Close call and my first skidmarks!

[Wallaby]

There have been a few terms used here that I have never heard of before, and am keen to learn more if these terms are the correct ones, namely: stable air turbulence (bad) from off-shore, off shore wave (a type of standing wave?), and clear blue turbulence (I think the poster means CAT Clear Air Turbulence?)

Do explain more for the sake of us Valies that only know about wirlwinds and thunderstorms!

I also would like to know more of these terms, but when you nearly got clapped out of the sky the only thing on my mind was, where is the next monster and if only I could see it in front of me. Does makes one feel very vunerable all of a sudden.

I have heard a lot of pilots that suddenly got lifted hundreds of feet straight up, but then most of the time there was nothing that flipped them over at the top. As my instructor said over and over: When in turbulent air, always be prepared for something trying to flip the plane over. Don't let your guard down and get caught unexpectedly.

[Morph]

Cassies place(500ft AMSL), SW wind. Check the pic.

You have those massive Piketberg mountains (3000ft) directly to your SW, and you were flying towards them. I would say definitely a standing wave. Standing wave requires stable air at ground level and very high winds over the mountains

The SW wind at ground level was about 20 mph, at 3000ft would have been much higher. Coming over the top of those mountains would have caused waves 5 miles or more away. Cassie's place is just over 5 miles away from that mountain.

My advise, be careful flying in that area when a strong SW or NE is blowing. You have those others to your NE as well and closer, only 2 miles away.

If there is a SW blowing fly straight out holding runway heading and head for Porterville before turning south.

A few of us including Gert Coetzee have been clapped by those Piketberg Mountains

They also call them mountain waves. Check here (http://www.flightsafetycounselor.com/mntwea.htm)

[Ou Man]

Had similar experience a few years back. Dead calm on ground level. Took of from FAFK (4h30Z), rooting Sandkloof. Just north of Wintervogel on 2000 Alt. something took hold of me and played Yo-Yo with my trike. Descended to 800 . Smooth as a babies butt. Definitely Easterlies over Paardeberg. (a very sobering experience)Other trike , on the same root on 3000 Alt had a smooth ride.
Moral of THIS story? Watch those mountains and feel the temp. If there is a slight haziness towards the mountains and the temp. is nice and balmy......me?......I would go fishing

[skybound®]

There is a condition that the hang gliders call 'Over the falls' It is when exiting a thermal and entering a differing pocket off air (more often than not will be descending air outside a thermal) your whole angle of attack changes and the glider 'dives' to recover.

Only discounting factor is normally at coastal areas, the air at the time of morning of your experience, may not be sufficiently unstable (high lapse rates and thermic triggering activities) for thermic development of the nature to cause such a violent ride.

The only definite is - that it was a different air mass which is identified by your temperature observation. That in itself will tell you to expect turbulence, whether mechanical or thermic.

[thermalator]

I have hundreds of hours racing paragliders in this area at midday at this time of year now you know why we love it

I'm afraid its a violently thermic area with lots of wierd micromet, including a very commonly forming convergence area right there:

Often a convergence zone on a line between piketberg peak & the N7 pass (wind westerly, VERY rough). fly north & you get a NW wind, fly south & you get SW.

But I would not go too far with fancy terminology - its just thermals - Monitor the wind if its gusty you have thermals

PS: I flew my motor glider to porterville(tappa's strip) for the paragliding comp in December. 7 hours flying time from Gauteng, no refueling Just a leg stretch in De Aar. Took some beeg thermals to 15000 ft passing Sutherland. I knew I was risking the Sea breeze arriving @ 16:15 & lowish on fuel. Ended up landing in strong Xwind - Don't want to try that again. You know that feeling when you touch down with full opposite rudder & hold it there (taildragger). Flew back to Gauteng the following weekend in 5.5 hours.

I absolutely love this area - you guys are lucky to live there !!

[FO Gyro]

What is most likely the cause of the turbulence that you experienced would be a huge temperature inversion. This will play havoc with your airspeed as you transition through it. Even in our Boeing 737, when we fly through a temperature inversion, the speed can drop off substantially (10-15 kts), and turbulence can be expected.

There are some good products on the SA Weather Bureau where they take readings every 12 hours, and one can see if a temperature inversion exists, prior to flying. Check this one out: http://aviation.weathersa.co.za/aviatio ... rofile.php Click on the station's link, eg: FACT.

[thermalator]

Wind direction often changes at the inversion, & that is a horizontal shear. which causes + or - airspeed changes & shake & rattle type turbulence in the narrow the shear layer.

The coastal inversion in the piketberg valley is normally LOW at about 3000 ft (but still well above wallaby's position), the air above is generally Northly versus southerly below. The thermals are only active below this altitude and the distance between them proportional to the inversion height - so you get lots of closely packed thermals compared to inland karoo areas.

In Cape town the SE'ster is a generally a low altitude wind pinned below the inversion, this means that the wind blows around, not over the cape mountains. So the SE'ster usually does not reach the piketberg valley, it has normally curled round to a gentle SW'ster.