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Operating in high wind shear conditions


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I'm a dual rated Pilot with most of my experience in fixed wing bush planes (500 heli 4000 fixed) flying in an area that is mountainous and commonly windy 20-30kts. Most of the places have a large gust spread and down drafts. Flying sea planes, everywhere we go is off airport and next to a mountain. In this environment we take off and land at higher speeds than normal operatons to give more control of the aircraft and resistance to downdrafts (airspeed is your life in a fixed wing).

 

I haven't flown helicopters in these conditions and was thinking how to go about it?. How do you manage a heavy load in wind shear/downdrafts? Do you take lighter loads to give you a larger margin on power? I'm not talking about enroute but takeoff, landing, and sling loading. Obviously we try to avoid nasty areas while flying, but for those times when you can't, how do you do it?

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Well, you are not worried about stall speeds in a chopper, as you are aware.

 

But keeping in translational for as long as possible allows good loads to be carried. Being aware of wind direction at all times will save you some frights, but all of us have been caught by surprise at some time by wind shear. I almost got pushed out of the sky on power line patrol in winter in the mountains by a wind rolling over a hill ahead of me - my thought was "This is gonna hurt!" as I descended rapidly towards the ground, but finished in the ground cushion. The wind had to spread out along the ground, and gave me the break needed to stop the descent. Took my crew back to base at 0830, cancelled the rest of the day, went to my motel and went back to bed!

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The hard answer is that most of the time you don't fly in high winds/large gust spreads. Helicopters, as you're aware, have wind limitations. If you're being asked to fly in conditions that exceed those limits then you're going to have to say 'no' to the boss. If the winds don't exceed the limits then there's some mountain flying techniques you can use, some of which were recently covered in another thread. Keeping the loads light helps, as you never know when you'll get in a downdraft and start pulling collective and keep pulling and pulling - so having some reserve power available is always nice.

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It also depends on what you are in - a teetering head machine, which has almost no control power due to its lack of offset, is far less tolerant of wind gusts than something like the BK117 or BO105 (rigid head) or the Eurocopter family of elastomeric heads.

 

I have been tipped to 120 degrees of bank in a BK in turbulent conditions, and the only reason we were out there was a rescue, and we were able to use the BK instead of a flimsy B206. (The "victim" was a failed suicide, who had stood on a cliff and shot himself, causing him to fall off the cliff. Not accurate enough or far enough. Having been rescued, he had a more successful attempt a few months later, which didn't need a helicopter.)

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Aircraft wind limits only come into play for start up/shutdown and hovering (rearward, sideward flight). Turbulence, is really what question is about and is the area where the teeter totter head struggles and power requirements fluctuate. The short answer is that the "how" is not as important as the decision to try whatever it is your doing in the first place. Until you have more experience, fly very conservatively with a large power margin. Please keep in mind though that all the excess power in the world may not save you from a bad decision. Find a senior helicopter guy in your area go have some fun.

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My experience has been just the opposite. Fixed wing in turbulence, especially severe or greater, can be quite violent.

I'm with you on this one. I fly in much worse weather in helicopters than I do in airplanes, but airplanes seem to be a much rougher ride with turbulence. I figured it had to do with the larger horizontal surface area of the wings vs the rotor blades. I've never researched why.

 

That being said, I've never been in a CH47, so I have no idea how it handles in turbulence.

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It's all to do with the wing loading, weight divided by the wing / blade surface area. A little Cessna with a big plank of a wing will suffer badly in turbulence. A Mirage fighter or F-104 has a high wing loading and copes much better.

A helicopter with a skinny little blade will punch through it a lot better than the Cessna, but beware if you teeter.

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