Stability?

This includes traditional teardrop shapes and styles

Postby Miriam C. » Tue Feb 22, 2011 12:51 pm

:o I can fly? Not! Mine is taller and more prone to leaning to the side if tipped but that is the soft springs. We have gotten in some 40+ mph cross winds that blew the truck but really not the TD. I just avoid that or slow down and pay more attention...had it up to 70mph with 8" tires!!!!! She's good!

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Re: Stability?

Postby Al Taloma » Wed Nov 19, 2014 11:47 pm

Hi, ole what's his name here,
Relative to most teardrops, and crosswind stability, you want your crosswind center-of-pressure (the center of your side area, in the case of a flat sided teardrop) well ahead of your wheels, and your center-of-gravity ahead of that. With certainty, your hitch point will be well ahead of all three. It's also best to have your center-of-pressure reasonably low, just as with your center-of-gravity. One can easily identify the most stable configuration for a bluff body trailer (big-n-boxy) by looking to our cousins, the long haul truck trailers.
Quartering crosswinds, headwinds, and gust loading are another matter. Because we seldom come across perfect 90 degree crosswinds, we usually get a combination of headwinds and crosswinds. Even though we have a wake behind our tow vehicles, the additional area and shape of the front of the trailer will add to the effect. Because most teardrops have a rounded nose, it helps to lessen the effect. Boxy trailers get affected the worst, and due to this, they often have their front corners radiused. It was found in the 70's that a 9 inch radius or greater would lessen the effects of quartering and headwinds by a significant amount, which is why you now see many RVs and trucks with rounded corners. Gust loading usually comes into play (poor choice of words if it's you fighting the gusts) when you have a significant moment arm between the rear tires of a car and the hitch point. Generally, the weight in most teardrops is enough that it doesn't cause problems, but towing with a light pickup truck and light teardrop with long and tall sides can be a problem. It's kind of a tail wagging the dog situation.
The two places we've identified that can be a problem are crosswinds on a box and gust loading when traveling very light, including the car. The other place we didn't mention is what happens with lift. Because you are usually in the wake of the car, the effect of lift should be reduced, but not eliminated. The use of vortex generators was mentioned, but those are usually found when one wants to generate more lift, not reduce it. I've found that a good set of surf racks tends to spoil the lift generated, plus they add a cool factor that can't be beat. You could call them ladder racks or fishing pole racks if you live in Iowa. If there is any doubt about your teardrop's aerodynamic behaviors, I'd recommend doing some performance testing under controlled circumstances to identify if you have a problem or not. It's usually best to do testing before you've added your interior and other extras, in case you find that you need to make changes to fix both mechanical dynamics behaviors and aerodynamics behaviors. Don't wait until the family is with you in the middle of Texas to find out that you may have built in a problem.
Anyway, enough of my blathering. Thanks for listening,
Al Taloma (1977 BS Aerospace Engineering, specialty in bluff body aerodynamics)
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Re: Stability?

Postby eamarquardt » Wed Nov 19, 2014 11:59 pm

Al Taloma wrote:Hi, ole what's his name here,...............................................
1977 BS Aerospace Engineering, specialty in bluff body aerodynamics


So much BS. I'm sorry, the devil made me say that. That said, #1 son, ME Cal Poly, Slo hopes to someday know half what I know, and #2 son, Petro. Engr. next May, hopes to be half the AH I am. I can think of no greater compliments.

Me, BA in Biology with about the same amount of physics as an engineer, a lot more chemistry than a typical engineer, and math through calculus (even though it's not required for a Biology degree) and a PhD. in real world experience with neuralgias and/or Atypical Facial Pain.

Cheers,

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Re: Stability?

Postby DrCrash » Thu Nov 20, 2014 10:07 am

Saw these on a tank wagon the other day . Did a google search and found this ...
http://www.airtab.com/gallery/large/CasitawithAirtabs.jpg
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