Is it not a volume of water that is displaced rather than a weight of water equal to the weight of the ship.

Tolka,

True, but the weight of water that is displaced has a volume so it has to go somewhere and eckhard is correct in what he says. I believe that you need to consider the water in the aqueduct to be part of a sealed system with a constant volume of water (i.e. including the 'ocean' at either end). The weight of water displaced by the ship will have a volume that is re-distributed throughout the sealed system resulting in an overall surface level rise, including across the aqueduct. Therefore, there will be a theoretical increase in the total load on the aqueduct - but it will be veeeeery small!

So, the budgies in the truck. Once airborne, is their weight transferred back to the truck's floor by the air downflow caused by their beating wings (assuming a sealed truck)?

Crikey! Isn't Physics wonderful that its laws apply to boats and aircraft.

The boat displaces its own weight in water (the Eureka! thing). An aqueduct typically isn't an enclosed space so if you lowered the boat from a crane, water would move out at each end and the overall level of the entire canal would rise just a smidge. If the boat grounds on the aqueduct then the aqueduct is subject to an increased load that corresponds to the weight of the boat less the weight of water that it is displacing even in its sunken state.

The most marvelous incarnation of this is the Falkirk wheel which looks great from the air. (It's a good few years since I circled it, but IIRC it's under the Edinburgh CTA). It has effectively two bathtubs, one on each end of a long bar. The tubs fill with water and the bar balances. A boat sails in and displaces its weight in water. Consequently, the bar is still balanced. I don't know how much power is needed to move a boat from one level to the other but I imagine it's tiny. A true marvel of engineering.

If 2,000 dead chickens each weighing 5lbs are loaded in an aeroplane it has a payload of 10,000lbs. If the same chickens are alive and flap their wings vigorously does the payload decrease and what is the affect on aircraft performance?

Synonymous with de-accelerate, as Flyingmac said,The use of the de prefix creates a compound word eg decapitate. In forming compounds the de is normally joined without a hyphen or space. If the second element begins with the letter e, or a capital letter, a hyphen is used. It is also preferable to use a hyphen if the compound brings together three or more vowels, as in de-accelerate, though scientific papers, among others often use deaccelerate, and ignore the preferable rule regarding the hyphen usage. Even my spell check allows de-accelerate, but flags deaccelerate.

Do a search and you'll find the word used in many places, scientific papers etc.

I suspect that if the aircraft had a mesh fuselage it would actually decrease the load on the aeroplane and as long as the birds remained out of contact with the airframe it would perform as if empty. Whether they'd keep up with the accelerations of flying is anyone's guess. On the other hand it rather defeats the purpose!

Are we getting more than a little abstract here? If we carry on like this someone will be asking whether a cat left in the hold is alive or dead (that one for Cabin Pressure afficionados).

According to Erwin Schrödinger, both.

Now we're talking PROPER physics!

TOO

Back to the OP's discussion...

There were letters in AOPA's magazine a while ago propounding the 'inertia' theory from someone styling themselves 'Bunbury'. I took it to be a hoax using the pseudonym employed in Oscar Wilde's 'The Importance of Being Ernest'.

Next..

'Flat Plate' theory of lift.

For those of you who aren't familiar, this is where all those fancy aerofoil sections are regarded as so much bunk and all that you need is a flat plate to generate lift.

If we keep this thread running long enough, it'll soon be 1st April, which is where all this stuff belongs.

TOO

Well, that is true. After all, a paper dart flies quite well, as does a kite.

The fancy aerofoils result in greater aerodynamic efficiency and also help the structures and design people to have room for spars, tanks, wheels, etc.

The tailplanes on many aircraft are simply flat plates.

But not if it's at the front as a canard!

That said Terry, the canards on Gripens and Typhoons are practically planar and rely on flat plate lift.

True! Actually I was thinking of smaller and slower things like longeze and e-Go. The tiny canard on e-Go produces a huge amount of the total lift at cruise speed.

Getting back to the original subject of this thread:

The following post which was provided by a contributor using the name “theheadmaster” in the thread concerning the Mallard crash in the Pacific Forum covers the matter very well.

For completeness the tailwind scenario is as follows:

If you are going from a 50 knot tailwind to a 50 knot headwind, the airspeed change is still 100 knots ahead to 100 knots in the opposite direction. So, 200 knots velocity change. If you want to work in groundspeed, it will be 150 knots (100 kts airspeed plus 50 kts tailwind) to 50 knot in the opposite direction (100 kts minus headwind of 50 kts). So, the velocity change is still 200 kts, the exact same value as nil wind. As mass is constant and velocity change is the same, the change in inertia is identical in all three cases.

