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The airworthiness certification authorities specify overall probability levels for catastrophic and less severe effects on aircraft and their occupants. In lightning standards concerning threat levels and zoning for lightning attachments we speak of high and low probabilities. But, despite the certification authority’s overall figure, only one attempt has been made to interpret what that figure means for lightning protection. That one attempt was made under the EC funded FULMEN programme to estimate the degree of accuracy needed in the process of aircraft lightning attachment zoning. Without some figures, how do we know how good our designs have to be. Furthermore, as the number of flight-safety critical systems on our aircraft increases, how does the probability of failure of each change to ensure the overall figure remains the same?

In the frame of the European project CATE (Composite and Advanced Aircraft Technologies Electromagnetic Protection), a full CFC mock-up has been designed and manufactured. Both measurements and computations have been carried out to investigate and to assess the coupling mechanisms throughout CFC structures. Different aspects have been covered: effects of apertures, effects of metallic devices, effects of protection on cables, … The understanding of the physical phenomena involved enables the formulation of general rules of protection which can be applied on very large aircraft at lower cost.

It is a view held by many, but not all, that whole aircraft testing for measuring levels and waveforms of induced cable currents and voltages should be carried out at moderately high levels of imposed external threat. The reason for this proposal is that the are a number of effects occurring during the passage of a lightning strike that will result in different cable transient amplitudes and wave-shapes, depending upon whether certain current or voltage thresholds are exceeded. These are the so-called non-linear effects. In this paper we argue that it is neither practicable nor technically correct to attempt to emulate these effects and test at very low injected current levels.

Lightning induced current and voltage pulses are defined in international standards as arising from three distinct coupling mechanisms: capacitive, inductive and resistive. These mechanisms at their simplest give rise to distinct characteristics in the induced wave-shapes relative to the lightning current pulse that caused them. It has long been the practice to decide from a particular induced wave-shape, which was the likely induction mechanism, and compare it in terms of peak amplitude only with the relevant qualification test waveform. This approach fails to take account of the fact that almost all induced waveforms are actually a sum of two or all of the coupling mechanisms, that the coupling is not simple but gives rise to much more complex wave-shapes than the qualification standards would imply, and that there are other critical parameters apart from the peak amplitude. It may also disguise the effect of possible building/rig resonances in test results.

During the System Development and Demonstration (SDD) phase of the F-35B Joint Strike Fighter (JSF) program it is a requirement to prove that the JSF aircraft can operate within existing military environments. Thus it is necessary to prove that the JSF aircraft can operate out of the same airfields, off the same aircraft carriers, and from within similar expeditionary environments that the USAF/USN/USMC and Royal Navy/Royal Air Force currently operate their existing fleet of aircraft. A major element in achieving this requirement is to determine the effect of the JSF STOVL variant’s hot JSF core jet efflux on the surfaces from which the aircraft is likely to operate. It is necessary to quantify potential damage to these surfaces (from a maintenance point of view) and establish whether the damage will be hazardous to the aircraft and/or ground crew/equipment. In order to fulfil this requirement a method of testing and accurately measuring surface erosion is needed.

This paper presents a detailed summary of the JSF STOVL Hot Gas Ingestion (HGI) sub-scale test program. It focuses on the System Demonstration and Development (SDD) phase of the JSF Program, where significant advances in the fidelity of testing have been made. It documents the improvements and refinements made to the dedicated test facility and powered wind tunnel model required for HGI testing. The paper covers an introduction to JSF and HGI, wind tunnel model hardware development, propulsion system calibrations, validation and understanding of the STOVL flow-field including comparison to full-scale data and test facility improvements. These improvements are also given perspective as the paper explains their practical effect in increasing the fidelity and confidence in the sub-scale test data, which will ultimately be used to support flight clearance for the F-35B aircraft.