Tiny Turbines | Flight Today | Air & Space Magazine

Tiny Turbines

Ever seen a radio-controlled model aircraft do 300 mph? Visit Metropolis, Missouri, this fall.

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AMID THE HIGH WHINE OF TURBINES SPOOLING UP, the booming rumble of hot exhaust gases, surges of jet blast kicking up waves of sand and grass, and the sharp smell of jet fuel, a Grumman F9F-5 Panther is in the initial stages of startup. Wearing regulation Navy blue and sporting a sliding canopy and tip tanks, it is a glossy, beautiful machine, one of the best-looking on the ramp. Stenciled below the canopy is “Comdr. Lewis Patton Jr.” However, Commander Patton will not be in the cockpit, which is occupied by a pilot figurine. He will be flying the Panther from the ground at this gathering of radio-controlled jet models and their pilots.

It’s a fine Friday morning in early October, day five of Superman Jet Week at Metropolis Municipal Airport in southern Illinois. Scale-model jets have been streaking past the show tents at 200 mph and performing extreme, seemingly impossible, and otherwise deranged maneuvers since shortly after sunrise. Most of these are big machines, some almost eight feet long, with wingspans of seven feet or more. Patton’s craft (84 inches in both length and span, 34 inches tall with gear extended, and 50 pounds in gross weight) will be joining them aloft as soon as he starts the engine, a procedure that, although the specifics differ slightly, takes about the same time as is needed for a full-size jet. “About 30 seconds,” Patton says. “Introduce air, propane, then back up to air, and then it spools up to idle rpm, and once the temperature’s okay, then you’re ready to go.” He uses propane first because it ignites more readily than Jet A fuel, a type of kerosene, which he’ll switch over to at idle speed—a mere 40,000 revolutions per minute. “Max rpm is 115,500,” he says.

Patton is monitoring the engine’s performance with a clutch of instruments in a red Radio Flyer wagon. Slung underneath the wagon is an air tank used to spin up the turbine; in the wagon is a propane tank, assorted wires and tubing, a frequency scanner, an engine data terminal with digital readout, a programmer, and myriad meters, dials, quivering needles, flashing lights, buttons, and switches.

Soon the engine is emitting a fine roar and the Panther trembles with barely suppressed intensity. The turbine is now feeding from two portable tanks of Jet A, one atop each wing. At max thrust, the tiny turbine engines burn 12 to 16 ounces of fuel or more per minute—at least a beer bottle’s worth—and the internal fuel cells are so small—22 ounces each (although a given craft may hold two or three)—that the engines must draw from external tanks until just before takeoff.

Finally, Patton’s assistant, Keith Yates, who wears a blue cap bearing the Superman “S” logo, switches to internal tanks, and Patton gathers up his cigar-box-size radio transmitter, which has dual joysticks, six toggle switches, and an LCD screen. Walking behind the Panther, he taxies out for takeoff.

Runway 36-18 is a standard 4,000-foot length of black asphalt. The model takes its position on a yellow stripe, the engine spools up to an earsplitting shriek, and the F9F blasts straight down the centerline. It’s off the ground, as if shot by a catapult, in seven seconds.

Though Patton, a retired middle-school band leader from Louisville, Kentucky, has sunk $11,000 in this machine, he does not baby it around the pattern. “He’s up there doing slow rolls on top of a perfectly vertical climb,” the announcer says. (Perfectly vertical climbs are pretty much the only type of climbs here.) This is followed by a vertical dive (ditto), then a thundering low pass down the runway, followed by a vertical pullup embellished with two snap rolls. At about 200 feet, the airplane goes over on its back, drops through a two-turn inverted spin, recovers… After about six minutes of further gyrations the Panther is low on fuel, so Patton powers back, transitions to slow flight, lowers the landing gear, and, while another model lands, makes a “gear pass” down the runway to check if all three struts are fully extended. Satisfied, he makes a slow climbing turn to downwind, then sets up an approach. With full flaps and gear intensifying drag, the airplane’s glide path resembles at best a controlled plunge, but at the last moment it levels off and Patton paints the thing on so smoothly you’d swear he was in the cockpit. When he applies the brakes, you can hear the tires squeal.

