HIRF and Lightning Aircraft Certification and Design

By Tim McDonald

This post describes why you would want to use an advanced simulation approach to HIRF and lightning aircraft certification and design.

The Problem

Hirf and lightning aircraft certification: Avionics Box from an Aircraft

  1. Design Phase: Vendors and avionics team needs to know the E3 transients/levels at their device interfaces
  2. Certification Phase: Need to know that the E3 transients/levels at each device is within the test and design level Hirf and lightning aircraft certification: SAE ARP 5412 and AC 20-158

And the E3 external environments must be applied to the entire aircraft to determine transients/levels at the equipment interfaces.

However . . .

  • The aircraft may not yet exist for testing
  • If it does exist, full-scale Lightning/HIRF testing is expensive
  • Full-scale  testing is complicated by the ground plane and return conductor system effects (ARP 5583 requires additional simulation support to full-scale testing)
  • A limited set of attachment scenarios, pins and cables can be practically assessed
  • What if there are design changes after the test?

Status Quo Approach to This Problem

In the past, groups may consider using test results from a previous aircraft project. A drawback to this approach is that the materials (use of composites) and bonding design may be significantly different between various aircraft. In addition, changes in the cable harness can change the interface transients by orders of magnitude.

Another approach would be to use simple analytical methods and apply a great deal of margin. A drawback is that if the estimate with excessive margin exceeds the existing COTS avionics equipment test levels, it results in a great cost, weight impact and schedule delay.

There are other CAD tools that may address the issue. However, they often suffer from poor CAD interoperability, lack validation heritage and cannot handle a full aircraft size. In addition, without harness co-simulation, the prediction may be incorrect by orders of magnitude.

Proposed Solution: EMA3D

Hirf and lightning aircraft certification: EMA3D is used for many major commercial air projects

EMA3D is a mature code that has been continuously under development since 1978 and has been applied to hundreds of systems. EMA3D is optimized for system level E3 including lightning and HIRF. EMA3D overcomes the limitations of other solvers noted above.

EMA3D CAD Interoperability

Hirf and lightning aircraft certification: F16 Model

The  EMA3D CAD environment is built on TranscenData’s CADfix. As a result, EMA3D inherits its features including CAD healing, automatic translation, and defeaturing. CADfix can import CATIA V4/V5, STEP, ProE, and almost all major formats.

CADfix has tools to quickly defeature and adjust geometry to capture important EM features of the model.

Actionable Predictions

Hirf and lightning aircraft certification: Flowchart Showing EMA3D Workflow from CAD to actionable predictions

The EMA3D work flow is described in the above flow chart. The distinguishing factor of EMA3D is the ability to provide transient predictions in a form that is directly useful by the certification or design program. The DO-160 levels are a concrete output from MHARNESS. An example of these predictions is shown below:

Hirf and lightning aircraft certification: EMA lightning prediction on a pin and the HIRF transfer function to a cable

EMA3D and MHARNESS can provide lightning and HIRF results that are directly comparable to DO-160 categories

Validation Heritage

Correlation between simulation and measurement is challenging. However, EMA3D has proven itself over many years on several important FAA certification programs. The McDonald Douglass MD-80 verification is shown below.

Hirf and lightning aircraft certification: The EMA3D simulation of the MD80 correlated so well with the measurement lightning transients that the FAA allowed the MD90 to forgo the usual lightning indirect effects testing on the full aircraft.

The EMA3D simulation of the MD80 correlated so well with the measurement lightning transients that the FAA allowed the MD90 to forgo the usual lightning indirect effects testing on the full aircraft.

Next, a validation for a GE engine controller is shown in the HIRF frequency band.

Hirf and lightning aircraft certification: These validation results for a GE FADEC for HIRF frequencies shows the correspondance between measurement (green) and test (red)

These validation results for a GE FADEC for HIRF frequencies shows the correspondance between measurement (green) and test (red)

Another classic validation of EMA3D is on one of the first carbon fiber fuel tanks. The validation is recorded in SAE ARP5415A. The impressive correlation of EMA3D and measurements is noted as a guide for future tank certification programs.

Hirf and lightning aircraft certification: saab fuel tank 1

Hirf and lightning aircraft certification: saab fuel tank 2

EMA3D is listed in the SAE Aerospace Recommended Practices guidelines as a method of determining component level lightning indirect effects transients (SAE ARP 5415 pg 152). Recent commercial, military, and NASA programs each have similar validation programs with successful correlation between simulation and measurement.
Recently, EMA has improved our cable harness solver to achieve impressive correlation with a DO-160-style tabletop measurement of bulk current injection. You can read more about the details here.
Hirf and lightning aircraft certification: The correlation of a DO-160 Test
EMA Demonstrates the Correlation of an MHARNESS Simulation and a DO-160-style Cable Measurement

Integrated MHARNESS

Hirf and lightning aircraft certification: MHARNESS, multi-branched, multi-conductor, multi-shield

Co-simulation with MHARNESS is now possible in EMA3D. In the lightning environment, MHARNESS gives transients at the pin level with greater accuracy. In HIRF simulation, integrated MHARNESS is essential in order to obtain the correct result. The code considers mutual interaction of wire harnesses with aircraft structure and other wire harnesses. This interaction is critical for accurate simulations. EMA3D version 4 has this simulation capability with the purchase of an MHARNESS license.

Simulation Platform Size

EMA3D is parallel with extremely efficient scaling on computational clusters. The cluster version of EMA3D has been successfully used by EMA and major aerospace partners to simulate entire aircraft in the lightning and HIRF environments.

Hirf and lightning aircraft certification: The surface currents on a 777 aircraft

Benefits of Simulation as a Method of Compliance

  1. Cost Benefits – $2.2 M savings estimate based on MD-90
  2. Schedule Benefits – Can begin effort now in parallel with design work
  3. Accuracy Benefits – No return conductor system to alter the results as in a lab test
  4. Synergies with Design Optimization and Parametric Studies – Full range of studies available with complete model
  5. Future Savings for Aircraft Modifications and Projects – Once the simulation approach is validated, it can be used for future projects

 

Synergies with other E3 Environments

An advantage of using EMA3D is that lightning and HIRF analysis can be performed on the same model. Other electromagnetic environmental effects (E3) that may also use EMA3D include:

  • P-static
  • Avionics design
  • Antenna placement and design
  • Electrostatic discharge
  • Fuel system lightning protection

 

Proposed Solution: EMA3D

Hirf and lightning aircraft certification: ema3d main logo

EMA3D improves on accuracy compared to using previous aircraft measurements, results from aircraft with different harness runs, unsuitable analysis or full-scale measurements. EMA3D overcomes limitations of other simulation tools. When combined with expert users, EMA3D provides predictions of aircraft in E3 environments with good correlation to measurement