SSD, like many people you appear to be assuming that because you have been doing something for many years, this must mean that you understand all about it. This is a false assumption.
Nope. I knew this stuff after my first lesson in a T28 glider. Probably even before that! It's not 'ard!
So, you've powered up, overcome the drag of the 50 knots wind speed, increased your airspeed to the 60 knots needed to lift off and started flying ... But then immediately turn downwind. What happens?
Your groundspeed increases to 110 kts in a sweeping downwind turn. Absolutely nothing else happens (disregarding any wind gradient affecting the lower wing in the turn, and assuming the odd visual effects at such low level don't confuse you into reducing your airspeed and possibly stalling the aeroplane).
Now let's imagine you take off, climb through a cloud layer, then turn downwind. This time you will be unaware of the bizarre visual effects of strong winds at low level because you will be above a cloud deck which is also moving (with the air the clouds are suspended in) at 50 kts over the ground.
Let's assume you are airborne in a hot air baloon above a cloud deck in a 50 kt wind. The balloon has zero airspeed of course, as do the clouds, so as you look out over the side of the basket nothing appears to be moving - not you, not the clouds. Then the clouds disperse... and you have a view out the basket of the ground rushing past at 50 kts!
In my experience it's usually model flyers who 'don't get' this. They remain convinced that their pride and joy experiences a gain of speed on turning into wind, and a loss of speed turning downwind. Just imagine if this were true.... an airliner goes into the hold at FL70 and 190 kts. Does the wind affect the airpeed as it flies around the holding pattern? Of course not! It will affect the ground track, though.