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From the Ray Prouty Archives: Emergency Maneuvering

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From the Ray Prouty Archives: Emergency Maneuvering

Old 16th Dec 2017, 11:48
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From the Ray Prouty Archives: Emergency Maneuvering

Rotor & Wing recently reprinted this Ray Prouty article: From the Ray Prouty Archives: Emergency Maneuvering - Rotor & Wing International
Ray discusses the helicopter limitations that a pilot needs to consider when deciding which emergency manoeuvre to choose when suddenly seeing a HV-line just in front of them.

The options that Ray discusses are:

- Pull-up
- Push-over
- 180 deg turn

While Ray explains - for each manoeuvre - which design limitations might be reached, and the short and long-term implications of breaching them, he doesn't actually say which emergency manoeuvre is most suitable to save your bacon.

If I may venture an answer: In all generality pulling-up is the way to go. It introduces the same change of direction (angular velocity) as a turn, and you make gravity work in your favour by slowing you down. Plus, while if choosing a turn, I would have to have turned by 90 deg within the remaining distance to the obstacle, with an aggressive pull-up I might be able to clear the power line long before even coming to stop.

Can one see it differently?
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Old 16th Dec 2017, 12:27
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Pull up and if you are going to hit the wires then hit them with the belly or bottom of the skids would seem most logical . Push nose down ..?? I dont think so unless you see the line above you and the move doesnt need to be too severe , especially in two blade machine ! Turning would only work if you have the distance and in that case pulling up would easier i would have thought but happy to be proved wrong ! Sadly all the wire strikes i have been involved with have not given the pilot time to do any avoidance and these were all at slow speed ( 50knots or so ).
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Old 16th Dec 2017, 14:11
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Well on one occasion I had to do two, first pull up to avoid catching the skid then push over to avoid catching the tail rotor.
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Old 16th Dec 2017, 15:22
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First, learn to take the good one trajectory to avoid HV power line ...
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Old 16th Dec 2017, 16:23
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Then, if you are going to pull, pull with both hands - the cyclic will alter the direction of total reaction ( plus increasing its magnitude thanks to flare effect) but the collective will add further magnitude, increasing the rate of change, whether you pull straight up or roll and pull into a turn.

As Ray points out, you are not going to G stall the rotor and, even if you exceed a transmission or engine limit, it's a whole lot better than taking a set of HT cables.

Remember this is Emergency Manoeuvring.
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Old 16th Dec 2017, 18:21
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Powerlines

As an ex crop sprayer, I could tell a tale or two... Pull up a bollard and I’ll tell you a few war stories about wires...
Ours of course were mainly 11kv that we went under at 3ft 😜
Always surveyed the fields at low level before spraying, especially looking for hidden posts in the trees.
As to valley high level wires.. 🤔
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Old 16th Dec 2017, 21:00
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Then, if you are going to pull, pull with both hands
That worked for me when I needed it.
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Old 16th Dec 2017, 23:11
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Would banking to 60 degs say (rather than turning) present the rotor at an angle to the wires, rather than parallel and thus create quite an effective wire cutter?

Last edited by jellycopter; 16th Dec 2017 at 23:13. Reason: Typo
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Old 16th Dec 2017, 23:47
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Jelly .... In the ones I have seen ,the wire , if hit by the blades , slides down them and then wraps around the mast and then also bends the control rods . ( one good reason to fly an Enstrom!!)
I am still hoping that some technology I am invested in will be able to detect a wire , live or dead , from at least 100m distance. Now I would like to sell that , as I do think it would save lives . ( but don't hold your breath as we have been working on it , for different reason , for last 5 years !!)
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Old 17th Dec 2017, 00:21
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100kn is about 50m/s. Two seconds is cutting it awfully close...
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Old 17th Dec 2017, 00:25
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I test flew an RAF helicopter equipped with a wires detector in 1979.
It consisted of a dial display with a "daisy petal" presentation to show the threat. It worked well some of the time...
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Old 17th Dec 2017, 00:27
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My unit had a CH-47C hit wires in 1985 that were spotted right before impact, the IP at the controls pulled up & banked, the wires were apparently cut by the fwd rotor which lost part of the tip on one blade. They also had a dent across the nose & broken chin bubble, very lucky.

A UH-60 crew that responded to the scene wasn't, they hit the same set at low speed & pretty much lost the rotor system & fell from a couple hundred feet.
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Old 17th Dec 2017, 12:15
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Originally Posted by aa777888 View Post
100kn is about 50m/s. Two seconds is cutting it awfully close...
I think two seconds is a reasonably long time. There is a lot you can do in two seconds.
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Old 17th Dec 2017, 14:35
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....like cancel two late lunches.......
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Old 17th Dec 2017, 18:40
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Originally Posted by Hot and Hi View Post
I think two seconds is a reasonably long time. There is a lot you can do in two seconds.
Perhaps. Us Robinson types are pretty johnny on the spot lowering collective when the horn sounds. But that gets practiced all the time (or should). Will there be an "instructor switch" on the wire detection kit, and how many will practice some sort of instant wire avoidance maneuver with it? And whatever gets practiced might be a crapshoot, because you won't see the wire, you'll be reacting automatically to something you assume is right in front of you and that can be avoided with some sort of fly-up maneuver.

Any warning is better than no warning, but 4 or 5 seconds would be better. As it happens, as an engineer I understand the technical challenges. Not saying it's easy!
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Old 17th Dec 2017, 19:04
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You never know we may get to 200m .... maybe flying slower when you are low level would also help . But not as much fun !!
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Old 17th Dec 2017, 19:12
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There are systems available already.
A Laserscanner - but that is quite a lot of extra weight
Or a software solution- as long as the database is updated properly.
I use the second system on an BK117D2 (Airbus H145) and the Helionix System works quite nice with first giving you a „Caution - Obstacle“ and shortly afterwards a „Waning - Obstacle“ and it works not only with powerlines but also with windcraft mills, chimneys (mostly grey painted and also sometimes hard to spot, when the lights are in cloud) and so on.
It even warns for terrain, when getting to low outside an airfield (and yes, it can be muted &#128521
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Old 17th Dec 2017, 21:11
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But it's the small ones not in the system that tend to get you ....having said that , if 95% of all cables were on a database that could save a number of accidents .
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Old 17th Dec 2017, 22:01
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@nigelh - if I fly so low, that a smal one may be a threat, I do a recce beforehand or land and wait for better weather.
With adequate warning flying in bad weather the software solution isn‘t a garantee but makes life much safer. Went around in low vis SP, even flying underneath a (big) bridge to avoid cloud and had to cross wires I knew, must be somewhere ahead. Was nice to get the hint in time to spot them in time........
Originally Posted by nigelh View Post
But it's the small ones not in the system that tend to get you ....having said that , if 95% of all cables were on a database that could save a number of accidents .
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Old 18th Dec 2017, 12:15
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But it's the small ones not in the system that tend to get you ....having said that , if 95% of all cables were on a database that could save a number of accidents .
they already are if you buy military produced maps with the wires overlay - 1:500,000, 1:250,000 and 1:50,000 see AIDU for details.

I think the DVOF - Digital Vertical Obstruction File also includes them but again you have to pay for it.

In recent years the mil introduced AMWAS - an off the shelf tablet with moving map and wires overlay for use in helicopters.
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