Rotor Blade Clearance
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Rotor Blade Clearance
I'm fixed wing type so forgive what might be a naieve question; but I was watching a video of a SAR Helio involved in a 'daring do' cliff rescue and wondered how on earth the crew can judge the proximity of the blades to rock. Of course, its no doubt something that comes with training and experience, but I wondered if there is an electronic device that gives the pilot an indication as to blade proximity- sort of like the things you have in cars for reversing- go beep when close and, beep beep beep when you're really too close. Or perhaps it when the winchman screams!
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wondered how on earth the crew can judge the proximity of the blades to rock.
Of course, some people get it wrong!
Cheers
Whirls
Join Date: Apr 2000
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I was fortunate enough to have a PPL(H) instructor who would answer my such questions by placing our R22 near to such an obstacle (tree in remote corner of secret airfield nr Stratford on Avon) and request me to observe. Light winds, good viz.
One notices that the blades are not blades anymore but a tangible disc.
Compare with rapidly whirling a string with a rock attached to the end over your head whilst next to a wall - you can move in very close, and 'tick' the wall (See Chicken Hawk) as long as you can watch the disc.
Of course all this takes place with your feet on the ground, good viz, both feet doing nothing and one hand in pocket.
Real pilots manage to do similar with radio load, multi-crew demands, wind, rain, turbulence, dark, instrument scans and someone on the end of a winch cable 50 feet above jagged rocks and thundering sea state.
The only consolation most of us have is they don't use an R22 to do it.
Regards
Cron
One notices that the blades are not blades anymore but a tangible disc.
Compare with rapidly whirling a string with a rock attached to the end over your head whilst next to a wall - you can move in very close, and 'tick' the wall (See Chicken Hawk) as long as you can watch the disc.
Of course all this takes place with your feet on the ground, good viz, both feet doing nothing and one hand in pocket.
Real pilots manage to do similar with radio load, multi-crew demands, wind, rain, turbulence, dark, instrument scans and someone on the end of a winch cable 50 feet above jagged rocks and thundering sea state.
The only consolation most of us have is they don't use an R22 to do it.
Regards
Cron
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Mmmmmmm ....
When doing that sort of rescue stuff the aircraft are often fitted with the Mk1 audio warning system ... ie a crewman who will in no uncertain fashion keep you informed as to how close you are to objects ....
The higher the pitch of his voice and the speed of his information delivery is a clue to how close you really are !!!!!!
When doing that sort of rescue stuff the aircraft are often fitted with the Mk1 audio warning system ... ie a crewman who will in no uncertain fashion keep you informed as to how close you are to objects ....
The higher the pitch of his voice and the speed of his information delivery is a clue to how close you really are !!!!!!
There have been many suggestions to trial a tip warning device with beepers etc but most are impractical and would most likely prove an unwanted distraction in a busy environment.
The winch operators are the key and they have to constantly scan tip and tail clearances whilst trying to watch the winchman's hand signals and voice marshal the aircraft.
On many helicopters the pilot sits quite far forward relative to the rotor hub so he would have to look over his shoulder to see the widest part of the rotor disc (not very comfortable or practical for accurate hovering).
A good training exercise on the ground is to have a member of the crew or ground crew stand just outside the rotor disc so the crew in the helicopter get used to judging the distance.
Our winchmen have Polycon (a winchmans intercom/radio) when they go on the wire but more often than not their attention is focussed on facing forward and getting safely to the casualty.
The winch operators are the key and they have to constantly scan tip and tail clearances whilst trying to watch the winchman's hand signals and voice marshal the aircraft.
On many helicopters the pilot sits quite far forward relative to the rotor hub so he would have to look over his shoulder to see the widest part of the rotor disc (not very comfortable or practical for accurate hovering).
A good training exercise on the ground is to have a member of the crew or ground crew stand just outside the rotor disc so the crew in the helicopter get used to judging the distance.
Our winchmen have Polycon (a winchmans intercom/radio) when they go on the wire but more often than not their attention is focussed on facing forward and getting safely to the casualty.
