The Eagle Ducatis

[Admin]

The dePrato Eagle 1 Ducati as it appears today and as it was last raced, with full fairing and disc brakes. The entire enterprise was a combination of passion and a yearning to learn by doing. (Bruno dePrato/)

Longtime readers will know Cycle World’s European editor, Bruno dePrato, is a man of many talents. In addition to being a fast, critical rider, he’s also a gifted engineer. Years ago he designed a pair of innovative chassis for two Ducati racebikes which were much admired by none other than Fabio Taglioni himself. Recently he was united with his first creation. Here’s the story of how that bike and its sibling—the Eagle 1 and Eagle 2—came to be. It’s hard to imagine a similar effort today.  —Mark Lindemann

In addition to being the late Marco Simoncelli’s uncle, Giancarlo Rossi is a passionate collector of racing motorcycles…especially those with a story. Most of them are Ducatis—including my Eagle Ducati 1. After 50 years, I never thought that I would see that bike again, or that seeing it would bring back such strong emotions. So now here I am, recalling an adventure that—with the perspective of time and some added wisdom—appears both wild and epic.

In 1970, back in Italy from college in South Carolina, I was hired by Alfa Romeo’s Aerospace division. This was my day job, but since Alfa Aero had no real R&D department, I started playing with motorcycles and writing technical features for the only motorcycle magazine then on the local media market: Motociclismo. In addition I paid regular visits to Dr. Vincenzo Surace, the real brain behind the Alfa 33/3 that paraded at the 24 Hours of Daytona, and the 3.0-liter Alfa-Brabham F1 boxer 12 and V12.

Meeting Dr. T

Supported by his positive comments, in 1971 I developed a rather innovative SOHC three-valve cylinder-head design that caught the interest of the Piaggio technical staff, who were then busy resurrecting the Gilera brand. While visiting Dr. Fabio Taglioni at Ducati, I saw some of his drawings for the bevel-gear 750cc V-twin, and started a great friendship that would last until his departure from this world. Not that our friendship was all cheers and smiles—Dr. T and I were from the same slice of Northern Italy where motorcycles are such a big part of the local culture that they are called just “motors” after the most dominant part of the whole.

Our first flaming fight came when we were pondering what the enthusiasts would expect from the new 750–900 V-twin in terms of performance and reliability. I made the bold suggestion that we should dump the old-style press-fit crank assembly with its related needle cages once and for all, and enter the age of solid cranks and plain bearings. He almost fired me.

The original Eagle was an exercise in chassis design. Here you can see the massive tubular backbone so reminiscent of Fritz Egli’s work, along with the triangulated engine hangers and rear section. (Bruno dePrato/)

Next came my criticisms about the chassis of the new (and very hot) Ducati 750/900 SS. At that time, Ducati had no real frame designer in the R&D department, or even a good specialist among their testers. Ducati had no frame specialist because the creed there was “Engine! Engine! Engine!” The frame was a mere annoyance, only there to keep the wheels in line. (At the time, Ferrari also had much the same attitude.) While Taglioni made very accurate calculations about the frame’s structural aspects (the 750/900 SS had excellent torsional rigidity), the bike’s steering geometry and weight distribution were all left to his “visual” intuition.

Dr. T’s Challenge

On the other hand, I was a strong disciple of the great British frame specialists. I dared to voice my opinion that this new Ducati chassis had an inappropriate combination of excessive steering geometry and weight distribution that was grossly biased to the rear, characteristics that made the old Ducati 750/900 a slow steerer and which gave the front end a heavy tendency to plow when pushed hard into slow to medium corners. In general, to me the bike appeared to be needlessly tall and just plain huge. Sure, the engine was indeed rather long, but it was also slim and not particularly tall. Dr. T. listened to my criticisms and finally froze me, saying, “OK, dePrato, let’s see how good you are when it comes to motorcycle frames.”

The gauntlet had been most conclusively thrown, and since it was Dr. Taglioni’s own glove you better believe that I took the whole thing very seriously. It was like I had been asked to pass yet another course in mechanical/structural engineering, but with Dr. Taglioni that was common practice, and it was OK with me too.

