"Ground cushion"

[gatt[_2_]]

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

[Bertie the Bunyip[_24_]]

"gatt" > wrote in
:

>
> 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

[WingFlaps]

On Feb 26, 7:04*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)
>

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

Cheers

[Bertie the Bunyip[_24_]]

WingFlaps > wrote in
:

> 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..


bertie

[WingFlaps]

On Feb 26, 7:28*am, Bertie the Bunyip > wrote:
> WingFlaps > wrote :
>
>
>
> > 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.

Cheers

[Larry Dighera]

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 longer.
>( 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.


http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-h-8083-25-1of4.pdf
OUND EFFECT
It is possible to fly an airplane just clear of the
ground (or water) at a slightly slower airspeed
than that required to sustain level flight at higher
altitudes. This is the result of a phenomenon,
which is better known than understood even by
some experienced pilots.

When an airplane in flight gets within several feet
from the ground surface, a change occurs in the three
dimensional flow pattern around the airplane because
the vertical component of the airflow around the wing
is restricted by the ground surface. This alters the
wing’s upwash, downwash, and wingtip vortices.
[Figure 3-7] These general effects due to the presence
of the ground are referred to as “ground effect.”
Ground effect, then, is due to the interference of the
ground (or water) surface with the airflow patterns
about the airplane in flight.

While the aerodynamic characteristics of the tail surfaces
and the fuselage are altered by ground effects,
the principal effects due to proximity of the ground
are the changes in the aerodynamic characteristics of
the wing. As the wing encounters ground effect and
is maintained at a constant lift coefficient, there is
consequent reduction in the upwash, downwash, and
the wingtip vortices.

Induced drag is a result of the wing’s work of sustaining
the airplane and the wing lifts the airplane
simply by accelerating a mass of air downward. It
is true that reduced pressure on top of an airfoil is
essential to lift, but that is but one of the things
that contributes to the overall effect of pushing an
air mass downward. The more downwash there is,
the harder the wing is pushing the mass of air
down. At high angles of attack, the amount of
induced drag is high and since this corresponds to
lower airspeeds in actual flight, it can be said that
induced drag predominates at low speed.

--> However, the reduction of the wingtip vortices due
to ground effect alters the spanwise lift distribution
and reduces the induced angle of attack and induced
drag. Therefore, the wing will require a lower angle
of attack in ground effect to produce the same lift
coefficient or, if a constant angle of attack is maintained,
an increase in lift coefficient will result.
[Figure 3-8]

Ground effect also will alter the thrust required versus
velocity. Since induced drag predominates at low
speeds, the reduction of induced drag due to ground
effect will cause the most significant reduction of
thrust required (parasite plus induced drag) at low
speeds.

The reduction in induced flow due to ground effect
causes a significant reduction in induced drag but
causes no direct effect on parasite drag. As a result
of the reduction in induced drag, the thrust required
at low speeds will be reduced.

Due to the change in upwash, downwash, and
wingtip vortices, there may be a change in position
(installation) error of the airspeed system, associated
with ground effect. In the majority of cases, ground
effect will cause an increase in the local pressure at
the static source and produce a lower indication of
airspeed and altitude. Thus, the airplane may be airborne
at an indicated airspeed less than that normally
required.

In order for ground effect to be of significant magnitude,
the wing must be quite close to the ground. One
of the direct results of ground effect is the variation
of induced drag with wing height above the ground at
a constant lift coefficient. When the wing is at a
height equal to its span, the reduction in induced drag
is only 1.4 percent. However, when the wing is at a
height equal to one-fourth its span, the reduction in
induced drag is 23.5 percent and, when the wing is at
a height equal to one-tenth its span, the reduction in
induced drag is 47.6 percent. Thus, a large reduction
in induced drag will take place only when the wing is
very close to the ground. Because of this variation,
ground effect is most usually recognized during the
liftoff for takeoff or just prior to touchdown when
landing.

During the takeoff phase of flight, ground effect produces
some important relationships. The airplane
leaving ground effect after takeoff encounters just
the reverse of the airplane entering ground effect
during landing; i.e., the airplane leaving ground
effect will:

• Require an increase in angle of attack to maintain
the same lift coefficient.
• Experience an increase in induced drag and thrust
required.
• Experience a decrease in stability and a nose-up
change in moment.
• Produce a reduction in static source pressure and
increase in indicated airspeed.

These general effects should point out the possible
danger in attempting takeoff prior to achieving the
recommended takeoff speed. Due to the reduced drag
in ground effect, the airplane may seem capable of
takeoff well below the recommended speed.
However, as the airplane rises out of ground effect
with a deficiency of speed, the greater induced drag
may result in very marginal initial climb performance.
In the extreme conditions such as high gross
weight, high density altitude, and high temperature, a
deficiency of airspeed during takeoff may permit the
airplane to become airborne but be incapable of flying
out of ground effect. In this case, the airplane may
become airborne initially with a deficiency of speed,
and then settle back to the runway. It is important that
no attempt be made to force the airplane to become
airborne with a deficiency of speed; the recommended
takeoff speed is necessary to provide adequate initial
climb performance. For this reason, it is imperative
that a definite climb be established before retracting
the landing gear or flaps.

During the landing phase of flight, the effect of proximity
to the ground also must be understood and
appreciated. If the airplane is brought into ground
effect with a constant angle of attack, the airplane
will experience an increase in lift coefficient and a
reduction in the thrust required. Hence, a “floating”
effect may occur. Because of the reduced drag and
power off deceleration in ground effect, any excess
speed at the point of flare may incur a considerable
“float” distance. As the airplane nears the point of
touchdown, ground effect will be most realized at
altitudes less than the wingspan. During the final
phases of the approach as the airplane nears the
ground, a reduced power setting is necessary or the
reduced thrust required would allow the airplane to
climb above the desired glidepath.




http://aerodyn.org/Wings/wings.html#ground
Wings in Ground Effect
The use of ground effect is generally regarded as a very efficient
means to increase the lift and decrease the drag.

[WingFlaps]

On Feb 26, 8:07*am, Larry Dighera > wrote:

>
> http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-...
> * * OUND EFFECT

HUGE snip

That's what I said -albeit more succinctly...

Cheers

[WingFlaps]

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 longer.

[Bertie the Bunyip[_24_]]

Larry Dighera > wrote in
:

> 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 longer. ( 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.


Bwawhahwhahwhahwhahhwhahwhahwhahhwhahw!


Go **** your alleged self Larry.


Bertie

[Bertie the Bunyip[_24_]]

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

[Bertie the Bunyip[_24_]]

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

[Dudley Henriques[_2_]]

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

[Bertie the Bunyip[_24_]]

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

[buttman]

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.

[Cubdriver]

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

[Bertie the Bunyip[_25_]]

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

[Bob Gardner]

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
>
>

[Bob Gardner]

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

[Dudley Henriques[_2_]]

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

[gatt[_2_]]

"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

[Peter Dohm]

"gatt" > wrote in message
...
>
> "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.
>
>
That is certainly an opportunity that more people don't have; but for those
who do, pelicans are far easier to watch sinply because they are larger and
spend more of their time gliding close to the shore line.

Of course, without some prior knowledge, it's also easy to be tricked--and I
suspect that they were the most likely source of both anhedral and wing
warping for the Wright Flier.

Peter

[Bob Gardner]

I cured students of landing flat (or on the nosewheel) by taking them to
Lake Union to watch floatplanes land. I get really riled up when instructors
get too pedantic in explaining things to students.

Bob Gardner

"gatt" > wrote in message
...
>
> "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
>