July 1, 1991
MARC E. COOK
Dick Rutan grips the airplane's twin throttles and signals the crewmember manning the external power cart for engine start. Another of the crew nestles two 8-foot lengths of clothes-dryer duct — wired side-by-side, shotgun style — against the twin exhaust pipes atop the engine nacelle to keep the raw methanol from streaming back over the cowling. As starter whirs to life, the planetary gearbox clanks and rattles like a Maytag full of Crescent wrenches. A moment of this acoustic torture and the motor springs to life, emitting an urgent moan more akin to a high-powered sports car than to a racing airplane.
This is only a test, a session to evaluate software changes, and only one engine will be running. But even though the crew has been through hundreds of starts, there's still a sense of urgency, anticipation. What is struggling from sleep is arguably the most sophisticated, modern piston engine yet fitted to an airplane. As such, it needs tender loving care in quantity accorded to thoroughbreds; that is, a lot. It does, after all, have a noble mission to accomplish. Alongside its twin brother, it might assist an equally high-technology airframe capture the world speed record for piston-powered aircraft and, perhaps, prove victorious in Unlimited-class air racing.
And then there's the smell: unburned methanol with a dash of castor oil. Yes, for all its painstaking development, the newest and brightest Unlimited racer and potential record-setter smells for all the world like a model airplane. For all your nose knows, you could be standing behind a radio-controlled eighth-scale Skyhawk.
Later in the afternoon, Rutan is back in the cockpit to test the latest round of software revisions to the engine management computer. Though the airplane is firmly anchored to terra firma, Rutan wears flight suit and helmet. As engine speed rises, the six cylinders' exhaust note turns harsh, and the insistent whine of two turbochargers becomes more prominent. Following a few minutes of low- and medium-power ground running, the liquid- cooled motor's stirring voice goes off song. Engine designer John Knepp consults the screen of a Macintosh computer linked to the engine controller and signals Rutan to shut the motor down. Knepp offers a fight smile. "Well, we fixed two problems today and found two more."
Unlimited air racing is a spectacular sport, dominated by spectacular airplanes. All are World War II-era fighters, or designs that borrow heavily from them, thanks to the requirement that the airplanes run piston powerplants. And in the world of speed, the more power the better, these ex- fighter/bombers — Mustangs, Sea Furys, Bearcats, Corsairs, and the like — still are the homes of the highest output piston engines. From crackling V-12 Merlins to 28-cylinder, four-row corncob radials, these powerplants are tuned to within an inch of their internal-combustion lives in the pursuit of speed. Lugging these slicked-up, pared-down mastodons through the air to complete laps at almost 475 miles per hour, the engines' life spans are measured in minutes, not hours. It is in some ways the sport of wretched excess.
But to Robert J. Pond, it is also a sport that is sacrificing rare and irreplaceable airplanes for the sake of competition. A warbird collector himself, he feels strongly enough that the historic airplanes should not be bastardized as racers to have put a reported $3 million into a project to design and build a clean-sheet Unlimited racer. The result of this investment and three years of hard labor by the Bob Pond Racing team is, predictably dubbed, the Pond Racer.
If the current crop of Unlimited racers — with names like Rare Bear, Tsunami, Strega, and Dreadnought — look like weight-room miscreants, Pond's aeronautical obsession appears to have just come from the ballet studio. Designed by E. L. (Burt) Rutan, the twin is a mere wisp of an airplane next to the current bruisers.
Though the Pond Racer has no canard and only the suggestion of winglets (and they're at the tail, for Pete's sake), it is instantly recognizable as a Rutan design. Weighing just 4,150 pounds at maximum gross weight (with 80 gallons of methanol in the wet wing), the Pond is a true lightweight compared to the current Unlimiteds. Extensive use of graphite in the composite structure helps make it so svelte; it weighs approximately 3,500 pounds empty. About all the Pond has in common with your average Unlimited is conventional gear.
Safety concerns dictated much of the Pond Racer's design. "We wanted to keep the pilot away from the engines, should one blow," Dick Rutan says of his brother's design. "It's been criticized as having too much wetted area," Rutan says, "but the safety is worth it." Each 20-foot-long boom carries an automotive-derived V-6 engine at the front, followed by the landing gear and radiators. The rear of the booms connect a forward-swept horizontal stabilizer to the centrally located cockpit and fuselage.
With a 25.4-foot span, the wing also is swept forward for structural reasons, namely for two hefty engine installations hanging way out front. Long-span, narrow-chord ailerons provide roll control, and they droop to mimic flaps. Postcard-size tabs control all three axes. Working space for Dick Rutan, the designated test pilot for the Pond Racer, is minimal. Asked if the 5.5 x 2-foot cockpit is comfortable, he responds: "No. But you don't have to spend much time there, either." Shoehorned into a space just big enough for the pilot is an instrument panel that is a model of miniaturization. An example: A pair of J. P. Instruments EDM-500 computerized engine instruments monitor all motor parameters and signal the pilot should any of them fall outside limits. These two instruments take the place of more than two dozen. The remainder of the instruments are all of the 2.25-inch variety to save space.
