Multiterrain Vertical Drop Tests of a Composite Fuselage Section

Abstract

A 5-ft-diameter composite fuselage section was retrofitted with four identical blocks of deployable honeycomb energy absorber and crash tested on two different surfaces: soft soil, and water. The drop tests were conducted at the 70-ft. drop tower at the Landing and Impact Research (LandIR) Facility of NASA Langley. Water drop tests were performed into a 15-ft-diameter pool of water that was approximately 42-in. deep. For the soft soil impact, a 15-ft-square container filled with fine-sifted, unpacked sand was located beneath the drop tower. All drop tests were vertical with a nominally flat attitude with respect to the impact surface. The measured impact velocities were 37.4, and 24.7-fps for soft soil and water, respectively. A fuselage section without energy absorbers was also drop tested onto water to provide a datum for comparison with the test, which included energy absorbers. In order to facilitate this type of comparison and to ensure fuselage survivability for the noenergy-absorber case, the velocity of the water impact tests was restricted to 25-fps nominal. While all tests described in this paper were limited to vertical impact velocities, the implications and design challenges of utilizing external energy absorbers during combined forward and vertical impact velocities are discussed. The design, testing and selection of a honeycomb cover, which was required in soft surface and water impacts to transmit the load into the honeycomb cell walls, is also presented. IntroductionHelicopter designers face major challenges in establishing crashworthiness due to the multitude of possible impact orientations and the unknown morphology of the crash site, with surfaces such as concrete and water being at the extreme. For hard and non-yielding impact surfaces, the vehicle's kinetic energy has to be managed by the airframe, and internal and/or external energy absorbing devices to ensure load attenuation and adequate post-crash cabin volume. Often, legacy airframes have little or no internal structure designed for crash energy management. Consequently, external energy absorbers with large stroke capability are often necessary.

Design and testing of crashworthy aerospace composite components

“…On ground impact it is triggered to unfold into a block of honeycomb, which then crushes down to absorb crash energy, thus protecting the fuselage. The device has been retrofitted on an MD-500 helicopter and two full-scale crash tests were carried out with and without the DEA with velocity components 7.9 m/s (26 ft/s) vertical and 12.2 m/s (40 ft/s) horizontal [25]. It was found that the helicopter with the DEA showed no structural crash damage, whilst the baseline helicopter had damage to keel beams and subfloor structure as well as buckled and fractured seat frames.…”

Overview of the NASA Subsonic Rotary Wing Aeronautics Research Program in Rotorcraft Crashworthiness

“…This drop test was conducted to evaluate the energy attenuation capabilities of the deployable concept for water impact and to generate test data for correlation with analytic models. More details on this test are reported in the paper by Kellas et al (2008). A 15-ft-diameter pool, filled to a height of 42 inches, was located beneath the drop tower.…”

“…These results demonstrate the importance of mesh discretization studies when using the SPH method for simulating water impact. Soft Soil Impact As a final evaluation, the composite fuselage section retrofitted with four blocks of the DEA was impacted onto soft soil (sand) at 37.4-fps, as reported in Kellas et al (2008). A 15-ft x 15-ft wooden box was built and located beneath the drop tower.…”

Crash simulation of fuselage section in the rebound process and the secondary-impact process

“…The Italian Aerospace Research Centre recently conducted a drop test of a full-scale fuselage section of a regional aircraft made entirely of composite materials (Luigi et al, 2019). In addition to the drop tests of the fuselage section, the impact tests of the subfloor structures were also carried out to investigate energy absorption capacities and impact loading responses (Waimer et al, 2017;Sturm et al, 2014;Kellas and Jackson, 2010). These experiments have facilitated the development of various research topics aimed at improving crashworthiness of aircraft.…”