Myth busting! I MIGHT STALL IF I TURN DOWNWIND!

[Ultralights]

yep so wouldnt it be correct to say the aircraft has more inertia when landing downwind? isnt that why it takes longer to stop

on final approach, in a 20 Kt headwind, IAS is 60 KTs, your groundspeed at touchdown will be 40kts, IAS still 60kts.

 

with a 20kt tailwind.. IAS is still 60 kts, but groundspeed is 80Kts, at touchdown groundspeed will be 80Kts, IAS still 60kts.

 

so in landing with a tailwind, your touchdown speed will be Double than if you landed in a a headwind,(in the example above) this is why you take much longer to stop with a tailwind, and why landing with a tailwind is NOT recommended. as even a small tailwind has a significant effect on landing (ground)speed and hence stopping distance required.

 

 

[griffo]

"That" Question of IAS vs G/S....

 

Hi all,

 

A Caution if I may be so presumptious...

 

Just remember the 'apparent slip' and the 'apparent skid' when doing all this stuff 'close' to the ground.....

 

You just keep the aircraft in balance...that little old ball in the hey-diddle- diddle...every time, and you will be ok.

 

The illusion is a joy to behold, but that is all it is, providing that, THAT little ball is in the middle...an illusion.

 

Enjoy your flying - and don't worry too much about things that aren't in 'The Mechanics Of Flight' by A.C. Kermode if ya really wanna get serious.

 

This book on the "Principles Of Flight', or its derivatives, are really REQUIRED reading if you wanna win all of those bar-room arguments / debates.

 

And, 'VK', I think you might find that your RATE of climb is no different when climbing in still (Calm), headwind, or tailwind.

 

What will be readily apparent is your differing ANGLE of climb in the given conditions - that is, the ANGLE of climb is RELATIVE to the ground, whilst the RATE...finish this sentence...

 

Cheers.:thumb_up:

 

 

[vk3auu]

I didn't say that my rate of climb straight ahead was different into the wind, I said that the rate of climb in a turn would be different, depending on which way the wind was blowing.

 

John Brandon, I'm sorry to disagree with you still, but momentum has nothing to do with relative wind direction.

 

David

 

 

[griffo]

Negative Sir!

 

Your RATE of climb will be exactly the SAME when climbing in a turn IF you keep your attitude, (IAS), Power setting (Full throttle) & angle of bank constant - usually at no more than 15deg bank whilst climbing - otherwise the extra drag at higher angles will 'negate' the power available which enables you to climb...

 

(Of course, as you climb up to the higher levels your power will usually decrease with alt.)

 

Try this next time....climb to a safe alt. then set the aircraft up in a climbing turn @ a 15deg A. of bank, - L or R - doesn't matter, trim for the climb, and without touching your power setting from full power - or whatever your particular aircraft engine power setting - observe your VSI, and I'll bet you, if you hold everything else constant, whilst climbing into/out of/ across wind / upwind / downwind / any bloody wind, your RATE of climb will NOT alter.

 

If you don't have a VSI, use your stopwatch.

 

After a while you will have forgotten from which particular direction relative to your flight path, the W/V is from!

 

You are simply moving UP in a body of air - which is itself moving over the ground in a particular direction at a particular speed = wind velocity = W/V, which does NOT affect the climbing RATE of your aeroplane.

 

It will certainly affect your ANGLE of climb - i.e. your flight path relative to the ground.

 

Climbing into a wind of say 20kts @ climbing speed of 60kts IAS = say 500ft/min over the ground at 40kts G/S. Plot this and see the angle produced.

 

Now do the same for downwind. 60kts IAS + the 20 = 80 kts G/S.

 

In the same 1 minute, the aircraft has still climbed 500ft, but now at a G/S of 80kts = further dist travelled = much 'shallower' ANGLE of climb.

 

But at THE SAME RATE!

 

To an observer on the ground, I have been known to make an aircraft 'Stand Still' - and even fly backwards - the fact that I was still doing 40kts into a 40 / 45 kt 'headwind' was lost on the audience of the time...

 

And I am sure that you can do this 'trick' as well...just keep that ball in the middle and watch your attitude i.e. IAS

 

I hope this helps,

 

Regards,

 

Griffo;)

 

Apart from accepting this, I would strongly advise that a GOOD book on BAK would be appropriate reading.

