Effect of wind on aircraft size

[biffo28]

How does the effect of a given landing crosswind differ with aircraft size and weight? Obviously a small aircraft (C172) will be affected by the wind because of its relatively low weight but on the other hand a larger aircraft such as a commercial airliner will be affected because of its large surface area.

I guess that its not as simple as working out a weight/surface area ratio, but for a given x-wind could we speculate which aircraft will be most affected?

Given that we have many youtube examples of commercial airliners landing in very strong winds (that I guess most light aircraft would not fly in), have I effectively answered my question?:O

[Golf-Sierra]

In the case of light aircraft I guess extremely strong winds can cause them to shed parts, perhaps even lift them up and break them to pieces so one could say that that strong winds have the effect of reducing aircraft size.

:}

Golf-Sierra

[BackPacker]

The most important factor is not size or weight, but stall speed. Because stall speed also determines Vref (usually somewhere between 1.2Vs and 1.33Vs) and thus how much influence the x-wind has on your approach path. A 15 knot crosswind in an aircraft with a stall speed of 45 knots/Vref 60 is a totally different matter compared to 15 knots cross in an aircraft with a stall speed of 100 knots/Vref 130.

Second factor is the size of the rudder area since that determines the amount of slip you can induce to counter the x-wind.

And then there's secondary effects. Do you have enough aileron authority to counter full rudder, do you have enough clearance under the wing (think underwing engines as on large airliners) for the bank angle you're introducing with the slip? Is maybe your undercarriage designed to withstand a certain yaw angle while landing?

[Shaggy Sheep Driver]

How does the effect of a given landing crosswind differ with aircraft size and weight? Obviously a small aircraft (C172) will be affected by the wind because of its relatively low weight but on the other hand a larger aircraft such as a commercial airliner will be affected because of its large surface area.


Do I detect a bit of a misunderstanding here of the effect of a steady wind on an aeroplane in flight? The weight of the aeroplane, or its surface area, make not one jot of difference. The only effect of a steady wind on any aeroplane (or balloon) is to affect groundspeed and track.

A changing wind (gusts, wind gradient) will have an en effect on the aeroplane in flight. A heavy airliner, for instance will be more affected by wind sheer than will a light aircraft because the big aeroplane has more inertia.

When it comes to landing in a cross wind, a faster aeroplane will be less affected because the cross wind is a smaller percentage of its airspeed (so, for instance, the angle of 'crab' on the approach will be less for a given wind in a fast aeroplane than a slow one). And the effectiveness of the flying controls, particularly the rudder, will help define the maximum crosswind an aeroplane can land in.

[jehan]

Can some one please ans this
two aircrafts same approach speed lets say 120kts but different size and shape(piper senca & B737)
Which one will have more drift corection angle & y.
thks

[Shaggy Sheep Driver]

If you mean difference between track and heading on a 'crab' approach, the bigger difference for a given wind will be for the slower one. Size and weight make no difference.

[BackPacker]

If the x-wind is the same and their approach speed is the same they need the same drift correction angle, assuming they're using the "crabbed" approach (and are thus flying in balance).

When they transition to the sideslip approach it depends on a large number of design factors such as the exact fuselage shape and the size of the rudder, how much bank is needed. And with airliners the exact position of the underwing engines also become a factor. Too much bank and the engines will contact the runway.

[Lord Spandex Masher]

60/TAS x wind speed = max drift.

Both would have the same drift if they had the same TAS.

[jehan]

thanks guys for your ans can u please elaborate y the momentum of heavy aircraft and size would not make a difference in the correction angle.

Thks

[Saab Dastard]

jehan,

Can you please do us the courtesy of not using text speak?

Thank you

SD

[Lightning Mate]

Can you please do us the courtesy of not using text speak?

Unfortunately most young people are able to do nothing else.

[BackPacker]

Jehan, you agree that the size/weight of the aircraft has nothing to do with the flying speed, do you? (Assuming the flying speed is above Vs and below Vne - and I agree large airplanes typically have higher values for those than small aircraft.)

So if a C172 and an airliner are both doing, say, 120 knots then they are doing 120 knots, right?

Now assume a 2-knot crosswind. If they don't correct for the crosswind they both end up two nm off-course after one hour of flight.

Over a distance of 120 nm, 2 nm offset is about 1 degree. (You can either use the 1:60 rule-of-thumb, or use arctan( 1/60 ) ). So to correct this offset, they both need to steer into the wind by 1 degree.

Again, all completely regardless of weight or size.

