Well, we're back from a disappointing event. Unfortunately, we weren't able to secure the record. There was a 5-9mph crosswind that contributed to an aero instability and we had to back out of the throttle at around 3/4 track on all three fairing runs. So goes land speed racing, I guess. Wish we could have done better! At the very least, she looks amazing!
That is a good idea, presumably your acceleration will be finished by the time you hit the timed portion. I can't remember if you've posted before on this but what is the relationship between CoP and CoG?
From the perspective of building and racing lots of streamlined human powered two wheel contraptions ...
Wiggle ~ weave is usually an alignment issue.
Two areas to check
1) Is the rear wheel pointing exactly straight ahead to the front wheel ?
2) is the rear wheel exactly on the same vertical plane as the steering axis ?
For the vertical plane check the forks are removed and an alignment checking tool is inserted thru the steering tube.
Small errors can cause bigger issues then can be imagined.
Absolutely. We have a significant amount of ballast weight available compared to last year too, but didn't get to test at the TM with it. 15+lbs extra on the front end is going to make a huge difference at Bonneville.
If the body is shaking around on the chassis the air flow becomes damaged and unpredictable allowing the center of pressure to move all over the shape.
My early streamliners experienced this problem.
Honeycomb or foam core monocoque bodies are the most aero predictable but if I recall correctly AMA Bonneville rules prohibit that construction technique.
Pretty sure Dennis Manning (BUB 7) created a separate motorcycle racing association to side step this problem.
They focused on the FIA record which allowed monocoque construction.
To solve a similar aero problem on a flying contraption we mounted tiny cameras all over, inside and out to watch where the problem started from.
We used low cost spy pen cameras. The camera when removed from the pen is tiny and easy to tape anywhere.
Once the body is ridged it's easier to "feel" where the CoP is on the shape. The feel will be more constant and predictable.
I describe the feeling as the "hand of god" pushing on the shape.
Ideally the CoP hits the center of the rider.
BTW ... the streamliner picture I posted earlier in this thread could only be operated in very low cross wind conditions.
The CoP was too far forward of the rider.
Previous bikes, designed for street use, were more stable in crosswinds.
Human Powered streamliners while obviously slower, experience the same conditions / problems and they weight 35 to 65 pounds (plus rider).
They solve without adding weight.
If the body is shaking around on the chassis the air flow becomes damaged and unpredictable allowing the center of pressure to move all over the shape.
Human Powered streamliners while obviously slower, experience the same conditions / problems and they weight 35 to 65 pounds (plus rider).
They solve without adding weight.
The single biggest problem for any land speed effort is finding places and times to test. I'm confident we could sort the issue in a tunnel or with more runs. We've talked about going to a drag strip test and tune. We'd have to make a custom rear sprocket and significantly modify our chain guard, but it'd probably be worth it.
Drag Racing will definitely give more seat time.
Many raceways have mid week "run what ya brung" classes which are supper handy for such tasks.
Thunderstruck "Tron" set it's records at a Wednesday night meet.
I made the chassis for Tron which was a bit of a junkyard build.
The front section came from an EMB (Electric Motor Bike) The rear tire and axle from a junior dragster.
Twin motors, Curtis controller.
As with all builds I double check and verify the alignment but it still had a strong side pull at top speed.
The pull was consistent always to the same side.
One of the Busa racers saw the issue and suggested to misalign the rear wheel slightly to compensate.
It fixed the problem and the bike jumped up in speed.
Torque flex in the frame was enough to create a problem.
Ya, for sure. We had an issue with starts this year at the TM as well, due to the tight leg holes in the fairings. Not near as much of a problem at Bonneville, but getting a bunch of runs at the drag strip would be great practice and that alone would gain us a few MPH.
PaPaSteve said:
As with all builds I double check and verify the alignment but it still had a strong side pull at top speed.
The pull was consistent always to the same side.
One of the Busa racers saw the issue and suggested to misalign the rear wheel slightly to compensate.
It fixed the problem and the bike jumped up in speed.
Torque flex in the frame was enough to create a problem.
Ya, for sure. We had an issue with starts this year at the TM as well, due to the tight leg holes in the fairings. Not near as much of a problem at Bonneville, but getting a bunch of runs at the drag strip would be great practice and that alone would gain us a few MPH.
This is interesting. Any noticeable roll moment when coming off throttle abruptly in the case above?
A small turn on the adjuster, the approach was go a little bit see what happens. Only required one adjustment.
Rear tire came from a junior dragster ... a wide slick when compared to what your running, more bite and larger overall influence to vehicle dynamics.
Michael Swallow was the rider.
Other then the solved constant pull problem I don't recall him saying anything about scary or weird control issues.
No weave or wiggle.
