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When the windmill stops.


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Suppose that you were going on trip. You obtain the forecast winds and create your flight plan, and you find that the winds will be anything other than headwinds not more than about 10 degrees either side of your desired track. Things are going well, and you find that the wind forecast is pretty spot on. Then the propeller jerks to a stop.

 

Do you continue on track, looking for a place to land, or do you swing around the the reciprocal direction of the forecast wind, and use it to maintain airspeed to maintain flying for longer while you search for a place to put down? 

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Any turn you do when unpowered will lose more height. Wind will change your groundspeed. Landing into wind is a way of reducing kinetic energy at that time. Nev

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It depends. You should know if there are suitable places to put down in the country you’ve just flown over. If so and they are within gliding distance that may be the better option especially if yo can turn back into wind on final. On the other hand if you’re over tiger country your best bet may be  to continue and find the most survivable spot you can.

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Pick your spot first and then line up as accordingly.

 

The wind direction has zero relevance to the amount of time you will stay up there, it only affects the distance covered.

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They didn't mention that gliding INTO a wind requires more airspeed to achieve best results .at "ranging"  The  same principle applies when flying across country.  Nev

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More airspeed may be needed for ranging when flying into a head wind, but that headwind is needed to reduce landing speed at the end. If you turn downwind you will travel further at a greater Ground Speed and need to turn into wind for the safest landing. Best bet is to always have an eye open for forced landing fields as you cover the ground, turn back if nothing into wind is suitable, otherwise try to keep your GS low.

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6 hours ago, rgmwa said:

It depends. You should know if there are suitable places to put down in the country you’ve just flown over. If so and they are within gliding distance that may be the better option especially if yo can turn back into wind on final. On the other hand if you’re over tiger country your best bet may be  to continue and find the most survivable spot you can.

As rgmwa said. We should already have a landable field picked out as part of our normal “gazing out the window”.

 

Also that old gem: “we shouldn’t be surprised when the engine stops; we should be surprised when it doesn’t.

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When I posed the question, I was thinking that most often you want to maximize the distance you can glide. That means getting your airspeed to the aircraft's best glide speed. If you have no thrust from the engine to move the aerofoil though the air to generate lift, why not turn into wind and let the moving air add a bit to the air movement resulting from the horizontal vector of your downward motion?

 

Turning into wind won't keep you aloft any longer? I know that it was only with RC gliders, but I could keep one of them stationary if I faced it into wind. 

 

 

 

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6 hours ago, old man emu said:

 why not turn into wind and let the moving air add a bit to the air movement resulting from the horizontal vector of your downward motion?

 

Turning into wind won't keep you aloft any longer? 

 

It doesn't work and no. You are just posting a variation of the down wind turn myth.

 

What does matter in a forced landing is being into wind for the landing especially if trees or rocks are involved. If we are flying an aircraft with a 55knot stall in a 15 knot wind we can land at 40 or 70knots ground speed. We know the energy to dissipate is a function of the velocity x velocity. So 4 x4 =16 or 7x7=49. Three times the destruction in the down wind landing. 

 

It was amazing that the cub pilot didn't die doing all those down wind turns so close to the ground😂😂😂

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7 hours ago, old man emu said:

When I posed the question, I was thinking that most often you want to maximize the distance you can glide. That means getting your airspeed to the aircraft's best glide speed. If you have no thrust from the engine to move the aerofoil though the air to generate lift, why not turn into wind and let the moving air add a bit to the air movement resulting from the horizontal vector of your downward motion?

 

Turning into wind won't keep you aloft any longer? I know that it was only with RC gliders, but I could keep one of them stationary if I faced it into wind. 

 

 

 

You most often want to glide to the best place to land. BUT if you want to maximise the distance you can glide, you will turn so you have a tail wind… and you will stay aloft for the same amount of time. 😆 

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Surely where you are headed will always trump how far you can glide. No good gliding further to land in a forest. So wind influences your decision as to where you can get to, but that may be up- down- or cross- wind.

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2 hours ago, APenNameAndThatA said:

…BUT if you want to maximise the distance you can glide, you will turn so you have a tail wind… .

Except that you will lose height making the turn so you need to factor that in.

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10 hours ago, APenNameAndThatA said:

if you want to maximise the distance you can glide, you will turn so you have a tail wind… and you will stay aloft for the same amount of time.

There's the source of the confusion.

 

Do you agree that the speeds quoted in the POH are "air speeds" - the speed of the air over the wing to produce lift.

 

Does the airspeed indicator tell you anything more than the speed of the air relative to the wing (pitot tube, actually)? Remember that on a windy day, the ASI will give an indication when the aircraft is still tied down.

 

For navigation, we know that you have to power up when flying into wind, but back off with a tail wind to attain a desired ground speed, which is covering ground distance over time.

