Turbulance! what size Trike wing

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gertcoetzee
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Postby gertcoetzee » Sun Jul 24, 2005 5:32 pm

What is the definition of severe turbulance? Today (see ZU-DVE log) I got caught in some turbulance where the tip of the wing must have dropped 2m since I experienced a 45 degrees or more deflection of the bar. Not quite what I need with only >20 hours, but probably good experience or warning. And what the heck do you do in this circumstance. I got such a fright that I let go of throttle - which I suppose is not a good idea. If not, should I not switch on the auto-throttle, and concentrate on keeping it sort of level. I climbed whilst turning away from the mountains, and it got better. Minor turbulance at lower levels on the wind side of the smaller hills later in my trip.

Any all advice will be appreciated.
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Postby Fairy Flycatcher » Sun Jul 24, 2005 6:39 pm

Nice one Demon! :lol: :lol: :lol:
Me- I do a 180 deg turn, figure out what caused the turbulence(Mostly large mountains or hills) , and try and climb out above it before resuming my course.
I am always amazed at how many high hour pilots don't know the first thing about what causes turbulence in the sky. Recently spoke to a 2500 hour instructor who said " I have always wondered what causes the turbulence, but usually just fly through it" There is a great book by Dennis Pagen called "Understanding the sky". Best thing I have ever did for my flying was to read that
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Postby Microwave » Sun Jul 24, 2005 8:09 pm

There is an aviation term "clear air turbulance (CAT)" which is often used in cases where the reason for turbulence is uncertain. Even heavy aircraft pilots can sometimes be uncertain about the cause of turbulence in some cases.

Its a different story if you are close to an obvious source such as a mountain or a gap in mountains, heavy winds, burned fields below etc etc :? I reckon that most high hours trike pilots have got a reasonably good understanding of most sources of such turbulence, where not to be and what to do in such cases.
Last edited by Microwave on Sun Jul 24, 2005 10:03 pm, edited 2 times in total.
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Demons definition

Postby gertcoetzee » Sun Jul 24, 2005 9:54 pm

Demon,

Well, if that is turbulance, then I must have experienced a mere fart (not clear air turbulance hehe). Would rather not experience your version, but I am sure I will, and want to be prepared when it happens.

Gert
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Postby Fairy Flycatcher » Mon Jul 25, 2005 7:12 am

Lying in bed with my skygod last night, we were talking about turbulence, and how different people cope with it differently. I asked him what his advice would be.

He said that if your wing is "unloading" (you are going negative and flying wires start to sort of snap into place), it is too turbulent. Get down or get away.
I reckon that most high hours trike pilots have got a reasonably good understanding
I completely agree with this, and am sorry that it came across differently. :oops: I am just amazed that anyone can fly without wanting to know too much about the sky they fly in. I know of quite a few in this area, and I think our relatively mild conditions at the coast is a contributing factor. It is rarely that our thermals exceed 1500', so the guys don't bother to learn about much. And wind seems to be too obvious a factor for people to question why it has the effect it has. Still hear many people talk of "wind pockets" and say "lapse rate" and they think it has something to do with swimming :o The instructor I mentioned just made a big impression on me for knowing so little.

It made me realise that "hours" do not always equate to "experience"

Sorry for any offence caused[/quote]
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Turbulance

Postby Flightstar » Mon Jul 25, 2005 11:59 am

Demon defined severe turbulence as inter alia conditions where it is only your seatbelt keeping you in the trike.

I was on a flight from Crosswinds to Van der Bijlpark at about 08:30 at 1000 ft agl one morning in calm and clear conditions,when I flew into severe downdraughts. It seemed like two huge potholes in the air .Whoop-whoop .........................feet off the nosewheel, arms struggling to get a proper grip on the control bar, heart in the mouth, etc.etc.!!!Luckily for me the seatbelt performed it's function well, as I would have been thrown clear of the trike without that restraint.

Apart from a nervous twitch near my left eye the rest of the flight went without a hitch in wonderfully calm conditions.

I don't know what caused the turbulence as I was nowhere near hills , built up areas or any such things.

