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SPRING THERMALS


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Im planning on flying tomorrow and i want to know if its ok to fly all day, or have i got to watch out for the spring thermals. Someone had mentioned to me that the spring thermals were worse than summer ones. Thought i had better check it out before i fly.

I fly a pap and a synthesis.

Thanks Clive

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Someone had mentioned to me that the spring thermals were worse than summer ones.

They can be much more violent, and current conditions make "bullet thermals" very likely. Clear night sky (maybe even frost) leaves cold ground and cold air with strong sunlight heating the ground unevenly. This produces small, fast thermal updrafts with sharply defined edges and descending air around them. Flying through this boundary can cause one side of your wing to be yanked up whilst the other side is pushed down, making collapses likely.

Several experienced PG pilots chose to land today as the air was too active, whilst others recorded 8m/s climbs to cloudbase and had great XC flights. The thermals were still active (but calmer) at 5pm.

Unless you have good active piloting skills and pitch control I would consider just flying morning and evening, and waiting out the most active part of the day - which could get quite gusty, bouncy & unpleasant (at best) if you go blundering through them with a motor. Free flying is different as you aim to turn and stay within the thermal where all the air is rising, so relatively smooth.

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My flight last week was T/O at 10:30. It was a little bumpy so I was on full fast trim all the way including the landing.

The peak readings on the vario showed 760 ft/min up and 520 ft/min down.

Apart from a little sink in rotor it was the first time I have flown through a block of sinking air, I wondered what was happening at first. I then realised and had to increase the revs to maintain level flight.

After I had landed it really kicked off so I was glad I was down.

An enjoyable flight all the same.

Cheers,

Alan

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GD

What's the rectangle rule Gordon?

Draw a rectangle around the clouds... if the rectangle is a vertical rectangle, then don't fly. If it's horizontal, then it's safer.

If you cannot see a clear section of cloud and don't know if it's an 'anvil' or not, look at the base of the cloud. If it's dark then its obviously high, and blocking light.... so dont fly....

GD

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Do spring thermals decrease as the day goes on or are they worse at the highest point of the sun like in summer?

I flew yesterday after a frosty night and was well aware it was going to be the bumpy from around 10 with the clouds telling us the same,but by midday the clouds had dissapated, we didnt go up but the clouds gone did it mean the thermals had gone or can you have strong thermals around with no teltale clouds?

I have always stuck to the rule of flying window 3 hours after sunrise and 3 hours before sunset apart from winter.

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Hi Matt, yes, they have the same cycle through the day but tend to be smaller, faster and more punchy in spring than summer or autumn (when the general air temperature is warmer).

You still get just as strong thermals without clouds (blue sky thermals), as cloud formation depends on lots of other factors such as dew poiint, and how moist the air is. Polar air masses (coming from North) tend to be dry, whilst a warm tropical air mass contains lots of moisture after blowing across the ocean. It also depends how dry the ground is.

Thermals can be great fun when you are looking for them, but unpleasant if they are strong and you just want a gentle flight.

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