And if you don't fancy complex (...) calculations, consider this. There's a rubber bathtub duck and an oil tanker floating around on the North Sea. Both are using no engine power whatsoever, and we are also disregarding wind. Both will then drift with the tide. Making the same speed over the ground, regardless of their size or weight. Same thing.

[Lightning Mate]

....and don't forget lateral stability attributes.....

[jehan]

thanks guys for ur ans and explanation really appreciate it.

[Shaggy Sheep Driver]

To quote one of the best films ever... "For the benefit of the uneducated I will translate.."

"....'ur ans' is perhaps yoofspeak for 'your answer'."

It's also gibberish.

[Jim59]

I think it's unfair to criticise Jehan's use of "text speak". I don't think he realises he is not writing in English.

[jehan]

Guys i apologize for for using text speech.

From the above post i get it that we don't use aircraft size/ weight in consideration for calculating drift or wca.

But for instance if there are 2 bodies different size but moving in same direcion SAME velocity and if you apply force from the side the one which has large momentum(due to its weight)will get deflected from its path less than the one one with small momentum(due to less weight). If this is the case then why cant we apply it to our aircraft.

Please give your input.
Thanks.

[darkroomsource]

But for instance if there are 2 bodies different size but moving in same direcion SAME velocity and if you apply force from the side the one which has large momentum(due to its weight)will get deflected from its path less than the one one with small momentum(due to less weight). If this is the case then why cant we apply it to our aircraft.

What you are saying is true, however if the wind is stable, you've already adjusted for that, and that's one reason size and weight are not factors. In the case of gusting winds, yes, the change in wind speed effects a force on the aircraft, for which momentum (related to 'weight' - actually mass, but for this discussion weight is OK) would affect the amount of movement.

Also to be considered is the 'shape' of the aircraft... a large tail could cause the plane to 'point' into the wind, a large front end could cause it to point away from the wind, an airplane with the nose wheel on the ground will be less likely to point into the wind than one with the nose off the ground or a tailwheel airplane... a high-lift wing could cause the plane to be affected more than a low-lift/high-speed wing

So yes, you are right, to a degree, however the shape of the plane, wing, and tail, wheel configuration, position at the time, speed, variance of the wind, and many other factors have effect on how much a crosswind will affect an aircraft. These other factors generally have greater effect than mass (weight) and size.

Generally, a 'big' airplane (think A380 or 747) will be less affected than a 'small' airplane (think Cessna 152), however to give an example where shape is more of a factor, think of the space shuttle versus an A380. The space shuttle has almost no lift compared to the A380, and thus the A380 is more affected by cross wind than the space shuttle, but the space shuttle is about 1/4th the size and mass (weight) of an A380.

[Shaggy Sheep Driver]

darkroom - not sure what you're saying there. Any steady wind (cross or not) has absolutely no effect on any aeroplane, from a glider to an A380 to a Space Shuttle, other than to vary its groundspeed and track. It has absolutely no effect on how it flies.

Regarding aligning with a runway which has a crosswind, this means a certain amount of sideslip has to introduced, usually yaw with the rudder to get onto the runway heading, with appropriate aileron to prevent a turn.

As I said before, the differnece between track and heading in a crabbed (flying in balance) cross wind approach depends only on speed. The slower the aeroplane, the greater the difference. Hence a Space Shuttle is far less affected than an A380 because the approach speed of the Shuttle is much greater than that of the 380.

The shape of the aeroplane has absolutely no effect at all in the air regarding differentt winds. Don't forget, to an aeroplane in the air THERE IS NO WIND! Wind is simply the air mass moving relative to the ground, and the aeroplane (or balloon!) is suspended in that air mass and so moves with it.

[Fly-by-Wife]

darkroomsource

The only time that an aeroplane can experience weather-cocking effects is when it's on the ground.

That's because when on the ground the wheels act as a pivot-point about which the aeroplane can rotate. The rotating moment is caused by a difference in the total wind load on the fuselage in front of and behind the pivot point.

This simply cannot happen in the air.

FBW

[darkroomsource]

darkroom - not sure what you're saying there. Any steady wind (cross or not) has absolutely no effect on any aeroplane, from a glider to an A380 to a Space Shuttle, other than to vary its groundspeed and track. It has absolutely no effect on how it flies.
As I said: size and weight are not factors

Using the shuttle I was attempting to clarify for the OP that even though mass (weight) has SOME effect, it is minimal. Using a rock and an aeroplane would be a better example. A paper aeroplane weight less than a rock. A paper aeroplane will be blown about in windy conditions, a rock will not (Unless it's REALLY windy), BUT a Cessna 172 which is much heavier than the same rock will also be blown about more than the rock in windy conditions. So weight (mass) is NOT a major factor in the effects of wind, cross wind, gusts, turbulence or any other changes in air flow. Shape is far more important.

