Subject:
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Re: Human Powered Helicopter
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Newsgroups:
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lugnet.org.ca.rtltoronto
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Date:
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Sun, 8 Aug 2004 21:34:08 GMT
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Viewed:
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613 times
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In lugnet.org.ca.rtltoronto, Ivan Louch wrote:
> Even though he only has to spin the rotors at 6.2 rpm and the total weight of
> all four blades is only 55.4kg, the sheer size of the “wing-span” is indeed
> daunting!
6.2rpm?!?!? As in, about once every ten seconds? Huh. That's pretty slow.
Hmm, looks like you missed something there. The "inner" rotor (which actually
has more surface area than the outer rotor) spins at 6.2rpm, but the outer rotor
spins at a mere 3.6rpm. I'll accept that they've probably done their math
right, and that it will actually be able to lift off the ground at those speeds,
but I guarantee people will be looking for wires when they come across an
in-flight video of it on the internet.
> All of this said, would anyone actually happen to know why this technology
> seems to be widely used only by the “Soviets” and only for military
> applications? Or at least am I not aware of any commercial co-axial rotor
> designs.
From the page you linked to, it sounds like maybe they haven't even "widely"
used them. The text appears to be four years old, but it says that they only
had a few of the Hokums, that it hadn't been "fielded" (I'm guessing that means
"used in actual combat"), and that it was competing with another helicopter
design to replace the Mi-24.
Anyways, while it may be a more efficient design, the co-axial rotor might
suffer from the same problem as the Wankel engine, in that it's probably more
prone to failures (unless they've got twin layers of bearings between the two
rotor shafts, they're going to be spinning twice as fast as the bearings for a
single-rotor design), and more difficult to repair both when something does go
wrong and whenever you reach the inevitable point of having to perform
preventive maintenance on it. I remember hearing that Wankel engine cylinders
have to be stripped down and refitted with completely new seals every 50,000
miles, while traditional piston cylinders could conceivably run over 200,000
miles without the head needing to be opened up, and they'll still run with leaky
seals, though your gas mileage will be shot all to heck. A smart military is as
concerned about long-term durability as they are about short-term efficiency.
That's exactly why the US military uses J-8 to run everything with an IC engine,
since that's the minimum common fuel that they can get away with using, and
while it's about as inefficent as you can get, it means they can refuel a jet
fighter from the spare fuel cans on the backs of Jeeps and Humvees if they need
to.
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Message is in Reply To:
 | | Re: Human Powered Helicopter
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| (...) Even though he only has to spin the rotors at 6.2 rpm and the total weight of all four blades is only 55.4kg, the sheer size of the “wing-span” is indeed daunting! (...) Ohh the co-axial rotors are just beyond sweet! I doubt I can sum it up (...) (20 years ago, 8-Aug-04, to lugnet.org.ca.rtltoronto)
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