 

If the windmill has stopped, then to get to a desired airspeed (best glide speed) which will keep you above ground for the longest time, you have to use the relative movement between the wing and the air. With a tailwind you have to convert the potential energy due to altitude to airspeed by descending. On the contrary, flying into wind  allows you to lessen the amount of the same potential energy you have to trade off to produce lift, so you stay up longer.

 

Are you able to show mathematically that an aircraft of 500 kg at 2000' agl  with a wind of 10 kts will hit the deck at the same time headwind or tailwind? Just for interest's sake.

 

According to the FAA Gliding clean, with the engine at idle, you may find the IAS for maximum endurance, precisely where the variometer shows the minimum descent speed. Then multiply that IAS by 1.32 That's the best glide speed. Going back the other way, if you multiply the best glide speed by 0.75, that's the maximum endurance speed. 

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12 hours ago, Thruster88 said:

t was amazing that the cub pilot didn't die doing all those down wind turns so close to the ground

That's because he's a stunt pilot who has practised the routine.

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Glide performance - https://skybrary.aero/articles/glide-performance

 

IMO, OME's wording in the first post is not correct. You wouldn't "swing around to the reciprocal direction of the forecast wind, and use it to maintain airspeed to maintain flying for longer".

 

You'd only want to swing 180° to reduce GS at the landing site - and you'd need to know if the wind speed at ground level at your chosen landing site, was strong enough to warrant a reversal of direction, that would make a major difference to GS in a deadstick landing. Of course, the terrain also has to come into the decision-making for a forced landing site.

A tailwind forced landing on an uphill slope would work out O.K., but a tailwind forced landing on a downhill slope, I would imagine is pretty much a nightmare scenario.

 

As I previously said, I'd be trying to avoid aircraft energy loss and altitude loss, caused by carrying out a 180° turn.

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1 hour ago, old man emu said:

There's the source of the confusion.

 

Do you agree that the speeds quoted in the POH are "air speeds" - the speed of the air over the wing to produce lift.

 

Does the airspeed indicator tell you anything more than the speed of the air relative to the wing (pitot tube, actually)? Remember that on a windy day, the ASI will give an indication when the aircraft is still tied down.

 

For navigation, we know that you have to power up when flying into wind, but back off with a tail wind to attain a desired ground speed, which is covering ground distance over time.

 

If the windmill has stopped, then to get to a desired airspeed (best glide speed) which will keep you above ground for the longest time, you have to use the relative movement between the wing and the air. With a tailwind you have to convert the potential energy due to altitude to airspeed by descending. On the contrary, flying into wind  allows you to lessen the amount of the same potential energy you have to trade off to produce lift, so you stay up longer.

 

Are you able to show mathematically that an aircraft of 500 kg at 2000' agl  with a wind of 10 kts will hit the deck at the same time headwind or tailwind? Just for interest's sake.

 

According to the FAA Gliding clean, with the engine at idle, you may find the IAS for maximum endurance, precisely where the variometer shows the minimum descent speed. Then multiply that IAS by 1.32 That's the best glide speed. Going back the other way, if you multiply the best glide speed by 0.75, that's the maximum endurance speed. 

I'm genuinely concerned that I have to share the sky with people who think this is correct...

 

Your IAS and rate of descent will be the same facing into or away from the wind. What will change will be your ground speed and angle of descent relative to a fixed point on the ground.

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13 minutes ago, Agamemnon said:

I'm genuinely concerned that I have to share the sky with people who think this is correct...

That's what I like about the people on this forum. - NOT.

If you ask a question for the sake of better knowledge, you immediately get attacked for being a fool. Nobody ever tackles the question to provide an answer, or else they take the proposition to extremes.

 

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3 minutes ago, APenNameAndThatA said:

Y all have to admit that the idea of gliding into the wind to maximise your glide distance is worth some LOL’s. 👍😆👍

Well you might say that, but do you ever provide anything more to substantiate your comment?

 

I asked you to show mathematically that 

13 hours ago, APenNameAndThatA said:

You most often want to glide to the best place to land. BUT if you want to maximise the distance you can glide, you will turn so you have a tail wind… and you will stay aloft for the same amount of time. 😆 

I thought I asked that politely and would get a considered answer. Things never change, do they?

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4 minutes ago, old man emu said:

That's what I like about the people on this forum. - NOT.

If you ask a question for the sake of better knowledge, you immediately get attacked for being a fool. Nobody ever tackles the question to provide an answer, or else they take the proposition to extremes.

 

You didn’t ask the question to improve your own knowlege…

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OME, the wings don’t know which way the wind is blowing when the plane is in the air. It does when the plane is stationary on the ground. Thats why you take off into the wind - to take advantage of the air flowing over the wings in order to reduce the length of your ground run. Same with landing. But once you’re off the ground the airspeed is the the speed of the plane through the air, or the speed of the air over the wings if you prefer. Your example of a glider being stationary while flying into the wind just illustrates the difference between ground speed and airspeed. As far as the glider is concerned it is flying at a speed that happens to match the wind speed over the ground.

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