Aero RV (custom boat tail for '95 Ford E-350 Class C motorhome)

[orbywan]

Originally Posted by ennored

"There is 18 inches of taper occurring on the first 24 inches of the 4'6" of each rib."

You mean the skin on any side is 18" from the front in only 24" along the skin? Or 18" total narrowing on both sides? And it's basically straight after that? And the ribs started 4 1/2' long? Of the finished tail is 4 1/2'?

What is the total taper? It starts at 96" wide (or close to that) and narrows to what? Maybe 48" (half) judging from the pictures?

Just trying to get in my head what it looks like vs. the Dryden (and other) tails for my graph in the other thread.

Thanks!

The body is 94 inches wide with 18 inches of taper on both sides making the rearmost portion of the boat tail 58 inches wide. The first 24 inches of each rib is tapered, leaving the remaining length straight. The ribs are 4' 4" long before hammering in the taper, once they are installed they add a total of 4' to the overall length of the body. Capisce?

It looks very similar to the Dryden model except for the increased taper in the front and the fact that my corners are compound curves, vs the Dryden model's being 90 degree bends on the corners. I calculated the amount of overall taper and the overall length by measuring the Dryden model and following the proportions as closely as I could.

[ennored]

Gotcha. Terminology was getting me. Rounded for the first 24", total inward dimension 18". It does sound a lot like the Dryden tail.

That's really what's getting me. Yours and the Dryden tail work very well but are quite a bit more aggressive than the template. Just not TOO aggressive apparently.

(And your RV is doubling my latest 9000 mile average. Diesel/gas is in there, but still, DOUBLE for about the same frontal area.)

[ennored]

So, a little more work in Excel...

I assumed you have a 22° angle on the straight part of your tail. Curved for the first half.

Looks like this:

(Scaled to the Dryden van width)

I'd say you nailed it. So the AeroRV, a Trailer Tail, and the Dryden van all have VERY similar shapes.

[orbywan]

Originally Posted by ennored

Gotcha. Terminology was getting me. Rounded for the first 24", total inward dimension 18". It does sound a lot like the Dryden tail.

That's really what's getting me. Yours and the Dryden tail work very well but are quite a bit more aggressive than the template. Just not TOO aggressive apparently.

(And your RV is doubling my latest 9000 mile average. Diesel/gas is in there, but still, DOUBLE for about the same frontal area.)

What kind of vehicle are we talking about? Maybe you've got other issues, like plugged air cleaner, over rich injectors, etc. Or, you're not coming out of open loop. Is it gas or diesel?

[orbywan]

Originally Posted by ennored

So, a little more work in Excel...

I assumed you have a 22° angle on the straight part of your tail. Curved for the first half.

Looks like this:

(Scaled to the Dryden van width)

I'd say you nailed it. So the AeroRV, a Trailer Tail, and the Dryden van all have VERY similar shapes.

Wow, nice graph. When you illustrate it like that it is very interesting how far the Dryden tail and the Aero RV tail are away from the template. I'm not sure, what is the trailer tail? Is that a visual representation of one of those fold-able boat tails you see on semi-truck trailers? The x and y axis are both inches, correct?

[ennored]

Trailer Tail is the foldable tail for trailers, yes. It's not really scaled to the Dryden van here, but it's just flat panel at 15°. They supposedly optimized the angle, and the length was the max the DOT allows. And it is in inches, using the Dryden van's 80" width as a normalizer.

[ennored]

Originally Posted by orbywan

What kind of vehicle are we talking about? Maybe you've got other issues, like plugged air cleaner, over rich injectors, etc. Or, you're not coming out of open loop. Is it gas or diesel?

It's in tip top shape. It's a 31' gas (V10 Ford) Class A, that's all. The roof is 11' feet high and it's 8 1/2' wide, so it does have a bit more frontal area, but as I said, you are doubling my mileage. And 8 is actually doing quite well, I have to keep the speed to about 60, less with a headwind to do that.

Here we are a couple summers ago in Colorado:

[orbywan]

Originally Posted by ennored

It's in tip top shape. It's a 31' gas (V10 Ford) Class A, that's all. The roof is 11' feet high and it's 8 1/2' wide, so it does have a bit more frontal area, but as I said, you are doubling my mileage. And 8 is actually doing quite well, I have to keep the speed to about 60, less with a headwind to do that.

I drove an almost identical vehicle that belonged to one of my sales reps to Albuquerque and back and averaged a little over 8 as I recall. He was 4 feet longer but he also had a Bank's power pack on it. You're considerably heavier taller and wider than the Aero RV, and you're gas powered, so I'd say that's about right mileage-wise. It would be interesting to see what a boat tail would do for it.

[ennored]

Originally Posted by orbywan

It would be interesting to see what a boat tail would do for it.

Exactly...

My motorhome has a fiberglass rear cap that is already about 14" long. I could take it off, fab up a temporary tail, test it, then make a nice tail by modifying my fiberglass cap. I am limited to adding 24 to 36" though, anything bigger won't fit in my garage. Hence the interest is less than optimum (template) tails.

[orbywan]

Originally Posted by ennored

Exactly...

My motorhome has a fiberglass rear cap that is already about 14" long. I could take it off, fab up a temporary tail, test it, then make a nice tail by modifying my fiberglass cap. I am limited to adding 24 to 36" though, anything bigger won't fit in my garage. Hence the interest is less than optimum (template) tails.

I think aerohead and the other experts here will tell you that 36 inches is enough to make a difference, probably even 24 inches. The only way to find out how much of a difference is to build it and see.

Do you tow anything with the RV? I tow with mine a lot so I extended my hitch over three feet, which was a project all by itself. However if your boat tail length is 24 to 36 inches there's several things you can do short of the major construction job I had to do on my hitch. If I remember correctly they had hitch extension kits at the trailer place that would extend the hitch up to 24 inches, and I've seen 36 inch extensions advertised.

If all you do is tow a tow vehicle (with all four tires on the ground) those extension kits should be adequate because all you're doing is leading the car around by the nose, you're not supporting the weight of the front end or the front half of a boat or cargo trailer.

You can also design your boat tail to accommodate a tow vehicle without extending your hitch by making removable panels in the lower half of the tail which you remove when you tow, and/or have movable panels that articulate when you turn (see aerohead's viking thread) etc.

That's putting the cart before the horse to a degree but keep it in the back of your mind when you start designing the tail. And if you do take the plunge and give it a try, my hat's off to you, most people just talk about it. Building mine was a ton of fun and I can't wait to do the rest of the mods. Good luck.