7 posts • joined 23 Feb 2012
You're going to need Energiser Lithium batteries.
To fire that lot off, I'd suggest Energiser Lithium AA's. They work down to -44 degrees C
You need two vane pumps
Similar to a turbine which provides pressure via two or three sets of vanes, you need a similar setup with this pump, but in the reverse. Two in series will bump up the vacuum....and change the PVC pipe to copper...the pipes will collapse. I discovered this attaching two pumps in series to drain a pond, and could hear the water boiling in the pipe as it collapsed, and the vanes having a hard time with vapour cavitation. All I got was a stream of spluttery water and vapour from the nozzle. In investigation of the cause I nearly lost my trousers at the inlet end.
PARIS - LOHAN twosome turn on
Use the KISS principle. Electronics introduce complexity and cost. More complexity = more to go wrong. There is an item that you have used that already delivers at 90,000 ft....PARIS' release mechanism! Adapt it to close a circuit and fire up the rocket . It's pretty bulky I know, but you're going to need a larger meteo balloon anyway with all that tackle blowing in the breeze. Even so, you could miniaturise the principle.
Even better way to get a vacuum
There is a simpler way of attaining a vacuum of 10-15mmHg. Source a 100mm dia 15m long steel pipe. Seal both ends and attach 2 valve taps to the top sealed end and one at the bottom. Attach one top valve tap to REHAB and fill the pipe with chilled water (2 degrees C will do) with the other. Close off the water tap and open the bottom tap and watch that air pressure drop baby. The chilled water will reach its vapor pressure somewhere close to the bottom of the pipe. This does mean though you will have to conduct this experiment in some suitable stairwell.
You need speed
Lohan is doomed to failure if you are going to launch from 90,000ft
With the current rocket motor the Lohan will not attain sufficient speed once leaving the launch rail to attain aerodynamic stability. There will be very little aerodynamic force to flight surfaces due to the low density of the atmosphere. Once the rocket leaves the rails, the aircraft will generate what is called circular yaw or ‘Dutch roll’ due to the shifting CG and low ‘True Air Speed’ (TAS) unless the rocket utilizes thrust vectoring or wing and tail control surfaces. In effect all stability will be lost and the aircraft will instantly start tumbling. Most amateur rockets passing 90,00 feet start corkscrewing at this height due to this effect. You need speeds in excess of Mach 1 in order to achieve stable flight at this height. You should be looking at an 2 stage L class motors with possibly Lohan being the 2nd stage (like the spy shuttle X37C) to get any way near the acceleration needed for stable flight.
The donkey will go stratasspheric
It is a wellknown fact that donkeys have had a disastrous past history with helium balloons. Eeyore for example.
A quick search of Google images will turn up several pictures of the Disney rendition of A.A.Milne's morose character going skyward.
Lohan's thrust may snap the member
Just thinking thay you guys should test the bending moment and shear force of Lohan on the carbon fibre truss as she fires up. Even though carbon fibre rods are extremely flexible and strong, they don't react kindly to sudden shear forces - causing the truss to fail.