Two questions that I've been wondering about -- w/t vortices andlift.

[Tman]

OK, these are trivial, but nonetheless been bugging me and the guys at
the airport don't have a satisfying answer;

1. Why do wing tip vortices sink? They're not made out of lead.
2. 747 overflies at FL 310 (or whatever). Is the weight of the airplane
ultimately supported by the earth's crust? How?


FWIW, my opinions on these: #1: because of a general downwards movement
of air in the wake, induced by lift. I've also heard that the
turbulence causes locally increased pressure and thus density, but I
s'pose it was also create locally reduced pressure -- so I don't believe
that factor.

#2: Yes, the wake of a overflying aircraft will cause a downward
acceleration of the air, which reacts with the surface of the ground
creating a locally higher pressure when it decelerates. Of course the
effect at FL310 is spread over such a large area that the effect at any
point is incredibly small, but it is spread over such a large area that
it in effect is supporting the weight of the A/C.

Ground effect at FL310 anyone?
T

[[email protected]]

Tman <x@x> wrote:
> OK, these are trivial, but nonetheless been bugging me and the guys at
> the airport don't have a satisfying answer;

> 1. Why do wing tip vortices sink? They're not made out of lead.
> 2. 747 overflies at FL 310 (or whatever). Is the weight of the airplane
> ultimately supported by the earth's crust? How?


> FWIW, my opinions on these: #1: because of a general downwards movement
> of air in the wake, induced by lift. I've also heard that the
> turbulence causes locally increased pressure and thus density, but I
> s'pose it was also create locally reduced pressure -- so I don't believe
> that factor.

The tip vortices do have a different pressure/temperature which can
be seen on humid days when vapor condenses and they become visible.

Though which effect is the dominate one that causes them to go down
I haven't a clue.

> #2: Yes, the wake of a overflying aircraft will cause a downward
> acceleration of the air, which reacts with the surface of the ground
> creating a locally higher pressure when it decelerates. Of course the
> effect at FL310 is spread over such a large area that the effect at any
> point is incredibly small, but it is spread over such a large area that
> it in effect is supporting the weight of the A/C.

> Ground effect at FL310 anyone?

Nope, that's the old rockets can't work in space because they have
nothing to push against arguement redressed.

F=ma doesn't require the accelerated air to bounce off of anything.


--
Jim Pennino

Remove .spam.sux to reply.

[Darkwing]

"Tman" <x@x> wrote in message
. ..
> OK, these are trivial, but nonetheless been bugging me and the guys at the
> airport don't have a satisfying answer;
>
> 1. Why do wing tip vortices sink? They're not made out of lead.
> 2. 747 overflies at FL 310 (or whatever). Is the weight of the airplane
> ultimately supported by the earth's crust? How?
>
>
> FWIW, my opinions on these: #1: because of a general downwards movement
> of air in the wake, induced by lift. I've also heard that the turbulence
> causes locally increased pressure and thus density, but I s'pose it was
> also create locally reduced pressure -- so I don't believe that factor.
>
> #2: Yes, the wake of a overflying aircraft will cause a downward
> acceleration of the air, which reacts with the surface of the ground
> creating a locally higher pressure when it decelerates. Of course the
> effect at FL310 is spread over such a large area that the effect at any
> point is incredibly small, but it is spread over such a large area that it
> in effect is supporting the weight of the A/C.
>
> Ground effect at FL310 anyone?
> T


I hope this doesn't turn into the "airplane on a treadmill" redux.

[Sylvain]

Tman wrote:

> OK, these are trivial, but nonetheless been bugging me and the guys at
> the airport don't have a satisfying answer;

here is an excellent website / online book that addresses many of these
questions:

http://www.av8n.com/ "See how it flies"

--Sylvain

[Bertie the Bunyip[_24_]]

wrote in :

> Tman <x@x> wrote:
>> OK, these are trivial, but nonetheless been bugging me and the guys
>> at the airport don't have a satisfying answer;
>
>> 1. Why do wing tip vortices sink? They're not made out of lead.
>> 2. 747 overflies at FL 310 (or whatever). Is the weight of the
>> airplane ultimately supported by the earth's crust? How?
>
>
>> FWIW, my opinions on these: #1: because of a general downwards
>> movement of air in the wake, induced by lift. I've also heard that
>> the turbulence causes locally increased pressure and thus density,
>> but I s'pose it was also create locally reduced pressure -- so I
>> don't believe that factor.
>
> The tip vortices do have a different pressure/temperature which can
> be seen on humid days when vapor condenses and they become visible.


Uh, no, that's not it. The vector as the air leaves th ewingtip is
generally downwards, that's why the travel is down. Also the reason they
travel out.