That frame backbone is a piece of steel tubing 4 inches in diameter and 1.5mm thick. Note the nickel plating. While the frame was totally Bruno dePrato’s design, he had it welded up by none other than Egli himself. (Bruno dePrato/)

It took me about one week to put everything together. I designed a very compact, very sturdy backbone-style frame inspired by those that Swiss master craftsman Fritz Egli had built to harness the mighty Vincent 1,000cc V-twin. The huge backbone tube (100mm in diameter, with a 1.5mm wall thickness) granted excellent torsional rigidity. To obtain a structure perfectly rigid on all flectional axes, I integrated the engine into the frame as a stressed member. Taglioni had done this with the Ducati 750/900 SS chassis, but with this new frame the effect and execution were more thorough.

To this purpose I designed four triangulated tubular elements connecting the backbone tube to the engine’s two front and four rear mounting bosses. The triangulated structures were immensely stiffer than the customary downtubes Ducati and even Egli used, and they prevented any flexional tendency on the longitudinal axis. The design was exceptionally good at coping with the asymmetric loads caused by the final drive’s chain offset.

The whole chassis turned out immensely rigid and stable, but that was almost inconsequential compared to the improvements in geometry. The stock Ducati 750/900 chassis had an enormous 61.5-inch wheelbase, and its front end had a whopping 30 degrees of rake and 5.5 inches of trail with 1.0-inch-offset triple clamps. On the other hand, my chassis had 27 degrees of rake and 4.0 inches of trail, but most importantly I pulled the front wheel all the way back while using the same swingarm length. In addition to shortening the wheelbase this radically readjusted the front/rear weight distribution. At the same time I also lowered the seat height by about an inch. All in all my new chassis had a 58.3-inch wheelbase, several inches shorter than the factory Ducati’s, and all that came out of the front end. Egli was extremely enthusiastic about the whole project, both because he fully approved my technical approach and because it was opening new perspectives to his own business, since at the time he was running out of Vincents to re-frame.

No rider-aid menus to scroll through here—just a rev counter and a cable clutch. Part of the Eagle 1 design exercise was to make the bike lighter, narrower, and better handling. But looking good wasn’t enough—it had to work in hand-to-hand racing combat too. (Bruno dePrato/)

In the spring of 1973, Egli welded up a test unit and sent it to me to check the accuracy of all the fittings and mounting points, which were perfect. Shortly after I got my copy of the hero frame, duly nickel plated as Egli used to do. My budget was very lean, so Dr. Taglioni helped me out with a 750 SS engine that had been sitting for a while in the race department. Nothing special, just a good mule motor left alone since development was totally focused on the new 900cc engine.

I went to Ceriani for one of its fabled “Coke-bottle-slider” racing forks. These had no provision for mounting a disc-brake caliper—at the time Giacomo Agostini still preferred drum brakes for his MV Agusta racers. While I hated drum brakes I loved that Ceriani fork, and I had a high-tech trick up my sleeve: Campagnolo’s Hydroconic brake.

The Campy Connection

Tullio Campagnolo, of bicycle fame, was a visionary old gentleman capable of incredible technical inventiveness. A few years earlier he started developing a new concept, inspired by aircraft brakes, and this eventually evolved into the Hydroconic design.

Walter Villa used the Campagnolo Hydroconic brake extensively on his 250–350cc world-championship-winning Harley-Davidson. When Tullio asked me to test it for road use, I checked with Villa about his experience; he assured me that the Hydroconic worked fine.

I modeled the tank and the seat after the legendary Harley XR-750 RR. An old craftsman hammered aluminum sheets of appropriate gauge to perfectly match the wooden molds, and he did a great job. The bodywork was painted black with gold pinstriping, and a friend created a good supply of stickers reproducing the Screamin’ Eagle shoulder patch of my beloved 101st Airborne Division, surmounted by the “Eagle” logotype (obviously in place of “Airborne”). While the shield’s profile didn’t match the original, it was still a good effort and got the message out loud and clear.

