Valley Engineering

Culver Props

Reprinted with the kind permission of EAA Sport Pilot Magazine,
Mary (Sweet Young Thang) Jones, Editor

By Jim Busha
Photos by Jim Raedar and Chris Miller

            Attendees at EAA AirVenture Oshkosh 2006 reported some wild sightings! The outrageous claims included spotting a black-and-white cow with a thick barn-door-style wing strapped to its back meandering toward the flight line making airplane noises instead of mooing. Other concerned and equally panicked individuals spoke of a zebra-striped, winged metamorphosis of an animal with a short round snout resting comfortably on the grass just south of the Ultralight Barn.

            Although the hot, humid Wisconsin temperatures during AirVenture 2006 may have contributed to these delusions, rest assured no wild animals were roaming the grounds.

            What the perplexed crowd "down on the farm" saw was another of Gene Smith's designs called the Backyard Flyer. It was no animal, even though it jumped off the ground like a jackrabbit with its hind legs on fire and flew like a goose with spoilers.

            For the last handful of years, Gene Smith has been bringing new creations to AirVenture, and this year was no exception. As usual, a crowd quickly gathered around the ultralight with rapid-fire questions following from young and old alike; all of them marveling at the ingenuity.

            "Normally we bring a two-place trainer to Oshkosh ," said Gene, "but this year we decided to showcase an ultralight. Judging by the reaction, I think we made the right choice."

            In reality, the Backyard Flyer is a simple-looking design, almost cartoonish in nature, and by many accounts resembles an oversized child's toy. But make no mistake, this airplane, along with its custom powerplant, drew attention from sincere airplane folks. The Backyard Flyer is a serious adult toy!

Meeting a Need

            Gene Smith and his son, Larry, call Rolla , Missouri , home and are co-owners of Valley Engineering LLC, maker of the Big Twin light aircraft engine that powers the Backyard Flyer, and Culver props, custom-made propellers for ultralight aircraft. Their companies are one-stop shops for aircraft builders and owners who wish to obtain speed reduction units for VW engines along with the hand-selected hardwood propellers.

            "Our engines and propellers are built the old-fashioned way, from scratch, one at a time," said Gene, a mechanical engineer by trade and a former Air Force F-86 mechanic. He began designing airplanes when he worked for International Harvester. But he soon found he didn't like city life, so he packed up his family and moved to Missouri where he began a long career of crop dusting. Although he was flying, the urge to design aircraft gnawed at him. Throughout the years, he's developed a number of innovative light aircraft and engines.

            "We found that many of our customers wanted a four-stroke V-twin engine for ultralight flying, with minimal weight and enhanced safety and durability." What Gene and Larry found to fill that bill is a 38-hp industrial V-twin engine that was primarily designed for the airboat industry.

            When the Smiths laid their hands on the airboat engine and started the modification process, the end result looked nothing like the original. "We removed the governor, which is not needed on a propeller drive," said Gene. "We then stripped off the intake manifold and carburetor because neither are suitable for aircraft use. The engine doesn't have an adjustable accelerator pump, so we used a Weber carburetor system that is totally adjustable." He also tuned and changed the emulsion tube along with the carburetor's main jet. "This engine has a diaphragm accelerator pump, which is very important for an aircraft engine. When you pump the throttle on a botched landing, you want a smooth power transition. Without the accelerator pump, you are liable to kill the engine, and then there's no way but down."

            Gene found that using a four-cylinder engine took out a lot of the "shake, rattle, and roll" commonly associated with the two-cylinder version. "For ultralight, the two-cycle is much harder to tame than the four-cycle," said Gene. "The power pulses are just about as great, but they are farther apart on the four-cycle. As expected, the torsional shake on the two-cylinder is much greater."

To counter any tooth-rattling effect, Gene developed a drive that uses a poly V-belt with a slack side idler that is elastically loaded and drives in one direction only. "I spring loaded the idler on the slack side," said Gene, "and it holds without slip in the forward direction. When the propeller tries to resonate (push/pull backward and forward), it breaks one cycle; when the propeller tries to overrun, the idler moves out and lets the belt slip just a little, all of which takes care of the shaking."

            With the compact Big Twin now running as smooth as a catfish through cool water, Gene also added another one of his exclusive designs, automatic carburetor heat. Gene has been using this on most of his VW engines since 1993 and describes the unit as extremely simple and foolproof.

"My design recirculates some of the exhaust gas from the exhaust pipe into the base of the carburetor. The flow of exhaust gas is pulled through by manifold vacuum and therefore is full on at idle when you need the most carb heat and practically closed off at full-throttle settings when there's little vacuum pressure. The amount of carburetor heat is graduated depending on throttle setting."

            While showing his new engine to the throngs of admirers, a concerned ultralight flier asked about the exhaust gas messing up or fouling the mixture rate. Gene was quick to explain that fuel, air, and exhaust gas can all live happily inside the carburetor with one another.

            "Exhaust gas is an inert gas," said Gene, "all the oxygen has already been burned out of it. That is why we can introduce exhaust gas and it doesn't change the mixture ratio of fuel to air at all. It is basically the same amount of fuel and same amount of oxygen being mixed at a reduced flow. The only noticeable difference I found was that the idle speed may increase a little bit."

