Ibra wrote:
For all this you have to fly really slow to notice this, if you fly at 70kts and hit +1000fpm thermal at best you get +10kts speed, if you fly at 100kts you will see +2kts…
You’ll see +10 kt at least at 100 kt. Flying level while in a 1000 fpm thermal will give you the same airspeed as if you where descending at 1000 fpm in still air.
There is your sink rate on still air at 100kts which differs from the one at 70kts, let say you have 1:7 at 100kts (-1400fpm) and 1:10 at 70kts (-700fpm), so there is 700fpm or 7kts delta between the two speeds that you need to account for with power or thermal strength, if you hit a +3000fpm at 70kts you will get +23kts, if you hit a +3000fpm at 100kts you will get +16kts, there is also more loss from acceleration inertia & control deflection in the latter
I am ignoring power for level flight it is the same story, just the numbers may slightly differ depending how thrust changes with speed delta, depending if it is fixed pitch, variable pitch or jet…
Ibra wrote:
There is your sink rate on still air at 100kts which differs from the one at 70kts, let say you have 1:7 at 100kts (-1400fpm) and 1:10 at 70kts (-700fpm), so there is 700fpm or 7kts delta between the two speeds that you need to account for with power or thermal strength, if you hit a +3000fpm at 70kts you will get +23kts, if you hit a +3000fpm at 100kts you will get +16kts, there is also more loss from acceleration inertia & control deflection in the latter
Well … I know from experience that in a C172 you get at least +10 kt at 110 kt with thermals weaker than 1000 fpm. The C150 has lower speeds, but I don’t think it differs enough that you would only get +2 kt.
Ok probably more than 2kts, not sure about L/D glide of C150 at various speeds, the hard bit is to know what is the strength of thermal without total energy variometer (or maybe maintain ASI and look at altimeter average? normal VSI & ASI are just too unstable for the task)
