On Sun, 6 Mar 2005 09:17:30 -0800, "Rich S."
wrote:

When I took physics out at the 'Dub, orbits hadn't even been invented yet. I
can barely remember attending, much less any of the course content.

Heck, Rich, you were playing "Rock, Rock, Rock," before paper and scissors had
been invented....

From a layman's point of view, it appears as though powered flight on our
Moon should require *less* power than on Earth. If your linen bag of termite
chow can fly in a one-G field on forty horsepower while beating aside air,
smog, clouds, bugs and rain, then our moonflitter should be able to paddle
along in one-sixth G under a lot less power. If you can carry fuel to go for
your hamburger on Earth, then what's the problem out there (other than a
scarcity of Mickey D's)? Absence of air should be an advantage in some ways.

Well, vacuum DOES eliminate drag, but as far as everything else is concerned,
it, well....sucks.

Look at is this way: All aircraft engines are rocket engines. They work by
expelling mass, with the amount of thrust depending upon the amount of mass and
the speed at which its expelled. "Jet" engines use burning gasses to increase
the velocity of the flow, while us poor ol' Fly Baby jockeys have to make do
with carving out a piece of air and throwing it backwards.

Down here in the soup, the mass to expel backwards is free. On the moon,
though, you have to bring that mass with you.

So...how much air, in mass, are we talking about?

Let's take a look at my Fly Baby. It's got a prop 72 inches in diameter. The
pitch is 48 inches...in an ideal world, every turn of the prop blade would shove
a chunk of air 72 inches in diameter backwards a distance of 48 inches.

How much air is that? Almost 200,000 cubic inches. But of course, that prop
isn't 100% efficient. Let's say it's only 1% efficient...that's 2000 cubic
inches of air being pushed backwards to provide thrust.

How much does that air weigh? About 1.2 kg per cubic meter. That's about
0.000043 lbs/cu-inch. Which is about 0.1 lb of air per prop rev.

And...the prop is revolving at about 40 turns per second, so that's about 4
pounds of "propellant" used per second. An hour flight in my airplane uses over
14,000 pounds of "rocket fuel"! Geeze, maybe I better review those Sport Pilot
regs again.... :-)

Ron "Hypergolic" Wanttaja