Class a motorhomes aerodynamics

[Piotrsko]

The dorsal gun was removed after the B model because it was buffeting the horizontal stab and causing control issues. I suspect while it looks aero, it probably isn't
However:https://weaponsandwarfare.com/2018/1...1-black-widow/

[sregord]

Originally Posted by Piotrsko

while it looks aero, it probably isn't

Interesting info... great website

[aerohead]

https://ecomodder.com/forum/showthre...d-e-18151.html

Originally Posted by sregord

I once saw..I think.. but now cannot find. an aerodynamic posting showing a gun turret on a BlackWidow...as a great example shape for a AC fairing/shroud. Anyone else come across it?
Aerohead: your interest in the P61... I thought maybe you could point me at it.

Seems like I posted an image of the gun turret at Orbywan's RV Motorhome thread.
It would have been from my PhotoBucket archive, which I've lost for many years now ( high-jacked for ransom by venture capitalists [ Greed is Good!] ).
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Found the reference:
Orbywan's ' Aero RV ( custom boat tail for '95 Ford E-350 Class C (motorhome)
page-17, # 163 ( permalink )
I usually have trouble linking from EcoModder sites

[freebeard]

Permalink:
ecomodder.com/forum/showthread.php/aero-rv-custom-boat-tail-95-ford-e-18151-5.html#post513839

Post number and page number are only loosely related. It's page 5 for me.

What I struggle with is getting Google Search to find anything. There was a thread on Blisters and Canopies, but Google is impotent.

[sregord]

Originally Posted by freebeard

Google is impotent.

Yes much of silicon valley is going through a confusing time.

[aerohead]

If the link performs, this will give a look into how commercial airliners are streamlining their fuselage mount Wi-Fi uplink antennas.
An okay design to model anything on the roof of an RV.
https://www.astronics.com/product?pr...ennas#F-Series

[sregord]

All good stuff.
I'm wandering a bit in the : Aeromodifications for large motorhome ...stream.
Very nice photoshop rendering by Botsapper...
...and your Reverse-Engineering Randy's motorhome..mod to CD ...
I'm still self "imaging" the boattail concept. Giving up the rear-mounted ladder will simplify whatever collapsible/fold-able option I go with.

I've already removed one of 2 roof ACs...there is so much unused space (for us) below the floor.

[aerohead]

Originally Posted by sregord

All good stuff.
I'm wandering a bit in the : Aeromodifications for large motorhome ...stream.
Very nice photoshop rendering by Botsapper...
...and your Reverse-Engineering Randy's motorhome..mod to CD ...
I'm still self "imaging" the boattail concept. Giving up the rear-mounted ladder will simplify whatever collapsible/fold-able option I go with.

I've already removed one of 2 roof ACs...there is so much unused space (for us) below the floor.

Just for drill, I did a thought experiment for a Motor Coach Industries ( MCI ) J400 Motor Coach, Cd 0.363, Af approx. 97.678 sq-ft, wake area 94.131-sq-ft, 8-mpg @ 65-mph, Diesel, BSFC 0.314806 lb/hp-hr, thermal efficiency= 39.256%, 2% accessory losses, 88.666% powertrain efficiency, CfR-R= 0.008725 @ 65-mph, 7.1089-lb/gallon, 136,775-Btu/gallon, 2546-Btu/hp; modified to get 9-mpg under the same test conditions.
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* The fuel economy allowed calculating the gross-hp.
* Thermal efficiency gave brake-horsepower.
* Accessory & powertrain losses gave Road Load Horsepower *.
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* I calculated the aero-hp and subtracted that from the Road Load, yielding the rolling resistance horsepower, to be used in further calculation.
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* To get to 9-mpg would require reducing the brake-horsepower by 19.04-bhp, 16.45 less aero hp, 24.778% less wake, 23.3% less base area, near the '1st-22-degree angle location on Mair's contour.
The only avenue open is to reduce the aerodynamic HP by 24.778%, which requires Cd 0.27305.
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* If we accept that we can reduce the drag a certain %, simply by reducing the wake size by the same %, then we'd need a wake = 70.7318- sq-ft.
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* I chose to use the 'width' of the motorhome for streamlining.
* And I chose to use W.A.Mair's boat-tail profile of 1969.
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After a bit of noodling, it turned out that I would 'hit' 70.7176-sq-ft with a tail 63-inches in length. It 'burns' 7.687-inches off the top, two sides, and bottom OEM dimensions, yielding a new:
Height = 117.375-inches, and Width= 86.635-inches.
I used a photo-enlargement of Mair's boat tail, and just 'scaled' all the dimensions off of it.
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Ignoring the wheels, and working only with the motor home's main body cross-section, according to the 'experts', this is essentially all the research we need to accomplish.
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Identical 'ribs' 63-inches by 7.687-inches,with the Mair contour along the curved 'outer', spaced all around the original aft perimeter would define where the 'skin' would be attached. Lights and license plate would be moved onto the 'new' rear. And it could be side-hinged, allowing one to 'swing-away' the tail for whatever reasons.
If constructed like a commercial awning, with aluminum skeleton, and stretched-fabric 'skin', it's weight would be 'meaningless, as far as adding any rolling resistance.'

[freebeard]

Like this?

[Piotrsko]

Hmmm aero with a scabbed on out in the flow awning messing up flow down the right side.