Class a motorhomes aerodynamics

[aerohead]

Ah! From your photo I see some nice edge radii up there on top!
Way good!
If that can transition into a gap-filler or tail, that's going to be great benefit as far as vorticity.

[sregord]

I’ve been reviewing “the Template” & Aerohead’s Full-boat-tail trailer with gap-fillers for Toyota T-100 pickup.
https://ecomodder.com/forum/showthre...tml#post255980 This needs a re-read.

Using Template#2
To build the supreme example of boattail trailer for a 102” wide 132” tall MH.…
>11’ tall maximum roof camber (=22’d x 1.78) to a theoretical rearmost tip equals 39.16’. 90% of 39.16’ =35.24’ 60% of 39.16’ = 23.5’….each 10% section is 3.914’
>using WAMair...(=22’dx1.9) to a theoretical rearmost tip equals 41.8’. 60% of 41.8’ = 25.08’

>8.5’ wide max camber (=17’d x 1.78) to a theoretical rearmost tip equals 30.26
60% of 30.26’ - 18.16’….each 10% section is 3.026’
>using WAMair...(=17’dx1.9) to a theoretical rearmost tip equals 32.3’ 60% of 32.3’= 19.38’

So, I’m thinking this trailer from ball hitch to the 60% cutoff of the sausage will be 18.5’ long, with the “tall” being about 6-8” taller than “wide”..where the taillights are attached.
...OR... a 5 foot straight section midway on the side to meet/catchup to the roof at 60% ...at 23.5’.
Is my math correct?

A castering wheelie bar, a tail-dragger....
32+24... this will be 56 feet long, will I need a different drivers license?

It appears that the Full-boat-tail trailer wheels are at a similar track as your T-100….as trailer is near the width of the truck at the axle, likely because you started with a boat hull. Not finding fault, & considering your careful opinion...to achieve the 22* taper from the 102” front end width to the end, could the track be narrower, say 6’, and still be a stable tail to this airship?
I was thinking of painting this Desert Tan... but maybe Silver is more appropriate.

[sregord]

Other option: Freebeard's Permalink #12.
Start with a 6.5' x 12' utility trailer (red), and best blend Bezier curves in 3D.
The roof angle(s) are likely too steep though...and the axle length(of a stock trailer) will cause need for wheel fairings outside of the envelope.
... but the length would be more manageable, and more space usable.

[freebeard]

Here's another one from the midnite modelling era I stayed up all night to complete it..



This is the template rendered as Armidillo banding. The taper in elevaion is relaxed to accommodate a door in the truncation. Sort of a Bolus turned around.

The example in Permalink #12 could be a hinged two-piece part that four-bar down into position and make the roof of the diffuser and a truncation/box cavity.

edit: What the heck, here's another one, a portable toilet/ice fishing hut:

[kach22i]

Originally Posted by aerohead

The 5-Cyl, BMW, Diesel-powered VIXEN, morphing-roof RV is perhaps the gold standard for mpg.
It's around here somewhere. If I could find it, I wouldn't be able to link it. Sorry.

I took these Vixen RV pictures back in May at a local Cars and Coffee.

[sregord]

kach22i,
A beautiful example... of a rare vehicle.
In today's fuel and supply chain troubles, the Vixen would be a better, less wasteful camping show piece.
I wonder how the Vixen's MPG compares to the popular Class Bs offered today?
https://www.fuelly.com/car/mercedes-...nter_2500/2021
Where do they hide the toilette and shower in there? On board restroom was #1 for buying a MH in the first place for my wife. #2 was to not have to pull the interior apart to create a sleeping space.

Again, A beautiful example... of a rare vehicle.

[aerohead]

Originally Posted by sregord

I’ve been reviewing “the Template” & Aerohead’s Full-boat-tail trailer with gap-fillers for Toyota T-100 pickup.
https://ecomodder.com/forum/showthre...tml#post255980 This needs a re-read.

Using Template#2
To build the supreme example of boattail trailer for a 102” wide 132” tall MH.…
>11’ tall maximum roof camber (=22’d x 1.78) to a theoretical rearmost tip equals 39.16’. 90% of 39.16’ =35.24’ 60% of 39.16’ = 23.5’….each 10% section is 3.914’
>using WAMair...(=22’dx1.9) to a theoretical rearmost tip equals 41.8’. 60% of 41.8’ = 25.08’

>8.5’ wide max camber (=17’d x 1.78) to a theoretical rearmost tip equals 30.26
60% of 30.26’ - 18.16’….each 10% section is 3.026’
>using WAMair...(=17’dx1.9) to a theoretical rearmost tip equals 32.3’ 60% of 32.3’= 19.38’

So, I’m thinking this trailer from ball hitch to the 60% cutoff of the sausage will be 18.5’ long, with the “tall” being about 6-8” taller than “wide”..where the taillights are attached.
...OR... a 5 foot straight section midway on the side to meet/catchup to the roof at 60% ...at 23.5’.
Is my math correct?

A castering wheelie bar, a tail-dragger....
32+24... this will be 56 feet long, will I need a different drivers license?

It appears that the Full-boat-tail trailer wheels are at a similar track as your T-100….as trailer is near the width of the truck at the axle, likely because you started with a boat hull. Not finding fault, & considering your careful opinion...to achieve the 22* taper from the 102” front end width to the end, could the track be narrower, say 6’, and still be a stable tail to this airship?
I was thinking of painting this Desert Tan... but maybe Silver is more appropriate.

