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