Peter Garrison– The Bugatti 100P was a beautiful blend of art and engineering.

Peter Garrison.

THE LEGENDARY BUGATTI 100P racer was a collaboration, begun in the late 1930s, between Italian-French car builder Ettore Bugatti and French freelance designer Louis de Monge de Franeau. The original aeroplane, its development interrupted by the outbreak of World War II, never flew. It now resides in the EAA museum at Oshkosh.

De Monge was an imaginative fellow who designed a number of unusual aeroplanes. If his designs share a single common trait, it is the same sort of sleek streamlining that he brought to the Bugatti project.

The general arrangement of the 100P was somewhat similar to that of the Bell P-39 Airacobra, which was hatched at about the same time. The Airacobra’s single 1,100-hp Allison engine was mounted behind the pilot, driving the propeller through a thick driveshaft passing under the seat. The 100P had two 8-cylinder, 450-hp Type 50B automotive racing engines, set one behind the other within the central fuselage. The reason for using two engines, which greatly complicated the design, was that Bugatti was committed to his own engines, and one of them would not have provided sufficient power to drive the aeroplane to an impressive speed.

The engines drove coaxial, contra-rotating props on the nose through long driveshafts passing to the left and right of the pilot. The coolant radiator, located in the aft fuselage, took in air through the leading edges of the horizontal stabilisers and exhausted it through louvers in the wing root fairing.

The original Bugatti P100 was considered the world’s most beautiful aeroplane.

Often praised as one of the most beautiful aeroplanes ever designed, the Bugatti had a peculiarly “artistic” form, a sort of Art Deco flavour, with a slender, perfectly streamlined spindle for a fuselage and dramatically tapered, nearly triangular wing and tail surfaces. The empennage was in the form of a Y; the short ventral fin housed the tailwheel.

‘lovingly replicated the original’

The slightly forward-swept wing had flaps split into upper and lower halves that could be deflected separately or together to serve as high-lift devices, airbrakes, or camber-changing flaps. Variations on this scheme, which Bugatti attempted to patent in 1942, have popped up from time to time since, for example on the B-2 bomber.

Starting around 2010, a team of volunteers, led by retired Air Force pilot Scotty Wilson and funded in part by a Kickstarter campaign, lovingly replicated the original, installing in place of the 4.7-litre Bugatti engines a pair of 1.3 litre Suzuki Hayabusa straight-fours of 200 hp each, originally designed for a 200-mph motorcycle. They dubbed the project, and the aeroplane, The Blue Dream.

Although the 100P is commonly described as an engineering marvel far ahead of its time, it incorporated several eyebrow-raising features. It is probably more correct to see it as of its time rather than ahead of it, and perhaps as an experiment rather than a marvel. I always intended to make contact with Scotty Wilson and discuss with him some of the intriguing aspects of the design, but, a chronic procrastinator, I never acted on the resolution.

The driveshafts, for example, were slender, and certain to invite torsional resonance, which occurs when the natural vibrational frequency of a driveshaft matches that of the engine driving it. Unlike turbines, reciprocating engines deliver power in a series of pulses, each of which imparts a twist to the shaft. Between power pulses, the shaft springs back toward its relaxed state. If the wind-up and spring-back of the shaft get into tune with the engine, a condition known as “torsional resonance”, forces build up that can break the shaft or damage the prop reduction gearbox. Torsional resonance can be controlled with various kinds of clutches and fluid drives, and sometimes by using a sufficiently light propeller. I was curious to know how it had been dealt with in the original 100P, and how in the replica.

The ill fated – but still beautiful replica.

The tail volume – a rough figure of merit, related to longitudinal stability, that is the product of the tail area and its distance from the centre of gravity – seemed to me to be on the small side, particularly given the proximity of the stabilisers to the wing and their V configuration. If a stabiliser is too close to a wing, the flow around it is dominated by the wing’s wake and it responds weakly to changes in angle of attack. I wondered, too, what sort of aerodynamic characteristics the horizontal stabilisers would have when their aerofoils lacked well-formed leading edges but had, instead, the large open slot of an air inlet. The inlets themselves, furthermore, seemed to me too small for such powerful engines.

I was curious, too, about the effect of the extremely long nose on longitudinal stability, particularly in light of the possible lack of authority of the empennage. The propellers were quite far from the centre of gravity, and tractor propellers are destabilising – that is, when the nose swings up or down or to one side, they tend to pull it farther in that direction rather than nudge it back. The effect is proportional to power, and even 400 horsepower, let alone 800, is a lot for such a small, short-coupled aeroplane to handle.

Finally, I had to wonder about the stalling behaviour of a wing with so much taper. Tapered wings tend to stall first at the tip. This is an undesirable trait, because it means that, since one tip is almost certain to stall before the other, the aeroplane will roll sharply toward the stalled wing. Even moderately tapered wings are twisted several degrees to delay the stall at the tip, but profile pictures of the 100P did not seem to show much twist. Large taper ratios – that is, a tip chord that is a small fraction of the root chord ¬- were common in the 1930s; perhaps their poor stalling characteristics were accepted as a necessary evil in exchange for the bending relief that taper provides for the wing spar.

With a wingspan of 27 feet, the 100P was small, and, with a gross weight of nearly 3,000 pounds, it was heavy. Nevertheless, its power loading was so low that it should have been quite a performer.

The Blue Dream made its first flight on August 19, 2015, with Scotty Wilson at the controls. The takeoff roll was long. It appeared, from online video, that Wilson was handling the plane quite gingerly, but that its in-flight stability was satisfactory. Unfortunately, it suffered a mishap on landing, swerving off the runway, reportedly because of a brake failure, and digging into soft, rain-soaked ground. Repairs were made and it flew for the second time two months later. Again, video showed what looked like a cautious flight, probably at much reduced power, but with good stability and control.

A long flightless interlude followed. I was puzzled. Once I began test-flying each of the aeroplanes I have built, I could not wait to fly again the next day. Why was The Blue Dream not constantly flying and being reported upon?

‘Tapered wings tend to stall first at the tip’

A number of explanations were possible. Perhaps the engines were misbehaving. There could have been problems with the propeller gearbox. But there would be no reason to hide problems of that sort. An alternative possibility, and one that might be more consistent with the lack of public communications and also with the events that would follow, was that the beautiful looking aeroplane had dangerous flying characteristics.

On August 6, 2016, Wilson took off for what was said, to my surprise, to be the aeroplane’s third and final flight before its retirement to a museum in England. Really? After only three brief flights?

Video shows it rotating rather abruptly, then establishing a shallow climb with a somewhat nose-high attitude. A man steps in front of the camera, eclipsing the aeroplane – a groan goes up – The Blue Dream has suddenly rolled left, dived into the ground, and burst into flame.

The National Transportation Safety Board produced a thorough and detailed account of the accident (CEN16FA307). The investigation was aided by the recovery of several onboard cameras, which recorded every detail of the pilot’s actions. In brief, it appeared that the aeroplane fell victim to its own novelties.

Shortly after takeoff the forward engine began to overspeed, perhaps because of a malfunction of the hydraulic clutch that protected the driveshafts from torsional vibration. Wilson, 66, a 10,000-hour air transport pilot, apparently distracted by his efforts to get the engine under control, allowed his airspeed to decay. The left wing stalled and at an altitude of 100 feet the aeroplane rolled into an inverted dive, and so the blue dream came to an end.

Leave a Reply