SOLO AMBITIONS

Adventurer Steve Fossett plans to take off from Salina, Kan.--perhaps as soon as early February--to be the first man to fly solo around the world, unrefueled.

He will be piloting the Virgin Atlantic "GlobalFlyer" built by Burt Rutan's Scaled Composites company here. Rutan also built Voyager, the first aircraft to fly around the world unrefueled, in a project put together by his brother Dick and piloted by him and Jeana Yeager in 1986 (AW&ST Jan. 5, 1987, p. 22). In contrast, GlobalFlyer has only a single crewman, and is jet-powered to speed and simplify the trip. Voyager took 9 days and GlobalFlyer could take as little as 2 days 17 hr.

While trials so far have gone well, engineers are still anxious about the record flight attempt because it will be heavier than any test. The fraction of weight that's structure is extremely low. The scariest part is being heavy on fuel at takeoff and climbing through turbulence, says Clint Nichols, the flight test and performance engineer. Handling, which so far has been reasonable, could take a dramatic turn with the final 15% increase in takeoff weight. And there's concern about whether the aircraft can descend quickly enough from high altitude, even with drogue chutes deployed, for the pilot to breathe oxygen adequately if the engine dies, causing a quick loss of cabin pressure.

GlobalFlyer has made 23 test flights so far to iron out the bugs and get the aircraft's systems into proper working order. Measured range performance indicates it can make the long trip. "It's in pretty good shape for the round-the-world flight," says Scaled project engineer and test pilot Jon Karkow. Fossett expects to fly it to the Salina mission base this month, possibly as soon as this week, then make a few flights of his own before the record attempt. He has already flown it several times from Scaled's facility here.

Mission sponsorship was originally by Fossett, and then picked up by Virgin Atlantic in October 2003 (AW&ST Jan. 12, 2004, p. 50).

The aircraft has a maximum takeoff weight (MTOW) of 22,000 lb. and a zero fuel weight with pilot of 3,700 lb., meaning that 83% of the MTOW is fuel, or conversely only 17% of it is not fuel. The structural fraction is lower than probably all other airplanes, and is especially impressive with a spindly wing aspect ratio of 32.5:1. Lift-to-drag ratio is estimated at 37.

The composite-material Voyager has been the exemplar of combined structural and aerodynamic efficiency, and had a zero fuel weight fraction of 28%. GlobalFlyer is a remarkable 39% less than that. It is also made mainly of graphite-epoxy composite, mostly in honeycomb form. One reason that GlobalFlyer is relatively lighter is the turbofan engine, which has higher thrust-to-weight ratio than Voyager's piston powerplants. Another reason is that much of Voyager's structure was thicker than needed because of minimum gauge limits; the bigger GlobalFlyer doesn't carry this extra weight.

The powerplant is a single 2,300-lbf. Williams FJ44-3 ATW turbofan. The fuel system has 13 tanks--six per side and one 31-gal. header tank in the aft fuselage that supplies the engine (see drawing, p. 49). Each side has a forward and aft boom tank with jet pumps that keep the header filled. An automated fuel transfer system switches among the boom tanks to maintain lateral and longitudinal balance. The boom tanks include sections inside the inboard wing. Each outboard wing has four fuel tanks that gravity-feed into the boom tanks by pilot-controlled valves.

Rare JP-4 fuel is being used because of its low freezing point to handle a three-day cold soak. The tanks were designed for a total of 2,915 gal. of heavier Jet A fuel but have measured a few percent small. With JP-4 at 6.35 lb./gal., they hold 18,000 lb., and full-tanks takeoff weight is 21,700 lb., 300 lb. shy of MTOW.