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In lugnet.space, Joel Kuester writes:
> In lugnet.space, Jesse Alan Long writes:
>
> > I appreciate the fact that you do agree with me but I must truthfully say
> > that I never considered the fact that friction does indeed keep together the
> > bolts on a space craft. Are there any other sceintific laws that either me
> > or Paul failed to consider in our thoughts about space craft, Duane? Thank
> > you for not seeing me as evil in the LEGO space bulletin board, Duane.
You're not seen as evil. It's just that if you're unsure of what you're
saying, don't try to make out that it's absoulutely right, and people won't
mind if your opinion differs from theirs.
> I believe Paul was poorly communicating a correct idea.
>
> The scientific law of friction is applicable everywhere, even in space. It
> is a law, and going to space won't make it go away.
> What you need to understand is how this law works. The friction that we are
> used to calling drag is the friction of air particles on a jet, or water
> particles on a submarine. The drag is much greater underwater because the
> water is denser with particles. This is an operation of matter states, ie:
> the density of a liquid state is more than the gaseous state, and the solid
> state is greater than the liquid.
Just to add to this, possibly blurring the arguments but hopefully drawing
nearer to a consensus. There is friction in space between a moving body and
the occasional particles it meets, but in a fluid such as air or water there
is also friction between adjacent particles (molecules) in the fluid. Fluid
molecules can not just move anywhere at any time and speed - they are
dragged by surrounding molecules - this is an explanation of the viscosity
of a fluid. This leads to various pressure effects which both lift and drag
aircraft, and cause swirls of turbulence as the fluid tries to rush in
behind a moving body. Turbulent (moving) air is at a lower pressure,
causing yet more drag behind an aircraft.
In space, molecules distributed sparsely throughout a vacuum have very
little interaction, and so have negligible viscosity. No matter how fast
you go, the molecules are still spread out. Quite simply, they do not
behave fluidly - merely as individual particles. So, a moving body would
only really impact with each one individually. This might cause it to roll
along the hull causing friction, or it may bounce off. Either will impart
some energy onto the hull, but neither case counts as viscous drag from a fluid.
> The reason drag is a moot point in space is because it is a near-vaccuum.
> The amount of particles is so low that you rarely bump into them, and
> therfore there is no effect. The lift a wing creates needs particles to
> move around the wing (faster on the top and slower on the bottom, due to the
> diffence in the surface areas of the top and bottom of a wing) and the
> difference in speed this creates causes a pressure tension to literally pull
> the wing up. I am just going by memory for this explaination right now...
> there is a lot more to it than that, but thats the basic concept behind wings.
[Okay, this is the geeky bit, and it goes way off-topic, but that hasn't
stopped anyone so far:]
Well, it was good enough for the Wright brothers, and everyone else up to
about 50 years ago. It's actually down to viscosity, and the angle of the
wing to the airflow, not it's shape. Have you ever questioned how even the
old barnstormers used to fly upside-down, if the curve of the wing had to be
on top to get lift?
If you just angle up a flat plate with rounded ends in a slow airflow, in a
wind tunnel with smoke lines, you see something quite interesting. You'd
expect air to be deflected downward by the plate, but it isn't. Forcing air
downwards creates pressure to force it back up again. What actually happens
is the air moves up to the wing, just under the leading edge, then the
airflow splits to go rearwards, but also circulates forward, up and over the
front. The lower airflow then curls around the trailing edge and meets up
with the upper airflow before drifting off rearward at exactly the same
height as it arrived. Overall, the air behind the wing is moving at the
same height and speed as it was in front, and there is no overall force
up/down or forward/back on the wing.
But, as you sharpen the trailing edge, and speed up the air flow, the
viscosity of the air means it can no longer curve up around the rear edge.
The rear circulation is forced further back, dropping off the rear edge of
the wing and leaving some wash in its wake. The circular motion at the
front continues, and this is what gives you the speed (and pressure)
difference above and below the wing.
Not convinced? Look at footage of US Navy steam catapult launchers. You'll
see each aircraft leaving behind a roll of steam as it is launced, left by
the trailing edge of its wings. This is the rear circulation being left behind.
Now the really geeky / head-spamming bit is this. You also get circulation
around the wingtips (look at Concorde landing). This is the higher pressure
air under the wing leaking around the wingtip and onto the top. These are
all simple pressure effects, but they're desparately trying to restore the
air to a neutral position. These swirls actually link the leading edge
circulation with the trailing circulation left behind in one giant toroid,
like a smoke ring stretched out all the way from take-off to landing. In
reality, in our viscous fluid, it disperses behind the aircraft, but
mathematically that's what's happening.
Don't care? Ah well... :-)
> few particles in space = insignificant friction to the craft.
> near vaccuum in space = no pressure and therefore no "lift" possible.
Quite so. I'm amused by sci-fi that gets it horrendously wrong. Macross is
a great one - using air-brakes, and banking by about 30° to turn in space.
Jason J Railton
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Message has 2 Replies:
 | | Re: Couldn't resist
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| (...) Well the A-wing flight control system doesn't discriminate between air and space flight either so it's control surfaces move in space as well, producing little affect except a little momentum. I think as a Valkyrie has 2 widely spaced engines (...) (23 years ago, 26-Jun-01, to lugnet.space, lugnet.off-topic.geek)
| | | Re: Couldn't resist
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| (...) The first problem I have, Jason, is that I am not sure that everyone else is right, either on these bulletin boards and I know for a fact that I am not probably right in my ways of thought in my life. Would an overheated engine become a (...) (23 years ago, 26-Jun-01, to lugnet.space, lugnet.off-topic.geek)
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Message is in Reply To:
| | Re: Couldn't resist
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| (...) I believe Paul was poorly communicating a correct idea. The scientific law of friction is applicable everywhere, even in space. It is a law, and going to space won't make it go away. What you need to understand is how this law works. The (...) (23 years ago, 25-Jun-01, to lugnet.space)
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