Flight computers, static fires, and more! (Patreon)

This past week BPS moved forward on a few fronts! First, let's talk about parachutes.

In the previous post, I talked about testing ejection charges. During the testing, I placed a charge in a placeholder airframe, and ejected a nose cone off. The test returned good results, so I performed a second test with the parachutes and webbing(shock cord) installed in the vehicle. This test returned poor results, and I can explain why! 

Think of the top half of Scout as a pressure vessel. It's not airtight, but for our purposes, we'll pretend that it is. When the ejection charge fires, the pressure in the airframe increases, and the air starts looking for ways to escape. The easiest way is to pop the nose cone off, so that's what happens. As soon as the nose cone is off, all the pressure is relieved. In some traditional model rockets the weight of the nose cone is large enough, and the friction of the parachute is low enough, that the cone actually pulls the parachute out with the momentum it has.

Scout's nose cone is 3D printed, and is extremely light, so it's inertia is quite low. That means there was not enough force to pull the chutes out, even with a fast moving nose cone. "So Joe, what is the solution?" Great question! I asked my friend, Charlie, the same thing and he suggested I try a piston based approach. By using a piston only slightly smaller than the airframe, we can effectively reduce the size of the "pressure vessel" in the rocket. With this piston, the charge pressurizes the vessel, which pushes the piston up. The piston pushes out the parachutes, shock cord, and nose cone, then itself, at which point the pressure is dumped outside the rocket. Here's a video of all the ejection testing: https://youtu.be/DdNQEEugiBc

Next up, is a series of static fire tests, held out in Los Angeles, CA. Jonny Hyman is a good friend, and fellow VTVL pursuant. He's working on achieving VTVL through hybrid rocket motors, and has built a motor test stand to work on them. Jonny has so far conducted 3 out of 4 planned static fires with the F15 motors Scout uses. The tests are returning some great data so far. We're looking specifically at the average number of milliseconds between sending current to the ignitor, and having the F15 come up to peak thrust. In addition, were looking to characterize the thrust differences between separate motors, which so far seem to be fairly small. The 4th test is on schedule to be conducted tonight, after which we'll start working with the data to solidify our results.

Lastly, yesterday the new PCBs for the Signal flight computer came in! I assembled all the parts and was able to boot up the computer and successfully read good values from all sensors. There are several small issues with incorrect part specs. Most can be fixed with the current build, though some will require a new shipment of PCBs :( The largest so far is the Signal GUI; the screen and buttons used to read out data and program the flight computer on the pad. I don't need this screen for my purposes, but the end users of this board will. I'm sure I can find a workaround for now, which will allow me to finalize the user interface of Signal Avionics. 

Bit of a large post, but that's all for now, thanks for reading!