ARRANGEMENT OF THE EMPENNAGE

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ARRANGEMENT OF THE EMPENNAGE

• Requirements
• A. Slipstream / Jetstream Effects
• A1. The empennage must never be in the jet efflux
  of the engines (must be outside cone w. 6 deg.
  semi-apex angle).
• Solutions
• A1.1 Divert the centerline of the jet.
• A1.2 Horizontal stabilizer dihedral.
• A2. The empennage must not be close to a jet
  efflux because the jet pumping effect will affect
  the direction of the airflow and diminish the
  stabilizing effect of the tail.
• A3. The empennage must be as far away as possible
  from sources of noise to avoid acoustic fatigue.

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ARRANGEMENT OF THE EMPENNAGE

• Requirements
• B. Stability Control
• A1. The fin and the rudder must provide the
  counteracting YM in case of engine failure.
• A2. The empennage must allow for a safe recovery
  from stall and spin (especially avoid deep
  stall).

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ARRANGEMENT OF THE EMPENNAGE

• 1. Fuselage or Fin-Mounted Stabilizer
• Pros
• Structural simplicity stiffness.
• Having one surface at the tip of the other
  increases the AReff by about 50 (winglets). As
  a result, the horizontal stabilizer can increase
  the slope of the fin by about 15.
• Cons
• T-tails may suffer from flutter and deep stall
  problems.

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Cessna 550
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BAE-146
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ARRANGEMENT OF THE EMPENNAGE

• 2. Twin Vertical Tail
• Pros
• Increased effectiveness of the horizontal
  stabilizer (winglets)
• If the fin turns out to be too large, rudder
  deflection will cause a RM as a result of the
  large vertical distance of its ac from the
  longitudinal axis of the ac. A twin vertical
  will minimize this effect (F-14, F-15, F-18).
• If twin tail booms are used, the twin vertical is
  the only solution available (Cessna Skymaster).
• Decreases combat vulnerability (A-10).

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Fairchild Republic T-46A
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F-14
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F-15
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F-18 Hornet
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Cessna Skymaster
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A-10 Warthog
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ARRANGEMENT OF THE EMPENNAGE

• 3. Butterfly Tail
• Pros
• Avoids damage to the tail when landing on
  overgrown terrain (sailplanes).
• Keeps tail surfaces clear of the engine efflux.
• Looks cool (V-tail Bonanza)!
• Cons
• Moving surfaces serve as both rudders
  (differential deflection) and elevators
  (simultaneous deflection) complicated control
  system design.

14
Thermik-Excel Vetron Sailplane
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Beechcraft V-Tail Bonanza