Flight testers work towards compatible growth with commercial spectrum demands

  • Published
  • By Laura Mowry
  • Staff writer
EDWARDS AIR FORCE BASE, Calif. --  In 1963, Don Thomson, an early instrumentation engineer at Edwards was quoted saying, "a good performance and flying qualities engineer isn't worth his salt if he needs more than 50 parameters for a single engine aircraft."

Fast forward 50 years and flight test for the single-engine F-35 Lightning II routinely includes up to 250,000 parameters.

At the time, we could not imagine how complex weapon systems would become, nor could we anticipate the massive amounts of data that would be measured and transmitted when conducting present-day flight test.

Aeronautical telemetry, which allows data to be measured and transmitted wirelessly from remote locations, plays a critical role in executing flight test. It is also used for atmospheric research, satellite communication and space launch vehicle monitoring - all requiring radio frequency (RF) communications.

"We use RF wireless telemetry here at Edwards to collect data from airplanes and transmitting it to the control rooms," said Tim Chalfant, Chief of Instrumentation for the 412th Test Engineering Group. "We have been using RF telemetry to safely and efficiently conduct flight test since the early 1960's. Before that we used other forms of telemetry, including the pilot's voice-over radio, which was much more limited than what we use today."

For the flight test community, telemetry allows testing to be completed safely and efficiently, keeping costs down and greatly benefiting the warfighter.

"All the data that flows from the airplane to the antenna to the control room moves very quickly through a certain RF frequencies. One airplane will be on one frequency while another airplane is on a different frequency. It's just like different cars listening to different radio stations. They can't all be on the same frequency because they would interfere with each other," said Doyle Janzen, 412th Range Squadron director.

"We take up a certain amount of spectrum; just like in your car when you tune into your radio station. You may tune to one center frequency but the radio station signal deviates the frequency based on the music signal to occupy a channel. It's not just one precise frequency; it's a bandwidth of frequencies," he added. "The same principle applies to our telemetry. Faster data requires a wider occupied bandwidth. Each band we use, like AM or FM on your radio has a fixed bandwidth capacity. This limits the number of airplanes that can fly at a particular time."

While the technology was developed and introduced during the 1960's, the amount of data recorded and transmitted continues to increase each year. With technological advancement and increases in system complexity requiring more data faster, the demand for available spectrum will continue to rise.

"Back in the early 1960's we used very low data rates. We were maybe talking about a dozen parameters, which could be anything we measure from temperature to pressure or an event. We only had a handful of parameters because of the technology we were testing and the technique we were using to transmit data over the RF link. Since then, data rates have grown exponentially," said Chalfant.

Today, in addition to growing data rates, the telemetry frequency bands used for flight test are increasingly sought for personal communication with wireless web devices and cellular telephones, as well as digital audio and video broadcast.

"Back in the 1970's the only thing I can recall having that operated wirelessly was maybe a garage door opener. Today, everything is wireless. Back then, all this spectrum was available and here at Edwards we were using it without a care in the world. The question now becomes, what do we do when we don't have enough frequencies anymore? This is an issue that is important to the future of flight test," said Janzen.

As the world becomes more and more connected and dependent on wireless technologies; aeronautical telemetry bands, currently operating at capacity in several regions, are increasingly threatened by the interference from emerging commercial interests.

That means the potential for an increase in mission delays or cancellations due to lack of available spectrum, which ultimately could lead to program delays and an increase in costs and unexpected risks.

According to Chalfant, more than 30 percent of the manned aeronautical telemetry spectrum has been auctioned by the Federal Communications Commission to commercial entities. With a finite amount of spectrum available the aeronautical community must become more resourceful and efficient to safely conduct flight test. It is a continuous, yet constantly evolving battle.

Fortunately, planning for the future is something that members from the Instrumentation Division and the 412th Range Squadron have made a top priority. Since the 1990's Edwards has provided subject matter experts who have participated in efforts locally, domestically, and internationally to battle spectrum encroachment.

They have teamed up with additional personnel from the Air Force and sister services, as well as agencies such as NASA, to work with the Department of Defense, FCC, Congress, and the wireless industry to protect flight test telemetering while addressing the ever expanding need for commercial wireless technology.

They are committed to increasing efficiency, relocating users and sharing technologies to address the need for more telemetry and more wireless capacities in a fixed spectrum environment.

Edwards personnel also work with the Department of State and commercial interests to address this issue internationally. That includes participating in the World Radiocommunication Conference, during which representatives from 189 nations meet every three years to address the allocation and assignments of wireless services. 

Representatives from Edwards, like Chalfant, remain active in awareness and outreach throughout the world as they are committed to finding a solution for accommodating the expanding commercial interests while preserving available spectrum for telemetering.

Finding a political solution is only half of the battle; besides protecting the telemetry spectrum they must work to increase efficiency, accommodating the increasing need for capacity. Personnel from the 412th Instrumentation Division and 412th Range Squadron are working with the DOD Test Resource Management Center to develop a real-time telemetry network that maximizes telemetering efficiency.

The system is called iNet, integrated Network Enhanced Telemetry, and it will revolutionize the way flight test is conducted.

Currently, there is only a one-way flow of data transmitted from the airplane to the control room where flight test professionals monitor the mission.

"Today, when an airplane is flying in our airspace, it is sending all this data down; from the moment the pilot taxis and turns everything on to the when he returns to the chocks. But, during testing a maneuver may last only 30 to 60 seconds where you want all that data. You don't need all that data when you're not testing, for example when the airplane goes off to a tanker to refuel," said Janzen.

iNet would allow those in the control room to choose when and how much data is recorded and transmitted during the mission. Eventually the technology could even link multiple aircraft on the same network.

"This technology will allow you on the ground to control how much data comes down. It's almost like you're plugged into the internet with the airplane. The control room can say we're done testing for a few minutes; the airplane recognizes the command and only sends small amounts of data in a standby mode until you're ready to resume testing," said Janzen.

"Once you're set up for the next test point the control room can crank up the data flow. It's this bidirectional control of how much spectrum is being used during the flight that will allow us to become much more efficient," he added.

Portions of the iNet technology are being used right now at Edwards with full development and implementation expected to be complete in about 10 years.

iNET will not only allow flight testers to move more data in the same spectrum, but it will provide the capability to change the data flow to meet mission requirements. It is a force multiplier in safety, efficiency and effectiveness for the future of flight test.