Downwind turn discussion
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In answer to Pilot Dar's original question starting this thread.
It obviously isn't.
I've read some rubbish over time, but some of this really takes the biscuit.
All this krap about Mass X V = the square root of an orange to the 10th power of a pile of horse ****e.
There is nothing to it.
An aeroplane flies round in circles in the air.....full stop. FFS.
Edit: Is there a misconception here about the term "downwind"?
As far as the wind or air mass is concerned , there is no "downwind".
Into wind or downwind are referenced from the ground.
It obviously isn't.
I've read some rubbish over time, but some of this really takes the biscuit.
All this krap about Mass X V = the square root of an orange to the 10th power of a pile of horse ****e.
There is nothing to it.
An aeroplane flies round in circles in the air.....full stop. FFS.
Edit: Is there a misconception here about the term "downwind"?
As far as the wind or air mass is concerned , there is no "downwind".
Into wind or downwind are referenced from the ground.
Last edited by Crash one; 14th Feb 2017 at 12:07.
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Hi Boss Eyed... No I think you have got it completely the wrong way round...
If you are going North downwind at GS = 199 kts a small control input could change your course by one degree... (your still effectively going North.)
But going into wind at Ground Speed =1 kt, the same control input could make your course change by 90 degrees (i.e. you fly west.)
In both cases your heading remains about the same, but the Course works out very differently.
For those not familiar with the Jargon, 'Course' is the track over the ground.
'Heading' is the way the front of the aircraft is pointing.
.
If you are going North downwind at GS = 199 kts a small control input could change your course by one degree... (your still effectively going North.)
But going into wind at Ground Speed =1 kt, the same control input could make your course change by 90 degrees (i.e. you fly west.)
In both cases your heading remains about the same, but the Course works out very differently.
For those not familiar with the Jargon, 'Course' is the track over the ground.
'Heading' is the way the front of the aircraft is pointing.
.
If there was a way to do it I think the mods ought to link the thread at this point back to the beginning, so creating an endless loop of horsesh1t, that all posters are forever doomed to read without ever breaking out.
Groundhog Day and Sisyphus spring to mind.
So while I still can, I'm going to duck out for a second time.
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... though if you touch down at 45 knots into a 45 knot headwind you will have zero kinetic energy 
.
Kinetic energy is of course proportional to Velocity squared so even a 10kt headwind will reduce your landing energy by around a half for an airspeed of 45kt since your groundspeed will be around 35kt.
The point is that the aircraft doesn't have any knowledge of what's going on around it. As an observer you can choose your frame of reference. You can make the maths slightly more complex by using an external reference and including the rotation of the earth (in the UK we have a linear speed of around 700mph because of that) or the speed of the earth round the sun (approx 70,000mph). You could decide that the whole of space was moving relative to the aircraft and that pulling back on the stick forces the earth down.
The key lesson from this long, tortuous path is that close to the ground, airspeed can be a friend. A quick glance at the ASI and timely correcting action with the stick and/or throttle can save your life.
. Kinetic energy is of course proportional to Velocity squared so even a 10kt headwind will reduce your landing energy by around a half for an airspeed of 45kt since your groundspeed will be around 35kt.
The point is that the aircraft doesn't have any knowledge of what's going on around it. As an observer you can choose your frame of reference. You can make the maths slightly more complex by using an external reference and including the rotation of the earth (in the UK we have a linear speed of around 700mph because of that) or the speed of the earth round the sun (approx 70,000mph). You could decide that the whole of space was moving relative to the aircraft and that pulling back on the stick forces the earth down.
The key lesson from this long, tortuous path is that close to the ground, airspeed can be a friend. A quick glance at the ASI and timely correcting action with the stick and/or throttle can save your life.
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I stand to be corrected of course.
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For those wanting to talk about flying, rather than physics, look away now.
Scifi, Most of what you say is true, but your conclusions are wrong - at least if you're trying to imply that the two examples' agility are different.
In particular, the statement "The first aircraft will be deflected from its course by one or two degrees, whereas the second will change its direction vector by a very large amount." is wrong.
You've used the term "direction vector". Difficult to know what you mean by that - but if it's velocity (which is a vector), then the change in it is the same for both aircraft. Similarly the change in momentum (which is just the velocity times the mass, and is also a vector) is the same for both aircraft. The course change (or track as I think we'd conventionally call it), changes dramatically, but that's just a direction and not a vector quantity, nor does any law of conservation apply to it.
That the momentum of your two examples is different is just a consequence of the frame of reference you are using - in that case that of the ground. In the air mass frame of reference, the momentums are the same.
And the fact that you've chosen a different frame of reference doesn't change the agility of the two aircraft. They are both equally agile - it's just that the ground is moving in respect of the airmass frame at 99 kts.
Paul
Has anyone mentioned 'Momentum' yet..?
Consider two cases... Airplane flying North at ASI of 100 kts with 99 kt tailwind, and second Airplane flying North at 100 kts into a 99kt headwind.
This makes the ground speeds 199 kt and 1 kt, respectively.
