to be behind the center because fin area should be more effective than body tube area for moving the CP, and measuring this thing should act as a sensitive test of how big the difference is.
So it's not a typical cardstock rocketry project, and strictly speaking it's not even a rocket because there's no place to put an engine. But it's a thing I made, and I wanted to talk about it.
It's built from 65# cardstock with a printed SVG template. There are some fit problems; I need to increase the allowances for paper thickness a bit next time.
It looks like the forum won't let me post an SVG file...