 

I can thoroughly recommend "THE MECHANICS OF FLIGHT" by Mr A. C. Kermode.

 

OR, any other "Principles Of Flight" epistle.

 

The response of others on this forum have been very thorough -IMHO - and I can only suggest these be read and digested further. However, if you have any further queries, don't hesitate to ask. I'm sure we (Collectively) can make progress with this.

 

 

[DrDexter1975]

OK this is my (slightly off topic) brain teaser given such a good opportunity!

How can a car travelling at 100kph be stationary at the same time?

 

 

A car is travelling down a perfectly horizontal road at 100 kph. The car has a perfectly vertical windscreen relative to the road surface and direction of travel.

 

 

Coming the other way on an exactly reciprocal heading is a fly travelling also at 100 kph (This is a high speed fly with a go faster stripe!)

 

 

The fly collides in the centre of the windscreen and (obviously) gives way. Its remains begin going back down a reciprocal to its original track.

 

 

OK for something to change path by exactly 180 degrees it has to first stop to change direction. If the fly was stationary at the point of reversal then what it was in contact with (the windscreen and by definition the rest of the car) had to also be stationary. Yet the car is travelling at 100 kph!

 

 

Why is this so?

 

 

Warning there is a bit of physics in this and also perceptions – I have had many people who cannot refute the logic but refuse to accept it.

 

 

Another quick one on perceptions:

 

 

We have a perfectly spheroid planet. The upper hemisphere is entirely land mass up to exactly the equator. The lower half is all water.

 

 

Is the northern hemisphere an island (land totally surrounded by water) or is the lower hemisphere a lake (Water entirely surrounded by land)?

 

 

T.

Sounds like the fly had a 100kph headwind - making the car stationary relative to the air movement.

 

 

[Guest TOSGcentral]

Wrong Dex! Back to the books and perception exercises. Deal with the facts given - I made no mention of wind at all!

 

Tony

 

 

[Yenn]

griffo. I believe you are incorrect when you say you will climb at the same rate in a turn, with the same attitude and throttle settings. It may appear to be true from watching the VSI, but the instant there is any bank applied the lift vector is inclined from the vertical and therefore reduces the rate of climb. At 15 deg bank it is not much, in fact the lift is 96.6% but it is still a loss of lift. At 45 deg of bank it is 70.7% and at 60 deg it is only 50%

 

 

[griffo]

G'day Ian,

 

Yep! You are correct! The RATE of climb will differ in a turn from that of S&L.....due to all of those other factors...Angle of bank, increased angle of attack to maintain the same vert. component of lift, increased power to overcome the increased drag due to.....etc etc and to provide the climbing power - power available above the best lift/drag ratio etc....and so it goes...... beyond what we were discussing here.

 

However, the point I was trying to make is, that, once established in a climbing turn,

 

then the W/V has NIL effect on your RATE of climb.

 

(I didn't mention S&L...only about putting the acft into the climbing turn)

 

The original query was that the acft would climb at differing rates in a headwind v tailwind......(hence my suggestion about the climbing turn where one is changing 'head/cross/ tail' wind constantly....sort of....)

 

NYET!

 

Once we are airborne, then we are simply flying in a body of air, which in itself may or may not be moving - CALM v BREEZE v cyclone - this movement is measured by us OVER the ground, relative to the ground, as a Northerly, or whatever - strong, medium, gentle or whatever - but does our aeroplane care??

 

NYET!

 

It is simply behaving as to the aerodynamic principles of flight...it may be 'bumpy' - turbulence due to W/V over terrain (mechanical turb) or due to convection currents on a hot day - but the airflow relative to the aeroplane, and hence its IAS, RATE of climb (NOT 'APPARENT' ANGLE) will be the same as always......

 

e.g. If my aeroplane, at a certain weight/load, with a certain power setting at an attitude which gives me a certain angle of attack - we see this as IAS - everything else being 'constant', will give me a RATE of climb of say, 500ft a minute, then it will do regardless of the W/V, and regardless of the acft heading. (into wind v downwind).

 

Don't even mention summer v winter yet....we are considering a specific day and point in time. Temps DO make a difference, and for a whole variety of reasons.

