h a l f b a k e r yThe embarrassing drunkard uncle of invention.
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(I've got this phobia about jumping off of cliffs) |
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slightly larger than standard... volume needed to lift you off the ground. |
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This is a biiiiiiiig hang glider. [+] |
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Even with an outsize wing (perhaps
1000 cubic feet of air, which would be a
big thick wing, as [david_s] points out),
and with good solar heating, you'd only
get a few kg of lift - less than the extra
weight of the larger wing, I think. Even
hot-air balloons need burners to get
the air hot enough to give sufficient lift,
and their volume/payload ratio must be
much much higher. |
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Not necessarily true [Basepair], see link. |
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Well really, [2-fries] - if you wanted
people to follow the link you should
have given it an obvious title! ;-) |
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I am impressed, but it's still clear that a
flyable wing wouldn't have sufficient lift,
alas. |
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I don't think it clear at all.
If the volume of hot air is sufficient for lift, and if the wing is aerodynamically shaped this will work, it will just have a very large wingspan. |
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Not necessarily. If you try to make a
very long wing (long enough to have the
same volume as the man-lifting
balloon), you need a lot of framework to
keep it tolerably rigid. Admittedly,
airships have a rigid frame, but (a) they
are not as long and thin as a wing -
they're not long cantilever structures;
and (b) they need helium to get useful
lift (helium has a lower density than
manageably hot air, I think). What I'm
getting it is that I don't think you can
make a lighter-than air hot-air balloon
with an aerodynamically stiff wing-
shape, however you scale it.
***However***, I'm not trying to pick
holes, and I may be wrong. Tell me the
dimensions of the wing you had in mind
and I'll take it all back :-) |
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Is there an engineer in the house? |
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I think there are a few engineers in the house but I am not one of them so I have no numbers for lift to weight ratios.
It's size would be roughly bigger than a bread box yet smaller than a Cessna. |
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A quick calculation. Suppose your
glider is the same size as one of the
wings of a Boeing 747-300 (one wing is
about 90ft long and maybe 18ft front to
back and 3ft top-to-bottom, as a rough
average). If completely hollow, it will
hold about 180 cubic metres of air, give
or take. Suppose that you can solar-
heat this up to the boiling point of
water (100°C), and that the outside
temperature is freezing (to give you the
best lift). In this case, the wing will give
a "hot air" lift of about 62kg. Even a
hang-glider weighs ?30kg?, so a wing
which is five times longer is going to
weigh easily more than 62kg. Hence,
even a wing this size is not going to be
self-lifting in a balloon kind of way.
Sorry, not getting at you - just an
interesting idea and I was curious about
the numbers. |
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Well that sucks, I thought for sure that this would be the one idea that finally made me rich. |
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[Po] May I please ask you to explain that link? I really don't see any connection. |
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:-( sorry. If it's any consolation, the
President of Boeing corporation
probably *is* rich, but is probably
unhappy. Well, maybe. |
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So it is basically a solar heated hot air balloon? |
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