Airplane Motion and Vertical Stabilizer Loads

John OCallaghan

WINDLocation of Wake Turbulence EncountersFDR accelerations were typical of wake encounters

Crew commented on wake turbulence

Wake was similar in each encounter

Effect of the Wake Encounters on the Airplane MotionNASA study indicates nothing unusual about wake.NTSB simulations determined that the effect of wake on airplane motion was minor.The airplane was not in or at risk of an upset.

Control Inputs Following Start of First Wake EncounterTime

Time = 09:15:51Control Inputs Following Start of Second Wake Encounter Start of second wake encounter Airplane in climbing left turn Controls approximately neutral

Time

Control Inputs Following Start of Second Wake EncounterTime = 09:15:52

Time

Time = 09:15:53.1Control Inputs Following Start of Second Wake Encounter Full left wheel input (78) Full left pedal input

Time

Time = 09:15:54.2Control Inputs Following Start of Second Wake Encounter Full right pedal input

Time

Time = 09:15:55.6Control Inputs Following Start of Second Wake EncounterFull right pedal input maintained

Time

Time = 09:15:57Control Inputs Following Start of Second Wake Encounter Full left wheel input Full left pedal input

Time

Time = 09:15:58.4Control Inputs Following Start of Second Wake Encounter Wheel moves right Full right pedal input

Time

Sideslip Angle Buildup Resulting From First Officers Control InputsAirplane flew as commanded until vertical stabilizer separation

Vertical stab. separation

Calculation of Vertical Stabilizer Loads

Loads dependent on airspeed, sideslip angle, and rudder deflection Aerodynamic loads determined by wind tunnel testing during airplane development No wind tunnel data available at the extreme sideslip angle corresponding to vertical stabilizer separationOther methods required to compute loads at time of separation

Computational Fluid Dynamics (CFD)

CFD is the use of computers to mathematically determine the aerodynamic characteristics of airplanes.CFD is used increasingly in the industry to supplement wind tunnel data and optimize airplane designs.

Computational Fluid Dynamics (CFD)

CFD studies directed by NTSB and reviewed by NASA Langley Research Center.

CFD is the use of computers to mathematically determine the aerodynamic characteristics of airplanes.CFD is used increasingly in the industry to supplement wind tunnel data and optimize airplane designs.Airbus CFD code has demonstrated capability for solving flow problems such as flight 587 vertical stabilizer loads.

CFD Results: Pressure Distribution Over Vertical Stabilizer Chordwise Distance (mm)Pressure Coefficient

Left SideRight SideCFD Results: Streamlines of Flow at High Sideslip Angle

TimeBending Moment History During Second Wake EncounterLimit LoadUltimate Load (1.5 x Limit)Ultimate Load (1.5 x Limit)Bending Moment / Limit LoadLimit Load

Base ofVertical StabilizerBending Moment

TimeLimit LoadUltimate Load (1.5 x Limit)Ultimate Load (1.5 x Limit)Bending Moment / Limit LoadLimit LoadBending Moment History During Second Wake Encounter

Limit load: Highest load expected in lifetime

TimeUltimate Load (1.5 x Limit)Ultimate Load (1.5 x Limit)Bending Moment / Limit LoadLimit Load Determined by conditions specified in FARs

Limit LoadBending Moment History During Second Wake Encounter

Ultimate load: Equal to limit load times safety factor of 1.5

TimeLimit LoadUltimate Load (1.5 x Limit)Ultimate Load (1.5 x Limit)Bending Moment / Limit LoadLimit Load Structure must not break up to ultimate load

Bending Moment History During Second Wake Encounter

09:15:5009:15:5209:15:5409:15:5609:15:5809:16:00-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.5TAIL BENDS RIGHTTAIL BENDS LEFTTimeBending Moment History During Second Wake Encounter

Conclusions

Airplane encountered wake turbulence twiceIndicated by FDR, CVR, simulation, and wake analysis

First officers control inputs following second encounter were unnecessary and excessiveSimulation indicates wake had minor effect on motionAirplane was never in an upset condition

Airplane responded to control inputs as expected until vertical stabilizer separationSimulation indicates large sideslip angles were the result of control inputs

Vertical stabilizer separated at a bending moment load well above ultimate loadDetermined by wind tunnel and CFD analysis

National Transportation Safety BoardAmerican Airlines Flight 587Belle Harbor, New YorkNovember 12, 2001

NTSB Board MeetingOctober 26, 2004