Static electricity generated by the helicop-ter should be discharged before attempt-ing a sling or rescue hoist pickup. Use a conductor between helicopter and the ground to discharge the static electricity.
Caution must be exercised when trans-porting external loads that exhibit un-stable characteristics. These loads may amplify any oscillation and cause the load to contact the aircraft.
a.
Load bobble. In forward .ight at the higher external cargo hook load weights, a slight vertical bobble may oc-casionally be noticed. If experienced, this bobble will in-crease in amplitude with a corresponding increase in air-speed or aggressiveness of maneuver. This bobble is caused by an external disturbance (e.g. turbulence or a control in-put) that triggers the natural elastic response of the sling. To correct, airspeed shall be decreased or limit aggressive-ness of maneuver until bobble is eliminated and pilot is comfortable with the aircraft’s control.

b.
Stabilator angle in level .ight. Due to the increased drag of external loads, collective position for a given level .ight speed will be higher. Correspondingly, the stabilator angle will be more trailing edge down than usual. Since the surface area and inherent drag of each external load varies, exact guidance relative to how much more trailing edge down angle that results is not possible.

c.
Collective friction. With external cargo hook sling loads, it is especially important to have collective friction set at a minimum of three pounds.

8.38.2 Flying Qualities with External ERFS Installed.

a.
Pitch Attitude vs. Airspeed. The ERFS installation naturally results in increased drag. Since this drag vector is below the center of gravity of the helicopter, the pitch atti-tude will be more nose-down for any speed beyond 60 to 70 KIAS. At mid to high gross weights (and most espe-cially at a forward CG) there is a slight pitch down at 50 to 55 KIAS. The installation of the ERFS results in a small increase in this nose-down tendency.

b.
Tank Vibration. It will be observed that the right hand tank(s) will vibrate more than the left tank(s). This is a normal occurrence.

c.
Stabilator Angle vs. Airspeed. With the increased drag of the ERFS, a given airspeed will require more col-lective which, due to the collective to stabilator coupling, results in a more trailing edge down stabilator angle. This is normal as no stabilator program changes were made for the ERFS.

d.
Roll Attitude Hold (FPS ON). With only the ERFS wings installed, the roll attitude hold feature of the FPS is

8-20 Change 4
not noticeably affected. With full 230-gallon tanks there is a very slight degradation of roll attitude stability, evidenced by a slower return to trim after an excitation (gust).
8.38.3 Collective Bounce/Pilot Induced Oscilla-tion.
NOTE
The friction force refers to the breakaway force required to move the collective stick in an upward direction. The three pounds force is measured with the BOOST servo and SAS ampli.ers operating and collective at mid-range.

To prevent vertical oscillation (collective bounce), the collective control system requires a minimum friction of three pounds measured at the collective head. Vertical os-cillation can occur in any .ight regime and may be caused by such events as SAS oscillation, turbulence, external load oscillation, and inadvertent pilot input into the collective. The oscillation causes the aircraft to vibrate. This vibration will be felt as a vertical bounce at approximately three cycles per second. If the severity of the oscillation is al-lowed to build, very high vibration levels will be experi-enced. During .ight, if vertical oscillation is encountered, the pilot should remove the hand from the collective grip; this should eliminate the oscillation.
　
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