# Parachute idea

I had an idea hit me out of the blue for a high quality parachute. A childs
nylon umbrella. just remove the metal tines attach some shroud lines and you
have a great chute. Is this a good idea or a bad one?
lets not forget 36" dolly umbrellas.
Whoa... Too much good tech info at one time. My brain can't handle this. There's enough good info here for 20 good rmr threads.
Thank you for the post. Whole new things for me to explore... after I get though the other 100 rocket things I must know more about.
Layne
Thanks to everyone who helped me on this.
Now I've decided not to use the idea, I'll say what it was all about:
There are a few competitions such as the above where hang-glider pilots try to fly as far as possible. Human power is allowed, but for various reasons propellors don't seem to work too well. They catch on the surface of the sea shortening the flight, and cause drag at the start of the flight when the pilot is not pedalling.
I wondered whether a really big water rocket might work, with the pilot using some kind of pedal-powered foot pump. Power is limited to about 1kw, so having a high specific impulse is a bad idea - you wouldn't be able to get enough thrust to stay airborne.
Using a lower exhaust velocity means that the pilot needs to expend less effort in order to produce the same amount of thrust, but this means that he has to carry more water. The problem is that even for a 6-10 second flight the mass of water the pilot would have to carry becomes prohibitive: the glide angle would decrease, but more importantly take-off gets harder.
It wasn't a daft idea until I'd done the sums,
VNE
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Just a friendly nit ...
The term 'specific' in engineering circles implys 'mass'. So the term specific impulse implies impulse per unit mass. Similarly specific fuel consumption implies performance per unit of fuel mass.
Therfore mass-specific impulse adds no additional information and is redundant in meaning.
SYSTEM specific impulse factors in the entire non-payload mass of the system.
VOLUME specific impulse is another useful coefficient.
Pardon the TECH post!
Jerry

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