Ask Captain Lim

Hi Capt Lim,

I was at the airport observing how planes take-off and land. I have 2 questions. Please correct me if I am wrong.

1. While the leading edge flaps were fully extended during take-offs and landings, I noticed the inboard and outboard flaps were at a smaller angle during take-offs when compared to landings. What is the reason for that? Don't we need just as much assistance from the flaps to create the lift required during the take-offs and landings? Is it because we need to create more drag during landing to slow the plane down?

2. How does a plane rotate after reaching V1? I always thought the rotation is brought about by moving the elevator up, but I did not see that during the take-offs.

Thank you in advance for you assistance and a wonderful website.

Regards,

Ken

Hi Ken,

1. You are right. The flaps on landing is selected to full extension because of the drag and speed factor. You get a lower landing speed with full flaps, hence a shorter runway. During the take off, you want the a flap setting that gives the best lift and the least drag. That is usually set at 5 degrees in the case of a Boeing 777. That is why the 5 degrees flaps is also known as the 'Take Off Flaps' whereas the 'Landing Flaps' is at 30 degrees.

2. During the rotation, the pilot would gently pull back the control wheel at a rate of about 2 degrees per second when the speed reaches the rotation speed (VR) and not V1 in the case of a Boeing 777. By doing so, the elevator moves up at the back and cause the nose of the airplane to pitch up and takes off. It is not easy to see the small movement of the elevators. However, if you were to look a the elevators during the pre-take off checks, you would notice their movement quite clearly because the pilot would be doing the mandatory test on the flight controls prior to the take off.