Hensley Arrow: How does it REALLY work?
There have been several discussions on this hitch that have become somewhat 'controversial'. I am NOT trying to stir this controversy/bashing back up. Instead, I'd like to see a good, intelligent di...
Forum Discussion
Modeling the Hensley's 4-Bar Linkage
Some of you have suggested that having a physical model of the HA's linkage would aid the understanding of how the hitch works. I agree. The following is a way to construct such a model.
Start with a 3' piece of lath or wood of similar dimension. Cut four pieces with lengths: 1 @ 9 1/8", 2 @ 7", and 1 @ 9 7/8". Drill a hole on the centerline of each piece 1" in from each end; i.e. holes spaced at 7 1/8, 5, 5, and 7 7/8" center-to-center.
Insert a flathead bolt, pointing down, through one hole of a 7" piece and also put the bolt through a hole of the 9 1/8" piece with a washer between the pieces. Do the same for the other 7" piece placing that bolt through the other hole in the 9 1/8" piece. Put a nut on each bolt.
Insert a flathead bolt, pointing up, through the second hole of one of the 7" pieces and place one hole of the 9 7/8" piece over the bolt with a washer between the pieces. Do the same for the other 7" piece. Put a nut on each bolt.
You now should have lath pieces in three levels with each end of a piece pinned to another piece at a level above or below. The lower level (9 1/8" piece) represents the front link of the HA which actually is the hitch head. The middle level (two 7" pieces) represent the side links. The upper level (9 7/8" piece) represents the rear link to which the TT tongue is connected and restrained from yawing relative to the link.
Glue a short piece of lath to the top of the 9 7/8" piece at its midpoint and perpendicular to it. This will represent the TT's tongue.
If you got the bolts inserted in the right directions. You should be able to hold the front link and cause the other links to rotate about their bolts.
If you project a straight line through the longitudinal center of each side link, the point of intersection of the lines defines the instantaneous center of rotation of the linkage (the Virtual Pivot Point). When the rear link is parallel to the front link, the projected lines should intersect about 52" ahead of the rear link. As you allow the linkage to turn, the VPP will move to the side and rearward.
Ron
Some of you have suggested that having a physical model of the HA's linkage would aid the understanding of how the hitch works. I agree. The following is a way to construct such a model.
Start with a 3' piece of lath or wood of similar dimension. Cut four pieces with lengths: 1 @ 9 1/8", 2 @ 7", and 1 @ 9 7/8". Drill a hole on the centerline of each piece 1" in from each end; i.e. holes spaced at 7 1/8, 5, 5, and 7 7/8" center-to-center.
Insert a flathead bolt, pointing down, through one hole of a 7" piece and also put the bolt through a hole of the 9 1/8" piece with a washer between the pieces. Do the same for the other 7" piece placing that bolt through the other hole in the 9 1/8" piece. Put a nut on each bolt.
Insert a flathead bolt, pointing up, through the second hole of one of the 7" pieces and place one hole of the 9 7/8" piece over the bolt with a washer between the pieces. Do the same for the other 7" piece. Put a nut on each bolt.
You now should have lath pieces in three levels with each end of a piece pinned to another piece at a level above or below. The lower level (9 1/8" piece) represents the front link of the HA which actually is the hitch head. The middle level (two 7" pieces) represent the side links. The upper level (9 7/8" piece) represents the rear link to which the TT tongue is connected and restrained from yawing relative to the link.
Glue a short piece of lath to the top of the 9 7/8" piece at its midpoint and perpendicular to it. This will represent the TT's tongue.
If you got the bolts inserted in the right directions. You should be able to hold the front link and cause the other links to rotate about their bolts.
If you project a straight line through the longitudinal center of each side link, the point of intersection of the lines defines the instantaneous center of rotation of the linkage (the Virtual Pivot Point). When the rear link is parallel to the front link, the projected lines should intersect about 52" ahead of the rear link. As you allow the linkage to turn, the VPP will move to the side and rearward.
Ron
