[gurps] Autogyro performance

[Anthony Jackson]

Brandon Cope wrote:
> I've known for quote some time that the formulas in
> VE2 didn't work for autogyros. They results in stall
> and top speeds too high and takeoff and landing runs
> too low. Anyone found a solution?

So, I have a program I wrote a while back for basic aerodynamics 
simulation. Let's assume a 10 ton vehicle with a wingspan of 60 feet, an 
aspect ratio of 8, and a drag coefficient of 0.025 (based on wing area, 
not cross-section, since that's how aircraft are rated). Also, we'll set 
stall angle for a life coefficient of 1.5. All of these appear to be 
fairly realistic numbers.

Its computed stall speed is 107 mph, at which speed it has a drag of 
roughly 1,650 lb, and requires a minimum of 352 kW power. This is near 
but not at its minimum power requirement, which occurs at 115 mph, and 
its minimum drag, which occurs at 151 mph. This is using standard 
aerodynamics.

Now, if we drop our reference speed to 50 mph, using fixed wing models, 
even if I can avoid stalling, I get a drag of 6,200 lb and a power 
requirement of 613 kW. If I use a helicopter model, power requirement is 
545 kW and the rotor is very nearly level.

If you were to cut power, the requirement for level flight would remain 
545 kW, which you would pay for with loss of altitude, which will result 
in a rate of descent of about 20 feet per second, or with a loss of 
speed, which would result in a deceleration of about 6 mph/sec.

I don't know what sort of effective attack angle an autogyro can manage.