h a l f b a k e r yQuis custodiet the custard?
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This is such an obvious idea that I'll be surprised if it doesn't
exist, but I may be Googling the wrong terms.
Drones, particularly recreational ones, usually have two- or
three-bladed plastic propellers. These get broken easily, or
can damage things and body-parts.
Novice drone pilots
may use a fixed prop-guard - usually a
plastic frame with four rings that sit around each prop.
However, the guard adds extra weight.
Why not build the shroud into the propeller itself? Each
prop
would be like a normal prop, but with a circular plastic
hoop
permanently fixed to the blade tips. A spinning hoop is
much
less likely to get broken in a collision than a spinning prop
blade, and will also do much less damage to anything it
hits.
Four such props will be a little heavier than four normal
props, but much lighter than the usual fixed prop-guard.
If the hoop had some vertical thickness to it (like a very
short
cylinder), it might even improve the efficiency of the props
by providing a partial ducted-fan effect.
p.s. I think we need a "Drone" category.
Rolls-Royce Spey
http://www.aviation...ges/html/G3844.html
Mid-span fan hoop [EnochLives, May 26 2015]
toy
https://www.google....u4CYAw&ved=0CB0QsAQ
They weren't all red plastic. [Vernon, May 26 2015]
Is this your patent? Its from 2014!
http://www.google.c...tents/US20140323009
[pashute, May 26 2015]
Over-lapping rotors
http://spectrum.iee...all-have-hoverbikes
Not sure about this idea, really... [neutrinos_shadow, May 27 2015]
Forum discussion on over-lapping rotors
http://diydrones.co...05844Comment1619370
Discussing this very thing! [neutrinos_shadow, May 27 2015]
Propeller design software
http://www.propgen....latest_download.htm
[Ling, May 29 2015]
Enrique would approve...
http://www.independ...nging-10288086.html
[zen_tom, Jun 02 2015]
(?) Single blade propeller
http://forum.keypub...221981&d=1381790211
J2 Piper Cub with single blade propeller [whlanteigne, Jun 02 2015]
Chinese lanterns, just think of one of these with an ultraplurality of eentsy holes so air flows easily
https://www.google....:specific,isc:white
[beanangel, Dec 14 2016]
[link]
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I remember a red plastic toy that was a prop with a flat ring
molded into the three tips. Think it was propelled by a pull
string and went flying up when yanked. |
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Does anyone know what the affect on efficiency of hooping
the blades is? Given that it reduces tip vortices and thus
noise, if it were actually efficient, I would expect it to be
common on wind turbines and the like. |
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At the very least, it is going to add spinning weight,
requiring a higher power motor for the same prop speed. |
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Doubt it'd work on anything larger than a toy: wicked precession. |
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//going to add spinning weight, requiring a higher
power motor for the same prop speed.// |
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Wrong. It'll need a higher power motor for the same
prop _acceleration_, but not for a higher speed. |
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//wicked precession// Yes, but I doubt this an issue
for a drone since (a) the props even with a hoop
aren't very massive and (b) the props are in opposite-
spin pairs. |
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//red plastic toy// I remember the very same thing -
they were the advanced air-toys of the 1970s... |
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I'm pretty sure I've seen this concept before although I don't
know where. Certainly some old-style aeroengines had a
mid-height hoop built into the fan to remove certain
vibrational modes <link>. |
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Regarding efficiency, it will reduce tip vortices as [MechE]
says, but this will be countered somewhat by drag on the
outer surface which will resist rotation. |
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Ha - I remember that plastic toy.... I always wanted and excuse to say this: "nick nack, paddy wack, give the drone a bone...." ha (no actual bone of course - I rarely bone anything) |
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Funny, I was thinking about this exact thing the other day. |
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I doubt it would be popular for racing type drones, which require very light props in order to be able to speed up and slow down the props very rapidly (adding mass to the props will make the drone much less dynamic). Likewise, using 3 bladed props instead of 2 gives you more thrust but ultimately reduces flight time due to the increased drag of the extra prop blade. So drag on the blade is obviously an important factor. The trend now is to go to very thin, high aspect ratio blades to minimise drag. |
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However for toy-type and learner multicopters, this would make a lot of sense. It would definitely be interesting to see if you could mould the outer surface into a duct - this might partially or fully offset the additional drag of the outer face. |
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[+] I think I saw a real helicopter with that ring... |
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RC Quadropters have them, and the Gazelle has its tail rotor
inside. |
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In google images one of the results for "rotor ring" is a device
around an airplane propeller that was claimed in the old days
to increase the plane's speed. |
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It isn't going to protect the prop as much as it seems like
it should. Because all of the ring mass is at the maximum
radius from the axis, almost all of the angular momentum
ends up in the ring. And drones, to be useful, generally
end up staying level; therefore, they tend to rise and