The Superman jet rally kicked off in 1988, when Jerry Caudle, a pilot who also happened to be manager of the Metropolis Airport and a modeler himself, put on a flying competition for radio-controlled jets. At that time, most jet models were powered by ducted fans, miniature piston engines driving seven-blade propellers inside ducts.

The rally drew 45 pilots. Ten years later, the Superman rally was regularly pulling in 200-plus enthusiasts from 30 states and a dozen countries. Last year’s event brought pilots and airplanes from Hawaii, England, Argentina, Venezuela, Germany, Finland, and Japan. Even Caudle, however, has trouble accounting for the rally’s hold over jet modelers. There are major radio-control jet events annually in Lakeland, Bunnell, and Lake Wales, Florida; Tucson, Arizona; Chino, California; and Whidbey Island, Washington, with regional contests held all around the country. “This is more or less a fun fly, where everybody gets to fly as much as they want,” Caudle says. “It’s just an annual event that in the last two or three years has been the largest event of its kind in the world.”

Location seems to have played no role in attracting an international crowd to Metropolis (population 6,700), which, being a 180-mile drive from St. Louis and the closest major airport, is equally hard to get to from everywhere. The city itself has a down-at-the-heels look, I tell him. “This city?” Caudle says, affronted. “It’s got a riverboat. They just paved every street and alley in town. It’s got all new sewers.”

Even with its magnificent sewers, however, this is a town of no particular charm, consisting mainly of used-car lots, video stores, tire outlets, bargain huts, gas stations, and closed businesses. On the other hand, there is the Superman effect.

In the early 1970s, resident Robert Westerfield, mindful that the legendary Man of Steel hailed from a fictional Metropolis, saw a golden opportunity: Why not officially declare the city the Hometown of Superman? Unconcerned that Superman was born on the planet Krypton and raised in Smallville, Kansas, the Illinois House did exactly that in 1972. Metropolis now boasts a Superman Car Wash, a Superman Museum, and a 15-foot bronze Superman statue smack in front of the Massac County Courthouse.

What all this has to do with the success of Superman Jet Week is debatable, for the only thing Superman and the scale-model jet fliers seem to have in common is an inordinate love of speed. “My husband’s Bandit easily does over 200 miles an hour. My BobCat will only do about 175 or so,” says Dawn Ellzey, a travel agent from Grand Prairie, Texas, and a modeler who also holds a multi-engine rating in full-scale airplanes. “The speed is a definite factor for the turbines.”

“That one is capable of 300 miles an hour,” says Patton of another of his models, a Predator 175. “But we’re regulated by the AMA [Academy of Model Aeronautics] to 200, so I’ll be flying half-throttle most of the flight.”

All this velocity is a function of the turbine engine, which is often the most expensive component of a model jet. Modelers generally build their own aircraft from scratch or kits, which range all over the map in price, materials, and amount of assembly required. A basic “sport” model is a conglomeration of balsa wood, fiberglass, and carbon-fiber composite materials that costs from $2,000 to $8,000 or more.

The turbines that power them are mechanically complex, technically demanding, and electronics-heavy precision instruments. The P200, a state-of-the-art JetCat engine made in Germany, is five inches in diameter, weighs less than five pounds, and, at a max rpm of 112,000 and exhaust gas temperature of 1,240 degrees Fahrenheit, gulps 23 ounces of fuel per minute to produce 50 pounds of thrust. Total cost, including accessories: $4,995.00. Put one of these in a model aircraft and everything starts to happen fast—sometimes too fast.

Early in the afternoon Mike Fuller is flying an Aermacchi MB339, a specialty sport model built by Jack Mathias. (It is not unusual for builders to have someone else do the flying.) Both live in Evansville, Indiana, and have driven here in a camper. With the airplane on final approach, Fuller senses that it’s handling a bit strangely and suddenly realizes he has forgotten to lower the flaps.

When he does, the airplane pitches down and before he knows it, makes what might politely be called abrupt contact with the runway. It bounces, which bends the nose gear (though Fuller does not realize this at the time), then slews into the grass but keeps streaking along. In order to finish with a proper approach and landing, Fuller firewalls the throttle for a go-around. The model shrieks back into the air but on the downwind leg it slows, staggers, and crashes in a bean field along the runway.