All the 'templates' are really for a 'fastback' coupe or sedan-type automobile. They're the most sensitive to 'tumblehome' requirements ( a 16% drag increase without it ).
The plan-view camber/ boat-tailing satisfies another three-dimensional flow requirement for low drag ( another 16% drag increase without it.
The 'long', fixed,2.8-degree diffuser of all three is a conservative compromise. The SAE 'departure' angle of 10-degrees is 'just' accomplished.
The 'elongation' restores the 'missing' length of the streamline half-body, allows the flow to decelerate without separating, reduces the wake to an absolute minimum, while producing the pressure recovery which makes for the drag reduction.
And the full wheel fairing package, conceptually, addresses the 70% wheel drag reduction Goro Tamai, of MIT, and MIT's Solar Race team witnessed and reported on in his book, 'The Leading Edge.'
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Moby is a different animal. It's more of a 'bus.' A rectangular cylinder with softened upper edges.
Years ago, I published a thought experiment for a Greyhound Bus, chopped 4-feet ( to get it's center of gravity down for roll-over protection ), pulling a gap-filled, full-boat-tailed trailer ( to carry all the luggage and cargo that would have originally been stored under the high floor ).
The idea was:
Stop rollover fatalities and spinel cord injuries, while maximizing mpg and range.
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We know from Hucho's book that a Cd 0.50 M-B bus drops to Cd 0.425 when pulling an identical bus, which itself drops to Cd 0.167 when riding the wake of the lead bus.( Figure 8.71, page-336, 2nd-Edition, Han Gotz, Daimler-Benz, 1987 )
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A trailer axle WOULD be narrowed, respecting the plan-taper.
Or, there's the option of a boat-tail.
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NASA's tail was okay in its truncated form, as far as wool tufts indicated.
When they added the 'stinger', it exceeded a slope which would maintain attached flow ( there's a research about the Lockheed C-130 Hercules tail drag in which NASA's tail is discussed ).
The stinger was stuffing the wake, but flow could not reattach, so there was no additional pressure recovery, a requirement for drag reduction.
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Just to further muddy the waters, there's a General Motors 'Optimum' boat tail that Texas Tech wind tunnel tested in 1995 with the 'TAILWIND PROJECT', at the Aero Lab.
It's a combination of the Ahmed body with 20-degree straight downslope, Bearman's 10-degree side angles, a 10-degree diffuser, and the Bruce Ruefer ( sp?)/ Scott Funderburk, 7%- body height, softened longitudinal edge radii, plus, all-softened 7% radii trailing edges. This would be the most easily fabricated. Length is 93.3% overall body height if memory serves me.
Which would work out at 123.15" for Moby. Kinda long! I'll verify that.
If you could figure out how to collapse it, it would be an option to the trailer.
I don't have my commercial vehicle work books with me.
Walter Korff, chief aerodynamicist for Lockheed Aircraft Co. designed a boat-tailed tractor trailer.
And Hucho's got Fachsenfeld's 'extensible' bus boat-tail, from the 1930s.
I'll try and have that for Thursday when I get back.
These tombstone technologies are some of the most visionary I've seen.

[sregord]

Originally Posted by aerohead

Just to further muddy the waters, there's a General Motors 'Optimum' boat tail that Texas Tech wind tunnel tested in 1995 with the 'TAILWIND PROJECT', at the Aero Lab.
It's a combination of the Ahmed body with 20-degree straight downslope, Bearman's 10-degree side angles, a 10-degree diffuser, and the Bruce Ruefer ( sp?)/ Scott Funderburk, 7%- body height, softened longitudinal edge radii, plus, all-softened 7% radii trailing edges. This would be the most easily fabricated. Length is 93.3% overall body height if memory serves me.
Which would work out at 123.15" for Moby. Kinda long! I'll verify that.
If you could figure out how to collapse it, it would be an option to the trailer.

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.

[aerohead]

Originally Posted by sregord

Other option: Freebeard's Permalink #12.
Start with a 6.5" x 12' utility trailer (red), and best blend Bezier curves in 3D.
The roof angle(s) are likely too steep though...and the axle length(of a stock trailer) will cause need for wheel fairings outside of the envelope.
... but the length would be more manageable, and more space usable.

The 'exposed' wheels are a 16% drag increase according to Elliott G. Reid at Stanford University.
The air would never follow that roofline I'm afraid. I'd have to do a comparison to establish where the boundary layer would separate.
The 22-degree 'limit' has been used by the Douglas Aircraft Corp., French navy, Swedish navy, US Navy, Dusky Dolphin, Atlantic Spotted Dolphin, Porbeagle Shark, Clark-Y airfoil just before burble-point, PGA and WPGA golf balls.
Kamm never went beyond 21.5-degrees.R.G.S. White used 20.5-degrees. The USEPA recommended 22-degrees.Volkswagen's lowest drag 'Flow-Body' was 21.5-degrees. NASA, 20-degrees, Daihatsu UFE-III, 13.5-degrees, Volkswagen XL1, 17-degrees, Mercedes-Benz IAA, 21-degrees, CYBERTRUCK, approx. 21.5-degrees, Mercedes-Benz EQXX, 13-degrees in plan-view, Buchheim, Piatek, and Walzer' curved-roof sedan, 21.5-degrees, GM Aero 2002, 21-degrees, LOREMO, 19-degrees, LIGHTYEAR ONE, 21-degrees.

[aerohead]

Originally Posted by sregord

kach22i,
A beautiful example... of a rare vehicle.
In today's fuel and supply chain troubles, the Vixen would be a better, less wasteful camping show piece.
I wonder how the Vixen's MPG compares to the popular Class Bs offered today?
https://www.fuelly.com/car/mercedes-...nter_2500/2021
Where do they hide the toilette and shower in there? On board restroom was #1 for buying a MH in the first place for my wife. #2 was to not have to pull the interior apart to create a sleeping space.

Again, A beautiful example... of a rare vehicle.

I'll have to verify, but I remember perhaps 28-mpg @ 55-mph, with the BMW 5-cyl Diesel.