Strong head wind on approach
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Strong head wind on approach
Playing in the circuit on Saturday I was noticing how quickly the height seems to come of on approach into a head wind. In my case we are talking, 15kts straight down the runway in a PA28.
Surely increased airflow would mean greater lift ? or is the increased drag in a low speed approach counter acting this ?
Surely increased airflow would mean greater lift ? or is the increased drag in a low speed approach counter acting this ?
Joined: Jan 2002
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From: Paros, Greece
Was the height actually coming off quicker or was it that you had a slower ground-speed which meant it seemed to come off quicker (i.,e. over a shorter ground distance), thus getting too low on the approach? Remember, the headwind should not have affected the actual airspeed at which you flew the approach, just groundspeed so there should have been no difference in lift, drag etc.
Sub Judice Angel Lovegod
Joined: Oct 2002
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From: London
Dewdrop
I think you need to go back to basics to work this out. Remember that the aircraft is performing with relation to the air it is in, not the ground (except in the case of momentum, but that, I think, is a little further up the learning curve for you.)
If you like, think of this as a triangle of velocities computation, but in a vertical plane....a bit of paper and a pencil will help.
I really think that it is better that you work this out, rather than just be told...it is an important bit of understanding, which will go in better that way!
Timothy
I think you need to go back to basics to work this out. Remember that the aircraft is performing with relation to the air it is in, not the ground (except in the case of momentum, but that, I think, is a little further up the learning curve for you.)
If you like, think of this as a triangle of velocities computation, but in a vertical plane....a bit of paper and a pencil will help.
I really think that it is better that you work this out, rather than just be told...it is an important bit of understanding, which will go in better that way!
Timothy
Joined: Sep 2002
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From: Savannah GA & Portsmouth UK
The headwind will make the approach angle steeper (you're going down at the same rate but travelling slower over the ground).
The other thing to watch out for is a reduction in airspeed as you near the ground. The wind speed on the surface is less than it is a few hundred feet up. As you descend your airspeed decays and your rate of sink goes up, hence the advice to fly the approach a few knots faster in a strong headwind.
Mike
The other thing to watch out for is a reduction in airspeed as you near the ground. The wind speed on the surface is less than it is a few hundred feet up. As you descend your airspeed decays and your rate of sink goes up, hence the advice to fly the approach a few knots faster in a strong headwind.
Mike
Joined: Mar 2002
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From: U.K.
Made me smile!
In November I came in to land at an airfield in the Californian desert. I was flying a 172SP into a strip with the wind straight down the runway and had the time to see this very same effect at work as the windspeed was a whopping 40kts!
This resulted in my having a GS of 35kts at 25 feet agl (according to the two GPS units in the aircraft at the time). It was astonishing looking over the nose to see the picture hardly change at all - as if I was coming in to land in a heli! I have it on video but unfortunately I'm not computer literate enough to post it here
I try to remember the aircraft as flying along in it's own block of air which is independent of the ground (except when it comes to windshear and momentum, as Timothy rightly points out - the aircraft being GS referenced in windshear conditions - hence the need to have some extra airspeed in hand). In a constant headwind as far as the aircraft is concerned there is nothing different going on (no change in lift or drag) but the 'block' of air that you are flying in is 'slipping back' relative to the groung and the runway. As a result, if you were to maintain your normal descent angle, once you had descended to the bottom of the 'block' of air you would pop out short of the runway.
Obviously, to reach the runway in a strong head wind you will need to reduce your rate of descent accordingly (which you will do automatically when trying to maintain the right 'picture' on approach). Certainly, in high wind conditions keep your approach speed slightly higher to enable you to maintain control if you encounter windshear and/or gusts nearer to the ground. It sometimes is a good idea not to put in the last stage of flap, or indeed, use no flap at all as this will give you better controllability in gusty conditions.
Haul.
