AirFlow Truck Company StarShip Semi - 0.28 Cd

[Shepherd777]

And we haven't even tweaked it yet!

Believe it or not, there's still a lot of low-hanging fruit left.

Image deleted. Sorry.

We could not use the template because the windshield would have been too far forward in this configuration.

[freebeard]

Help me out here. The green line is the cumulative Cd not counting but not ignoring the downstream effects?

The tractor's contribution is 0.095 because it is being drafted by the trailer?

The taper in the rear causes an 80-90 count increase in drag?

I suspect I'm missing something. Or just totally wrong.

[some_other_dave]

I think I might be seeing something that says the truncation of the trailer is accounting for an 80-90 count increase in drag. Possibly that means 0.08-0.09 higher Cd?

So if you tapered the trailer, you might see less of a spike there.

BTW, the front of the template can almost be ignored. Don't worry about where it puts your windshield. It's the rear of the vehicle that contributes the most to Cd, as you're seeing with that big jump at the tail of the vehicle.

That's an interesting graph, BTW. I wonder how it gets made, and how reliable it is? Very cool if it is reliable!

-soD

[Shepherd777]

Originally Posted by freebeard

Help me out here. The green line is the cumulative Cd not counting but not ignoring the downstream effects?

The tractor's contribution is 0.095 because it is being drafted by the trailer?

The taper in the rear causes an 80-90 count increase in drag?

I suspect I'm missing something. Or just totally wrong.

I think that you are mostly correct freebeard. I am unsure on your second point regarding the tractor contribution. My aerodynamicist has not debriefed me yet on this chart, but that is supposed to happen tomorrow.

[Shepherd777]

Originally Posted by some_other_dave

I think I might be seeing something that says the truncation of the trailer is accounting for an 80-90 count increase in drag. Possibly that means 0.08-0.09 higher Cd? soD, I think that may be a viable assumption.

So if you tapered the trailer, you might see less of a spike there. We would absolutely see less of a spike there. The dilemma is trailers are made to haul a certain amount of freight. And most trailers cube-out before they gross out. In other words, all of that cubic capacity is used in a high percentage of loads. There are many more loads of cereal and toilet paper, than say anvils. So here in the good ol' US of A, we cannot taper the rear of the trailer like they have experimented with in Europe. Our shippers would never allow that. All high-cube loads are based upon and created using so much cubic feet of capacity.

BTW, the front of the template can almost be ignored. Don't worry about where it puts your windshield. It's the rear of the vehicle that contributes the most to Cd, as you're seeing with that big jump at the tail of the vehicle. We were concerned with the template on the front end only to the extent of where it placed the windshield in relation to the drivers eyes. It was way too far forward and we really couldn't relocate the driver and passenger locations at all. I absolutely agree with you that the rear of the vehicle is most important. Think how much the Cd would have spiked there without that 48" boat-tail there.

That's an interesting graph, BTW. I wonder how it gets made, and how reliable it is? Very cool if it is reliable! It absolutely real and reliable. We used ANYSYS CFD software. There are 70,000,000 data points (yes, 70 million) in that model and it took over 800 hours of parallel-processing CPU time to do that graph.

x

[freebeard]

I think that you are mostly correct freebeard. I am unsure on your second point regarding the tractor contribution. My aerodynamicist has not debriefed me yet on this chart, but that is supposed to happen tomorrow.

The second point:



Now you have some questions for tomorrow.

[Shepherd777]

Originally Posted by freebeard

The second point:



Now you have some questions for tomorrow.

I hear you on your point. But because we have a mechanical gap-sealer between the tractor and trailer at speed, this vehicle is acting as one unit and does not have a lead/draft configuration.

But like you said, I'll know more later today.

[wdb]

Subbed, going for popcorn. Neat stuff!

[cRiPpLe_rOoStEr]

Originally Posted by freebeard

It makes me think about an eventual advantage of using a foldable canvas cover in the gap between the cab and the trailer, something similar to that one used between the modules of an articulated bus.

[Shepherd777]

Good news and Bad news.

The Good news: I now know exactly why we were getting that disturbance at the rear of the vehicle, and I now know exactly how to fix it.

The Bad news: I cannot elaborate on the problem or the fix and had to remove that image. We found something profound and I don't want to let the bad guys (all the large semi truck OEM's) know what we found. Sorry but they are at my web site all of the time. And when I introduce an aero fix, and it appears on their trucks 6 months later as a poor implementation with some dopey fairing.