The Back Yard Flyer UL
by
Sparky Barnes Sargent, EAA 499838
Reprinted with the kind permission of EAA Light Sport Pilot and Light-Sport Aircraft Magazine
Mary (Sweet Young Thang) Jones: EAA Director Of Publications

          Take a closer look at the Back Yard Flyer UL (ultralight) and you’ll likely be struck by its clever design, which includes four features not usually found in a single-seat ultralight vehicle. Those fea­tures—the four-cycle engine, electric start with alternator and battery, differential braking with the rudder pedals, and a BRS ballistic parachute - were chosen to enhance the ultralight’s performance and ground handling and to add an extra margin of safety for the pilot. There’s more Junkers-style ailerons, a custom Culver prop, a prop speed reduction unit (PSRU), and a one-piece, cantilever wing that can easily be stowed in a streamlined position to facilitate storage.

            A father and son team—other­wise known as Valley Engineering LLC - from Rolla , Missouri , designed and brought the Back Yard Flyer UL to life. Gene Smith is an easy­going, Affable southern gentleman. Paired with his quick-witted and good-natured son, Larry, the duo has created a niche in the ultralight world. They've developed their own airframe arid engine, and their own propeller business, too. Obviously, that's more work than two people can handle, so Gene’s wife, Juanita, along with Larry’s daughter, Alaina, and son, Grant, all participate in airplane building and propeller mak­ing. With this trio of family-run cottage industries, they have every thing they need to produce a legal Part 103 ultralight. When asked how long it took to design the Part 103 Back Yard Flyer UL, Gene laughed softly and speculated, “Several sleep­less nights.”

ONE THING LED T0 ANOTHER

            In 1994, Gene flew his first custom built ultralight from his home in Missouri to FAA AirVenture Oshkosh. While flying from the ultralight field there, he heard complaints that some folks were climbing out too steeply on takeoff. Concerned, he inquired if he was one of them. “No, you’ll never get a Volkswagen engine to climb out too steep,” he heard.

            That did it - the challenge was on. “When somebody pokes your pride a little bit, it spurs you to do some­thing,” chuckled Larry. “That’s actu­ally how we got into the prop speed reduction unit.”

            At home after the show, they devised a bolt-on, belt-driven reduc­tion unit for Type 1 VW engines. (See “The Quest for Affordable Power EAA Sport Pilot And Light Sport Aircraft, April 2008.) In 1997, Gene flew to AirVenture in his Volkswagen-pow­ered, tricycle-gear ultralight and was rather pleased when he heard the sharp admonishment, “That’s too steep a climb-out!”

            Three years ago, the Smiths brought another new single-seat, high-performance Volkswagen-pow­ered ultralight to AirVenture. It had an 8-foot propeller on a 100-hp engine, with super Junkers-flaps that had 40 degrees ot flap deflection with the ailerons. Its takeoff run was only 62 feet. They didn’t even have a name for it, but that didn’t deter the customer who purchased it. Larry asked where he intended to fly it, and the fellow told him, “I’m going to fly it out of my backyard!” The Back Yard Flyer UL had a name.

            Gene had been a basic fight instructor (BFI) for years, so for a while he and Larry focused their efforts on a two-place Back Yard Flyer, demonstrating the prototype at AirVenture 2005. With the advent of the FAA’s light-sport aircraft (LSA) rule, they contemplated going the LSA route, but ultimately decided to build an ultralight. “We thought the experimental LSA would be great, but we got into the details of the first one having to be a special LSA,” Gene said. “The paperwork required for manufacturing and selling the ISA is beyond our capability, so we’re limited to building amateur-built.”

            The Smiths devised their own two-cylinder, four-cycle engine l)y modifying an engine that was built for airboats. Their Big Twin has a peak horsepower of 40 hp at 4000 rpm and a continuous horsepower of 32. Weighing only 120 pounds dry - including the prop and PSRU - it burns 5 quarts ot gas per hour at nor­mal cruise (per Valley Engineering’s brochure). I he debut of this V-twin engine was in their low-wing, single-place Back Yard Flyer at AirVenture 2006 “Animal Attraction! The Backyard Flyer,” EAA Sport Pilot, December 2006. Ultralight enthusi­asts took note of the new light air­plane engine, as did the judges, who gave it the Ultralight Innovation Award for its custom powerplant. The engine and PSRU required spe­cial propellers, and there was only one source for them.