This resulted in my having a GS of 35kts at 25 feet agl (according to the two GPS units in the aircraft at the time). It was astonishing looking over the nose to see the picture hardly change at all - as if I was coming in to land in a heli! I have it on video but unfortunately I'm not computer literate enough to post it here
I try to remember the aircraft as flying along in it's own block of air which is independent of the ground (except when it comes to windshear and momentum, as Timothy rightly points out - the aircraft being GS referenced in windshear conditions - hence the need to have some extra airspeed in hand). In a constant headwind as far as the aircraft is concerned there is nothing different going on (no change in lift or drag) but the 'block' of air that you are flying in is 'slipping back' relative to the groung and the runway. As a result, if you were to maintain your normal descent angle, once you had descended to the bottom of the 'block' of air you would pop out short of the runway.
Obviously, to reach the runway in a strong head wind you will need to reduce your rate of descent accordingly (which you will do automatically when trying to maintain the right 'picture' on approach). Certainly, in high wind conditions keep your approach speed slightly higher to enable you to maintain control if you encounter windshear and/or gusts nearer to the ground. It sometimes is a good idea not to put in the last stage of flap, or indeed, use no flap at all as this will give you better controllability in gusty conditions.
Haul.
Joined: Aug 2002
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From: UK
Its also worth increasing airspeed on the approach with a strong headwind especially if the circuit is busy. With everything tearing downwind the circuit can end-up being extended too far, only making matters worse.
140
140
The Original Whirly
Joined: Feb 1999
Aviation Qualifications: CPL
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From: Belper, Derbyshire, UK
Dewdrop,
To look at it ridiculously simply, you're descending at the same rate as normal, but the wind is pushing you backwards at the same time, so you cover less ground.
Same as what everyone else said, but I'm a simple soul myself who prefers explanations that don't have me tying myself in knots visualising it.
To look at it ridiculously simply, you're descending at the same rate as normal, but the wind is pushing you backwards at the same time, so you cover less ground.
Same as what everyone else said, but I'm a simple soul myself who prefers explanations that don't have me tying myself in knots visualising it.
Joined: Oct 1999
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From: UK
With a nice steady and strong wind blowing down the runway, taildraggers can do a wheel landing and roll to a stop with the tail still up. About 30 knots does it for the Chippy, but you can keep the tail up 'till almost stopped in any decent headwind.
SSD
SSD
The Original Whirly
Joined: Feb 1999
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From: Belper, Derbyshire, UK
I remember a story an instructor told me way back. He was coming back to Welshpool with a student, and the wind had really picked up, to...35-40kts I think he said. It was crosswind at Welshpool and out of limits, so they diverted to Shobdon. By the time they got there the wind was even stronger, but straight down the runway. 
I remember him telling me they landed the PA38 "and it stopped dead immediately". Must be quite something to experience.
I remember him telling me they landed the PA38 "and it stopped dead immediately". Must be quite something to experience.
Joined: Nov 2003
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From: UK
My friend was at low key doing a PFL to the airfield the other day when i was downwind doing a glide.
30 kts down the strip, how I laughed and prepared some banter for him as his glide path would have put him down about 1/4 mile away from the runway.
Turned finals late and laughed as my glide path would have put me 1/4 mile away from runway too. Upon landing straight to QFI's office for more pretty pictures of planes and glidepaths in wind.
30 kts down the strip, how I laughed and prepared some banter for him as his glide path would have put him down about 1/4 mile away from the runway.
Turned finals late and laughed as my glide path would have put me 1/4 mile away from runway too. Upon landing straight to QFI's office for more pretty pictures of planes and glidepaths in wind.
Joined: Apr 2000
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From: south of 60N
Back in the late 80s I was making an approach to EGLL on what was then 23L. It was the day that Mr Fish of the met office said we were not getting a hurricane, The Approach speed was 150 kts and the ground speed 70Kts The turbulence was something else. A touch of the WTFAIDH. But I was younger and more impressionable then.
Joined: Apr 2000
Posts: 264
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From: south of 60N
Back in the late 80s I was making an approach to EGLL on what was then 23L. It was the day that Mr Fish of the met office said we were not getting a hurricane, The Approach speed was 150 kts and the ground speed 70Kts The turbulence was something else. A touch of the WTFAIDH. But I was younger and more impressionable then.
