Spike Jones wrote:
>
> Mike Lorrey wrote:
>
> > ...a 30 shp engine should do the trick. Spike messed up on scaling
> > those 5 hp radio controlled helicopters, I think, since aerodynamic
> > efficiency doesn't scale linearly...
>
> That's right. The longer rotor is more efficient for lift/power
> requirement. Of course it then requires more power to
> cancel the greater torque and of course gets heavier and less
> convenient to use.
>
> What I think would be worthwhile is to research as
> many VTOLs as we can find online, find their maximum
> shaft power rating and their lift at that rating (craft
> weight plus max payload.) Then we can create a graph
> with rotor diameter on the horizontal axis, the ratio
> of power to weight on the vertical. That relationship
> should be nearly linear, if I recall the equation from
> my helicopters textbook correctly.
Here's one datapoint: A news release in Pop. Mechanics this month about
an entry for the Sikorsky Prize (human powered helicopter) from the U of
Quebec, which houses one human being generating 0.9 hp, turning, AFAICR,
two two bladed rotor disks with 76 ft. diameters. This device should, it
is claimed, be able to hover 3-6 feet in the air for x minutes.
While this is certainly underpowered and oversized for a commuter
vehicle (do you think? ;) ) and is taking advantage of ground effect, it
does demonstrate that minimum horsepower is highly dependent upon the
design of the vehicle in rotor diameter, blade area, and vehicle weight.
Mike
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