Your UFO sightings for today

The fewer blades a propeller - or helicopter rotor - has, the more efficient it is. (Essentially, this is because the more blades you have, the more turbulent becomes the air each blade's trying to push around. Helicopters with lots of rotor blades have so many because a rotor with fewer blades would be unmanageably large, or require a radical redesign.)

So, ridiculous though this sounds, one-bladed propellers are actually the most efficient kind. Just one blade sticking out from the hub, on one side. Like a football rattle.

I think one-bladed props have actually been used in ultra-fast control-line model planes for ages, with just a counterweight on the other side of the prop from the blade. (And yes, they do also use pulse-jets!) There's at least one swishy-looking counterweighted one-bladed ceiling fan, too.

If you want large size or high power from a one-bladed prop, though, you're out of luck, because the single blade creates unbalanced thrust that'll wear your shaft bearings away in no time. (You may also have some difficulty finding test pilots.)

The single-bladed helicopter may be coming into its own, though, now that we've got tiny, powerful jet and electric motors, and somewhat better batteries, and low-power super-lightweight computerised control systems.

All this means we can now make a one-bladed helicopter, on the "samara" or "sycamore seed" principle, except powered - it's spun by a little normal propeller, on an outrigger.

In the olden days there'd be no way for an aircraft like this, whose whole airframe spins, to do anything very useful. But nowadays... well, just look:

It's probably not even tremendously difficult to shoot video from such a thing, today. In the olden days it would have required a nicely constant rotational speed, at the very least - but now if you want to look in a particular direction, it's pretty easy to just grab a fast frame at roughly the same spot in the rotation each time. Then you rub a little cheap digital signal processing on the output, to stop it jiggling from side to side or "tearing" as the platform spins too fast for the sensor chip to grab a whole square frame.

It probably wouldn't even be hard to run a few-hundred-frame-per-second camera (or a few cheap 30fps ones) with no position detection at all, and just stitch all the video together into a 360-degree panorama, with variable frame rate in all directions, back at base.

I have this image of some game-company 3D artist trying to get a thing like this put in, as a recon tool, in a sci-fi shooter set in the year 2100, and everybody telling him it was way too crazy. I bet powered sycamore seeds will actually be dropping bugs through people's windows inside five years.

6 Responses to “Your UFO sightings for today”

  1. Chris Lineker Says:

    Someone please fly the lighted version over a ufo believers conference

  2. mesh Says:

    I'm still not sure how they actually control it, some weak googleing just found a reference to using the earths magnetic field to sense rotation.

    Hm, on second viewing of the big model I guess I overestimated the RPM. I was thinking a servo wouldn't be fast enough to twist the blade up and down once every turn, but at about 4 rotations per second it should be doable.

    If I were to make a small one, I'd probably try an electromagnetic "servo", as seen on some cheap foam parkflyers. You could adjust the effective control throw by varying the duty cycle of the magnet. An IR sensor could detect a stationary IR source (maybe on the transmitter) to sense rotation!

    Now I want one!

  3. aramid Says:

    Since we're talking about a radio-controlled seed pod, you're making the camera issue far too complicated...You shouldn't need any computer wizardry, or any stationary IR source tracking, or anything like that. You'd be totally set with one fast servo, modified for continuous rotation, connected to a cheap heading-lock helicopter gyro.

    There are a few drawbacks to this, of course - the camera (and any RF video link) will have to be mostly self-contained and run off their own power source, since there's a pivot between them and the flight batteries, and the mechanical complexity (and therefore durability) is somewhat higher than with the computer-witchcraft approaches. Still, in at least some applications it seems like a reasonable price to pay for the simpler implementation.

  4. Shadowex3 Says:

    Save the weight on that kind of effort and put some dumpable counterweights on one end and a couple grenades on the other.

  5. Jon Richfield Says:

    I came up with the samara idea in the eighties, though I did not at the time realise that the 1-bladed prop was so efficient. In fact I based the idea on what I was informed was the fastes known protozoan; it used its body as a blade and a single flagellum to spin it like a samara. (Don't ask me about is steering!!!

    I soon thought out a lot of frills, like applications and its attributes in combat,but unlike the picture of the model, I was thinking in terms of a ramjet at one end. I also considered having a jet at each end, but rejected it in favour of a jet at one end and controls, camera, weaponry etc at the other. I was uncertain about the practicality of controlling such a device, and suspected that the only practical means would be by warping the surface and adjusting the angle of the engine. piezoelectric control sounded marvellous, but I did not think that it would be practical. Then I saw on television that a professor of aircraft construction in some southern state (Arizona, Texas, New Mexico,??? Can't remember) was in fact applying such controls experimentally. I e-mailed him, and he was quite encouraging about my idea but whether he took it any further I cannot say. Certainly I could do nothing of the kind, not having any skills that way. Anyone interested in discussing some of my initial ideas about the attributes and possible applications can e-mail me.
    Jon Richfield

  6. badcommandorfilename Says:

    I'm having trouble seeing how this is more efficient. Even though the vertical lift is being generated by a one bladed propeller, the thrust is provided by a multi-bladed propeller.

    In my engineering experience, the best efficiency comes from fewer, larger blades rotating at slower speeds (all of which reduce turbulent flow). The actual driving force of this device comes from a very small, very fast, multibladed propeller.

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