Not a happy camper....crash while towing - Page 3 - Fiberglass RV


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Old 07-31-2015, 09:15 AM   #29
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Name: John Michael
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Couple of thoughts.

First, amazed the stick built rv stayed together. I always expect them to unfold in these situations.

I always use a mini bungee cord to secure my seven pin connection after the cable got so stiff during zero degree towing that it unplugged itself. Not sure why the cable is so stiff even at higher temps. I considered stripping off the cable's sheath and replacing it with something more flexible, but the bungee seems to do the trick.

Cheers all, john
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Old 07-31-2015, 10:02 AM   #30
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Curious, John... the cover flap on my TV's connector engages a tab on the plug to hold it in. Does yours have that? I can see it might slip off on a good bump in extreme cold, or if the spring was weak. Not that I have any plans to tow in extreme cold... for us that's anything below freezing.
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Old 07-31-2015, 10:03 AM   #31
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on RV.net..."A guy over in the TT forum (RCMAN46) who lives in the area worked out how far the markers are spaced apart. He then used this to calculate the speed of each vehicle. He calculated that the Semi was going 69.9 and the F250 was going 78."
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Old 07-31-2015, 10:22 AM   #32
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That about perfectly matches my experience in ID last month. Trucks tend to drive about 70 MPH and the trailer guy was just below the speed limit of 80 MPH.
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Old 07-31-2015, 10:44 AM   #33
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Trailer stability does tend to have a relationship to speed. One thing about a trailer that is a "little" loose in the rear but manageable, it is only manageable until it suddenly ain't. That threshold can be razor thin. One more mile per hour, a few mile per hour wind gust at the wrong angle, a bit of rough pavement at the wrong time....

If you ride the edge sometimes you are going to fall off. If you don't have clue one where the edge is you either are cautious or you find it the hard way.

On the highway today found myself watching the back end of a pop up behind a good sized SUV using every bit of the lane for sway at every bump (Mich. roads so we have bumps don't you know) Me I would have been slowing down, this _____ (rookie, idiot, careless, clueless, unsafe, etc. pick as many as you want and add more) put on more speed to pass!

Back end of that trailer was to "wag the dog" and I could see the back of the SUV swaying a bit. I decided a lane over and 5 miles slower would give me more time to react. Kept it on the road but not by much and where a person aware of the danger would have needed clean undergarments, this person appeared totally oblivious. Not a Darwin award winner but certainly a up and coming contender.

Nice thing about this forum, the people that might do what that pop up driver was doing through inexperience come here, ask questions, and learn enough to not do it.
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Old 07-31-2015, 11:35 AM   #34
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Quote:
Originally Posted by RogerDat View Post

On the highway today found myself watching the back end of a pop up behind a good sized SUV using every bit of the lane for sway at every bump (Mich. roads so we have bumps don't you know)
Roger, saw a similar rig not that long ago. A big Ford Excursion towing a tongue high pop up. He was going 70MPH and the pop up was wagging back and forth to beat the band. It supports the old theory that " if everything is wrong with the rig's set up a large heavy tow vehicle will help keep it on the road"......... most of the time!
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Old 07-31-2015, 01:41 PM   #35
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Originally Posted by Jon in AZ View Post
Curious, John... the cover flap on my TV's connector engages a tab on the plug to hold it in. Does yours have that? I can see it might slip off on a good bump in extreme cold, or if the spring was weak. Not that I have any plans to tow in extreme cold... for us that's anything below freezing.
Yeah my flap was engaged. Extreme cold was the likely culprit. I asked an RV dealer for a more secure latching plug/jack and he recommended the bungee. Seems a bit of a Rube Goldberg solution to me, but it works. No problem since. Still looking for a higher quality arrangement. That cable is incredibly stiff in cold weather.

John
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Old 07-31-2015, 01:44 PM   #36
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Trailer stability does tend to have a relationship to speed.
I think aerodynamics play a big part in that. European wind tunnel tests on trailers (not fifth-wheels) towed behind cars showed that all lost tongue weight due to aerodynamic lift on the front of the trailer body. In effect, the faster you go, the nearer you get to a negative tongue weight with all that implies.

This is the reason that all European trailers - being in Europe they are expected to be towed with hitch weights that are low by US standards - have sloping fronts as that was found to largely counteract the aerodynamic lift at speed and so avoid negative hitch weights.

What is interesting is how they get record-breaking trailers to remain stable at very high speeds, 140mph or so. Admittedly the record is currently held by a GMC 2500 towing a 2,700lb trailer so that ratio of tug to trailer must help.
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Old 07-31-2015, 02:08 PM   #37
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Trailer stability does tend to have a relationship to speed. One thing about a trailer that is a "little" loose in the rear but manageable, it is only manageable until it suddenly ain't. That threshold can be razor thin. One more mile per hour, a few mile per hour wind gust at the wrong angle, a bit of rough pavement at the wrong time....

If you ride the edge sometimes you are going to fall off. If you don't have clue one where the edge is you either are cautious or you find it the hard way.
This.

