Weather and ground effect

I was wondering if someone can shed some light on a phenomon I keep
experiencing. I took a Mooney up to warm it up prior to an oil change.
There was 70 degree crosswind at 20 gusting 28. Needless to say, there was
moderate turbulance below 8K. As expected, I got beat up pretty good just
briefly flying out of the pattern to do a full systems check. The plane was
all over the place during the approach. I could keep the plane in an
imaginary box but inside that box, I was at the mercy of the elements. Once
I got the plane safely into ground effect, everything smooths out for the
touchdown and rollout. This is not the first time I have experienced this.
Nearly everytime where there is turbulance and gusting winds, it seems that
if I can safely make it into ground effect, the turbulance and gusts either
go away or have little effect. It makes for beautiful landings after an
uncomfortable approach. Why is this?

Thanks in advance,
Kevin Chandler

In a previous article, "Kevin Chandler" said:
go away or have little effect. It makes for beautiful landings after an
uncomfortable approach. Why is this?

What you're calling "ground effect" is actually the zone where the wind is
in the "boundary layer". Right at the bottom, turbulent air will hit the
gound and "stick", then each successive "layer" of air above it will slow
down a bit relative to the one below it, but also stop moving across the
layers. So near the ground, you get lower wind speeds but also more
laminar flow.

That's kind of a layman's summary of the science behind it. Pedants will
now point out every little simplification I made as an error.


--
Paul Tomblin http://xcski.com/blogs/pt/
There is no substitute for good manners, except, perhaps, fast reflexes.

Simply due to your airplane having a low wing and short "legs."

John.
--
John T Lowry, PhD
Flight Physics
5217 Old Spicewood Springs Rd, #312
Austin, Texas 78731
(512) 231-9391

"Kevin Chandler" wrote in message
...
I was wondering if someone can shed some light on a phenomon I keep
experiencing. I took a Mooney up to warm it up prior to an oil change.
There was 70 degree crosswind at 20 gusting 28. Needless to say, there
was
moderate turbulance below 8K. As expected, I got beat up pretty good just
briefly flying out of the pattern to do a full systems check. The plane
was
all over the place during the approach. I could keep the plane in an
imaginary box but inside that box, I was at the mercy of the elements.
Once
I got the plane safely into ground effect, everything smooths out for the
touchdown and rollout. This is not the first time I have experienced
this.
Nearly everytime where there is turbulance and gusting winds, it seems
that
if I can safely make it into ground effect, the turbulance and gusts
either
go away or have little effect. It makes for beautiful landings after an
uncomfortable approach. Why is this?

Thanks in advance,
Kevin Chandler

"Paul Tomblin" wrote in message
What you're calling "ground effect" is actually the zone where the wind is
in the "boundary layer". Right at the bottom, turbulent air will hit the
gound and "stick", then each successive "layer" of air above it will slow
down a bit relative to the one below it, but also stop moving across the
layers. So near the ground, you get lower wind speeds but also more
laminar flow.

That 'boundary layer' effect which includes 'wind gradient' is also what
allows one to land in seemingly impossible xwinds. I've now twice
experienced x-winds too high to maintain a proper slip (wing low, fuselage
aligned) during final but once within a wingspan or so of the ground, the
xwind is reduced just enough to let me 'assume the position'.

Are there any other effects that might be at work here. Would flying in
'ground effect' somehow smooth out the bumps? Would this effect be
significantly different in Maule versus a Mooney because of wing location?
(I wrestle with my Maule in the flare but found once the Mooney (201) was in
ground effect, a smooth landing was assured.) Just thinking out loud here.

"Kevin Chandler" wrote in message ...
I was wondering if someone can shed some light on a phenomon I keep
experiencing. I took a Mooney up to warm it up prior to an oil change.
There was 70 degree crosswind at 20 gusting 28. Needless to say, there was
moderate turbulance below 8K. As expected, I got beat up pretty good just
briefly flying out of the pattern to do a full systems check. The plane was
all over the place during the approach. I could keep the plane in an
imaginary box but inside that box, I was at the mercy of the elements. Once
I got the plane safely into ground effect, everything smooths out for the
touchdown and rollout. This is not the first time I have experienced this.
Nearly everytime where there is turbulance and gusting winds, it seems that
if I can safely make it into ground effect, the turbulance and gusts either
go away or have little effect. It makes for beautiful landings after an
uncomfortable approach. Why is this?

