News Article

The Spin Doctor
Date: Jun 20, 2014
Author: Eric Stewart
Source: KitPlanes ( click here to go to the source)

Featured firm in this article: Catto Propellers of Jackson, CA

Craig Catto is nearing his fifth decade building propellers for Experimental aircraft. Those first propellers still hang above his desk: small hand-carved wood props that spun at 8000 rpm in front of the McCulloch 12-hp two-stroke go-kart engine he was using to motorize his Icarus II hang glider. He tells the story of testing them in the backyard of his childhood home, using bathroom scales to measure thrust and methanol to send the tips past Mach 1. One can only imagine what the neighbors thought.

These days Catto tries to avoid the sound barrier and depends on aerodynamics, rather than methanol, to push the envelope; the deafening scream now is not from his propeller tip speed, it's from demand for his props. Riding the coattails of the Van's RV revolution, word quickly spread to other Experimental communities about the awesome performance of Catto props. His props are so hot in fact that there is a four- to six-month wait time, and if he gets the type certificate for Super Cubs, he figures he'll be able to take orders for $1,000,000 worth of props over the three days of the Alaska Aviation Trade Show.

Catto's propellers dominate the biplane class at Reno and hold numerous world records in speed, time to climb, and altitude. His props have powered the last four consecutive winners in the Experimental bush class at the Valdez fly-in STOL competition, helped take Bruce Hammer and his Glasair 1 to first place in last year's AirVenture Cup, and pulled NASA's Pathfinder to more than 80,000 feet in 1998. Recently, Catto props have become popular among unlimited aerobatic pilots due to their excellent performance and low inertia; Australian unlimited aerobatics champion Paul Bennett has a Catto up front on his Pitts S-1S.


The Icarus II motorization began in 1975, when Catto was just 15—before he even had a driver's license (though he had just gained his glider ticket). "I can't believe my parents let me do that," he quips, as he recounts the story. When I ask how he had the confidence to attack such a project, he laughs and simply says, "I had no clue. I didn't know any better."

The Icarus II was a foot-launched glider, and when Catto first took his motorized version to the sand dunes along Pismo Beach (south of San Jose where he grew up), the rat finks in their dune buggies laughed at the tall geeky kid with the Rube Goldberg contraption of wings and wires. Undaunted, Catto dove into the wind, at first "barely moonwalking over the ground," he laughs, but soon buzzing along 12 feet above the dunes, a bevy of Super Beetles trailing behind and cheering him along as he flew up several miles of coastline. He landed with his 15 minutes of fame secured, and an entrepreneur. His first aviation business was selling the Icarus II motorization kits—complete with hand-carved propeller, of course.

Within two years, he was selling kits for a pair of flying-wing gliders of his own design, the CA-14 (wood wing) and CA-15 (fiberglass and stamped aluminum). He still has the informational brochure, which is surprisingly professional in its layout for someone fresh out of high school (Catto graduated high school in just two years). He continued to buzz around in ultralights of his own design, winning "best float" at the 1977 Everett, Washington 4th of July Parade (flying 200 feet above the parade route with the King Broadcasting logo on the underside of his wings), and being featured on the TV show, To Tell the Truth, that same year, and in People magazine a year later. All while still a teenager.

Goldwinger, Odd Jobs, and Prelude to a Swift

In 1979 Catto jumped into a Citabria and went airport hopping along the west coast, north from Grass Valley, down south to Mariposa, looking for a place to set up shop (to the relief of his parents' neighbors, no doubt). At Jackson County Airport, about 40 miles southeast of Sacramento in the foothills of the Sierras, he found a large hangar he could rent for $500 per month. There he established a factory to build kits for a canard ultralight he'd designed called the Goldwing.

In conjunction with Brian Glenn, to whom he had licensed the rights, Catto built more than 1500 kits—his first large production success. "The first six months were great, but then Glenn realized he wasn't making any money, and things got harder after that," says Catto.

