This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Beluga XL is a transport aircraft that is used to carry large and heavy aircraft sections between Airbus facilities in Europe. Transported sections are mounted on jigs called TCUs (Transport Cargo Units) that assure safe restrain and transportation during flight and handling during manufacturing.



Loading and unloading process of Beluga XL is automated with power drive units (PDU) that move TCU’s in cargo hold, and Power Locking Units (PLU) that secure payload inside the cargo hold. PLU’s have a safety feature to deploy automatically in the case of the power loss.



During normal operation, PDU’s will slow down from 0.2m/sec to 0.05m/sec before PLU’s deploy and secure the TCU inside the aircraft.



In the case of accidental power loss or emergency stop, there is a possibility that a high speed moving TCU’s will be abruptly stopped against deployed PLU’s. This case can cause high accelerations and loads on transported section, jig and the aircraft that exceed normal design cases. Initial calculation of acceleration with simplified model estimated a value of 2.0g, exceeding the design value of 1.5g (limit). The high values were also confirmed by scaled down bench test.



After this initial assessment, a further analysis was launched in order to better quantify this effect and to take into account all relevant parameters. Initial model assumed single degree of freedom with stiff jig and CG at the same level as the Power locking Paws. A more refined model was created with 1.5 and then two degrees of freedom that takes into account jig stiffness. FEM was used to estimate the stiffness of the typical jigs. Also, a more representative test was requested on actual Aircraft and jig.



The two degree of freedom model with jig stiffness shows significantly reduced accelerations. The maximum calculated value is about 1.1g, below design values of 1.5g. The acceleration at jig CG is lower than for jig basement and the highest value occurs for the stiffest jig (A330 Centre fuselage section).



Due to this analysis and additional test it is concluded that this case does not represent a risk for payload, jig and aircraft. A potential costly and time delaying modification has been avoided. An upper limit of jig stiffness is specified in TCU interface specification in order to limit the maximum acceleration below 1.5g.