Another Lift Story

[HELModels]

I've been training on a small CD-Rom powered pusher of my own design for a while now and I am starting to find lift.
I went out flying today in cold but calm conditions. I fly from a bean field surrounded by roads and buildings and just when I thought my flight was ending I got hoisted aloft by some mysterious force. I was flying at about 1/3 throttle and noticed that she was getting lower and lower. When I would fly over a very gentle mound in the terrain, I would see a brief surge upward, so when I was about a foot off the ground I maneuvered my way over toward where she went up once before and sure enough I gained about 10 feet. I stayed away from the back side of that mound and flew where she seemed to want to go and then bam it happened again. This surge got me another 20-30 feet of altitude without touching throttle. Then I flew around in a circle and watched the wings and when I saw the wings jostling, I worked that area and before I knew it she was back up around 150 feet. I could not have done this power off, but I didnt use extra throttle either.

Anyway, I thought I would share a good flight.

[HELModels]

What a difference a few days can make. Went out today and got a lesson in signs of big lift. I tossed from the top of the knoll and was getting the occasional bump and then she steadily was losing altitude until I had no altitude and landed. Again, I didnt use power to help her plight since I was interested in reading the conditions. So, she landed and I walked over and picked her up, contemplating using the remaining mah to try it again. I noticed the wind suddenly went away so I throttled up and launched. Everything was going fine until the wind went from 0-5 to about 30 mph. She went vertical for a few seconds and then got violently flung downwind. I used full rudder to turn her back and then pointed the nose to the ground and did a waterfall landing....I have no intention of flying 3D, but the maneuver got me on the ground.

I think this what I learned:

1) Lift is accompanied or preceded by sinking air?
2) There will be a lull in wind before the rising air?
3) When the big lift hits, it can be accompanied by highly turbulent winds near ground level?

[wingsnapper]

Lift is surrounded by sinking air (worst is behind the thermal). Yes there is a lull in the wind, but it usually indicates the themal is just infront of or above you. That 30mph rush of wind was the themal passing you by. The air that flung your plane down was the sink that lies just behind lift. If you notice a wind shift, you should assume that there is a thermal pulling the air in it's direction... thus altering the prevailing conditions.
JS

[trashmanf]

3) you want to be as high as possible for the real big thermals! Obviously close enoiugh to see your plane... but, the thermal is usually very small and concentrated (thus the highly noticable updraft) near the ground, then as you get higher in it, the lift will spread out over a larger area, making it easier to circle in the lift the whole time. Remember to head a bit downwind the higher you go!