Ship motion pitch and roll limits are often developed for helicopters on ship decks to ensure peak loads at airframe tie-down points are not exceeded. However, the cyclical loading on the airframe due to ship motion and the effect on aircraft fatigue is generally not taken into account.
Using OnDeck AVT can develop an estimate of the load spectrum that is likely to be applied to a helicopter over a period of time in a given seaway. Load spectrums may be developed from simulated undercarriage loads, tie down point loads or restraint system loads (RAST, ASIST).
During any one day a ship may pitch and roll around 8,000 times and the effect this has on accumulative fatigue damage can be of concern, particularly for helicopters not designed for maritime operations. By computing the stress levels in each component and using a S-N curve for the material the number of allowable cycles may be determined. Detailed knowledge of the structure is required for this later step.
AVT has conducted fatigues analyses for the Black Hawk.