The lower half of the radiator cooling flaps ARE used fof landing flaps along with the pair inboard of the ailerons as noted already. The top cooling half flap does not do much on the model. Its supposed to add drag to ahlp slow the plane down, but doesnt really do much good.

You WILL need all four sections of the actual landing flaps to function, especaialy if the plane weighs over 16 pounds like mine. The upper cooling flap things can be glued in place and it wont harm anything.

I did make the upper halfs functional, but by separate servos from the flaps all together and a separate switch. So I could control tbhem independent of the flap function. I never used them except as "hey look at this: on the ground.