Classic beauty from every angle. (Bruno dePrato/)

In Bologna there was only one shop for special Ducatis and that was NCR. I brought all my bits and pieces there. Owners Giorgio Nepoti and Rino Caracchi were good friends: they assembled my Eagle-Ducati, but they did not like it much—in their eyes it wasn’t the kind of Ducati they’d been so successful with. Still, they did a fine job (except for the rear light and related support plate), and I thought my Eagle looked so much smaller and more compact than a Ducati 750/900 SS. Plus it tipped the scales at a mere 345 pounds.

Neilson, Schilling, and the California Hot Rod

In 1975, after Cycle magazine’s Cook Neilson rode his Phil Schilling-prepared Ducati 750 SS to victory at Daytona, Ducati invited Cook to Italy for well-deserved honors and celebrations. I was part of the welcome party and I asked him to make a detour to briefly look at my Eagle Ducati. I guess he liked what he saw—I ended up contributing to Cycle until the end of its run, and then moved over to Cycle World. Since my bike would never pass any homologation test, I rode it on the street using a cloned dealer plate. It was fun and adequately fast, but above all it was great on twisty backroads.

By this time I had left Ducati to become technical editor for a pair of Italian weekly magazines: Autosprint and Motosprint. In 1978 a young man full of enthusiasm for the sport came to me and asked me if the bike was for sale. I don’t know how he heard of my Eagle Ducati since I’d never publicized it, but I must say I welcomed his offer—I was growing tired of having to constantly stay on the lookout for the Italian police when riding on the road.

The buyer wanted me to act as technical manager for his racing team, and we started working to turn my Eagle into a real racer. First we bought one of the 900 SR engines that Ducati produced in limited number for endurance racing. I always loved endurance events, and covered them for the magazine as a reporter in addition to my technical-editor duties. Those SR engines were good, reliable units, featuring sand-cast crankcases accurately machined by Ducati’s tooling department, the same as the Factory/NCR team stuff. Engine output was acceptable for the time, about 80 hp. To get more out of these engines you needed the attention of Franco Farnè, Ducati’s chief race mechanic. But Farnè was also the third partner at NCR and, same as Giorgio and Rino, he was totally devoted to supporting, tuning, and honing only what came out of Ducati. And in fact the semi-official NCR-Ducati bikes had engines bored to 950cc, special heads, racing cams, and absolutely exclusive 41mm Dell’Orto PHM carburetors; this gave them a real 100-plus hp.

The Eagle proved itself at no less of a track than the legendary Misano. In addition to being the bike’s current owner, Giancarlo Rossi is also the late Marco Simoncelli’s uncle. Note the Simoncelli tribute banner outside the Misano track today. (Bruno dePrato/)

So we had to be content with the engine in its standard state of factory tune. But my mechanic was a very good one, Sergio Baroncini, and had acquired a great deal of experience racing Ducati 250-350-450 singles in the Italian FMI championship. Off came that lovely Ceriani fork and the Campy Hydroconic, replaced by a much stronger 38mm Marzocchi fork and Brembo brakes.

To repay my faith in his Hydroconic brake, Tullio Campagnolo granted me a supply of his impeccable 18-inch magnesium wheels. These were shod with the best rubber of the time: Dunlop K81 tires. We added a full fairing, and the Eagle was repainted in the sponsor’s light blue.

The Eagle’s First Race

The first contest of the Endurance World Championship season was fast approaching, the Misano 1,000 Kilometer race. Our rider was a young, enthusiastic man named Giorgio Boselli, but he proved totally inadequate. On our first test together he lapped Misano slower than I could on a Honda CN400. I was fast at Misano, but because I was so busy writing and trying to earn a living, I’d never gotten an FIM license.

