Aerodynamics Matter !!

[Ron-C]

Hello All. First post here... wanted to share some data on aerodynamics.

I am designing an ultralight (under 100 lbs/ft) small travel trailer and wanted to find out the effect of shape on aerodynamic drag. I modeled up 2 trailer designs using SolidWorks CAD software then applied CFD (Computational Fluid Dynamics - a virtual wind tunnel) to test them.

The baseline trailer was a box shaped design with slightly rounded corners - essentially flat nosed cargo trailer. Then I created 4 versions of a swept profile trailer steeper at the front and with a longer sweeping tail in different widths.

Results showed that a swept profile trailer 7" wider than the baseline box trailer at the same height would have 45% less drag force. Looking at it the other way around, it would take almost twice as much force to pull the box trailer!

My conclusion, the shape of the trailer is way more important than the size of it. This means that a larger trailer would require less fuel to pull if it is the right shape.

There are lots of other factors including the shape of the tow vehicle, speed, temperature, etc. but this is at least some food for thought.

Now I am working on a developing an aerodynamic shape that is functional 🙂
Ron

[Passin_Thru]

Laminar flow mmay be what you want. Study wing & fuselage shapes.
Your mileage may vary.

[twichers]

One of my fav threads here

[K_and_I]

DutchmenSport wrote:
OK, a thought just hit me, and a vision in my head .... picture this: Tow a trailer at supersonic speed! First, it would give a new definition to "Smokey and the Bandit!" if you you could even possibly keep control enough to keep it on some of our US of A roads! So every Smokey in your path is now left leap years in the dust. Now ... what does that camper look like! Well, I would imagine about the only thing left attached to the tow vehicle would be the coupler! The rest of the trailer would be splinters stretched out for miles ... long before reaching any supersonic speed! It's just a hilarious image that all of a sudden bounded in my head! How fast is supersonic anyway?

[Slowmover]

Mike-s

Weren't you the guy who excoriated another about pointless insults on the forced router thread two months ago? Check the mirror. And buy better quality booze.

Build threads take time. Quite a few years on some forums. This one is still at at the conceptual stage. So questions about how to allocate a fuel budget are par.

The "utility" of a travel trailer design. Has to have inputs: propane, water and electrical "storage". And less directly, TV fuel. The "winner" is the combined rig that best fits the OPs wants. Separating out need from desire. Nights aboard on an annual basis AND total distance travelled. All of which can be quantified.

Let me spell that out for you: the TV spec which consumes less fuel towing and solo and that also is a close match to solo needs is the better choice. The TT need not be quite as efficient. Aero is then more about handling winds than pure HP reduction. A less dramatic shape. But first, a handle on annual fuel consumption via budget. X-dollars represents Y-miles. No matter how many or of what type.

If it's of no interest to you, why post?

[westend]

Could you estimate / measure the distance from the back of truck to front of TT?

Estimate: 6 feet


Ron,
If you get a usable design, please, post it up in this thread so enquiring minds can see what you came up with.

[mike-s]

Slowmover wrote:
in answer to the idea here and on other threads in re MPG concerns being misplaced, another approach is to factor RV travel as part of an annual fuel budget and work to reduce solo fuel consumption primarily by fewer trips to avoid cold starts thus fewer miles, and to drive the remaining miles at a higher level of skill.

Probably better to just not post replies to 9 month old threads when you're drunk.

[Slowmover]

Ron C, anything new?

I re-read this today in reference to something else and looked for any new posts by you, here or elsewhere.

Also, in answer to the idea here and on other threads in re MPG concerns being misplaced, another approach is to factor RV travel as part of an annual fuel budget and work to reduce solo fuel consumption primarily by fewer trips to avoid cold starts thus fewer miles, and to drive the remaining miles at a higher level of skill. I've outlined in another thread how I was able to do this and make 5,000-miles of RV travel "free".

The best approach is still a clean sheet. I bought both TT and TV with fuel economy as a top specification. Along with longevity of both vehicles. 6-mpg as noted by one thread participant is unacceptable to me. Instead, I average 15-mpg with a one ton truck and 35' TT in a 17k combined rig of 63' length. Wholly consistent with than a dozen others in the South Central US using Dodge CTDs to haul 28-34' Airstreams weighing from 7-11k at under 65-mph.

It may not pay to reinvent the wheel. A trailer of this type isn't "old" until about 25-years. Refurbish it, and get on down the road. Depreciation bottoms at the 10-15 year mark.

[Ron-C]

westend wrote:
Ron,
I haven't given up on your efforts. How goes the designing?

Still going strong. I have been through over a hundred variations trying to refine my TT shape. Now that I am into the finer details, the solving has really slowed down and is taking a long time to process. Thanks for the patience.

Just so I understand it right... Your setup is
'03 F-250 4x4 CC with a full cap (level across the top of the cab)
'71 Starcraft Wanderstar

Could you estimate / measure the distance from the back of truck to front of TT?
Ron

[westend]

Ron,
I haven't given up on your efforts. How goes the designing?

[westend]

93Cobra2771 wrote:
Pretty much my thinking exactly. Now, if your TV had a cap, or was a suburban or excursion, and had the wind deflector, things would likely be a bit better since the mounting surface would be much closer to the TT.

Some type of flexible membrane between the TV/TT would be an ideal solution. Of course that won't happen without a bunch of money and time/engineering. I think there have been some 18wheeler concepts at one point or another with a setup like that...

westend wrote:
I plan to fabricate my own out of aluminum plate and integrate it into a cargo rail system on the top of my truck cap. Assuming it will be as far back as possible to get wind above the trailer. I can make an estimation of the spans of the wind shield as 24" X 72". Deployed height might be 16".

[Keen_Family]

Great idea - and a neat thread - keep it up Ron-C.

[93Cobra2771]

Pretty much my thinking exactly. Now, if your TV had a cap, or was a suburban or excursion, and had the wind deflector, things would likely be a bit better since the mounting surface would be much closer to the TT.

Some type of flexible membrane between the TV/TT would be an ideal solution. Of course that won't happen without a bunch of money and time/engineering. I think there have been some 18wheeler concepts at one point or another with a setup like that...

[travelnutz]

93Cobra2771,

Being so far in front of the trailer's front would likely cause a lot of turbulence behind the deflector due to the deflected air being sucked back down to the fill the "partial vacuum" that was created by the deflector forcing the air up and away. Separating air creates a high pressure/low pressure scenario. Think of it like what causes an airplane wing to lift/suck the plane up off the ground or the curve shaped sail on a sailboat to suck the vessel thru the water.

The low pressure area created by parting the air "which is a partial vacuum" pulls hard to relieve the lacking air in it. This suction is very powerful as can be witnessed by opening a vacuum packed can of coffee or other items. Airplanes are not pushed off the ground and sailboats are not pushed along, they are sucked to lift or move by lowered air pressure sucking toward high pressure. Weather and storms have the same effect. Think weather fronts, hurricanes, tornados, etc and how powerful they are and they usually have the added factor of temperature differences in play too.

[93Cobra2771]

I spoke with a fiver driver who had the aeroshield in the link above. He said he had picked up roughly 1mpg, give or take. Don't know if it would help as much on a TT, since the front of the TT is so far away from where the deflector mounts.