Class a motorhomes aerodynamics

[aerohead]

Originally Posted by sregord

Ahmed body


So the "Stemco-TrailerTails" are truncated variations of this then...sort of
..with some limitation(DOT or can't make it longer than 1/2 the width), keeping them 4 foot long.

Yes. They're compromised a bit because their perimeter isn't air-tight, but the folding feature was probably the deal breaker for drivers.
BMW and the Wagonner's( sp?) have run fixed, composite boat tails which probably perform better aerodynamically, but drivers aren't fans. I haven't seen any for many years.
And I believe that five-foot tails are allowed by DOT if inflated.

[sregord]

BMW?
Did you mean Mercedes Benz?

[aerohead]

Originally Posted by sregord

BMW?
Did you mean Mercedes Benz?

In the Los Angeles area of Southern California, BMW used to have their own tractor-trailer transports, which featured fiberglass boat-tails.
The tails were hollow, and served as the rear closure for the trailer van. Cargo could extend into the tail, effectively giving them 'legal' illegal-length rigs. Perhaps a DOT perquisite for stretching USA energy supplies.
The Waggoners Trucking also ran these tails on their company-owned rigs.
If you'll scroll down far enough, you'll see a rig with a NOSECONE and in the rear, the boat-tail lifted for loading.https://www.truckingtruth.com/trucki...oners-trucking

[sregord]

Originally Posted by aerohead

They're compromised a bit because their perimeter isn't air-tight...
And I believe that five-foot tails are allowed by DOT if inflated.

OK Lets step back a couple, please.
The "Stemco-trailertail" which the drivers didn't like...doesn't seem to be on the market anymore. "They're compromised because their perimeter isn't airtight".
You referring to where the the trailerTail attaches to the corner of the trailer? correct?. as the Mercedes Benz trailer"tail" is open, and Betterflow

https://www.youtube.com/watch?v=4uQQtcRVPNg

has another european foldaway that is open ended. Both "compromises" to ease driver PITA issues.

[freebeard]

At 2:11 he totally cuts the other truck off.

The new truck at 3:02 owes a lot to Luigi Colani.

[sregord]

I found it on page 338. Figure 8.64

..and further reading: 8.5.4.5 Add-on devices on the rear end
The only drag reductions achieved(by 5%)were by the addition of non-ventilated cavities. Figure 8.65 Base-flow modification devices

[aerohead]

Originally Posted by sregord

OK Lets step back a couple, please.
The "Stemco-trailertail" which the drivers didn't like...doesn't seem to be on the market anymore. "They're compromised because their perimeter isn't airtight".
You referring to where the the trailerTail attaches to the corner of the trailer? correct?. as the Mercedes Benz trailer"tail" is open, and Betterflow

has another european foldaway that is open ended. Both "compromises" to ease driver PITA issues.

I might have 'tightened' my language! Sorry.
It is the 'attachment' perimeter of the Trailer-Tail which compromised its performance.
As an 'angled' box-cavity, the 'loose' fit to the trailer van allows turbulence to contaminate the pressure rise potential of the elongation.
If you'll examine United States Patent Number 4,682,808, by Bilanin, you'll see that a 'proper' box cavity has an 'airtight' connection to the trailer's rear.
Zero porosity.
It's okay to be 'open' at the rear, but not the top, sides, or bottom. The 'leakage' destroys some of the pressure recovery, the whole idea for elongation.
-------------------------------------------------------------------------------------
The very last iteration of the Betterflow semi is what you want, for what's presented.
They're using the full height of the trailer (minus ground clearance ) for streamlining, and their boat-tailed cavity fits snugly against the trailer van, perfectly protecting the pressure rise.
It's almost as good as Renault's, 1987, V.I.R.A.G.E.S. concept semi-trailer, Cd 0.298 ( with 29.5", 5-degree boat-tail, and fully-enclosed wheels ), SAE Paper 870714, Figure 6.
I do take issue with the central, 'catamaran' ducting. Solar race teams have discovered the catamaran design to have the highest drag. And it precludes the lowering of the height of the cargo floor, which terrifically impacts frontal area, center-of-gravity, and propensity for rollover / blow-over, while running dead-headed.
Having had a Class-A drivers license, I've always struggled with the wisdom of placing cargo four feet above ground level. School buses especially!
--------------------------------------------------------------------------------------
PITA to the driver seems to be a real issue within the industry.
( I'd just fully-professionalize driving, pay them all a salary, and remove the gun-to-the-head, ticking- clock anxiety over load-in/off-load time vs daily mileage ).

[aerohead]

Originally Posted by freebeard

At 2:11 he totally cuts the other truck off.

The new truck at 3:02 owes a lot to Luigi Colani.

Yes, when Colani came to the USA, with his 'cycloptic' semi full of aero toys for Bonneville, he had emblazoned the cab with 'Cd 0.40, or Cd 0.42' graphics, really low for the time. I'll have to dig that out my archival nightmare.

[sregord]

Your patience is very much appreciated.

Originally Posted by sregord

I found it on page 338. Figure 8.64

..and further reading: 8.5.4.5 Add-on devices on the rear end
The only drag reductions achieved(by 5%)were by the addition of non-ventilated cavities. Figure 8.65 Base-flow modification devices

more from 8.5.4.5...The best geometry, with a cavity depth of 0.13d, reduced the drag coefficient by 5 per cent.

0.13 times 11'(tall) = 17.16"
0.13 times 8.5'(wide) = 13.26"

Originally Posted by aerohead

It's okay to be 'open' at the rear, but not the top, sides, or bottom. The 'leakage' destroys some of the pressure recovery, the whole idea for elongation. -------------------------------------------------------------------------------------
The very last iteration of the Betterflow semi is what you want, for what's presented.
They're using the full height of the trailer (minus ground clearance ) for streamlining, and their boat-tailed cavity fits snugly against the trailer van, perfectly protecting the pressure rise.

gluing, shaping, epoxing 2 or 3" thick pink foam to the perimeter of the rear edge, adding 13+" to the overall length of Moby ...like building a foam tail on an Insight... maybe?

[freebeard]

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