Anybody else had similar experiences?
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Re: Turbulance

Postby Sonex711 » Mon Jul 25, 2005 12:27 pm

Flightstar wrote:...Anybody else had similar experiences?
On my dual "long" crosscountry for my MPL we were flying a leg from Britz to Rustenberg. About 5 miles out of Britz there was a loud "crack" and we dropped about 100' in a second or 2. Clear skies, no wind to speak of, lovely highveld winter's day. I quietly shat myself :oops: . I thought something had broken off the t-bird. We put it down to windsheer or something like that.

When we did a full-stop at Rustenberg, I was very tempted to have something a bit stronger than coke.
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Postby Morph » Mon Jul 25, 2005 2:29 pm

I had one of those between Fisantekraal and Morning Star at about 11am on a perfectly clear cool day. I was taking a lovely little lady for her fist microlight flip. 1000' AMSL one moment, then 2 seconds of free falling, followed by a 1000fpm climb. She was remarkably quiet at the back and when I asked her if she was OK she quietly said "I had a moment there" When we got to Morning Star I could see absolute relief on her pale face.

I have tried to work out what it was, there was a NE blowing and I specifically routed to the north of Rondebossie to avoid the leeward side of the hill. Further study said it could have been a standing wave from the hills downwind, but the only hills downwind were Perdeberg, about 15miles away. There was no fires, tar roads or even high temperatures to speak of. :?:
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Postby Fairy Flycatcher » Mon Jul 25, 2005 2:44 pm

For waves to form, you need the following:

Wind - 15knots or more - although this can be upper winds (the winds hitting the mountain), not only on the ground.

Stability - Should be unstable close to the ground, with a stable layer (like an inversion, or even just a drop in lapse rate), and then instability above that

Terrain - a mountain at least 500 ft high.

Waves can continue for many kilometers away from the mountain, and this depends on how stable the stable layer is, how flat the area behind the mountain is and how strong the wind is. Waves can be from 2 - 32 km apart, although 10km is the average, and there are usually multiple waves, diminishing in severety as they get further and further away.
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Postby Morph » Mon Jul 25, 2005 3:07 pm

Thanks FF, I remember it being bumpy below 1000ft and fine at 1500ft. The NE was not particularly strong, in fact I would say it would probably be in the light category although I dont know what the upper level winds were like.

Looking at the map Perdeberg was directly NE of my location at 15.4miles. THe highest peak is at 2487ft. Based on your average of 10km per wave I probably hit the second wave. :idea:

I do know the guys complain about conditions being bumpy when the NE is blowing. We do have a number of mountain ranges in the 20 to 50 mile range north and east of Cape Town and I have experienced NE's at 25mph so perhaps it's the terrain that is causing said bumpiness. Way down on the deck it's fine, 500 to below 2000, bumpy and by 2500 its smooth again. Some of the ranges extend up to 5000ft.
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Postby Fairy Flycatcher » Mon Jul 25, 2005 7:36 pm

Waves are actually very smooth, and can give wide-spread long lasting lift on the up-wind side - for all the glider-folk out there.

It is the wave rotor which is the killer. The turbulence can be severe with strong shears and random gusts. These are under the waves, and are generally about the same height as the mountain that caused the wave in the fist place.

As there are multiple waves extending many kilometres behind mountains, these tumble drier rolls of turbulence can be encountered very far from the mountains, although they are less and less severe as the waves also dissipate.

The most common conditions for wave formation in SA is just after the passage of a cold front. Unfortunately, that is also when we have our best viz, and everyone wants to jump in the trike to go fly.

We flew into wave rotor, caused by the prevailing Westerlies over the Drakensberg, while flying along the wild coast in a Piper Arrow. The only time ever that I go airsick :oops:
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Postby Slurp » Tue Aug 16, 2005 1:31 pm

Talking about turbulence,

When last did any of you strip down your wings and seriously inspect your plates, bolts, cables, suages etc. Especially if yove done some bumpy trips, and trailering??

I was coming up to my annual on 375 hours, and just "got that feeling". Ended up replacing landing wires that had a few strands missing in the king post. Not a place you can inspect very often.

I guess you should keep listening to those "Angels" (-)
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