Von Kármán Profile
Meanwhile I’ve decided to house the secondary ebay (electronics bay) in the rocket’s nose cone, I’ve spent some time to study the various options available to do so. All of them would require the build of a new ebay because existing 4” models won’t fit in a 4” nose cone. The main problem is that the available diameter rapidly decreases toward the top, and therefore it minimizes the length of the ebay. And that doesn’t work for me, since I need a fair length as shown in earlier posts. Another option is to drop the traditional architecture of an ebay and to seal the two aluminum mounting rods directly into the nose cone’s top, and use a bulkhead to close the cone. However, this approach has two drawbacks. First, the spacing between the rods suffers the same diameter reduction problem as the custom ebay. Second, it leaves the electronics un-protected. So instead, I’ve decided to buy a new 4” nose cone kit designed to house a 4” ebay. I’ve also used the opportunity to upgrade the rocket with a Von Kármán profile (5.8:1 length-to-diameter ratio), which minimizes the drag for a given length and diameter. A much better performance than the conical 3:1 length-to-diameter ratio profile I’ve initially picked. If you are interested in nose cone profiles, this NASA paper mainly studying the exhaust nozzles’ performance in wind tunnels also contains a secondary study on nose cones, mentioning the VK profile. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100019443.pdf. Of course, many other references are available on the web. I am still working on my shopping list for other key components. I hope to have all parts in-house – except the engine – early 2017!