Removable Aerodynamic Fairing?

[PaulC]

I have trouble understanding why so many people can not grasp the principles of aerodynamics and, then realising that they are generally talking gobbledegook. The gains, aerodynamically, when towing a TD would be so minimal that it would probably take you all a 100 years, or more, to realise any financial benefit. If Andrew can be so kind as to put up his drawings of what happens to the air as it passes over a motor vehicle you should all be able to see that your time would be better spent travelling that beautiful country of yours.
Cheers
Paul

[Steve F]

I have trouble understanding why so many people can not grasp the principles of aerodynamics and, then realising that they are generally talking gobbledegook. The gains, aerodynamically, when towing a TD would be so minimal that it would probably take you all a 100 years, or more, to realise any financial benefit. If Andrew can be so kind as to put up his drawings of what happens to the air as it passes over a motor vehicle you should all be able to see that your time would be better spent travelling that beautiful country of yours.
Cheers
Paul

I put a small roof spoiler on the rear of my TD, are you telling me it was all for nothing It must be doing something as I don't get a drop in economy behind my little Jeep (18lt/100 with and without the TD)



Cheers
Steve

[PaulC]

That looks so cool Steve 18l/100 I'll stick to my old 2.8 Hilux. 12l/100 or my Navara 3.0TD , 10l/100. Both these figures do not alter when I fit the TD behind it.

By the way, where'e the spoiler in that pic

Cheers
Paul

[Steve F]

Its just an extension on the rear of the roof, when I put on the roof it hung over the back so I trimmed it and left a small spoiler, cant really see it in the pic. Actually 18lt/100 may be a bit on the bad side, I haven't adjusted the speedo so it's more like 16lt/100.... Much better

My lovely new Mazda 6 is only 8.6lt/100 though, and it's only got 1800km on it so far and mostly city driving



Cheers
Steve

[PaulC]

A mate of mine had the sports version of the Mazda. Nice car. After someone decided they liked it more than he did, he traded it for a commode door.

Cheers
Paul

[angib]

The underside if the Aliner is pretty rough aerodynamically with lots of protruding pipes, frame members, etc. Do you think a rubber air-dam on the front of the trailer would help?

It looks to me like the bottom of the trailer is above the bottom of the car and in that case I bet you couldn't do anything to the underside of the trailer that would make it tow more easily. The Cobalt is probably doing a fine job as an air dam!

Why don't the big semi truckers use this instead of the big fiberglass fairings that they do?

On a big semi, the trailer sticks out above the top of the tractor unit, so those fairings make sense - they become the front of the trailer body. But most teardrop trailers are travelling in the wake of the tow vehicle, so adding a fairing in front of them doesn't make much sense, unless they stick up well above the tow vehicle.

However I should say that I stole the half-round idea from one British manufacturer of truck/trailer body fairings that use this design.

Andrew

[RICHARD FURROW]

Thank you Andrew for you patience and explanation. Sometimes I can get myself in trouble by trying to think outside the box. I must say that I have truly enjoyed, and have learned much from your contributions to this forum. I know that when I get started on mine, I will have many less mistakes, redos, save some money, and have a nicer and safer TD from what I have learned from this Website.

Ricky

[QuietOutdoorsman]

http://autospeed.com/cms/A_109778/article.html?popularArticle

This is a well put together article that gets a lot of the basic concepts across while not getting too bogged down in the science. The science of aerodynamics is really interesting, but I recommend a few years at the university instead of asking one of us brainy types to explain it all on this forum. I prefer to keep that brain cell in retirement anyway!

What it really all boils down to, is that a gradually tapering teardrop shape is already very aerodynamic. On a taller vehicle like most any SUV, the frontal area is not increased with most TDs (except a standy perhaps). So the only real increase you'll see in drag is from air flow pressure on the side of the trailer with just a minor amount from airflow over the top of the vehicle. As the article states, narrowing the tail end (boat tailing) can help with drag from the side pressures.

On a smaller vehicle you are adding to the frontal area, increasing drag, and there is very little to do about that in a practical sense. If you could devise a way to create a ridgid and smooth surface (on top, bottom & sides) that connects the car body to the TD to create a bridge to continue the laminar airflow lines, you could reduce drag. That bridging is basically impossible on a standard trailer (2 wheels & single hitch point) due to the need for the pivot point at the hitch ball when turning. I have seen pics on this forum of a single, center wheel trailer (2 hitch points on the bumper & 1 centered wheel), and perhaps the bridging concept is possible with that type of trailer since there is no pivot. The trailer would be whipped around every corner like a tail on an aligator.

Dirk

[brian_bp]

Why don't the big semi truckers use this instead of the big fiberglass fairings that they do? I really do appreciate the discussion. Best ay to learn is listen, then ask questions later!

