Thermal?

[matt_k]

Hi Guys

Just watched this video and red all the comments,lots of different views,seems very light winds but apparently it was mid afternoon- thermic?whats your opinion?http://www.youtube.com/watch?v=Q-KvuHYfedw

[nigel_d.]

I would say that he flew through his own wake but also a low angle of attack also contributed. Hope it becomes known though.

[alan_k]

Got to be wind shear with the speed the canopy deformed, IMHO.

Cheers,

Alan

[nigel_d.]

What might have caused the wind shear please Alan? I just want to know how not to have that happen to me - or anyone else.

Cheers

Nige

[alan_k]

Quote off t’internet: ‘Wind Shear (windshear, wind gradient) is described as difference in wind speed and direction over a short distance in the atmosphere. Wind shear is broken down into vertical and horizontal components. Horizontal wind shear is seen across weather fronts and near coastal regions. A vertical wind shear is found near the surface, or at upper levels of the atmosphere. Wind shear is a meteorological phenomenon that occurs over short distances, although it can be associated with larger scale cold fronts’.

In the context of our fabric wings the strength of the shear that can cause trouble is quite small, as the ‘overpressure’ within the wing keeping its aerofoil shape is surprisingly low.

As commented on the video at 28 seconds in, it looks like a wind streamer at the side of the frame and the windsock are showing different wind directions. The wind strength is low so any thermic activity close by can shift the wind dramatically only a short distance away from the windsock, without it being registered by the windsock.

I suggest avoiding periods where the forecast is nil or very low wind plus warm/hot temperatures that give rise to thermal activity. Don’t fly in the middle of the day when the wind sock/streamer shows the direction continually changing with low wind strength.

Just my opinion, cheers,

Alan

[jock]

I THINK SOME PEPS FORGET OR DONT UNDERSTAND THERMALS FULLY.PARAMOTORING IS BEST EARY MORNING OR EVENING FLYING IN THE SUMMER TIME WHEN THE THERMALS ARE WEAK.WINTER FLYING IS MORE SUITED TO MIDDAY FLYING.ON A LIGHT WIND DAY WITH LOW CLOUD BASE,AND BIG FLUFFY CLOUDS,THE THERMIC COND/WILL BE GREAT.IF YOU FLY THOURGH A STRONG THERMAL YOU WILL GET FULL FRONTAL BIG TIME.THATS WHY WHEN PGS GET IN A THERMAL THEY TURN AND FIND THE CORE AND GO UP WITH THE THERMAL TIL IT WEAKENS,IVE HAD BIG FULL FRONTALS LEAVEING A THERMAL TO EARLY.MOST OF THE TIME A PPG CAN FLY THOURGH A THERMAL BUT LOW CLOUD BASE AND STRONG THERMALS WILL CACTH YOU OUT.YOU NEED TO THINK ABOUT THE COND/ON THE DAY AND STAY ON THE GROUND IF YOUR NOT PILOT WITH LOTS OF HRS..ALWAYS CHECK RASP FOR THERMIC COND/ON THE DAY////MY 2P WORTH,MAYBE A COURSE ON THERMALS WOULD GO DOWN WELL FOR THOSE WHO NEVER DO PG OR NEWBIES...WHEN AND WHEN NOT TO FLY....

[gavrob]

Jock,

You say... ALWAYS CHECK RASP

Could you elaborate?

Many thanks,

Gavin.

[aquatix]

Gavin - RASP is a visual table of thermal updraft velocity http://rasp.inn.leedsmet.ac.uk/RASPtable.html

It gives a useful overview of likely thermal strength, but no help with micro conditions that effect us - such as flying over a freshly ploughed field or tarmac car park where you might hit a very strong thermal bubble on a sunny day.

A good knowledge of meteorology is vital in this sport, plus an understanding of how your own wing reacts to thermals (ie is it pitch positive or negative as it enters & exits them), followed by practice in active conditions.

Even when flying in apparently benign mornings or evenings you can stumble across strange pockets of 'turbulent' air which all add to the fun .....

[gavrob]

Jock,

Many thanks for the reply, explaination, and the link - looks like a very useful site.

Regards,

Gavin.

[poz]

If you watch the video carefully, you'll see that he did something just before the collapse which looked like it caused it. He raised his knees and pulled his arms down slightly, almost like he was trying to get into his seat. This confuses me because the collapse looks like it was caused by pulling hard on his A's

Have a close look.

I'd really like to know the cause of this, because another 10 feet higher or more and this could soooo easily have been a fatal crash.

Dan

[alan_k]

Just watched it over a few times, can see the knees being raised (why?) but can't see any hand movement.

Alan

[matt_k]

Maybe the speed bar got trapped or caught when he lifted his knees up?

Hmmmmm would love to know, lets get his number and call him up!

[norris]

IF YOU FLY THOURGH A STRONG THERMAL YOU WILL GET FULL FRONTAL BIG TIME.THATS WHY WHEN PGS GET IN A THERMAL THEY TURN AND FIND THE CORE AND GO UP WITH THE THERMAL TIL IT WEAKENS

1) JOCK -- YOUR CAPS LOCK IS ON!

2) In the video in question the pilot has an assymetric, not a frontal.

3) If you fly through a stromg thermal you MIGHT get a frontal, but you can also get an assymetric instead!

4) Most PG's circle in the core of a thermal to gain height, not cos they're frightened to leave it

best regards, Norris.

[matt_k]

So was it was a thermal that caused the collapse?.

[norris]

So was it was a thermal that caused the collapse?.

I don't know Matt. I tend to think it was wake turbulance as there did not seem to be any lift component in whatever caused the collapse, given the limited amount of time in which to view it, and although he was close to the runway I don't think that was wide enough to generate a thermal and the rest of the field appeared to be grass. The pilot was quite close to the ground so I think it is entirely possible that wake turbulance in the form of a wing tip vortex could have been slowly dissipating and he turned and flew back into it. I could be wrong of course, but that is what I think.

[Radical]

Hi there

I've occasionally flown through another gliders wake and although it wasn't pleasant it didn't seem to have enough oomph to cause the large assymetric collapse this poor chap had.

Or have I just been lucky?

Cheers

Steve

So was it was a thermal that caused the collapse?.

I don't know Matt. I tend to think it was wake turbulance as there did not seem to be any lift component in whatever caused the collapse, :

[Guest]

Also think about what comes out of the back of the prop. (and where it goes)

SW

[aquatix]

Hi there

I've occasionally flown through another gliders wake and although it wasn't pleasant it didn't seem to have enough oomph to cause the large assymetric collapse this poor chap had.

Or have I just been lucky?

Cheers

Steve

I've suffered tip tucks whilst gliding & soaring near to others, and also caused a few when people get downwind of me. At about 120kg all up (for free flying) I would guess the maximum down force from each of my wing tips would produce less than 60kgs.

Deliberately inducing an assymetric collapse by pulling down all my A lines only requires a fairly light tug of about 10 - 15kg (guesstimate) and even less to hold them down once collapsed. Adding the extra weight of the paramotor to the wing tip vortices, plus the combined effect of this with the prop wash, it stands to reason that anyone trying to sneak up behind me would get a rough ride !!!