Originally Posted by SuicideSaints
I guess I owe you an apology and have to re-tract my previous statements. I just saw a post where a guys TT blew over in the wind. How knew, this is the first I have ever heard of this happening. I apologize and will say that it is a possibility! I would still say it is unlikely but possible.
I agree with all of the previous posts that a jack under a slideout shouldn't be used to level a trailer. My original recommendation assumed that the trailer had already been levelled using jacks under it's corners and that a jack under the opened slide would be no more than snug, and not weight bearing.
I did some additional research on wind effects and found the following formula that describes the amount of force exerted on a wall by the wind:
F = 0.00256*(V**2)
where F is the force in pounds per square foot and V is the wind velocity. for a 60mph gust, this amounts to 9.216 pounds / square foot. For a TT thats 12' tall and 25' long with 2' clearance for the tires, that's 250 square feet. That 60mph gust will exert a force of just over 2300 pounds against the side of the trailer!
Standard force analysis (from physics) says that the effects of the force can be represented by assuming that it's all applied at the vertical center of the wall. That would be 5' from the bottom of the wall and 7' above ground. The support against which this force is applied is the jacks on the opposite side of the trailer, where they are resting on the ground. If we assume that the trailer is 9' wide, the horizontal and vertical sides of the force triangle are 9 and 7. Using trigonometry to solve the force triangle (sin(arctan(7/9)) gives the proportion of the incident force that represents the lifting force on the windward wall. This component of the force generated by the wind will be 61% the horizontal component. This yields an effective lifting force on the windward side of the trailer of over 1400 pounds.
It's easy to see why a broadside wind can tip an RV over. I spent six weeks this winter in a location that regularly gets wind gusts over 70mph. Fortunately, these gusts only arrive from a single direction (they're from the nearby mountain range) so I park the RV facing in the same direction that the wind blows. The back of the RV has a much smaller surface area and the distance from the rear of the rv to the front jacks changes the force distribution in my favor.