Durand Reinstatement

Planning a kit for the unique Mark V negative-stagger biplane.

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Instead of a tailwheel, it sits on tricycle landing gear. Its biplane wings are set backwards in a negative stagger. There are full-span flaps on the upper and lower wings, and spoilers instead of ailerons. And the large canopy slides forward. The Durand Mark V is unlike any other airplane seen since its designer, William H. Durand, introduced it at EAA Oshkosh in 1978. Nearly 40 years later, it caught the eye of homebuilt flight line passersby at EAA AirVenture Oshkosh 2017 when Durand Industries LLC reinstated its existence with plans and the ultimate goal of a kit.

Built in 1978, government surplus instruments fill the Mark V’s panel. The brake lever extends below the throttle quadrant.

The company is recreating Durand’s fifth design in SolidWorks, said Jim Swatosh. The 3D CAD files are the first step in turning the scratch-built design into a kit. There is no hard timeline to this goal, but plans are available now.

Swatosh learned about the airplane during the resolution of a business issue unrelated to it. Without going into the details, Swatosh acquired the airplane, all 92 sheets of the original plans, and the rights to the airplane from Jim Durand in 2013, three years after his father passed away at 96.

Swatosh first saw the airplane in a storage unit in Balsam Lake, Wisconsin, just across the St. Croix River from his home in Stillwater, Minnesota. Even in its dismembered state, the design captured Swatosh’s heart, “like that 1940 Ford you see going down the street when you’re a kid.”

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Jim Swatosh demonstrates the forward-sliding canopy and unobstructed ease of stepping into the cockpit.

When he acquired the airplane, Swatosh didn’t think about selling plans and producing a kit until he learned more about the designer, whom he reverently refers to as “William.” By 1987, Durand had sold 75 sets of plans; that number grew to 91 in 1998. As near as Swatosh can tell, approximately 12 Mark Vs were built, including five confirmed flyers. Swatosh owns two of them, Durand’s prototype, and another, built in Canada, which flew on floats.

What he most admires about the Mark V is that “everything is designed; it wasn’t thrown together,” said Swatosh, an appreciation born of his career in business and manufacturing. Beyond that, “my history has been restoring old things,” he explained. “I’ve restored a lot of century-old homes; the Durand is a different sort of restoration.”

The Durand Mark V outside Nick Jilek’s hangar at Wisconsin’s New Richmond Regional Airport.

The Mark V has also reinvigorated Swatosh’s aviation aspirations. In 1978, he was a student pilot who’d soloed and logged 20 hours of dual. Life postponed his private pilot certificate, which he is once again pursuing.

His initial efforts to reunite the Durand’s parts revealed that not all airframe and powerplant mechanics have the knowledge and skills necessary to recreate missing parts, like the left stabilator, and reassemble an Experimental/Amateur-Built aircraft. Nick Jilek is now the airplane’s mechanic and pilot. Working from his hangar at Wisconsin’s New Richmond Regional Airport, also across the river from Stillwater, Jilek made his first homebuilt test flight in 1982 and “averages 350 hours a year in everything from a Mooney Mite to the [twin turboprop] Merlin.”

It was chance that introduced Swatosh and the Mark V, but it’s a good kit candidate because Durand designed it specifically for the scratch builder. He explained this in detail in three EAA Sport Aviation articles in 1978-79, which are on the Durand Industries website, www.DurandMarkV.com.

With the brake lever extending below, the throttle quadrant holds the parking brake, throttle, and mixture.

A Practical Airplane for the Amateur Builder

That is how Durand summarized his clean-sheet design. Its mission is “day VFR pleasure flying with lots of visibility,” and a panel with room for avionics and (large government surplus) instruments necessary for occasional IFR flying. Instead of making builder-pilots and their passengers adapt themselves to the airplane, he adapted the airplane to their needs through a “unique but purposeful combination of old and new—negative stagger cabin biplane with modern full-span flaps, spoilers, stabilator, forward-sliding canopy, tricycle landing gear, and all-metal construction.”

With the negative stagger and a canopy that rolls forward smoothly on the drawer rails of an office filing cabinet, pilots and passengers can step effortlessly into the 44-inch wide cockpit without bending or folding their bodies, bumping their heads, or leaving a muddy footprint on a seat cushion. (Replacing the missing steps that extend forward of the leading edge is on Jilek’s to-do list.)