With the race only a week away I called Arturo Venanzi, a very good friend and a good rider who had won the Italian 350cc GP title the year before. He was very enthusiastic about the new racing opportunity and made himself available for the first practice session—and very fast he was. We needed a second rider to team up with him, and Arturo suggested that Graziano Rossi (Valentino’s father). Graziano rushed to Misano, but the NCR team protested his entry for being registered too late—they had heard of Arturo’s fast lap times and feared Graziano might be even faster on the bike. They also protested the exhaust system that Ducati themselves had supplied with the engine, so we had to choke it up a little, throwing away a couple of horsepower.

But our real problem now was the lack of a second rider. Luckily Sergio found a young racer with a valid registration but whose bike had been withdrawn: Francesco Natalini. He was rather inexperienced, but he appeared determined, and in fact the two set lap times that put my Eagle Ducati on the fifth spot of the grid.

Motorcycles today are never as light and elemental as the Eagle 1—even today’s dirt bikes are more complex and visually dense. Imagine what a great streetbike this must have been when our editor was riding it in Italy. (Bruno dePrato/)

Arturo took the start and settled into the leading pack, headed by Marco Lucchinelli on a very fast Ducati NCR. Then, to my delight, I saw my light blue Eagle gain positions, lap by lap, until it zapped Lucchinelli’s NCR Ducati and took the lead. That was too much!

The cheers lasted only a few laps. Arturo suddenly started losing positions due to a misfiring engine due to a dying battery. The electric regulator Ducati supplied with the engine lacked the circuitry to charge the battery from the generator. We kept changing and recharging batteries at every stop, but our race had gone down the drain. Arturo saved the day by setting the lap record for the production class at 1:28.6, two-tenths quicker than Lucchinelli who, trying to keep pace with my Eagle, had broken the desmo rocker arms of his NCR Ducati engine, this due to the rather brutal valve acceleration derived from the bike’s ultrahot desmo cam grinds.

Franco Farnè and the NCR gang accused the time keepers of being wrong. But the one and only Dr. Taglioni walked over to me to shake hands and congratulate me for my chassis project, adding, “I am not a frame specialist.” Wow, that was like an additional graduation diploma! The bike’s sponsor was happy too, and gave me instructions to prepare the machine for the upcoming Bol d’Or, motorcycling’s ultimate endurance race.

Italian Intrigue

Ducati’s racing department offered us a complete engine overhaul for the race. This was a real bonus for a small team like ours, so Sergio took the engine to the factory. For the “Bol” Arturo Venanzi hired Graziano Rossi and the two made a great team, with the right spirit to handle the 24-hour challenge and the ability to bring the bike home and in a good final position. We all knew that we did not have the power to win, especially on a very fast track like Paul Ricard, so we agreed about a rather conservative strategy.

First test proved that we had to be ultraconservative. After a few laps Arturo came in reporting, “This is not our Misano engine. This is a sheep of an engine,” and Graziano joked, “Down that long Mistral straight they pass me with so much speed differential that I feel like I’m standing still.” The engine was so mild that it would not pull with any of the sprockets I had provided. But at least in such a state of tune it would last 48 hours, not just 24 hours.

Nevertheless, Arturo and Graziano were able to qualify the Eagle around the middle of the 54-bike field. After three hours things appeared a little rosier: The Eagle was steadily racing around the 13th–15th position, and we all knew that by midnight that many of the ultrahot bikes, like the Yamaha TZ700, would pack up. If everything ran as smoothly as it did for the first three hours we might finish within the top 10, or even better.

The Eagle 1’s engine has a story of its own to tell, as full of intrigue as any Italian opera. (Bruno dePrato/)

In the meantime the factory Ducati was battling for front spots against those Yamahas, and I must say that keeping pace with a TZ700 was a show of superb performance by that Ducati-NCR. By the fourth hour my hopes collapsed. A Kawasaki 900 bored to an illegal 1,200cc exploded, lubricating a large section of the track. Eight bikes crashed before the section was flagged, including my Eagle. That was the end of the whole adventure. We picked up the pieces and headed for home.