“I just lost airspeed,” Fuller tells Mathias later. “When I made that turn and started downwind, all of a sudden it slowed down and I said ‘We’re in trouble, we’re in trouble.’ I was just trying to coast it and get a rudder turn and get in, and it never picked up speed.” “But you don’t think the engine quit,” says Mathias.

“Yeah, I do,” says Fuller. “There’s no way that that engine shouldn’t have powered me out.”

“God, that was ugly!” Fuller adds. “What is your saying, Jack? ‘Run out of airspeed…’?”

“You run out of airspeed, altitude, and ideas, all at the same time. That’s what causes accidents.” Much laughter.

Later, Mathias sent the engine back to the manufacturer, SWB Turbines of Neenah, Wisconsin, where technicians found the combustion chamber clogged with grass clippings but otherwise undamaged.

Earlier that day, Dave “Stick” Valdez, who drove a van from his home in Orlando, Florida, was admiring his fiberglass BVM Maverick Pro as it performed a split-S, a maneuver he’d done at least a hundred times. Five other aircraft were aloft simultaneously, including a balsa model flown by Kevin McLeod, a Canadian from Burlington, Ontario. Both pilots had their eyes glued to their aircraft, Valdez watching his come straight down from the top of a loop, McLeod monitoring his as it turned from crosswind to upwind, when suddenly both saw that the two models had merged. Fragments fluttered into the nearby acreage, whereupon Jerry Caudle trundled off in his golf cart to pick up the pieces.

“It happens,” Valdez says later. “It’s nobody’s fault. You can do whatever you want here, as long as you maintain that oval pattern. And we were both doing it.”

“This was my third flight of the day,” McLeod says. “And everything was going real good until…I speared him from behind.

“The engine’s come out quite well,” he adds, eyeing his SimJet 1200 turbine as it cooled on the ground. “I haven’t run it up yet. It looks like it might have ingested a little bit of dirt, but there’s no damage to the compressor blade and it spins over smoothly, so that’s usually a good sign.”

Indeed, a little FOD (foreign object damage) is nothing insurmountable here, not with the presence of the Repair Technology International trailer and turbine mechanic Carlos Villarreal. Based in Miami, Villarreal travels from one jet rally to another with his mobile repair shop, in which he can rectify practically any engine failure short of a major burnup in just a few hours.

“I have a balancing machine in the trailer, I’ve got a lathe, I’ve got all kinds of welding equipment—everything I need.” His workbench is covered with what seems like hundreds of wrenches, screwdrivers, drills, pliers, torches, and so on, all neatly stowed in their allotted spots. He has an endless supply of ceramic ball bearings, bearing housings, combustion chambers, turbine wheels, compressor wheels, glow plugs—the works. Jet engine repairs are not cheap—a simple bearing change, the most common fix, is $295—but at least you’re flying again.

Spend some time on the rally grounds and you realize that the emblem of BVM Jets is omnipresent. The trademark appears on hats, jackets, T-shirts, coolers, and the wings and fuselages of the models. BVM stands for Bob Violett Models, a top manufacturer of radio-controlled jets. “Probably 40 percent of the aircraft out here are Bob Violett’s kits,” says Vernon Montgomery, a modeler from Mississippi who is flying a BVM F-4 Phantom II.

Violett flew the Douglas A-4 Skyhawk during the Vietnam War. “I flew a combat tour over North Vietnam,” he says. “I got shot at a lot, dropped a lot of bombs and rockets and missiles—flew 83 missions off the USS Hancock.” He flew the Vought F8U Crusader with the reserves, and in peacetime, he flew Lockheed Electras and Boeing 727s for Eastern Air Lines for 18 years.

“I started off as a modeler very early in life,” Violett says. “They say I taught myself to read to be able to build models around five years old—that’s how the story goes.” In the early 1980s he started building models and selling them out of his garage. Today he runs a factory in Winter Springs, Florida, oversees 20 employees, and keeps expanding the technical boundaries of turbine-powered model aircraft.