When stepping on a rudder pedal, the “inactive” pedal moves only slightly in the opposite direction.

“I have rated gentle flying characteristics, short-field capability, personal comfort, cross-country usefulness, occupant safety, and structural simplicity more important than extremely light weight, high cruising speed, or other strictly competitive numbers,” wrote Durand. He designed visual references into the airplane. The forward-sloping cowl parallels the ground line between the tailskid and main gear. For an average-height pilot, “this flat surface will align with the horizon when the airplane is in the correct attitude for a minimum speed touchdown.”

Still, like many homebuilts, the Mark V embodies its designer’s personal predilections. “I suppose that most pilots would prefer toe brakes” (and Jilek leads that list). But Durand wrote that he too often rode them unintentionally, so the Mark V has a brake lever. Connected to a single master cylinder, the lever extends below the center quadrant that is home to the parking brake lock, throttle, mixture, and carb heat. A steerable nosewheel guides the way, and all three gear legs are sawn from thick Scotchply, a 3M composite material used for the same purpose on Grumman American two-seaters.

Durand also did not like bending an ankle backwards when he pushed on a rudder pedal. So in the Mark V, full deflection of the “active” pedal causes the “inactive” pedal to move aft only slightly. With dual sticks, all of the other controls are conventional. Along the bottom edge of the panel, spring-loaded map pockets double as padded knee protectors, and the four-position flap handle and trim lever are between the seats. The trim lever controls the stabilator’s anti-servo tabs. “Its position indicates the amount of trim…and [it] acts as a miniature control stick,” Durand wrote.” Jilek seconds this.

Given its canopy, ventilation is crucial. Bilateral plenums supply temperature-controlled air to the sidewall vents. A diverter sends defrosting air to the windshield. The cabin airflow exit control is in the overhead console with a speaker and cabin and panel lights. A second detent on the canopy’s overhead locking cam latch holds it open a bit for increased taxi ventilation.

Cutaway view of the Durand Mark V.

Designed for Garage Construction

When designing a homebuilt, Durand wrote, designers must consider the range of possible builder-pilots and their shops. “His flying experience may be limited, and his experience as an airplane builder, nil. Everything considered, the [pulled]-riveted all-metal biplane seemed to offer the right combination of compact dimensions, general wing area, and simple, clean, odor-free construction resulting in a really durable machine.”

The open cowl doors provide easy access to the Lycoming O-320.

Members of EAA Chapter 80, which Durand helped found in Omaha, Nebraska, built the prototype on a “4×8-foot plywood table in a 14×18-foot shop that also included a workbench, drill press, stove, and our local EAA chapter library.” Builders will need more room for final assembly, a bending brake, and a welding kit for the control fittings, engine mount, and exhaust system.

With the negative-stagger biplane’s 24-foot-6-inch wingspan and 36-inch wing chord limiting the travel of its center of pressure, Durand wrote that the Mark V’s shorter, lighter, less expensive 20-foot-3-inch fuselage does not sacrifice stability. Investing nearly four years designing it, “stress analysis and weight and balance calculation paralleled the continual modification of the layout to achieve the simplest and most direct solution to the problems associated with airplane design.”

The overhead console is home to the radio speaker, panel and cockpit lights, and the knob that controls the amount of air that leaves the cockpit.

In addition to easy entry, the negative stagger contributed some “desirable aerodynamic characteristics [such as] inherent flare-out at touchdown, flaps that don’t require a trim change, and excellent anti-stall properties.” Those full-span flaps were important to Durand. “Since the airplane was going to be based and test flown at my backyard grass strip, Durand Sky Ranch, short-field capability was a must.”

Explaining the negative-stagger aerodynamics, Durand noted that the lower wing is ahead of the CG and the upper wing is behind it. While both wings have the same span, chord, and angle of incidence, “the actual angle of attack is different [because] the trailing wing is working somewhat in the downwash of the leading wing. This changes the lift contribution from a 50-50 situation to about a 53-47 basis, with the lower wing being slightly more effective.”

The overhead cam latch that secures the canopy has a second notch to provide additional ventilation during taxi.

When the angle of attack approaches the stall, Durand wrote, the airplane does not rely on one wing for all of its lift. The lower wing stalls a few degrees before the upper. In this situation, the upper wing becomes more effective; being “behind the CG, its lift causes a nose-down pitch while working at or near its maximum lift coefficient.”

