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High Speed Ditching Facility - SMAES

The SMAES project (Grant Agreement 266172 - FP7-AAT-2010-RTD-1) is aimed at improving the capabilities of simulations tools in simulating the aircraft ditching event. Such tools are used by aircraft developers from pre-project phase to certification. As reported on the project web site www.smaes.eu, the key developments are:

  1. Improved models for the calculation of ditching loads including both analytical and detailed fluid dynamics models. Inclusion of the effect of the complex flow physics in ditching is critical to prediction of ditching loads.
  2. Reliable and predictive aircraft models for structural behaviour under dynamic fluid loads.
  3. Demonstration of the methods on representative future aircraft design concepts.

Within this project CNR-INSEAN is responsible for the execution of guided ditching tests on aluminum and composite plates. The tests are aimed at providing to the consortium a wide dataset for validation of the computational tools. The experimental configuration was proposed by one of the industrial partners of the project, Airbus Military, who considered very important to conduct experiments at almost full scale velocity in order to avoid the complicate scaling of all the physical variables involved. The test conditions have been agreed between CNR-INSEAN, Airbus Military and DLR.

High Speed Impact Facility

Within this context, a new high speed ditching facility has been designed and built at INSEAN, which is able to perform tests at horizontal velocity in the range 30 to 50 m/s. The facility is composed by a guide, total length of about 64 m, suspended over the INSEAN towing tank #1 by five supports. The guide can be inclined in order to achieve the same vertical velocity component, 1.5 m/s, independently of the horizontal component. The specimens to be tested are firmly connected to a model which is towed by a trolley running along the guide. The total mass of the model with all the instrumentation is about 200 kg, and the total mass of trolley and model together is about 800 kg. The trolley is accelerated by a catapult composed by a total of 8 elastic cords. The cords are attached to a U-shaped bar which embraces the trolley and accelerate it to the final speed. This is a rather massive component as the U-shaped bar is about 300 kg and each elastic cord is about 130 kg. In order to prevent any interference of the acceleration system on the test, shortly before the impact point the braking system on the U-shaped bar enters into play and the trolley is left free to impact the water. When the plate touches the water, a jet developes which propagates along the plate. For the purpose of the SMAES activities, the experiment is over once the jet root (and the correspongind pressure peak) arrives at the forward edge of the plate. At that time, the flow is free to move upwards and a intense spray develops which is hitted by the model advancing. This effect, together with the flow associated to the displacement of the water in front of the model, provides the high horizontal loading needed to reduce the speed of the model before the end of the guide. In the last portion of the guide a set of tyres is put to absorb the remaining energy. The catapult is charged by a winch that tow an auxiliary trolley which holds the main trolley through a pincer kept closed by an hydraulic piston. The auxiliary trolley is equipped with two ratchets which are used at the launch time to hold the system locked onto the teeth located at regular distance along the guide. The release point is selected in order to achieve the desired impact speed and to compensate in this way the loss of strength of the elastic cords. For safety reason the facility is operated remotely from outside the building with two web cameras are used to look at the ratchets and at the release point. Below a top view of the facility is provided together with pictures taken during the test execution.

Instrumentation on board

The model is equipped with an on board acquisition system which is operated through Remote Desktop. The system is composed by a ragged Dewesoft-SBOX PC with a 100 GB SSD, 4 Dewesoft-SIRIUS modules (8 analogic chs, 8 digital chs, 1 CAN port) and one DEWE43 (8 analogic chs, 8 digital chs, 2 CAN ports). Measurements are taken in terms of pressure (18 probes, Kulite XTL 123B, 300 psi full scale range, sampled at 200 kS/s), accelerations (2 Kistler M101 and 2 Kistler M301A, 1000 g range, sampled at 20kS/s) and strains (6 or 8 biaxial rosette are used depending on the plate thickness, sampled at 20 kS/s). The total forces acting on the plate are measured by 4 cells for the vertical components (Kistler 9343A) and 2 cells for the horizontal direction (Kistler 9363A). 

Additional details

Movies

Top view of the ditching facilityTop view of the ditching facilityTest Sequence - 1Test Sequence - 1Test Sequence - 2Test Sequence - 2Test Sequence - 3Test Sequence - 3Test Sequence - 4Test Sequence - 4