Aerodynamics Discuss the concepts of aerodynamics here

Downwind Turns

Old 03-11-2009, 12:09 AM
  #176  
slipstick
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Originally Posted by Moxus View Post
so, we assume that the aircraft takes a 180 degree turn, and no energy is spent or gained, because has been at constant absolute velocity.
now, when you fly upwind, the speed of the air flowing over your wing is:
(ground speed + wind speed)
when you fly downwind, the speed of the air flowing over your wind is:
(ground speed - wind speed)
For that to make any sense you need to define the relationship between what you call "absolute velocity", "ground speed" and "wind speed".
Originally Posted by Moxus View Post
that clearly shows that your wing has less velocity relative to the surrounding air when flying downwind that upwind, when keeping absolute speed constant.
And now you've introduced another undefined term "absolute speed". Is that ground speed, air speed, wind speed or some other as yet unmentioned speed ?

If groundspeed upwind is 10mph, groundspeed downwind is 40mph and wind speed is 15mph how exactly does 10+15 demonstrate any difference from 40-15. Both show an airspeed of exactly 25mph.
Originally Posted by Moxus View Post
complicated problem made simple. good engineering.
Slightly complicated problem made really confused by attempting a solution without defining the references and terms you're using. Rotten engineering .

BTW it might help slightly if you didn't keep using "wing" and "wind" when you meant the other one .

Steve
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Old 03-11-2009, 12:28 AM
  #177  
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ok, sorry. here comes teh definition:

"ground speed" would be the aircrafts velocity relative to the ground. wich is, the speed that the aircraft appears to be moving, for you.

"air speed" would be the speed of the aircraft relative to the airmasses.

"absolute speed" is the aircrafts speed. period. its not relative to anything but complete standstill. for example, you say that the speed of light is 300 000 000 m/s, but you never say relative to what. that is absolute speed, relative to complete standstill.
all physical factors are relative to complete standstill (and keep in mind, the earth moves, so you, or the plane, standing still on the ground is not complete standstill). in this case, that is the aircrafts inertia that depends on absolute velocity.
for all practical measures the absolute velocity would be the same as ground speed in this case, but the reason i wrote absolute velocity is to put the physicists and engineers to the right thoughts, and forget ground speed, because that has nothing to do with the aircrafts behaviour.

if it looks confusing, the red line through the tread is that the inertia of mass relates to absolute velocity (roughly groundspeed if thats easier to visualize), but the aerodynamical forces related to the airspeed, and when the airspeed and absolute velocity is not the same (wich is the case when its wind), then this will necessarily affect the aircrafts behaviour, as aerodynamcal forces and inertia of the plane will apply in different ways depending on the planes orientation. namely, up the wind or down the wind.
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Old 03-11-2009, 01:41 AM
  #178  
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Wind, airspeed, and plane position.
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Old 03-11-2009, 01:56 AM
  #179  
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Originally Posted by slipstick View Post
For that to make any sense you need to define the relationship between what you call "absolute velocity", "ground speed" and "wind speed".

And now you've introduced another undefined term "absolute speed". Is that ground speed, air speed, wind speed or some other as yet unmentioned speed ?

If groundspeed upwind is 10mph, groundspeed downwind is 40mph and wind speed is 15mph how exactly does 10+15 demonstrate any difference from 40-15. Both show an airspeed of exactly 25mph.

Slightly complicated problem made really confused by attempting a solution without defining the references and terms you're using. Rotten engineering .

BTW it might help slightly if you didn't keep using "wing" and "wind" when you meant the other one .

Steve
I agree. they would come to the same Answer. thus proving that there is no change in IAS up or down wind. (That is; Provided you are maintaining the Same IAS up and down )

without Values I don’t know if you are saying the Ground speed remains constant. IE 40 up wind and 40 Down wind. or if you are just Plane Confused.
If you are talking about keeping ground speed constant then you will find that that is already a thing not to be done. You fly Competition and want your Plane to fly constant relative to the Judges. then you have a point of discussion. But we are talking about doing constant G turns. or flying the plane through the air, not around a ground based track.

There is no dispute that there is a difference in Lift etc when you track a constant Ground speed around a Ground based track with wind in the formula.

Bryce.

