The London Air Ambulance use helicopters with NOTAR (https://en.wikipedia.org/wiki/NOTAR). It's really noticeable how quiet they are compared to other helicopters. They also often land and takeoff on the street - which is pretty cool to encounter on your morning commute. https://www.youtube.com/watch?v=jHsd-YShYds
What I find strange (?) is that the LAA does not seem to be run by the government, but by a charity:
> London's Air Ambulance Charity is a registered charity that operates a helicopter emergency medical service (HEMS) dedicated to responding to serious trauma emergencies in and around London.[3] Using a helicopter from 08:00 to sunset and rapid response vehicles by night, the service performs advanced medical interventions at the scene of the incident in life-threatening, time-critical situations.
> When London calls, our team are there to reach those urgently in need of life-saving care. Our vision is to end preventable deaths in London from life-threatening injury. Our mission is to save more lives in London through rapid response and cutting-edge care. We are a charity that works alongside the NHS and our life-saving service is made possible by you; our supporters.
My experience with computer fans is the smaller ones are much (much) noisier than larger ones moving the same amount of air (because they have to spin faster). Unclear why these are quieter - is it just the electrical power? From the article it seems like they have better control of the speed so can turn them off on the ground, so perhaps they're only quieter in some situations.
1) somewhat counterintuitively, in small helicopters the tail rotor can be actually louder than the main one
2) with traditional design the rear rotor HAS TO spin if the main rotor is spinning
3) with this design the rear rotor can stay still, and actually as the article points out at speed you don't have to use it as the air generates enough force on the tail to keep the helicopter straight so to speak, so the entire machine should be quiter in flight.
4) and finally yes, you can keep the rear rotor still on the ground which is safer for ground crews and quiter at the same time
I'd guess you're mostly correct. OTOH, though these fans could easily cost ~1,000X more than a computer fan. And that extra $$$ might unlock some pretty fancy noise-reduction technologies.
Silly question, but I wonder if manufacturers have done R&D for some kind of, er... emergency anti-twisting baffle?
I'm imagining something vaguely like a giant air mattress that inflates out the back/bottom when the tail rotor fails, a supplementary vertical fin.
I suppose that the benefit might not be that big If all that does is change the fuselage spinning from "extreme" to "severe." Above a certain rate helicopter is still going to go down.
13 comments
[ 6.3 ms ] story [ 213 ms ] threadSome basics: https://en.wikipedia.org/wiki/Stealth_helicopter
> London's Air Ambulance Charity is a registered charity that operates a helicopter emergency medical service (HEMS) dedicated to responding to serious trauma emergencies in and around London.[3] Using a helicopter from 08:00 to sunset and rapid response vehicles by night, the service performs advanced medical interventions at the scene of the incident in life-threatening, time-critical situations.
* https://en.wikipedia.org/wiki/London%27s_Air_Ambulance_Chari...
> When London calls, our team are there to reach those urgently in need of life-saving care. Our vision is to end preventable deaths in London from life-threatening injury. Our mission is to save more lives in London through rapid response and cutting-edge care. We are a charity that works alongside the NHS and our life-saving service is made possible by you; our supporters.
* https://www.londonsairambulance.org.uk/about-us/how-we-are-f...
They currently need to replace their existing helicopters, so if you live in London, please consider donating.
https://www.londonsairambulance.org.uk/up-against-time-appea...
1) somewhat counterintuitively, in small helicopters the tail rotor can be actually louder than the main one
2) with traditional design the rear rotor HAS TO spin if the main rotor is spinning
3) with this design the rear rotor can stay still, and actually as the article points out at speed you don't have to use it as the air generates enough force on the tail to keep the helicopter straight so to speak, so the entire machine should be quiter in flight.
4) and finally yes, you can keep the rear rotor still on the ground which is safer for ground crews and quiter at the same time
Edit: Also from 2020, not really "new".
I'm imagining something vaguely like a giant air mattress that inflates out the back/bottom when the tail rotor fails, a supplementary vertical fin.
I suppose that the benefit might not be that big If all that does is change the fuselage spinning from "extreme" to "severe." Above a certain rate helicopter is still going to go down.