Wednesday, August 23, 2006


Just in case anyone reading this is a rocket engineer or knows one....
My dream is to be able to use a small solid fuel rocket to get me into the air, I'm not greedy, I'd be quite happy with as little as 500ft above the ground. I just want to be able to get into that first thermal and then I can sort myself out. I don't know how efficient rockets motors are, I know you need about 4.5 lt of fuel to carry 1 ton up approx 6000ft with a conventional aircraft. Assuming that the chemical energy stored in a solid rocket is similar to avgas, and the efficiency is only 50% of an internal combustion engine it would still seem to suggest that 5kg of rocket fuel should carry 500kg up 3000ft....
Of course the really cool thing about a solid rocket motor would be that it burns its own weight during the climb so that what is left would be negligible.
I like the idea of having a fixed thrust line, I would want the rocket to remain parallel with the keel at all times, probably not actually in the keel as you want the push on the C of G and the keel would be above that, but it would be a neat option if the physics could be worked out...
I have seen the sort of rockets that I want, with solid fuel rockets you can pack them to get the exact results you need.
I was thinking of nose down, wings level, ignition... Then you get 2 seconds of smoke before 20kg of thrust kicks in, that would be just enough for you to make sure you are comfortable or drop the nose of the glider onto the ground if you need to abort. Then 30kg for a couple of seconds (start walking) and then 40kg for the 15 second take-off and climb out. 40KG is about what you get from a power harness. Then once you are on the base bar it should ramp up smoothly to about 1G (about 120KG in my case)  If with 40kg of thrust you can climb at about 300ft/min then perhaps you might get better than 1000ft/min so only a 30 second final burn would be required... So all up less than a minute of burn time and it would get you into that first thermal with an unadulterated glider and harness and no extra weight or drag.
Of course an aerotow or car tow is always going to be the simplest option if you can find one, but I could fit a whole box of these rockets into the boot of my car ;-)
Its too light for Pap Hill again, Thurs look like the best afternoon now.

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