descend fairly vertically - so if the prop hits something,
there's a pretty good chance it's going to come up into the
blades, rather than striking the edge of the ring. |
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Stopping a blade while the attached ring has all the
momentum can cause more damage than without. Not
always, but enough that in the design trade-offs, the
lighter un-ringed prop usually will win. |
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// it's going to come up into the blades, rather than
striking the edge of the ring// |
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That's a point, although in my own droning, I tend to
hit things sideways, or at least at a shallow enough
angle that the rim would hit before the blades. Also
note that the optional fixed prop-guards simply put a
fixed ring of plastic around the blade. |
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As a kid, I've had little helicopters with a ring connecting
the rotor tips. |
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// Likewise, using 3 bladed props instead of 2 gives you
more thrust but ultimately reduces flight time due to the
increased drag of the extra prop blade.// |
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There's also wake to consider. A 2 bladed prop blade is
running into the wake of the blade 180 degrees away
from it. You add another blade, it's 120, the prop blade is
going to run into more severe wake turbulence from the
blade ahead of it. The blades operate less efficiently
when they operate in wake turbulence. The number of
blades goes up when more air needs to be moved, but the
blade length can't increase, either because you don't
want the Spitfire's prop to hit the ground, or you don't
want the prop tips to go supersonic. |
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I wonder if there's any advantage to having a one-
bladed prop? |
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With a counterweight, obviously. |
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[EDIT] OK, single-blade propellers are wkte. |
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//A 2 bladed prop blade is running into the wake of the
blade 180 degrees away from it. // |
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I don't think this is true. The wake from any particular rotor
blade corkscrews downstream. Each blade sees 'clean' air
regardless of the blade count unless there is some other
physical obstruction upstream. |
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The Wikipedia article on single-bladed propellers
mentions that one of their advantages is reduced
wake interference. |
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I presume it's more of an issue at low forward speeds
- at 300mph and a prop speed of 3000rpm, the plane
will move about 1.3m in the time it takes the prop to
make a half-turn. |
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Yes, perhaps at very low flow (or descent) conditions. In
hovering flight it shouldn't be an issue. |
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On a somewhat related topic, I wonder if you could reduce
the planview area of a quadcopter by allowing the four
rotors to overlap. In this design aerodynamic interference
would be critical, but single bladed rotors may solve this
problem. If necessary the rotors could be located in slightly
different planes to allow maximum overlap. |
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In a quadcopter, you need some distance between
the rotors to give you good control of pitch, yaw and
roll. |
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Maybe you could open a manufacturing facility in Turin. |
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It's a simple study in risk/reward ratios. You might
get
a 10% reduction in deaths of people running into your
rotor but a 20% reduction of thrust efficiency. |
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So 20% divided by 10% gives you your risk to reward
numerology. It's simple science, so any simple
scientition or
mathematicist could tell you that. |
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My numbers may be slightly off since I don't know
what I'm talking about, but that's the general idea. |
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//It's a simple study in risk/reward ratios. // Ah, but the people that die are *not me* because I'm always more careful when the quad is close to me, but less so when it's close to others. |
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My thoroughly pragmatic view skews the risk/reward ratio in a way I'm sure you didn't intend. |
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That said, the damage potential for multicopter blades should not be underestimated. They carve flesh with disturbing ease. Someday someone's going to come up with sharpened titanium propellor blades, combined with oversized and over braced motor shafts, and create a truly formidable weapon. (Hmm, perhaps a fluid coupling on the prop drive end and this could probably be quite robust as well...). <cue sound of hand drier kicking off in the background> |
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It's not a matter of getting your head around the problem,
it's getting the problem around someone else's head. |
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Motors in quadcopters are brushless, it should be pretty
easy with sensor-equipped motors to make sure that
intermeshing blades never touch. The fewer the blades the
easier it is. |
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More blades must produce less efficiency per blade,
otherwise helicopters would all be using many more, the
rotor disc is a huge, cumbersome and vulnerable device,
chopping 33% of the radius with another blade would lead
to much easier design... shorter tail boom for one. |
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(pretty sure that) quadcopters use differential motor thrust to change attitude: there goes meshing down the tubes, unless you want to change propeller pitch instead (more complex hub assemblies, but on the bright side you only need one motor). |
