Testing Sliding Electrical Contacts for Aerospace Applications Using NI LabVIEW and National Instruments Data Acquisition Hardware

Author(s):
Jon Moore, Ph.D. - Defense Holdings, Inc.
Daniel Alley, Ph.D. - Defense Holdings, Inc.

Industry:
Aerospace/Avionics

Products:
LabVIEW, DAQPad-6016 for USB w/Screw Term

The Challenge:
Developing and building a cost-effective platform for running long-term tests on the sliding electrical contacts of a propeller deicing system while simulating Navy aircraft flight profiles.

The Solution:
Using National Instruments data acquisition hardware and NI LabVIEW software to build a complex test system that is affordable, flexible, and capable of handling all necessary measurements and simulations.

Defense Holdings, Inc. (DHi), a National Instruments Alliance Partner, developed and manufactures an innovative electrical contact known as the metal fiber brush (MFB). MFBs offer significant advantages over graphite brushes, an older technology currently used in aircraft and other applications. MFBs have a lower contact resistance than graphite brushes, so they can carry more electrical current in the same area. They are flexible, so they maintain better contact as they slide along a surface and do not crack or break. They also wear at a slower rate and create less wear debris reducing the frequency of periodic cleanings.

In 2003, we began working with the U.S. Naval Air Systems Command (NAVAIR) to develop new sliding electrical contacts for use in airborne systems. NAVAIR had previously reported a variety of problems stemming from their use of graphite brushes in the propeller deicing system. In the old system, brushes pass current from the main electrical system to the propeller by sliding on metal tracks called slip rings that are attached to the propeller. Navy maintenance personnel reported that graphite brushes were wearing very quickly as they slid on the slip rings, often chipping or breaking. Also, the graphite dust created as the graphite brushes wore, if not cleaned regularly, mixed with oil and hydraulic fluid and built up in the deicing system. This build-up of dust and fluids, which can be electrically conductive, shorted-out the deicing system, causing fires in the front of the aircraft. Under the federal Small Business Innovative Research (SBIR) program, we were contracted to develop state-of-the-art electrical contacts that would solve the Navy’s problems. 

Brushes operating in aircraft propeller deicing systems face several challenges:

•         The low amount of moisture in the air at high altitude

•         Temperature changes affecting system operation between sea level and flight altitude

•         Vibration and run-out of the slip ring due to propeller vibrations and thrust

•         Hydraulic fluid contamination from leaking seals in the vicinity of the brushes

To predict the performance of MFBs in this environment, it is necessary to collect information on the current flowing through the system, the voltage drop across the brushes, the temperature and wear of the brushes, air temperature, and system vibration coupled with the introduction of hydraulic fluid contamination into the system. During the planning stages for this project, DHi determined that our researchers needed to conduct tests under conditions that simulated the high altitudes typical of Navy aircraft missions. Using in-house technical expertise, we built our own testing apparatus to simulate the varying system and environmental parameters of the aircraft deicing system while recording all the relevant performance factors. 

Prior to adopting the NI platform, brush testing measurements were recorded by hand and transcribed into spreadsheets for graphing. Data was taken only when personnel were available, and testing was usually stopped overnight. Several years ago, we incorporated LabVIEW and NI hardware into our brush testers, to automate data recording and run tests unattended 24 hours a day. Unfortunately, these testers were only designed to run at ambient temperature and pressure. A new tester that analyzed brush performance in environments simulating high altitudes would require exceptional control over the environment and operating conditions. This, in turn, would require an unprecedented number of controls and sensors for the tester to function as envisioned.

During development of the tester mechanisms and electronics hardware, we designed subsystems to use isolated controls for the current supply, vacuum pump, heater, chiller, drive motor direction and speed, gas inlet valves, control panel lights, and instrumentation controls. We developed custom electronic hardware containing various amplifiers, filters, and protection circuits, because of the combination of low-level voltages and high currents. The data acquisition system allowed feedback for rotational speed and temperature and included many digital status indicators and analog readings for current, wear, voltage drop across brushes, pressure, motor control feedback, and temperature measurements. In total, we determined that at least 12 analog inputs, two analog outputs, and 30 DIOs were necessary. We chose the NI DAQPad-6016, because it was capable of accommodating all these signals in one cost-effective, USB-connected device.

Using LabVIEW, DHi created control software that can be used to execute long sequences of temperature, current, air pressure, and rotational speed changes to simulate flight profiles carried out by aircraft during their missions. This is critical to the current and continuing success of our brush development program. Without automated testing of this sort, test parameters could only be changed when personnel were available, severely limiting the effective test time available. This automation also ensures that tests are uniform for each new design, making comparisons of their relative performance meaningful.

The tester software employs tab controls to display different sets of indicators and graphs for data visualization as well as for programming the timing of changes in altitude, temperature, and rotational speed. This tester can perform the needed measurements while simulating the altitude and temperature changes of an aircraft in flight. The automation of this testing was accomplished by using LabVIEW and NI data acquisition hardware and permitted continuous testing of the brushes. This sped up the testing during development, compressing what would have taken weeks of actual flight time into days. These tests also served to prequalify the components in the laboratory before installing them on Navy aircraft.

The development of this tester and the success of our testing program directly contributed to the award of further government funding for this project and the progression of our brushes to ground-based testing and eventually to flight testing on U.S. Navy aircraft.

Author Information:
For more information on this Case Study, contact:
Jon Moore, Ph.D.
Defense Holdings, Inc.
US
Tel: (434) 295-2478
jmoore@dh-inc.com

Browse All Case Studies »