AirFlow Truck Company StarShip Semi - 0.28 Cd

[freebeard]

Having seen the image (which I did not save), I think I know what it is. Not saying though, in case they follow you here.

Was it posted on your site?

Can you talk in general about interpreting the green curve?

[Shepherd777]

Originally Posted by freebeard

Having seen the image (which I did not save), I think I know what it is. Not saying though, in case they follow you here.

Was it posted on your site? No. We don't have any build pics or other info of the new truck on the web site like we did on the last truck. It's a shame that we can't post them for folks at EcoModder and other interested parties. But building these hyper fuel mileage Class 8 trucks is my business, not a hobby. So I hope everyone here understands.

Can you talk in general about interpreting the green curve? Sure thing. Basically if you recall that graph in your minds eye, the green curve plotted total drag. The way cool aspect of it is that it continuously scans the whole length of the vehicle (23 meters, or 76 feet) front to rear, and gives feedback exactly where the drag is lower or where it increases. And with all of those 70 million data points plotted into the CAD model, that green curve appears to be very, very accurate. Wherever there is a "blip" in that green curve, we were able to figure out exactly what was causing that anomaly from viewing the magnified CAD model. Think of that green curve as a road map, telling you exactly where to work on the vehicle to obtain a lower Cd. Or, where you have designed your vehicle very well, to obtain very low drag.

x

[freebeard]

The way cool aspect of it is that it continuously scans the whole length of the vehicle (23 meters, or 76 feet) front to rear, and gives feedback exactly where the drag is lower or where it increases.

This is the part I don't get. I guess I meant how is the green curve generated. It seems extremely useful compared to a single, raw value for the whole shape. What is the 'it' doing the scanning?

[Shepherd777]

Originally Posted by freebeard

This is the part I don't get. I guess I meant how is the green curve generated. It seems extremely useful compared to a single, raw value for the whole shape. What is the 'it' doing the scanning?

"It" utilizes waves of streaming particles, like particle curtains or particle walls, passing over the body. Here's as much as I can show:


Above, the particle wave curtains are passing over the center of the trailer.
You'll have to use your imagination on how it looks passing over the tractor and boat-tail.

Here are the particles at the vehicle wake:

[freebeard]

Thanks. Got it.

[aerohead]

With the gap-sealer,the rig becomes an aerodynamic singularity,like a bus or motorhome.
The component drag breakdown for the 1977 Omnibus Lastauto,Stuttgart intercity bus (from Hucho),with Cd 0.36:
*nose = 0.041
*surface friction = 0.055
*wheel drag = 0.064
*base drag = 0.20
--------------------------------------------------------------------------
Today's European M.A.N. rig is rate at Cd 0.30.
Renault's longer-boat-tailed V.I.R.A.G.E. of 1987 was Cd 0.29.
Bob,I think you've got 'em on the run!

[Shepherd777]

Originally Posted by aerohead

Bob, I think you've got 'em on the run!

Hey Phil -

Thanks for the kind words.

On the new StarShip, we actually obtained 0.19 Cd or below for the first 71 feet of the 76 foot long rig. And now we know how to fix the area at the rear of the trailer that was causing that spike up to 0.28 Cd. So I'm hopeful that we can get it down just into the teens. A 0.19 Cd is our dream goal for a drag coefficient number, and that is what we are working towards.

[ennored]

This thesis on CFD modeling of trucks was mentioned before here.

It has some of the same style cumulative plots as was above (search for "accumulated" in it).

Same kick up in Cd at the transition to the Trailer Tail style flat rear plates.

[skyking]

Originally Posted by Shepherd777

Hey Phil -

Thanks for the kind words.

On the new StarShip, we actually obtained 0.19 Cd or below for the first 71 feet of the 76 foot long rig. And now we know how to fix the area at the rear of the trailer that was causing that spike up to 0.28 Cd. So I'm hopeful that we can get it down just into the teens. A 0.19 Cd is our dream goal for a drag coefficient number, and that is what we are working towards.

More power to you, don't get me wrong. I just can't see a number like that without violating the cargo rule. I will be watching with great interest.

[aerohead]

Originally Posted by Shepherd777

Hey Phil -

Thanks for the kind words.

On the new StarShip, we actually obtained 0.19 Cd or below for the first 71 feet of the 76 foot long rig. And now we know how to fix the area at the rear of the trailer that was causing that spike up to 0.28 Cd. So I'm hopeful that we can get it down just into the teens. A 0.19 Cd is our dream goal for a drag coefficient number, and that is what we are working towards.

In NASA's paper on big-rig aero they make mention of a publication by the Rocky Mountain Institute in which the lower limit expected for a semi-tractor rig would be Cd 0.13.
I'm not going to pay for RMI's report,so I have no idea where that quanta was sourced from,or if RMI did there own evaluation.
Walter Korff of Lockheed considered Cd 0.20 doable in 1963.Here's his idea