PS. It would be a good thing if you could start a new thread on the Topic of something similar to "Ground Tracking Downwind upwind"
it is important to know and understand.

Bryce. (Again )
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Old 03-11-2009, 02:24 AM
  #180  
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Originally Posted by Sparky Paul View Post
.
Only relative to the ground!
Only relative to the ground!
The airplane is IN/carried by/flies with the air mass, whether the air mass is moving or not.
This is extremely basic aerodynamics.
You ( I won't waste the time ) can "calculate" the plane's motion relative to anything you want.
The airplane (and I) won't care.
It flies IN the airmass.
Yes. I understand that.
I don't think you and I disagree.
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Old 03-11-2009, 08:42 AM
  #181  
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Moxus, some of what you are saying is correct, some is wrong. Your attempt to explain / differentiate “absolute speed” and “ground speed” needless and useless. Most of your explanation is for the situation as if the plane is making a sudden turn with the rest of the acting forces lagging behind, (post 173) in practice this simply does not happen. (3D planes is behaving differently and cannot be part of the discussion) In a sharp turn there are forces acting on the plane that is not applicable to the same extend as a gentle turn and you don’t mention those. Using one example as an explanation for everything else is not reasonable.

In post 175 you said "NO ENERGY IS LOST OR GAINED". Wrong! Energy is continuously lost via drag and replaced by thrust and / or up draft in the case of a glider. One can say “The sum total of energy lost and replaced / gained remains equal.” KE is not totally irrelevant, it does play a part in the whole system, but is not the sole or major role player as was said before. You said “to change its path takes force (not neccessarily energy…” Please explain force without energy. And “if speed is kept constant, and only direction of travel is changed, no energy is used.” Impossible! And “only a force applied.” Again ??? And “keep that in the back of your head.” As if that was the last word on the subject.!?

You again bring in “ground speed” as if it has something to do with a plane flying and you build an argument on that. It is plainly wrong. You say “now, you can always point out that the wind will accelerate the aircraft so the aircraft speed wont be constant, and that is true. but because of the aircrafts inertia, this wont happend instantly. it has a lag, and for the period it takes the wind to accelerate the aircraft, thats a period where you got reduced lift.” You conveniently forget that the turn is not instantly and that everything happens over time, even if it is seconds, it is time. Any energy gained or lost is a continuous process; the wind is not waiting for a few seconds before it is acting on a change.

“complicated problem made simple. good engineering.” That is what you think.
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Old 03-11-2009, 10:21 AM
  #182  
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Originally Posted by Moxus View Post
"absolute speed" is the aircrafts speed. period. its not relative to anything but complete standstill.
...
all physical factors are relative to complete standstill (and keep in mind, the earth moves, so you, or the plane, standing still on the ground is not complete standstill).
....
for all practical measures the absolute velocity would be the same as ground speed in this case
How confused can you get. First you say "speed is only relative to complete standstill", then you say "the earth moves so the ground is not at complete standstill" then you say "absolute velocity is the same as ground speed". Which would only be true if the ground was at complete standstill and you've only just finished saying it isn't .

These downwind turn discussions always get to the point where confusion sets in and people can no longer even understand what they're saying themselves let alone what anyone else is trying to say. Time for me to give it a rest I think.

Steve
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Old 03-11-2009, 10:49 AM
  #183  
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Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana] Most of your explanation is for the situation as if the plane is making a sudden turn with the rest of the acting forces lagging behind
Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana] in practice this simply does not happen. (3D planes is behaving differently and cannot be part of the discussion) In a sharp turn there are forces acting on the plane that is not applicable to the same extend as a gentle turn and you don’t mention those.
wether the turn is sudden or not doesnt matter wether its a 3d plane or not does not matter either, the lag occurs anyway. you can use an hour to make your turn, the inertia of mass does still work against the wind force, trying to accelerate your aircraft in the opposite direction, and when turning, this inertia does still make your aircraft speed relative to wind lag behind ever so slightly.

Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana]Using one example as an explanation for everything else is not reasonable.
yes it is. its the same forces at play, just in different quantities. and since noone here can calculate these forces, we have take the second best. an understanding of the forces at play. and as mentioned earlier, the forces at play are exactly the same, they just work in different quantities depending on your plane type and turn radius and wind speed and the phase of the moon, and everything else you CANNOT calculate here, so i suggest we ignore it. its just derailing the topic into a chasm of problems we never can solve anyway.

Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana]In post 175 you said "NO ENERGY IS LOST OR GAINED". Wrong! Energy is continuously lost via drag and replaced by thrust and / or up draft in the case of a glider.
these is factors wich is irrelevant for the problem in question.
as mentioned several times now, stop making the problem more complicated than it really is. if you ever opened a physics book, you see that aerodynamic drag is always always ALWAYS ignored, even at university level.
they can still explain things such as coreolis effect, and ballistic trajectories.
you dont need aerodynamic forces here either, to screw up the problem in question. because if you start calculating with that, the whole topic is in that chasm of unsolved/unsolvable problems.

Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana] You said “to change its path takes force (not neccessarily energy…” Please explain force without energy. And “if speed is kept constant, and only direction of travel is changed, no energy is used.” Impossible! And “only a force applied.” Again ??? And “keep that in the back of your head.” As if that was the last word on the subject.!?
that is the last word on the subject. if you dont believe it, i can take you in a crashcource of circular motion, and hence prove that centripetal force is contantly changing the speed of a given mass, without adding or removing any energy.
this however is way off topic and requires nasty mathematics.
just accept it, because its well established science.
you know that planet earth is orbiting the sun without having added energy or speed (or lost) from its trajectory.
its straight forward motion is still bent into a circular motion, and the force (gravity of sun) is not doing any work on the earth.
simply explained, you can look at a 90 degree turn at constant speed.
all velocity in x-direction is lost, but then again, the exactlu same velocity in y-direction has appeared "out of nowhere".
the explaination is that all the energy that is lost in x direction is regained in y direction, and hence the total energy spent is 0, but the trajectory is still changed.
this is also possible for other situations than circular motion.


Originally Posted by rebell View Post
[COLOR=black][FONT=Verdana]You again bring in “ground speed” as if it has something to do with a plane flying and you build an argument on that. It is plainly wrong. You say “now, you can always point out that the wind will accelerate the aircraft so the aircraft speed wont be constant, and that is true. but because of the aircrafts inertia, this wont happend instantly. it has a lag, and for the period it takes the wind to accelerate the aircraft, thats a period where you got reduced lift.” You conveniently forget that the turn is not instantly and that everything happens over time
as explained to steve, i mention "ground speed", because it might be easier to visualize than absolute speed, because in this situation, for all practical measures, working with ground speed or absolute speed will be the same.
it it has plenty to do with the aircraft!
all mass has inertia when its moving at speed, and this speed is NOT the speed relative to the surrounding air. this speed is absolute speed, or ground speed if you want. and as for that sudden/hour long turn problem again, its the same forces at play, just at different quantities.
you can use 3 years on your turn, you still got ever so slight lag.
but for the sake of simplicity........'
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Old 03-11-2009, 11:09 AM
  #184  
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Originally Posted by slipstick View Post
How confused can you get. First you say "speed is only relative to complete standstill", then you say "the earth moves so the ground is not at complete standstill" then you say "absolute velocity is the same as ground speed". Which would only be true if the ground was at complete standstill and you've only just finished saying it isn't .
oh dear :P i thought i should say groundspeed instead of absolute velocity because people not familiar to textbook language physics might find it easier to visualize. how miserable wrong could it be
well, its good you ask questions, and your question is good
ground speed is not the same as absolute velocity, but for the sake of simplicity, lets forget it.
because your speed, the speed of your aircraft, the speed of the wind can be seen as vectors. and one vector can be the same as many smaller vectors of many different directions, added together. right?
so, what you do is saying that:
aircraft speed = speed of planet earth + speed of wind + IAS
ground speed = speed of planet earth
your speed = speed of planet earth + your walking speed.

you see that all of these has a vector in common, and thats the speed of planet earth. so for the sake of simplicity, you can remove that, because your position/or speed, relative to the aircraft is not going to be affected by the speed of planet earth, because you got that exactly same speed and direction yourself.

so, for determining position relative to earth/ground, you can indeed ignore that.but, as mentioned before, the reason is said absolute speed anyway is because physical factors does still relate to absolute standstill. and in this case, that is the aircrafts inertia.
now, the earth is moving so slowly that you can even still ignore the earth speed, and use earthbound referenses as "zero".