            “We had to have a wide prop blade, with lots of diameter, for the reduction drives. David Miller of Culver Props had several patterns he built for us, but then he went out of business. So we ended up buy­ing his business sight unseen,” said Gene," adding, “He loaded it all up in a tractor trailer and sent it down to us. Then he and Bill Powers came down and spent a week with us, and we learned how to build props. It’s a great thing for us, because we have the need for so many prop variations, and we can easily customize these hand-carved, wooden Culver props.”

Continually  Contemplating improvements for their ultralight designs, they wanted to build a new Back Yard Flyer that would “have brakes, electric start, and if possible, carry its own battery and alternator, with a four-stroke engine,” Gene said. “We said, ‘Can we do that and still meet 103?’ We worked on it pretty hard, and we succeeded. The first one came in well under the weight. On the second one we added just a little bit of wingspan, and it still came out to 249 pounds dry - no oil, no fuel, no parachute. With the 24-pound allowance for the parachute, it all weighs out with 5 pounds to spare.”

WING AND AILERON DESIGN

             The Back Yard Flyer UI has a deep­ly cambered and tapered cantilever wing that is bolted to the fuselage with five half-inch bolts. The over­all shape of the wing is somewhat reminiscent of Ford Trimotor's wing. the wing chord (not counting the ailerons) measures 60 inches in the middle, tapering to 44 inches at the wingtips, and the wing has a thick­ness of 10 inches in the middle lapel ing down to 7 inches at the tip. Gene designed the wing and explained that the depth in the mid­dle is for strength and that the taper is to concentrate less lift at the tip and more lift toward the middle, so that the spar. a triangular truss, will be strong and light.

            Other notable features about the wing include its one-piece design, trailing-edge ailerons, and unusual method of “folding.” While work­ing on the wing one day, which was original designed as a three-piece wing, Larry mentioned to his father that he wished they didn’t have to take the wing apart. Couldn’t they just make it one piece? “I wanted a 25-toot one-piece wing. Dad started scratching his chin, and pretty soon, here he comes back with two pro­peller scraps. He’s got a bolt going through them on two angles, and he says, ‘Look! I can make it rotate and level at the same time.’ I couldn’t get hold of the concept for a week “ said Larry, adding, “We had to get it built on the plane before I could figure it out!”

Elaborating on the concept, Gene explained, “Of course, the wing is on the airplane with an angle of incidence now, and if you’re going to rotate it, then that angle has to come back to horizontal, or else it’s going to hit the tail. So I had to make the pivot and keep the wing level with the horizon as it swings around over the fuselage. All it takes is a compound angle on the pivot point. I just kept messing around, drilling holes in those scrap boards until I finally got it working. The swing wing rotates 90 degrees, and it takes about two minutes to transfer it from one position to the other.”

Junkers-style ailerons (or flaper­ons) are mounted externally on the trailing edge, adding about 10 inches of chord to the wing. “As the stick comes back for landing, the ailerons droop about 15 degrees,” said Gene, “and that limited amount makes for an easy landing. In a normal airplane, when you make correc­tions for a little balloon on landing,

LANDING GEAR

            Another striking feature on this tail­wheel-configured ultralight is the main landing gear design, an aes­thetically  pleasing combination of form and function. Try to imagine how the Smiths achieved that partic­ular radius while bending the tubing. Gene knew that standard spring gear is far too heavy for an ultralight, so he mulled it over and came up with a solution “The gear components are just like a J-3 Cub, except for where you’d normally have the bun-gee cords. I thought, ‘Why couldn’t you just use we curved piece of metal?’ because a curved tube will stretch, and it’ll have enough spring in it to bounce back.”

            Larry added, “A fellow asked me yesterday what kind of special press we had to form those, and I said, ‘Oh, it’s our secret!’ If you don’t have a propane tank, you can’t make them. It takes two of us, but we bend the tube around the bottom of a propane tank, and when it touches at the top, then the curvature is ideal for the gear leg.”

READY TO FLY

The Back Yard Flyer UL is sold as a finished, fly-away legal ultralight. Valley Engineering LLC doesn’t even have plans available for it (they just don't like paperwork! “So much of it requires aluminum welding, and that’s pretty demanding - not every-one can do that,” explained Gene. “We put everything on and flight test it, to where we know it’s performing perfectly.”

            The Smiths estimate they can build one every month and a half, So there likely won’t be too long a wait­ing period for those fliers who want to experience the freedom and fun of flying a true ultralight from their back yard. “We don’t sell anything we haven’t tested, even in our engine packages,” Larry said. “It has to be finished and ready to go before we’re happy to let it go. We’re proud of our total package: four-stroke, elec­tric start, legal Part 103, spring gear, swing wing - it has so many features, all in one plane.”