 

Thanks for your patience;)

 

 

[Khaled Salah]

MYTH: I MIGHT STALL IF I TURN DOWNWIND!

 

 

 

 

 

 

i have read about this being a myth many years ago, yet i still see it's not (it is only not noticeable on low rate turns) . I wont talk of ground speed...yes, ground is just a ball of dust but its the relation between momentum/inertia and relative wind speed. if you fly at 100Knt into 20Knt wind then momentum = (80^2)*mass....change your direction to tail wind position rapidly and your momentum would almost be the same ""like throwing pin ball in U shape track"" (the engine power will guarantee restore momentum relative to power setting but inertia wont let happen in zero time).....

 

NEVER MIND the physics stuff.....think of wind shear, it's a rapid change of wind direction...if you dont act against mild wind shear, you'll lose some IAS/ lift until engine power restores the momentum/airspeed .

 

The so called myth is a physical fact, theoretically possible but maybe non had ever encountered it coz it only happen with rapid turn rate...i dont know how much rapid but if for example you made a 180 degree turn from into wind to tailwind direction in couple of seconds then it'll take few seconds to pick your original IAS up again

[turboplanner]

Your last line pretty much says it. The myth would be correct if you could make the 2 second turn and that would be the equivalent of wind shear.

 

Must admit I've never counted the seconds for a 180 degree turn but suspect it would be more than enough time to neutralise the effect of momentum.

 

I think most people would be looking down at the ground and percieving the ground speed slow down.

 

 

[Guest davidh10]

Perception Brain TeasersOK this is my (slightly off topic) brain teaser given such a good opportunity!

 

How can a car travelling at 100kph be stationary at the same time?

 

A car is travelling down a perfectly horizontal road at 100 kph. The car has a perfectly vertical windscreen relative to the road surface and direction of travel.

 

Coming the other way on an exactly reciprocal heading is a fly travelling also at 100 kph (This is a high speed fly with a go faster stripe!)

 

The fly collides in the centre of the windscreen and (obviously) gives way. Its remains begin going back down a reciprocal to its original track.

 

OK for something to change path by exactly 180 degrees it has to first stop to change direction. If the fly was stationary at the point of reversal then what it was in contact with (the windscreen and by definition the rest of the car) had to also be stationary. Yet the car is travelling at 100 kph!

 

Why is this so?

 

Warning there is a bit of physics in this and also perceptions – I have had many people who cannot refute the logic but refuse to accept it.

 

Another quick one on perceptions:

 

We have a perfectly spheroid planet. The upper hemisphere is entirely land mass up to exactly the equator. The lower half is all water.

 

Is the northern hemisphere an island (land totally surrounded by water) or is the lower hemisphere a lake (Water entirely surrounded by land)?

 

T.

The fly and car situation can be looked at in several ways. The simpler is to think of the fly as a compressible object and thus as it splatters (compresses), it passes through 0kmh on its way to -100kmh (with respect to the road and its original direction) as the windscreen imparts energy to it. As I said, this is a simplistic view and easier to understand, but not strictly accurate.

 

Note that the description attributed +100kmh to both the car and the fly, but in opposite directions... Implicitly, two points of reference.

 

We could change our point of reference to be the windscreen. Now the windscreen is, by definition, stationary and a fly travelling at 200kmh hits it and stops. The fly has undergone a massive acceleration (physics does not talk of deceleration, just negative acceleration with respect to a reference point.). The force creating the deceleration is imparted by the inertia of the windscreen (and the car to which it is attached). Another view is that the kinetic energy that the fly possesses, by virtue of its relative speed to the windscreen is dissipated in its own destruction.

 

Now we understand that kinetic energy is also measured relative to a reference point. Everything is relative, but often in conversation, the reference point is implied or assumed.

 

We could just as easily take the fly as the reference point and it is now, by definition, stationary. The windscreen is approaching it at 200kmh, and when they meet, the windscreen imparts energy to the fly to cause acceleration from 0 to 200kmh. A much easier concept to understand.

 

We won't complicate the explanations by delving into "conservation of energy".

 

Why is this easier to understand? Because we have changed the reference point such that the changes that are happening are easier to comprehend for humans who, for the most part of their lives use the Earth as the reference point for most things. It is easy to become confused when the reference point is changed, or a situation is described with some parts relative to one reference point and other parts relative to a different reference point that is moving with respect to the first reference point.

