[gurps] Autogyro performance

[David Scheidt]

On Mon, Apr 6, 2009 at 12:31 PM, Onno Meyer <Onno.Meyer at gmx.de> wrote:
>> Minimum speed for 30 mph, take-off run of 30 yards,
>
> v = speed
> a = accel
> t = time
> d = distance
>
> So we have roughly v = 13 m/s after d = 27 m.
>
> v = a*t <=> v/a = t
> d = 0.5 a t^2 <=> d = 0.5 a (v/a)^2 <=> d = 0.5 v^2/a <=> a = 0.5 v^2/d
> a = 0.5 * 169 m^2/s^2 / (27 m) = 3.12 m/s^2
>
> Assuming constant acceleration, the autogyro would need
> an acceleration of roughly 7 mph/s for that takeoff run.
> Not surprisingly, Vehicles agrees.
>
>> 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.
>

Which it almost certainly was.  Autogyros have pretty friendly stall
behavior.   When an airplane stalls, the lift drops abruptly to close
to zero, so the plane falls at 1 g, until it hits the ground, or it's
got enough air speed to generate lift.  As an autogyro slows down, its
rotor produces less lift.  When it produces less lift than necessary
for level flight, the autogyro falls, but the lift produced by the
rotor doesn't fall to zero, it's just less than what's needed to keep
it in the air.  So the autogyro falls with an acceleration much less
than one g.

Autogyros are probably not easily coverable by the rules in Vehicles,
as they're very different beasts than fixed wing aircraft, or
helocopters.

-- 
David Scheidt
dmscheidt at gmail.com