DynaVibe Helps Make Aviation History
On the eve of World War II, Ettore Bugatti – the legendary sports car designer – was busy trying to build an airplane. And what a plane it was: a technological marvel in art deco; the most elegant aircraft that would ever grace the skies. Except, it never flew. Bugatti built just one of his visionary airplanes in 1939, designated the 100P, but it remained grounded with plans to fly it scrubbed because of the war. Spirited away to a hiding place to avoid being seized by the Nazis, it remained in mothballs even decades after the war. Today the restored but not airworthy 100P resides in the AirVenture Museum in Oshkosh, Wisconsin.
Enter Scotty Wilson, whose aviation career spans five decades and nearly 11,000 hours in aircraft ranging from Cubs to F-16s. He is also a certified aircraft mechanic who had a vision to build and fly a replica of the 100P. In 2013, Wilson led a team that funded the “RÊVE BLEU” (Blue Dream) project via Kickstarter. The dream became reality on August 19, 2015 when aviation history was made as the Blue Dream took its maiden flight.
The Bugatti 100P was – and is – an extraordinary airplane with an innovative, timeless design. Originally designed to fly at a top speed approaching 500 MPH, the 100P is driven by two engines located behind the cockpit, connected via drive shafts and gearboxes to two, contra-rotating propellers.
The 100P’s unique, complex power plant and propeller assemblies intensified the need to balance the propellers. RPX Technologies, the makers of the DynaVibe propeller balancing system, has been in dialogue with Scotty Wilson and the Bugatti team for a few years, reviewing the potential vibration problems of such a unique airplane. The range of possible issues with the 100P included torsional vibration, resonance and contra-rotating prop interactions not typically seen on most aircraft.
When the Blue Dream team had the Bugatti ready to run the engines leading up to the first flight, RPX met Scotty to balance the 100P’s props. Matt Dock, RPX co-founder and engineer, used the DynaVibe GX2 to perform this task, setting up the DynaVibe accelerometer on the propeller gear box, as close to the props as possible. The photo tachometer was mounted on the outside of the fuselage as pictured.
With this configuration of the DynaVibe accelerometer and phototach, it was easy to setup the DynaVibe GX2 for a non-typical installation by using the display and arrow keys to position the location of the accelerometer, phototach, propeller blades, and direction of rotation. Even with the odd angles of the phototach and accelerometer, the GX2 was able to compensate for the atypical setup and provide a great balance in minimal runs.
Before starting the balancing run, Matt did an initial spectrum analysis to determine what possible vibrations might exist in the 100P. The DynaVibe GX2 (pictured below) revealed vibration only in the prop spectra, so Scotty and Matt proceeded to dynamically balance the 100P’s propellers.
Matt and Scotty first turned their attention to the prop that rotates counter-clockwise. The initial vibration measured was significant, at 0.37 Inches per Second (IPS). Even though the 100P’s props are relatively small, the fiberglass spinner is fairly large, and custom made and therefore a likely cause of propeller assembly imbalance. During the first balancing run, the DynaVibe GX2 provided an exact solution for how much weight to add and where to add it. After three runs total, the counter-clockwise prop was balanced and Scotty observed that the annoying vibration in the panel was gone!
The clockwise rotating prop was addressed next by setting the DynaVibe GX2 up for a new balancing job. This prop was initially smoother than the counter-clockwise prop, exhibiting a vibration of .19 IPS, and after three runs Scotty and Matt easily got the vibration down to just 0.06 IPS.
With the props in balance, Scotty and Matt used the DynaVibe to check the vibration from the long drive shafts in the airframe. The Bugatti uses a pair of Hayabusa engines driving automotive style drive shafts with u-joint connections in multiple locations. U-joints typically generate a torsional vibration at twice per revolution speed. Bearing vibration was also examined, providing the Bugatti team with valuable, preventative benchmark data about these critical components.
On August 19th, with balanced props, the Bugatti 100P – the Blue Dream – finally took the air for its historic, first flight. RPX will continue to work with the Bugatti group to help with any issues in the future. Watch the exciting video of the first flight of the Bugatti 100P:
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