Aeromodifications for large motorhome

[crmears]

Jim,

Thanks for the comments on fuel economy. Those are pretty much the standard tips. You are getting about 2 mpg above what is typical for that coach so it is working for you. I am convinced that the biggest improvements to mpg for our big motorhomes is to make them more aerodynamic and drive 55 while using the techniques that you mentioned. I am removing the AC units and other junk from the roof of my Alfa. Also putting on fender skirts and a boat tail. Some awnings will be removed and other will have fairings. You probably saw a picture of my Alfa earlier in this thread. My boat tail will no be like the one photoshoped on my photo. My hope is to get a consistent 11 mpg from my Cummins ISC360.

Randy

[skyl4rk]

Originally Posted by crmears

I do not think that we should attempt to copy the shape of a wing. Wings are designed to use airflow to create lift. The action of creating lift with a wing induces drag.
Randy

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?

[jime57]

Originally Posted by crmears

I am removing the AC units and other junk from the roof of my Alfa.

Randy, I had not realized that you had an Alfa. The high ceiling and corresponding increase in frontal area will make your job a little tougher. My 2000 Newmar only has a 6'6" ceiling so lower frontal area. As a tall guy, I've often admired those Alfas

Traditionally, motorhome designers have not given much attention to aerodynamics. If you look at the amount of frontal area created by the tall storage compartments you can see how they could have improved frontal area quite a bit. Also, the airconditions could have been integrated more smoothly into the overall design.

[crmears]

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?

I agree that some information from wing design is useful in considering when building a boat tail. But as you said "wings are designed to produce the most lift with the least drag." We do not want to produce lift. We just want to reduce drag. I maintain that we should copy the fuselage. Fuselages are simple and considering wings only make this process unnecessarily complicated.

Randy

[crmears]

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?

Forgot to add. I am not attempting to atain the ideal boattail. I think that I can obtain 90% of ideal for 10% of the effort and time. Trailer would be too complicated and expensive for me. Did you look at the link to the kitplane fuselages that were flat. Several other aircraft have flat fuselages.

[winkosmosis]

Originally Posted by crmears

That which you label as "incorrect theory" is taught in FAA approved flight schools as fact. No point for me in debating this so I will leave it at that.

Just because the FAA teaches something doesn't make it true. Go to my thread about this topic and you can discuss it there:
http://ecomodder.com/forum/showthrea...lli-17552.html

[slowmover]

How many miles are you contemplating over how many years for this coach?

I'd re-shroud the A/C units. Not having them is a mistake, IMO. Just the removal of humidity is important in an RV which are -- as a class -- constantly and adversely affected by this. The emphasis on the roof is being overdone, IMO. Other areas are "hotter".

I sure like the photoshop efforts above!!

[KamperBob]

Originally Posted by slowmover

I'd re-shroud the A/C units. Not having them is a mistake, IMO. Just the removal of humidity is important in an RV which are -- as a class -- constantly and adversely affected by this. The emphasis on the roof is being overdone, IMO. Other areas are "hotter".

I have to agree. The roof is say 9' above ground (plane of symmetry). The sides are say 3.5' from the center (plane of symmetry) of the RV. The sides present more surface area to free air. I'd expect more gains from side work. That said, the UK teardrop trucker guys seem more interested in curving the one high roof than the two tall sides. To quote Darrell Cartrip "maybe [they] know something we don't." (wink)

[jime57]

Just completed 1,314 miles on 120.023 gallons. That works out to be 10.95 mpg, so 11 mpg can be done by just using the techniques I outlined earlier. It was mostly Interstate, and that makes a difference of course.

I have 30,000 lb. Newmar with a small car/dolly in tow.

I'd think that some good aero work would get us to 12 mpg.

I'm seeing the long haul truckers using side plates on their trailers between the truck rear wheels and the trailer wheels. Apparently they are finding that closing off that huge open area improves the aero of the combination. Of course, that is pretty much taken care of on most motorhomes by the inclusion of compartment doors in that area. A short boattail still looks like most productive first step.

[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.