but that would gained protests from those who harshly claim that ground speed is irrelevant, because the aircraft doesnt "see the ground". and that is also true, so i had to explain in some way that "ground speed" is in fact relevant for the aircrafts inertia, without saying that the aircraft is in some way dependant on the ground. so.... *sigh*... how do you say it.
i hoped i would get away with using absolute speed and ground speed interchanging :P but i didnt.

edit: typo

Last edited by Moxus; 03-11-2009 at 12:06 PM.
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Old 03-11-2009, 01:38 PM
  #185  
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I don’t know if I want to waste my time to argue with your laughable ideas; it is typical of a young student thinking he knows everything now that he is busy with his studies. You speak as if you are the professor now and speak to people not knowing anything, not knowing what qualification and experience people have here.

I just hope that the plane I am flying in will not decide it is going to ignore drag and lift, because then I will be in big trouble. We are not talking textbook theories here, we are talking real world. Once you know how to differentiate between the two and actually know the terms you are talking about, come back and talk again.

These downwind turn discussions always get to the point where confusion sets in and people can no longer even understand what they're saying themselves let alone what anyone else is trying to say. Time for me to give it a rest I think.
I could not agree more.

Rebell, signing off.
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Old 03-11-2009, 01:47 PM
  #186  
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Oh my, I sure hope yu'uns aint thinking about all this when out flying. Cause it's way too much to think about, and far too complicating.

Ok, back to the train and "Stick and Rudder"
Again, here directly from Stick and Rudder, chapter 6, "Wind Drift"

The airplane does not feel the wind.

"If the train passenger does not look at the moving scenery outside, he cannot tell which way the train is moving; if the pilot does not look down at the ground, he cannot tell which way the wind is blowing. Like the train passenger, the pilot can even draw the blinds, or climb above a solid overcast, so that you cannot see the ground, and you will not know if you are flying in a gale or a calm. In short, the wind does not have any effect on airspeed, lift, stability, and control: an airplane, once in flight cannot "feel" the wind.

Motion with the air

Look next at the airplane's motion with the air. This is exactly the kind of motion that a train passenger performs just by sitting still-or rather the kind of motion he performs, because of being in a moving train, regardless of what antics he may cut within the train. Regardless of what maneuvers the airplane executes within the mass of air that surrounds it, it helplessly participates in the motion of that air mass; it "drifts" with the wind.
Beware of thinking that the airplane drifts because the wind is blowing against it. It would be like saying that the passenger in our train gets to Chicago because the train his coach pushes, shoves, kicks, and pummels him to Chicago. It implies that the wind is pressing harder against one side of the airplane than the other. This is not so; the wind cannot blow against the airplane, because the airplane doesn't present itself to be blown at; it yields without any resistance: it moves with the air.

A pure example of this kind of motion, drift, is the travel of the free balloon. Here is one aircraft that has no motion at all through the air(other than perhaps climb or descent) but moves only with the air. The free balloon has no "airspeed", no "realtive wind". To it's pilots it always seems to be flying in a complete dead calm. Even though it may be flying in a gale and drifting accross the country at 50mph, there still wont be even the gentilest breeze in it's basket. This is because it yields completely to the motion of the air, and participates in it: the balloon dose not push against the air, and niether does the air push against the balloon; hence no forces arise.
Flight students sometimes argue that the wind must be exerting forces on a drifting balloon-else why would there be any drift? The arguement is drawn from a mistaken understanding of elementary physics, which would be cleared up by re-reading pages 1-10 of almost any college text on physics. The answer is that wind cannot exert any forces on the drifting balloon, precisely because the balloon's drifting. Or by expressing the same thing in other words, the balloon drifts precisely because drifting will nullify all wind forces on it.

Altogether then, the path that the airplane takes over the ground is always compounded of those two types of motion: it's motion through the air and it's motion with the air. The two are entirely dissimilar. Motion through the air produces lift, drag, stability and control. Motion with the air is the free balloon sort of motion-it has no further effects on the airplane other than to move it. The two are dissimilar; yet to the eye they are indistinguishable. The eye, which cannot see the air but can only judge by reference to the ground simply records the compound of the two-the resulting motion of the airplane relative to the ground.
This causes confusion for the pilot-especially for the beginner. Even though he may understand it in theory, he is still only a ground animal, not an air animal. He still can only see the ground, not the air. His sense of balance, his sense of motion, his nervous system tend to react simply and naively to his observed motion over the ground, whether he wills it so or not. But since his motion over the ground includes both motion with the air and motion through the air, his resulting control actions are bound to be wrong. He must learn to discriminate between the two, and discriminate continually."

