Cargo trailer drag estimating

[slowmover]

( The infamous John Z?)

That's not turbulence, that's some white powdery dust coming from inside that Moho.😏

[ennored]

And the GMC was never tested in full scale. Only a small model was tested. I'd bet the real CD would be a bit higher than .31...

[aerohead]

Originally Posted by ennored

And the GMC was never tested in full scale. Only a small model was tested. I'd bet the real CD would be a bit higher than .31...

Real Cd would require a trip to Palo Alto,California's big NASA Ames tunnel.
If they'd kept the graveyard/cemetery off the roof like in the original advertising photos there might be a shot at 0.31.
Vixen was credited with Cd 0.295 and its basic form isn't terrifically different than GM's motorhome.Probably a model also.
Daimler is still doing models today.Their tunnel can't handle the length of the longer vehicles.

[ennored]

I was thinking the Vixen went to a wind tunnel. Rereading some stuff, looks like it was .26 as a model at U of M's windtunnel, then .29 "was recorded" at the Bendix Proving Grounds in South Bend Indiana. Maybe they did coastdowns? I'm not familiar with what Bendix had in South Bend.

Makes sense the Vixen would be a bit better, it has a gentle taper at the rear, not just a radius like the GMC (or Airstream).

Oh yeah, not sure if John Delorean worked on the GMC but, Bill Collins, the creator of the Vixen, did work for Delorean.

[aerohead]

Originally Posted by ennored

I was thinking the Vixen went to a wind tunnel. Rereading some stuff, looks like it was .26 as a model at U of M's windtunnel, then .29 "was recorded" at the Bendix Proving Grounds in South Bend Indiana. Maybe they did coastdowns? I'm not familiar with what Bendix had in South Bend.

Makes sense the Vixen would be a bit better, it has a gentle taper at the rear, not just a radius like the GMC (or Airstream).

Oh yeah, not sure if John Delorean worked on the GMC but, Bill Collins, the creator of the Vixen, did work for Delorean.

One article on the GMC mentioned six different design teams involved during the gestation.

[Fourbtgait]

As a footnote to this conversation, I ended up building a Benroy style small trailer.
Tow vehicle- 2014 Toyota 4runner, LT tires, front lifted 0.89", 72" tall, 72" wide. 60 mph average trip roads 21 mpg packed with camping gear.
Trailer is single axle 3,000 lb capacity. Box is 72" tall, 60" wide. Wheel wells extend out. Total weight estimated at 1,650 lbs. Trailer box sits 3 1/2-4' behind 4runner.
Milage loaded at 60 mph, same basic roads dropped to only 18 mpg. So not the 30% drop as typical. Yes, closing the box/vehicle distance would help. Yes, the top 3' of the box is in turbulant air. Yes, rounding the corners would help, but be a pain to build. I would post a picture of both hooked up, but dont have any at a hosted site?
Overall not bad, happy with the mileage drop.

[freebeard]

Yes, rounding the corners would help, but be a pain to build.

http://ecomodder.com/forum/showthrea...tml#post481517


The rule of thumb is radius=4% of gross width, so on a 72" width you'd want 6" diameter half-circles.

[ennored]

Speaking of rounded corners:



Another example from the same builder:


More of his stuff

[Fourbtgait]

Ummmm. To me, when I talked of radiousing the corners, I meant that literally. The nose of the trailer box does have a 30" radious. When I say corners, I am meaning the sides/top/front/rear corners or edges. I came up with a way to do that using 1/4" bead/cove cedar but then would need an interior framework to do so. Or mock up a full scale mold. I also explored fully rounding the nose, both directions but realized the loss of space especially when constrained by side door placement.

[Hersbird]

The idea on that Hi-Lo/Towlite was to fake the radius corners. That point was especially bad because the thing is 8' wide and those sharp corners were just hanging out in the wind. So even though it's a fake radius the air should somewhat just stack up in the pocket between then, but the air coming off the side of the tow vehicle doesn't just slam into the corner. Plus it cost about $15 and looks weird which I like as well.
Someday I will build a whole new top with radiused top/side corners, a front arch and closer gap to TV, and a slow boat tail taper. And it will drop a bunch of weight as the factory top is really heavy. Then maybe the minivan will be a candidate to tow it.
I am pretty happy with the results as I get 14 mpg everytime I take it out, but have been having trouble getting the 18mpg I used to get unloaded. Basically it's not even a 20% hit. My standard hardside puts mpg at 9.5 and I never go above 65 often keeping it at 55-60. The Towlite we spend more time at 65.

Do you got any pics Fourbtgait? I love to see the end product.