Catto's Acro-X. Craig joined the "Caterpillar Club" when he was forced to bail out and parachute from 500 feet when the Acro-X lost its canopy, jamming in the wing cross brace wires. Looks like a cross between a Vari-EZ and a TIE-fighter? Yep, both Lucas and Rutan had premiered their classic works a few years earlier. Note the wingtip-mounted wheels, a la the original Quickie.

When production ceased in 1982, Catto decided to build propellers full time. He moved his shop up to his home atop Mokelumne Hill, where it has been ever since, until moving back down the hill to a new 10,000 square foot facility at Jackson Airport earlier this year. That said, Catto's curiosity and entrepreneurial spirit run wide and his professional work extends far beyond propellers: in addition to hang gliders and ultralights, he built two airplanes of his own design, the Solo (a composite ultralight resembling the Cessna 150) and Acro-X (a composite knockoff of a Star Wars TIE-fighter). He has built wings and tails for several gold class Formula 1 Reno racers (Endeavor, Outrageous and Scarlet Screamer), patented an articulating snowboard, and even sold his design for a solar-powered electric standup scooter to a Japanese company. He visited the country twice. "It was an awakening for me to see that level of social organization," he says with admiration.

As we flip through Catto's scrapbook, we begin talking about flying wings (Catto was invited by owner Howard Long to fly the prototype Mitchell wing). He was one of the initial developers of molds for rigid-wing hang gliders, and I ask him if he is familiar with the SWIFT. Familiar turns out to be an understatement. "The SWIFT wouldn't be here if it weren't for the work we'd done," says Catto.

The story begins in January 1985, when Catto, Brian Robbins, and Eric Beckman set out to design and build a revolutionary new hang glider that they named Odyssey. Key to the development of the Odyssey was a rigid wing utilizing a molded D-tube of composite construction. Few aircraft so well embody the definition of composite: the wing skin was fiberglass, Kevlar, carbon, and Mylar over ribs of aluminum and foam. The project progressed rapidly over the next two years, and in 1989 Brian Porter joined the team and piloted the Odyssey to first place in the U.S. National Hang Gliding Championships in Dunlop, California.

Coincidentally, a team of grad students under the leadership of aeronautical engineering professor Ilan Kroo at Stanford University had also begun work on designing a high-performance glider with some of the same objectives as the Odyssey at almost the exact same time. In contrast to the Odyssey team though, Kroo's team had never gotten beyond computer analysis, although as an article in the January 1991 issue of Hang Gliding wrote, "The design became perhaps the world's most thoroughly analyzed glider." Fortunately, one of the Stanford PhD. students met Porter at a fly-in, and it wasn't long before the Stanford team, building on the lessons learned with the Odyssey, flew their own rigid-wing hang glider called the SWIFT.

Catto points to another picture of a fly-in in the scrapbook. The ultralight-crowded field looks curiously like a baseball diamond. "Yep, it's a baseball field at Half-Moon Bay. This was the Half-Moon Bay Air Race," Catto confirms. There are crowds of people more or less defining the edges of the "runway" that points out to sea, and a party atmosphere. "Looks like the crowds waiting for Lindbergh, doesn't it?" laughs Catto. It's easy to forget that for a brief heyday in the '70s and '80s, hang gliding was a huge part of the Experimental aviation movement and together with ultralights served as a gateway—as it did to Catto—for many of today's captains of Experimental aviation.

Catto's Numinous Corkscrews (CNC)

Until recently, Catto built all his propellers by hand. Laser-scanned measurements have revealed that pitch was accurate to within 0.2 degrees, and profile accuracy was "pretty scary," says Catto. "I scared myself sometimes when I threw templates on. I'd carve them down, throw the templates on, and it was spot on. When I saw that, I said to myself, ‘I've been doing this too long.'"

