Plane spotters in the Denver area started noticing something different on the taxiway at Centennial Airport last year, and it wasn’t typical airport activity. It was Boom’s ground crew conducting engine runs on its supersonic demonstrator, XB-1.
Among other things, XB-1’s engine runs are establishing the installed performance of each of its three General Electric J85 engines. These are small single-shaft turbojet engines previously installed in Canadian F-5 aircraft (the Canadair licensed-built version of the American Northrop F-5 Freedom Fighter).
While XB-1’s J85 engines are a tried and true design, they have never been installed and operated in this particular experimental aircraft with this specific inlet. Hence, the need for extensive testing.
The team is using engine runs to determine that everything functions as designed, from the stall susceptibility (due to the unique installed configuration), to the performance of the engine’s accessory gearbox that powers hydraulic pumps, generators and more. This, in turn, is enabling the checkout of all the other systems on the aircraft, such as the flight controls and avionics.
Here’s a behind-the-scenes look at XB-1 engine runs.
In order to access the taxiway directly from the Boom hangar, the airport granted Boom permission to build a gate between the two. In a matter of minutes, XB-1 is on the taxiway.
The ground crew tows XB-1 to a large apron (ramp) that has reinforced anchors in the ground for tethering the aircraft. The tethers prevent XB-1 from moving during all of the events, which will eventually include all three afterburners (which is the highest thrust the aircraft will generate). Other aircraft can also use the apron, so the airport puts out a Notice to Airmen (NOTAM) that the team is performing testing.
Engine runs are conducted in a build up fashion: first one engine at idle; then all three at idle; then power settings all the way up to full afterburner; then various rates of throttle movement. The process eventually builds up to a rapid throttle movement from idle to afterburner that mimics what a pilot might do in a late go-around maneuver.
Back at Boom’s hangar, the flight test team monitors the tests from the control room. They watch video captured by a camera on XB-1’s telemetry antenna while monitoring the weather and the test pilot’s multifunction display. The team also has displays showing different parameters of the aircraft that are also transmitted via the telemetry antenna.
The vehicle following XB-1 carries yellow hoses, which the team uses to run air into the engines to start them. They also use similar hoses to run cooling air into the aircraft bays to ensure electronics maintain the correct temperature.
Taxi tests at Centennial Airport will go from barely moving to 60 knots, which is about 70 mph (112 km/h).
Not all ground tests happen on the airfield. The first time the team “swings” the landing gear, they will conduct the test on a special stand in the hangar. The stand allows the aircraft to be held off the ground while the landing gear is moving.
For Doc, the road to flying XB-1 has encompassed military service, a Stanford doctorate in aeronautics and astronautics, and being the test pilot for several prototype aircraft. A former U.S. naval aviator, he’s a graduate of the United States Naval Test Pilot School and has flown more than 5,000 flight hours in 50 aircraft types and has 900 carrier arrested landings (landing on an aircraft carrier deck).
Flight Testing Continues in Colorado and California
Ultimately, XB-1 ground testing will demonstrate the functionality of all aircraft systems, and determine that each system meets or exceeds specifications. The next step is flight testing in California’s Mojave Desert.
Once the aircraft arrives in Mojave (via flatbed), the team will work their way up to higher taxi speeds on the long, wide runway of the Mojave Air & Space Port. During these tests, XB-1 will likely reach 135 knots, which is around 155 mph (249 km/h). XB-1 is expected to leave the ground on the first flight at around 185 knots, around 212 mph (341km/h).