In order to evaluate unconventional control of an aircraft in flight, the Flight Dynamics Laboratory of the Air Force Systems Command sponsored an Advanced Fighter Technology Integration (AFTI) program. On Dec 26, 1978, General Dynamics was awarded a contract to convert the sixth FSD F-16A (#75-0750) into an AFTI aircraft. It capitalized on the experience gained with the F-16 CCV (Control Configured Vehicle) (#72-1567). The aircraft was handed over to the company in March 1980.
F-16 AFTI in flight. You can clearly see the CCV canards below the air inlet. (NASA
The AFTI F-16 was fitted with twin canard surfaces mounted below the air intake. Those canards had been taken from the CCV/F-16 CCV. The aircraft was also fitted with a bulged spine which housed additional electronics. It had a full-authority triplex Digital Flight Control System (DFCS) and an Automated Maneuvering Attack System (AMAS), providing six independent degrees of freedom. It had been designed to be fault tolerant, so that no single failure should affect correct operation. In the event of a second fault developing, the system was able to revert to a standby condition which would permit safe flight to continue. To guard against unforeseen failure modes which might bring the entire digital flight control system down, the system incorporates a simple analog backup flight-control system.
Voice-Controlled Interactive Device
An unusual piece of cockpit equipment is the Voice-Controlled Interactive Device (VCID); made by Lear-Siegler. This voice control system (with a dictionary of 32 to 256 words) is used to control the AFTI's avionics suite. In the early stages of VCID testing only simple, one-word commands were used such as 'menu', 'data', the points of the compass, numbers, and the phonetic alphabet. Only non-critical functions such as navigation are controlled by the VCID. In a later stage tests were conducted to investigate the feasibility of complex multi-word command recognition.
The problem lies not with the hard- or software, but with the fact that the system is only trained for one voice, and performance quickly deteriorates with the quality of the speech. Few pilots are able to keep talking when pulling 5+ G's (as shown by studies undertaken by GD in a centrifuge; although one person supposedly kept grunting commands even at 9G), and the noise-level in an F-16 cockpit during high-G manoeuvre easily reaches 120dB. Overall, study results were quite promising as the system managed to respond accurately to a staggering 90% of the commands spoken.
Helmet-Mounted Target Designation Sight
Another technique tested in the AFTI F-16 was a helmet-mounted target designation sight. In stead of using a traditional throttle-mounted cursor control to designate the target, the AFTI pilot only needs to look at it, and align the target with the 0.5in (12.7mm) cross hairs incorporated in his visor. By depressing the designate button, target lock is achieved and minor adjustments can be made by using the cursor controller. Also, the FLIR and radar are automatically slaved to head movement.
The relative position of the pilot's head in the cockpit is determined by using a magnetic field, generated by a transmitter mounted on the canopy directly behind the pilot's head, and a 0.113kg receiver on the helmet. Furthermore, the system is capable of telling the pilot were to look to find his target. This is achieved by use of four LEDs (up, down, left, right) which (when lit) tell the pilot which direction to turn his head.
The AFTI program
The AFTI took to the air for the first time at Fort Worth on July 10th, 1982 , General Dynamics pilot Alex V. Wolfe being at the controls. Following manufacturers trials carried out at Carswell AFB, Texas, the AFTI/F-16 was moved to Edwards AFB (California) for a two-year program of 275 flight tests. Phase I testing was primarily devoted to evaluate the DFCS and involved the demonstration of direct translational maneuvering capability. This testing was completed on July 30th, 1983.
The 1984 Phase II testing started with a dummy, then an operational FLIR mounted in the wing root. Standard F-16C avionics were fitted, and the Automated Maneuvering Attack System was installed. During Phase II testing, which lasted until 1987, the AMAS enabled the AFTI/F-16 to translate in all three axes at a constant angle of attack and to be pointed up to six degrees off the flight vector.
The digital flight control system gave the pilot a new freedom in maneuvering, making it possible to assume unorthodox flight attitudes, using nose pointing, direct force translation, and other unconventional means of maneuvering. The aircraft was also used to test and evaluate a variety of single-place cockpit layouts and systems. Pilots evaluated heads-up and head-down displays, voice interaction command systems, synthesized speech voice warnings, and touch-sensitive display screens. This aircraft also tried out products from the Air Force Microcomputer Applications of Graphics and Interactive Communications (MAGIC) project, which studies pictorial formats for situation displays in all three axes.
In September of 1987, the F-16/AFTI team received the Air Force Association's 1987 Theodore von Karman Award for the most outstanding achievement in science and engineering.
Advanced research programs
Close Air Support studies
Head-on view of the AFTI F-16, revealing the wingroot mounted FLIR. (NASA photo)
During the following years, the AFTI/F-16 became associated with Close Air Support (CAS) studies, some of them conducted by NASA. These studies were in support of the proposed A-16 or other future close air support/battlefield air interdiction aircraft. The AFTI/F-16 was upgraded with an F-16C block 25 wing and with block 40 F-16C features such as APG-68 radar and a LANTIRN interface. It went through a five-phase CAS evaluation program over 1988-1991, testing such low-level battlefield interdiction techniques as automatic target handoff-systems (in which target data was transferred from ground stations or from other aircraft to the AFTI/F-16), the Pave Penny laser-designator pod, off-axis weapons launch techniques, and various digital systems.
GPWS and GCAS programs
As the U.S. Air Force wanted to reduce the "Controlled Flight Into Terrain" (CFIT), which persists as a major cause of military tactical aircraft crashes, they started to develop an advanced ground collision system. Significant progress had been made with the introduction of the Ground Proximity Warning System (GPWS) in the 1970's as it dramatically reduced CFIT accident rates.
The final line of defense is a Ground Collision Avoidance System (GCAS) that determines the pilot is not aware -even with warnings- of his current situation, so it automatically executes a recovery. A technology development and demonstration study using the AFTI F-16 test-bed over the last decade verified that a terrain-avoidance system was feasible.
The AFTI aircraft during A-GCAS tests (NASA photo)
The AFTI Advanced or Automatic Ground Collision Avoidance System (Auto-GCAS) relies on a digital terrain data base and accurate navigation inputs. It also goes a step beyond warning the pilot; it actually executes an aggressive fly-up recovery through the F-16 autopilot. The correlation between aircraft position and the digital terrain data base depends on radar altimeter time history, although Global Positioning Systems or inertial navigation inputs could also be used. A GCAS algorithm combines digital terrain system data with the aircraft's current flight parameters, then predicts a recovery profile and executes an escape maneuver through the autopilot. The escape manoeuvre is a roll-to-wings-level 5g fly up. For AFTI testing, the GCAS only activates when minimum terrain clearance is projected to be 50-150 ft. However, the minimum terrain clearance can be any distance desired. It was arbitrarily chosen to be a minimum of 150ft normally and 50ft for strafe as a reasonable buffer.
In 1995 the AFTI F-16 has conducted more than 1,000 auto recovery tests. In November 1996 the AFTI F-16 tests established Auto-GCAS warning criteria by defining appropriate activation altitudes. Researchers are sensitive to triggering he system too high and having it become a nuisance that impedes normal pilot operation. About 20 flights have been executed.
In January 1997, a two-year program aimed at "migrating the AFTI software into production hardware" has begun. Follow-on Auto-GCAS testing have been done on a production Block 25 F-16D in 1998.