When applying AddRelativeForce object reaches higher speed when rotated

I am working on a helicopter game.
The helicopter object has a Rigidbody2D component. (for gravity etc.)
when pressing the “down” button on the keyboard I use Rigidbody2D.AddRelativeForce to apply force to the objects’ position on the “y” axis.

r_2d.AddRelativeForce(new Vector2(0,20));

it seems that if the helicopters’ angle is not 0 the helicopter’s speed increases faster.

when the helicopter’s angle was 0 the it reached in 3 seconds the speed of 40.
when the helicopter’s angle was 45 the it reached in 3 seconds the speed of 58.

Why?

Because at 0 rotation all of the force you apply is fighting directly against gravity.

Think of the extreme opposite: if you apply a relative force “up” when the chopper is upside down, both gravity and the applied force would move the chopper down and it would surely move a lot faster than when applying a force straight up against gravity’s pull