We've enjoyed reading your comments over the past day regarding the possible launch system for our Low Orbit Helium Assisted Navigator (LOHAN) Vulture 2 spaceplane. Click here for a bigger version of the LOHAN graphic Following a successful test of LOHAN's fantastical flying truss (see vid, below), we concluded that we'd go …
You're going to have to apply a perfectly linear force to slide off a rod, any angles and you'll just end up applying a turning moment to the launch rod gripping it like a vice.
You must test it suspended on a string, as it would be in the real situation, not a rigid vice clamped rail!
Are you using a rail at all?
Rail? What rail?
Re: Re: Why...
Well, that's because we see it as the best method for getting the thing launched. Simple as that.
LOHAN flies high after taking entire rail in one effortless quick snort ...or shot? ...something like that.
I still think you should launch/release LOHAN balloon rig off donkey, if only for headline writing purposes.
LOHAN's mighty flaps!
I propose a rod and pin configuration mounted at the end of the truss, hence:
Pinned In Static Start Firing/Launch Atttitude Pylon System.
...or PISSFLAPS for short.
Not trying to rain on Lohan's Balloons, but if the PARIS launch height can be taken as a measure, and the rocket motor adds a further, let's say, 300metres, then you're going through all that trouble for an extra 1.5% of height.
Of course it's the adventure that makes it worth it, but the effort/ return ratio is somewhat low seeing the increased risk of terminal malfunction at the climax.
Re: launch trouble...
Two simple words:
As you know, pyrotechnics make everything 126% more awsome.
LLP (LOHAN launch platform} for a single balloon
Simple solution is to make a large L with 15 foot? arms from 1/2 ? inch tubular graphite (old fishing rods) . Hinge the arms at point of the L. Attach correct counter weight at hinge point. Connect tips of arms with fishing line to form 90 degree or less angle. When one tip of the L is attached directly to balloon the center of gravity of the assembly will cause the lower tip (where launch pad is fastened) to hang off-center of the balloon. When the launch pad is attached at the correct angle to the lower tip the rocket will clear the balloon. Hinging the L facilitates launching.
Why not test fire?
It would seem that even a low level test of any launch system using a smaller rocket would be a good way to test any of the suggested launch options. If at 100 feet the rocket is able to leave the platform it would give a good idea of how it might perform at a higher altitude. After all if a test rocket doesn't make it off the platform at 100 feet, it's not going to do it at height.
If you could only get the launch pad assistant to quit smoking the pipe, you could safely substitute hydrogen for helium. You would then have a Low Orbit Hydrogen Assisted Navigator with twice the lift. At the extreme launch altitude air/hydrogen pressure will be low enough that even if the exhaust ignites the balloon, it will be a slow burn, allowing the rocket to escape.
As well as having the vulture slung under the platform instead of on it, why not have it supported only by a rigid structure at the business end of the rocket, using a material that will quickly melt and get out of the way.
A comment in one of the earlier articles mentioned using two concentric tubes, the outer sealed at the bottom and fixed to the launch rig, the inner forming LOHAN's engine exhaust. With the whole setup near vertical there's no need to actually secure the craft to the launch platform. There's the thermal contraction of the tubes relative to each other to take into account, though.
instead of rods..
how about 2 U shaped channels to retain the craft? kind of like this little txt art [<o>] you can build in sufficient tolerance to allow for thermal expansion without causing the craft to jam in the rails.
Just a thought :-)
Long rod, fixed at one end, with two eyelets on the top of the craft. No twisting possible, just have to make sure the eyelets don't freeze to the rod. Maybe heat the rod?
One not-too-tight inverted "U" at the rear of the craft, an even looser one at the front, and a nylon or teflon 'skid' with a groove down the length a little back from the front "U"; at rest, it's free from the rod by a few mm. Because of the clearance it can't freeze to the rod. Then, as the motor starts to develop power, it may want to push the nose up in the direction of the rod. The grooved skid together with the rear "U" will now provide guidance.
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.
Do you need an extra rod? Can you not fit a curly clip thingy (technical term that) to the top of LOHAN and attach her to the truss itself?
Or carve a groove into the bottom of the truss and attach LOHAN to a pin of some sort that'll then plough through the groove on ignition?
Launch rails for rockets are an established tech, and certainly work. They have done since the days Biggles was flying Sopwith Camels.