Back in April of 2004, I traveled to California to test-fly the Hevle Classic two-seat Fly Baby for KITPLANES magazine. The pilot report was published in the August 2004 issue of KITPLANES magazine.
The following is "kinda" that article. It is, in fact, an early draft of the article that was printed in the magazine.
Why put this one on the web page instead of the final version? This version includes a lot of background information of interest to Fly Baby fans, but not as illuminating for general audiences. This version goes into greater detail on the history of two-seat Fly Babies, and on the design differences between the standard model and the Hevle Classic. I decided this information wasn't really needed for the magazine article, and cut it (about 700 words) prior to sending it to the magazine.
One drawback: This article isn't as polished as the one I finally submitted....so it'll read rougher. But Fly Baby fans will gain a bit more information.
By Ron Wanttaja
In shops around the world, for the last four decades, thousands of men and women have labored on a little homebuilt called "Fly Baby." At once old-fashioned and modern, with sprightly performance on its little Continental engine. While they were considered a bit "common" in the 70s and 80s, they're now a rarity among the legions of aluminum and composite homebuilts.
While they're proud to talk about their airplanes, most Fly Baby owners get a little tired of one question:
"Is a two-seat version available?"
It's one the late Peter M. Bowers, the designer of the Fly Baby, handled repeatedly. He even eventually included a short article in the plans, "The Two Seater Problem," to explain why such conversions were fraught with problems.
Yet, over the years, people couldn't resist the call. The first ones were side-by-side, fighting the tremendous drag of a double-wide open cockpit. Most fell by the wayside.
The Fly Baby's similarity to WWII trainers like the Fairchild PT-19 led others to tackle tandem-seating versions. These found a varying amount of success, but the designs never seemed to make it out to where others could build them.
At least, until Eric and Stacy Hevle came along. Their Hevle Classic tandem Fly Baby is not only a beautiful, great-flying aircraft, it's available in plans as well as in kit form.
Both brothers went into aviation, but initially took different routes. Stacy went on to Wichita, as a fabrication and sheet metal craftsman working in Cessna's experimental shop. Eric went on to get is instrument, multi-engine and commercial ratings, and also earned his A&P license with an IA endorsement.
At one point, Eric came home to help his Dad, maintaining the company's ag airplanes. He intended this to be only a brief stop on his progression upward through the aviation industry.
But Ron Hevle and his partner knew they needed an on-field maintenance operation. They offered to "stake" Eric to his own business, building a large hangar on the company airport. Stacy joined him ("I always wanted to come back," he says), and Hevle Aviation was born.
The company began as a full-service maintenance facility, but soon branched out to homebuilder assistance. With their extensive shop facilities and access to a private, 3000-foot paved runway, they attracted a number of people building RVs, Harmon Rockets, and Murphy Rebels.
One project was the restoration of a Piper PA-11 Cub Special. The aircraft had been idle for about 35 years. The Hevles rebuilt the airframe and its Continental C-85 engine, but ended up installing a Lycoming O-235 engine instead.
So with their latest project completed and a perfectly good Continental engine left over, the Hevles decided to build a homebuilt to match it. They'd build the plane on a tight budget, scratch-building as much as they could.
Eric found the ideal project in a listing of homebuilt aircraft: The Bowers Fly Baby. "Yeah," remembers Stacy, "But we wanted to make it a two-seater."
They ordered a set of plans from Pete Bowers, then called him to discuss a two-seat tandem modification. "The big question was the CG," says Eric. Still, Pete knew there had been several successful tandem Fly Babies. The Hevles decided some more research was in order.
David Munday, a physics and aeronautics researcher at the University of Kentucky, had embarked on a similar project a year or two earlier. Munday had tracked down several of the successful tandem Fly Babies and their builders. He'd examined the structures, found out what worked and what didn't, and did his own computations.
He documented his research and work on his web page (www.ase.uc.edu/~munday/flybaby/), and, when he'd finished his fuselage layout drawings, posted those as well. "It looked so good," says Eric. The Hevle brothers contacted Munday, and used his fuselage truss layouts for the Classic.
The aircraft slowly took shape. The fuselage itself is a foot longer than the single-seat version, basically as a "plug" located just behind the original cockpit. CG considerations dictated that the wing move aft about the same distance, and the landing gear mounts were also moved to maintain the proper geometry. The aft cockpit is placed in the area formerly used for a baggage space.
The landing gear itself was made from welded streamline steel tubing, vs. the laminated spruce called for by the Fly Baby plans. "I know steel tube better," says Eric Hevle. They built it in just two nights.
For improved pitch stability and control, the span of the horizontal stabilizer was increased by two feet.
But the wing was basically stock. Due to the increase in weight over the stock single-seat Fly Baby, they decided to increase the wing spars and the fuselage longerons from ¾" thick to a full one inch. The single-seaters have had occasional problems with the wing bracing system, so they boosted the flying wires to 3/16" (from the stock 1/8") and used one of Bowers' alternate methods to attach them to the wing.
