Take off with 0 degree of flap does not add drag, but it may reduce lift at a given airspeed
I meant if you just add 10° of flap.
Because 10° (1 stage) is so often used, it is easy to think that all aeroplanes use 1 stage. I had an arguement with an instructor on a checkout once - he wanted me to use 10° of flap in the Warrior, and I was sure that it was 2 stages. Anyway, him being the instructor I did it his way, and we survived.