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Autorotation “parachute”

Not for people though.
  [vote for,

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)

Frankx, Oct 16 2019


       I'm sure something like this has been baked in the Real World, and for human use.   

       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.
MaxwellBuchanan, Oct 16 2019

       Yes, but you're anatomically preconfigured to bounce well ...
8th of 7, Oct 16 2019

       Oddly enough, I know a bloke who "went in" (as the cheery phrase has it) twice, and got away with it both times.
MaxwellBuchanan, Oct 16 2019

       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.   

       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.   

       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.
doctorremulac3, Oct 16 2019

       //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.
MaxwellBuchanan, Oct 16 2019

       Thanks [DrR]   


       I wasn’t imagining any of that complexity. The airframe spins with the blade. Hence “not for people”
Frankx, Oct 16 2019

       (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.   

       (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.
doctorremulac3, Oct 16 2019

       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.   

       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.
Frankx, Oct 16 2019

       Several thousand metres is generally considered too high; the payload will drift from the DZ by an unpredictable amount.   

       For the military, precision placement is vital.
8th of 7, Oct 16 2019

       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.
Frankx, Oct 17 2019


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