Frontal Sq'

rbpru wrote:
If there were a shape or gizmo that made enough of a mileage difference without effecting the utility of a TT, it would be standard on every semi on the road.

There are a few items that help but nothing that amounts to a major break through; except perhaps for an electric or hybrid powered pick up.

Some semis have air foil extensions at the rear, on the top and sides that angle in to help it break out of the air stream. And I've mentioned before that many have the long under side panels directing the air flow out in front of the tires to control turbulence.

MFL wrote:

rbpru wrote:
If there were a shape or gizmo that made enough of a mileage difference without effecting the utility of a TT, it would be standard on every semi on the road.

There are a few items that help but nothing that amounts to a major break through; except perhaps for an electric or hybrid powered pick up.

I agree, and yes air flow matters, especially in a controlled environment, such as wind tunnel tests, or still air. In the real world, we are towing our boxes in varying wind speeds, and direction. There is not much help for angled or side wind, which is worse than towing into a straight-on headwind.

Jerry

The point of aero design for a TT is just that: crosswind handling. No squared edge box has it. Wind force piles up — trapped — and increases the length of the TT. High ground clearance and open undercarriage makes it worse.

Enclosed undercarriage, low ground clearance and radiused edge (curved) sidewalls allow the wind to pass. Exerts a pull versus a push as it goes over. Much easier to deal with.

I can continue down the road still with one finger on the wheel when the boxes are having to pull over. That’s not any exaggeration.

Besides an indefinite lifespan it’s the reason to have one. Less HP in every situation, and always better handling when it matters most: crosswinds.

.

mountainkowboy wrote:

Old-Biscuit wrote:

mountainkowboy wrote:

Old-Biscuit wrote:
Use the 'flat figure'.....width x height

Curves will just make it less.

Besides..frontal area is least of concerns.
Trailer GVWR, tongue weight are more important factors when it comes to 'can it be towed'

So would that be "I don't know? I didn't ask if I can tow it, I was looking for a formula.

Actually I do know......

Here's the formula for a curved surface. Have fun!
Curved surface formula------- 2 pi r^2 + 2 pi r h.

And after you get it worked out you will realize it doesn't matter all that much.....just use the simple 'flat' formula ----W X H

That is true I got the formula PM's to me and it isn't a significant amount of change. As others have stated the curve is mainly for less drag while towing.

So what is the issue :H

rbpru wrote:
If there were a shape or gizmo that made enough of a mileage difference without effecting the utility of a TT, it would be standard on every semi on the road.

There are a few items that help but nothing that amounts to a major break through; except perhaps for an electric or hybrid powered pick up.

I agree, and yes air flow matters, especially in a controlled environment, such as wind tunnel tests, or still air. In the real world, we are towing our boxes in varying wind speeds, and direction. There is not much help for angled or side wind, which is worse than towing into a straight-on headwind.

Jerry

If there were a shape or gizmo that made enough of a mileage difference without effecting the utility of a TT, it would be standard on every semi on the road.

There are a few items that help but nothing that amounts to a major break through; except perhaps for an electric or hybrid powered pick up.

drsteve wrote:

I always thought those were about keeping the back window clean. In the days of the old station wagon, gas was 25 cents a gallon. Nobody cared about MPG.

When we made one hundred dollars a week, $.25/gallon gasoline was just as expensive as $2.50/gallon when earning a thousand a week today. That is the cruel lie of inflation. People did care and the Economy runs were very popular.

mountainkowboy wrote:

LVJJJ wrote:
You're all worried about the wrong end of the TT. If the TT is a flatback the vacuum created by them acutally tries to suck the TT backwards, so, as I did, install an air deflector to direct the air flow down the back of the TT in order to help it detach itself from the air stream, that's where the major drag is.

I've heard this...has anyone tried the airtabs? I think that's what there called. Was your deflector like the old station wagons used to have? Redirecting the air off the roof down to break up the vortex?

I always thought those were about keeping the back window clean. In the days of the old station wagon, gas was 25 cents a gallon. Nobody cared about MPG.

I could care less about any savings in mileage (I still say if you're worried about gas mileage, you'll not have much fun RV'ing, towing sucks up gas).

What the aerodynamics of the Trail Cruiser does for me is allows me to tow a larger heavier trailer with my anemic low compression engined '94 GMC Suburban.
Used to towed a 22' '04 Tahoe Lite (yeah right) with a front profile that was flat at the bottom 18" or so then sloped steeply back to the roof, and had the poorest design feature ever, a flat back. weighed about 5000 loaded. The Trail Cruiser is 26' 11" long, weighs 4800 (certified scale) lightly loaded and is much easier to pull. Probably 5500+ loaded.

When we decided we didn't like the 48" wide double bed, underneath a bunk (hard to get in and out with bad knees, shoulders, etc., and since we had had a 30' Trail Lite a few years ago, we decided that we had to find a certain Trail Lite or Cruiser with a queen bed and couch slide. Took about a year, with 700 mile trips to see junk, finally found one 35 miles away.

Some of you would make excellent detectives and I´m glad you don´t live next door.

Instead of guessing what the OP has in mind, why not just ask the question?

He may not answer now as it looks like he´s under investigation for asking a simple question that no one here has the answer to much less the manufacturer.

I thought about them but didn't bother after researching.
Air tabs have been tried. People I met that have used them didn't notice a mpg advantage but a cleaner rear of the RV . They also might help a little with stability in the wind but IMO, it would depend on the TT they were installed on.
As far as measuring MPG, the road, weather conditions would need to be identical to measure accurately using specific equipment other than someone's fuel gauge and how many gallons they had to pump back into the tank. Take those opinions with a grain of salt.

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23208771.cfm

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23094344.cfm