Ducking under helicopter blades - why?
Discussion
Just watched Dirty Mary, Crazy Larry again and one thing got me thinking.
When people run for a helicopter that has it's blades spinning, why do they duck down?
On a R22 or something, yes, I can understand that but you get people ducking even when running up to chinooks and other big stuff.
Anyways, that film always impresses me in the quality of the flying, stupid but enjoyable.
When people run for a helicopter that has it's blades spinning, why do they duck down?
On a R22 or something, yes, I can understand that but you get people ducking even when running up to chinooks and other big stuff.
Anyways, that film always impresses me in the quality of the flying, stupid but enjoyable.
I fly in a Sikorsky S76 every five weeks, to or from my ship. It is not a big chopper, but not exactly small. We always duck a bit when walking under the blades, because the pilots tell us a sudden crosswind can cause the bladed to wobble up and down quite a bit. Sometimes they load up the blades to keep the chopper pushing down a bit on the ships helideck, which also causes them to curve down a little more than normal.
People have been hurt, or beheaded, through such simple things as walking bolt upright.
People have been hurt, or beheaded, through such simple things as walking bolt upright.
The blades can deflect quite a lot - as demonstrated here...
https://www.youtube.com/watch?v=I3Pp4vOr3SE
https://www.youtube.com/watch?v=I3Pp4vOr3SE
Because - on a windy day, there is a possibility that the disc can deflect downwards a very surprising amount! As has been said, this has caught out (sadly deceased) people in the past. Just Google round and you'll see what I mean.
Also, as far as I know - if the machine is sitting with the engines a Flight Idle then the rotor speed is spinning at a decent rate which prevents some deflection of the disc; however if the machine is sitting with the engines at Ground Idle then it will also be in a low rotor speed state, which means that the disc is more likely to deflect.
This is why, when the chopper I sometimes work with starts up, our Pilot tells us to stay away from the disc until he gives us a thumbs up - when he does, we can then approach the aircraft and it is apparently when the engine is up to Flight Idle mode, and the disc is the least likely to deflect in wind.
HTH...
Also, as far as I know - if the machine is sitting with the engines a Flight Idle then the rotor speed is spinning at a decent rate which prevents some deflection of the disc; however if the machine is sitting with the engines at Ground Idle then it will also be in a low rotor speed state, which means that the disc is more likely to deflect.
This is why, when the chopper I sometimes work with starts up, our Pilot tells us to stay away from the disc until he gives us a thumbs up - when he does, we can then approach the aircraft and it is apparently when the engine is up to Flight Idle mode, and the disc is the least likely to deflect in wind.
HTH...
HD Adam said:
I remember an accident in the SNS in 1992 on the Viking Platform where the HLO got his head chopped off
This was a Dauphin 365n and like the S76 mentioned by King Herald, you'd better duck if you approach from the "wrong" direction.
Thats a photo of one taxiing though, they don't normally have the rotor head tilted down like that. I agree with you though - not wise to be all macho and walk bolt upright into the blades.This was a Dauphin 365n and like the S76 mentioned by King Herald, you'd better duck if you approach from the "wrong" direction.
griffin dai said:
run under a Chinook & get someone to film you 
It's quite hard to walk on board a chinook standing straight due to the rotor wash/jet wash so leaning forward a bit and tucking your head down is a good technique.
I believe a chinook can have upto 4ft of blade sag on the front rotor!!
As has been said, rotors are hinged, they have to be or else the whole thing wouldn't fly. The amount of deflection can catch anyone out.
When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
HD Adam said:
I remember an accident in the SNS in 1992 on the Viking Platform where the HLO got his head chopped off
This was a Dauphin 365n and like the S76 mentioned by King Herald, you'd better duck if you approach from the "wrong" direction.
I was working on the Viking platform, although on leave at the time, and i believe it was decided that the blades were caught by a gust of wind. Anywhere forward of the pilots was considered a no go area, i went out to satellite platforms most days and you had to be extremely vigilant as HLO to keep people out of the danger areas.This was a Dauphin 365n and like the S76 mentioned by King Herald, you'd better duck if you approach from the "wrong" direction.
Hainey said:
As has been said, rotors are hinged, they have to be or else the whole thing wouldn't fly. The amount of deflection can catch anyone out.
When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
Looking at the photograph of the Dauphin, I'd rather approach from the rear!When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
The worst time is starting or stopping the rotors in gusty winds when the blades are very prone to 'sailing'. Its amazing how much a modern composite (and very thick) blade can sail in gusty winds. I've seen blades almost touch the ground on closedown when they are normally rotating 15 feet or so above you.
I always duck down when I walk in and out of the disk area, even though blade sailing with the engines driving at normal rotor speeds is very unlikely, however I would never walk in or out the disk area during any start or stop.
I always duck down when I walk in and out of the disk area, even though blade sailing with the engines driving at normal rotor speeds is very unlikely, however I would never walk in or out the disk area during any start or stop.
Forgive me if this is a dumb question as I have never been near a helicopter with blades spinning, but why WOULDN'T someone duck when approaching a helicopter? It's a normal human reaction to duck under something that's head height so my thinking would be that people will duck if the blades are low and not duck if they are high, or are the blades going so fast you can't really see them when you are up close?
Halmyre said:
Hainey said:
As has been said, rotors are hinged, they have to be or else the whole thing wouldn't fly. The amount of deflection can catch anyone out.
When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
Looking at the photograph of the Dauphin, I'd rather approach from the rear!When you lift off and go forwards, after about 20kts you get the disk 'flapping back' which really changes the dynamics of the handling and shows how much movement there is in the whole system. Ask the pilot to describe it as you go through it and you'll start to get an understanding of the physics of the whole system.
The ducking thing is something I always brief any pax about. That and never, ever approach from the rear, always the front. Those are my two golden rules at the pre flight briefing.
yeah you can change the rules a little when you fly something with a fenestron!All technicalities aside, when I'm getting on a chopper (which has happened exactly once mind) I duck, because cool-headed logic or not, there are big spinning sharp things moving around my head at speed.
Equally, I could walk up and down a kerb stone without falling off for any amount of time I fancy, but asked to do something like this
Even if it was the calmest wind day in the history of the earth, I'd be clamped around it like my life depended in it.
Equally, I could walk up and down a kerb stone without falling off for any amount of time I fancy, but asked to do something like this
Even if it was the calmest wind day in the history of the earth, I'd be clamped around it like my life depended in it.
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