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#31
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Al-Ko Trailer Tongue failure
To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides.
Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied. Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball. The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#. I'm sure the engineering types in this group will have fun pointing out the errors in my thought process. ;) JJ |
#32
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Al-Ko Trailer Tongue failure
So... What was the fix?
On 7/9/2016 11:12 PM, Ramy wrote: Got a very quick reply from Alfred that my issue is simple to fix and not a big concern so I am relieved. Excellent customer service. Ramy -- Dan, 5J |
#33
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Al-Ko Trailer Tongue failure
On Sunday, July 10, 2016 at 1:20:11 AM UTC-7, wrote:
To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides. Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied. Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball. The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#. I'm sure the engineering types in this group will have fun pointing out the errors in my thought process. ;) JJ Well, one thing is that the bolts are in double shear and so should be good for twice that. I'd go more with the fatigue argument. With a large overhang, sometimes the trailer gets into some serious pitch oscillations with large reversing stresses. Not amenable to simple analysis. Trust me, I'm an engineer: https://youtu.be/rp8hvyjZWHs |
#34
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Al-Ko Trailer Tongue failure
Fix? Best to roll down drivers window and listen for any scraping noise as you exit any parking area. Stop immediately if trailer skid makes contact. Probably best way to proceed is un-hook trailer and move it by hand past the curb problem area.
JJ |
#35
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Al-Ko Trailer Tongue failure
To fix the rotating issue I mentioned (not the main issue in this thread) I will need to order a little sliding part to replace the damaged one.
Ramy |
#36
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Al-Ko Trailer Tongue failure
Interesting analysis jj, mine failed on a new tongue hitch, I lost the vertical bolt and part of the hitch plate but it was because the tail end of the trailer drags occasionally when entering or departing deep curbs at entrances. Putting the entire weight of the trailer on the younger at the ball and the back skids of the trailer. The best way I see to reduce this chance is whenever possible go across the depressions at at relatively low angle of 45 degrees or less if possible so only one wheel of motorhome and or trailer goes in the depression at a time. Traffic can make this a chore at times but it works.
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#37
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Al-Ko Trailer Tongue failure
Thanks Ramy. ...And JJ's solution is the most elegant!
On 7/10/2016 9:42 AM, Ramy wrote: To fix the rotating issue I mentioned (not the main issue in this thread) I will need to order a little sliding part to replace the damaged one. Ramy -- Dan, 5J |
#38
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Al-Ko Trailer Tongue failure
If you have frequent issues with dragging, consider shimming your trailer axle with a 1" or 2" tube.
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#39
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Al-Ko Trailer Tongue failure
On Sunday, July 10, 2016 at 8:43:34 AM UTC-7, wrote:
Interesting analysis jj, mine failed on a new tongue hitch, I lost the vertical bolt and part of the hitch plate but it was because the tail end of the trailer drags occasionally when entering or departing deep curbs at entrances. Putting the entire weight of the trailer on the younger at the ball and the back skids of the trailer. The best way I see to reduce this chance is whenever possible go across the depressions at at relatively low angle of 45 degrees or less if possible so only one wheel of motorhome and or trailer goes in the depression at a time. Traffic can make this a chore at times but it works. Some people react to the tail dragging by using a drop coupler on the tow vehicle. This puts the tongue of the trailer in a lower and more vulnerable position, the condition JJ warns of. The trailer should be level. You should be able to rig the glider with the trailer hooked to the vehicle. Spindelberger sells lift kits in a couple of heights. They are pretty inexpensive, and easily installed between the body of the trailer and the axle. Here's a photo of one on an ASH26E trailer which had 13" wheels. The 26 trailer is long and this one was too low. https://www.dropbox.com/s/37wtbsd4cs...20Kit.jpg?dl=0 Spindelberger would normally have parts galvanized, but made my part to order and needed to put together a larger batch. As I wanted it right away, it ended up painted. Jim |
#40
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Al-Ko Trailer Tongue failure
On Sunday, July 10, 2016 at 12:19:29 PM UTC-4, wrote:
If you have frequent issues with dragging, consider shimming your trailer axle with a 1" or 2" tube. A size large (diameter) tires does the same. 1/2" at the axle gives about twice that much more clearance at the aft end of the trailer. Of course, if you rig while the trailer is hitched to the tow vehicle, that changes the angle of departure when you're pulling the fuselage out (watch out for scrapes) and forces you to lift the spars off the dollies from a higher position. Nothing is free in this world. Chip Bearden ASW 24 "JB" |
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