For my convenience its good to have the bladetips painted in bright daylight colour like red or yellow, so its easier to see the end of the rotordisc. For night operation one searchlight pointed to the tip area also helps a lot. As far as i remember, there are also rotortip-lights ( mounted in the blades ) available ( Blackhawk? ).
skadi
skadi
Last edited by skadi; 14th Oct 2008 at 11:43.
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I was once asked "how do you know if you are too close?" That's easy I said, if you get too close it makes a big stuff off bang, and so we fly close to things outside of the "big bang area".
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I've always found that the higher the crewmans voice gets the closer you are to the object to avoid. Also a shower of leaves when it is not Autumn is a bit of a clue.
I have posted this photo elsewhere but it may amuse you, NOSIG to see it as a proximity warner would have been useful, especially when we had to get on at night.................
I have posted this photo elsewhere but it may amuse you, NOSIG to see it as a proximity warner would have been useful, especially when we had to get on at night.................
Last edited by bast0n; 14th Oct 2008 at 08:47. Reason: Cocked up the picture insert!!
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During very closely supervised confined area training, when landing with the rotor disk about 7 feet from a tree, you're watching the disk very carefully. You really have a hightened sense of clearance, when the mentor pilot tells you that a blade strike on even to smallest of branches requires a $135,000 inspection and mandatory replacement of parts.
A couple of dodges from the Far East when going into tight clearings.
Hover at a couple of hundred feet so that your shadow is in the clearing. As the shadow is the same size as you, the sun's rays being parallel, you can see how much room you have. When it is very tight descend with the scenery close to the nose for the tail rotors sake, The downwash will push the leaves down so then move forward until they are affected by the rotor tip vortices and kick up.
That's as close as you can get.
Hover at a couple of hundred feet so that your shadow is in the clearing. As the shadow is the same size as you, the sun's rays being parallel, you can see how much room you have. When it is very tight descend with the scenery close to the nose for the tail rotors sake, The downwash will push the leaves down so then move forward until they are affected by the rotor tip vortices and kick up.
That's as close as you can get.
Hovering AND talking
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Hover at a couple of hundred feet so that your shadow is in the clearing.
Cheers
Whirls
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Whirls - I note that you come from this lads territory! Are you of sound mind?
Bishop Bonner who is said to have been the man responsible for burning over two hundred heretics ...
I like the idea of looking at your shadow, but as you said not hugely practical in the summer, nor on a boat nor if you cannot see directly underneath the aircraft!! Also one should always remember that the main rotor is much better at clearing small trees than the tail rotor................
Bishop Bonner who is said to have been the man responsible for burning over two hundred heretics ...
I like the idea of looking at your shadow, but as you said not hugely practical in the summer, nor on a boat nor if you cannot see directly underneath the aircraft!! Also one should always remember that the main rotor is much better at clearing small trees than the tail rotor................
Nice idea with the shadow but there are 2 main problems apart from not having much sunshine in the UK:
1. The length of your shadow changes with the angle of the sun so it will only work if the sun is directly overhead (look at the long shadows cast near sunset)
2. As Baston has said, you need to be able to see directly under the aircraft to see the shadow in this case - not very likely in most aircraft and certainly not to the point where you could see the whole fuselage, let alone the rotor disc.
Back to picking good markers and a careful recce methinks.
1. The length of your shadow changes with the angle of the sun so it will only work if the sun is directly overhead (look at the long shadows cast near sunset)
2. As Baston has said, you need to be able to see directly under the aircraft to see the shadow in this case - not very likely in most aircraft and certainly not to the point where you could see the whole fuselage, let alone the rotor disc.
Back to picking good markers and a careful recce methinks.
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A couple of dodges from the Far East when going into tight clearings.
Hover at a couple of hundred feet so that your shadow is in the clearing. As the shadow is the same size as you, the sun's rays being parallel, you can see how much room you have
Hover at a couple of hundred feet so that your shadow is in the clearing. As the shadow is the same size as you, the sun's rays being parallel, you can see how much room you have