Lateral Stability and Tail Sizing Lecture 11 ME EN 415 Andrew Ning - - PowerPoint PPT Presentation

ME EN 415 Andrew Ning aning@byu.edu

Lateral Stability and Tail Sizing

Lecture 11

Lateral Stability

Coefficients

cn = n q∞Swbw

roll

croll = roll q∞Swbw

n

Yaw Stability

n β

Roll Stability

flying into page

Φ L W

Dihedral

Φ φ

Statistical Tail Sizing

Tail Types

74 AIRCRAFT DESIGN AIRFOIL A Somemulti-engine aircrafthave counter-rotating

propellersto minimizethe

engine-out yawing. The tails are also a key element of stability, acting much like the fins on an arrow to restore the aircraft from an upset in pitch or yaw. Although it is possible to design a stable aircraft without tails, such a design is usually penalized in some

• ther area, as discussed in Chapter 20.

The other major function of the tail is control. The tail must be sized to provide adequate control power at all critical conditions. These critical conditions for the horizontal tailor canard typically include nosewheelliftoff, low-speed flightwith flaps down, and transonic maneuvering. For the vertical tail, critical conditions typically include engine-out flight at low speeds, maximum roll rate, and spin recovery. Note that control power depends upon the size and type of the movable surface as well as the overall size of the tail itself. For example, several airliners use double-hinged rudders to provide more engine-out control power without increasing the size of the vertical tail beyond what is required for Dutch-roll

• damping. Several fighters, including the YF-12 and the F-107, have used

all-moving vertical tails instead of separate rudders to increase control power. Preliminary methods for sizing tails are provided in Chapter 6, and stability and control analysis methods are provided in Chapter 16.

• Fig. 4.30

Aft tail variations.

most aircraft designs, the con' and control at the lightest wei have such a tail arrangement

• thers.

The "T-tail" is also widely tional tail because the vertica tail, but the T-tail provides co Due to end-plate effect, thl the horizontal tail clear of more efficient and hence a:ll! the horizontal tail, which red Injet transport aircraft sud engines mounted in pods on stylish, which is not a trivial The cruciform tail, a ce arrangements, lifts the horize the B-1B), or to expose the high angle-of-attack conditi< with a T-tail, but the cruci However, the cruciform tail ~ effect as will aT-tail. The "H-tail" is used prim~ during high angle-of-attack c( in the propwash on a multie H-tail is heavier than the c. smaller horizontal tail. On the A-lO, the H-tai: heat-seeking missiles when' H-tails and the related triple. to allow an aircraft such a~ hangars. The "V-tail" (Fig. 4.31) is horizontal and vertical tail fOJ tions of the force exerted UP! and vertical tail area, the req from the Pythagorean theore the arctangent of the ratio of r wetted area of the V surfaces and vertical surfaces. However, extensive NAC satisfactory stability and con same total area as wouldbe re Even without the advantage e ference drag but at some pen and elevator control inputs m movement of the V-tail "rude When the right rudder pee vator deflects downward, and Tail Arrangement Figure 4.30 illustrates some of the possible aft-tail arrangements. The first shown has become "conventional" for the simple reason that it works. For

Raymer, Aircraft Design

AIRFOIL AND GEOMETRY SELECTION canard capable of downward deflectionsof 45 deg or more can be used to put the nose back down under almost any situation. This permits optimizing the wing's aspect ratio and sweep without compromising for pitch-up avoidance (see Fig. 4.21), but requires a sophisticated flight control system. Such an approach was used on the X-31, capable of flight at 90-deg angle of attack. A subtle aerodynamic benefit can be obtained with a canard configuration. If both wing and canard are highly swept, the canard vortex can be made to interact with the leading-edge vortex on the wing, increasing its strength and therefore augmenting its lift. This beneficialinterference is very geometry depen- dent and is difficultto predict. The SAAB Viggen and Rockwell HiMatboth used this effect. Canard advocates sometimes claim a lift and trim drag advantage for the canard configuration when compared to an aft tail. It is quite true that the canard's lift reduces the lift that must be produced by the wing. This permits a smaller wing and, all else being equal, would reduce the wing's drag due to

• lift. Traditional aft-tail designs frequently fly with a download on the tail to

produce natural stability, which increases the amount of lift that the wing must produce and therefore increases its drag due to lift and increases trim drag. However, a modem and sophisticated aft-tail aircraft is designed to a slight level of instability so that it normally flies with an upload, not a download

• n its tail. This is the very reason that computerized flight control systems

with artificial stability were developed and put into production, first on the

5 Flyingwing

ng ;ed Ity )le a&-

:>st

~e, rol nd its er, lal to Ie. te-

• f

ed

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79

Aft-strake

• r back porch
• Fig. 4.34

Other tail configurations.

Raymer, Aircraft Design

Statistical Tail Sizing

VV = lV SV bwSw VH = lHSH cwSw

Control Surfaces

Flight Controls

Flight Controls