Hey guys (and gals too I guess...),
Some of you may remember that
I built a gravity racer for the 2017 "adult" soapbox derby here in Portland. Things went well and I won it overall on my first try.
The Mk I on the way to victory in 2017:
I was then asked (on this very forum!), "Whatcha going to do to it now so that you're faster next year?"
At the time, I didn't know it but the answer was I was going to build a new one. I developed a very specific vision for the new one, to be called the Mk V, which I couldn't just modify the Mk I to achieve. So I built another, and although I didn't document it here, I did document it on
this thread in another forum.
That build was also eminently successful. I won overall again in the Mk V. The Mk I was run to 3rd overall by a friend as well, so it was another very good showing for the Scuderia.
The Mk V on the way to victory in 2018:
I love the event. It's a blast. We will be on the hill again for 2019. I think the Mk V has the potential to go even faster and I would be hard pressed to build something else which might out run it. But I think I'm going to try. It will be difficult to put aside a car that is running within a sneeze of the track record which was set on a MUCH more favorable (HOTTER) day. But I think I am going to try. Why you ask? Read on.
At SEMA this fall, I chatted with someone who runs at Bonneville with a sidecar motorcycle and we had a conversation I just couldn't get out of my head. He asked me why I did a couple of things a certain way and then told me what he did and why for his decade of builds and going to the Flats, and what the results were from their wind tunnel testing. Sometime during that ~10 minute discussion, I realized I was going to be building a new car for this year.
I dug up some used go-kart running gear and acquired an old junked bike to put together a prototype chassis, adding in the front wheel of a pocket bike. This minimizes the height of the running gear underneath the bodywork. I think there's a bit more rolling resistance with smaller, wider, and stickier the kart tires, but I am hoping the smaller size turns into an aero advantage once at speed (>20mph or so). In switching to a single steered front wheel, it also simplifies/reduces the components out in the airstream as well.
My main concern is stability through the Learning Curve. I was pulling almost 1g laterally through there last year and I really don't want to have it flop over on me. The track and overall width will be similar, although narrower, but I am also thinking I will be able to keep it even lower overall than the Mk V as well. Dynamically, I don't think the corner cares if I have one wheel in the lead or in the trail position, as long as the height of the CG is low enough to keep some weight on the inside wheel. I would be curious if anyone has any evidence to the contrary. There was a lot of discussion when the Delta wing came out. I am not afraid to give the concept my own shot.
So, without further adoo, I introduce to you the working prototype for the Scuderia Kouba Mk VII:
It doesn't look like much right now but it will come around. The handlebars are on there just as placeholders, it will not be driven head first. I have the steering planned out regarding how to get it steered while laying down with my head at the stern. At this point the proof of concept indicates that it can be done, so I will be giving it a shot.
I have a new frame started which should be much more square and flat, and it will carry a wider track rear axle- it will be the go-kart front end with fixed tie rods, so that I have independently rotating rear wheels. I still need to figure out a few dimensions for it but it's definitely on its way. Watch this space for further updates.
Constructive comments and thoughts encouraged regarding the 1F2R configuration. That is the component of this build which breaks new ground for me. We clearly got the 2F1R to work well, I hope the single front wheel can apply the needed force to swing the front end around the corner without rolling me tangentially off the course.
I look forward immensely to this adventure!
Chris