Pierre Terblanche’s Motorcycle of the Future

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Our man Cameron met with the great Pierre Terblanche to discuss the forward-looking features of his new 3D-printed bike. (Neale Bayly/)

Traveling to Birmingham, Alabama, and the Barber Museum’s new Advanced Design Center, I met with Pierre Terblanche. The former Ducati design specialist described what he has tried to accomplish in his new prototype, modeled entirely (save for its wheel rims) by 3D printing.

Terblanche’s thesis is that, despite impressive technological advances in the three decades since he designed Ducati’s Supermono, those advances—and much common sense besides—have failed to appear in new motorcycle design.

To evaluate his ideas he has built a non-running but full-scale prototype, a New Supermono if you will, whose parts emerged from the Barber Design Center’s large HP 3D printer, mostly in a nylon material. While working in CAD is quick, nothing stimulates the mind like a full-scale 3D object, the very reason traditional styling development used clay and wood. The 3D printer adds accuracy, speed, and the ability to store the executions digitally.

Motorcycles Have Become Too Big

In profile, the “3D Supermono” initially looks like a fairly normal design exercise. Then the eye takes in details, starting with the bike’s diminutive size and going on from there. (Neale Bayly/)

Terblanche’s first general observation is that motorcycles are too big; they’ve grown out of human scale. Electric lifts in the center display two bikes: the original 1992 Supermono and Pierre’s new prototype, both powered by internal combustion (IC) engines with a single horizontal cylinder. The original’s 549cc engine makes 75 hp unsupercharged; the new bike with its Rotrex supercharger “makes” 137 hp, enough to reach current power-to-weight levels while retaining the scale of the nimble original. In four-wheeled vehicles the trend has been to use smaller, lower-friction, and therefore more fuel-efficient engines, and to maintain their power level at market expectation through turbocharging. The approach could help motorcycles to meet future fuel-consumption legislation as well, if it comes.

Radiators Are Too Big, Too

Terblanche’s second big change is to eliminate the giant, ineffective water and oil radiators used by today’s powerful motorcycles, located as they are immediately behind the front wheel like a sail from a square-rigged ship. To allow the desirable forward engine position, today’s rads are tightly up against the front of the engine, complicating hot-air outflow. Using wind-tunnel data, Terblanche cites measurements of air velocity at the rear surface of such coolers, showing that high flow exists in only a small circle at upper center plus a narrow vertical strip at each edge. This illustrates that much of such radiator area is nonfunctional. To remedy that he has designed the new bike’s chassis as a front-to-rear duct with the coolers mounted in the middle.

Carefully chiseled tailpiece hides a lot of carefully thought out heat dissipation. (Neale Bayly/)

Air enters on either side of the steering head at the front and is smoothly decelerated by widening the passages until they unite at the coolers. Once through the radiators, the heated air is accelerated through a nozzle to exit at the rear, into an area of normally low pressure. The single exhaust pipe exits nearby; this presents the possibility of using exhaust momentum to pump air through the duct even at low vehicle speeds. (Such exhaust pumping was used to move cooling air on the 1947 Convair CV-240 airliner and 1958 DHC-4 Caribou military-transport aircraft.) Aerodynamic drag results when higher pressure exists on the front surfaces of a vehicle than on the rear, so feeding the outflow from the coolers into the low pressure behind this prototype motorcycle can reduce drag.

This is not a new idea. Important World War II combat aircraft such as the British de Havilland Mosquito and North American Mustang employed such ducted coolers for the purpose of eliminating cooling drag or even producing a slight net thrust. How? Such ducted radiators are actually low-grade jet engines, taking in cool air, expanding it by adding heat energy, resulting in an outflow velocity higher than inflow velocity. To learn more, Google the Meredith effect.

Parts of this concept have appeared on racing motorcycles, such as those of the late John Britten and on at least one of the Kenny Roberts Team two-stroke 500 triples of the late 1990s, placing the radiator horizontally under the rider’s seat but not attempting to reaccelerate the downward-emerging hot air.

Aerodynamics and Closing the Wake

Engineers know that motorcycles have drag coefficients (Cd) that are scandalously high—approximating those of a box truck. The Cd of a given shape roughly compares its drag with that of a flat plate, perpendicular to flow, having the same frontal area. Motorcycles have two problem areas: 1) because they’re short they’re chopped off behind the rider, creating a turbulent wake that carries away significant energy, and 2) the exposed front wheel, fork, and brake assembly creates turbulent flow that streams past the lower half of the vehicle, adding to wake turbulence and drag.

