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
Wow, this has been pretty technical reading in many instances, but a great discussion on how this hitch really works.
I will try to add a couple of points as well. Keep in mind, that I am a new Hensley owner, but have pulled with it about 2000 miles.
If everyone's discussion about the VPP is correct, and that the Hensley projects the VPP to an area about 20 inches behind the rear axle, wouldn't a Pull-Rite, or a fiver, allow less reaction from the TT to the TV, due to the fact that both a Pull-Rite, and a fiver, place their pivot point at the rear axle. That 20 inches has to still allow some lever action for movement, compared to the Pull-Rite or fiver. Still, no tests that I have ever seen will say that a TT equipped with a Pull-Rite or a fiver exibit less sway or reaction than a Hensley. In most instances, they are equal, or perhaps I should say, "Perceptibly Equal." Maybe that 20 inches of difference is reduced enough from the normal hitch distance to pivot point to make all of the difference?
Also, I don't have all of the technical terms for what I observe, but I will try to share my observations. With the linkages in the Hensley, The hitch almost has to pivot slightly backwards to make its pivot sideways, to allow turns. When the TV is pulling the trailer, the trailer, due to inertia, will try to resist forward movement, making the tendency of the TT to stay in place (or essentially backwards from the moving TV). This allows a natural backwards movement of the pivot in the black and orange parts of the Hensley.
Now, if the TT is to infulence movement on the TV, It must actually move forward relative to the TV. Now, since TTs are not equipped with engines, the only way that it can move forward is due to the TV stopping quickly, or when going downhill, if the TT tends to gain speed quicker than the TV.
Anyone with a Hensley Hitch knows, and is told in the manual, to set the boost higher on your brake control to prevent this forward (and sideways) movement of the TT on the hitch. I suppose the same thing could happen going down a steep grade if you were to decelerate, and engine braking was holding the TV back without the trailer brakes, although I have never heard of this being an issue. Perhaps this is because the differences in inertia between TV and TT are not great enough going downhill, and these differences only come in to play when the brakes on a TV are applied without the TT brakes coming on strong enough.
Perhaps an illustration could be used similar to a motorcross bike swingarm linkage type rear suspension. When the rear tire hits a bump, the arc of the swingarm is the same as the arc of the bump, which allows the swing arm to rise in an arc over the bump which has an arc going in the same direction.
Now, think of that motorcycle going very fast in reverse, hitting the same bump. The arc of the bump is going to be exactly the opposite of the arc of the swingarm, causing that swingarm to resist its movement. On a small bump (small force), if the motorcycle is going fast enough, the swing arm will still move, because the forces will overcome. If you hit a larger bump (more arc), the swingarm will tend to resist movement, due to the fact that the arcs are going in opposite direction. Oh, the swingarm will still move, but it would require much more force to do so (read greater speed, which will result in more force).
OK, now picture hitting a bump which has a 90 degree angle (straight up and down). If your motorcycle is going forward, the rear axle would still tend to go up and over it (it would be a rough ride, but it would tend to go over it.) The front might have an issue, but that is a different story. Now, if you hit the same bump in reverse, the wheel would tend to not go over it, due to the arcs being in opposite directions. Again, if going fast enough, the wheel might rise and go over this "bump", but after transmitting significant forces to the machine (probably would break something) and the rider (again, probably would break something).
I once had an ATV with a front swingarm suspension, and I noticed this tendency first hand.
So, perhaps the TT will resist the movement against the arc of the links in the same manner? The TT could force the links to turn, but it would require much more force than is routinely put out by a TT acting on a TV.
Maybe this is all manifested by the discussion on VPP and the like? Maybe this is the actual engineering explanation of what I have just attempted to explain? Could be. I am not an engineering student, nor do I even claim to be close to one. But, I do try to visualize things.
I hope I have been able to add to this enjoyable discussion, and hope that my response was not totally stupid. Carry on.
I will try to add a couple of points as well. Keep in mind, that I am a new Hensley owner, but have pulled with it about 2000 miles.
If everyone's discussion about the VPP is correct, and that the Hensley projects the VPP to an area about 20 inches behind the rear axle, wouldn't a Pull-Rite, or a fiver, allow less reaction from the TT to the TV, due to the fact that both a Pull-Rite, and a fiver, place their pivot point at the rear axle. That 20 inches has to still allow some lever action for movement, compared to the Pull-Rite or fiver. Still, no tests that I have ever seen will say that a TT equipped with a Pull-Rite or a fiver exibit less sway or reaction than a Hensley. In most instances, they are equal, or perhaps I should say, "Perceptibly Equal." Maybe that 20 inches of difference is reduced enough from the normal hitch distance to pivot point to make all of the difference?
Also, I don't have all of the technical terms for what I observe, but I will try to share my observations. With the linkages in the Hensley, The hitch almost has to pivot slightly backwards to make its pivot sideways, to allow turns. When the TV is pulling the trailer, the trailer, due to inertia, will try to resist forward movement, making the tendency of the TT to stay in place (or essentially backwards from the moving TV). This allows a natural backwards movement of the pivot in the black and orange parts of the Hensley.
Now, if the TT is to infulence movement on the TV, It must actually move forward relative to the TV. Now, since TTs are not equipped with engines, the only way that it can move forward is due to the TV stopping quickly, or when going downhill, if the TT tends to gain speed quicker than the TV.
Anyone with a Hensley Hitch knows, and is told in the manual, to set the boost higher on your brake control to prevent this forward (and sideways) movement of the TT on the hitch. I suppose the same thing could happen going down a steep grade if you were to decelerate, and engine braking was holding the TV back without the trailer brakes, although I have never heard of this being an issue. Perhaps this is because the differences in inertia between TV and TT are not great enough going downhill, and these differences only come in to play when the brakes on a TV are applied without the TT brakes coming on strong enough.
Perhaps an illustration could be used similar to a motorcross bike swingarm linkage type rear suspension. When the rear tire hits a bump, the arc of the swingarm is the same as the arc of the bump, which allows the swing arm to rise in an arc over the bump which has an arc going in the same direction.
Now, think of that motorcycle going very fast in reverse, hitting the same bump. The arc of the bump is going to be exactly the opposite of the arc of the swingarm, causing that swingarm to resist its movement. On a small bump (small force), if the motorcycle is going fast enough, the swing arm will still move, because the forces will overcome. If you hit a larger bump (more arc), the swingarm will tend to resist movement, due to the fact that the arcs are going in opposite direction. Oh, the swingarm will still move, but it would require much more force to do so (read greater speed, which will result in more force).
OK, now picture hitting a bump which has a 90 degree angle (straight up and down). If your motorcycle is going forward, the rear axle would still tend to go up and over it (it would be a rough ride, but it would tend to go over it.) The front might have an issue, but that is a different story. Now, if you hit the same bump in reverse, the wheel would tend to not go over it, due to the arcs being in opposite directions. Again, if going fast enough, the wheel might rise and go over this "bump", but after transmitting significant forces to the machine (probably would break something) and the rider (again, probably would break something).
I once had an ATV with a front swingarm suspension, and I noticed this tendency first hand.
So, perhaps the TT will resist the movement against the arc of the links in the same manner? The TT could force the links to turn, but it would require much more force than is routinely put out by a TT acting on a TV.
Maybe this is all manifested by the discussion on VPP and the like? Maybe this is the actual engineering explanation of what I have just attempted to explain? Could be. I am not an engineering student, nor do I even claim to be close to one. But, I do try to visualize things.
I hope I have been able to add to this enjoyable discussion, and hope that my response was not totally stupid. Carry on.
