Saturday, August 23, 2008

Report 6 from Speedweek

August 22nd – Three runs in a day!
Following the successful morning run at over 280 mph, the team was able to turn the vehicle around fairly quickly, and was back in line around 4pm after refueling, and making some changes to the inverter setting, bumping up the power setting from 80 to 90%.
The 4pm run started with a quarter mile speed of 224 mph, about 7mph faster than the morning run, and the first mile was also faster than the morning run by about 7mph. Unfortunately the system shut down in the second mile and Roger coasted to a stop. While refueling back at the pits, the team reviewed the data and it was clear that the shut down had been caused by an inverter limitation. The power setting was dialed back to 85%, and at 6:45 Roger was strapped in and ready for the third run of the day.
That was an exciting run – the quarter mile speed was 21mph faster than the morning run, at 238 mph, the first mile was completed at 249, and the middle mile recorded a 269 mph speed, also 21mph faster than the morning run. When we heard that number over the PA system, we knew that the 300 mph goal was within reach. Unfortunately the inverter cut out again in the last mile, and the speed on the last mile was only 249.
In spite of this last-second set back , the team was very upbeat – Roger reported greatly improved acceleration, and the speed increase was also aided by the fact the the team decided to limit the truck push-off to only a few seconds, letting Roger accelerate away as quickly as possible.
Later, after an enlightening conversation with Tony Davis of Saminco and further analysis of the data, it became apparent that the inverter shut down is cause by currents on the AC side in excess of 1,000 A. With a satisfactory explanation in hand, the team was ready to prepare for the next day.

August 23rd –
This morning the first order of business was to adjust the inverter settings. The team decide to follow a two-step process. 1. Dial down the power to 83%, hoping to stay below the inverter limit throughout the run, and 2. Later, increase the power setting back to 90% but include some software limits to prevent the inverter from ever being asked to deliver current beyond its limitations. This should allow the inverter power to be significantly increased except when the increase would exceed the limit.
If you consider that the low-speed torque is already limited because of mechanical shaft limitations, it is reasonable to state that the Team has extracted every watt of usable power from the Ballard stacks – a significant achievement. I am not sure that we ever thought that we would exceed the limits of the electric traction system...
Well the BB2 is almost ready to be towed to the line...

At 10:10 local time the Bullet was off to its best start ever, reaching over 272 in the middle mile. The run has just ended and the final mile speed was in the 260s. I am guessing that the inverter cut out again. But Roger was able to extract a few more mph in the first and middle miles – BB2 is running faster every time, and after we re-program the inverter we might see some very exciting speeds!

We expect a 2- to 3-hour turn around time, which would make it possible to think about three, maybe four runs today.

Stay tuned!

P.S.: attached you will find a phenomenal picture taken by Kevin Ponziani riding in a chase vehicle. You can clearly see the water and water vapor exhaust streamlines hugging the tail end of the Bullet – no separation, perfect aerodynamics. Kudos to Kim Stevens, BB2 aerodynamic designer, and currently aero engineer with the BMW Sauber Formula 1 team in Zürich, Switzerland. Go Kim!!

Go Bucks! Go fast!

1 comment:

Anonymous said...

That 300+ mph mark is sooo close. Who wants to go FAST? Go Bucks!