Ok, now all that above is talking to a pilot who is in the plane, so it goes even more so to us remote pilots observing it all from a fixed postion on the ground for our perception of these truths are even worse!
But know in your mind that it is, all true. So train yourself to react accordingly, and ignore how it may look or seem to be.

Oh, and also above all else, leave the calculator and slide rule at home.
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Old 03-11-2009, 01:53 PM
  #187  
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rebell:

i understand perfectly that everyone here is of different background, some less educated than me, others perhaps way more. i try to speak in a way that everyone can understand. neccessarily, those of you with good knowledge of physics will probably feel like im underestimating you. but please bear with me, not everyone had that much physics in school. they might be reading too.

sabrehawk: yep, you are right. i dont thnik about this for a second when im flying, and i dont have time to think much at all when flying either. the reason im so sure is just as much that i experienced it in practical terms, and im then just trying to explain my practical experience with theory. if i hadnt seen it happend in real life i would probably had doubts about my own theories here.
for your theory about that the aircraft cant feel the wind. thats a truth with modifications.
some factors (for example airspeed) relates to the windspeed outside, and will therefore be unaffected by wind. if you travel 100 mph IAS, you wont know if its calm or gale force winds. thats true.
but then, is the factor that is not affected by wind. thats the inertia of masses.
if you fly 100 mph IAS upwind, in a 100mph wind, you are flying 100 mph IAS, but 0 mph in respect to the inerta of mass. in the opposite case, flying downwind, you are flying at 200 mph with respect to the inertia of mass.

so, when shifting from upwind to downwind, the inertia of mass needs an acceleration to accound for the 200 mph difference in ground speed, when turning from upwind to downwind.
note that there is not just a change in direction, but also in absolute value.
in the case of flying 100mph in a calm, and doing 180 degree turn, you are only changing the direction of travel, not the absolute value of speed, wich is 100mph all the time.
that is, when you turn from upwind to downwind, you need an acceleration both to change your direction of travel (with speed), and an acceleration to change your absolute speed.
in a calm, you only need an acceleration to change your direction of travel. not the absolute value of your speed.
that is because the inertia of the mass of the aircraft does not relate to wind. it relates to absolute speed/ground speed.
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Old 03-11-2009, 02:18 PM
  #188  
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Hehe, well its not my theory at all but that of Mr. Wolfgang Langwiesche, the author of Stick and Rudder.
I am merely his student.

And he wrote all this long ago in 1944, and it is all still very true and even more relied upon now than when the book was first put into print.

Just ask any good CFI, and most any full scale pilot.
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Old 03-11-2009, 03:47 PM
  #189  
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Originally Posted by Moxus View Post
rebell:
<the part that shows no comprehension of the condition being discussed snipped out>
.
There is obviously no communication going on here.
The plane does not react to the ground, nor vice versa, when it's flying.
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Old 03-11-2009, 04:48 PM
  #190  
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Yuppers, precisely.

The only time that the ground affects the airplane, is when the plane is on the ground.
And thats also the only time the airplanes can "feel" the wind. Once free of contact with the ground, it becomes the wind's passenger and moves with it, not against it, nor ahead of it or behind it.

One disadvantage to us as ground based pilots, we are ever constantly visually aware of the only thing that wind affects,...........the plane's groundspeed and ground track.