However momentum (which is affected by weight/mass and speed) does have some affect on the effects of other forces being applied to an object, whether those forces are gravity, propulsion, or wind. It is just that in the case of something designed to fly, the shape has more influence on the effects of wind than does the mass of the object.


@Fly-by-wife, I beg to differ, weather cocking can be seen and felt in flight. It will be about EITHER the point with greatest resistance (as in the wheels when on the ground, or a pivot point in a wind tunnel) OR it will be about the centre of gravity in flight. This is what we experience in turbulent air when the plane pitches or yaws. It is that some parts of the plane will present more drag than others, and thus be affected more - BUT it is absolutely NOT related to weight (mass) or over-all size of the aircraft.

[BackPacker]

FBW, I don't entirely agree. An aircraft has mass, and thus momentum, and the center of gravity (around which it will pivot) might not be the same as the aerodynamic center on which a cross-gust might act.

In fact, the fin is designed to have a large aerodynamic cross-section to any crosswind, a small aerodynamic cross-section to any headwind, and to sit well behind the center of gravity. So it acts as a weather-vane, weather-cocking the aircraft into the relative wind and thereby removing any sideslip. Whether that sideslip is induced by the pilot or caused by a gust of wind is irrelevant.

And if the aircraft yaws because of a gust of wind, I would call that weather-cocking, even in flight.

[BackPacker]

Using a rock and an aeroplane would be a better example. A paper aeroplane weight less than a rock. A paper aeroplane will be blown about in windy conditions, a rock will not (Unless it's REALLY windy),

I don't think it's a *better* example. In fact, I find the example worse.

A rock and a paper aeroplane on the ground will be blown about, or not, because the forces exerted by the wind are higher than the friction between the object and the ground, or not. The rock is denser so will experience less aerodynamic force and more friction, so it takes a higher wind to blow it about.

And a rock and a paper aeroplane that are free-falling will be blown about by the wind equally. However, it takes a while before the wind has overcome their momentum fully, and before that happens the rock will be on the ground. So it might appear that a rock will fall straight down, even in the wind, but that's just because it takes a while for the wind to "catch" it.

And that momentum is the key. Assuming steady conditions (non-gusting x-winds for instance), the weight, size and shape of the aircraft don't matter one bit. But if you assume non-steady (gusting) conditions, it becomes a matter of the actual weight of the aircraft and it's size. Or better yet, it's aerodynamic shape as seen from various angles.

[Shaggy Sheep Driver]

A rock isn't an aeroplane. It isn't flying suspended in the air mass as the paper dart is, it's falling through it. Comparison invalid.

If you want to demonstrate that a steady wind has no effect on a flying machine other than to affect track and ground speed, a hot air balloon, an A380, and Concorde would be good examples to use.

[jehan]

so to summaries the weight and size does effect the but it is very small and so can be neglected as the main factors are aircraft speed ,wind speed & wind direction and also shape of the aircraft.

Is that rite.
Thanks.

[Shaggy Sheep Driver]

so to summaries the weight and size does effect the but it is very small and so can be neglected as the main factors are aircraft speed ,wind speed & wind direction and also shape of the aircraft.

Is that rite.

No, that is not 'rite' (sic).

I don't know how many times I have to say this....

Oh, never mind. If you didn't read it the last 'n' times I wrote it you won't read it if I write it again.

Just go back and read my posts. It really could not be put more simply than I already have.

[Lightning Mate]

If I may say so, this thread has become silly.

There is a lot of bumph here, but not all of it is.

LM (ex-RAF QFI)

[jehan]

Lighting mate @ sir can you please provide us with right information on the mentioned topic.

thanks

[Shaggy Sheep Driver]

LM has alluded in his post that the correct information has already been given in the thread. Along with a lot of dross.

I agree, it's now got silly.

[Lightning Mate]

Lighting mate @ sir can you please provide us with right information on the
mentioned topic.

Shaggy Sheep Driver already has.

I don't have the time.

[darkroomsource]

But Shaggy is ONLY talking about "steady wind"
I have yet to land in a "steady wind", ever.

[mikehallam]

Taking the discussion away from steady wind conditions and wind gradient, I imagine gusts feel worse in a light a/c - which is all I fly - and they react rather quickly by change of height or trying to move off line on short finals, especially with trees around.

However a massy plane will have substantial inertia and during the landing phase if/when hit by a gust would surely be unlikely to change its attitude, unless the new wind direction is sustained. Thus it would continue as directed because a short burst of wind energy relatively is not very significant.