>
> Though which effect is the dominate one that causes them to go down
> I haven't a clue.
>
>> #2: Yes, the wake of a overflying aircraft will cause a downward
>> acceleration of the air, which reacts with the surface of the ground
>> creating a locally higher pressure when it decelerates. Of course
>> the effect at FL310 is spread over such a large area that the effect
>> at any point is incredibly small, but it is spread over such a large
>> area that it in effect is supporting the weight of the A/C.
>
>> Ground effect at FL310 anyone?
>
> Nope, that's the old rockets can't work in space because they have
> nothing to push against arguement redressed.
>
> F=ma doesn't require the accelerated air to bounce off of anything.

It's not bouncing off anything, but the wieght of the airplane is still
borne by the air, ultimatley, though some of that is traded as drag.

Is a fly buzzing around the inside of th same ariplane contributing more
weight wehn it lands on the edge of your coffee cup?


Bertie
>
>

[Bob F.[_2_]]

"Bertie the Bunyip" > wrote in message
...
> wrote in :
>
>> Tman <x@x> wrote:
>>> OK, these are trivial, but nonetheless been bugging me and the guys
>>> at the airport don't have a satisfying answer;
>>
>>> 1. Why do wing tip vortices sink? They're not made out of lead.
>>> 2. 747 overflies at FL 310 (or whatever). Is the weight of the
>>> airplane ultimately supported by the earth's crust? How?
>>
>>
>>> FWIW, my opinions on these: #1: because of a general downwards
>>> movement of air in the wake, induced by lift. I've also heard that
>>> the turbulence causes locally increased pressure and thus density,
>>> but I s'pose it was also create locally reduced pressure -- so I
>>> don't believe that factor.
>>
>> The tip vortices do have a different pressure/temperature which can
>> be seen on humid days when vapor condenses and they become visible.
>
>
> Uh, no, that's not it. The vector as the air leaves th ewingtip is
> generally downwards, that's why the travel is down. Also the reason they
> travel out.

They travel outward because that's where the lower pressure is.
--
Regards, BobF.

[Bertie the Bunyip[_24_]]

"Bob F." > wrote in
:

> "Bertie the Bunyip" > wrote in message
> ...
>> wrote in news:l5f6n5-hp7.ln1
@mail.specsol.com:
>>
>>> Tman <x@x> wrote:
>>>> OK, these are trivial, but nonetheless been bugging me and the guys
>>>> at the airport don't have a satisfying answer;
>>>
>>>> 1. Why do wing tip vortices sink? They're not made out of lead.
>>>> 2. 747 overflies at FL 310 (or whatever). Is the weight of the
>>>> airplane ultimately supported by the earth's crust? How?
>>>
>>>
>>>> FWIW, my opinions on these: #1: because of a general downwards
>>>> movement of air in the wake, induced by lift. I've also heard that
>>>> the turbulence causes locally increased pressure and thus density,
>>>> but I s'pose it was also create locally reduced pressure -- so I
>>>> don't believe that factor.
>>>
>>> The tip vortices do have a different pressure/temperature which can
>>> be seen on humid days when vapor condenses and they become visible.
>>
>>
>> Uh, no, that's not it. The vector as the air leaves th ewingtip is
>> generally downwards, that's why the travel is down. Also the reason
they
>> travel out.
>
> They travel outward because that's where the lower pressure is.


Well, in a way, yes, but they travel outward molecule by molecule so
it's a bit lie saying the wind blows because the trees wave back and
forth.
The spanwise flow is stronger on the bottom than the top of the wing and
the tendency is for the flow to travel around the edge of the wingtip.
It's all down to the force applied on them as they stream off the end of
the wing. all of the componenets of lift add up to them traveling out
and down, ultimately.


Bertie

[BT]

why do spinning baseballs curve.. the same effect from the spinning
vortices.. and the effect of the initial movement of the vortices as it
leaves the wing tip is down

"Tman" <x@x> wrote in message
. ..
> OK, these are trivial, but nonetheless been bugging me and the guys at the
> airport don't have a satisfying answer;
>
> 1. Why do wing tip vortices sink? They're not made out of lead.
> 2. 747 overflies at FL 310 (or whatever). Is the weight of the airplane
> ultimately supported by the earth's crust? How?
>
>
> FWIW, my opinions on these: #1: because of a general downwards movement
> of air in the wake, induced by lift. I've also heard that the turbulence
> causes locally increased pressure and thus density, but I s'pose it was
> also create locally reduced pressure -- so I don't believe that factor.
>
> #2: Yes, the wake of a overflying aircraft will cause a downward
> acceleration of the air, which reacts with the surface of the ground
> creating a locally higher pressure when it decelerates. Of course the
> effect at FL310 is spread over such a large area that the effect at any
> point is incredibly small, but it is spread over such a large area that it
> in effect is supporting the weight of the A/C.
>
> Ground effect at FL310 anyone?
> T