Fortunately in 2009, Catto was approached by CubCrafters to supply props for its Carbon Cub SS kits. Catto realized then that there was no way he'd be able to meet demand without introducing automated manufacturing processes (he had a single helper and made at most eight or nine props per month). So, with zero experience in industrial manufacturing, Catto purchased a laser scanner, a used 5-foot x 10-foot CNC router, Rhino 3D CAD software, and CAM software.

"The manuals for these four tools were over 900 pages. So every night after work, I'd come in and read the manuals to figure out how to make this thing work. I even called the cable company and told them to temporarily suspend my TV subscription so that I could focus," says Catto. "I would sit in my kitchen and read and think I had it figured out, then go out to the shop and get as far along as I could on the CAD. Then I'd stumble, so I'd go back and read some more, and I'd get through the CAD and make it to the CAM. Suddenly it was creating tool paths, and now I could actually hook it up to the CNC machine to make stuff."

Within 6 months, Catto had decoded the system and began manufacturing his first CNC'd props. These days, the CNC chatters constantly. The number of full-time helpers has increased from one to five, and the company is currently shipping 50-60 propellers per month. A second CNC machine has been added to the tooling stable, and Catto has his sights set on gaining STC approval for Cubs and eventually even Cessnas.


So how about performance? At the slow end of the spectrum, Catto's props have become all the rage for STOL aircraft, since the low speeds do not necessitate a constant-speed prop and a premium is placed on weight savings. Fixed pitch are, of course, significantly lighter than constant speed, and Catto's props are among the lightest fixed-pitch propellers, typically weighing 10 to 14 pounds, depending on diameter and number of blades. The results from the annual Valdez STOL competition speak for themselves.

Catto Props has also recently teamed up with Just Aircraft to produce propellers specific to the SuperStol (see the October 2013 issue of KITPLANES for the SuperStol and Highlander kit review). Previously, customers were limited in their choice of props for the Rotax installation, with optimization being achieved via ground-adjustable units that were geared more towards higher cruise speed LSAs.

"I'll talk about this out at Oshkosh this year," says Catto, "but the problem with ground-adjustable props is this: ideally if you increase the pitch one degree at the tip, halfway out should be about two degrees, and four degrees nearer the hub. But on ground-adjustables, you change the whole blade the same one degree. This changes the spanwise loading—it can be all over the place, so you never have an ideal spanwise loading. That is where we can typically see big improvements in efficiency." By designing a prop customized to the SuperStol and Highlander engine and aerodynamics, Catto's props are much more efficient—to the tune of 25-30% improved climb rate with no penalty in cruise.

"I've been trying for years to get props made for STOL aircraft, and there wasn't a manufacturer I approached who didn't say ‘no,'" says Troy Woodland, designer of the SuperStol and Highlander. "One told me to send them a purchase order for 50 props and they could do it. Well, at Oshkosh last year, I was again in the tent of one of the big manufacturers trying to convince them to make me a prop, with no luck. I went back to my booth and 15 minutes later Craig happened to walk by, and we started talking props. He committed right then and there to make a prop for the Rotax/SuperStol and Highlander combo.

"As far as I'm concerned, this prop is a game-changer for us. I can take off in my parking lot (see the video) on any given day, and before, in order to pull that trick, I needed a breeze. Getting 400 pounds of thrust from a Rotax is unheard of —I used to be getting 375 pounds or less, depending on the prop—and now we are getting 440 pounds on a stock 912S. To me a 20-pound increase used to be huge, so 65 pounds is just unbelievable.

"With development, our planes have gotten a bit heavier. I'm usually not worried about getting in somewhere, but I was sometimes nervous about getting back out. Catto's prop has solved that problem for us. And with the SuperSTOL landing gear, prop clearance is not an issue." Within 24 hours of announcing the joint venture, Catto had three orders for Catto Highlander props.

