An ongoing program that may strike fear and loathing into the hearts of the MUFON / UFON aficionados was described in fascinating detail at the January 17, 2001 Section Dinner Meeting at the TRW Forum. For Gordon Ow, CEO and President of GO AIRCRAFT, LTD. (GOAL) is, as we speak, developing "The High Speed Vertical Takeoff and Landing (HSVTOL) Aircraft" and it’s a dead ringer to a traditional flying saucer. Unfortunately, the UFO buffs may be chagrined. The GOAL HSVTOL is based on well proven earthly technologies and does not claim outer space ability.

Mr. Ow described the program, whose first two phases have been funded by DARPA and supported by NASA, to an enthusiastic audience of about 35. As suggested by the title, the UFO-like vehicle rises vertically, driven by an enclosed fan system which rotates on a system of air bearings which join the non-rotating central fuselage with the complete fan-encompassing periphery. The rotating, toroidal outer fan assembly section is driven pneumatically by fan jet engine gases which are diverted via ducts from the fan jets into a plenum chamber which then feeds into many individual, tangentially mounted, rocket nozzles which drive the fan assembly.

Once up to speed, the momentum engendered by the spinning outer fan assembly section has converted the vehicle into a large gyroscope. When the fan blades are articulated into a lifting configuration (open), the fan section takes air in through the upper surface and accelerates it downward via fan action to provide vertical lift, while the gyroscopic effect automatically provides stability in pitch and roll and is also used as a gyroscopic means of flight control.

The central fuselage features the usual top-side glass cockpit-like bulge and, in one troop- carrier version, shows a large passenger section behind the pilots’ control area. Transition to horizontal flight consists of bypassing more and more propulsive gases from the fan assembly to rearward facing exhaust nozzles in order to accelerate the vehicle forward while reducing the fan rpm and relying more and more on the disc lifting body to provide aerodynamic lift, as the forward speed increases.

At the completion of transition, the fan blades are again articulated to a closed position to form a smooth outer mold line for the upper side wing surface. Once in forward flight, the engines propel the vehicle like a Conventional Takeoff and Landing (CTOL) aircraft except for a very small amount of thrust bled to turn the fan at a very low rpm to permit maintenance of gyroscopic stability and control. Directional control is enabled by using small cold gas jets and the usual ‘bank to turn’ method is used to maneuver. To turn the HSVTOL in flight, torque is applied to the gyroscope by means of aerodynamic control surfaces that causes precession of the gyro-plane to the desired bank and pitch angles.

Engine-out fail-safe is achieved by turning the craft into a conventional glider by completely stopping the rotation of the outer fan assembly section and gliding at very low airspeed and at a high angle of attack. For example, stall speeds are as low as 65 knots at 38 degrees angle of attack. The landing gear is normally to be used for vertical landings and taxi operations, and is planned to be very light.

The Phase I program started in May 1997, and conceptual design was conducted on a 15 foot diameter proof-of-concept demonstrator and a 45-ft diameter 24-man troop carrier as a baseline design for performance studies. Design mass characteristics were determined. Wind tunnel tests were conducted at Mach 0.4 in the Boeing blow-down tunnel on Douglas St. on a 1.5 foot diameter model to measure aerodynamic lift, drag, and moment characteristics. Performance estimates showed that, for the same payload, the HSVTOL could travel about twice as fast, twice as far, and almost twice as high as the ill-starred Osprey. The range also greatly exceeds that of a Harrier-type vehicle.

With only a modest lift-to-drag ratio, long range comes by way of the large volume inherent in the saucer shaped wing body, enabling large weights of fuel (high fuel fractions) to be carried internally. In addition, the large planform wing area results in a very low wing loading that enables very high altitude cruise for lower specific fuel consumption at relatively low angles of attack for lower induced drag. Near-zero moments at these low angles of attack also result in a low trim drag. The design is efficient structurally, leading to lower structural weight. It is also inherently more stealthy than either of the existing VTOL designs mentioned above.

The Phase II program was completed during 2000. In it, a full scale, 15 foot diameter fan (for the demonstrator) was designed and built. Aluminum, carbon-carbon, and fiberglass are main construction materials. No sophisticated or expensive fabrication techniques were used. Tooling utilized was inexpensive, common hobby shop variety. To stay within Mach number limits and retreating blade stall limits during transition, the upper operating limit on a 15-foot diameter fan is about 760 rpm or fan blade velocity of 400 fps.

Tests were conducted to measure fan thrust at various rpm’s at the Wyle Lab facility in Corona. The fan was powered by a T-53 gas turbine mounted on a Wyle Lab centrifuge drive shaft. The fan was supported on air bearings. Load cells measured fan thrusts and pressure readings were obtained on fan blades to correlate thrust. Thrust readings correlated very closely and exceeded predicted values.

DARPA considered the fan test successful and indicated that the next step was to seek commercialization investments and move to Phase III (proof-of-concept demonstration). During Phase III, GOAL plans to design and build a 15 foot diameter demonstration vehicle and conduct a flight demonstration of the pneumatic power system and the flight control system.

As a subcontractor to GOAL during Phase II, the Draper Lab developed a preliminary gyroscopic flight control architecture, control algorithms, an assessment of the gyroscopic-based flight stability and control system using their Simulink software and formulated a gyroscopic flight control development roadmap. GOAL provided configuration and mass properties data that was used in the Simulink software. Both air jets designs and aerodynamic supplementary control sizes provide by GOAL were employed.

Ow stated that the vehicle scales nicely to larger diameters for larger transports. For the larger diameter, the fan rpm is reduced considerably to maintain the same tip speeds at approximately 400 fps. The vehicle can also be scaled to smaller, lower-powered vehicles, manned or unmanned, at higher fan rpm’s, but fan tip speeds limit the ultimate reduction in size.

Funding to proceed on a flight demonstrator is now being pursued. Ancillary studies indicate that a large diameter lifting fan combined with multiple fan-jet engines in a reusable first stage launch vehicle design may also represent a novel way to put payloads into orbit, given the very high thrusts and orders-of-magnitude higher specific impulses attainable.

I was intrigued by the HSVTOL concept. Even though the end result is an airplane of less than optimum lift-to-drag ratio, it can achieve long ranges with offsets in high speed cruise at very high altitudes at lower specific fuel consumption rates and very high fuel fractions. Its compactness, efficiency as a VTOL craft, and versatility for a number of missions, both unmanned and manned, make it an attractive ‘’what if?’ package.