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Re: (TFT) Re: Demon slingshot

Date: Sun, 09 Apr 2006 14:53:27 -0700
From: Peter von Kleinsmid <pvk@oz.net>
Subject: Re: (TFT) Re: Demon slingshot

...Magic Carpets are stronger fliers than the Flight spell, but do you really
think they beat, say, a 1910 biplane for performance?

Some real-world ceilings:
Jet fighter (F-15 absolute ceiling): ~30km
Jetliner (Boeing 747): ~14km
Very good WW2 fighter (P51): ~13km
Biplane (Spad): ~7km

*Good* question. Given lack of runway requirements, general lousy aerodynamics, etc., I have always made the assumption that magic carpets (and the flight spell, for that matter) behave as you say here...

I guess if we assume Magic Carpets use levitation or contragravity or
something, then it would make sense they could float higher.

... and that whatever they do for lift is not related to aerodynamics. That's not, I guess, the same as saying it doesn't depend on having air, though. Suppose a magic carpet is a shag carpet on the underside, and the threads form little spinning corkscrews, throw streams of air downward, and turn it into a big helicopter-like device? Gotta have air for that, and it puts a definite ceiling on operations. As I said, I made the above assumption for both Flight and Magic Carpet.

But then, how high is the atmosphere of your Cidri, and what do people have
to do to stay alive up there, and does a magic carpet ever stop working at
high altitude, or are you saying it'll do for a spaceship if you can only
keep the passengers alive?

If it *is* contra-gravity, it falls off like 1/r^2. So eventually, just when you really need it to get back, it stops working. "Houston, we have a problem."

This problem is the same for the local rotating reference frame I assumed for Long-Distance Teleport, by the way - what are the boundaries of the planetary system? I don't know a good answer to this.

 >4) Hang a launch gate out over the North pole and build the facility.

Sounds like an amazing feat in itself, especially if Cidri is super-enormous.

*Impossible*, if Cidri is a ringworld-like construct, or some other geometry. Yes, all my analysis depends on an Earth-like Cidri, possibly with some parameters scaled up or down. And yeah, getting to the North or South pole might be a trick. As Rick pointed out, there are alternatives, they are just mathematically tougher.

Not to mention mathematics. Modern aerospace teams have their work cut out
for them doing this even with banks of computers and hundreds of engineers,

Yup. On the other hand, Tsiolkovsky did practically all of the analysis on his own, early in the 1900's. He did have Newton to rely on, though, but that pair is about all it took for Earth, in terms of mathematical innovation. That implies that a pair of really sharp wizards is about all it'd take on Cidri.

I'm _not_ sure though, that it follows that vertical gates would be

That's not a terribly unreasonable restriction. Actually, thinking about it, one might also levy the restriction that gate transport must conserve total energy in an inertial reference frame. That would mean:

1) At the same latitude, no change in altitude, since that would change the potential energy of whatever is being transported.

2) For change in latitude, kinetic energy changes (due to rotation of the planet). That has to be compensated by an equal and opposite change in potential energy, i.e. gates nearer to the poles have to be higher in altitude (above the geoid, or roughly above sea level).

Tides would muddy the situation still further, so it might be that some long-range gates only work at certain phases of the Moon(s) and/or times of day. That would be somewhat Tolkien-esque.

Picking sites for gates might be a *lot* trickier, in that environment. And getting up a hill would simply require walking up it - no wizard's road. And the demon slingshot idea falls apart completely.

There could also be other side-effects, like yes, you can get lots of
energy, but it comes out of the local mana field, and you end up creating
large low-mana or no-mana areas where magic doesn't work right, or at all.

a la Niven's "The Magic Goes Away", if I remember correctly. Yeah, that would be another really nice touch.

					- Mark
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