Engineering company in Turkey solves flight operator dilemma of increasing wing loads without limiting flight envelope.
Aircraft wing modal testing has played a significant role recently for RMC Engineering, a Turkish partner of data acquisition specialist, Dewesoft. Challenged with assessing the flight envelope for the aircraft of a local flight operator under different wing load conditions, RMC used modal testing and data acquisition and analysis to determine the natural frequencies of the wings and predict under which conditions undesirable wing flutter would occur.
With increased wing payloads affecting when flutter would occur, the company risked having to reduce flight speeds and heights and thereby narrowing the flight envelope and increasing flight duration and operational costs.
According to RMC, the flight envelope of the existing configuration of the aircraft was unknown and so the company performed wing modal tests both for the current and modified configurations during a restrictive time availability of just two days.
The tests had to be performed very quickly with preliminary modal analysis being performed on-site for data validation purposes. The whole data acquisition and excitation process was completed using Dewesoft Sirius data acquisition (Sirius HD and Sirius STG with analogue outputs) on a Dewesoft MS-440 modal shaker with 440N output force.
Sirius DAQ is a USB and EtherCAT data acquisition system designed to be flexible, modular, expandable and secure. The device prevents frequent errors during the measurement process and offers virtually unlimited configuration possibilities. Slices are available from 1 to 16 analogue channel configurations that can be daisy-chained together. An array of different analogue amplifiers is available giving the possibility to connect virtually any sensor.
The modal shakers enable the testing of larger and more complex structures and the use of various excitation signals. The Dewesoft series of modal shakers are lightweight and powerful with electromagnetic actuators, which can go up to 15 kHz and provide force levels up to 440N with a maximum 25mm stroke.
For the test, the wing was fitted with several Dynalabs 3002DE uniaxial accelerometers and a modal shaker was attached to the tip of the wing. With the structure modelled graphically within the software geometry editor, the excitation (input) and response (measurement) points were selected. The modal shaker provided force input and acceleration sensors measured the response. The test points were excited while the software collected the data. Burst random vibration was delivered to the wing and data collected for analysis.
The Modal test module was used to generate burst random signals to the shaker and preliminary mode shapes were animated by choosing the peaks in the Frequency Response Function (FRF) plots. FRF plots are automatically calculated during the measurements allowing visualisation of the phase and coherence of the measurement locations. Visualising the preliminary mode shapes provided confidence in the quality of the measurements. The detailed analyses were performed later in the RMC head office.
The Modal test module is part of the Dynamic Signal Analysis (DSA) package within the software and can be used to assess the overall results of the testing.
In the case of the Turkish operator, the analyses concluded that the aircraft could be used with the proposed payload modification without detrimental effect on the flight envelope. As the tests lasted for just two days, the operations of the aircraft were not severely affected.