CRUISE & AIRWORK

Buffet Boundary

  • The high-speed and low-speed buffet boundaries define the usable maneuvering range of the airplane.
  • At altitude, the two buffet limits can move closer together, creating a buffet transition zone.
  • Increased load factor raises the effective aircraft weight and reduces buffet margin.
  • Example from the manual: a 25° bank increases load to about 1.10 g. cruise
  • At high speed, buffet may occur because of increased angle of attack and compressibility effects.
  • Pronounced buffet can occur at normal bank angles near the high-speed buffet boundary.

FLIGHT CONTROL CHARACTERISTICS

Longitudinal Control

  • Changes in thrust, flaps and speed brakes affect pitch and trim.
  • Increasing thrust tends to pitch the nose up.
  • Decreasing thrust tends to pitch the nose down.
  • Pitch changes can be corrected mainly with stabilizer trim.
  • Extending the landing gear at higher speeds causes a noticeable nose-up pitch.
  • Flaps are primarily intended for takeoff, approach and landing.

Flap Effects

  • At higher altitudes, lateral control capability decreases; therefore flap extension is limited to below 20,000 ft.
  • Flap extension from 0° to 14° causes a slight pitch-up.
  • From 14° onward, further extension tends to produce a nose-down pitch.
  • Larger flap extensions require noticeable trim changes.
  • Extending inboard flaps tends to pitch the nose up.
  • Extending outboard flaps tends to pitch the nose down.
  • Because outboard flaps have the greater effect, extension above 14° results overall in a nose-down tendency.

Speed Brakes

  • Rapid speed-brake extension can create a temporary nose-up pitch.
  • Raising only the inboard spoilers tends to pitch the nose down.
  • Raising only the outboard spoilers tends to pitch the nose up.

LATERAL CONTROL

  • Roll control is provided by:
    • inboard ailerons
    • outboard ailerons
    • spoilers
  • Full control-wheel travel raises the appropriate spoilers to about 40°.
  • If the control wheel is not fully displaced, spoiler response may be reduced.
  • With flaps up, the inboard ailerons, assisted by spoilers, provide roll control.
  • With outboard ailerons operating, full roll authority is available at lower flap settings.

DIRECTIONAL CONTROL

  • Primary directional control is by the hydraulically powered rudder.
  • If all auxiliary hydraulic pressure is lost:
    • the rudder reverts to a control-tab and balance-panel system
    • maximum rudder deflection is reduced to about half
    • pedal forces increase significantly. cruise

707 HANDLING CHARACTERISTICS

  • Control response is generally slow.
  • Allow time for aerodynamic response after control inputs.
  • Avoid unnecessary spoiler use to keep maneuvering smooth and comfortable.
  • Use of inflight speed brakes under normal conditions is not recommended, because of aerodynamic backwash and increased stabilizer loads.

YAW DAMPER

  • The yaw damper should be used at all times, including:
    • taxi
    • takeoff
    • flight
    • landing
  • Normal turns are made mainly with aileron control.
  • The yaw damper provides the required rudder coordination.

MACH TRIM

  • Above approximately Mach 0.81, the center of pressure moves aft.
  • This creates a natural nose-down pitching tendency.
  • The Mach Trim system counteracts this by commanding nose-up trim.
  • The system can be overridden by:
    • main electric trim
    • manual trim wheels.