Atmospheric research in harsh environments using NRC T-33 research aircraft

Citation

(2006), "Atmospheric research in harsh environments using NRC T-33 research aircraft", Aircraft Engineering and Aerospace Technology, Vol. 78 No. 2. https://doi.org/10.1108/aeat.2006.12778baf.003

Atmospheric research in harsh environments using NRC T-33 research aircraft

Atmospheric research in harsh environments using NRC T-33 research aircraft

Keywords: Aircraft, Environmental testing

The National Research Council of Canada Institute for Aerospace Research (NRC Aerospace) has joined forces with Transport Canada to obtain data on aircraft emissions from commercial aircraft flying at cruise altitude over Canada. The project was initiated to address concerns about the potential adverse effects of such emissions on Canada’s sensitive northern environment as they accumulate in the polar air mass before precipitating out onto the ground, and to obtain technical data to support International Civil Aviation Organization regulatory development. To carry out these studies, NRC Aerospace is adding new instrumentation to its T-33 research aircraft to enable it to collect emissions data while flying behind commercial aircraft. The first proof-of-concept flights will take place in 2006 over the St Lawrence Seaway air routes between Ottawa and Quebec City, and over polar routes arising out of Toronto.

Anthony Brown, NRC Aerospace research officer and test pilot, said, “Environmental concerns about the effect of aircraft emissions have grown in recent years. The biggest issues relate to the climatological consequences of emissions resulting from aircraft flying at level cruising altitudes between the upper third of the troposphere through to the lower stratosphere. Transport Canada is particularly concerned with the entrapment of such emissions in Canada’s polar air mass, where there is little latitudinal circulation. When they finally precipitate downwards, the result is ground level pollution and water contamination in the fragile ecologies of northern Canadian tundra and boreal forest regions.”

With this concern growing, international civil aviation organizations are seeking substantiated data as they reconsider emission standards on what a jet transport aircraft can leave behind in the way of gases and solid particulate matter. Measurements have been taken over Europe for some time, but since none exists for Canada, the International Aviation Office at Transport Canada and NRC Aerospace set up an initiative to obtain the needed information.

NRC Aerospace is adding new instrumentation to the NRC T-33 research aircraft to improve its flight inertial data processing and acquisition systems, and a uniquely designed air data boom system. Pressurized under-wing pods containing air chemistry instrumentation to measure levels of carbon dioxide, nitric oxides, other gaseous species, water vapour and particulate matter, are also being installed.

Brown said, “The T-33 aircraft was used in the past for convective and boundary layer turbulence studies. It’s a very rugged airplane that can handle harsh and adverse environments, and these capabilities are needed for the measurement of aircraft emissions data. The sophisticated instrumentation we’re putting on it will enable us to obtain accurate aircraft emissions data to support Transport Canada’s mandate and tackle a part of the atmospheric research domain which is not generally addressed.”

The completed pods were recently installed on the aircraft, with data gathering flights following shortly thereafter. All wake sampling will be coordinated through Air Traffic Control (ATC), who will advise aircraft in whose wake the T-33 will fly about its position and intentions. Initial flights will take place along the St Lawrence Seaway in the main traffic routes between Ottawa and Quebec City. These will be followed up with flights over the initial segment of polar routes arising out of Toronto. Three flight profiles are planned. The first profile, from ground level up to about 28,000 feet, and the second one, an enroute intercept behind individual aircraft at altitudes of 28,000-38,000 feet, will be in the jet wake region behind individual aircraft. The third profile will consist of aerial work before and after the daily passage of aircraft through the designated area. Flights will take place in two or three separate blocks to allow for data analysis that will guide the flight profiles of subsequent stages.

Experience gained from this project, along with the newly equipped T-33 research aircraft, will place NRC Aerospace in an ideal position to support future atmospheric research, including a wide-scale emissions data gathering project being considered by the North American Carbon Program Steering Committee for sometime around 2009.

