AeroVelo is excited to announce a new sponsorship with GMC. The synergy between our two companies comes from our mutual passion for precision engineering and innovation. GMC generously offered us access to GM’s Milford Proving Ground in Michigan for testing and further development of Eta. When it opened in 1924, the Milford Proving Ground was the auto industry’s first dedicated auto testing facility. It is an amazing facility that covers over 4000 acres and has a seemingly endless variety of tracks, road conditions and specialty surfaces. As engineers, being able to visit and test in facilities like this is a great privilege.
We tested for two full days and it turned out to be an invaluable experience for the team and produced a lot of very useful data that will help us further refine the bike's performance and handling before September. We also had the opportunity to meet one of GMC’s aerodynamic engineers who spent the better part of a day with us while we were testing.
Going in to the first significant road tests of the season, we had several objectives. First and foremost, we wanted a shakedown trial and handling re-evaluation for Eta, and we wanted to assess various improvements we over the past year. Finally, we hoped for the first time this year to test the handling of Eta at high speeds.
Earlier this year we performed multiple tests at Bombardier's Downsview airport in Toronto, which led us to make many mechanical changes to the bike. We refined the handling qualities of our steering by adjusting the front fork geometry, in particular the fork head-tube angle and wheel dropout location. We performed several tests to address concerns about the stability of the bike, its controllability and response, as well as how well it stood up against cross-winds. The Downsview tests showed us that the bike didn’t need a fin to make cross-wind gusts, and that steering modification was sufficient to make the bike easy to control in even larger gusts. Through our tests at the Milford Proving Ground, we confirmed that the revised steering geometry made the bike more stable, easier to handle, and overall better for delivering serious sprint power while remaining in control.
This year we also made some mechanical changes to the drive-train, the front wheel-well design and fitting, and had built new disc wheels that needed to be tested on the road. At Milford, all these improvements performed as well as we hoped. In particular, the disc wheels were robust to a variety of road conditions and are the most solid wheels we’ve ever built.
We’re always trying to gather more data on the various aspects of the bike’s design and functionality. For example, Eta has a latex membrane that seals the front wheel fairing to the rest of the shell while still allowing the front wheel to turn. We needed data on how this flexible surface behaves in airflow at high speeds, so we attached GoPro cameras to the bike. The footage revealed that there was only slight outward deformation of the latex surface at speed, and that the aerodynamic shape we intend the bike to have near the front wheel is preserved.
Another area of improvement we wanted to look into during this road test was to determine if our ventilation and airflow inside the shell was sufficient for optimal rider performance. We took GoPro video of the exhaust and other areas of interest inside the bike to assess the flow. We had limited the air intake at the rear of the shell and the exhaust ports in the wheel-wells, as less ventilation means less drag. To measure CO2 buildup, we implemented a custom-made Arduino-based sensor system. Unfortunately we found that the CO2 sensor was saturated at times beyond its 2000ppm concentration limit, so we couldn't tell how high the concentrations actually got. We'll need to install a new sensor capable of measuring higher levels of CO2 and take readings a second time when we go back to the track for another road test in August. Fortunately these saturations were only at lower speeds and lower efforts, because 2000pm is a lot of CO2 for an athlete to breathe in!
Finally, we wanted to validate the structural model of the bike, especially the vibration characteristics of the frame. We did this test by taping iPhones and Android phones all over the carbon structure to measure the vibrations at various points. We used the phones’ internal accelerometers (which are very sensitive to small motions) and a logging app to record every motion of the phone (and hence the frame) throughout a run. This approach yielded a lot of valuable data which we were able to correlate with our custom structural models. We found that we needed to stiffen up the frame in a few locations, and we've already taken measures to achieve that. Most excitingly, this also indicated that we could reduce frame weight (via carefully applied sandpaper) in some areas, and we’ve been able to shave off a few kilograms! Reduced weight on the frame means less mass to accelerate to top speed at Battle Mountain, and may make as much as 0.5Km/h difference in our top speed on its own.
A big goal of ours at the Milford Proving Ground was to try to get Eta up to very high speeds prior to the race at Battle Mountain. We had a prototype integrated a propeller-driven power-assist module that would help Eta reach and sustain speeds of 140km/hr. Unfortunately, we experienced some setbacks here. We were unable to push Eta high speeds because we were limited by the surface of the track we were using. Our specific test track was designed primarily for durability testing, not speed-testing, and was therefore carefully engineered for certain road roughness characteristics. This is a long way from the smooth stretch of Nevada highway on which the World Human-Powered Speed Challenge will take place. So in order to remain in control of the bike, we maintained slower speeds over a substantial portion of the track. This was the only test of the trip that didn't yield satisfactory results, but it wasn't a total disappointment because it proved that the disc wheel structure is sufficiently robust for any rough, real-world conditions the bike will see.
Thankfully, due to the great partnership we have built with GMC and their team, this road test session was just the first of the summer. On a return trip, we will put Eta on one of the facility's high-quality straightaways so we can reach high speeds on a road surface comparable to what we'll have at Battle Mountain.
We gained a lot of confidence at Milford because Eta proved that it handles and performs well in its current configuration. The main focus from now on will be improving Eta's robustness and readiness as we approach Battle Mountain.
Having the opportunity to test Eta at the Milford Proving Ground has been crucial to our chances of success at Battle Mountain this year, so we'd like to thank GMC for partnering with us and supporting our goal to make Eta the fastest human powered bicycle. Thanks as well to the AeroVelo team members on the track for the weekend for their expertise, hard work, and dedication!