Every time I've towed a combination that tried to come unglued at some point, it had a critical speed at which it tried it. 5 MPH below that speed and everything was fine.

Note that this is after I've looked at things like proportion of tongue weight and tow vehicle loading as part of the combination setup before pulling out.

I've taken to testing that behavior on purpose (better the devil you know): I'll take a new combination (say an unusual load package on my one axle utility trailer) up to a speed I am just about positive is safe, say 35 MPH, and then I'll jink the tow vehicle like I was avoiding a road hazard. If everything tracks nicely, then I'll repeat the operation at 45 MPH. If I'm going a good ways and need to make the best time, I'll repeat it again at 55 MPH. The goal is to set up an oscillation on purpose to see if you can get one.

At some speed, the combination will start to talk back - the inertia of the trailer in combination with tire tuck, aerodynamics, spring squat...all that stuff will cause it it try to start the combination oscillating, generally noted by a distinct cyclic back-and-forth pull on the steering wheel and the rear end of the TV trying to sway to and fro. If you catch it below the critical speed, it will self damp in one cycle or so, especially with a little help from trailer brakes or just holding the wheel steady.

That wiggle is your hint that you probably don't want to go a whole lot faster than that. It might be 40 MPH on a 'close to the edge' combination. Or it might be faster than you care to go anyway (my utility trailer when empty tracks behind the car perfectly - I'm sure it has some critical speed, but it's well above any I care about).

If you've found the critical speed and you drive below it, you know that you will be able to avoid an asphalt alligator or be passed by a big truck without ending up sideways in a ditch, because you've already demonstrated that the combination is safe below that speed.

The tricky part is that the slope of the oscillation curve is quite steep - you can go from 'that is a little wiggly' to 'very scary' in about 3 MPH of road speed - which means that going downhill can get excessively exciting if you're not aggressive with the brakes. It's worth finding out where 'wiggly' is before you're surprised by it.

The day I brought my Casita home, I performed this test on it, which resulted in cushions on the trailer floor and some open cabinet doors among other things. The good news is that it tracks very well behind my TV and I really don't have any stability concerns with the combination up to any practical speed (and no, I don't regard 80 MPH as a practical towing speed).

As we perfect our loadout, I'll retest to verify that we haven't done something weird. I suspect we won't have, as I have already schooled my spouse in the importance of low and forward for heavy things, and in the TV best of all if it's heavy.
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Old 07-31-2015, 02:52 PM   #38
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I was travelling at about 100 km/hr, (62 miles/hr) at night, pulling my 4500 on the way to the west coast along the number 3 highway. As I came across a narrow bridge I saw something in the road, just after the end of the bridge. It was a deer laying down, and facing away from me. It's head was up, so I can only conclude that it was bedding down while enjoying the residual heat in the asphalt. I was completely aware that I was pulling a trailer, but choose to do an emergency swerve, hopping that I would be able to control the resulting trailer sway, after I missed the deer. There was no sway, not even a wiggle. I had packed carefully and I had 10% of the weight on the tongue. But still, I expected some trouble.

I think the fact that I tow with a van helps my towing stability. The front of the trailer is in the wind shadow of the van. No Karman vortex street to initiate sway. The most stable place is directly behind the van.

On that trip we did however experience sway:
Almost lost a wheel
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Old 07-31-2015, 04:16 PM   #39
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Sometimes all you need is a bungee....or perhaps a bit of DUK Tape.

*hit happens ! Don't let it happen to you.
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Old 07-31-2015, 05:45 PM   #40
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Euro Towing - Again

Quote:
Originally Posted by Andrew Gibbens View Post
I think aerodynamics play a big part in that. European wind tunnel tests on trailers (not fifth-wheels) towed behind cars showed that all lost tongue weight due to aerodynamic lift on the front of the trailer body. In effect, the faster you go, the nearer you get to a negative tongue weight with all that implies.

This is the reason that all European trailers - being in Europe they are expected to be towed with hitch weights that are low by US standards - have sloping fronts as that was found to largely counteract the aerodynamic lift at speed and so avoid negative hitch weights.

What is interesting is how they get record-breaking trailers to remain stable at very high speeds, 140mph or so. Admittedly the record is currently held by a GMC 2500 towing a 2,700lb trailer so that ratio of tug to trailer must help.
As mentioned earlier, Most countries have a lower speed limit for towing than the U.S. meaning that they can have lower hitch weight ratios. I think that we all know that if something is going to happen that it's usually above 55MPH when it does.....
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Old 07-31-2015, 05:46 PM   #41
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[QUOTE=John Linck;538764] Still looking for a higher quality arrangement. That cable is incredibly stiff in cold weather.

I converted to a coiled cable
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Old 08-01-2015, 04:07 AM   #42
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I've taken to testing that behavior on purpose (better the devil you know).....
Sensible preparation and a great description.

It's when the frequency of the wobble gets towards zero when trouble strikes - shimmy several times a second isn't a threat, but sway that takes two seconds from one side to the other is right on the point of disaster.
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