h a l f b a k e r yYou think: Aha! We go: ha, ha.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
The Magnus Effect, which makes a baseball curve, is is most simply illustrated with a cylinder spinning around its long axis. The cylinder's surface carries the surrounding air with it like a whirlpool. If the cylinder is dropping through the air, with the long axis horizontal, the spin pushes against
the approaching air on one side, and pulls along the approaching air on the other. The air pushes and pulls back, and the cylinder goes sideways--it glides like a wing, for much the same reasons. (See links for NASA math on cylinders and the Wikipedia of baseballs.)
If you'd like to test or demonstrate this, you can easily. Spin-launch a cardboard tube, or two paper cups taped base-to-base, with an elastic string to make a toy Magnus Flyer. (Link)
The invention/idea here is simply that any cylindrical rocket body would glide back to Earth if spun properly. The glide ratio would depend on several factors, but should be better than a parachute, although less than a solid airfoil. The weight should be less than either.
The spin could be induced several ways, but the simplest is a drogue chute pulling a cord wrapped around the cylinder. Vanes, shafts and motors are all possible to start and to maintain the spin, and would take too long to describe. (Extending a flex shaft with a controllable propeller from each end, is one way.)
Steering is also possible a variety of ways, related to the spin mechanism. In guidance, a simple video camera could use the spin as part of its scanning function.
A spinning cylinder could be landed in water. A better landing area would be a field of stiffish bristles of a height roughly equal to the diameter of the cylinder--for a model rocket, grass would serve.
Lift of a rotating cylinder.
http://www.grc.nasa...2/airplane/cyl.html
NASA, math and Java. [baconbrain, Feb 25 2008]
Magnus effect
http://en.wikipedia.../wiki/Magnus_effect
That first illustration should be other way up. [baconbrain, Feb 25 2008]
MAGNUS FLYER - Let's Make It:
http://sln.fi.edu/wright/magnus.html
Get two cups and put them bottom to bottom. [baconbrain, Feb 25 2008]
[link]
|
| |
Why didn't people like this much? |
|
| |
I think the problem with it lies in its not working. |
|
| |
For the Magnus effect to work, you need forward motion
as well as rotation. If the rocket were falling (with its
long axis parallel to the ground) and were also made to
spin around the long axis, the Magnus effect would only
provide a force parallel to the ground. |
|
| |
If you want to get lift, you would have to (a) spin the
rocket around its long axis, parallel to the ground, and
(b) drive it horizontally. That's difficult to do. |
|
| |
Not if you lose rockets … |
|
| |
[MaxwellBuchanan], I thought you were smarter than that.
As the rocket is falling, the Magnus Effect provides a sideways force ("lift"). Therefore, it is no longer fall straight down, but also has a sideways component. Depending on the weight of the rocket (generally "lots") and the amount of Magnus Effect effected, the motion could contiune to rotate, until reaching whatever the glide-path ratio is for a rocket in Magnus Effect. Being un-powered, it will be unlikely to rise above the g.p.r.
I think this is a good idea (altough, as stated, depends on the amount of Magnus Effect that can be attained) and I don't know how I missed it the first time around. |
|
| |
//[MaxwellBuchanan], I thought you were smarter than
that.// Almost everyone makes that mistake. |
|
| |
If there is no net (vertical) lift, then I suspect its rate of
descent will not be reduced. With luck, you could make the
rocket hit the ground at 150mph vertical plus 50mph
horizontal, as opposed to just a plain old boring 150mph
vertical. This could be useful, but only under circumstances
which are difficult to imagine. |
|
| |
The vector math seems sketchy. The lift force in
whatever direction it goes will cause a drag force
and slow the rocket down a few clicks. |
|
| |
The lift force will act perpendicular to the missile's velocity vector so any horizontal motion will give vertical lift and slow the rate of decent. If the missile had no weight or drag then (given an initial forward speed) it would describe circular motion about an axis parallel to its rotation axis. Because it does have weight it will glide. The glide slope is just defined by the lift-to-drag ratio which can be whatever you want it to be by changing the spin. |
|
| |
Aeroplanes with rotating cylinders for wings have been tried and do work, although I think the mechanical complexity makes them impractical. The implementation on a rocket ought to be easier. I might try to calculate the required spin rate if I get a few minutes. |
|
| |
// mechanical complexity makes them impractical. // |
|
| |
Flettner wings are actually very simple, mechanically. There are
lots of problems - mostly around control systems, and
inefficiencies compared to Sikorsky-type horizontal rotors, but
they have been shown to work. |
|
| |
What if the horizontal motion from the Magnus effect were to
approach (but not reach) escape velocity, tangential to the Earth's
surface? Might we not then skim the rocket across some broad
stretch of ocean, decelerating it a little with each skip? |
|
| |