Update, dovetail angles...

Okay record...This is just an update, people continually ask me how to determine angle of dove... This seems to come up quite a bit. Very simple. Take the length you'd like for the dove, my example here will be five feet. (I'd like a five foot dovetail) So we're adding five feet of length to overall usable bed space, at 8 feet wide, that adds 40 square feet. I did it by the numbers. We know we have to get to the ground, I've already got five feet planned for dovetail and I'm going to fabricate flip over ramps to match bed height in travel position so that my usable bed space is all flat for hauling things loaded by forklift. (stand up ramps are much easier) I suggest making a mock up with wood, maybe 2X4's 10 feet long. The angle depends directly on your bed height, in some cases with a higher bed you will need a longer dovetail and ramps to get to the ground. If you're making flip over ramps and you'd like to add loading surface level with bed you'll need to keep some key points in mind.

The ramps cannot be the full dovetail length. (same length doesn't allow surfaces to mate level)
The front legs/feet on ramps must contact ground (only when weight applied) forward of ramps themselves. (if legs/feet are directly under the front of ramp, when the weight transfers from ramp to dove the ramps will lift up at the low end causing major damage to wheeled vehicles)
Ramps cannot contact ground when lowered to ground, the front legs/feet would stop ramp from getting into lowered position.

To determine the angle correct for dove, position your 2X4's at matching level of bed with opposing end on ground, Measure your angle. Mine worked out to be 15 degrees. All that matters is a balance between ramps and dove and you must get to the ground.
The perfect system isn't possible. You have compromises and are looking for the best compromise for your application... You can always use wood to compensate for needing to load irregular items. in fact, to load my forklift I will lay down 3/4 inch plywood on ramps and dove to make it smoother on small forklift wheels and distribute the weight better. To load my VW Passat (low to ground) I would need to raise the car with wood 3-4 inches and adjust ramps accordingly. So basically, my ramps are too steep to load cars. Trucks are a non-issue. Tractors, wheel loaders, rough terrain forklifts, manlifts and such would be perfect for loading. Lower ramps, drive on, chain and roll...

Been busy working people. Ramps completely installed with assist springs and primed. I'll come back to the install to share details about assist springs, solid hinge rod etc. I need to do bids for work. Also, I had all ramp diamond plate sheered to exact size for simplicity and will weld the sections on as time permits.
NOTE: Full spool of copper coated .045 welding wire ran out doing some final welding on ramp structures. (50 lb spool, all of it in trailer... I just loaded a spool of copper coated .035 (44 lbs)

and I'm enjoying it in relation to the .045, pleasant change...)

ramps

Making ramps...4 inch channel main supports (3) @ 55 inches long... spaced 20  inches apart, total 40". Angle cut @ 40"  2 1/2" .25 wall angle crossmembers (9) spaced 5" apart (crest to crest) I used 3" channel for legs straight down from channel and miter cut foot ends to match feet squared on floor. (almost) By that I mean I took wooden shims and raised the front of one front channel foot and raised the rear of the other front channel foot. I'm no engineer, but it seems to me the feet shouldn't be identical in how they contact the ground, I believe they're more stable this way. Whenever I run into a situation where I don't know how to do something, I think of a guy smarter than me, then I think, what would he do...Heh!  Obviously the front feet/foot of each ramp needs to be out further, (in front of) ramp surface to prevent ramps kicking up with weight on them, (actually at the weight transfer point from ramp to dove) and this brings into focus the issue of just how will the ramp feet clear the ground when raising or lowering... The ramps need to match the bed height when in travel position and they must be off the ground in lowered position, only coming into contact with ground when weight added to them such as when loading something... You can readily observe in my images that I put smaller legs and another foot behind the front legs/feet for additional support. Ramps are very heavy. In an attempt to save weight as much as possible without sacrificing strength, I'm adding diamond plate to bottom of ramps (flipped over on dove this will be the travel loading surface) and welding the angle cut ends of channel main supports to diamond plate to prevent twisting forces that would naturally occur during loading heavy equipment. (this is as opposed to adding more weight with structural crossmembers)
I need two sheets of 1/8" (nothing will be driving on ramps in travel position therefore 1/8" is sufficient) diamond plate for this because each surface is now 57"X 40". As well, I'm considering the difficulty in finding a shop with a large metal brake and braking the small end over the angle cut mainframe channel 3 or 4 inches for a nice starting surface for ramps... I may have the two sheets sheared at 57X40 and weld it for simplification and add a smaller piece of angle to top to finish starting surface, either way will look good... Of course I could brake the opposite end over the hinge side of the ramps far enough to add two additional tail lights. This would actually make more sense because with my current set up about 40% of my bumper lights will be covered by the 1 1/2 inch solid steel hinge rod... Who knew the ramps would be the most complicated part of the trailer? So there you have it, there are some variables, but anybody can get the general idea of how I did this and you can adjust yours to your own ideas or use mine... I'm including detailed images of my ramp side hinges, 3/4 X 2 1/2 inch, cut, mitered, welded, drilled 1 9/16" holes, cut off corners, rounded with grinder... First image is pattern for hinges required. I'll fabricate bumper side hinges today. Last two are ramps in progress. Have a nice day!