High speed ditching facility

Scope

The High Speed Ditching Facility (HSDF) is built to perform water entry tests with a horizontal velocity component up to 48 m/s with a vertical/horizontal velocity ratio in the range from 0.03 to 0.05. The facility was designed and built during the EU-funded FP7-SMAES project and it was further developed and extended in its potentialities during the H2020-SARAH project. The facility makes it possible to test plates, bodies, or structural components in conditions close to those occurring during the aircraft ditching event. It is composed of a guide, 64 m long, suspended over the Umberto Pugliese towing tank by five bridges. The guide can be rotated to achieve different vertical/horizontal velocity ratios. The specimens to be tested are firmly connected to the acquisition box towed by a trolley running along the guide. The acquisition box and the specimen can be rotated to allow the impact at a pitch angle in the range from 4 to 16 degrees.

The trolley is accelerated by a catapult composed of a total of 8 elastic cords. The cords are attached to a U-shaped bar which embraces the trolley and accelerates it to the final speed. Shortly before the impact point, a braking system acts on the U-shaped bar so that the trolley is left free to impact the water. The total mass of the system composed by the trolley, acquisition box, and specimen is between 850 kg and 900 kg thus making the velocity reduction during the test generally negligible (less than 1%). When the leading edge of the specimen arrives at the still water level and touches the water, the front faces of the specimen and of the acquisition box impact the water and the velocity drops sharply; next, a damping system absorbs the remaining energy. The test velocity is controlled within +/- 0.5 m/s by adjusting the release point of the catapult and compensating in this way the loss of strength of the elastic cords. The use of the elastic cords to accelerate the trolley does not allow to control the test speed very precisely and thus a careful assessment of the test repeatability was conducted soon after the installation.

The onboard acquisition system can acquire up to 40 channels at 200 kS/s. Measurements can be done in terms of accelerations, pressures, loads, and strains. The measurements are supported by the underwater movies done by a high-speed camera operated at 3000-5000 fps, depending on the specific test conditions.

Main characteristics

Horizontal Test Speed (max)	47 m/s
Vertical/Horizontal velocity ratio	0.03-0.05
Specimen size (typical)	1200 mm (L) 650 mm (W)
Available measurements	Loads, Pressures, Strains, Accelerations, Underwater visualization
Number of channels	40 at 200 kS/s