: Improved flap performance could be concluded when the flap produces a Fowler action, where the Fowler action is defined as "the measure of change in position of the leading-edge of the flap in the plane of the chord of the fore element." Also the extended chord could be defined as the cruise airfoil chord plus the Fowler action; this increase in airfoil area increases the achievable lift without significant increase in drag.
Additional deployment of a Fowler flap beyond this point of extension involves deflection, which adds drag and substantially increases camber.
Not having pylon-mounted engines helped simplify things a lot, but the real tricks were in the slotted Fowler flaps and leading-edge slats all 727s came with, and which are now commonplace aboard jet transports of almost any size and configuration, as well as general aviation airplanes.
Fowler's Fowler flap
. Fowler, an engineer who worked for the U.S.
Kudva described the new segmented multiflap structure as "like a two-segment Fowler flap
." The upper airfoil control surface will have the smooth shape needed to reduce the shock strength with boundary-layer separation.
The Fowler flap
common to Cessna singles actually moves aft and downward at the same time, effectively increasing the wing's chord and physically increasing lifting area.
He noted that because Cessna used Fowler flaps
that moved aft and down during extension, that there had been concern about an increase in stall speed with flap gap seals.
To achieve the balance of high-speed, high-altitude cruise and low-speed approach and landing performance, the wing will have modest sweep, inboard and outboard Fowler flaps
and large ground spoilers.
A push-rod operated lifting canard--stabilizer and elevator--was installed just below the midpoint of the cowling, full-span flaps replaced the ailerons and Fowler flaps
and a complex spoiler system referred to as "Wren's teeth" was created for roll control.
But high-wing airplanes with huge Fowler flaps
can float way more than we want when those flaps are fully deployed, reducing sink momentarily and adding to any tendency to float in ground effect if too fast.
The combination of the long span, Fowler flaps
with vortex generators and gurney strips on the trailing edge produce a full-flap stall speed of 50 knots indicated or 61 KCAS.
In order to keep the stall speed down, long-span Fowler flaps
are used, creating a lack of room for ailerons.