--- Onno Meyer <[email protected]> wrote:
> > Minimum speed for 30 mph, take-off run of 30
> yards,
>
> Assuming constant acceleration, the autogyro would
> need
> an acceleration of roughly 7 mph/s for that takeoff
> run.
> Not surprisingly, Vehicles agrees.
So far my designs have fallen a bit short of this
(although so far only one is an historical design).
One ability of some autogyros to briefly power the
rotor to get it to full rotation speed, then disengage
the power and apply it all to the prop needs to be
accounted for. This can radically shorten the take-off
tun to single-digit yards. And no, this gearing isn't
nearly as heavy or complicated as a helicopter
transmission.
> > landing roll of 3 yards.
>
> decel 70, or roughly 3.5 Gs. That is way beyond
> anything
> Vehicles would allow, unless it was below 30 mph
> prior
> to the landing.
Dave has already explained this. Basically, the power
to the prop is cut way back and as the autogyro drops
below minimum speed, the rotors autorotate the craft
to the ground relatively softly. A autogyro can nearly
land vertically this way.
Also worth noting that since the rotor is unpowered,
the autogyro can safely land even if the engine cuts
out.
> To get the stall speed (i.e. minimum level flight
> speed)
> down to 30, what about larger rotor area in
> proportion
> to the body?
They don't appear to be oversized compared to a
helicopter of similar size, but autogyros might have
one more rotor. I've found, curiously, that raising
the rotors wing area to the 1.75 power produces
minimum speeds in a realistic range (the number came
from toying with the C.30 design).
> Take a flimsy structure and cloth
> armor,
> and the weight shouldn't be prohibitive. Drag goes
> up,
> but then autogyros were not exactly noted for speed.
Most autogyros were in the 100-110 mph top speed
range.
Again, laying with numbers, raising the rotor area tot
he 1.5 power int he drag calculation seems to give
good results, but I need to test more real world
designs.
Worth noting that the wings on earlier autogyros was
for control, not lift, and when Cierva figured out how
to use rotors for control, the wings were dumped.
> That could also help to explain the low stall speed
> of
> modern designs. They're little toys, with a better
> area to weight ratio.
I'm not sure I could call them toys -- they are just
very light aircraft. One YouTube video was a
promotional film showing the advantages of a light
autogyro over a light helicopter, including one being
used by police for search and rescue.
Brandon
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