Enter the Backyard Flyer

As Gene and Larry tweaked the Big Twin engine to their liking, they realized they needed a platform to showcase it. To save time, money, and energy, the Smiths could have bolted the engine onto an existing airframe from a kit manufacturer or relied on an already built ultralight. For most people, that would have been the route of choice, involving the least amount of work. But Gene and Larry Smith aren't like most people. Both father and son realized they wanted an original Smith-designed aircraft, one as unique as the engine that would power it.

            "We sat down and started from scratch," said Larry. "We sketched out a design the old-fashioned way, using paper and pencil and no computer. One of our goals was to stay practical and create an affordable, easy-to-fly, safe ultralight. But our main goal was to have fun, and I think we achieved all of the above."

            Gene and Larry said the wingspan is about 27 feet, and the fuselage length is about 17 feet. They described the wing as a big Hershey bar bolted to an aluminum tube. They calculated the wing's breaking point at 6g and found that it will withstand 4g with no deformation. The two best attributes to the Backyard Flyer, according to Gene, are the engine and the use of the Junkers-style ailerons.

            "As an old crop duster pilot, I felt that I had to have a lot of control authority," said Gene. "That's why the big Junkers ailerons worked so well. I can pull the stick all the way back into my stomach as I coax the Flyer into a full stall. The airplane will start to sink, but I have full roll control. That is extremely important when you're on a base to final turn, as those ailerons keep you from rolling inverted in case you get too slow. I feel that is a wonderful safety margin to have, noticeable roll control under full stall conditions."

            Beyond the well-proven design of the wing and ailerons, the rest of the Backyard Flyer retains a utilitarian look and feel. Its construction is aluminum tubing; the main spar is a 6-inch tube with a reinforcing spar cap on the top and bottom. They also incorporated a flying tail into the design because it is easier to build, involves few parts, and is lightweight.

            To meet the 254-pound empty weight limit for a Part 103-legal ultralight, they lightened the flywheel by seven pounds and removed the alternator, ending up at 252 pounds.

            Gene and Larry experimented with various propeller sizes and found the best propeller was a 2-to-1 reduction and a 74-inch-diameter propeller. "We could get more thrust with a 3-to-1 reduction ratio and an 84-inch propeller, but that's overkill for a 40- hp engine," Gene said.

            One thing that Gene and Larry wouldn't skimp on was the installation of an emergency parachute; they chose a BRS 600 Soft Pack ballistic chute. "Safety in the air is a huge issue for us," Gene said. "That's why we created an airplane that will land comfortably in the 20-30-mph range,

have full control in a stall configuration, and provide the pilot with a recovery backup system in case of a structural failure or loss of power over rough terrain. With that said, every airplane we build will have a parachute installed."

            When I asked the Smiths about cockpit instrumentation, they both laughed. Gene responded in his Southern drawl: "It ain't much, partner!" He was right. Sticking to their claim of simple and plain, the Flyer's steam gauges consist of an airspeed indicator, Tiny Tach, and an oil pressure gauge located on the engine, "So you can lean out, feel the wind in your face, and see the gauge from the cockpit," said Gene.

Family Business

            Gene and Larry estimate they can build a new, made-to-order Backyard Flyer every two months for about $12,000 to $15,000, depending on desired equipment. They rely quite heavily on their workforce, most of which is family. Gene's wife, Juanita, has earned the nickname "Dopey" because she does most of the gluing of the fabric and is considered the icon of the building process. Larry's daughter, Alaina, and son, Grant, assist with gluing and rib stitching. Both are quickly becoming a third generation of Smith aircraft builders. There is one more employee left to be mentioned, and although his last name isn't Smith, he is still considered family.

            "Shane Starks is our prop maker and finisher," said Larry. "He creates masterpiece propellers from rough blocks of hardwood." Larry explained how they became prop makers. "Culver Props built a custom-order prop for my father some years ago. When he wanted another one, we learned the company was out of business. Instead of reinventing the wheel, we bought the company and moved everything to Rolla. Since then, we whittle about five custom propellers a week. We start with a large hunk of wood glued up together, 8-1/2 inches wide, 5 inches thick, and 51 inches long, and draw an outline on wood in black magic marker and then attack it with a chainsaw.

            By the time Shane is done cutting and smoothing, and all the wood chips and dust have settled, the result is a handcrafted, finished propeller in perfectly balanced condition."

            When a new Backyard Flyer is built and the last screw tightened, the Smiths perform a debugging process before it is allowed to leave the nest.

            "I like to run the engine at least five to 10 hours to make sure the rings are seated early on in the break-in process," said Gene. "That is important as it establishes long life in these engines because they are not babied early on. We also test-fly the airplane to make sure the rigging is correct and everything is balanced to specifications. We want to be 100 percent sure everything is working correctly before we turn the airplane over to its new owner."

            If you want to have some flying fun with the added knowledge that built-in safety features are the main concern and the idea behind the aircraft's design, pay a visit to the Smith Ranch in Missouri and see for yourself what a truly tamed animal the Backyard Flyer is.

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