But it turned out there was more. A few days later, while working to refurbish the Eagle, our technician Sergio Baroncini called and said, “These are not our racing cams; these are street cams.” Ducati and NCR had sabotaged us in the best Machiavellian fashion—real sports!

The sponsor quit in disgust, putting the Eagle in his den for a while, then selling it. The bike changed hands a number of times, finally ending up in Germany. Eventually Giancarlo Rossi bought it.

The bike is not in its original shape, and could never be after all these years. The seat is right, and the tank too, but it’s made of fiberglass now, though correctly molded after the original aluminum tank. The color is the sponsor’s light blue. But “she” still looks right to me. My baby.

Eagle Ducati 2

Despite all odds, I gave the chassis-building challenge a second try. On the basis of my Eagle 1 experience my Eagle 2 was a good effort, but the whole adventure was a lot less gratifying and a lot less epic. Times had changed. Fritz Egli had focused his great abilities on Corvettes, and it was hard finding good craftsmen ready to cooperate with that extra dose of enthusiasm that’s so essential to a project like this. Completing the bike took so much time that when it was done it was no longer eligible to race under the new FIM rules.

The Eagle 2 was a real test bed of experimental ideas. In this shot with part of the fairing removed, you can clearly see the underslung fuel tank, an idea Honda played with too on its NR500 GP bike. (Bruno dePrato/)

Still, I love my Eagle 2 for the concepts I incorporated in the project. The frame structure started with a huge backbone, same as with the Eagle 1, but now shorter, which made the rear cylinder head more accessible for servicing. The triangulated elements connecting the backbone tube to the engine mounts now intersected to form a three-dimensional pyramidal structure, enhancing stiffness. The engine was set a little higher than on the Eagle 1, while the seat height was the same.

The Eagle 2’s frame backbone was much shorter than its predecessor’s. Here too you can see the small upper fuel tank (unpainted aluminum) which gravity fed the Dell’Orto carbs. The slick-shod bike rolls on Campy wheels. (Bruno dePrato/)

The increased ground clearance allowed me to locate the gas tank under the engine. It was fabricated from aluminum sheet and was shaped to fit inside the lower half of the fairing. To make it stronger and safer, the aluminum shell was wrap-bonded in fiberglass. Protected from most crash damage it held a healthy 5.5 gallons. An immersed fuel pump fed a 1-gallon tank located in the usual fuel-tank position. Refueling was through a cap here, while a hose of adequate diameter connected to the main tank. The  Dell’Orto carburetors were gravity fed.

The front-end geometry was a minor evolution, with 26 degrees of rake and 4.3 inches of trail using triple clamps with 1 inch of offset and an 18-inch front wheel. The rear suspension was my special trick: a parallelogram type, with swingarms hinged directly to the massive rear engine mounts. Wheelbase was slightly increased to 59.0 inches for even better front/rear weight distribution. I enlarged the engine to 950cc, and to protect myself from any further Ducati/NCR backstabbing, I discarded the whole desmo valve train and went to regular “spring” valves, developing an advanced polydyne cam profile that delivered excellent performance in total safety.

The Eagle 2 in profile. This right-side view clearly shows the parallelogram rear swingarm construction. (Bruno dePrato/)

While I conceived the bike for racing, unfortunately it never raced. I rode it for testing at the track and it proved very sure-footed and nimble, totally predictable in its dynamic reactions and with great traction even at extreme lean angles. The collector who bought it raced it with success in club events until it was worn out. He then sold it, but kept that magic non-desmo 950cc “bevel gear” Ducati engine for himself. It was able to rev to 9,500 rpm easily and made very, very good power. The great Dr. T did not approve, but once he checked the power curve he came over and shook hands. He was always like that, and nobody at Ducati ever was or has ever been so loyal and ethically correct as he.

Gratzi, Fabio. You have been a father to me.

Giancarlo Rossi (left, red jacket) owns the Eagle 1 today. Here he stands with Bruno dePrato, reuniting the bike and its creator decades later. Machines like this came from a time we may never see again. (Bruno dePrato/)

View the full article