Aeromodifications for large motorhome

[aerohead]

Originally Posted by skyl4rk

Wind tunnel tests are used to determine the wing profile shape that produces the most lift with the least drag, so at least some of wing design is useful as a model for an aerodynamic vehicle. A vertical wing shape as a trailing edge to the RV would be ideal, however it would be far too long.

Have you considered an aerodynamic trailer?

Abbott and Von Doenhoff issue a strong warning against anyone attempting to interpret wing performance data outside the context of 'flight conditions' for which they are designed.
Aspect ratios and ground effect render the data meaningless.Sorry.

[Frank Lee]

There ARE non-roof a/c units.

[orbywan]

All I was getting at when I brought up the 'wing' analogy was that when you make the turn from the vehicle side to the surface of the boat tail, it seems to me that it should be curved at that point, similar to the shape of a wing, to keep the air from separating at the turning point.

If the curve involved creates a little lift, which I doubt, I'm betting it's still more efficient than having a tight angled turn in that much surface area.

[winkosmosis]

Originally Posted by orbywan

All I was getting at when I brought up the 'wing' analogy was that when you make the turn from the vehicle side to the surface of the boat tail, it seems to me that it should be curved at that point, similar to the shape of a wing, to keep the air from separating at the turning point.

If the curve involved creates a little lift, which I doubt, I'm betting it's still more efficient than having a tight angled turn in that much surface area.

Yeah, that's the reason aerodynamic vehicles have curved transitions rather than sharp ones.

[crmears]

Originally Posted by orbywan

Randy I have to agree with slowmover, I think removing the A/C units is not in your best overall interest. Personally I think the humidity issue might be an issue if you lived in a humid region, but more importantly how about the comfort of the people in the RV?

Is gaining a couple of tenths mpg worth not having some A/C when you finally find the time to go visit somewhere interesting and relax? Unless you plan on relocating them in the basement compartments like some of the Prevost converters do, I'd say that's a bad idea compared to building some fairings to cut the drag as much as possible.

On the other hand, as they say in Oklahoma, it ain't none of my business so never mind.

Regarding the removal of the roof ac units: Alfa motorhomes are 12 foot 4 high without the AC units. The AC units are 14 inches tall. So my rig is 13 feet 6 inches with the AC units. The AC units are aftermarket units installed because the coach was used as a classroom in south Texas. Besides.....the Alfa has a basement AC unit. You can see the condensor area behind the rear wheels on the passenger side. I had no idea that so many people would be concerned about my comfort. (I was smiling as I typed that.)

Jim, the man with the Newmar who got almost 11 mpg, has a rig that is about 12 inches lower than mine and his engine si 60 hp less. I think that I am about 3000 or more lbs also. In addition my 2007 model engine has some polluition add ons that are known to hurt the fuel economy.

Randy

[skyking]

You sly dog, you were holding out on us! Hidden AC unit, argh...............
I can't yank mine it is all I have so I am fairing it over.

[orbywan]

Yeah, I pictured you going down the road with the windows open, the wife throwing cold water on everyone to prevent heat stroke, while staring darts at you for taking off the AC units.

[hondaguy72]

You said the trailer would be too costly. As a bodyman something like this Enclosed 5X8 Trailer could be easily modified and integrated into the rear modifications botsapper posted (totally awesome) to complete the aero advantage of a full boat tail. Loving this thread.

[crmears]

Originally Posted by hondaguy72

You said the trailer would be too costly. As a bodyman something like this Enclosed 5X8 Trailer could be easily modified and integrated into the rear modifications botsapper posted (totally awesome) to complete the aero advantage of a full boat tail. Loving this thread.

A trailer has some possibilities but here are the negatives for me. Extra weight, extra rolling resistance, another set of axles to maintain, extra license for the trailer, could never tow a vehicle which is often very important. It is also almost impossible to back up a 40 ft. motorhome with a trailer attached.

On the plus side I can imagine hauling things in the trailer.

Most of my miles will be with a 3500 lb. tow vehicle attached so the boat tail will need to be above the height of a compast car. There might be some way to incorporate the tow vehicle into the tail but for now I am expecting that it will ride under the boat tail.

[aerohead]

Originally Posted by orbywan

All I was getting at when I brought up the 'wing' analogy was that when you make the turn from the vehicle side to the surface of the boat tail, it seems to me that it should be curved at that point, similar to the shape of a wing, to keep the air from separating at the turning point.

If the curve involved creates a little lift, which I doubt, I'm betting it's still more efficient than having a tight angled turn in that much surface area.

If the vehicle has completely flat sides,you'd apply the same curvature from the
'Template' as you're using on the roof,as the sides permit.
If the vehicle is taller than it is wide,just use the 'Template' for the width,then copy that curvature for the top.
The 2011 Prius boat-tail trailer illustrates the first condition.
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By using the same curvature,top and bottom,it's a way to help prevent longitudinal vortices which have enormous drag.And it avoids the tight turn you mention which would trigger separation right there.