Ever notice while on final approach and you cut the throttle how the plane seems to slow down? Well, it does but only it's groundspeed has slowed, it's airspeed has not changed.
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Old 03-11-2009, 06:57 PM
  #191  
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*cencored by myself. people uneducated in the ways of physics might find it offensive*

go and grasp the term ABSOLUTE VELOCITY. i have explained it in an earlier post, no point in repeating myself.

alternatively, read here: http://en.wikipedia.org/wiki/Velocity

opening lines: velocity is the rate of change in position.
it doesnt need to be relative to anything. and thats absolute velocity. the speed of an object. period.
this is what physical forces works on. NOT windspeed. the planes inertia doesnt know the weather forecast, to calculate how it should work forces on your aircraft that specific day.
you need to grasp that to see that the aircrafts inertia has nothing to do with windspeed.
and when you do, then you see that there is a relationship between forces dependant on windspeed, and forces dependant on absolute speed, that changes when turning from upwind to downwind.

and btw for those of you who cant stick to topic and just have to attack me as a person, i also think it is cheap of you to do just that. i dont know if you are out of fair points, or if you are just about on the same level as people posting comments on youtube, not being able to post a single sentence without discrediting other posters. i dont want to know either, i dont have much in common with people who leads discussions on that level.

Last edited by Moxus; 03-11-2009 at 07:35 PM.
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Old 03-11-2009, 07:37 PM
  #192  
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Mmmm, yup may all be true but still means nothing to a "Peckerwood" like me.
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Old 03-11-2009, 07:42 PM
  #193  
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to be perfectly honest, this whole topic means nothing to anyone. its to complicated to be calculated, so its useless even if you do understand the forces at play, because you cant predict them accurately.
i see i was terribly stupid to join this conversation, such can of worms type of debates never ends well, no matter what the topic is.
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Old 03-11-2009, 08:09 PM
  #194  
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are you talking from a point of view where the aircraft is flying a constant ground speed?

or are you talking from a point of view were the aircraft is flying a constant IAS?
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Old 03-12-2009, 01:23 AM
  #195  
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Originally Posted by HX3D014 View Post
are you talking from a point of view where the aircraft is flying a constant ground speed?
.
The third drawing above.
.
or are you talking from a point of view were the aircraft is flying a constant IAS?
.
The second drawing above.
Two different scenarios.
We developed the "tactical mode flight director" for the Lockheed P-3 ASW airplane specifically to permit the pilot to fly and maintain a constant radius constant airspeed turn around a floating sonobuoy in a wind.
The flight director would command the bank angle needed to do this relative to the location of the sonobuoy and the plane's location in the circle.
The third drawing above shows how the bank angle changes to do this.
Airspeed remains constant, but as the plane's flight is referenced to a point on the ocean, the combination of airspeed and wind speed alters the bank angle while keeping the radius constant.
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Old 03-12-2009, 09:12 AM
  #196  
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Originally Posted by Sparky Paul View Post
.
The third drawing above.
.

.
The second drawing above.
Two different scenarios.
We developed the "tactical mode flight director" for the Lockheed P-3 ASW airplane specifically to permit the pilot to fly and maintain a constant radius constant airspeed turn around a floating sonobuoy in a wind.
The flight director would command the bank angle needed to do this relative to the location of the sonobuoy and the plane's location in the circle.
The third drawing above shows how the bank angle changes to do this.
Airspeed remains constant, but as the plane's flight is referenced to a point on the ocean, the combination of airspeed and wind speed alters the bank angle while keeping the radius constant.
The Question supposed to be directed to Moxus, My boo for not addressing him directly.

His statement seems wrong. but seems ok'ish to the scenario you pictured in Pic # 3.

In that Pic #3
how did you wash off the Ground speed as you Flew downwind to the crosswind leg?
how did you wash off the Ground speed Between the downwind a crosswind leg? (Same question rephrased)
IE from the part where you say there would be Max Bank angle to the crosswind section.
(Clarification of the question;
from the 12O'Clock position on the pic to the 3O'Clock position of the picture)


Moxus;
A can of worms debate needs to be taken by directly catching each worm.

For all to understand what worm some one is Wrangling, you need to Nominate the worm. Just reaching in an grabbing may result in a mixed batch of worms with no Identity.

Lets Specify what worm you are trying to catch by Clearly Stating;
What type of turn
IE
A turn done with constant IAS at a set bank angle?
A turn done with a Constant Radius around a Fixed point on the Ground while maintaining a Constant IAS or Constant power setting?

or one done with a Constant radius around a Floating/drifting balloon with constant bank angle and constant IAS.

(Given that all these are to be held at a constant altitude)

Bryce.

I was confused when you said that the lift increased because of the increase in airspeed over the wing, because we were talking about (At the time of the calculations being presented) a turn around a Floating balloon with Constant IAS. the debate being presented in that case by Cbatters was that the IAS would not stay constant because of a perceived need to accelerate the aircraft to a greater Ground speed for the Downwind leg.

