Pawns Velocity set

[anonymous_user_e10f80c4]

Part of MyPawn:

void AMyPawn::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );
	if (!OnGround)
	{
		FVector temp = physiks.CalculatePhysiks(GetVelocity());
		GetMovementComponent()->Velocity.Set(temp.X,temp.Y,temp.Z);
	}

}

Part of myPhysiks:

FVector myPhysiks::CalculatePhysiks(FVector vel)
{
	if (vel.IsNearlyZero())
	{
		return gravDirektion *gravity;
	}
	else
	{
		return vel += gravDirektion *gravity;
	}

}

so i just want to simulat gravity and update my velocity at every tick but why is my velocity geting a reset to almost zero so that it dosent move unless i use the funktion AddMovementInput?