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Evening Thermals


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How dangerous are they?

I took off last night at 8pm, 30 minutes before sunset, and 'found' a few thermals (around 2-300fpm up)(tow on the bump scale). The wing didn't do anything funny and I wasn't really getting tossed around that much, until I flew over a metal roof barn at 200 feet(three on thee bump scale). The upper winds were pretty strong as I was almost parked so I didn't want to go higher, but I also didn't want to hover around 200 feet with thermals. I think I might start flying first thing in the morning to avoid thermals all together, at least until I get some more experience.

Does anyone have any input regarding evening thermals and if I am just being paranoid?

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How dangerous are they?

Does anyone have any input regarding evening thermals and if I am just being paranoid?

You are righ to be cautious. Thermals are not "dangerous" but if you are unsure how to deal with them or what to expect they can cause you problems.

I dont know how much you know already about thermic activity, causes, behaviour etc. And the explanation can be a long one! It calls for a club theory session, which we've talked about before but I'm unsure if we have got round to it? What area are you in?

Basically a column, or more likely in the evening, a bubble of air is rising through the atmosphere because it is warmer than the surrounding air. The speed it rises at is proportional to the difference in the temperature. In the evening the difference is likely to be smaller than at a hotter time of day. 200 to 300 feet per minute is quite a mild thermal ascent rate (about 1.5 metres per second).

When you move from air that is not rising to air that is rising your wing's Angle of Attack increases, it slows the wing, and you swing forward. The wing wants to accelerate forward to catch you up and the result is you get pitched back then dive forward into the thermal. As you get knocked back you let your hands up and as you dive foward you bring your hands down. this is called "active flying" and it means you are keeping the wing above your head rather than letting it nod forward and pitch back. I am assuming that you are not flying a reflex wing? If you are then what I have just told you is not the correct response!

as you enter the thermal you will feel like you are in a lift as your stomach "drops" and that is the "bump" you feel. Once in it you lose the sense that you are going up as you settle to a steady ascent rate.

As you leave the thermal you move from air that is rising to air that is not and your angle of attack changes again; it gets lower and this is when you might get a deflation of part of the wing. To guard against this fly with some brake applied when in rising air.

If you do get a deflation it is not a big drama, your wing is designed to immediately reinflate (I am assuming you are flying a "beginner" rated wing?

If one side deflates you just lean towards the flying side and carry on your course, the other side will spontaneously re-inflate. If the centre deflates, the tips often remain flying and the centre pops straight back out again even before you get time to look to see what made that rustling noise.

What wing do you fly?

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If the winds were strong and you were only 200ft up then it could have been mechanical turbulence (rotor) from the barn, don't forget you should be 500ft away from any structure/vehicle/person or vessel unless taking off or landing, plus the higher up you are - generally the smoother it gets and the more room you have for your safety envelope.

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Low level asymetric collapse is the biggest cause for concern in the pg community

It you were hardly moving the rotor off that barn would easily be cabable of collapsing your wing.

by no means is a low level flight especially for the experienced a great cause of concern.

However in windy conditions, flying at low level it is dangerous.

my personal rule is never overfly any obstacle - even trees in a high wind, due to the rotor. always choose a no obstacle route for a landing if you can.

height is your friend

Kind regards

simon

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First off, thanks for all the great replies, makes me feel a lot better (I was starting to think I should sell my PPG for a powered hang glider)....

I am flying a Fresh Breeze Simonini, and a Powerplay Sting wing (DULV 1, DHV 1/1-2) and I have a total of 5 hours experience. I also have 12-15 hours hang gliding experience.

I do fly actively, I think, I keep about 5 lbs brake pressure (number 2 according to the PPG Bible) and I check my surges. I just don't have the experience to feel if I am flying properly.

As Dan the Man said, it is probably just turbulence. The more I think about it and the field I flew from it just makes more sense than thermals 30 minutes before sunset. It is also the strongest wind I have flown in with my ppg. There was a small 'ridge' where I was feeling the lift the most, only about 30 feet high and I was around 150' up so I am not sure if that is what I was feeling but it makes sense.

Also the only reason I went over the barn, which I knew would be bumpy, was because there was a field on the other side more suitable for landing and I wanted DOWN. LOL.

Simon thanks for the great link, learned lots of stuff

:D

As for flying higher, that is what I wanted to do but I figured I would end up going backwards.

All added up, it is obviously Idiot Pilot Error for even taking off. I am just glad I was safely able to learn something from it. Thanks again everyone and happy flying.

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Also the only reason I went over the barn, which I knew would be bumpy, was because there was a field on the other side more suitable for landing and I wanted DOWN. LOL.

Just thinking that a field "suitable for landing" would include, in its selection, the likely state of the air in the approach path.

getting into a field does not have to be from the downwind side on a straight descent path. There is a recognised approach technique that effectively skirts the edge of the field with a downwind leg along the side of the field, turning crosswind before the downwind hedge and tuning into wind to land in the centre of the field. Normally you would use a left hand circuit for collision avoidance reasons but with no other aircraft in the vicinity you could choose whichever circuit was best. This is how many airfields operate and for similar reasons, no aircraft likes flying through turbulence near the ground.

This approach would avoid getting into areas of turbulence from obstacles downwind of the field.

There is another approach called the "constant aspect approach" which can get you into an even smaller field and still keep you in the smoothest air. I wont go into detail here but Simon probably has a link to an article that describes it.

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Sorry for the delayed response, been working. Gotta pay for the toys you know.

I am not learning by myself, just increasing my experience by myself. I learned how to fly from Don Jordan in Monticello, Indiana. I also fly hang gliders, but they don't usually require the calm weather that ppg's do.

Good advice on the landing field, the thing of it is that it was right beside the field I took off from. Less than a football (american) field away.

I have gone flying since my last stupid excursion. The winds were calm, the air was smooth, the field was much bigger, and I only got to 50 feet. Spent most of my time just circling the field. Low on upwind, high on downwind, smooth conservative turns. Made me realize why I bought it, what a great flight. :D:D:D:D:D:D

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