Catto has also recently finished certifying his props for the LSA Carbon Cub SS to AS™ standards—the first propeller manufacturer to achieve AS™ status. "Overall we've been very pleased with our relationship with Catto Propellers," says Randy Lervold, general manager at CubCrafters. "The AS™ certification standards are going up all the time, and the propeller standards have become particularly difficult. The AS™ requirements for a propeller now require five hours at full rpm, 45 hours at 90% power, and 100 hours total service time. We worked closely with Catto on the certification, and the propeller performed flawlessly. Even before the AS™ certification, we had been using Catto props, which have consistently outperformed everything else we have tried."

In between slow and blistering is the vast playground of most Experimentals that are Catto's bread and butter: RVs, Zeniths, Velocitys. Catto actually got his start in the Experimental aircraft market with the Long-EZ/pusher crowd. "For canards it's not a matter of ‘if' something goes through the prop, but ‘when,'" laughs Catto. "My props are known for taking the abuse. Over the years I've had four canard owners call me and credit my prop with saving their lives when major airframe parts—including an entire lower cowl—went through the prop and it still got them back home safely."

As many customers with unique needs attested to in the research for this article, Catto is quite willing (and even excited) to test new propeller ideas—especially projects that push the performance envelope. Bruce Hammer, winner of the 2013 AirVenture Cup, had tried numerous props on his Glasair. "Catto's was by far the best and strongest. One great thing about Catto is that he is very receptive to new ideas and working with the customer. If the prop is not performing the way you expect, he doesn't blame it on you or make you feel stupid; he works together with you to educate you and determine how to get the best performance for your airplane/engine package."

The ultimate litmus test, of course, for any prop is racing. Mike Thompson, Sport Air Racing League (SARL) chairman and founder, echoed Hammer's sentiments: "Exposure to the hyper-speed crowd (like Bruce Hammer) made me understand that high-rpm composite props are the key to success. Attached to the motor of most serious small race planes in the 100- to 250-hp range you will find a Catto prop." Thompson was also impressed with the smoothness of the prop as compared to his non-race aluminum fixed pitch, as well as Catto's uncanny ability to accurately predict speed at race rpm based on customer-supplied data in the non-race configuration.

Due to the extremely high rpm used on Formula 1 racers, Catto's wood core design can't handle the stresses imposed on the blade by high-G turns; for this, a solid carbon blade is necessary. However, his props are popular in the Biplane class where engine rpm is less extreme. Karl Grove, pilot of DragRacer, credits Catto with being instrumental to the continued improvement of Race #25 over the last four years at Reno.

"Catto is perhaps one of the most down-to-earth guys that I've met in air racing and aviation," says Grove. "Since the first time we met, Catto has continued to push the envelope every year with new concepts and prop designs in the search for that extra few rpm or hundredths of a second. He's always up for a challenge and ready to tackle the impossible by developing new construction techniques, new testing equipment, and diagnostics—where in my opinion he leads the industry."

Catto props are also a favorite for absolute speed and other records, where the prop can be optimized for a single flight condition. "Catto has been very supportive of our projects," says Dr. Paulo Iscold, professor of aerodynamics at UFMG in Brazil, consultant to several Red Bull and Reno air race teams, and holder of four world records with his CEA-308. "The first prop that he sent for our 308 was almost perfect, and the second prop was better than perfect. I'm not afraid to say that Catto's props are the best aerodynamic setup in the world today. He has been trying many different ideas through the years, and his propellers incorporate many features that are not listed in the usual literature. On the 308 I must remind you that we set the 3 km absolute speed record and the 3000 m time-to-climb record with the same prop!"

Catto props have set ten FAI world records in speed, altitude, and time to climb. By the time this article reaches press, that number may have increased if Iscold's Anequim achieves its predicted performance in its attempt on the C-1a record.

Catto will have a booth at AirVenture this year and will be giving two talks on propeller design and the CarbonCub AS™ prop certification. Stop by and say hi to the Doctor of Spin.