As one might expect, the fuselage was the hardest part of the construction. "The wings went together easy," says Eric, "Except the wingtip bows." The wingtip bows are laminated from 10' long strips of 2 ½" wide 1/8" thick spruce, then carved to the proper shape. Not a skill one picks up, maintaining Skyhawks and Air Tractors.
Things don't always go as planned. "We were looking to do the airplane as cheap as possible," says Eric Hevle, "But we kept running into different small radial engines."
It wasn't just idle speculation. They had begun to worry using a C-85 on the tandem. The CG wasn't coming out where they wanted it, and they were loath to extend the nose. In addition, they were concerned about the airplane being underpowered at their anticipated gross weight.
Finally, they came across the Rotec R-2800 seven-cylinder radial engine. The 110-HP Rotec had the power they needed, and the higher weight of the Australian engine brought the CG exactly where they needed it. They talked to Rotec, and were impressed with the engineering that went into the engine as well as the testing process it had gone through.
But engineering, testing, CG, and weight weren't the major factors in the decision. "We wanted it for aesthetic purposes," says Stacy. For inspiration, a photo of the engine went up where both men could contemplate it regularly: Above the toilet in their shop.
The Radial eventually arrived, and the Hevles had few problems integrating it to the airframe. The firewall remained in the same position, with a new engine mount to match the attachment points for the Continental mount. The Rotec is installed with one-half degree of downthrust and one degree left offset. A 12-quart oil tank fits above the engine's accessory section. A heat shield is installed behind the exhaust collector ring, and a narrow boot cowling covers the accessory case and oil tank.
As a part-time project, building the Tandem took a while. Eric
estimates the total build time at 2000 hours, over about four years of
calendar time. The airplane first flew in January 2004.
Having flown Fly Babies for the past 17 years, the Hevle Classic offered comforting familiarity. The Bowers trademark tail shape was unchanged, and the graceful elliptical wingtips testified that the brothers had overcome their problems with the wingtip bows. The 12-inch stretch of the fuselage isn't immediately noticeable, but the twin cockpits make it obvious that this isn't an ordinary Fly Baby.
That impression is more than confirmed by the silver gleam of the Rotec Radial on the front of the fuselage. I'm rather a fan of the small Continentals, and tend to recommend that Fly Baby builders stay with the well-proven A65 through O-200 series.
But that Rotec sure looks good, on the nose of the old-fashioned Fly Baby.
Between the Rotec radial and the changes made to the airframe, the Hevle Classic's empty weight is about 250 pounds more than that of the typical A65-powered single-seat Fly Baby. With a six-hundred-pound useful load in addition, the large-diameter flying wires and the welded attachment fittings are very reassuring. The internal wing bracing was beefed-up in size, too.
While the landing gear legs are now welded streamline tubing instead of laminated spruce, one thing that hasn't changed from the single-seater is the shock absorption system for the landing gear: There isn't any! The tires provide the only buffer for hard arrivals. The Hevles are designing a shock-absorbing gear similar to that of the Ryan PT-22.
In most small biplane or parasol homebuilts, access to the front cockpit takes a certain amount of agility. One usually ends up trying to squirm under the wing into the cockpit, while carefully avoiding breaking the rear-seat windshield.
Not so with the Hevle Classic… a tallish step onto the wing walk, and over the landing wires, and one can just step over the cockpit sidewall and slide into the seat. Being of rather generous mass and cursed with bad knees, I'm sensitive to access issues. I had absolutely no problem getting into and out of this airplane, from either seat.
With the front cockpit in the same position as the single-seat version, the sight picture forward was identical to what I was used to. It had about the same amount of room as the single-seater, as well. Shoulder width is 22 ½", the same as the single-seater. The uncluttered floor offers a generous 43" of legroom to the simple welded-tube rudder pedals.
Visibility forward past the Rotec was surprisingly similar to the view with a Continental mounted up front…the engine diameter is only a few inches bigger than the depth of the fuselage. One cylinder poked slightly above the cowl line in the center, but the visibility to either side of the cylinder head was actually better than I'm used to with the Continental.
Eric fired up the engine, and we taxied out to the runway at the Hevle family's private airport. For those who eagerly wonder if the Rotec has "the radial sound," the answer is, sadly, no. The R-2800, with its 3700 RPM redline and 3:2 reduction drive, sounded a bit like a the result of a midnight mating between an O-200 and a Rotax 912.
But no matter what engine is mounted up front, neither the noise nor the look matter when the knob goes to the firewall. When Eric hit the throttle, the airplane seemed to lunge forward. This Fly Baby had about 40% more horsepower than I was used to. Despite its extra weight, the tandem accelerated quickly, popping off the ground in a few hundred feet. Eric flew for a bit in formation with their PA-11 for more photos, then I took over the controls.
The elevators were a bit heavier than the single-seater, and the ailerons are lighter. Bowers' plans, of course, don't include instructions for a dual-stick setup, so the Hevle's borrowed the setup used in the RV-4. The mechanical advantage for pitch and roll are different, which makes the control feel somewhat different.