Thanks in advance,
Kevin Chandler

I have noticed this too, and IMHO, the most dominant effect is the
diminished wind as you descend below the treeline. An 8-knot gust
factor is not much to worry about. However, if the surface wind is
20G28, the winds at 500' was probably like 30G50 which is enough to
kick you around. As you descend, you will not only notice a drop in
gust, but also a drop in total wind, which will cause a drop in
airspeed and an increased sink rate. This is something to be cautious
about on windy days at airports that are surrounded by tall trees.

I don't believe that the boundary layer has a significant effect here,
as it is too thin (compared to the aircraft size) to be noticeable.

"Maule Driver" wrote in
news
"Paul Tomblin" wrote in message
What you're calling "ground effect" is actually the zone where the
wind is in the "boundary layer". Right at the bottom, turbulent air
will hit the gound and "stick", then each successive "layer" of air
above it will slow down a bit relative to the one below it, but also
stop moving across the layers. So near the ground, you get lower
wind speeds but also more laminar flow.

That 'boundary layer' effect which includes 'wind gradient' is also
what allows one to land in seemingly impossible xwinds. I've now
twice experienced x-winds too high to maintain a proper slip (wing
low, fuselage aligned) during final but once within a wingspan or so
of the ground, the xwind is reduced just enough to let me 'assume the
position'.

Which is one of the reasons I teach transitioning to the slip in the
flare rather than before. At 200agl you may not have enough rudder to
maintain runway alignment, but it may be just fine once you get down into
the flare.

"Andrew Sarangan" wrote in message
. 158...
"Maule Driver" wrote in
news
"Paul Tomblin" wrote in message
What you're calling "ground effect" is actually the zone where the
wind is in the "boundary layer". Right at the bottom, turbulent air
will hit the gound and "stick", then each successive "layer" of air
above it will slow down a bit relative to the one below it, but also
stop moving across the layers. So near the ground, you get lower
wind speeds but also more laminar flow.

That 'boundary layer' effect which includes 'wind gradient' is also
what allows one to land in seemingly impossible xwinds. I've now
twice experienced x-winds too high to maintain a proper slip (wing
low, fuselage aligned) during final but once within a wingspan or so
of the ground, the xwind is reduced just enough to let me 'assume the
position'.

Which is one of the reasons I teach transitioning to the slip in the
flare rather than before. At 200agl you may not have enough rudder to
maintain runway alignment, but it may be just fine once you get down into
the flare.



Boundary layers are tiny.
Close to the ground the vertical component of air movement is constrained.
Maintain coordinated flight until the flare; then slip.
Keep the momentum vector nailed down the centerline.
That keeps you going straight in the transition to slip in the flare.
Use the correct airspeed for your craft; no more, no less.
Blue skies.
H.
CP AS&MEL IA

"Paul Tomblin" wrote in message
...
In a previous article, "Kevin Chandler"
said:
go away or have little effect. It makes for beautiful landings after an
uncomfortable approach. Why is this?

What you're calling "ground effect" is actually the zone where the wind is
in the "boundary layer". Right at the bottom, turbulent air will hit the
gound and "stick", then each successive "layer" of air above it will slow
down a bit relative to the one below it, but also stop moving across the
layers. So near the ground, you get lower wind speeds but also more
laminar flow.

That's kind of a layman's summary of the science behind it. Pedants will
now point out every little simplification I made as an error.


--
Paul Tomblin http://xcski.com/blogs/pt/
There is no substitute for good manners, except, perhaps, fast reflexes.

Thanks Paul,
All these years I just assumed it was simply surface friction. Your summary
makes better sense. If there were no other forces present,(another
assumption) surface friction would only make matters worse?

MG

I don't believe that the boundary layer has a significant effect
here, as it is too thin (compared to the aircraft size) to be
noticeable.

According to "Meteorology for Scientists and Engineers", by Roland B.
Stull, the boundary layer is about 2 km in height.

Would flying in 'ground effect' somehow smooth out the bumps?

If anything, it would make it worse. There is a "lift slope curve"
associated with each aircraft which determines how much lift comes
from a particular increase in AOA. When the curve is shallow, then a
large increase in AOA only produces a small increase in lift. This is
associated with low aspect ratio wings, such as a delta wing.

In ground effect, for any aircraft, the lift slope gets steeper.
Therefore, a small increase in AOA, such as produced by a gust will
produce a larger increment in lift, i.e., a bigger bump.