Violett’s star product is a scale F-100F Super Sabre, which, in pictures at least, is indistinguishable from the real thing. And, Violett says, it flies even better. “We use gyro augmentation on these jets, on the vertical axis and the rudder,” he says. “As in all swept-wing airplanes, they have something innate: Dutch roll. Anytime the airplane is upset, one wing is always advanced in angle of attack, so it’ll pitch up a little bit, and that causes more drag, and so it starts an oscillation.” The airplane ends up wagging its tail from side to side like a happy dog. To dampen the oscillations, Violett and his engineers attached piezoelectric gyros to the rudder, devices that sense Dutch roll and cancel it through slight rudder movements.

“They make you look like a much better, smoother pilot,” Violett says of the gyros. “They take all the wiggle out of the airplane.” The resulting stability is much in evidence when Violett maneuvers his Super Sabre through a flawless four-point roll, a maneuver that, because of its difficulty, is rare among jet modelers.

At 5 p.m., free beer and pizza are served in a tent near the food stand where, earlier in the day, $3 elk burgers were sold. One of the last to fly is Gary Jefferson, a packaging materials salesman from Monroe, Ohio. He wants to get in just a couple of more flights before he has to quit for the evening.

It’s getting cold and overcast now, not to mention gusty, and Jefferson’s wife, Sandy, has pulled on a coat, though it doesn’t seem to help much. Even the family dog is wearing a red blanket.

Jefferson, undaunted, blasts his FiberClassics Rookie around the pattern and goes through the customary show of wild aerobatics until he can barely tell which side of the model is up. “See, you can still tell the fin’s on top,” he says, squinting into the gloom. Finally it’s too dark even for him. He makes one last, perfect landing. The engine spools down. Time for a beer.

Sidebar: The Primordial

In the 1950s and ’60s, the Dyna-Jet Red-Head pulse-jet engine was the hot ticket in control-line model airplane circles. Based on the same operating principles as the engine that powered the German V-1 buzz bombs of World War II, it produced self-sustaining resonant shock waves. A mix of lantern fuel and air was ignited in a combustion chamber, and the resulting explosion would force a spring-steel valve (the sole moving part) behind it to slam shut. As the blast exited the exhaust tube, a wave of low pressure rippled back toward the chamber, sucked open the valve, and drew in another charge of fuel and air. The mixture, ignited by the heat remaining in a spark plug, repeated the cycle until fuel was exhausted.

Whether one mounted it on a hardwood stick fuselage with tiny wings and went for straight speed (Dale Kirn set the first Academy of Model Aeronautics record for jet speed, 154.98 mph, with a Dyna-Jet in 1954) or encased it in a model F-86 or MiG-15, producing a Dyna-Jet-powered model at the local flying site drew a crowd faster than a bag of free money.

Everything about the Dyna-Jet was abrupt. It was either completely off or way-the-hell on. It took a ground crew and a certain finesse to evoke just the right conditions for the pulsing explosion cycle to become self-sustaining. An old Ford ignition coil fired a spark into the combustion chamber while a bicycle pump ushered a blast of air and white gas through the intake nozzle; the latter more often than not would just drizzle out the tailpipe. It was usually easier to set the grass on fire than to get the Dyna-Jet lit. Once a few loud burps got the combustion chamber hot enough to ignite the next charge, one lucky start attempt would result in a sudden and devastatingly loud roar, and the model would strain in the holder’s hands while the pit crew attempted to maintain their wits long enough to disconnect the starting apparatus and clear the launch area. The previously curious cluster of spectators would scatter for cover. Just getting a Dyna-Jet-powered model airborne was its own pinnacle of achievement—unlike stunt, combat, or any of the other categories that require actual flying.

When the pilot gave the signal for release, the model would lunge forward and roar around a circle defined by the control lines until velocity overcame the high wing-loading (the amount of weight the wing had to lift). In due course the craft would climb to cruise altitude (shoulder height). For the next few minutes, there was little for the pilot to do but hang on, hope the control system did not come apart, and wait for the fuel to run out. The series of gasoline explosions caused 250 individual pulses to cascade out the tailpipe every second, creating a Doppler-shifted wail of indescribable proportions while the hapless model was flung by its gigantic blowtorch, constrained by two improbably slender control wires and the grim determination of the pilot.

About the time spectators began to creep closer, the concussive roar would abruptly cease. The model would then best be flown onto the ground as quickly as possible. In the silence that ensued, all present would absorb the event and then store it in the little alcove of memory reserved for Truly Remarkable Incidents.

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