The first has considerable Momentum (Mass x Velocity) the second has almost none.
So if they are both disturbed by a similar force (a gust of wind, or a control movement.) The first aircraft will be deflected from its course by one or two degrees, whereas the second will change its direction vector by a very large amount.
Consider two cases... Airplane flying North at ASI of 100 kts with 99 kt tailwind, and second Airplane flying North at 100 kts into a 99kt headwind.
This makes the ground speeds 199 kt and 1 kt, respectively.
The first has considerable Momentum (Mass x Velocity) the second has almost none.
So if they are both disturbed by a similar force (a gust of wind, or a control movement.) The first aircraft will be deflected from its course by one or two degrees, whereas the second will change its direction vector by a very large amount.
scifi, if that were correct then aircraft would be more agile when flying downwind than upwind.
And they aren't.
And they aren't.
Hi Boss Eyed... No I think you have got it completely the wrong way round...
If you are going North downwind at GS = 199 kts a small control input could change your course by one degree... (your still effectively going North.)
But going into wind at Ground Speed =1 kt, the same control input could make your course change by 90 degrees (i.e. you fly west.)
In both cases your heading remains about the same, but the Course works out very differently.
For those not familiar with the Jargon, 'Course' is the track over the ground.
'Heading' is the way the front of the aircraft is pointing.
If you are going North downwind at GS = 199 kts a small control input could change your course by one degree... (your still effectively going North.)
But going into wind at Ground Speed =1 kt, the same control input could make your course change by 90 degrees (i.e. you fly west.)
In both cases your heading remains about the same, but the Course works out very differently.
For those not familiar with the Jargon, 'Course' is the track over the ground.
'Heading' is the way the front of the aircraft is pointing.
In particular, the statement "The first aircraft will be deflected from its course by one or two degrees, whereas the second will change its direction vector by a very large amount." is wrong.
You've used the term "direction vector". Difficult to know what you mean by that - but if it's velocity (which is a vector), then the change in it is the same for both aircraft. Similarly the change in momentum (which is just the velocity times the mass, and is also a vector) is the same for both aircraft. The course change (or track as I think we'd conventionally call it), changes dramatically, but that's just a direction and not a vector quantity, nor does any law of conservation apply to it.
That the momentum of your two examples is different is just a consequence of the frame of reference you are using - in that case that of the ground. In the air mass frame of reference, the momentums are the same.
And the fact that you've chosen a different frame of reference doesn't change the agility of the two aircraft. They are both equally agile - it's just that the ground is moving in respect of the airmass frame at 99 kts.
Paul
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All this theory and scientific stuff is way over my wee heed, it reminds me of a driving trip to Vegas where I pulled over at a truck stop for lunch. Bellying up to the breakfast counter I was within earshot of 3 gentlemen who were obviously truckers, the sporting of clothing with head to toe advertising logos of Kenworth and Mac was a dead giveaway. While eagerly awaiting my very first try of the days special Chicken fried steak with lashings of biscuits and gravy I picked up the topic of their conversation being their respective educational backgrounds and the reasons for each getting into the trucking business. One guy in fantastic southern drawl stated adamantly that the reason he left high school early was he realized he was wasting his time attending a maths class as he observed
"How the hell are you supposed to add A's, B's and C's and get something? "
I thought to myself well done that man, there's no point trying to get your head around a subject you know fine well is way over it, which is pretty much how I feel about this thread.
"How the hell are you supposed to add A's, B's and C's and get something? "
I thought to myself well done that man, there's no point trying to get your head around a subject you know fine well is way over it, which is pretty much how I feel about this thread.
Last edited by piperboy84; 14th Feb 2017 at 18:03.
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I thought to myself well done that man, there's no point trying to get your head around a subject you know fine well is way over it, which is pretty much how I feel about this thread.
Hi again, its me.... Unfortunately you are overlooking the fact that the ASI only measures forward velocity (pitot tubes only face forwards.)
So the statement by Worrab... ... though if you touch down at 45 knots into a 45 knot headwind you will have zero kinetic energy
Is not absolutely true...
To land, you also need a downward velocity, so many ft/sec, so you can still have considerable downward Kinetic energy, which can compress your suspension and bounce you back into the air... (been there, done that..)
Also the pitot tube will not pick up any sideways velocity, which you will have when you bank in a very strong headwind.
A Velocity Vector is what is displayed on an ATC Radar screen, and shows the direction and speed that the aircraft is moving... It gives them some indication of the position you will be in in the next few minutes.
.
So the statement by Worrab... ... though if you touch down at 45 knots into a 45 knot headwind you will have zero kinetic energy
Is not absolutely true...To land, you also need a downward velocity, so many ft/sec, so you can still have considerable downward Kinetic energy, which can compress your suspension and bounce you back into the air... (been there, done that..)
Also the pitot tube will not pick up any sideways velocity, which you will have when you bank in a very strong headwind.
A Velocity Vector is what is displayed on an ATC Radar screen, and shows the direction and speed that the aircraft is moving... It gives them some indication of the position you will be in in the next few minutes.