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A normal quadcopter is only able to vary the speed of its four propellors. There are no tail rotors or any other control surfaces. Pitch is controlled by varying the speed of the front and rear props, and forward/rear translation is achieved by sustaining a given pitch angle and holding altitude. Yaw is controlled by varying the speed of the diagonal pairs of props (rear left and front right will rotate one way, rear right and front left the other - thus neutralising yaw when in balance). Roll is controlled by varying the left and right pairs of propellors, and lateral movement is achieved by holding a roll attitude while maintaining altitude. The only other input is varying speed of all four props - which produces vertical translation. |
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//Motors in quadcopters are brushless, it should be pretty easy with sensor-equipped motors to make sure that intermeshing blades never touch// Methinks you underestimate the momentumn of the props versus the power of the motor, and the need to change speed of props constantly for control. The fact that control input is via varying speed of the props, you couldn't possible intermesh them (unless you switched to variable pitch blades instead. This has been done, for some acrobatic quadcopeters, but is mechanically complex and inneficcient). |
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//Methinks you underestimate the momentumn of the props
versus the power of the motor,// |
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Well, with a better motor power/momentum ratio we
should be able to control the props through their arc, single
bladed props could easily be sped up/slowed down to miss
each other while the average speed is maintained for thrust
reasons. If you have really good control, you could have all
four rotors overlapping. |
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Ot just stagger them vertically. |
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Actually what would be really cool would be if the
individual blades could tilt dynamically so as to just
miss eachother. |
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If you're going to change the pitch of your blades, then your
peripheral shroud is going to be unfeasible due to
complexity/weight. Staggering them vertically is a boring
solution compared to single blade/complex electronics. |
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//unfeasible due to complexity/weight. Staggering// |
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You will be hearing from my solicitor - that phrase
was lifted verbatim from my autobiography. |
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//that phrase was lifted verbatim from my autobiography// |
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...was lifted verbatim from my autobiography |
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... was lifted verbatim from the Coroner's narrative verdict ... |
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// My numbers may be slightly off since I don't know what I'm
talking about // |
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//More blades must produce less efficiency per blade// |
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The key parameter is the rotor disc loading, which is the
thrust per unit swept area. The lower the loading the
better from an aerodynamic perspective. For a _fixed_
loading you're better off with several lightly cambered
blades than one heavily cambered one. In reality I suspect
vibration and pitch mechanism complexity are just as
powerful drivers in selecting the blade count. A two-bladed
rotor also occupies significantly less hangar space than a
four-bladed design, although some military helicopters
have detachable blades for this reason. |
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Strangely enough, I used the linked software, last week, to
help design a 30 inch propeller for circulating water in a
quench tank (it works with different media). |
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There are obviously more complex simulations available, but
this is good for playing around with, especially varying the
number of blades. |
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I think you could surround the entire drone with something like a hyperporous Chinese lantern, it would be aerodynamically ok, because the air would pass through the massive amount of hyperperforations, yet if it bounced up against something it would be harmless. |
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going further, the propellers could be made of microsize hollow beadlets, sort of like the form of instant ice tea microspheres, so that if they did contact something, the propellers would spontaneously disintegrate, at a force harmless to human tissue. and of course they could make it out of PLA or starch to make it extra harmless. |
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A high rated (amazon) toy is National Geographic's $49.99 drone! |
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What is a //hyperperforations//? |
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// harmless to human tissue ... make it out of PLA or starch to make it extra harmless. // |
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What's wrong with razor-edged SilON ceramic ? Light weight, stiff, durable, slices through exposed flesh like a katana through warm butter ... |
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The cuts are very clean, not really that painful ... you'll bleed out long before you realize how serious the wounds are. |
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hyperperforations. Think of the Chinese lantern full of holes 1/10 the size of a period. |
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Ah, right. So "hyper" in the usual sense of "tiny", then? |
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