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This should ideally reduce the tendency of VTOL aircraft to destroy landing helipads, since the vast majority of the air being pushed around is ambient temperat
by ashtonkem 6y ago
This should ideally reduce the tendency of VTOL aircraft to destroy landing helipads, since the vast majority of the air being pushed around is ambient temperature rather than being turbine or low bypass turbofan exhaust.
But it doesn’t solve the problem that VTOL aircraft like this are fundamentally unsafe, as they lack the ability to glide effectively and they don’t have the option to autorotate should the propulsion system fail. Helicopters are already significantly less safe than airplanes, and VTOL aircraft tend to be less safe still.
Even the Harrier, which at least could fly normally, was notoriously crash prone, with an accident rate 3x higher than the contemporary F/A-18. The V-22 is proving to be a pretty reliable marine killer in its own right, and that’s before you account for its abysmal uptime and tendency to be grounded.
Perhaps this aircraft will fix some of the issues of past VTOL aircraft, but I’d still be super wary about getting in one.
- nradov 6y agoMost of the recent powered lift aircraft designs include a rocket assisted recovery parachute to use in case of power loss. However there can still be a dead zone: too high to survive a crash but too low for the parachute to be effective.
- jillesvangurp 6y agoI guess with some designs they could also reduce impact via e.g. the autorotor effect that a helicopter would use if the engine dies. Obviously does not apply to this particular setup. But most designs have at least some lift, which means there is some optimal glide ratio that minimizes vertical speed. Finally, having separate, isolated systems helps as well. This is also common with multi engine aircraft where an all engines out scenario is very rare. It's a challenge but not necessarily something that can't be addressed. Even some simple airbags could help here.
- nradov 6y agoMany powered lift aircraft designs have very little aerodynamic lift and so the glide ratio is close to zero. And regardless of lift, they generally lack the articulated control surfaces necessary to establish a controlled glide. Autorotation only works if the rotor system has significant rotational inertia and a cyclic (blade pitch) control. Most powered lift designs have multiple small, low-inertia fixed-pitch rotors. If you lose power you're going straight down and probably tumbling out of control. Airbags can help a little in some low-altitude crash scenarios but if the aircraft is falling out of control then there's no way to guarantee that the airbag will be oriented the right way. It's just not practical to cover an entire aircraft in airbags like NASA did on the Pathfinder Mars landing: the technology doesn't scale up.
- ashtonkem 6y ago> If you lose power you're going straight down and probably tumbling out of control. The Osprey has a really nasty habit of doing this. A number of them have crash landed upside down from relatively low altitudes, which is a very bad thing.
- nradov 6y agoYou're referring to a vortex ring state, which can hit helicopters flying low and slow. It has nothing to do with surviving an engine failure in a powered lift aircraft.
- ashtonkem 6y agoVortex ring states in multi-engine VTOL aircraft have the unpleasant tendency to flip the aircraft over, which is markedly worse than being up right at least.
- ashtonkem 6y agoMost non-helicopter VTOL aircraft cannot autorotate. The V-22 cannot, for example; not enough inertia in the blades to pull that off.