Ricky

The fairings mounted on top of the cab (or better, on the front of the trailer) are exposed directly to the airflow - they're the front of the combination. The fairing proposed by Andrew ignores the middle part of the trailer front, because it is behind the tow vehicle so it isn't facing the airflow (the tow vehicle has that honour).

[RICHARD FURROW]

This Website backs up a lot of what we all been talking about. It is quite interesting. When you really think about it, like someone earlier said, it want make a lot of difference in the long run unless you do a lot of cross country traveling, or several thousand mile a year at interstate speeds.
Anyway, here is the Website:

http://www.marama.org/diesel/frieght/co ... roOvw2.pdf

[brian_bp]

This Website backs up a lot of what we all been talking about. It is quite interesting. When you really think about it, like someone earlier said, it want make a lot of difference in the long run unless you do a lot of cross country traveling, or several thousand mile a year at interstate speeds.
Anyway, here is the Website:

http://www.marama.org/diesel/frieght/co ... roOvw2.pdf

Interesting read. Thanks, Richard.

The most basic commerical semitrailer is a simple rectangular brick. That sounds like a really bad shape, but as long as the brick is much longer than it is high or wide (true of semis), it's better than the small trailers behind our tugs. Current semi tractors are not well connected to the trailer aerodynamically, but they're still much better than out tug-to-trailer matches.

The potential improvement in some of our rigs (ones with the trailer wider or taller than the tug) may be proportionately greater than the semi rigs could see, due to both the inferior shape of our short trailers, and the poor match between tug and trailer.

[angib]

I was looking for examples of the half-round truck body fairings used in Britain and instead came across this government agency guide to truck aerodynamics:
http://www.energysavingtrust.org.uk/upl ... 7QaiH3.pdf

Of course it's about Yurpeen trucks, that are different from Merkan ones, but some ideas are transferable.

Andrew

[sushidog]

Great information all!

I agree, it would be difficult to justify even a couple hundred dollars worth of aerodynamic mods, if only towing a couple thousand miles a year, as most of us do.

However there's a reason for my inquiry. My Aliner is as much of learning tool for me as a camper. My DW and I are planning a full-time mobile retirement in a small camper, such as a Chalet XL1938 or a Hi-Lo type trailer, which will be towed by a minimal tow vehicle (such as a v6 Toyota Rav-4, Sienna or similar vehicle) for economy sake.

The reason for such a tiny rig is primarily economy while towing, as we plan to tow 30-36,000 miles a year for an indefinite number of years. If fuel prices double or even triple by then (a distinct possibility given the $1 a year gas has increased over the last 3 years) this is the only way we will be able to afford it, given our modest means.

Right now, I'm taking a 10-12 mpg hit when pulling my little Aliner at highway speeds! A small improvement in aerodynamics will be easily noticed on this "test rig" which can later be applied to my full-time rig. So I'm banking that the lessons I learn now, experimenting with my little Aliner will pay big dividends in the future.

Granted no-one wants to live in a rig this small, however, I've lived in much more modest accomodations while serving my country. After much thought and careful consideration, my DW and I would much rather live in a small, hard-sided, pop-up camper that we can afford to tour our beautiful country in, than live in a 30 footer parked in a single location for months at a time, because we can't afford the fuel to move it. If gas prices rise to the $12 a gallon level (God forbid) as Sen. Obama envisions, almost all full-timers might be forced to face similar decisions.

I think the ultimate full-time mobile retirement rig (should someone decide to build one) would be an ultra-lightweight (1/2 ton towable), aluminum framed, Hi-lo type fifth wheel that would protrude no higher than a pick-up cab when towing. This hypothetical 25 ft long camper would come to a teardrop shape in the rear with Airstream style rounded edges everywhere. Such a rig might have an even lower Cda than an a naked pick-up, returning similar mileage to an unladen truck on near level roads.

[RICHARD FURROW]

Sushidog,
Your Aliner is neat. That is a great hit on your mileage. How much does the camper way? Is it much wider than the car?
I agree with you on the big campers. I would think I would enjoy a smaller one more because I do not want to stay at the same place more than a couple of nights. We like to travel to different places. I feel the small campers are so much more maneuvable then the big ones. I don't think I would really want a large one if the gas was cheaper.

[PaulC]

The reason for such a tiny rig is primarily economy while towing, as we plan to tow 30-36,000 miles a year for an indefinite number of years.

That's an average of between 82 miles and 98 miles per day for every day of the year. Not wishing to be a party pooper but I think you'll be missing a lot of that great country of yours if you try to do that many miles in a year. My Kids averaged 43miles per day on their trip around Australia. They didn't want to miss a thing and still did.
Cheers
Paul