.
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Scifi.
This is not the ladies cross stitch forum.
Some of us actually already knew that pitot tubes point forward.
Your conclusions are all wrong.
An aircraft landing, progressively runs out of kinetic energy in all directions in the air as its airspeed slows down. It has no kinetic energy in the ground reference until it makes contact with the ground.
It can have vast amounts of speed in one frame of reference and nothing in another.
It is the transition from one frame of reference to another that causes all the problems.
How simple can it get?
This is not the ladies cross stitch forum.
Some of us actually already knew that pitot tubes point forward.
Your conclusions are all wrong.
An aircraft landing, progressively runs out of kinetic energy in all directions in the air as its airspeed slows down. It has no kinetic energy in the ground reference until it makes contact with the ground.
It can have vast amounts of speed in one frame of reference and nothing in another.
It is the transition from one frame of reference to another that causes all the problems.
How simple can it get?
C1,
But if you keep power on as required to hold 40 kt into 40 kt breeze ready to land but say 25 ft up & still too high, you hover, (after a fashion).
When you decide to fly nearer the deck it will land and whilst shutting down, remaining facing into wind as you, brakes on, wait for a wing walking team.
Deck being the operative word as it's how high performance naval a/c manage short runway landings - with carrier 'steaming' into wind plus arrestor hooks. u.s.w.
Come to think of it a suitable bit of elastic stretched across any runway could be fun & solve many landing possibilities.
mike hallam.
But if you keep power on as required to hold 40 kt into 40 kt breeze ready to land but say 25 ft up & still too high, you hover, (after a fashion).
When you decide to fly nearer the deck it will land and whilst shutting down, remaining facing into wind as you, brakes on, wait for a wing walking team.
Deck being the operative word as it's how high performance naval a/c manage short runway landings - with carrier 'steaming' into wind plus arrestor hooks. u.s.w.
Come to think of it a suitable bit of elastic stretched across any runway could be fun & solve many landing possibilities.
mike hallam.
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Still on my to-do list is to fly backwards. Looking out might be a bit tricky.
There are rumours of someone having done a take-off into a strong wind, reduced throttle, flew backwards and then landed on the runway they took off from. I guess in something like a Chevron this is a very real possibility?
There are rumours of someone having done a take-off into a strong wind, reduced throttle, flew backwards and then landed on the runway they took off from. I guess in something like a Chevron this is a very real possibility?
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C1,
But if you keep power on as required to hold 40 kt into 40 kt breeze ready to land but say 25 ft up & still too high, you hover, (after a fashion).
When you decide to fly nearer the deck it will land and whilst shutting down, remaining facing into wind as you, brakes on, wait for a wing walking team.
Deck being the operative word as it's how high performance naval a/c manage short runway landings - with carrier 'steaming' into wind plus arrestor hooks. u.s.w.
Come to think of it a suitable bit of elastic stretched across any runway could be fun & solve many landing possibilities.
mike hallam.
But if you keep power on as required to hold 40 kt into 40 kt breeze ready to land but say 25 ft up & still too high, you hover, (after a fashion).
When you decide to fly nearer the deck it will land and whilst shutting down, remaining facing into wind as you, brakes on, wait for a wing walking team.
Deck being the operative word as it's how high performance naval a/c manage short runway landings - with carrier 'steaming' into wind plus arrestor hooks. u.s.w.
Come to think of it a suitable bit of elastic stretched across any runway could be fun & solve many landing possibilities.
mike hallam.
They had hooks down but I don't think they used them!
I thought it might help to point out to the confused that it's actually change in velocity that should be considered (i.e delta v in any frame of reference, rather than v in an arbitrary frame). But on second thoughts, they are clearly sufficiently confused already.
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Hi again, its me.... Unfortunately you are overlooking the fact that the ASI only measures forward velocity (pitot tubes only face forwards.)
So the statement by Worrab... ... though if you touch down at 45 knots into a 45 knot headwind you will have zero kinetic energy Is not absolutely true...
To land, you also need a downward velocity, so many ft/sec, so you can still have considerable downward Kinetic energy, which can compress your suspension and bounce you back into the air... (been there, done that..)
Also the pitot tube will not pick up any sideways velocity, which you will have when you bank in a very strong headwind.
A Velocity Vector is what is displayed on an ATC Radar screen, and shows the direction and speed that the aircraft is moving... It gives them some indication of the position you will be in in the next few minutes.
.
So the statement by Worrab... ... though if you touch down at 45 knots into a 45 knot headwind you will have zero kinetic energy
Is not absolutely true...To land, you also need a downward velocity, so many ft/sec, so you can still have considerable downward Kinetic energy, which can compress your suspension and bounce you back into the air... (been there, done that..)
Also the pitot tube will not pick up any sideways velocity, which you will have when you bank in a very strong headwind.
A Velocity Vector is what is displayed on an ATC Radar screen, and shows the direction and speed that the aircraft is moving... It gives them some indication of the position you will be in in the next few minutes.
.
