Downwind turn discussion
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From: cambridge
The tendancy to sink on final approach can be overcome by having the cabin full of birds which are flapping their wings. I note from today's paper that a Saudi airline is doing just that by carrying a large number of falcons, so it must be correct!
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From: UK
Meikleour
Yes. If the aircraft is moving from an airmass moving at one speed, to an airmass moving at another, then inertia is an issue in the sense that it will take time for the aircraft to accelerate to recover its desired airspeed. That's what happens as we go through wind shear on approach.
Where that doesn't happen is if the aircraft stays in one airmass, whatever speed it is moving at relative to the ground. It's fairly easy to do the sums to demonstrate this, and it doesn't matter which frame of reference you use, the result is the same, though the algebra is a little trickier in one case than the other.
The Bernoulli/Newton reference (for lift from a wing) is not really a good analogy. They are both ways of explaining lift that pilots use, but neither of which actually explain what's going on. (Listen to John Finnemore's Cabin Pressure for a very funny sketch on this). Newton's laws of motion are hugely accurate, at least until you get to relativistic speeds, and I don't believe we're built an aircraft like that yet.
I went back and read your comment. Don't know is the answer, although if this was happening during the descent that would be entirely reasonable since you can get different winds at different heights (and then see my first paragraph above).
Good points both - I stand corrected. Thinking more about it, I suspect that gusts are quite a big issue, particularly when air may not be moving horizontally, thus seriously modifying the AoA. And it's gustier closer to the ground. But you can see this effect in when thermaling a glider at a high angle of bank close to stalling speed - it's not uncommon to find the glider starting to auto-rotate as one wing hits an adverse gust. Easily fixed with some forward stick and opposite rudder, but you really need to be able to do it from feel.
cats_five
Sounds sensible. For those of us that do mountain flying it's entirely possible to be turning within a low few hundred feet of the ground in rather gusty conditions. But I think the key is if you'r going to put yourself in a position where a spin is possible (ie slow, gusty, turning), then being high enough to recover might be smart. So we do the low turns quickly.
Yes. If the aircraft is moving from an airmass moving at one speed, to an airmass moving at another, then inertia is an issue in the sense that it will take time for the aircraft to accelerate to recover its desired airspeed. That's what happens as we go through wind shear on approach.
Where that doesn't happen is if the aircraft stays in one airmass, whatever speed it is moving at relative to the ground. It's fairly easy to do the sums to demonstrate this, and it doesn't matter which frame of reference you use, the result is the same, though the algebra is a little trickier in one case than the other.
The Bernoulli/Newton reference (for lift from a wing) is not really a good analogy. They are both ways of explaining lift that pilots use, but neither of which actually explain what's going on. (Listen to John Finnemore's Cabin Pressure for a very funny sketch on this). Newton's laws of motion are hugely accurate, at least until you get to relativistic speeds, and I don't believe we're built an aircraft like that yet.
I went back and read your comment. Don't know is the answer, although if this was happening during the descent that would be entirely reasonable since you can get different winds at different heights (and then see my first paragraph above).
Good points both - I stand corrected. Thinking more about it, I suspect that gusts are quite a big issue, particularly when air may not be moving horizontally, thus seriously modifying the AoA. And it's gustier closer to the ground. But you can see this effect in when thermaling a glider at a high angle of bank close to stalling speed - it's not uncommon to find the glider starting to auto-rotate as one wing hits an adverse gust. Easily fixed with some forward stick and opposite rudder, but you really need to be able to do it from feel.
cats_five
Sounds sensible. For those of us that do mountain flying it's entirely possible to be turning within a low few hundred feet of the ground in rather gusty conditions. But I think the key is if you'r going to put yourself in a position where a spin is possible (ie slow, gusty, turning), then being high enough to recover might be smart. So we do the low turns quickly.
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From: LFMD
You will need to turn finals a lot higher than 500' to be able to recover a spin.
The problem isn't that it's impossible to recover an incipient spin in less than 1000', it's that most people have never experienced one and so aren't spring-loaded to start the recovery, and probably go through a significant panic time before they recall some vague, distant memory of what they're supposed to do. And that WILL kill you.
Which is why imo getting some spin training (and other unusual attitude stuff) is a REALLY good idea, once you have a couple of hundred hours under your belt. (It is dangerous though - it led me to a seriously expensive aerobatic habit).
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From: Scotland
Anyway, it is not wind shear it is wind gradient, wind shear is when the wind is traveling in a different direction at a lower level, not slightly slower due to surface friction.
Landing towards high trees or a hill, you have a headwind on final and a sudden rotor generated tailwind just before you land. That's the shear.
Landing towards high trees or a hill, you have a headwind on final and a sudden rotor generated tailwind just before you land. That's the shear.
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From: Aus
Next week we will discuss Schuler tuning
but the net effect is a "did we land or were we shot down" landing
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From: Quite near 'An aerodrome somewhere in England'
The usual explanation was "the copilot landed it" (not Concorde specific).
"That was a very nice landing, Captain" said the ATC chap in the tower.
"Not me, mate", I replied, "That was the co-pilot's landing - and yes, very good it was too!"
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From: Cambridge
You will need to turn finals a lot higher than 500' to be able to recover a spin.
