9 posts • joined Wednesday 11th July 2012 16:50 GMT
Re: GPS to trigger LOHAN's rocket motor... Are you sure?
Lol, I think you've got a bit confused there Jimbo in Thailand. 384403km is the distance to *The Moon*. Earth orbiting sats are nowhere near that far away, Low earth orbit says are typically about 800-100km altitude, GPS sats are about 20,000km altitude.
Altitude is a bit less precise than lat and lon but still good enough to 50-100m, which is plenty for a rocket going to many 10s of km.
Re: LiPo suction
Rechargeable battery, maybe. But LiPo's do not have the power density of some lithium primary cell chemistries. Also the temp performance is very very poor, as someone else mentioned.
Re: Wind blows in wrong direction.....
Needless to say, of course not. This is not 'Nam, there are rules. ukra.org.uk for the UK rules.
Re: Alternatives to Thermite.
You don't want faster burns! That's not a good thing. However you're right that a bit of it might help activate the thermite, but I've not found activating the thermite to be a problem so far.
I am pleased! It's good stuff. However, I advise you to not make a large batch and store it, but instead make small amounts each time. And discard the leftovers. Even if you put the paste (it's pretty safe when wet) in a nice screw top jar, you'll get crystals growing up into the screw thread of the container which will go off from the frictional heating next time you open the container. It's fascinating to watch but worth avoiding. The base pyrogen paste is made from letting an estes motor dissolve in water. The cardboard tube will sort of collapse and go mushy (just fish it out, along with the little cermic nozzle that was inside it) and the propellant will dissolve. You might want to help it along by breaking it up a bit with a screwdriver once it's wet. I added about 20% IPA (not the beer) to the water to help it as a solvent.
Re: Silicon seal
We have suffered the same problems as you with low pressure ignition. The flame front from the burning igniter products dissipates too quickly (thanks to the low ambient pressure), before it's had enough time to transfer enough thermal energy into the propellants to get the party started.
You can either plug the motor (would have to be done very well to hold a seal for the couple of hours of balloon ascent) or modify the igniter. We have in the past used some special sauce that was a bit of pyrogen dissolved in water (which makes a paste) with aluminium powder and iron oxide powder (rust). This paste (I call it rocket bbq sauce, but I am silly) can be applied to the igniter head in several layers (dip, let dry, dip, let dry, etc for 5 or 6 times, like coats of paint) and then will produce a lot more energy, the thermiting ali and rust powder especially are in liquid phase (molten iron) rather than gaseous as they react, which helps with gets you round the hot gases dissipating in the low pressure. You'll get molten iron being sprayed onto the inside of the motor. This will get it started.
Re: Ever see the sparks below the nozzle on a Liquid Fuel rocket just before ignition?
This is not correct I'm afraid. The sparkers are there to burn off any leaking fuel before the engines start, so it doesn't gather somewhere and explode at some later time.
All the ignition is done inside the combustion chamber itself by the rocket engine. The sparkers play absolutely *no* role in the ignition.
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