h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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Sycamore seeds retard their fall by having a single-
bladed
rotor that autorotates - the air-flow causes the spin,
which
generates lift slowing the descent. Same as a helicopter
in
autorotation “flight” mode.
Whereas a parachute has to be very precisely made and
rigged to ensure opening
and stability during descent, a
single blade like this develops stability through the
balance
of weight, airflow and gyroscopic forces. If you look at
sycamore seeds, they have great variation in size and
geometry, and still achieve their purpose when quite
damaged. That doesn’t work for a parachute.
For air-dropped equipment that’s robust to fairly high
rotational accelerations. So not people. Oh, and zero
steerabity.
But perhaps munitions, food drops, returning samples
from
space. Maybe this design would be viable as an aero
braking system for reentry also (compared to, say, Virgin
SpaceShip
One “shuttlecock” configuration)
[link]
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I'm sure something like this has been baked in the Real World, and for
human use. |
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However, I would still plump for a parachute since (a) it can be packed
into such a small volume that you can (and do) carry a spare and (b) it is
surprisingly tolerant of a lot of imprecision, abuse and damage. I have
seen people land perfectly safely under an old-style round canopy with a
line-over (meaning that one of the lines has gotten over the top of the
canopy, converting it into a sort of flying bra). I myself have landed under
a square canopy which had decided to suffer a 5ft split down the middle
when it opened, but was sufficiently airworthy to fly and land nicely. |
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Yes, but you're anatomically preconfigured to bounce well ... |
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Oddly enough, I know a bloke who "went in" (as the cheery
phrase has it) twice, and got away with it both times. |
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Couple of issues that I'm seeing. The blade would have to
be stiff so that's structural weight you don't have with the
very thin, self inflating cloth of a parachute. You also
have the pivoting
mechanism, ball bearings and such that add additional
weight. You could probably do some kind of inflatable or
carbon fiber affair but at some point you've got to ask
what your getting for all this trouble. |
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I think auto-rotation landings on a helicopter utilize flair
and an increase of the angle of the blades, collective I
think it's called, at the last moment to convert the torque
in the spinning blade into downward air movement just
long enough to ease the machine onto the ground, so to
get the most effect now you're adding an active control
system that senses when you're about to land and changes
the angle of the blade. |
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Of course if you run all the numbers and pound for pound
you're getting some advantage over a the simple bed-
sheet on strings parachute model, or inflated bouncy
balloons for that matter, then fine, but doesn't look
promising to me. |
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//auto-rotation landings on a helicopter utilize flair// They
sure do; any pilot that can pull one off is just oozing panache.
The important thing is to remember to flare at the right
moment. |
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//pivoting//...//bearings//... |
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I wasn’t imagining any of that complexity. The
airframe spins with the blade. Hence “not for
people” |
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(max) Hard to put your finger on, but there's a certain je
ne
sais
quoi inherent in not turning your aircraft into an
exploding
fireball by smashing it into the ground on landing. |
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(Frankx) I've just seen collapsed
parachutes that are spinning quite quickly hit the ground
without much effect on the speed of descent but like I
said, if you do the numbers and it makes sense, you might
have something, I'm just not seeing where the
advantage is. |
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So... this isn’t about placing people on the ground
gently, safely and controllably, in the way that a
modern parachute rig does. This is about ejecting
inanimate “fairly robust” payloads from some-
several-thousand-metres, and getting them onto
the ground with limited impact velocity with a
cheap, simple, damage-tolerant design. |
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A springy Carbon-fibre pole/rib, and a single layer
fabric wing (like a wind-surf sail) as a rotor. No
controls or suspension lines. |
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Several thousand metres is generally considered too high; the payload will drift from the DZ by an unpredictable amount. |
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For the military, precision placement is vital. |
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Hmm, //several thousand metres//. I’m wrong of
course. I was thinking of jump altitude rather than
opening altitude. For non-personnel parachute
drops, presumably something like 100 to 300m
under canopy. |
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