You assumed correctly!

However, as it has well explained above, slowing a plane alone will be dangerous for the "fast ones", which have airfoils and weight that help them fly fast, but do not help much in slow flight.

Basically, an airfoil shape that is good for high speed (symmetrical=low drag-low lift coefficient) is not good for low speed, and vice-versa (cambered =high drag-high lift coefficient).

Birds like hawks know about that fact, and they modify the shape of the airfoil of their own wings at will, in order to accommodate the speed of flight for diving and for patrol.

Airplane’s designers have tried to copy that trick by adding devices to the wing they design.
Those devices are slots (for the leading edge) and flaps (for the trailing edge).

Some flaps are able to modify the camber or curvature of the airfoil of the wings by deflecting.
More complex flaps, like the ones that big airliners deploy at landing (together with slots), modify the camber of the airfoil by deflecting, and also increase the area of the wing by getting extended at the same time (these are called Fowler flaps).

For moderate angles of deflection, simple flaps increase the lift of the wing and its capacity to fly slowly (more lift than drag increment); for higher angles of deflection (up to 60 degrees), simple flaps slow down the plane for landings (more drag than lift increment), as you have assumed.
This is a convenient sequence, since the wing is ready for slow flight before the flight velocity gets reduced.
The reverse process is used for take-off.

For slowing effect only (like for after landing), air brakes are used instead; these create a lot of drag, just like a parachute, but they don't modify the flying characteristics of the wing.


Copied from
http://www.centennialofflight.gov/es...vices/TH17.htm

“Flaps may be used to increase the maximum lift coefficient, increase the wing area, or both. A change in the maximum lift coefficient may be realized by a change in the shape of the airfoil section or by increased camber. The trailing-edge flap is one method of accomplishing this. The maximum lift coefficient for an airfoil with a simple flap is greater than that for the unflapped airfoil. Also, the coefficients of lift are increased over the entire angle-of-attack range. The stall angle for an airfoil with a simple flap is essentially unchanged from that of the unflapped airfoil. This is opposed to the slot operation where a higher stall angle was obtained. The flapped airfoil reduces the disadvantage that the slot has in high landing angles.

A Fowler flap is hinged so that it can move back and increase the airplane wing area. Also, it may be rotated downward to increase the camber. A very large increase in maximum lift coefficient is realized.

There are many combinations of slots and flaps available for use on airplanes. For example, the arrangement on a Boeing 737 airplane uses a leading-edge slat and a triple-slotted trailing-edge flap. This combination is a highly efficient lift-increasing arrangement. The slots in the flaps help retard separation over the flap segments and thus enhance lift.

It may also be noted that flaps in an extreme down position (50° to 90°) act as a high-drag device and can retard the speed of an airplane before and after landing.
Spoilers are devices used to reduce the lift on the airplane wing. They may vary the total lift and control the glide angle, as they do on gliders, or on large commercial jets, they may be used to help the aileron control by "dumping" lift on one wing and thus help to roll the airplane. Also, on landing, with spoilers up, the lift is quickly destroyed and the airplane may quickly settle on its landing gear without bouncing.

Dive (or speed) brakes are used in airplanes to control descent speed. Whether slowing down quickly when approaching for a landing, after landing, or in a dive, these aerodynamic brakes are helpful. Essentially, they promote a large separation wake and increase the pressure drag.”


“This is the final test of a gentleman: his respect for those who can be of no possible service to him.”
– William Lyon Phelps, educator, journalist (1865-1943)