Class a motorhomes aerodynamics - Page 4 - Fuel Economy, Hypermiling, EcoModding News and Forum

sregord · 05-23-2022, 01:28 PM

Thank you Aerohead & Freebeard & MetroMPG for your interest in this project...of mine.
Our last couple treks have been from Virginia City, NV(6000'ASL) via CarsonCity(5360'ASL) over the Sierra Nevada(7780'ASL) to near Yosemite(4000'ASL) to spend camping trip with Grandkids, and back. <5% @55MPH, 45MPH on the uphill grades = 7.9998 mpg. I've been hypermilling as much as is practical, but its a little scary "letting her go" downhill on a 2 lane highway.

I re-read the Aerodynamic Seminar(s) ...#5:
"It was Klemperer of the Zeppelin Werks who discovered the low drag 6 to 1 length to width ratio which gave the airships a drag coefficient of Cd0.04 in 1932."

.... with a 32 foot MH... 8 foot wide(...11' tall)... that means I could?have a potential 16' long boat-tail(48' overall). Yikes, I was thinking more 2-3 foot "fleetaero.com/rocketail/" .

aerohead · 05-23-2022, 01:46 PM

Quote:

Originally Posted by sregord

Thank you Aerohead & Freebeard & MetroMPG for your interest in this project...of mine.
Our last couple treks have been from Virginia City, NV(6000'ASL) via CarsonCity(5360'ASL) over the Sierra Nevada(7780'ASL) to near Yosemite(4000'ASL) to spend camping trip with Grandkids, and back. <5% @55MPH, 45MPH on the uphill grades = 7.9998 mpg. I've been hypermilling as much as is practical, but its a little scary "letting her go" downhill on a 2 lane highway.

I re-read the Aerodynamic Seminar(s) ...#5:
"It was Klemperer of the Zeppelin Werks who discovered the low drag 6 to 1 length to width ratio which gave the airships a drag coefficient of Cd0.04 in 1932."

.... with a 32 foot MH... 8 foot wide(...11' tall)... that means I could?have a potential 16' long boat-tail(48' overall). Yikes, I was thinking more 2-3 foot "fleetaero.com/rocketail/" .

I believe that boat-tail length is capped @ 48-inches, unless its inflatable, then you've got 60-inches to work with.
Since the MH has the more narrow 'width' dimension, all geometry for the tail could be based upon the 96-inches.
The W.A. Mair contour is a known quantity.
NASA used a tail very similar to it for their van / 18-wheeler experiments.
GM had an 'Optimum' boat tail in the 1980s, which, while it had no compound surfaces, it did have generous edge radii, which helped kill vorticity before it ever got a chance to form.
I'd give you a link to an image, but I can't.
Texas Tech University's Dean of the Mechanical Engineering Dept. office could probably provide a reprint of ' Project Tailwind, which Professor Carver participated in. It could be of value.

freebeard · 05-23-2022, 02:01 PM

The Zeppelin aeroform is not as pertinent as the work Mair did on torpedoes.

You have fineness ratio going for you.

sregord · 05-23-2022, 03:07 PM

A series of 3- 12+" sections ..ala "Mercedes IAA concept:"or tri-fold closet doors- seems a bit complicated...problematic
...which brings me back to Freebeard's original idea (Post#12).
The MH has no need for access to a "loading dock"..unless a toy-hauler. So design with rigid flat bottom(Naca vent to inflate?), would close(w/cable & pulley) to conceal the "fabric" upper, only need to consider taillights.

aerohead · 05-23-2022, 03:33 PM

Quote:

Originally Posted by sregord

A series of 3- 12+" sections ..ala "Mercedes IAA concept:"or tri-fold closet doors- seems a bit complicated...problematic
...which brings me back to Freebeard's original idea (Post#12).
The MH has no need for access to a "loading dock"..unless a toy-hauler. So design with rigid flat bottom(Naca vent to inflate?), would close(w/cable & pulley) to conceal the "fabric" upper, only need to consider taillights.

1) It will help stabilize the entire envelope.
2) A light-kit could be integrated into it. Traffic near you need to see your functions from all vantage points.
3) And likely, the rear license plate.
4) A passive-inflation tail has been patented and tested. Mine was forced-air, using a 12-VDC Bosch heater blower off of a VW Westfalia Camp Mobile. Many of today's inflated, outdoor advertising displays use a small, high-static-pressure air handlers to keep the envelope taught.
5) I designed a two-way, reversing 'valve' which allowed the inflation fan to also evacuate the envelope. It's a simple guillotine, slide-port mechanism.