The use of the word MOMENTUM rather than the word INERTIA in the above statements would have been more accurate, but the meaning is quite clear.

So regardless of whether we use the ground or the air mass as our reference frame, and whether we use still air, headwind or tailwind, the aircraft will experience the same acceleration.

Everything which has mass has inertia, so whenever an aircraft is manoeuvring its inertia will affect its performance. But this effect will be the same regardless of whether the air is still, a headwind or a tailwind. So it is not true to say that the inertia of an aircraft does not affect its performance in a downwind turn. It is simply that the effect is the same as that in any other manoeuvre.

The danger when turning from downwind to upwind, is that half way through the turn the aircraft will be flying across the wind. This will cause it to drift downwind. If the pilot interprets this as having insufficient bank angle, he/she will be tempted to bank further into the turn. At low speeds this risks entering a stall/spin.


Megan you have argued that the only reference frame which is relevant is the air mass, because this is the only one which affects the performance of the aircraft. It is certainly true that the interactions between the aircraft and the air mass are the only ones which influence lift and drag. But the purpose of flying is usually to get from one place to another. For this purpose the most relevant reference frame is the ground. You have also stated that you are only talking about accelerations in the fore and aft direction. The fore and aft direction is a valid coordinate if your reference frame is the aircraft, but it is not valid if you are using the air mass reference frame. Whatever reference frame we choose to use, the coordinate system must be fixed relative to that frame. The fore and aft axis of an aircraft is not fixed relative the air mass in which it is flying.

Brian you asked:

It comes from the wings. In a 60 degree banked turn the aircraft experiences a 2g acceleration. The vertical component of lift is equal to the weight of the aircraft and the horizontal component is approximately 1.7321 times the weight of the aircraft. (in the triangle of forces we have 1 squared + 1.7321 squared = 2 squared). That horizontal force of 1.7321 times the weight, is accelerating the aircraft towards the centre of the turn. One factor which is often forgotten is that the wings generate much greater forces than the engine and propeller. Any fixed wing aircraft can be supported by wing lift, but how many can hang vertically on the propeller thrust?

Quite!

I blame this on the way that the 'four forces' are displayed in most diagrams.

The four arrows are shown as roughly equal in length, whereas for a typical small propeller aircraft, the vertical forces should be about ten times bigger than the horizontal forces.

The problem is fitting the forces in to a conveniently-proportioned diagram on the text-book page and displaying them to scale.

Surely the danger is that the pilot uses the ground as their frame of reference when they should be using the air and their ASI? Well-banked turns are not dangerous unless airspeed is inadequate - or is that simply glider pilot speak? (we regularly fly 45 degrees of bank)

In gliding though we're taught that a well banked turn increases the stall speed but decreases the spin risk. It reduces the speed differential between the wing tips, and the pilot is less able to over-rudder. In a slow, shallow turn, particularly if being blown downwind or running low on height, the pilot may be tempted to try and use rudder to increase the rate of turn.

I was doing a standard BGA exercise in a Puchacz (which has a reputation for spinning) a couple of weeks ago. At 20, 40 and 60 degrees of bank the glider was stalled and the airspeed noted. Stall speed increased significantly at 60 degrees, but it showed no inclination to spin. A slow shallow turn with a little extra rudder and it won't hesitate.

Yeap, skidding turns low and slow can be bad for your health.

eckhard,
I agree. In the glider case, specifically my club's DG-1000 two-seater, the maximum AUW is 760 Kg and the best L/D is 46.5 to 1. So the total drag in 1G flight is 16Kg! I've read that opening the cockpit window and putting your hand out, can double the drag.

G'day Kieth, you're correct, but extending the argument beyond that to which I was referring. That was, changes taking place while turning from into wind to downwind while maintaining a constant ASI.I was speaking strictly re the case of turning from upwind to downwind. Nothing else or more.As you say usually, but not always. The time when ground reference comes into the picture is answering what's my drift, GS and ETA.I know what you are saying, if an aircraft accelerates there will be an incremental difference seen between the body frame and air mass frame due the change in AoA. The point I obviously did not make well enough is that, there will be no acceleration sensed in the longitudinal axis, with respect to either the body or air mass plane in an aircraft making a turn from upwind to downwind while maintaining a constant ASI.

An example of taking something out of context.Helicopters do it every day on every flight, and not only hang, but climb. :p

pro·pel·ler (prə-pĕl′ər)
A device consisting of a series of twisted blades mounted around a shaft and spun to force air or water in a specific direction and thereby move an aircraft or boat.

But Helicopters are also known as rotorwing aircaft. I can think of just a couple of rotorwing aircraft in history which were also equipped with propellers. Otherwise, they are propelled by a lift vector?