Joined: Dec 2002
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From: Bristol and Forest of Dean
Chaps,
Obviously agree with all of the above, but it's possible Dewdrop may encountered some wind shear near the ground which would have increased the rate of decent if he checked the stick forward to maintain airspeed without increasing power.
Just a thought...
Kingy
Obviously agree with all of the above, but it's possible Dewdrop may encountered some wind shear near the ground which would have increased the rate of decent if he checked the stick forward to maintain airspeed without increasing power.
Just a thought...
Kingy
The Original Whirly
Joined: Feb 1999
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From: Belper, Derbyshire, UK
Kingy,
Good point, hadn't thought of that.
Also, different airfields have different conditions. At Welshpool, the hills plus the farm on final for runway 04 somehow produce turbulence that always increases your rate of descent at that point. When learning to fly there, I learned to allow for it. But does it vary in different wind conditions? Can't remember...but it could.
Good point, hadn't thought of that.
Also, different airfields have different conditions. At Welshpool, the hills plus the farm on final for runway 04 somehow produce turbulence that always increases your rate of descent at that point. When learning to fly there, I learned to allow for it. But does it vary in different wind conditions? Can't remember...but it could.
Joined: Jan 2002
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From: Paros, Greece
I really don't agree with this increasing power and speed on final to 'overcome' the headwind. If the engine quits on final, it'd be REALLY, REALLY, nice to be able to glide to the field and the method suggested will not allow this - it makes the approach look and feel 'normal' when it isn't, hich I consider dangerous.
I'd be attempt to make the final leg much shorter and accept the very steep approach but at normal airspeed. The downside of this is that visibility of the threshold is poor as it'll end up beneath the nose. The upside is as mentioned above.
Abviously, if you've already overdone it on downwind, speeding things up on final would be good, but I'd still be tempted to keep the height on until I was in gliding range. I've been practicing this recently, and it felt a bit odd at first as the 'picture' outside the window is very different, but I think it's a good technique to have, particularly in case you ever need to make a forced landing into a strong wind.
If you approach the field flying, say, 20kts faster than usual, and forget to slow down because the 'picture' looks exactly the same, you are probably going to make a very poor landing, or even several!
Anyone more experienced care to comment/correct me?
and the method suggested will not allow this - it makes the approach look and feel 'normal' when it isn't, hich I consider dangerous.I'd be attempt to make the final leg much shorter and accept the very steep approach but at normal airspeed. The downside of this is that visibility of the threshold is poor as it'll end up beneath the nose. The upside is as mentioned above.
Abviously, if you've already overdone it on downwind, speeding things up on final would be good, but I'd still be tempted to keep the height on until I was in gliding range. I've been practicing this recently, and it felt a bit odd at first as the 'picture' outside the window is very different, but I think it's a good technique to have, particularly in case you ever need to make a forced landing into a strong wind.
If you approach the field flying, say, 20kts faster than usual, and forget to slow down because the 'picture' looks exactly the same, you are probably going to make a very poor landing, or even several!
Anyone more experienced care to comment/correct me?
Why do it if it's not fun?
Joined: Jul 2001
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From: Bournemouth
Knobby,
Agree with what you're saying in some cases - but it all depends on the circumstances. It certainly wouldn't be appropriate for an instrument approach, for example. And in the case of Welshpool which Whirly described, if it was a pilot's first time at the airport he might not know about the windshear until he encounters it (or even if he's been told about it he has no way of knowing how strong it is) which would make it difficult to compensate for in advance
FFF
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Agree with what you're saying in some cases - but it all depends on the circumstances. It certainly wouldn't be appropriate for an instrument approach, for example. And in the case of Welshpool which Whirly described, if it was a pilot's first time at the airport he might not know about the windshear until he encounters it (or even if he's been told about it he has no way of knowing how strong it is) which would make it difficult to compensate for in advance
FFF
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