A Sample Feature From Aviation News

The Rogallo Parasev:
A revolution in flying wings

In the 1950s an Italian-American engineer named Francis Melwin Rogallo built a flexible wing known in Italian as the ‘ala Rogallo’. It was conceived when the (then) Langley Memorial Aeronautical Laboratory, Va, wanted a system whereby kite-parachutes could use basic principles of lift to control the landing point of heavy objects dropped from high altitude. Reflecting on those early days when Rogallo wings became part of a NASA plan to slow heavy loads from high speeds and land them safely on the ground, we reflect on a failed application developed later into one of the more successful, and cheapest, ways to get airborne

Above: Test pilot Milton Thompson and a motley collection of ground crew, including a motorcyclist preparing to ride ‘chase’, show off the Parasev 1-A with Dacron lobes. The trusty Stearman tow aircraft was one of several types supporting this little known programme that began at the Flight Research Centre in 1962. (Photo, DFRC).

Prompted by the Korean War, it all began with a classified US Air Force project in 1952 to drop cargo by parachute on a controlled descent to a specified location. Pre-positioning materiel and dropping support equipment to army ground units would, said the army, be enhanced if the load could be guided to a pre-designated area. Some studies even spoke of TV cameras and remote controlled lift devices to guide the kite-parachute down to the ground. Out of studies conducted by the Air Force and some work done at contractor laboratories, inflatable wing-sections emerged as a likely solution to the problem of controlling the descent trajectory of a free-falling parachute. Folded tight for compact storage, inflated by an inert gas during descent, a fabric ‘wing’ would unfold, chrysalis-like, from a container between the conventional parachute above and a payload directly below. Released after wing inflation, the parachute would float away as the load it had been connected to began a controlled glide.

Parallel universe
The idea was similar in concept to the inflatable ‘wing’, a contemporary devised by the Research and Development Establishment at RAF Cardington and produced from spare balloon fabric. With a 60hp McCulloch engine, the design resembled a conventional aircraft in every essential aspect down to aerodynamic control surfaces, with vertical stabilisers and a tricycle gondola, the seated pilot suspended beneath the wing at stick and rudder controls. This concept was taken up by ML Aviation Ltd to produce the Utility Aircraft, tested from 1954. In it, Peter Twiss officially qualified for not only being the fastest pilot in the world – but also the slowest! Yet the ML Utility was not what Rogallo had in mind when he designed the kite parachute at Langley Laboratory to satisfy research driven by the secret military mission. The kite-parachute was designed for remote control but had its greatest application when linked to heavyweight drops. From there it was to develop a failed application that could, had it succeeded, have revolutionised the placing of heavy objects at precise spots on land – including manned spacecraft returning from orbit.
As conceived, the Rogallo wing consisted of two partial conic sections sharing a common side with both cones pointing forward, filled with air to give the wing its familiar shape, not solely confined to low-speed applications. Slow wings could incorporate wide, shallow cones while fast and supersonic wings would have long, thin, narrow cone shapes. The design was not very efficient but it worked well enough to give it an application.

Above: British inventiveness stimulated an inflatable wing aircraft, produced by ML Aviation Ltd in the mid-1950s as the Utility. Twelve wings were tested and three aircraft were built (XK776, XK781 and XK784). Conceived at the Research and Development Establishment, RAF Cardington in 1953, its true potential was realised on the other side of the Atlantic. (Photo, Av News Files).

Patents applied
Rogallo successfully patented the design, but the application that funded his research at the old National Advisory Committee for Aeronautics went away, to be replaced by a new one for a different age. When the National Aeronautics and Space Administration (NASA) formed in October 1958 it expanded a wide and diverse range of aeronautics programmes and projects, one of which applied wings to cost-effective ways of reusing expensive hardware. Within two years, responsibility for big rocket booster development managed by the army was transferred to NASA and along with it, a mandate to turn a costly one-off launch vehicle for big spacecraft into a reusable system. Engineers began to examine the possibility of dropping spent rocket stages into the sea by parachute but quickly moved on to lifting kite-parachutes of the type designed by Rogallo. That, and the safe recovery of manned spacecraft on land, drove the next development that would take the Rogallo wing to a higher level of test.

In late 1961 NASA was engaged in the daunting task of planning the development of Apollo moon landing spacecraft, declared a national goal by President Kennedy in May that year. As an interim vehicle between the tiny one-man Mercury spacecraft and the more advanced three-man Apollo, NASA opted for a Mercury Mk II carrying two crewmembers, a vehicle soon to be known as the Gemini spacecraft. For that, a ground landing was preferred over a splash-down at sea to save costs, US Navy recovery assets and to increase safety for the crew. It was a concept that had already received the attention of Robert R Gilruth, director of the Space Task Group when, back in May 1961 he commissioned studies on a Rogallo type ‘Parawing’ for spacecraft recovery. North American Aviation was awarded a development contract for a test programme involving a unique capsule-shaped vehicle with fully inflatable Parawing. The wing was one thing, development of an operational spacecraft recovery system was quite another. In late November 1961 a full-scale NASA Paraglider research programme was launched.