NE way. if you wish to come back with specifics, detail you worm and then Grab it

Bryce
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Old 03-12-2009, 05:57 PM
  #197  
Sparky Paul
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"In that Pic #3
how did you wash off the Ground speed as you Flew downwind to the crosswind leg?
how did you wash off the Ground speed Between the downwind a crosswind leg? (Same question rephrased)
IE from the part where you say there would be Max Bank angle to the crosswind section.
(Clarification of the question;
from the 12O'Clock position on the pic to the 3O'Clock position of the picture)"
.
The commanded bank angle is computed from the radius of the turn, airspeed and wind speed.
As I recall, it was a relatively simple equation, but it's been 40 years and the mind is going.
Because of the need to consider wind speed moving the airplane off the commanded radius, the down wind bank angle with the highest wind speed needs the steepest bank angle to hold the radius... and upwind, the airspeed and windspeed combine to command a low bank angle for the radius.
There's no "groundspeed" per se, just the airspeed-windspeed-radius to consider.
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Old 03-13-2009, 11:39 PM
  #198  
JetPlaneFlyer
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Originally Posted by Moxus View Post
velocity is the rate of change in position.
it doesnt need to be relative to anything. and thats absolute velocity. the speed of an object. period
So if the 'change in position' is not relative to a 'anything' then how do you know if it's moving or not? If you believe in 'absolute velocity' then you must believe in an 'absolute datum' (a point somewhere that's at 'absolute rest') from which all absolute velocity is measured

You actually claim, in places at least, that the earth's surface at the very point you, Moxus, are standing is this mythical 'absolute datum' that 'absolute' movement of everything in the whole universe is measured from?

In others you appear to be claiming that the centre of the earth is the datum for absolute velocity.. Why the earth?.. Why not the sun or any one of the other bodies in this solar system or any others?

Why do you think that the planet you stand on is the absolute datum for everything? Is this not a little arrogant? What if you went to Mars and started flying your model in circles in the wind.. What would be it's 'absolute velocity'.. Would it still have to be measured from the 'absolute datum' back on earth? Or are there many 'Absolute datums' all moving relative to each other?.. In that case they are not very 'absolute' are they?

You can measure velocity from any point that you like.. THERE IS NO ABSOLUTE VELOCITY. Once you abandon the concept of absolute velocity then absolute inertia , absolute momentum and absolute kinetic energy go with it, because they are all related to velocity. Once these things go then the 'downwind turn' becomes irrelevant.

The idea of ‘absolute velocity’ was abandoned in physics close to 100 years ago along with the concept of ‘the ether ‘.. Ever heard of Relativity?

Steve

Last edited by JetPlaneFlyer; 03-14-2009 at 09:15 AM.
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Old 04-16-2009, 04:35 AM
  #199  
starcad
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Hahaha! I love these threads as this one pops up about every two to three years.

Cbatters I hate to disagree but if the wind stops blowing the air still has mass ( physical ) and the plane still has thrust creating airflow over the wings creating lift and won't drop like a rock. "Stick and Rudder", is by far one of the best books on flight you could read and explains everything you have been disagreeing with. BTY did you realize that lift is directly proportional to thrust and that bank is in-directly proportional to lift.

The only times I've dropped like a rock. I got caught on the leeward side of wind sher over some mountians and in a micro burst when landing under a thunder storm (stupid me got caught by the thunder storm and only full power saved my bacon)

Read, 'Stick and Rudder', it will really help you understand how planes fly and why. From full scale to models.

Guy
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Old 04-16-2009, 05:03 AM
  #200  
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Ah Moxus, it's your point of reference that has you confused.

if you fly 100 mph IAS upwind, in a 100mph wind, you are flying 100 mph IAS, but 0 mph in respect to the inerta of mass. in the opposite case, flying downwind, you are flying at 200 mph with respect to the inertia of mass.

Should be, if you fly 100 mph IAS upwind, in a 100 mph wind you are flying 100 mph IAS, but 0 mph in respect to ground speed. In the opposite case, flying downwind, you are flying at 100 mph IAS, but 200 mph with respect to Ground speed.

Guy
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