Note winglets and overall slippery aero shape, especially rounded low-drag nose and the sculpted rear to help the bike close the hole it makes through the air. (Neale Bayly/)

For an example of an ideal low-drag shape, consider a fish such as tuna or salmon: Their surfaces are smooth and uninterrupted, and their maximum cross section is forward, allowing a long tapering tail that smoothly closes the fish’s wake behind it with minimum turbulence loss. In 1968, an excellent fairing was developed in the Caltech wind tunnel for Harley-Davidson’s antique side-valve KR roadracer. This also had its largest cross section well forward, and its sides tapered inward to the rear. How many times have I, walking through race paddocks, seen fairings mounted in “snowplow” fashion, becoming wider to the rear, enlarging the wake and creating extra drag? I recall the remarks of an aerodynamicist friend who had just returned from Bonneville: “Many of the shapes I saw out there would’ve gone faster backward.”

Subsonic Shapes for Subsonic Speeds

Terblanche’s prototype has the smoothly rounded nose that produces lowest drag at subsonic speeds. Because wind-tunnel work shows that airflow behind the rider is separated and turbulent, this bike has no “streamlined” seatback. The bodywork surfaces are smooth, contrasting with many current sportbike fairings, which are made up of many separate elements or “shingles.”

Rationalizing the Suspension

Terblanche has long wondered why the industry continues to place the front suspension units inside the fork tubes, rather than using a single central unit that is 1) less expensive, 2) easily accessible/replaceable, and 3) provides damping and ride-height adjustments in a single location.

Exquisite 3D printing is evident throughout, as on these lovely adjustable footpegs. (Neale Bayly/)

With present-day inverted forks, the only connection between the two sliding members is the axle. Even today, a wobble or passing over bumpy pavement while leaned over can tilt the front wheel, knocking brake pads back enough that the lever comes back to the bar at the next corner. Terblanche’s version of the telescopic fork therefore provides two joined parallel and cylindrical tubes, carried by the steering-head bearings, and resembling a bicycle’s fork (Y-shaped). Moving up and down upon the tubes are a pair of sliders joined by a robust arch over the top of the front tire and by the front axle (no more front-wheel tilting and no more pad knock-off). The lower end of the single front suspension unit attaches to the top of this arch. The fork tubes contain no damping apparatus or oil; they are just guides to define the front wheel’s movement. He proposes further that the guide tubes be made in smaller-than-usual diameter so they disturb as little airflow as possible over the steered assembly. Their stiffness? A bit of arm-waving here; perhaps reliance upon internal bracing.

In addition to this limited streamlining of the fork itself, the sides of the lower fairing have moved outward, providing a surface for airflow streaming past the front wheel to attach itself rather than continuing back as a turbulent free stream.

In action, Terblanche’s design is identical to a conventional telescopic fork. Why not one of the alternative front ends people persist in calling “high tech”? Why not constant wheelbase or constant trail designs? Because such alternatives have not demonstrated superior performance.

Simplicity and Reduced Parts Counts

When Terblanche designed the Ducati 999, his brief was to simplify. He asks why modern motorcycles have electrical systems with tangles of wires running everywhere. Shouldn’t most of the “wire” be in one place, in the form of one or more printed circuit boards (PCBs)? Shouldn’t the alternator and voltage regulator be integrated into a single-wire system? The more parts there are, located all over a bike, the more time-consuming assembly and service become. Wasn’t single-wire CAN bus supposed to end tangles by integrating coded switches into each single-wire consumer of power, all messaged by a central unit?

All electronics are attached to the alternator; behind that is the (planned) supercharged single. (Neale Bayly/)

This prototype has its electronics (battery, PCBs, ignition, ECU) attached to the front of the alternator, located on the left.

Ease of Access

Having seen race-team mechanics crowded around their bikes, each one seeking to attend to his specialty, Terblanche proposes two more simplifications. First is a single jack point low on the engine crankcase. A two-pronged lever lift engages matching holes, allowing the whole bike to rise 20mm clear of the ground for wheel changes. Second, electronics access is placed on the left side of the machine and suspension access on the right. Additional access is provided by the hinged seat, forward upper fairing, and the dummy “tank.”

Comprehensive Adjustability

Because the “rider triangle” of bars, seat, and pegs is individual to each person, shouldn’t all be easily and quickly adjustable? Accordingly, windscreen height, tank longitudinal position, and pegs are readily movable.

High Performance from a Simple Engine

How can a 699cc engine deliver 130-odd horsepower? A Rotrex centrifugal compressor and the plenum chamber needed to mediate between the compressor’s steady flow and the engine’s intake pulsing are located forward near the engine’s horizontal cylinder. Fewer parts and centralization of functions translate to lower build cost and greater affordability, a trend we see in the present popularity of parallel-twin engines.

It was energizing and exciting to spend time with an experienced practicing designer with definite ideas. What comes next?

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