Game Development Reference
In-Depth Information
squared (V 2 ). This means that the experimentally measured drag force is divided by the
quantity (1/2) ρ V 2 S to get the dimensionless drag coefficient. Depending on the object
under consideration, the drag coefficient data will be presented as a function of some
important geometric parameter, such as attack angle in the case of airfoils, or length-
to-height ratio in the case of canopies. Here again, Hoerner's Fluid-Dynamic Drag is an
excellent source of practical data for all sorts of fuselage shapes and appendages.
For example, when an aircraft's landing gear is down, the wheels (as well as associated
mechanical gear) contribute to the overall drag force on the aircraft. Hoerner reports
drag coefficients based on the frontal area of some small-plane landing-gear designs to
be in the range of 0.25 to 0.55. By comparison, drag coefficients for typical external
storage pods (such as for fuel), which are usually streamlined, can range from 0.06 to
Another component of the total drag force acting on aircraft in flight is due to skin
friction. Aircraft wings, fuselages, and appendages are not completely smooth. Weld
seams, rivets, and even paint cause surface imperfections that increase frictional drag.
As in the case of the sphere data presented in Chapter 6 . This frictional drag is dependent
on the nature of the flow around the part of the aircraft under consideration—that is,
whether the flow is laminar or turbulent. This implies that frictional drag coefficients
for specific surfaces will generally be a function of the Reynolds number.
In a rigorous analysis of a specific aircraft's flight, you'd of course want to consider all
these additional drag components. If you're interested in seeing the nitty-gritty details
of such calculations, we suggest you take a look at Chapter 14 of Fluid-Dynamic Drag ,
where Hoerner gives a detailed example calculation of the total drag force on a fighter
The flaps located on the inboard trailing edge of the wing in our model are used to alter
the chord and camber of the wing section to increase lift at a given speed. Flaps are used
primarily to increase lift during slow speed flight, such as when taking off or landing.
When landing, flaps are typically deployed at a high downward angle (downward flap
deflections are considered positive) on the order to 30° to 60°. This increases both the
lift and drag of the wings. During landing, this increase in drag also assists in slowing
the aircraft to a suitable landing speed. During takeoff, this increase in drag works
against you in that it necessitates higher thrust to get up to speed; thus, flaps may not
be deployed to as great an angle as when you are landing.
Ailerons control or induce roll motion by producing differential lift between the port
and starboard wing sections. The basic aileron is nothing more than a pair of trailing-
edge flaps fitted to the tips of the wings. These flaps move opposite each other, one
deflecting upward and the other downward, to create a lift differential between the port
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