A Mechatronics measurement system for ship air wake studies with uavs

This research focuses on the development of novel instrumentation system for wirelessly estimating ship air wake patterns in real-time. Air wake caused by the super-structure of cruising naval ships often leads to restrictive aircraft launch and recovery envelopes. Such flight envelopes are generally determined through actual flight testing which is frequently difficult to schedule, expensive, potentially hazardous and highly subjective. Currently, the launch and recovery wind limits and air operation envelopes are primarily determined via the subjective analysis of test pilots. The aim of this research is to experimentally determine air wake pattern to validate existing CFD air wake models.


The developed system uses a low cost UAV (i.e., RC helicopter) that is flown in the lee of a cruising naval ship and its attitude disturbances are monitored with an onboard IMU (Inertial Measurement Unit). Concurrently, the relative position of the UAV is determined by comparing the GPS derived position of the UAV with that of a reference position on the ship. Fig. 1 shows the ship and the RC helicopter used in the experiments. A USB powered pilot input receiver module was developed to read pilot inputs from the radio controller in the form of PWM signals. Fig. 2 shows the pilot input receiver module.


During underway flight operations, the ship's craft master attempts to keep the ship under the same relative wind over deck based upon the reference anemometer. The developed system uses a Back Propagation Neural Networks (BPNN) to predict the component of IMU readings arising from pilot inputs alone. This predicted IMU data is subtracted from the actual measured data to obtain the actual disturbance due to air wake. Fig. 3 shows overall architecture of the proposed system for air wake measurement.


IMU data and pilot inputs are recorded during these flights to calculate air wake and overlaid on the helicopter trajectory. Fig. 4 shows a sample air wake pattern generated from the system where the red regions depict high air wake and the blue color shows regions of low air wake.

 

HELI
Figure 1. Experimental Setup: (a) YP676 training vessel (Top),( b) Instrumeted RC Helicoper on Deck (Bottom).

 

 

 

Figure 2. Pilot Input Receiver Module.

 

 


Figure 3. Overall system architecture.

 


Figure 4. Ship air wake distribution for one of the test flights with wind direction of 15°.

 

 

 

 

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