[brian_]

Congratulations!

The bike looks good; even in bare form it's a clean design.

It's good to see that Bonneville went well for at least one EV team this year... the cars and an enclosed motorcycle didn't fare so well during Speed Week earlier in August.

Bonneville Motorcycle Speed Trials (still showing only 2019 records and results; the 2020 event was cancelled)

As far as I can tell from the rules, "A" is a frame classification of special construction (i.e. not production), and "APS" is the Partial Streamlining variant of that. "W" is the engine classification for electric, and there are specific technical rules of electric vehicles (section 3.22-L-24), with three classes by weight (up to 150 kg being the lightest).

 

[brian_]

If I remember from my basic aerodynamics training, for stability, you always want the center of mass ahead of the aerodynamic center. This applies to aircraft, rockets like the new Spacex Starship, and motorcycles, particularly with dustbin type fairings, like this one.

Yes, but if the centre of aerodynamic pressure is too far behind the centre of mass, it is apparently difficult to control the vehicle - to make it turn if you need to. One of the fully streamlined two-wheeled entrants at Speed Week made a video about that.

One advantage with electric bikes is that the batteries can be easily moved around to adjust the center of mass.

But the battery is also bulky, and tends to fill almost all available space, so it can be hard to move much. There is likely more room to move the relatively dense engine in a conventional vehicle.

 

[brian_]

Yes brian, you do not want to overcorrect a problem and then create another problem. The main task at Bonneville, AIR, is to point your vehicle in a straight line and try to keep it that way for the whole speed run. Unless, coleastering, you were on some kind of slalom course.

Right... but with any side wind, the apparent wind direction and the direction of travel are not the same, thus the need to fight the vehicle's tendency to "weathervane".

This is the video that I mentioned earlier:
Lark Streamliner | Vehicle Dynamics part 1
I haven't seen the rest of the series, and the aero work here is crude, but he does discuss the centre of pressure vs. centre of mass issue.

Do you mean an ICE vehicle as a "conventional vehicle"? In my crazy ICE car days, the first thing we usually did to improve the balance of the vehicle, was to move the 12V battery to the trunk. It sure was a lot easier than moving the engine! In a relatively open structure, like coleastering's bike, it would be very easy to move portions of the battery to different locations. Or, even easier to move ballast around, as he apparently did, to improve the straight line performance.

Yes, I moved the battery in my first competition-prepared vehicle, too. It was, after all, a convenient box of lead; it wasn't an enormous thing comprising a large fraction of the vehicle mass and volume, as an EV battery is. Also, the car was production-based so moving the engine would be difficult, in contrast to these land speed competition streamliners which are custom-designed, allowing the designer to determine engine placement.

In most production EVs the battery would be even more difficult to shift in position for competition use than the engine would be in an ICE-powered vehicle... but of course we're not talking about a production bike here.

This bike is nice in this aspect because the rider straddles a backbone with battery and other components hung under it, so those components can be shuffled for ballast. The general layout is fixed in the only really practical configuration: two wheels, a tailcone behind the rear wheel, and everything else between the wheels. If you look at a typical enclosed streamliner (with two wheels or four) any significant shift of major components such as battery would mean relocating the driver's compartment - it's a substantial design change, not a tweak of mounting points.

Of course small lumps of ballast are the easiest things to move, but a well-designed vehicle has minimal ballast (when complete, unlike the unfaired version of this bike) because just about anything else - battery, motor, structure, etc - is a better use of mass (which has to be supported and accelerated) than just ballast. Ballast is for tuning (as Cole is using it), not to fix fundamental design problems.

 

[brian_]

I think the veracity of that statement is too dependent on the engine and battery placement in a given vehicle. How am I going to shift the engine/transaxle around in a front wheel drive vehicle?

I thought we were talking about land speed streamliners - you can put the motor where ever you want, and don't need to drive any specific axle. Even production front-wheel-drive cars have been built with the engine ahead of, over, and behind the front axle line.

It would be a good idea for the DIY builder to, if possible, have some provision(s) for adjusting vehicle balance, if a problem should arise. The batteries being quite heavy, seem to me to be a good candidate for doing this.

Absolutely! It's just easier to move a relatively small engine than a relatively larger battery, and most of these streamliners don't have a bunch of extra space to have half-filled boxes of battery modules so they can be shifted around like ballast in a submarine's tanks.