ok to level with (built-in) rear jacks, for winterizing? - Page 3 - Fiberglass RV


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Old 11-19-2012, 02:03 PM   #29
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Name: Dave W
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I do have a bit of an engineering background, so just out of interest I did a few crude calculations to see what difference in maximum bending moment on the frame you may get for two cases:
1) 13 ft (2000 lb) trailer supported on wheels (1800 lb) and hitch (200 lb), and
2) 13 ft (2000 lb) trailer supported on jack stands placed under frame at front and back of fibreglass body.
I had to make a number of assumptions regarding dimensions, centre of gravity of trailer, etc; but conclusions are:

1) Supporting on jack stands alone can result in a significantly larger bending moment on the frame than for the case with the trailer supported on wheels and hitch alone (my calcs showed about 1.6X wheel support case)
2) Moving the jack stands even small distances along the frame but towards the axle results in a significant reduction in the maximum bending moment on the frame (my calcs showed about 0.6X wheel support case by moving jack stands 2 ft closer to axle).

I don't know how much reserve capacity is built into the frame, but it seems to me that if you were going to support the frame on jack stands to reduce the loads on the tires, it would make sense to move your jack stands a little closer to the wheels if possible to better balance the bending moments acting on the frame. Of course, your trailers are likely to have significantly different dimensions and loading conditions from what I assumed, so take what I say with a grain of salt.

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dave
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Old 11-19-2012, 02:11 PM   #30
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I put scissor jacks under the frame, as close as possible to where the axle attaches, to lift my trailer just slightly, about 1", to take pressure off the axle and tires while stored. If I lift near the rear bumper, the trailer flexes just enough that the door sticks when I open it. I also deploy the rear stabilizers because I do enter the trailer maybe once a week.
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Old 11-19-2012, 02:22 PM   #31
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Well Dave I have a hunch (may have to do with reading my manual and watching videos from Scamp) that your rough calculations and resulting assumptions are probable correct.

Tom you can go for the degrees, certifications, fingerprints, etc but I would be happy with just a signed 8 x 10 glossy of the party from Scamp - with the words "Forget the manual! Just Jack It UP!
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Old 11-19-2012, 02:26 PM   #32
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Quote:
Originally Posted by Ice-breaker View Post
........... conclusions are:

1) Supporting on jack stands alone can result in a significantly larger bending moment on the frame than for the case with the trailer supported on wheels and hitch alone (my calcs showed about 1.6X wheel support case)
..........
cheers
dave
I agree, and as others have posted, I support mine on jack stands right at the axle.

That said, I'd wager that you easily exceed 1.6 times the static bending stress when you hit a railroad track at a good clip. I suspect that the Backus connection was inferring that you could take some weight off the axle with the stabilizers, but I doubt they'd recommend lifting the whole trailer off the ground.
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Old 11-19-2012, 03:42 PM   #33
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Funny that I get the same reaction in the door fit that ThomasE gets when jumping up those stabilizers too tight (and that's with the entire molded shell surrounding the opening and a plywood floor. Doesn't take all that much to wrack a door opening, twist a frame, etc. If it returns after the torture, that's fine but why push the limits. As to the bending moment calculations, stretch the frame out from 13 to 17' and the deflection certainly won't be less. If any amount of damage short of breaking its back is acceptable to you, cowboy it all ya want.

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Old 11-19-2012, 04:03 PM   #34
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Quote:
Originally Posted by Carol H View Post
I would be happy with just a signed 8 x 10 glossy of the party from Scamp - with the words "Forget the manual! Just Jack It UP!
How 'bout just some original drawings/ handwriting by Scamp's creator with the language "show him rolling in mud happy"?


http://www.comicartfans.com/galleryp...44&gsub=118897


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Old 11-19-2012, 05:31 PM   #35
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If I lift near the rear bumper, the trailer flexes just enough that the door sticks when I open it.
As in my example with the old Dodge Dart!!! WOW, someone agrees with me for once!
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Old 11-19-2012, 05:33 PM   #36
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If I lift near the rear bumper, the trailer flexes just enough that the door sticks when I open it.
Quote:
Originally Posted by mary and bob View Post
As in my example with the old Dodge Dart!!! WOW, someone agrees with me for once!
My Karmann Ghia convertible's doors would jam when the top was down. Body bending.
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Old 11-19-2012, 06:59 PM   #37
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As in my example with the old Dodge Dart!!! WOW, someone agrees with me for once!
LOL Bob I suspect there are more agreeing with you than you may think
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Old 11-19-2012, 07:47 PM   #38
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Hummm, I have no dog in this fight, but wish I could find the picture that was posted of a 1990s Scamp with a twisted frame because someone tried to lift it from the rear bumper. I'll have to look some more, it may have been posted pre-hack. Sigh.
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Old 11-20-2012, 02:47 AM   #39
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Smile Use a little logic

You are risking placing stress a several thousand dollar frame is not designed for in order to possibly save a couple of $100 tires.

The video from Scamp on winterizing does not mention removing weight from the tires.
If you do want to remove the weight, I would jack each side up as shown in the video on changing tires, and then place jack stands or wood blocks under both ends of the axle so that the tires are not setting on the ground.
I stored a boat trailer for 25 years on the tires and the flat spots that did form disappeared after a few miles.
I am not an expert, but I do sleep in a Trillium often. LOL
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Old 11-20-2012, 05:29 AM   #40
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My '92 LeBaron's doors jam when the top is UP !
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Old 11-20-2012, 01:27 PM   #41
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Originally Posted by Donna D. View Post
Hummm, I have no dog in this fight, but wish I could find the picture that was posted of a 1990s Scamp with a twisted frame because someone tried to lift it from the rear bumper. I'll have to look some more, it may have been posted pre-hack. Sigh.
Pretty sure Brian P? once indicated (a couple of years ago) that when he jacked up the trailer from outside the undercarriage area - if I recall correctly he had the jacks under the bumper area & as a result he couldnt close the trailers door. I think he had a Boler though. May have been on the same thread that someone else mention having over cranked the rear stabilizers on a newer Casita and had the same result. Both parties if I recall correctly felt it was a clear indication of the frame twisting/bending.
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Old 11-20-2012, 01:36 PM   #42
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Are we still talking about lifting the trailer with its stabilizers?

If so, I offer the following quote from
RV Tow Tips, How to tow RV, RV Towing, RV Tow Guide, Guide RV Towing
Quote:
Warning: Do not attempt to use the stabilizer jacks to raise or lower the trailer, or use to support the total weight of your trailer. The jacks are only meant to stabilize your trailer in a level position. Attempting to raise the trailer by use of the stabilizer jack can cause damage to the jack, trailer frame, or both.
Many other reliable sources prolly available in case anyone cares to look...

Francesca
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