Upon furter investigation, it seems like the drag significantly increases at high AOA, thats why its loosing airspeed at turns, and refuses to accelerate after take off. it seems like the drag increases rapidly above 10 units of AOA and it decreases significantly below 3 units of AOA resulting in rapid acceleration. This tendency described above is absolutely correct, considering the Viggen is a high AOA delta wing configuration, and generally the induced drag is exponentially increased by the increase of AOA. However the change in drag both at the higher and lower end of the scale feels as it is changing by the power of 3 insted of the power of 2.