Early aircraft designs typically consisted of a series of cables, chains, cranks and various other mechanisms to operate the systems which made the aircraft fly.  Although these systems were considered “state of the art” at the time, they were plagued with inaccuracy and reliability issues.  Due to increasing advancements in the field of electronics over the last 60 years, mechanical flight control devices are being replaced or augmented with electronic circuitry for enhanced accuracy, reliability and, most of all, human safety.  However, these changes give rise to myriad new concerns related to electromagnetic interference (EMI) of critical on-board electronic systems.

These concerns are based on the phenomena where electronic circuitry fails to operate as intended (i.e. becomes susceptible) when exposed to high levels of electromagnetic radiation. Therefore, the need for EMI testing has never been more important for all commercial and military aircraft in use today. High Intensity Radiated Field testing, commonly referred to as HIRF testing, is designed to verify and ensure safety during flight and landing of new and/or modified aircraft. In accordance with SAE ARP5583 Guide to Certification of Aircraft in a High-Intensity Radiated Field (HIRF) Environment can be conducted using high-level or low-level test methods.

High Level Tests are performed using peak and average field levels determined for one of three particular HIRF environments over a test frequency range up to 18 GHz. This process uses a direct drive method up to the first airframe electrical resonance, and a radiated field test methods above the first airframe resonance. High level tests are used to verify the aircraft’s “safety of flight” controls maintain critical functionality while exposed to the simulated HIRF environment. This requires several factors to be considered prior to testing such as the need for specialized high power test equipment, aircraft system instrumentation and flight emulation, RF hazards regarding fuel ignition and personnel exposure and adherence to national RF transmission rules and regulations. Often times the aircraft size prohibits the use of conventional anechoic lined EMI test chambers and special permits are required for performing the testing process outdoors. However, this will usually be accompanied with limitations on power levels and/or frequency selection.

Alternatively, Low Level Tests can be used to determine the transfer function between the external RF environment to the aircraft’s internal wire bundles or fuselage. This approach is preferred over high level testing for its reduced RF exposure levels and RF hazard considerations.  However, the Low level test requires a complex analytical modeling approach to ensure compliance. Generally, 2-D and 3-D computational models of the airframe up to the first electrical resonance are required. Models are required to estimate the level of influence ground plane coupling will have on low level swept current test results, especially where it is impractical to elevate the aircraft safely due to its size.

The NTS system innovation team has developed and implemented automated test profiles using Totally Integrated Laboratory Environment software (TILE), and computational modeling profiles utilizing Microwave Studios software through Computer Simulation Technologies (CST). NTS is fully equipped to achieve the most severe HIRF Environments specified in SAE ARP 5583, accompanied by a staff that is highly experienced with complex in situ testing programs.  Additionally, NTS/Lightning Technologies Inc. (LTI) is one of the world’s leading experts on direct effects lightning on aircraft, and has performed lightning qualifications on virtually every aircraft type in flight today. NTS is the only organization in the world to offer aircraft-level testing for both HIRF and Lightning. Please contact us for more details at www.nts.com

Expanding our service offerings for customers in the aerospace and defense industries, NTS Santa Clarita has recently broadened its portfolio of service offerings to include Fuel Component Testing services. The new Fuel Component Testing site is used for the development and qualification of fuel line parts and subsystems. Any individual device or subsystem that is part of an engine or fuel system – such as fuel pumps, hydro-mechanical fuel controls and shutoff valves – requires qualification testing to the RTCA DO-160 environmental standards for airborne equipment or the Mil-Std 810 environmental standards for a broad range of military equipment. The new fuel testing site recently installed at NTS Santa Clarita is a state-of-the-art facility for simulating the most stringent environmental conditions.

Specifications of the new Fuel Component Testing facility at NTS Santa Clarita:

• Fuel capacity of 2500 gallons
• Fuel super-cooling with three 30-ton refrigeration systems with capability to cool below – 65°F
• Fuel heating capability to 135° F or higher
• Fuel polishing capability to Level 2 cleanliness standards
• Three separate fuel component test loops with flow capacity ranging from 500 to 1,000 GPM
• The ability to combine loops for higher flow rates
• Modular to allow simultaneous set-ups at the same facility
• Adequate room for future expansion and modification
• State of the art DAC and control system

The new Fuel Component testing services at NTS Santa Clarita are currently online and available to customers. More information can be found at www.nts.com or by calling 1-800-270-2516.

Jeff Viel our Director of EMI/ Engineering for NTS Boxborough, MA is a US Marine Veteran, bringing 20 years of industry-specific knowledge and experience. Jeff has a BSEE from North Eastern University and 14 years with NTS.

A question that is often asked of Jeff is, “Will a COTS power supply pass MIL-STD-461 Testing?

This is a difficult question to answer, but in most cases I would say no, not without a few modifications. The main reason for this is due to test requirement variances between defense and commercial standards.

For example, MIL-STD-461 uses Test Method CE102 to evaluate the conducted emissions levels on a product’s input power lines similar to methods described in CISPR and FCC. Both utilize 50 uH LISNS of similar type construction, and relatively similar resolution bandwidths. However one notable difference is MIL-STD-461 requires peak detection, versus quasi-peak, and average detection to capture the worst case emissions envelop.

A second notable difference is that the MIL-STD-461 CE102 conducted emissions measurements start at 10 kHz, where most commercial specifications do not perform this measurement below 150kHz. Based on these commercial certification requirements almost all COTS power supplies switch below 150kHz, many even switch as low as 70-75kHz, so that the 2nd harmonic of the switching frequency is also below the 150kHz limit. This requires less lowpass RF filtering to meet the commercial specs, thus reducing the cost to build and reducing the chances of failing costly EMI testing. However, as a result of these design implementations, measurements between 10 kHz and 150 kHz are generally problematic.

