Design

Chapter 8

Second half

Landing Gear Configuration

• Tailwheel– PROS

• simple to make & install

• added very little weight and drag

– CONS• complicates landing & taxiing operations

• yawing tendency is amplified

Landing Gear Configuration

• Tricycle– PROS

• CG is ahead of the main gear & adds stability on pitch & yaw motion

• hard impact on nose gear causes a pitch down motion decreasing lift

• yawing motion is counteracted by the forward CG

• improved handling qualities

• greater visibility

Landing Gear Configuration

• Tricycle – CONS

• Nose gear has to withstand considerable impact

• Its size and location add a fair amount of drag

• The main gear is fairly aft and complicate attachment to the rest of the plane

Tail Design

• The purpose of the tail surfaces is to provide adequate stability and control.– The horizontal tail provides longitudinal stability

and control• The vertical tail give the same qualities in the directional

sense

• The total horizontal tail surface provides longitudinal stability

• The elevator provides pitch control

• Rudder for yaw stability

Tail Design

• Conventional vertical tail– the single vertical fin mounted above the horizontal

stabilizer– a large fin can result in significant rolling moment

from rudder deflection

• Twin vertical fin– two smaller fins and contribute to directional stability– endplate effect on the horizontal stabilizer make it

more efficient

Tail Design

• T-Tail

• purpose/advantage– to place it out of the wing’s downwash

• downwash reduces the stabilizing effect of the horizontal tail & this is greater at high angles of attack

• at full stall the downwash ceases and the wing’s wake flows directly aft.

Tail Design

• T-Tail Disadvantages– The T-tail experiences a sudden loss of

effectiveness and a rapid pitch-down motion results in a deep stall.

– T-tail also has the additional weight required for heavier structure necessary to support the horizontal tail in this position

Tail Design

• V-Tail– A single surface on either side of the centerline is

canted upward to provide horizontal and vertical tail effects

– the vertical projection provides longitudinal stability– the horizontal projection provides directional

stability– This arrangement reduced the drag slightly over the

conventional tail arrangement

Tail Design

• V-Tail– CONS

• The main objection is the extremely complex control system required to get pitch and yaw control from a single control surface.

• The V-tail is also susceptible to Dutch roll tendencies

V-Tail & T-Tail

• Both popular on sailplanes to keep the tail surfaces high to keep from being damaged in landing

• Both also have good spin recovery characteristics

First Estimation

• Weight– best place to start is gross weight; so many

other parameters depend on this value– figure 8-15 p. 235, Table 8-1 p.236

• Wing– wing loading or weight to wing area ratio

First Estimation

• Power– power required, horsepower

• Range– fuel consumption

Initial Estimation Example

• Page 240-243

• Payload

• Cruise

• Range

• Certifiable under FAR part 23

Computer-Aided Design

• Aerodynamic engineers use computers to model flow patterns.

• Panel Method:– Three-dimensional bodies can be molded as a

collection of flat panels and fluid flow relations applied to each of these panels.

– Figure 8-17 p. 245– Finite element methods simulate large structure

with small elements connected by nodes.

Quiz on Chapter 8

Take out a sheet of paper

Include today’s date and your name

Quiz on Chapter 8

• Compare and contrast the t-tail and the v-tail.

• Why do aerodynamic engineers use Computer aided design (CAD)?