WFT??!!!????:ugh:

What's an "air mass plane"? Is it an aeroplane made out of thin air? Maybe made from a mass of air? Can you make it plain for the masses? We're not on the same plane, that's plain! It's Sunday, I'm off to mass. Err!

It beautifully sums up the total confusion some seem to have about a simple concept when they try to over-think it and end up over complicating it when trying to explain their confusion to others!

If we all stick to using the ASI to tell us how fast we are flying instead of looking at the ground all will be well. I do look at the ground to judge height - a necessity for a field landing in a glider, and indeed for the variation in the circuit between windy and still days.

That is quite true. Looking at the ground will not tell you your airspeed.

But:

And therein lies the risk. It is quite natural for a pilot to want to monitor his/her height, position and trajectory over the ground. But unless he/she is aware of the wind conditions and fully understands the effects that this will have on his/her ground speed and direction, he/she may misinterpret the signs. If this causes him/her to and bank too far into the turn or use too much rudder, the consequences may be fatal.

Megan
I really do think that you need to go back and read your posts throughout this thread and see what impact they have had on the readers. The exasperation registered by some contributors should make it obvious to you that many of your comments have added nothing to the general understanding of this subject.

Maybe glider pilots are more aware of the wind? After all the effects are very obvious in a thermal or when soaring a ridge.

However why is a well-banked turn dangerous in a Cessna (for example) and not in a glider? Simple answers only please!

A well banked turn is no more dangerous in a Cessna than a glider, provided the ball is kept in the middle. But glider pilots are more familiar with turning at high bank angles and what to do with the rudder.

Cessna pilots could learn?

Could and should 😀

A bit presumptuous I think.

Why?
Icreasing skill is usually a good thing! ;)

Presuming the Cessna pilot needs his skill improved more than the pilot of any other aircraft.

It wasn't me that first invited the comparison between Cessna pilots and glider pilots. I'm assuming we meant Cessna to be shorthand for 'the average ga pilot flying for leisure on a ppl'.
And I can tell you that more often than not, the average ga pilot, when invited to demonstrate a steeply banked turn (at altitude) during a biennial flight manages about 30degrees of bank maximum. Glider pilots have to be comfortable at much higher angles for continuous turning in thermals.

Another sweeping generalisation. I fly a C172.

I was taught 60 deg steep turns and still do them - now it seems 45 deg is regarded as a steep turn.

That was exactly my meaning, and mentally I was including 3-axis microlights as well.

I just don't agree with these generalisations. There is never any accuracy in them.

Brian Abraham, as you appear to be wading in to defend some of the mixed up nonsense that megan comes out with, and you boldly state that this mysterious "air mass plane" that megan refers to is:Please explain EXACTLY what - in your own words - an "air mass plane" is, and what its relevance - if any - is to this discussion about aircraft turning in 3D space.

I'm sure the Wiki page you referenced will help to remind you that a plane in this context is a 2 dimensional flat surface. How does any such 2D plane become an "air mass plane", and what EXACTLY is the significance of the "air mass" label given to any such 2D plane? What relevance is any "AIR MASS" to any of the infinite number of 2D planes in space? What is this "Plane of reference" you take his "air mass plane" to be?

Probably, both megan and you are confusing the notion of a 2D PLANE with an inertial FRAME of reference, which could be a valid starting point for a sensible discussion to start from. Other than both words happening to rhyme, there is no connection between any such inertial FRAME of reference and any PLANE that you and megan seen keen to claim has any relevance.

A few contributors to this thread make accurate, valid scientific statements and give equally valid answers and facts; Keith W and PaulisHome to name just two. They are outnumbered by others who like to mix up jumbles of half-truths and myths using occasional precise scientific terms in inappropriate, inaccurate and confusing ways, which unfortunately spreads their own confusion to others.

Unless you can justify your bold claim that you cannot understand how the term "air mass plane" could be confused by anybody, then you are placing yourself squarely in the latter category, along with megan.

Keith W and PaulisHome are correct in what they say. In contrast, the repeated offerings from megan contain little of substance, and much of it is simply wrong. How odd that you should come out in support of some of megan's muddled nonsense, whilst apparently ignoring Keith W's very valid reprimand to megan that their contribution adds little, if anything of value to the discussion.

Edited - it appears that Brian Abraham has chosen to delete his post in support of megan's nonsense rather than try to explain his theories about a "Plane of reference" being an "air mass plane". Pity, I was looking forward to the explanation.

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.


.

No they won't. Because they only have the momentum of their individual 100knots in their individual air mass.
You will see things differently because you are still on the ground.
I'm goin up the pub!!!!

scifi, if that were correct then aircraft would be more agile when flying downwind than upwind.

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.


.