This not only reduces the altitude lost in stall recoveries, it delivers an “inherent advantage” on landing. Approaching the runway, ground effect acts on the forward lower wing, gradually increasing its lift. Acting ahead of the CG, “it gently raises the nose for what might be termed an automatic flare requiring little, if any, help from the pilot.”

There are separate heat and airflow controls for each seat.

Upper and lower full-span flaps not only slow landing speed (and landing distance), they eliminate the need for trim changes often necessary when extending partial-span flaps, which change the wing’s center of pressure. The Mark V proportions “the lift of the two staggered wings in the flaps-down mode so that their composition center of pressure does not move rearward.” Durand did this with different full-flap deflections, 40 degrees on the upper and 45 degrees below.

Full-span flaps made spoilers as the only roll option. The simple flap is 4.75 inches wide, 69.5 inches long, and hinged at the leading edge. Operating individually, full deflection is 40 degrees.

The right spoiler in full deflection. The control surface behind it is a full-span flap.

Building the prototype “tested the plans and revealed dimensional errors, inadvertent omissions, and related improvements.” Given his “I’d rather be flying preferences,” Durand focused on easy access for maintenance and servicing, and a quick but thorough preflight inspection. He mounted the battery, for example, in a swing-out box in the tail cone, so builders can service it outside the airframe and not have to worry about a prop strike when jump-starting the airplane in cold weather. At the other end, to change oil without removing the cowling, there’s an opening aligned with the sump quick drain.

The trim lever and flap handle are in the console between the seats.

Three Subassemblies

The Mark V fuselage is composed of three subassemblies: the cockpit, the baggage area and cabane, and the tail cone. Durand compared the cabin assembly to framing a house, with “a center girder, floor joists, and wall studs [2.5-inch channels drilled for wiring], and a top plate.” For occupant protection and structural stiffness, the cockpit is skinned inside and out. The floor and bottom skin join with keel channels to create a box beam that runs the length of the cockpit and provides attachments for the lower engine mount, nosewheel, and Delrin control bearing.

Like the nosewheel, the main wheels are bolted to the Scotchply gear legs. Also visible is the glasspack muffler.

The wing employs a two-piece spar comprised of 0.050-inch material bent into modified J-sections joined by pulled rivets. Builders can fabricate each spar in its full 10-foot length or in shorter sections using the low-stress splices indicated in the plans. The rear spar and flap spar are formed of 0.040-inch stock. The 0.032-inch leading-edge channels are nonstructural; they align the nose ribs during assembly. Since all four wings are the same, builders need only one rib form block. Except for the lower wing walkways, the wings are skinned with 0.020-inch Alclad.

Builders fabricate the tail cone from the bottom skin up. They mount the bulkheads to this skin, which eliminates the need for an assembly fixture. Only straight bends form the parts of this stressed-skin structure. Except for the back channel that runs across the top of the bulkheads, primarily as an assembly convenience, there are no longerons or stringers, “only skin stiffeners between the frame locations, which are riveted in place prior to their incorporation into the structure.”

To make subassembly alignment easy, the fuselage bottom is flat from the tailpost to the firewall. The prototype’s builders aligned the tail cone and forward fuselage on a one-piece aluminum ladder supported by two sawhorses. They adjusted the subassembly alignment until the canopy rails were even.

The canopy looks like blown Plexiglas, but it is 1/8-inch Lexan cut and bent cold. A tough, pliable polycarbonate, Lexan costs more than Plexiglas, Durand wrote, “but you don’t have to build or borrow an oven to heat it before bending.” The canopy frame holds it in place, and its curvature produces a rigid surface that eliminates the need for corner posts that would block the occupants’ view.

The main landing gear is essentially an independent chassis, with Scotchply legs bolted to a steel carry through that absorbs all the bending stresses. Aluminum saddles mate this chassis and the fuselage. An automotive glasspack muffler is located between the main gear legs to mute the roar of the 150-hp Lycoming O-320.

Scratch building is the first of three options for building the Durand Mark V. The plans include hardware and material lists and diagrams for getting the greatest number of parts out of 4×12-foot sheets of metal. As the SolidWorks CAD effort continues, Durand Industries will incrementally offer complex and welded parts, and then kits, said Swatosh. “I just found a company that makes rotationally molded polyethylene fuel tanks.” Made of welded aluminum, “the Durand fuel tank is a work of art, but it takes time to build, and I want to give builders options.”

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