Hi Guys, air turbulence certainly does exist at low altitudes... I have
flown into an airfield in GB where very large aircraft are produced. The
fabrication building is HUGE and only 500m from the threshold of RW22.
With any wind speed of over 12knotts, in the right direction, this causes
ROTOR to occur on Final. (No wonder they used curved hangars in the
past.)

Just to put some maths to the speeds needed to remain above stall....

1 / cos AOB = G force eg, 1/cos60 = 2g

sqr G = increase in stall speed eg. sqr2 = 1.414

so a S+L stall speed of 40kts becomes 56.6kts at 60deg AOB. (an increase
of 16.6kts.)

Pete

At 01:09 03 September 2012, Frank Whiteley wrote:
On Saturday, September 1, 2012 10:15:02 PM UTC-6, John Sullivan wrote:
At altitude thermals flow generally vertically relatively unrestricted.
=20
At birth, even on a perfectly flat surface, thermal air must=20
=20
transition from a flat, shallow disk shaped zone feeding in from=20
=20
360 degrees, crashing in, upwards ,which introduces a rotational=20
=20
component. Add orographic features and wind effects to these=20
=20
forces occurring in such a short period of time, over a relatively=20
=20
small area, and the air is very chaotic indeed.
=20
Although I agree that low level air can be chaotic, the disk or torus
model=
s are not accurate, though okay conceptual exercises. See the Wayne
Angevi=
ne article linked earlier in this thread. If you accept that a number of
p=
lumes coalesce into larger thermal plumes, then you'll understand why you
s=
ometimes encounter a 'thermal' which for some reason you just can't seem
to=
center in. That's because you are circling in and out of multiple
adjacen=
t plumes. Surface objects can certainly create turbulence within the
wind
=
gradient.

Frank Whiteley