"Ground cushion"

WingFlaps wrote in
:

On Feb 26, 7:28*am, Bertie the Bunyip wrote:
WingFlaps wrote
innews:b1bb5238-0162-4f60-8516-621f3
:



On Feb 26, 7:04*am, Bertie the Bunyip wrote:
"gatt" wrote

ews.com:

In the book "Takeoffs and Landings" by Leighton Collins--who is
referenced in "Stick and Rudder"--there is no mention of the
term "ground effect."

Rather, Collins talks briefly about "ground cushion" and how air
"piles up" beneath the wings.

Do people still teach this?

Wel, it's a rose by any other name sort of thing.. Basicaly what's
happening is the air around the wing's pressure is influenced by
the ground. You have a high below the wing in flight and it gets
higher and influences the way the air flows around the wing
keeping it laminar longer
.
( slower)

I thought it was purely due to a reduction in induced drag. This
causes the lift vector to be larger.

??I'm not with you here..


OK, I'll explain myself but I'm sure you know this stuff -you're not
trolling me I hope ...
The wing produces a force vector that is broken into 2 components lift
and drag. The wing tip vortex is a major contributer to the rotation
of the wing force vector. Within ~1.5 wingspans the wing tip vortex is
suppressed by friction with the ground. This has two effects : a big
reduction in drag (so you float a long way in landing as you do not
shed energy so fast) and the rotation of the wing force vector towards
vertical increases lift. In landing/takeoff configs the high AOA leads
to a very backward wing force vector so ground effect increases lift a
lot in those configs. This then easily explains a take off stall -as
you rotate and climb out of ground effect drag increases and lift
decreases. The loss of lift requireds you to further increases AOA
which further increases drag. If drag becomes greater than thrust you
stall.


OK, had forgotten most of that, in fact. The drag reduction goies hand in
hand with what I said as well, but I didnt see the connection via the
direction you were coming from. I had completely forgotten about the
vortice thing. When I had to explain ground efect, I used the explanation I
just posted . I think it was anyway. It's been a while since I taught
private pilots. It doesn't come up much these days.


Bertie

Bertie the Bunyip wrote:
WingFlaps wrote in
:

On Feb 26, 8:07 am, Larry Dighera wrote:
On Mon, 25 Feb 2008 18:04:57 +0000 (UTC), Bertie the Bunyip
wrote in :

Wel, it's a rose by any other name sort of thing.. Basicaly what's
happening is the air around the wing's pressure is influenced by the
ground. You have a high below the wing in flight and it gets higher
and influences the way the air flows around the wing keeping it
laminar longe
r.
( slower)
I find it curious that an alleged airline captain has failed to
mention the reduction in induced drag that results due to the
interference with the wingtip vortices when operating in ground
effect.

Perhaps it did note poke the induced drag memory cells? Maybe our
Bertie actively suppresses his drag memories?

Groan!

Bertie
Perhaps if you came out in drag, Ken might like that better :-))

--
Dudley Henriques

Dudley Henriques wrote in news:57GdnSCRcp-
:

Bertie the Bunyip wrote:
WingFlaps wrote in
:

On Feb 26, 8:07 am, Larry Dighera wrote:
On Mon, 25 Feb 2008 18:04:57 +0000 (UTC), Bertie the Bunyip
wrote in :

Wel, it's a rose by any other name sort of thing.. Basicaly what's
happening is the air around the wing's pressure is influenced by the
ground. You have a high below the wing in flight and it gets higher
and influences the way the air flows around the wing keeping it
laminar longe
r.
( slower)
I find it curious that an alleged airline captain has failed to
mention the reduction in induced drag that results due to the
interference with the wingtip vortices when operating in ground
effect.

Perhaps it did note poke the induced drag memory cells? Maybe our
Bertie actively suppresses his drag memories?

Groan!

Bertie
Perhaps if you came out in drag, Ken might like that better :-))


Eww!

Bertie

On Feb 25, 11:04*am, Bertie the Bunyip wrote:
"gatt" wrote :



In the book "Takeoffs and Landings" by Leighton Collins--who is
referenced in "Stick and Rudder"--there is no mention of the term
"ground effect."

Rather, Collins talks briefly about "ground cushion" and how air
"piles up" beneath the wings.

Do people still teach this?