No matter, really…the elevators on the Tandem cannot be described as "heavy," merely heavier in comparison to the light feel of the single-seater. They're perfectly acceptable, and the lighter ailerons are definitely an improvement.
Pitch stability was neutral to slightly positive; displacing the stick at the trim speed produced a slow-cycle hunting in pitch for several cycles until it damped out. A turn from a 45-degree left bank to a 45-degree right one took a bit over two seconds. The characteristics are similar to those of the single-seater.
With no way to communicate with Eric in the back seat and only abbreviated instrumentation up front, I was reluctant to stall the airplane on this flight. I contented myself with some slow flight prior to the return to the airport. The familiar sight picture made me quite comfortable on approach, and I managed a fairly smooth touchdown.
The rear cockpit is slightly harder to climb into, as it sits partially behind the trailing edge of the wing. Still, I managed without too much difficulty.
The room isn't as generous in the rear cockpit… it's located behind
the point where the fuselage starts to taper, and the shoulder room is
about an inch less. The legroom, restricted by the front seat, is
a bit shorter, too… about three inches less than the front seat.
The Hevles plan to widen and lengthen the steel-tube kit fuselage, which
would take care of both of these issues.
(It should be noted that the author has abnormally broad shoulders, and the room in the rear seat of the current Classic is the same as many homebuilts in this class.)
The rear cockpit contains all the required controls and gauges, including a digital tachometer for the Rotec. Scott heel brakes are installed, and a quadrant-type control on the left sidewall handles the throttle duties. The Hevles have the pitch trim connected to the quadrant knob ordinarily used for carb heat, with the heat control mounted lower on the sidewall.
On climb-out, I was forced to throttle the Rotec back slightly to keep from exceeding the redline. The 76 x 46 prop was probably a good, conservative starting point, but a prop with a bit more pitch is probably in cards. One curiosity was the behavior of the electronic tach...the LCD digital readout blanked out for a second every time the throttle position changed.
Control feel was about the same as from the front. However, the rear seat is well aft of the CG, and any miscoordination with the rudder is obvious. I had noticed the lack of a skid ball during my preflight; five minutes in the rear cockpit proved how superfluous one would be. I was, literally, behind the aircraft, with any miscoordination wagging me back and forth through an arc in space. A bit of practice, though, and things seemed about back to normal.
While the front seat had been mostly draft-free, the rear cockpit was windier. The slipstream curved past the windshield on both sides and hit me right on the cheekbones. Goggles are a necessity. The two windshields are identical, so it's probably due to the turbulence caused by the front cockpit.
The airplane showed about 85 MPH at cruise, but the Tandem was using the stock Fly Baby pitot/static boom, which has some problem with static error. Formation flying has shown the plane cruises closer to 100 MPH. A timed climb revealed a climb rate of about 750 FPM (1000' MSL, 70 deg F day). I experimented with the elevator trim, then I just set it for cruise and forgot it. The heavier feel on the elevator wasn't a problem.
Back on the power for slow flight and some stalls. The airplane shows a lot of buffet before the break. Surprisingly, the stall was a lot more gentle that my single-seater…my plane has a definite, sharp break, but the tandem just dropped the nose a bit. Of course, the weight of a tubby aviation journalist in the back seat helped keep the nose up. But I was able to hold the tandem in the stall and easily keep the wings level with rudder, something that takes great care in my stock airplane.
The unfamiliar sight picture caused me to flare a bit high for the landing, but that tough steel-tube landing gear soaked it up.
I'm happy to report that the answer is now an emphatic, "Yes!"
The Hevle Classic has all the romance of the single-seat Fly Baby, but with the ability to share the fun with a friend. The structural upgrades look more than adequate to handle the extra weight.
The stiff landing gear will take some getting used to. But it's more of a threat to the ego than aircraft....the tough structure can take more than the pilot can. In any case, once available, the Hevle's shock-absorbing gear will take care of this issue...and will probably be retrofitable to the single-seaters, as well.
I liked the Rotec Radial more than I thought I would. It's not a gimmick; it's a well-behaved aircraft engine that looks to be a good alternative to the Rotax 912 or Continental IO-240. Of course, Rotec is not as established as these two companies.
For those who want to go tandem, Hevle Aviation offers a variety of options. A complete kit with a welded steel-tube should soon be available, with an anticipated price of around $15,000. The Hevles are planning several engine options, including the Walter Mikron, as well as the Rotec.
For those who prefer the traditional scratch-built approach, plans are available for the wooden-fuselage version. Basic CAD diagrams showing the fuselage layout sell for $50, and a full-scale fuselage layout for $130. In both cases, a set of the standard single-seater plans are required, which can be obtained from the estate of Pete Bowers for $65.
Many people who considered Fly Babies in the past have built some of the small biplanes instead, just because they were available as two-seaters. The Hevle Classic tandem Fly Baby just removed this excuse. Besides, you won't have to build as many wings!
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