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Downwind takeoffs/landings


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Normally, downwind landings are frowned upon because you can run out of power in a single or a heavily loaded twin and then get into an over torque situation or a crash. Also, if landing in dusty conditions as we do in the desert then the dust cloud will roll along in front of you and obscure your view of the ground - if you land into the wind the dust will normally stay behind you enough to let you land.

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If you are in the hover, pointing into a 10-knot wind, there is already a positive airflow across the disc and you are using less power than if there was no wind. If you continue the takeoff into wind, you will reach translational lift sooner, and will have safety speed/climb speed sooner, and with less speed over the ground - kinetic energy. If you subsequently have an emergency, you have less kinetic energy to get rid of - less damage if you bump into something.

 

Now point downwind. Start to move forward. Your airflow over the disc is going down from 10kt and you will need more power - even more if the tail is twitching and you are dancing on the pedals. You get to 10kt groundspeed, and you are at zero airspeed, the most power-hungry time. Increase power, continue accelerating, and eventually hit translational, but you have 22kt groundspeed. If you have already run out of power before this, you will bump into the ground at around 20kt, enough to do serious damage.

 

Similar with a downwind landing - the aim will be to finish with zero groundspeed over some spot, but to get there you have came back through 10, zero, and now minus 10 knots, your power requirement is through the roof, and you might not have enough pedal control to overcome the weathercocking.

 

And as the apache dude says, dust clouds will add to your woes.

 

But if you have plenty of power and pedal control, there are many situations where a downwind landing is the way to go. In most situations, though, do it into wind. The only thing you should always do downwind is have a leak.

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With a tailwind at a hover, the main rotor may have ETL, or will at least be near it, so power required is somewhat reduced. As you start to move forward with a tailwind, the apparent wind goes to zero as your groundspeed approaches windspeed, thus more power is required. Add to this the additional power required to keep the fuselage aligned out of the wind, and power required could exceed power available. On the approach, you may end up with zero airspeed while still well out of ground effect, and you need HOGE power available. Usually it's not a huge issue, but it could be, and you need to be aware of all the things that could bite you. Sometimes a downwind takeoff or landing is the only option, so you need to have some practice at doing them. I don't do them if I can avoid it, but I have done them when necessary. It's an interesting experience, and you need to be paying close attention to what is happening in case you need to abort or change your plan.

 

FWIW, another thing you should always do downwind is spit. :P B)

Edited by Gomer Pylot
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See, I always want to autorotate into the wind; that's my strategy. Flying really low, like cruising along downwind below 300' pretty much assures that the landing will be straight ahead if the engine quits. Let's not delude ourselves into thinking that we'll instantly recognize the engine failure and call on our nonexistent Chuck Aaron skills and whip that bad boy 'round into the wind in a nanosecond. Not gonna happen - you and I will probably be so preoccupied with getting the nose up and keeping the rotor in the green that we'll just land straight ahead. Downwind. With ground run. Which is something none of us want to do. So I don't cruise below 300' if I'm not into the wind.

 

Same with downwind takeoffs/landings. Sure, they can be done. I've done 'em when I've had to. But it's not my first choice. And I'm always *super* conscious of all the things that can go wrong (most of which have already been cited above). Even when I'm operating at an airport, I'll always depart (more or less) into the wind until I get 300' before turning on course. And that's no b.s. Overly-fussy, you say? Needlessly conservative, you sneer? Anal? Paranoid? Yeah, maybe all of that. But there's something inside of me that just makes me uncomfortable when I'm below 300' agl and not into the wind. YMMV.

 

Options. I like options. And operating downwind certainly limits your options greatly.

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Downwind are disadvantageous for lots of reasons, as mentioned. Power failures at low speed, low altitude and with collective set to climb power do happen, and that's why I operate into the wind whenever that allows a survivable landing. A great forced landing, into the wind and on to unsurvivable terrain is a bigger loser than operating downwind. Plan to survive by having a plan. I would also guess that a majority on VRS accidents happened in aggressive downwind descents...

 

I am a BIG fan of what the Army called 'high overhead approaches' in problematic terrain instead of airplane traffic patterns. (That's my preferred approach for off airport landings.)That's circling descent with the landing point always in reach, with the final descent into the wind. Bend it however you need to keep the clear flat parts in reach.

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I heard it was dangerous to take off or land downwind. Can someone explain why this is dangerous?

 

Downwind maneuvers are not inherently dangerous; however, the lack of knowledge about downwind maneuvers can put you in a precarious situation. Instead of teaching students how to handle downwind maneuvers, many flight schools still promote these taboos, myths, and fears about downwind flight. This has been one of the training weaknesses that may have led to many settling and LTE accidents.

 

Had they received some training and experience in downwind maneuvers they could have remained steps ahead of their aircraft, by being aware and comprehending the feel of the aircraft and what it’s telling them.

 

If you’re planning on working utility, were you’re working at gross weight most ever turn, you’re going to have to takeoff, maneuver, and land with winds from all directions. You’ll have to learn and experience working in conditions with full left pedal, at the stops. All part of production oriented projects that require you to get the most out of the helicopter.

 

You’re on a powerline job in mountainous terrain doing skid transfers in 10-15 knot gust. The project manager doesn't want to hear you can’t get it done because the tower wasn’t built facing in the prevailing wind direction. The manager knows better; he’s seen it done. He's seen pilots position themselves with respect such wind conditions.

 

Given, it’s always better to work into the wind; however, always be prepared and knowledgeable of the real world that we working in.

 

Below are graphical presentations of what’s been talked about in the above post with regard to passing back through zero airspeed (climbing the hump), resulting in downwind maneuvers requiring additional power.

 

Landing_zpsbshrju5h.png

Takeoff_zpsa3zdvln5.png

Edited by iChris
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I hate to try to piggyback on anything iChris posts.

His replies are the gold standard to my way of thinking at least.

But I have an almost irresistable urge to add, downwind operations require no more power than no wind operations under the same loading and atmospherics.

It does however require additional logistics and considerations.

Lengthened takeoff and landing distances for instance.

Another consideration is engine out operations which are complicated greatly by downwind operations.

Also ETL backwards should be given very careful consideration.

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Sometimes you just have to take off or land downwind. If you do, get in ground effect before you get below translational lift, and consider that, when landing, you will at some point in the landing phase, before coming to a stop over the ground, find yourself effectively flying backwards in respect to the relative wind.

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