Trailer Design (1 Viewer)

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Leland, NC
I can't seem to figure out why most people/companies build a trailer with a second frame for the hitch. I don't understand why don't they all just do it like the one in the 2nd picture, where its part of the main frame. Can someone explain please.

car-hauler-wood-floor-trailer-2018-1.jpg


FMCW-7K-18D-done1.jpg
 
I can't seem to figure out why most people/companies build a trailer with a second frame for the hitch. I don't understand why don't they all just do it like the one in the 2nd picture, where its part of the main frame. Can someone explain please.
Cheaper to cut metal than have it bent, would be my guess. Also the former design would be easier to repair than the latter, IMHO.
 
It has to do with where the highest stress in the frame is. This is almost always at the front edge of the deck or box. By building the tongue to go under the main part of the frame the designer doubles (at least) the Section Modulus of the frame at that point. The first picture is the only correct way to build a trailer frame.

You'll see it done like the second picture a lot on here (BTW, it is crap, do not buy one like that!). The only reason that it works is because the loading is not usually high enough to stress the frame. As soon as the loading goes high enough and stays that way that front cross-member may as well be the pin in a hinge because that is what is going to eventually happen. "Trailers: How to Design and Build" by M.M. Smith goes into all of this in good detail without it being too buried in "Engineer-speak". Too bad the book is out of print and costs a bloody fortune on Amazon as I've found no other that treats the topic as well.

Alternately, look up how to do a "Shear-Moment" diagram and do one for a trailer. It won't be easy because none of the common example represent exactly how a trailer frame is loaded, but it can be derived.
 
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It has to do with where the highest stress in the frame is. This is almost always at the front edge of the deck or box. By building the tongue to go under the main part of the frame the designer doubles (at least) the Section Modulus of the frame at that point. The first picture is the only correct way to build a trailer frame.

You'll see it done like the second picture a lot on here (BTW, it is crap, do not buy one like that!). The only reason that it works is because the loading is not usually high enough to stress the frame. As soon as the loading goes high enough and stays that way that front cross-member may as well be the pin in a hinge because that is what is going to eventually happen. "Trailers: How to Design and Build" by M.M. Smith goes into all of this in good detail without it being too buried in "Engineer-speak". Too bad the book is out of print and costs a bloody fortune on Amazon as I've found no other that treats the topic as well.

Alternately, look up how to do a "Shear-Moment" diagram and do one for a trailer. It won't be easy because none of the common example represent exactly how a trailer frame is loaded, but it can be derived.
Ditto this and you can use lighter materials with a stronger design which means more profit.
 
Mechanical Engineer and agree with ntsqd with regards to highest stress point and ability to deal with it better with a separate beam under the front of deck.
 

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