A common solution is to tune the power line filter to a lower cutoff frequency in an effort to provide adequate switching noise suppression. How this is done depends on what procurement group it is being sold to. The U.S. Navy has strict limitations on the amount of line-to-ground (common-mode) capacitance a power line filter can have. Line-to-ground capacitance for each line shall not exceed 0.1 microfarads (μF) for 60 Hertz (Hz) equipment or 0.02 μF for 400 Hz equipment. For submarine DC-powered equipment and aircraft DC-powered equipment, the filter capacitance from each line-to-ground at the user interface shall not exceed 0.075 μF/kW of connected load. For DC loads less than 0.5 kW, the filter capacitance shall not exceed 0.03 μF. In these cases, the limitation on common mode capacitance will require the introduction of bulky series inductive chokes to achieve the same performance.

The added weight, cost, and footprint restrictions are all common challenges which must be resolved prior to becoming certified to MIL-STD-461. If pre-compliance test data is available which shows the frequencies, and amplitudes which need to be attenuated, a series of band-reject (Notch) filters can be implemented. This will substantially reduce the size and weight of the compliance filter as it is only attenuating the discrete frequencies of interest.

If you are interested in more information related to this question or have any others for Jeff you can contact him at Jeff.Viel@nts.com

The market for umanned aircraft systems (UAS) has exploded in recent years and NTS has been there from the beginning, conducting test programs for UAS components, systems, payloads, and completely integrated air vehicles for such clients as the US Air Force and Boeing. “Since UAS manufacturers focus primarily on constructing aircraft, they look to outside partners like NTS to design and test pods and payloads, the components that give UASs much of their functionality”, says Mike Mindt, NTS Aerospace Marketing Director.

In December 2010, we increased our capabilities when we acquired Mechtronics Systems Incorporated (MSI) in Albuquerque. As a result, NTS Engineering Services can provide a complete suite of design, development, and testing services for pods and payloads for UASs, as well as prototype design, integration, and limited production for field trials.

This year, the Federal Aviation Administration (FAA) streamlined the process by which public agencies can apply for authorization to operate UAVs and increased the length of the authorization from one to two years. These less stringent regulations will allow federal, state, and local government agencies to more quickly launch UAVs for such purposes as aerial photography, surveillance, monitoring forest fires and environmental conditions, and protecting our nation’s borders and ports.

Mike Mindt, Marketing Director for Aerospace at NTS, explains the unique position NTS Engineering Services finds itself in at the beginning this new era in UAV flight and widespread adoption of the technology.

The NTS Engineering Services group offers complete engineering solution support from concept to prototype for everything from test equipment; fixtures; hydraulic and complex electro-mechanical systems.

NTS Pittsfield, formerly Lightning Technologies, Inc. (LTI), is among the newest members of the NTS family and is one of the world’s most complete simulated-lightning test laboratories. The specialized and unique equipment at NTS Pittsfield can duplicate all of the electrical characteristics of natural lightning as well as the transients it induces in electrical and electronic systems.

When an object is struck by lightning, it can instantly be heated to temperatures of 20,000°C or more and experience a jolt of electricity of 250,000+ amperes. But the problems aren’t restricted to direct hits; a component that’s up to a kilometer away from a lightning strike can suffer damage from the electromagnetic fields that travel through the earth. Knowing what kind of damage a component will sustain directly or indirectly from a lightning strike is a vital part of the design process. Engineers at NTS Pittsfield study the effects of lightning upon a structure or system by isolating the components of the lightning waveforms and electromagnetic fields and evaluating their effects through individual simulations.

The obvious field for this sort of testing is aeronautics because it’s imperative that aircraft continue to function after lightning strikes to ensure the safety of passengers and cargo. Mike Dargi, General Manager at NTS Pittsfield, explains. “What we do revolves around aircraft certification and studying the effects of direct lightning hits on components such as radomes, antennas, wing skins, fuel tanks, and areas on the fuselage. These need to be protected, and the protection needs to be verified.”

They also measure the indirect effects of lightning on aircraft and components. “We do testing on full aircraft by putting low-level lightning currents through the airframe and measuring the induced transients, voltages, and currents on the wiring. From these measurements we can determine if the shielding is adequate and can be certified.”

Mr. Dargi reports that other industries can benefit from lightning testing. “Since golf course irrigation systems are often computer controlled they can sustain damage by a direct or indirect lightning strike, so we work directly with the manufacturers of these types of systems. We also work on government ground-based radar installations, both on the engineering and testing sides, and we’ve tested the effects of lightning on buried fiber optics cable for the telcom industry.”

NTS Pittsfield has also done work for the entertainment field. “We’ve done some filming here for the Weather Channel, Discovery Channel, National Geographic and a few others,” Mr. Dargi recalled. “Recently, we did some filming for a London production company working on a new program for Discovery about the Bermuda Triangle. A Cessna had disappeared there a number of years ago and they wanted to test some theories about how lightning may have led to a crash.” NTS Pittsfield has also worked with the Walt Disney Company to test attractions at EPCOT and Typhoon Lagoon, as well as the zip line that an actress portraying Tinker Bell rides during the nightly fireworks display in the Magic Kingdom.

The engineers at NTS Pittsfield are devoted professionals who bring both expertise and an insatiable curiosity about lightning and its effects to their work. Adds Mr. Dargi, “For our engineers, it’s not just a job or a career, it’s a passion.”

For further information on Direct and Indirect Lightning please visit http://www.nts.com/services/lightning.