September 13, 2006 With two aircraft flying about 50 feet apart at hundreds of miles per hour, aerial refueling, even under the most ideal conditions, is an exacting manoeuvre. In the last few weeks, both Defense Advanced Research Projects Agency (DARPA) and Boeing have demonstrated new technologies that will improve safety for tanker aircrews and the airplanes receiving critical fuel. DARPA), in a joint effort with NASA Dryden Flight Research Center, performed the first-ever autonomous probe-and-drogue airborne refueling operation on August 30, at Edwards Air Force Base, California. Boeing meanwhile, used its new KC-767 Tanker to demonstrate a new technology using a series of cameras mounted on the tanker's fuselage. The KC-767 Remote Vision System (RVS) provides high-definition stereoscopic imagery to the aircraft's boom operator stationed behind the KC-767 cockpit.
DARPA’s demonstration was conducted with a NASA F/A-18 configured to operate as an unmanned test bed. The Autonomous Airborne Refueling Demonstration (AARD) system used GPS-based relative navigation, coupled with an optical tracker, to provide the precise positioning required to put a refueling probe into the center of a 32-inch basket dangling in the air stream behind an airborne tanker. The tanker was equipped with a small relative navigation pallet, but production refueling equipment was not modified in any way. Pilots were on board the F/A-18 for safety purposes.
Autonomous in-flight refueling is a critical enabler for affordable, persistent, unmanned strike systems. “This flight is a significant milestone – it demonstrates that autonomous systems can employ the benefits of air-refueling that have proven so valuable to military aviation,” said Lt. Col. Jim McCormick, DARPA program manager.
“We chose to demonstrate the probe and drogue refueling method because it is the most challenging for autonomous systems. The precise station-keeping capability we’ve demonstrated applies equally to the boom and receptacle method used by most Air Force aircraft,” noted McCormick. The same technology also promises to enhance reliability, safety and the range of operating conditions for air refueling manned aircraft.
The flight was the seventh of eight planned for the 15-month AARD proof of concept program. For this particular test, the pilot provided approval to proceed at several stages of the maneuver, but was otherwise hands-off. Operationally, unmanned systems are expected to locate the tanker, form up, accept clearances, refuel, and disengage without any human intervention.
System performance fully met expectations for the flight. “The end-game movement of the autonomous system had none of the last-second, high-gain stabs at the basket that we often see with human pilots. This computer approach was unbelievably stable and smooth, with deliberate movements throughout. And when it missed, it was just as smooth when backing up to a restart point,” said NASA test pilot Dick Ewers.
The AARD system was operating in benign flight conditions when it successfully engaged the basket in two out of six attempts. As important as the successful engagements, the system safely recovered from each missed attempt. Miss tolerances were tight for this first attempt. During one of the missed attempts, the pilot observed the probe was actually inside the basket when the system pulled back. More robust tracking algorithms and relaxed miss tolerances are planned to be demonstrated on a final flight later this month.
DARPA initiated AARD under the former Joint Unmanned Combat Air Systems program. The AARD system was developed by Sierra Nevada Corp., with team member OCTEC Ltd. providing the optical tracking system. Omega Air Refueling Services operated the modified 707-300 tanker used for the tests.
Successful demonstration of the AARD capability will allow unmanned air system developers and planners to leverage, with confidence, the operational advantages of in-flight refueling.
The Boeing KC-767 Tanker Advanced Camera System
Using a series of cameras mounted on the tanker's fuselage, the KC-767 Remote Vision System (RVS) provides high-definition stereoscopic imagery to the aircraft's boom operator stationed behind the KC-767 cockpit. Boeing flight crews recently activated the RVS while on a test flight and evaluated the system using a Cessna Citation in the receiver's position.
"This advanced technology will give KC-767 aircrews wingtip-to-wingtip visibility behind their aircraft," said Mark McGraw, Boeing vice president for Tanker Programs. "In addition to improving safety, RVS will enhance all-weather, day/night refueling capabilities for military forces around the world."
Following the RVS flight, Boeing KC-767 crews flew to Edwards Air Force Base, Calif., where they completed two weeks of takeoff performance testing and certification required by the Federal Aviation Administration.
Since its first flight in May 2005, the KC-767 Tanker has logged more than 120 flights and 360 hours. Boeing is building tankers for both Italy and Japan, with delivery to the Japan Air Self-Defense Force in February 2007, followed by delivery to Italy in mid-2007.
In addition to flight-testing the KC-767 for international customers, Boeing is competing for a contract to build the U.S. Air Force's next-generation tanker aircraft.