Wel, it's a rose by any other name sort of thing.. Basicaly what's
happening is the air around the wing's pressure is influenced by the
ground. You have a high below the wing in flight and it gets higher and
influences the way the air flows around the wing keeping it laminar longer..
( slower)

Bertie

No, its not.

On Mon, 25 Feb 2008 09:46:30 -0800, "gatt"
wrote:

Rather, Collins talks briefly about "ground cushion" and how air "piles up"
beneath the wings.

Do people still teach this?

All I can say is, if you rely on that ground cushion to soften the
impact, you will be sorely disappointed.

Blue skies! -- Dan Ford

Claire Chennault and His American Volunteers, 1941-1942
new from HarperCollins www.FlyingTigersBook.com

buttman wrote in
:

On Feb 25, 11:04*am, Bertie the Bunyip wrote:
"gatt" wrote

ews.com:



In the book "Takeoffs and Landings" by Leighton Collins--who is
referenced in "Stick and Rudder"--there is no mention of the term
"ground effect."

Rather, Collins talks briefly about "ground cushion" and how air
"piles up" beneath the wings.

Do people still teach this?

Wel, it's a rose by any other name sort of thing.. Basicaly what's
happening is the air around the wing's pressure is influenced by the
ground. You have a high below the wing in flight and it gets higher
and influences the way the air flows around the wing keeping it
laminar longer
.
( slower)

Bertie

No, its not.


Yes, it is.


Bertie

I have found that in the early stages of discussion, ground cushion puts a
useful picture into the student's mind...we can get into downwash later.

Bob Gardner

"gatt" wrote in message
...

In the book "Takeoffs and Landings" by Leighton Collins--who is referenced
in "Stick and Rudder"--there is no mention of the term
"ground effect."

Rather, Collins talks briefly about "ground cushion" and how air "piles
up" beneath the wings.

Do people still teach this?

-c

If the goal is to give the student an easy-to-grasp concept, ground cushion
is just fine *as an introduction to the discussion.* If the goal is to use
technically correct phraseology at all times whether it penetrates the
student's skull or not, then reduction in induced drag and downwash angle do
the trick.

Bob Gardner

"Cubdriver" usenet AT danford DOT net wrote in message
...
On Mon, 25 Feb 2008 09:46:30 -0800, "gatt"
wrote:

Rather, Collins talks briefly about "ground cushion" and how air "piles
up"
beneath the wings.

Do people still teach this?

All I can say is, if you rely on that ground cushion to soften the
impact, you will be sorely disappointed.

Blue skies! -- Dan Ford

Claire Chennault and His American Volunteers, 1941-1942
new from HarperCollins www.FlyingTigersBook.com

Bob Gardner wrote:
If the goal is to give the student an easy-to-grasp concept, ground
cushion is just fine *as an introduction to the discussion.* If the goal
is to use technically correct phraseology at all times whether it
penetrates the student's skull or not, then reduction in induced drag
and downwash angle do the trick.

Bob Gardner

"Cubdriver" usenet AT danford DOT net wrote in message
...
On Mon, 25 Feb 2008 09:46:30 -0800, "gatt"
wrote:

Rather, Collins talks briefly about "ground cushion" and how air
"piles up"
beneath the wings.

Do people still teach this?

All I can say is, if you rely on that ground cushion to soften the
impact, you will be sorely disappointed.

Blue skies! -- Dan Ford

Claire Chennault and His American Volunteers, 1941-1942
new from HarperCollins www.FlyingTigersBook.com

I agree. I've used the "ground cushion" analogy many times when opening
up the issue of ground effect with primary students. Using chalk and a
blackboard to demonstrate how, and where the cushion forms under the
airplane is one of the ways to take this first step. Once the student
knows ground effect actually exists and what it does, THEN is the time
to begin to explain the "devil in the details" :-)

--
Dudley Henriques

"Bob Gardner" wrote in message
. ..

I have found that in the early stages of discussion, ground cushion puts a
useful picture into the student's mind...we can get into downwash later.


I like that explanation. He also made a reference to watching a seagull
glide over calm water, and flare to land.

Granted, I suppose there are readers who might never have seen a seagull
over water (?) but physics aside it's a clear, memorable representation of
the general idea.


....which reminds me of photo series in the Jepp Instrument/Commercial
textbook showing a wayward seagull who forgot to lower his landing gear.
The book indicates that even natural born aviators do it on occasion, which
is why checklists are important. Won't forget that one either.

-c