Wednesday, July 11, 2007

This weeks plans.

We are planning to do a test fire again this Saturday. We have made a number of changes. We have added very very fast butterfly valves just after the main (slow) ball valves. We hope this will have a bit more linear throttle action and be somewhat faster. Toward that end we have set up a flow test with an exact engine string, pressure transducer, ball valve, butterfly valve , pressure transducer,turbine flow meter , long tube and pintile orifice. We have started mapping how linear the valve is and it's flow response. This will all be on the test stand before Friday.

In addition I found some very small isolated thermocouples and we will instrument the fuel temperature rise for this event. So this weeks fireeing should generate some good data. I always planned to have the thermocouple, but the non-isolated version had some ground loop problems that totally swamped the signal I was trying to measure.

On the stability and control front I upgraded my helicopter from a Trex 450 to a Trex 600, it no longer wallows with the IMU, GPS and computer attached. We will report more on this effort next week.


Anonymous said...

Out of curiousity are you using an off-the-shelf butterfly valve, or did you make your own? And how much faster has it turned out than just using a ball valve?

Anonymous said...

I'm wondering about the stability of your system design with engines widely spread. The Masten design is similar and they seem to be having a lot of problems, if their videos are any indication. Though I am not a rocket scientist, it seems to me that having the engines at the end of such long moment arms is likely to exaggerate minor inconsistencies in the thurst and timing of firing, making the control problem a lot harder. On the other hand, clustering the engines in the middle, like the Armadillo design (but they just have one engine) would tend to just cause the vehicle to lift a bit more slowly, since the thrust vector would point straight up the axis of the vehicle.

Anonymous said...

Armadillo's first vehicle was a four engine high grade peroxide monopropellant one. It had long lever arms and solenoid engine throttle control (ie binary on/off). They even flew one person a few meters with a bigger version.

I think it was in in 2003 or 2004.

I don't think there's anything fundamentally wrong with Paul's approach. Actually the four tank/engine modules attached with stretching string is an ingenious way of handling the landing shock. :)

Anonymous said...

From comparing Masten's and Armadillo's control programs (on the basis only of the videos I've seen), it seems that either Masten's control systems sometimes aren't reacting fast enough. I've seen several of their videos where the thing just flies off at strange angles. Some of that may be the thing with the engines not all lighting at the same time.
I'd also be careful in checking that the thrust between the different engines matches up closely. if 85%throttle is 25 lbs different thrust between the two, your ECS system is gonna have a fit trying to compensate!

- Jesse

High Power Rocketry said...

: )

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