Mismatched trailer and tow vehicle..help me move

[sparksnsaaben]

Hello aerodynamicists and trailer owners. Due to some bad stuff, I'm moving from Colorado to Florida. I just purchased a trailer that has the volume and weight capacity that I need.

However, I experience a massive amount of drag at interstate speeds. The tow vehicle is a 1997 SAAB 9000 CSE with a turbocharged 2.3l engine. At speeds below 50 to 60 mph, I can barely notice it behind me. At 75 mph I can maintain speed in 5th gear with close to maximum boost. At 90 mph I can maintain speed in 4th gear at maximum boost. During those tests, trailer stability and engine temperature were excellent. Without a trailer 30+ mpg is easily achievable at 80 mph. The vehicle has a manual transmission and I feel confident that it will not suffer adverse effects by pushing it to it's limits as they sit in current form.

I am an ASE certified Master Auto Technician that has pushed these engines and drive-trains much further than what my current problem is. These cars have brakes and handling capabilities similar to a truck's.

I don't want to run my engine that hard for 2000 miles. Also, I believe that with some aerodynamic modification, I can greatly improve my fuel mileage.

From the research that I've done, it seems like my biggest disadvantage is the difference in my car's height versus the flat surface of the trailer.

My spoiler is at 3'7", my car roof is at 4'10", the trailer is roof 8' tall with it's current tongue weight.

I believe that adding a "nose" to the trailer made out of 2x4s and OSB will greatly reduce my drag. My car is also a few feet narrower than the trailer. I have two weeks for preparation, but only a narrow window of time for the trip.

What minimum height should I build my aerodynamic "nose"? What is the best shape, one plane, three planes, etc.? I am also considering adding a "boat tail" if that would result in a significant fuel savings. As of right now I believe that fixing the front aerodynamic disparity is the only thing required to meet the law of diminishing returns.

A picture of the rig can be found at (sorry, I don't have enough posts to provide an unbroken link) :
imgur
.com/5QjkL

Thanks.

[SentraSE-R]

I'd model a deflector on the Saab similar to what the big-rig tractors have. They're single plane, so much easier to construct. Or I'd just drive slower. After all, you're only doing a 2-3 day drive. What's another 6 hours?

[euromodder]

Welcome to ecomodder.

[sparksnsaaben]

Thanks for posting the picture for me and the warm welcome.

[euromodder]

Originally Posted by sparksnsaaben

At speeds below 50 to 60 mph, I can barely notice it behind me

Then stick to those speeds.
Surely it'll take longer, but it'll save a bunch of gas.

What minimum height should I build my aerodynamic "nose"? What is the best shape, one plane, three planes, etc.?

A bulge above the trunk height will do.
See On Aerodynamics Pull Trailers as an exemple.

An approximation of a bulge with angled plates will work, just not as well.

I am also considering adding a "boat tail" if that would result in a significant fuel savings.

Boattailing the trailer would give a considerable reduction in drag.
Even simple angled plates will work.
Almost anything is better than a square shaped back.

Just don't add a round or circular tail fairing.

As of right now I believe that fixing the front aerodynamic disparity is the only thing required to meet the law of diminishing returns.

Changes to the front have smaller effects on the drag than curing the rear end.

Rounding off the trailer's front corners will help.

A spoiler on the car roof might help, but the gap is pretty large.
A nosecone on the upper part of the trailer (anything above trunk height) will likely work better.

A vertical splitter plate on the tongue can help to prevent crossflow.

Putting angled deflectors in front of the trailer tyres, and boattails aft of them will also help.

[skyking]

best money is a quick, simple boat tail and drive slower.

[dennyt]

I agree, I'd go with a boat tail & drive slower. If it's for a one-time use, get some coroplast (sign shop) and aluminum angles. OSB can add up to hundreds of pounds.

[skyking]

Originally Posted by dennyt

I agree, I'd go with a boat tail & drive slower. If it's for a one-time use, get some coroplast (sign shop) and aluminum angles. OSB can add up to hundreds of pounds.

yup, or even EMT conduit. Hit it with a hammer to make a flat spot, drill. Big bag of zip ties

[sparksnsaaben]

Great ideas everybody. Now what do the laws have to say about boat tail size and tail light placement? What angle should the boat tail have in relation to the body? Open or closed design?

[skyking]

12 degrees, and I *think* you can get away with 4' aft of tail lights most everywhere. but check that.
Top and sides, bottom not necessary. Open to the back.