Class a motorhomes aerodynamics

[freebeard]

Simulpost!

If you're going down the path of PVC pipe then pack it with hot sand to make any bends and allow for spring-back.

[aerohead]

Originally Posted by sregord

So ..I'm headed to HomeDepot for 8 pieces of 1" pvc pipe.
strap them to the 4 corners of Moby with corner tees on the other end, wire then together & pull until I'm at 20*.

You guys are great. to put up with me.

I recommend Schedule-40. Aside from greater strength, it can pull into a fine curve, like an enormous french curve drafting tool!
Establish three accurate points, bend the pipe across them and, voila!
Also, PVC can be bent while heated carefully to create permanent-memory shapes. Yard sprinkler installation guys do this all the time.
Harbor Freight Tools has a fine $16 heat gun.

[sregord]

Originally Posted by aerohead

I believe that it's one of his papers which goes into the shortcomings of NASA's boat-tail, and that of the entire tail structure of the Lockheed C-130 Hercules.

That's the one...VG's are the solution to all that is wrong with the pudgy C-130

Originally Posted by aerohead

I recommend Schedule-40. Aside from greater strength, it can pull into a fine curve, like an enormous french curve drafting tool!
Establish three accurate points, bend the pipe across them and, voila!

Originally Posted by freebeard

If you're going down the path of PVC pipe then pack it with hot sand to make any bends and allow for spring-back.

the white 1" Sch40...yes. It looks like the local HD only sells Sch40...10 & 20' lengths
Great visual aid

[aerohead]

Did you catch the mention of sub-boundary-layer thickness 'nubs' with respect to VGs? It's the only mention I've come across.
I keep a 20-foot length of Schedule-40 in the shop, out of the sunlight and elements.
There are old-time photos of automotive design studios, with draftspeople working on full-scale drawings, with full-scale drafting instruments; which would translate to the full-scale styling bucks under the bridge fiducials.
In the movies,' Tucker, The Man and His Dream', and 'Ford vs Ferrari', you can see both the wooden armatures for the Torpedo, by Alex Tremulis, and Shelby Cobra Daytona Coupe, by Peter Brock.
'Old School'.

[aerohead]

I'll try a link to SAE International technical paper 2013-01-2414, by Hirz & Stadler, Graz University of Technology.
It's semi-trailer technology.
The long and the short of it was:
* they tapered the trailer roof only and tested.
* then they tested this configuration, plus adding plan-taper boat-tailing.
* with the roof-only modification, wake area was reduced by 13.7%, which reduced drag by delta-Cd 15%, increasing Diesel mpg by 6.5%, at a presumed 83-km/h.
* with roof taper and side taper, the wake was reduced by 30.95%, which reduced drag by delta-Cd 23%, for a Diesel mpg improvement of 10.2%.
* without the plan-taper boat-tailing, there's a 34.7% drag penalty.https://www.sae.org/publications/tec...-2414/preview/
* Averaging the two, it works out at about 4.38% mpg increase/ 10% drag reduction ( Diesel engine @ 83-km/h )
* the Graz model is :
-648-inches ( 54-feet ) in length.
- 100-inches ( 8.333-feet ) in width
- 156-inches ( 13.0-feet ) overall height
- approx. 10-inches ground clearance
--------------------------------------------------------------------------------------
1) the 'bent' roof exposes the flow to deceleration
2) the deceleration increases static pressure
3) static pressure behind the rear panel increases ( base pressure )
4) increased base pressure reduces pressure drag
5) reduced pressure drag reduces total drag ( the reason for 'aerodynamics' )
6) adding plan-view tapering amplifies the effect for maximum drag reduction, highest fuel economy, range.
7) gasoline has only 81.76% of the chemical energy of Diesel, so gains for a gasoline-powered rig would have to be adjusted down accordingly, plus a loss in thermal efficiency in ICE gasoline vs ICE Diesel.

[sregord]

Originally Posted by aerohead

I'll try a link to SAE International technical paper 2013-01-2414, by Hirz & Stadler, Graz University of Technology.
It's semi-trailer technology.
The long and the short of it was:
* they tapered the trailer roof only and tested.
* then they tested this configuration, plus adding plan-taper boat-tailing.
* with the roof-only modification, wake area was reduced by 13.7%, which reduced drag by delta-Cd 15%, increasing Diesel mpg by 6.5%, at a presumed 83-km/h.
* with roof taper and side taper, the wake was reduced by 30.95%, which reduced drag by delta-Cd 23%, for a Diesel mpg improvement of 10.2%.
* without the plan-taper boat-tailing, there's a 34.7% drag penalty.

I've added the EAEC2011_B10.pdf to my reading
https://www.researchgate.net/publica...rcial_vehicles
Has many of the same referenced %s... and gives me some visuals.
I think the commercial truck improvements are certainly applicable to Moby.

[sregord]

We had our annual family "camping" trip, this last weekend. First time Moby with a brain(UltraGauge) that communicated. Down from VirginiaCity(6000'asl) to Reno(4478'asl) to Stampede Res(5954'asl) and back. 55-60mph on the Interstates, 35-40mph on the paved 2 lanes.
Averaged 8.36 MPG. Sure was fun watching the InstMPG- 999.9 when coasting downhill. Moby ran great.

https://www.fuelly.com/car/ford/f53/2000
Looks like I'm doing better than most, who're likely pushing along at 70mph.

I really have to keep a lookout at the rearend overhang, behind the "short 208in" wheelbase of the RV. Adding 2+ feet to the rear, that I can't see in the mirrors has me a bit worried.

[aerohead]

Originally Posted by sregord

We had our annual family "camping" trip, this last weekend. First time Moby with a brain(UltraGauge) that communicated. Down from VirginiaCity(6000'asl) to Reno(4478'asl) to Stampede Res(5954'asl) and back. 55-60mph on the Interstates, 35-40mph on the paved 2 lanes.
Averaged 8.76 MPG. Sure was fun watching the InstMPG- 999.9 when coasting downhill. Moby ran great.

https://www.fuelly.com/car/ford/f53/2000
Looks like I'm doing better than most, who're likely pushing along at 70mph.

I really have to keep a lookout at the rearend overhang, behind the "short 208in" wheelbase of the RV. Adding 2+ feet to the rear, that I can't see in the mirrors has me a bit worried.

Nice! My brother's Ford chassis-based motorhome, with the V-10, at 55 mph averaged 6.6-mpg from Carson City, to Ogden, Utah and back.
Yes! Long overhang! You're not obligated to add any length. 'Normal' driving could provide enough anxiety as it is.

[sregord]

Single best stress reliever when driving Moby...
Marked windshield, where the lane lines are, with orange tape.

Its the parking lots, gas stations & sharp turns on narrow road intersection where I have to watch the tail swing.

[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.