Fantastic day yesterday. Even although while looking at the weather
In the morning I thought this was going to be a DIY day.
It was still worth the drive down from Aberdeen to Fife as some time could have been spent on theory if conditions were poor.
On arrival at East Lomond conditions were humid , hazy with very light winds. This turned out to be a very educational day. By the time we reached the top the sun was although not breaking through was managing to heat the ground as small thermals were popping through.
Murray: “IR passes through the clouds, like certain types of glass IR can pass one way (in to the greenhouse/room) but not out… the reason for this is the ‘frequency shift’…. IR direct from the sun is (from memory) a higher frequency than the IR radiated back to space from the ground, hence on a cloudy night the local air temp/world remains warm while on an otherwise identical night but with no cloud cover the temp drops rapidly and a frost can occur, all due to the (lower frequency) IR radiated from the ground being reflected by the cloud cover back to the ground i.e. ‘trapped’ … on the clear nite it simply radiated back into space and is lost..
So in summery, cloud cover (daytime when out flying) will reduce the temp ‘contrast’ so it feels LESS hot in hazy sun than if it was direct sun this generates thermals low down/ground level but far less punchy. As the PG pilot gets higher the strength of the RISING thermal is more to do with the actual (environmental) lapse rate, so thermals rising into cooler air speed up ‘get stronger/puncher’.” :END
I spent some time testing the air and trying to get a feel for the thermals and
Change in wind direction prior to take off. It was surprising how in such
Light conditions ( ridge lift that is ) how much the wind direction and strength changed
over such a short period of time swinging from south easterly through to southerly in seconds.
Meaning standing on the top plateau my Nova Pheron was nodding left to right almost like a
Metronome. In addition tension on risers were changing so much that I had good practice
At reversing and controlling frontal collapses. Although not perfect at this I’m sure My DHV 1 Nova Pheron was not helping. ( think I need to cut the wing tips off – Murray get the old Singer looked out )
Murray :”This yaw of the wing (and on low DHV wings significant roll due to tip curving down) is a classic indicator of a light wind lifty thermal condition and required a diffrent approach to launching TIMING than a variable wind ‘ridge lift day'” :END
Most flights were generally short from top with hill side landings just below the plateau.
( even Murray on the odd occation didn’t manage a top landing )
At about 2pm The sun managed to squeeze through for 30 mins and the cycles changed for a while with increased thermal activity.
One specific flight, where my launch timing was right ( more good luck than judgement ) I flew straight into a decent thermal which took me up about 100 ft I rode out about 3 or 4 punchy small thermals which allowed me to stay about at take off height until a large cycle ( large for the day that was ) came through which took me to approx 600 ft above take-off for a nice 20 minute flight.
Who would have thought yesterday was flyable 🙂
Alan c