I HATE the Wind - Aero Semi Trailer Blew Over

[Patrick]

How about jacks or some cribbing under the back end? That would prevent compression of the suspension and tires and move the roll center up a lot. It should make it much more difficult to tip over.

[Shepherd777]

Originally Posted by instarx

You seem to have years of experience modifying trailers - have you heard of aero trailers being more tippy in high winds?

I can remember one incident almost 30 years ago in Montana, with my first aero trailer. It had full skirts and covered wheels and tires just like this one. We had a full load heading to Canada, but the high cross-winds almost blew us completely off the road. I don't know if the skirts contributed to that.

I have been in contact with the trailer manufacturer, and others, and they have not heard of any incidents like this one with trailers with skirts. But remember, this is one of the only van trailers on the planet with full side skirts. All other trailers only have half the surface area of these skirts.

I have never heard of an empty moving van trailer blowing over, but I am sure it happens. They have side panels just as low, and much smaller tires.

[euromodder]

I hope it didn't blow over again.
Was it badly damaged ?

Trailers, busses, caravans, ... they all flip when the winds get too high and come from the right / wrong direction.

[KamperBob]

I agree - that sucks!

I've seen videos of semi trailers and smaller cargo haulers blown over by cross winds. IIRC they all were classic "box" shape with right angle edges. Never an airstream or tanker truck for example. That makes me wonder more about roof treatment. I realize there are height restrictions due to bridge and tunnel clearances. But safety first. Sure makes me wish I had proper CFD capabilities to investigate... (sigh)

[Shepherd777]

Originally Posted by euromodder

I hope it didn't blow over again.
Was it badly damaged ?

We had constant high winds here all last night, with gusts 50-60mph. The trailer was still upright when I arrived at my shop this morning. So I'm still thinking it was low-level wind shear when it blew over last week.

About $2k damage, not counting the grand it cost me to turn it right-side-up.

4 roof bows, 10 feet of new roof, one upper corner structural member, and one side radius panel. It could have been much, much worse. When it was on its side, I thought the wrap on that side would be completely totaled. But astonishingly, there was only a couple of tiny, almost in-perceivable, scratches in the wrap. It woulda cost me prolly another $10k to re-wrap that side.

Originally Posted by KamperBob

Sure makes me wish I had proper CFD capabilities to investigate... (sigh)

One of our sponsors is SolidWorks, so we do have the $14k SolidWorks Flow Simulation CFD program. We just never ran it at a yaw or direct crosswind angle. Mayhaps we will now.

[SlideWRX]

Originally Posted by Patrick

How about jacks or some cribbing under the back end? That would prevent compression of the suspension and tires and move the roll center up a lot. It should make it much more difficult to tip over.

That would help. Of course video would tell us how much of an effect the suspension had - did it start rocking before going over? Did one large gust topple it? I think in either situation stabilizing the rear end would have helped.

If those aero covers hid some arms that could swing out a couple feet away from the trailer and jack down to the ground you could get really stable. kinda like they spread apart for back hoes, but it wouldn't have to be *nearly* as strong.

Tom

[Frank Lee]

I'd imagine an empty semi-trailer's suspension isn't all that supple.

[slowmover]

Weight versus wind-loaded area is the problem. The lack of side radius allows no relief.

From a discussion on RV.net about towing in high winds, the following is a formula from the State of Wyoming Department of Public Safety in re wind loads.


Evaluation of Intelligent Transportation System Alternatives for
Reducing the Risks of Truck Rollover Crashes Due to High Winds FHWA-WY-07/01F


If you want to calculate an estimate of how much wind speed is required to overturn your trailer, you can use

V = SQRT(W*b/{0.00666*l*(h-h2/2)*(h/2+h2/4)})

where
V = wind speed, mph
W = trailer weight, lbs
b = trailer width (tire center-center), ft
l = trailer length, ft
h = trailer height (from ground), ft
h2 = tire height, ft

For example, with W=8000#, b=8', l=30',h=10',h2=3' -- the calculated overturning wind speed is 81 mph.

As expected, the most sensitive factor is trailer height. If the height is increased to 12', the overturning wind speed reduces to 67 mph.


These calculations are for square box trailers.

.

[aerohead]

If I had to shoot from the hip,I'd say that in a pure crosswind condition the van is at around Cd 0.85.As soon as it is popped,its in full separation,top and both ends,with an enormous leeward wake.The delta-p just sucks it over.
With less packaging efficiency,an Airstream trailer,with its generous corner radii allows for attached flow over and around, with even a smidegeon of pressure recovery on its leeward side before separation occurs,generating half the wake volume.
And I agree with others with respect to the side skirts having little or no contribution to the roll moment.
The position and magnitude of the C.P. overwhelms the mass and C.G..
Maybe some water bladder low profile ballast until you can get better protection? Pull the cork when you're near ready to roll.I know its a waste of H2o,although it could be captured and recycled.
Hard to stomach the photos! Glad it wasn't any worse.You've got a lot of skin in the game,I hope in the long run that you'll be able to look back and laugh.
I've been humbled by the air many a time.

[spacer]

Tying down a tractor trailer, especially solidly enough to keep this from happening, is probably asking a bit much of the drivers, especially those who won't even bother to kick the tires before firing it up and wheeling it out onto the highway.
We tend to park in groups because we have to... especially east of the Mississippi, parking is kind of a precious commodity.
We tie down airplanes all the time, but for obvious reasons, we're a lot more apt to be careful with those.

How about a set of "blow out" panels in the fairings? Secure them against the sort of pressure they'd see going down the road, but if a rogue crosswind hit the rig, the panels (hinged and secured with magnets or the like) would release at a certain point, allowing some of the air through. Or, avoiding moving parts, a set of finned vents might relieve some of that pressure without sacrificing the aero advantages of the fairing.

And, yeah... the moment arm at the top of the trailer is FAR more likely to generate the roll force needed to take it over, but every little bit can help, especially if the lack of relief at the bottom increases overall pressure against the side of the trailer.