Highly Maneuverable Aircraft Technology (thing)
In 1975 Rockwell was contracted to produce two HiMAT aircraft for a research program run by NASA and the Air Force Flight Dynamics Laboratory between 1979 and 1983. The project aimed to explore requirements to increase manoeuvrability in future aircraft. At the time, researchers at the Dryden Flight Research Center were developing digital fly-by-wire systems that could be operated from the ground, which made it possible to experiment with highly-manoeuvrable aircraft designs. HiMAT was intended to be a testbed for these and other technologies.(1)
Rockwell delivered both HiMAT aircraft at a cost of $17.3m. They were designed as unmanned craft, so were about half the size of a conventional fighter jet. There were several reasons for this: First, it was considerably cheaper than building a full-scale aircraft, which would have been necessary if the pilot were to be on-board. Second, the smaller scale meant development and construction time would be shortened; the aircraft would not need to be 'man-rated' - tested to ensure it was safe for a human pilot - since the pilot would not actually be in the aircraft. Man-rating is always one of the most time-consuming and expensive parts of any aircraft's development. Third, the aircraft could be subjected to stresses that a human pilot would be unable to withstand. Finally, a pilotless plane would provide an opportunity to test the ground-based flight control systems pioneered by Dryden.
Aircraft Design & Construction
The aircraft was novel in configuration and construction. It was actually designed around a core component to which new wings, control surfaces or vectored nozzles could be added(3). All available images of the aircraft seem to show it in the same configuration, but the changes between different parts may have been minor. The aircraft had large, semi-delta wings mounted at the rear of the 23.5ft fuselage with small fins at the tips called winglets; used on commercial aircraft such as the Boeing 747-400, they reduce drag and provide corresponding improvements in fuel economy.
Large, swept-up canards were fitted roughly central on each side of the nose, in leiu of elevators and tailplanes used by more conventional aircraft designs. The twin vertical stabilizers reached backwards from mounting points towards each wing root, running through each wing from front to back.
In a fairly risky venture (mitigated by the fact that the aircraft was pilotless), about 30% of the HiMAT aircraft incorporated unproven composite materials including fibreglass, epoxy graphite and carbon fibre(5). These, it was theorised, would provide the structural integrity the aircraft would need to make the high-stress manoeuvres it was intended to perform. The results of testing these materials would later prove invaluable in the design of the X-29. In another effort to speed up the design (again, acceptable because the HiMAT aircraft was pilotless), CAD tools were used to develop the airframe. This drastically cut down on the time needed to test the design in wind tunnels, but it meant that several of the initial flights of the aircraft had to be devoted to deriving stability and control data.(1)
HIMAT in Flight
The first flight of a HiMAT aircraft took place on July 27th 1979. As with the X-24 and Rockwell's record-setting hypersonic X-15, all HiMAT sorties began with the craft being carried up to 45,000ft on a wing pylon of a B-52 and being launched by airdrop (although it was quite capable of taking off under its own power). It was controlled by a NASA test pilot on the ground in a 'virtual cockpit' scenario, using video feeds from cameras on the aircraft. The 'cockpit' on the ground contained all the normal flight controls - control stick, rudder pedals, throttle, sensor displays etc - and transmitted all control impulses by radio to the aircraft, where the onboard computer translated them into movements of the control surfaces.
In case of a failure of the telemetry system, HiMAT craft were always tailed by an F-104 chase plane, whose co-pilot could control it from his seat if needed. After the flight concluded the craft landed on a dry lake bed with the aid of a camera mounted in the nose, touching down on landing skids similar to those used on the X-15.
Performance & Results
The HiMAT craft had a top speed of about mach 1.5; its main focus of research was manoeuvrability in the transonic speed range of 600-800mph, where superior performance is both difficult to attain and most important(2). Largely due to the inclusion of the large canards in the design (and because it was unmanned), the craft was capable of making turns at a sustained 8 gees at near the speed of sound, with a turn radius less than half that of conventional fighter planes. Such manoeuvres would render a human pilot unconscious. As a point of comparison, the F-16 - still considered one of the most manoeuvrable aircraft currently in service - has a maximum sustained turning capacity of about 4.5G.
An interesting product of the HiMAT program was a configurable autopilot which could be preset to perform certain manoeuvres repeatedly with great accuracy, which would not be possible with human control. This meant that large quantities of reliable research data could be collected while the autopilot was repeating the manoeuvres, and that other small factors in the craft's configuration could be altered by the pilot while the craft was under control of the autopilot. This technique of applying an autopilot to repeat test manoeuvres proved very useful in testing of future experimental aircraft.
The HiMAT program also provided valuable research data on the performance of certain composite materials under flight conditions; many of these materials are now used in operational aircraft. The program also resulted in advances in digital flight control systems, capable of monitoring and correcting potential flight hazards - something that would prove vital in the design of unstable aircraft. It worth noting that the manoeuvrability of the HiMAT aircraft still wildly outstrips any currently in service.
The last flight took place on January 6th, 1983; the two craft flew 26 sorties between them. They are both now on display to the public - one in the Smithsonian Institute's National Air and Space Museum, the other at NASA Ames Research Center.