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@stux Interesting and related: did you know a helicopter can land safely from any height even with completely down engines.
Not *any*, no.
There are regimes of altitude and airspeed where autorotation cannot provide a safe landing.
https://en.m.wikipedia.org/wiki/Helicopter_height%E2%80%93velocity_diagram
If you are in those regimes then its pilot error.
Thats a bit like saying a plane cant land safely if it intentionally nose dives right before landing (picking up too much speed).
Obviously it only works if the airspeed are controlled by the pilot on the way down.
@freemo @nlarson830 @stux Beyond a certain point you cannot slow down your descent by increasing pitch. You have to fly forward to recover, and if there is something in the way, you crash. As I recall this happened during the Bin Laden raid.
Then there are machines like the Osprey that cannot autorotate, and if the power fails you are dead. It has a complex transmission that is supposed to let one engine spin both rotors, but if the transmission fails, sorry about that.
@freemo @nlarson830 @stux I wonder if the next generation Osprey could be electric backup. Have an electric motor/generator inline with the turbine gearbox on each side. Under normal conditions these are the power generators and engine starters. In the emergency case, one runs as a motor powered by the other to keep both rotors going.
You would need to handle a serious overload for at least a few minutes. Perhaps make it liquid cooled with the coolant allowed to evaporate during an emergency.
@freemo @nlarson830 @stux Vertical flight, taking off straight up and landing straight down, looks cool in the movies. Just re-watched the Airwolf movie and there is some seriously dangerous helicopter flying in there!
There are a bunch of gotchas. Taking off straight up can kill you if the power fails. Landing straight down can kill you even if the helicopter is fine. You are descending into your own downwash, which reduces your lift and makes you fall faster.