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Down wind demon (or not?)


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The downward turn myth suggests that there is a practical physical difference that an aircraft will experience between the two situations of;

1) flying along upwind, and turning through 180 degrees to flying downwind.

and

2) flying along downwind, and turning through 180 degrees to flying upwind.

The only difference is in relation to the ground, however, an aircraft doesn't care where it is in relation to the ground, and only flies in relation to the air through which it is moving. This can be considered it's frame of reference. Someone making these turns in an aircraft will perceive them differently, because of the way the ground moves beneath them. However, as any pilot who has either flown simulated or real IMC (ie can't see where he is going) will tell you that it is impossible to tell any difference whatsoever when you remove the ground from the equation.

The article claims that an aircraft turning downwind will lose altitude unlike one turning upwind, due to some fictitious changes to it's energy levels. In reality, any aircraft, turning in any direction will tend to lose altitude unless power is added, for the simple reason that the wings lift is diminished at increasing angles of bank.

This one has being doing the rounds since Orville Wright was a wee lad, and I thought it had been debunked by now, never mind a magazine publishing an article on it!

Stroll on.

Anyone who doubts this, just go for a fly, and fly in a circle. Keep your eyes glued to your altimeter. Without looking at the ground, it is impossible to tell which way the wind is coming from. At no point will your rate of descent suddenly shoot up, just because you have turned downwind.

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Spot on Phil, I think the myth came about because of the errors made by some pilots when their perception of whats happening is skewed by the fact they look at the ground and not their instruments, for us with minimal instruments its something we need to be aware of, the whole "downwind demon" scenario is covered well by Geoff goin on the DVD risk and reward.

Dave.

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I agree.

However I would like to add the following spice to your irrefutable logic - woof!! :shock:

Paragliders normally fly hills, flying into wind the airmass is travelling up the hill = lift is good.

going downwind you are no doubt dropping unless in a thermal, as the ground feature (hill) has gone. Hence why some people may get confused.

The key is the when hill flying you are generally flying towards the rising air.

once above 500 foot this benefit has usually gone unless very windy, in England the green and pleasant land. Scotland and Wales could be different.

Simon

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It's easy to deal with, just keep your eyes shut when landing or taking off :-)

Landings always have scared the bejasus out of me, I'm much better with my eyes closed. When your passengers screams get really loud, ease back on the stick.

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It's easy to deal with, just keep your eyes shut when landing or taking off :-)

Landings always have scared the bejasus out of me, I'm much better with my eyes closed. When your passengers screams get really loud, ease back on the stick.

This adds a whole new dimension to "Flying blind" I love the above quote

"When your passengers screams get really loud, ease back on the stick"

Dave

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its not only in turns that the downwind demon can appear, it can also happen in climbout.

Dave.

Very true, if you do a turn on your initial climb out, although your rate of ascent doesn't change (any more than normal) the amount of ground that you cover increases dependant on the wind speed making it seem like you are climbing slower.

The only time I can think of that upwind/downwind CAN make a difference in my opinion is in non-laminar conditions. Momentary gusts can effect the airspeed as well as the groundspeed of the glider until it has a chance to stabilise in the changing wind speed.

Sort of on subject, an example of extreme downwind landing on a PG

Cheers

Mark

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  • 1 month later...
A form of sand yachting then?

Hehe :)

It does prove the point of the non existance of the downwind demon though.

He is flying along at a rate of knots but his descent is quite slow. If the downwind demon were to be believed he would be dropping like a stone.

As he landed on a flat soft(ish) surface on his bum he was fine, the trouble starts when you try to run off the speed as it's impossible.

Cheers

Mark

:propbreak:

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Interesting one isn't it Mark?

I believe that part of Jeff Goin's 'Downwind Demon' is the groundspeed at which you hit the obstruction. The other bit is wholly visual surely. Your rate of descent doesn't change, it just appears to be shallow because it is visually elongated by the tailwind. Think in terms of a stretched graph, height against distance.

If you were to turn at low level back into a strongish wind the visual effect is quite startling. You appear to be flying sideways and slowing rapidly as you come into wind. Plenty of Demons there! :lol:

Have I got that right? ... the other Demon is drink of course.... nuffink to tadoo with wind, that's Curry. :evil:

Edited by Guest
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A form of sand yachting then?

Hehe :)

It does prove the point of the non existance of the downwind demon though.

He is flying along at a rate of knots but his descent is quite slow. If the downwind demon were to be believed he would be dropping like a stone.

As he landed on a flat soft(ish) surface on his bum he was fine, the trouble starts when you try to run off the speed as it's impossible.

Cheers

Mark

:propbreak:

Mark the down wind demon is not an actual occurance, but its what happens in the mind of the pilot, its more a thought process than an action.

Dave

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Couldn't agree more, but a poorly worded post from me, methinks.

I meant to say that the video establishes the fact that there is no difference in airspeed/rate of ascent/descent when flying downwind from upwind.

It should therefore reinforce in the objective pilots mind that this physical state does not exist he can then dismiss it from his mind when he does his next turn downwind.

What he does need to be aware of though is his ground speed if he is low enough to bump into anything protruding into the sky (or indeed coming in to land)!

Of course even flying would be nice at this stage after 6 weeks with no prop after sending it for minor repairs/balancing with the propellor repair chap :(

Cheers

Mark

:propbreak:

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