Research would focus on stowing and deploying the wing, making sure that the crew could control the descending vehicle, and on stability and handling qualities. For a time it seemed this could be the answer to bringing spacecraft back from orbit safely and routinely at a pre-designated landing site, but there were differences of opinion. Engineers at Langley Research Centre, so renamed after the formation of NASA, were optimistic – this was, after all, the place from where all thought of manned flight into space had originated – but the Flight Research Centre (FRC) at Edwards, Calif, were highly sceptical and technical staff were not inclined to believe it was even a workable idea. Nevertheless, it was at the FRC that most of the initial testing would be conducted, subscribing to the view that nobody would know until a rigid test programme had been implemented. To do that a test vehicle had to be designed and two pilots in fervent support of the concept were Neil Armstrong and Milt Thompson.

Above: Paasev 1-B in fight with the smaller Dacron lobe canopy revealing tow line, rigging and control devices divided between ropes and control stick. Earlier versions of the ‘spaceframe’ adopted an overhanging rod for directional control, significantly modified as a result of some near-disasters. Tests revealed control and handling difficulties that did little to inspire confidence in the system. (Photo, DFRC).

What’s in a name?
By late 1961 Armstrong and Thompson were heavily committed to the winged hypersonic DynaSoar programme. When approached by them to develop a Parawing test programme, FRC boss Paul Bikle assigned instead four engineers to a development effort led by a fifth man, Charles Richards. By Christmas the team had grown to nine engineers and the project had a name: Parasev, an abbreviation of Paraglider Research Vehicle. Seven weeks later, Parasev 1 was ‘rolled’ out. Resembling a grown-up, unpowered tricycle with angled tripod mast on top of which sat a Rogallo wing, this was a simple, low-cost test vehicle and not the definitive inflatable wing envisaged for Gemini. Nevertheless, it was an historic moment, the first NASA research aircraft constructed totally in-house, registered with the Federal Aviation Administration as such on February 12, 1962.

Unpowered, Parasev 1 had an open framework ‘fuselage’ fabricated from welded 4130 titanium steel tubing, the keel and wing leading edges constructed of 2.5in diameter aluminium tubing. The sweep of the leading edge was held to a constant 50º by a rigid spreader bar and the pilot sat in the open, strapped to a seat with no enclosure of any kind. Rate of descent would be controlled by tilting the wing fore and aft and turns would be made by titling the wing from side to side using an overhead control stick. The structure below the Parawing itself was known as the spaceframe and only one would be built, utilised for four separate wing designs. Parsev 1 incorporated an overhead control rod in front of the pilot’s seat. The wing had a linen membrane, contested by the sail-maker asked to sew it together according to a planform generated at the FRC. Engineers Dick Klein and Gary Layton had visited the sailmaker and because cloth-covered aircraft used Irish linen, that seemed to them the way to go. It was, he said, totally the wrong decision and the sailmaker offered to use Dacron instead. He was overridden by technical arguments, much to the embarrassment of Klein and Layton at a later date! In giving the wing flexibility, a nylon bolt was attached to the trailing edge of the 600sq ft membrane, fixed firmly only at the wing tips, the rope being unrestrained and free to equalise load between the two lobes.

First tests were carried out by towing Parasev 1 behind a six-cylinder Harvester utility truck across the desert, the device lifting off at about 40kts ahead of a motley collection of cars, trucks and motorcycles collectively charging across the dusty ground driving ‘chase’ on the diminutive machine. By now Milt Thompson, along with Bruce Peterson, had been assigned to ‘fly’ the Parasev. Floating it along the ground while getting to know the handling characteristics before attempting more ambitious manoeuvres, it was not an untroubled learning curve. Flapping violently in the wind, the lobes bulging and straining in a most alarming way, the linen wing was giving problems, including flutter at the trailing edges. Longitudinal and lateral stick forces were considerable. Flying the Parasev was, said Peterson, more difficult than the later, more sophisticated, Lifting Body series of unpowered gliding vehicles. Several changes were made to the rigging arrangement and control modifications were tested but few responses were effective and none were predictable. On the fifth flight aloft, Peterson got out of phase with the control lag and a sinusoidal wallowing motion set in, but at the moment the tow-truck began to slow down the Paresev flipped over and crashed to the desert floor from a height of 10ft, just 10sec after lift-off. Peterson survived intact but the Parasev did not, a rebuild necessitating a new designation – and a new, Dacron-covered Parawing!

Above: Parasev 1-A provides backdrop for a posed shot of NASA astronaut ‘Gus’ Grissom (left) and test pilot Milton Thompson. Grissom would die in the Apollo fire on January 27, 1967. Thompson was one of 12 pilots to fly the hypersonic North American X-15 and would also test Lifting Body research vehicles. He died on August 6, 1993. (Photo, DFRC).

Above: Parasev 1-A provides backdrop for a posed shot of NASA astronaut ‘Gus’ Grissom (left) and test pilot Milton Thompson. Grissom would die in the Apollo fire on January 27, 1967. Thompson was one of 12 pilots to fly the hypersonic North American X-15 and would also test Lifting Body research vehicles. He died on August 6, 1993. (Photo, DFRC).

For the rest of this feature please see the March 2007 issue.