On Sun, Mar 16, 2014 at 08:28:46PM +0000, Roger Bell_West wrote: >On Sun, Mar 16, 2014 at 08:00:02PM +0100, Onno Meyer wrote: >>The problem is that they don't really look like ducted fans. >>How fast has the air to go through those little nozzles? > >Each square metre of nozzle/rotor/etc. exhausting air at jet engine >speed can provide about 10kN of thrust*. A full-up Apache at 10,433kg >(MTOW) would need 10.4m^2 of exhaust area to get off the ground. (Its >actual rotor has an area of 168m^2, so it actually needs to throw air >downwards at only 22m/s.) What's the MTOW of the vehicle? > >* thrust/area = airdensity * speed^2 > modern jet engine exhaust speed = ~200mph > standard air density = 1.225kg/m^3
Higher-spec jet engines can run at higher speeds: a PW306A can exhaust at 613knots, which makes the total required area about 0.84m^2. Of course, the last thing you want to do is point that at the ground, because the ground will get blasted loose and sucked into your jet intakes. _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