But in principle I agree with n5296s too. It should be entirely possible to recover from an incipient spin in much less height than that (and is). It's just that a small but non-zero stream of pilots (with spin training) get themselves into a situation where they don't.
Paul
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From: Cambridge
And at the risk of confusing people, I thought I'd share the following.
Some sea birds have a rather neat trick called dynamic soaring. It uses wind gradient to stay airborne without flapping their wings. Very neat trick if you can do it.
Close to the sea the wind is going slower than the wind a bit higher up. By climbing through the wind gradient, airspeed increases and they can extract energy. Then turning downwind, they descend through the gradient, increasing airspeed in the dive. Repeat doing linked semicircles and they stay airborne and move along without flapping.
It has been done in a glider, but it's a bit tricky.
Paul
Some sea birds have a rather neat trick called dynamic soaring. It uses wind gradient to stay airborne without flapping their wings. Very neat trick if you can do it.
Close to the sea the wind is going slower than the wind a bit higher up. By climbing through the wind gradient, airspeed increases and they can extract energy. Then turning downwind, they descend through the gradient, increasing airspeed in the dive. Repeat doing linked semicircles and they stay airborne and move along without flapping.
It has been done in a glider, but it's a bit tricky.
Paul
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From: UK
n5296s, re Concorde. What you describe is a wind gradient effect. As I said in my earlier post, these changes in windspeed with height near the ground (unlike a steady-state wind relative to the aircraft which has no effect) do indeed have very real effects on aeroplanes.
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From: UK
mikehallam - very true, and particularly effective on Concorde where there is lot more wing area, and a lot closer to the ground on landing, at the back of the aeroplane rather than the front.
A Concorde captain described to me landing the beautiful white bird as easy if you maintain the attitude. But as the aeroplane flies into ground effect this acts much more at the back of the aeroplane because of the above, and tends to force the nose down just before touchdown. This must be countered by the pilot easing back just enough to prevent that nose drop and maintain a constant attitude, whereupon the main wheels, he said, will touch down in elegant style.
Thus one does ease back on landing as in a conventional aeroplane, but it's not a flare, it's just to counter that ground effect... effect!
A Concorde captain described to me landing the beautiful white bird as easy if you maintain the attitude. But as the aeroplane flies into ground effect this acts much more at the back of the aeroplane because of the above, and tends to force the nose down just before touchdown. This must be countered by the pilot easing back just enough to prevent that nose drop and maintain a constant attitude, whereupon the main wheels, he said, will touch down in elegant style.
Thus one does ease back on landing as in a conventional aeroplane, but it's not a flare, it's just to counter that ground effect... effect!
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From: S.E.Asia
I was taught in my PPL training back in 1981 that low and slow was an area to avoid.
Height and speed is my motto and I am still here.
In my early helicopter training I was stressed to focus on the avoid curve.
Helicopter Aviation
Height and speed is my motto and I am still here.
In my early helicopter training I was stressed to focus on the avoid curve.
Helicopter Aviation
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From: UK
I agree entirely Cats 5, which is why we don't fly slow in a finals turn.
But in principle I agree with n5296s too. It should be entirely possible to recover from an incipient spin in much less height than that (and is). It's just that a small but non-zero stream of pilots (with spin training) get themselves into a situation where they don't.
But in principle I agree with n5296s too. It should be entirely possible to recover from an incipient spin in much less height than that (and is). It's just that a small but non-zero stream of pilots (with spin training) get themselves into a situation where they don't.
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From: GLASGOW
If you do a regular recovery as soon as you feel the stall/spin breaking away, 500' is plenty. Not, again, that I'm recommending going out and trying it at that altitude.
I have read hundreds of reports where, let's say, all,perished from a loss of control/spin in, within the circuit pattern.
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From: Scotland
I was once on final in a glider with an instructor, at 400 ft he said "I have!" And spun it losing 200 ft. "You have" he said as two Tornadoes roared overhead at 4/500 ft. I recovered it and landed, along with "what the f**k". So it is possible.
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From: GLASGOW
I am sure it is, but with respect a glider may handle differently to a powered aeroplane. I have only had one flight in a powered motor glider, so would not be qualified to confirm the above. Sounds like an interesting experience you had......
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From: cambridge
Not wishing in any way to dampen a thoroughly entertaining read, but has anyone, witnessed, completed, heard of, a spin recovery, in the circuit, from 500'
I have read hundreds of reports where, let's say, all,perished from a loss of control/spin in, within the circuit pattern.
I have read hundreds of reports where, let's say, all,perished from a loss of control/spin in, within the circuit pattern.
.....it happened because I pulled a lot of G in a hard turn.
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From: LFMD
I have read hundreds of reports where, let's say, all,perished from a loss of control/spin in, within the circuit pattern.
If you read what I wrote, it wasn't, "it's easily survivable, anyone can do it." It was, "someone who is familiar with spin recovery should be able - in any reasonable type - to detect and recover form an incipient spin in less than 500'". I then went on to say that most low time pilots, who aren't familiar with spins, will probably panic for long enough to make the fatal difference.
I experienced one incipient spin while I was training, and solo (practising power on stall recoveries). It took me a second or so to realise what was going on, and recover. At 3000' it made no difference. At pattern altitude maybe it would have.
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From: GLASGOW