Diseño Alas Opt

Aileron Design

Chapter 12
Design of Control Surfaces
From: Aircraft Design: A Systems Engineering Approach
Mohammad Sadraey
792 pages
September 2012, Hardcover
Wiley Publications

12.4.1. Introduction
The primary function of an aileron is the lateral (i.e. roll) control of an aircraft; however,
it also affects the directional control. Due to this reason, the aileron and the rudderare
usually designed concurrently. Lateral control is governed primarily through a roll rate
(P). Aileron is structurally part of the wing, and has two pieces; each located on the
trailing edge of the outer portion of the wing left and right sections. Both ailerons are
often used symmetrically, hence their geometries are identical. Aileron effectiveness is a
measure of how good the deflectedaileron is producing the desired rolling moment. The
generated rolling moment is a function of aileron size, aileron deflection, and its distance
from the aircraft fuselage centerline. Unlike rudder and elevator which are displacement
control, the aileron is a rate control. Any change in the aileron geometry or deflection
will change the roll rate; which subsequently varies constantly the rollangle.
The deflection of any control surface including the aileron involves a hinge
moment. The hinge moments are the aerodynamic moments that must be overcome to
deflect the control surfaces. The hinge moment governs the magnitude of augmented
pilot force required to move the corresponding actuator to deflect the control surface. To
minimize the size and thus the cost of the actuation system,the ailerons should b e
designed so that the control forces are as low as possible.
In the design process of an aileron, four parameters need to be determined. They
are: 1. aileron planform area (Sa); 2. aileron chord/span (Ca/ba); 3. maximum up and
down aileron deflection (  Amax); and 4. location of inner edge of the aileron along the
wing span (bai). Figure 12.10 shows the ailerongeometry. As a general guidance, the
typical values for these parameters are as follows: Sa/S = 0.05 to 0.1, ba/b = 0.2-0.3, Ca/C
= 0.15-0.25, bai/b = 0.6-0.8, and Amax =  30 degrees. Based on this statistics, about 5 to
10 percent of the wing area is devoted to the aileron, the aileron-to-wing-chord ratio is
about 15 to 25 percent, aileron-to-wing-span ratio is about 20-30 percent, and theinboard
aileron span is about 60 to 80 percent of the wing span. Table 12.17 illustrates the
characteristics of aileron of several aircraft.
1

b

A
ba/2

Ca

Sa/2

A

bai/2
a. Top-view of the wing and aileron
Aup

Adown
b. Side-view of the wing and aileron (Section AA)
Figure 12.1. Geometry of aileron
Factors affecting the design of the aileron are: 1. the required hingemoment, 2.
the aileron effectiveness, 3. aerodynamic and mass balancing, 4. flap geometry, 5. the
aircraft structure, and 6. cost. Aileron effectiveness is a measure of how effective the
aileron deflection is in producing the desired rolling moment. Aileron effectiveness is a
function of its size and its distance to aircraft center of gravity. Hinge moments are also
important because they are theaerodynamic moments that must be overcome to rotate the
aileron. The hinge moments governs the magnitude of force required of the pilot to move
the aileron. Therefore, great care must be used in designing the aileron so that the control
forces are within acceptable limits for the pilots. Finally, aerodynamic and mass
balancing deals with techniques to vary the hinge moments so that the stickforce stays
within an acceptable range. Handling qualities discussed in the previous section govern
these factors. In this section, principals of aileron design, design procedure, governing
equations, constraints, and design steps as well as a fully solved example are presented.
12.4.2. Principles of Aileron Design
A basic item in the list of aircraft performance requirements is the...