On reflection even landing a very light a/c demonstrates this effect.

Landing the Rans S6 into a strong wind through the gap in the trees at my base strip, she always suffers short sharp turbulences and wind direction changes caused by it tumbling through & around the trees etc. Thus mostly I've found it best - whilst very prepared to pedal etc.,- to hold my controls as she'll emerge a few lengths later on the same path and skew for the last phase immediately before round out the same as she started with just before.

Hope that practical attempt helps the conundrum.

[Fuji Abound]

MikeH

Yes.

On a practical note it is always revealing when you watch a pilot new to twins fly a twin for the first time.

Consider perhaps a 20 knot gusting cross wind and in most if not all singles the pilot will be working reasonably hard (some more than others ;)). Now fly the same approach in one of the more substantial twins (perhaps and Aztec is as good an example as any) and you instantly wonder what all the fuss is about - it just becomes a complete non event.

The difference is quite surprising at first, even if the approach is not nearly as much fun.

Of course aerodynamically there is a great deal more going on than the aircraft changing from any old light single to any old heavy twin but most pilots are interested in how in looks and feels rather than the physics.

[darkroomsource]

Mike,
As you've noted as you land when the wind changes direction or speed the aircraft feels the effects of changes in forces on its surfaces.
A heavy aircraft will have momentum in its favour, obviously, however and if you have the same aircraft landing with different weights, you'll see a SMALL difference between the two loadings.
However if you have two aircraft with the exact same weight, but one of them has a tail surface that is 4 times the size of the other, you will see a DRASTIC difference between the two aircraft.
Mass (weight) DOES have an effect on the affects of wind, however shape has a much greater effect.

[Shaggy Sheep Driver]

As one nears the ground on a crosswind approach and the 'steady' wind is augmented by coriolis effect, wind shear, wind gradient, and ground-feature-induced gusts, and mass becomes a factor.

A big, heavy aeroplane will be more affected by wind gradient and wind shear, less by gusts. A light aeroplane will be less affected by wind gradient and shear (but will still be affected to some degree), and more affected by gusts.

The shape of the aeroplane makes not the slightest difference on the approach and landing until it's no longer flying and it becomes a non-flying object sitting on the ground.

[darkroomsource]

The shape of the aeroplane makes not the slightest difference on the approach and landing until it's no longer flying and it becomes a non-flying object sitting on the ground.
Tell that to NASA and every Aeronautical Engineer in the world, because they obviously don't need to worry about the shape of a wing, and all the time they've put into wing technology has been for naught.

[Shaggy Sheep Driver]

The shape of the aeroplane makes not the slightest difference on the approach and landing until it's no longer flying and it becomes a non-flying object sitting on the ground.

Tell that to NASA and every Aeronautical Engineer in the world, because they obviously don't need to worry about the shape of a wing, and all the time they've put into wing technology has been for naught.

darkroom - you have (I suspect deliberately) taken part of my quote out of context.

We're talking about the effect of wind here. If the aeroplane arrived on the ground it fulfilled the requirements for flight while it was landing. Once tied down and the aeroplane becomes a 'land object', different rules apply. Which as I know you know was what I was referring to.

[Lightning Mate]

Oh for fcucks sake you ill-informed twats!!!!!!!!!

[jehan]

guys nobody out here is actually answering my question.

My question was "Why is aircrafts momentum, size and shape not taken in consideration while determining drift angle"

can some one please give me a simple explanation.

Thanks.

[Sillert,V.I.]

guys nobody out here is actually answering my question.

My question was "Why is aircrafts momentum, size and shape not taken in consideration while determining drift angle"

can some one please give me a simple explanation.

Thanks.

Imagine sitting on the ground watching a large weightlesss box of still air blowing in the wind. The only thing which affects the movement of the box is the speed of the wind.

Now imagine being in the box watching an airplane flying inside it. Since the air inside the box is still, the only thing which affects the movement of the airplane in the box is the speed of the aircraft.

Put the two together, and hopefully you will see that the only variables which affect the motion of the airplane relative to the ground are the speed of the wind and the speed of the aircraft.

[BEagle]

Drift angle is simply the steady state angular difference between track and heading. End of.

Transient effects due to gusts and turbulence may be influenced by wing loading, momentum and gust response.

Lightning Mate, I understand your frustration!

[24Carrot]

This has already been answered several ways, but I will try one more.