The cockpit begins about a foot behind the leading edge of the wing and terminates in a large central vertical fin and rudder, the total length of the fuselage is 16 feet. Small winglets are included on the horizontal stabilizer, and their size will soon be reduced. They enhance lateral stability, which Rutan claims is so good that they are not really needed.
At press time, the Pond Racer had made eight flights at speeds of up to 360 mph (312 knots) using about 40-percent power, which is a long way from the desired top speed of 530 mph (460 knots); that goal is predicated upon the current record for piston-powered flight held by Lyle Shelton's Bearcat of 528 mph (458 knots). According to Rutan, the airplane handles well, with little adverse yaw and excellent directional stability. It is, however, marginally pitch stable, according to Rutan, and one of the development projects is to improve that.
Rutan also says that ground handling of the Pond Racer is exemplary. "I thought at first the landings would be tough, but then I realized that you can see the ground coming up to meet the mains. It's a sweetheart." His eyes sparkle when he tells you that the Pond Racer has the wing loading of an F-15. "This is a long way from Voyager," he says.
The heart of any racer is the engine, and each of the Pond Racer's has a heart not so much of gold, but of silicon. A dictionary-size computer, nestled above each engine near the fire wall, is responsible for timing and duration of the fuel injection and ignition systems and control of the wastegates, as well as collecting data from myriad sensors in the engine bay. After a flight, the computer can be tapped for information ranging from boost pressures to ignition-timing maps. Computer control makes for fast, straightforward troubleshooting; in fact, for ground testing, the on-board computer is linked to the Macintosh to make minute adjustments.
In every sense, the engine, built by Electramotive, Incorporated, in Vista, California, is at the forefront of technology. The fuel injection system, for example, uses two sets of injectors per cylinder, one high-flow and one low-flow; together, they can handle the engine's widely varying fuel demands. At maximum power, 1,000 horsepower at an engine speed of 8,000 rpm, it will gulp more than 220 gallons per hour of methanol per engine.
This is a long way from the engine's roots, too. Based on the V-6 found in the previous-generation Nissan 300ZX and the current Pathfinder sport-utility vehicle, the Electramotive engine has seen tremendous success in Nissan's racing cars. For the past six years, the Nissans have been the cars to beat in the International Motor Sports Association's grand-touring, prototype (GTP) class — a class conceded to be on the leading edge of auto racing and the springboard for a lot of new technology. The cars until this year have been powered by the Electramotive engines. While its roots might be Nissan, the engine's sole off-the-shelf parts are the cylinder heads, and they are substantially modified. The block, pistons, valve train, and all major components are either built at the Electramotive plant or sourced from the many high-performance aftermarket shops in southern California. In the Pond Racer application, the basic Electramotive engine is almost identical to the Nissan race cars'.
Squeezing a great deal of power from a 3.2-liter (194-cubic-inch) engine requires high engine speeds and tremendous turbo boost, up to 50 inches. To put this in perspective, the road-going 300ZX turbo now in production makes 300 hp from a 3.0 liter engine; in the car's favor are four- valve-per-cylinder heads (the Pond Racer's has two valves per cylinder) and intercoolers for its twin turbos. Each bank of three cylinders feeds (and is fed by) its own turbocharger, which works with an electronically controlled wastegate. There are no intercoolers in the Pond Racer — there simply was no place to put them. Methanol fuel was specified to help reduce combustion temperatures.
Truth be told, getting the horsepower from this engine will not be as daunting as was the packaging. Viewing the engine with the cowlings off shows more hoses, ducts, and wires than motor, it is the classic case of 10 pounds of flour in a 5-pound bag. According to designer Knepp, the original plan was to have the turbos and associated plumbing as well as the computer located behind the fire wall. Space considerations moved all that hardware forward, making the nacelles as crowded as a Tokyo subway at rush hour. Making it all fit can be said to be a genuine engineering miracle.
These engines unleash their mighty motive force through planetary gearboxes that in race trim will have a 3.74:1 reduction ratio — at 8,000 engine rpm, the props turn at 2,139 rpm. (For development purposes that ratio is 2.6:1.) The gearboxes drive four-blade aluminum propellers. And why not composite props, you ask? Cost is one consideration, and aerodynamics is another. The blades, built by Hartzell and designed by airfoil guru John Roncz, are machete-thin at the tips, a feat that could not be accomplished with composite props. The reason for the thin airfoil is to reduce drag, because the tips will be working in the transonic range — about Mach 0.98.
Rutan won't speculate about whether the team will be ready for the Reno Air Races this September, but it's clear from the intense pace of development that the deadline looms large in the crewmembers' minds. If they miss the race, the Pond Racer will be pointed snout-first at a world speed record run — actually that will happen regardless of Reno, but Pond himself would sure like to see the airplane race in the desert first. For Rutan and for Pond, the airplane's maturation cannot happen a minute too soon. To prove that an unconventional design can be not only competitive, but a winner has long been a credo held by the brothers Rutan. And to Bob Pond, seeing his namesake racing endeavor succeed would slake his considerable thirst for success, and, perhaps, even save a few old warbirds in the process.
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