 

The answer to the planet.. Lake or Island depends on which half of the planet you are standing, and thus assume as your reference point.

 

 

[turboplanner]

I'm not sure whether you're cunning or clever David, my mind isn't elastic enough. I've just come off reading a book about hyperspace and how some stars move in concert with others light years away, yet move immediately, and the mathematical equations which a guy put together in the 19th Century but which only now are being confirmed by computer - a fourth dimension, but I didn't understand that either.

 

 

[Guest davidh10]

.. I've just come off reading a book about hyperspace and how some stars move in concert with others light years away, yet move immediately, and the mathematical equations which a guy put together in the 19th Century but which only now are being confirmed by computer - a fourth dimension, but I didn't understand that either.

Year, but it is all good food for thought... Have you read "A Brief History of Time" by Stephen Hawking? It's a good read. The last chapter is his layman's explanation. The rest of the book is a primer to get you to the point where you can read the last chapter!

If any of that bends your noodle, try reading about String Theory, where they postulate either 9 or 26 dimensions! It rapidly exceeds my understanding.

 

I've always loved physics. My interest started by watching Julius Sumner Miller's "Why is it so?" on TV (many years before he stooped to advertising chocolate) and then during one school holiday period when in Grade 6, I found his "Quiz Questions in Physics" paperbacks at a local book store. My father had to explain most on first encountering each type, and show me how to solve them, but I enjoyed doing that as a brain exercise while not persuing outdoor activities.

 

In teen years, I loved the Murgatroid Mind Stretcher puzzles published in a newspaper. I cannot remember which paper now, but they were good fun. Mostly logic puzzles like these.

 

 

[Thirsty]

One of my favourite " it depends on your point of reference examples" was from a book written by someone attempting to make Einstein's theories easier to understand.

 

We all know nothing can travel faster than the speed of light right? So I'm standing here and a spaceship zooms past me doing 10Knots slower than the speed of light. Inside that spaceship, at the rear, a kid throws a baseball towards the front of the spaceship at 11Knots. To him the ball is travelling at 11Knots but to me the ball is travelling at the speed of light + 1 knot.

 

Not a very practical example and the ball can only travel "faster than the speed of light" for as long as the spaceship is but it makes you think.

 

 

[turboplanner]

That reminds me of the days when truckies had to put up with portable scales which could be set up quickly on whatever highway the Inspectors chose.

 

Overloading fines were huge.

 

A line of trucks would form as the slow process continued.

 

Someone noticed a guy walking along beside his truck banging on the sides with a stick.

 

"What are you carrying?" he asked.

 

"Pigeons", was the reply

 

 

[Powerin]

That reminds me of the days when truckies had to put up with portable scales which could be set up quickly on whatever highway the Inspectors chose.Overloading fines were huge.

A line of trucks would form as the slow process continued.

 

Someone noticed a guy walking along beside his truck banging on the sides with a stick.

 

"What are you carrying?" he asked.

 

"Pigeons", was the reply

This would work if the back of the truck was open, with open cages for example. But the truckie would get booked for overloading if the birds were flying inside a closed container.

 

 

[facthunter]

The effective weight would be the same if they were flying in the closed container as if they were standing in there. If it was only a wire cage there would be a different result. Nev

 

 

[turboplanner]

You Einsteins are too good for me.

 

So how did they lift 1100 tonne blocks of stone at Baalbeck in Lebanon and set them on a 2 metre high foundation?

 

 

[facthunter]

Mines not hard. I'm certainly no Einstein either. Nev

 

 

[turboplanner]

Well you're smarter than me. I would have said they were detached from the vehicle

 

 

[facthunter]

Well, we can let it run for a while. Nev

 

 

[pudestcon]

Just stop it willya, my head hurts.

 

Pud

 

 

[facthunter]

I know how it feels. I just read this thread in it's entirety. Goes back a while. Windshear effects and visual illusions should be dealt with, as they are the things that cause angst. Nev

 

 

[Powerin]

Just stop it willya, my head hurts.Pud

 

 

[Thirsty]

I agree and it all really comes down to which reference you are using - easy once you understand that.