In article 0s_cg.1058$1i1.24@attbi_s72,
"Dave Lyon" wrote:
"John Husvar" wrote in message
...
In article oxZcg.1087$No1.766@attbi_s71,
"Dave Lyon" wrote:
What does the assembly weigh and what is the burst pressure? If the
burst pressure is 300 psi and the disk is one inch in diameter, the
thrust at the moment of burst will be (Pi (0.5)^2)(300)= (0.785)(300)=
236 pounds. The impulse (integrated thrust) will be proportional to
tank volume.
Anyway, this thrust is enough to make most compressors move.
Joe Gwinn
Wouldn't that thrust assume you were pushing against a stationary
object?
Would it decrease relative to the distance the "hole" was to the floor
(or
wall)?
Not quite, the jet stream of pressurized air needs nothing to press
against. Its thrust is independent of anything but the pressure
relationships in the vessel and the nozzle, in this case the tank and
hole. It'd have as much thrust with a vacuum surrounding it. 'tis how
rockets work.
Swoosh! 
If there is no benefit from being near the ground for our air compressor
rocket, then why do airplanes and hover crafts have a benefit from ground
effect?
I'm not trying to be a butt, just trying to learn something.
Well, our air compressor rocket may gain a little bit of lift from the
air rebounding off the ground toward it, but it won't be much. the one
shown probably got a fair bit from the big flow when the seam parted
though. I doubt the thrust from a burst plate's area would even move it.
For real fun one could try breaking the valve off a full-pressure
compressed gas tank. Those will move quite a bit.
Airplanes are said to be in ground effect when their altitude above the
ground is less than their wingspan. There is a slightly increased lift,
but it's relatively small and not terribly significant to a plane's
flight characteristics. If you've felt the slightly mushy springy
feeling as a plane takes off or lands, that's ground effect.
I feel it more on landing because all the laundry's hanging out;
trailing flaps, sometimes leading flaps, landing gear, etc. Hell, one of
the flights I was on recently, the pilot deployed the spoilers during
the descent. Sure as hell felt that! Plane went from feeling like a
slightly bumpy roller coaster to feeling like a Maytag on Spin with bad
bearings and an unbalanced load. (and I was stuck inside, riding the
agitator
Ground Effects Machines like Hovercraft operate best when they have a
skirt where the pressure can build and support the hull. That kind of
ground effect isn't really much related to aircraft ground effect. Some
designs without skirts were tried, but the ground effect was much
reduced and wasn't too reliable.
Real rockets are out of any possibility of reacting to ground effect so
fast that it's doubtful anyone can notice it. But they don't need the
atmosphere to "push against." They just use the force the exhaust
pressure and mass exert on the top of the combustion chamber.
The old balloon thing would work as well in space as down here.
Now for something really scary: Every launch, the astronauts are riding
with the lowest bidder. (and with the guy who said the rocket's OK to
launch, who they hope hadn't had tee many martoonies at lunch.
Recent events have shown that might not be a valid assumption.
--
Bring back, Oh bring back
Oh, bring back that old continuity.
Bring back, oh, bring back
Oh, bring back Clerk Maxwell to me.