To: NickLappos
AC-27-1 paragraph 27.177.b.2 recognizes that some helicopters experience excessive flapping of the main and tail rotors when the helicopter is in a sideslip. To establish this side slip/flapping limits the respective rotors should be instrumented. CFR-14-27.177 requires testing of the controllability at side slip (out of trim) of plus 10-degrees, left and right (at 0.6 VNE) and CFR-14-27.351 requires full deflection of the tail rotor pedals while airborne from 0 to 0.6 VNE to attain a ninety degree side slip (left and right).
You are correct 14-27.351 deals with the structural loads reacted when placing the helicopter in a 90-degree sideslip right and left at speeds from 0 to 0.6 VNE. The point I was trying to make is that this maneuver when demonstrated under 14-27.351 would cause extreme flapping of the main rotor. This conclusion is based on the Georgia Tech evaluation of the problem and how the FAA reacted to this report. They placed restrictions on out of trim flight and sideslipping stating that this would result in extreme flapping of the rotor system resulting in either mast bumping or rotor incursion or both.