The NRC also reports that it recently conducted a pilot study that measured the characteristics of enroute commercial aircraft wake turbulence. Four flights using the NRC Falcon 20 research aircraft were made out of Ottawa, Canada at altitudes of 24,000-39,000 feet behind cruising aircraft at separation distances of 1-30 miles. On several occasions during those flights, the Falcon experienced aerodynamic g-loading, flight path upsets and an engine flameout, when it became entrained by the trailing vortices. These perturbations, which occurred at wake lengths of 8-13 miles, well within permissible separations, were large enough to knock anyone standing within the aircraft off their feet. Further research is needed to better understand the flow mechanisms that can cause such upsets. NRC Aerospace is therefore outfitting a more rugged aircraft, the NRC T-33, to continue these investigations.

Commenting on these tests Anthony Brown, said, “Turbulence is an ongoing concern to air transportation safety. Every aircraft generates a pair of trailing wake vortices which undergo instability for a substantial length of time and distance. An aircraft travelling through these wake instabilities could experience substantial aerodynamic loading and flight path upset, enough to severely knock passengers or flight attendants off their feet and cause injuries. Our goal is to obtain data on the flow phenomena to clarify the risk and highlight the desirability, or the need, to develop wake vortex turbulence warning instrumentation that can be installed on aircraft.”

Most wake vortex encounters occur during takeoff and landing, but a few have occurred with aircraft in the enroute configuration. Such encounters are likely to increase with reductions being made in enroute vertical airspace separation. The enroute configuration is also increasing in frequency and density as departing aircraft climb earlier to reduce noise and minimize terminal airspace occupancy time. What is more, continuous descent approaches, where the aircraft remains in the enroute configuration well into the base region, are likely to become widespread as they improve fuel efficiency while reducing noise and emissions. These changes, and the lack of substantial research on the adequacy of current enroute wake separation distances, point to a need for more data.

The two-phase pilot study carried out in 2004 with the NRC Falcon 20 research aircraft is a first step towards addressing this need. In the first phase, NRC Aerospace worked with Montreal ATC to establish open flight procedures for using commercial aircraft as wake generators. A methodology for gaining wind perturbation data to identify vortex strength, location, orientation, flight path, and instability state was also developed. In the second phase, wake characteristics were measured at altitudes of 24,000-39,000 feet over wake lengths of 1-30 miles. Assisted by ATC, the Falcon 20 was vectored in at about 5 miles behind commercial aircraft coming in or out of the North Atlantic Track System and the Polar Track to Japan. Descending to the wake generator’s altitude, the pilots carried out wake survey traverses around the trailing pair of wake vortices delimited by condensation patterns. By going around these vortices they avoided the large perturbations within the flight path, yet were able to collect the required data.

Brown said, “On a number of occasions, however, the entrainment effect of the trailing vortices sucked the research aircraft through the vortex cores, causing us to experience loading and flight path disturbances. These perturbations occurred with wake lengths of 8-13 miles, which is within the distance that an aircraft could legally be crossing or following a large wake generator. The fact that the substantial perturbations occurred at such distances indicates that more data needs to be gathered in this region in order to understand the flow mechanisms. The Falcon 20 is a rugged airplane, but it was not our intention to fly through the vortices. Largely for that reason, we will continue our research with a more rugged aircraft, the NRC T-33, which is currently being instrumented for flights in 2006. This aircraft will give us more comfort when taking measurements in such a harsh atmospheric research environment.”

In the meantime, NRC Aerospace has initiated ground studies on passive sensing instrumentation to sense the presence of wake vortex flow fields around landing aircraft. If these studies are successful, the instruments will be modified and installed on the NRC T-33 for use in passive sensing of wake vortex flow fields during flight.

The National Research Council Institute for Aerospace Research is Canada’s national aerospace laboratory, undertaking and promoting research and development in support of the Canadian aerospace community in matters affecting the design, manufacture, performance, use and safety of aerospace vehicles.

Details available from: NRC Institute for Aerospace Research. Tel: +1 613 991 5738; E-mail: michelle.gagnon@nrc.gc.ca; Web site: www.nrcaerospace.com