The aircraft's inertia is proportional to its weight, which equals Lift in steady flight.
It has various kinds of speed stability designed in, and the restoring forces are significant fractions of the Lift force.
This means the restoring forces are significant fractions of its weight, and and so the correcting accelerations are significant fractions of "g" (9.81 m/s/s or about 20 kts/sec).

Imagine a trimmed aircraft with centred controls flying in zero wind.



Now imagine a 10 kt wind starts to blow from the left.

Because of dihedral, you should soon get something like a 1/4 of the Lift force accelerating the aircraft to the right.
That's a 1/4 of the weight. Which will accelerate the aircraft at 1/4 G, which is about 5 kts/sec acceleration.
So 2 seconds after the wind started to blow, the sideways airspeed has gone.

Inertia (or Momentum if you prefer) is relevant for a couple of seconds after the wind changes, but not at all after that.

The bottom line is: aircraft are designed not to fly sideways.



Now imagine a 10 kt wind starts to blow from straight ahead.

Precisely because the aircraft has inertia, it will not instantly change ground speed, but it will instantly gain airspeed.
If the aircraft is travelling at 90 kts, the Lift will increase by about 25% (airspeed squared counts) and gravity will slow it as it climbs.

After a few seconds the airspeed and Lift have returned to normal again, but the groundspeed has changed.

The bottom line is: aircraft wing Lift depends on airspeed, not groundspeed.



I have not worked the numbers in detail, because I am trying to get a point across, not write a book.

Over a one hour flight, there may be a few seconds of transient adjustment to changing wind conditions, and the detailed aircraft behaviour over those few seconds will depend on the aircraft's inertia.
Those few seconds are of no significance.

The aircraft flies in the air, and the air moves over the ground. End of!

[darkroomsource]

guys nobody out here is actually answering my question.

My question was "Why is aircrafts momentum, size and shape not taken in consideration while determining drift angle"

can some one please give me a simple explanation.

Different question than in the original post.

Momentum (mass/speed), size, shape are only factors when the forces acting on the object change.

You can take a few physics courses at university to get the complete explanation, in order to understand static and dynamic forces, but I'll try to give a brief explanation.

Acceleration (or deceleration) in any direction is affected by Mass (weight), but an object that is at a constant Speed has no acceleration, so Mass is not a part of the equation.

The force equation is F=MA where F is force, M is Mass, and A is acceleration.

Speed is calculated as V=D/T where V is velocity, D is distance and T is time.

When speed is to be calculated as a result of acceleration, V=Vo + AT where Vo is the initial velocity, A is acceleration and T is time.

If the forces on a aeroplane change (wind speed or direction changes or power changes or control changes), then the speed (and thus ground track) will change and this change will be a factor of Mass.

However if the forces do not change, then the ground track (Velocity) will NOT be affected by Mass (weight)

In a moving wind-mass (block of wind) the if the aeroplane were 'stationary' in the wind it would be travelling the same speed and direction of the wind.

To make things simple, let's say that the wind is blowing toward 090 at 20 knots.

And to continue to make things simple, let's say the plane is pointed 000 and is travelling at 100 knots.

As the plane moves toward 000 at 100 knots within the block of wind it is also moving toward 090 at 20 knots as a result of the wind moving across the ground.

Weight doesn't come into it at all.

If the plane weighs 1000kg it will be going to 000 at 100 and to 090 at 20.
If the plane weighs 9999kg it will be going to 000 at 100 and to 090 at 20.

[mikehallam]

"Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia Mathematica, which states:

The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line."

mike hallam (with thanks to Wiki.)

[24Carrot]

There seem to have been a lot of very good responses to a pretty minimal input from jehan. Perhaps it is time to put the boot on the other foot.

Jehan, perhaps you would care to explain why you think weight, momentum, or aircraft shape should have any effect on drift angle.

Let us take darkroomsource's example.

Let us have two aircraft in a crosswind: same speed, same location but vertically separated, and with different weight and shape.

You propose that, because of momentum or shape, they require different drift angles. Let us suppose they make no wind corrections, so I take it they must drift, but drift at different rates? At any rate they cannot remain one above the other if they require different drift angles, and are not getting them?

So which of the following do you believe:

a) One of the two 100kt aircraft gains on the other, because of its momentum or shape.

b) One of the two aircraft on the same 000 heading flies more sideways than the other, because of its momentum or shape.

I am sure that any suggestions as to the physics behind all this will be heartily appreciated by all.:)

[Mutley Eugenius]

I know its a bit late but I don't think anyone ever said...

Because the drift is caused by the air moving, not the plane(s) moving. Therefore all aircraft supported by that air will be influenced equally.

[mikehallam]

Gusts and inertia and steady wind are not equal for all planes.