Creamy Robot Goodness

So I’ve been working on a project for a couple of weeks now and I guess I haven’t said anything about it on here. Well here it is: I am trying to develop a rocket-boosted ramjet, and I want to be possibly the first amateur to actually fly a ramjet-powered vehicle. (A group in Israel launched a rocket-boosted ramjet a year ago, but it took 5 years of senior design groups and a professor to pull it off, and it only burned for about 2 seconds before burning out prematurely — I’m hoping I can do better.) For the uninitiated, a ramjet is basically the simplest type of jet engine. It has no moving parts, and above about Mach 3 it’s actually the most efficient way to move through the atmosphere. The thing that makes it tricky is that it generates barely any useful thrust until it’s going at least 200-400MPH. That’s a tall order for an RC aircraft engine, but what about a rocket? It’s been done by NACA/NASA and a couple of world militaries, so it’s obviously possible, and I’m hoping to do it myself. I’ve been developing a simple Excel spreadsheet to simulate the performance of a vehicle which is powered by any combination of rockets, ramjets, and cannon power. I’m by no means an expert at this sort of thing, but I think it’s a good start. I pitched my current version over at the pulse-jets.com ramjet forum, but haven’t gotten much feedback yet. I have been exchanging ideas with James Irvine (of Australia), and he may actually make me a simple ramjet engine to experiment with.

Unfortunately with the current version I have been unable to produce a Decker-inspired design that is self-sustaining. I am hoping this is due to an inaccuracy in the drag model. I am considering trying to determine a model of the drag forces empirically, possibly by building a scale model of the vehicle and flying it on a known rocket engine. Perhaps by tweaking frontal area and Cd values in RockSim and in my spreadsheet until they agree with actual flight data I can come up with something usable.

Hmmmmm….. How about a tool that read in flight data in the form of acceleration and/or altitude over time (maybe altitude would be easier for most people to come up with), along with a thrust curve for the motor, and it would produce a graph of estimated drag force? Of course the results would vary from flight to flight, but the more flights, the more accurate the data. Flying the same rocket a number of times, this tool could produce a statistically useful summary of drag forces vs speed. With a direct model of drag forces, one would not even need to mess with something so crude as a Cd. Oooohhhhh….. And one could even fly a version of the rocket without the ramjet engine attached in order to determine how much drag is caused by the ramjet engine itself. Oh man that would be useful….

This entry was posted on Tuesday, December 4th, 2007 at 9:51 pm and is filed under News, Projects, Rockets. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.