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
In the Accident on I95 thread, it was suggested that a HA would have forced the trailer to pivot similar to a 5th wheel and that using a HA would have prevented the wind from swinging the trailer. I responded with:
Will,
The HA does not force the trailer to pivot similar to a 5th wheel in the first 15 degrees. When the TV and TT are aligned straight ahead, the HA moves the pivot point ahead about 47" and not all the way to the TV's rear axle as a 5th wheel does. Also, at an angle of about 4 degrees, the pivot point is only moved forward about 24". Beyond 4 degrees, the pivot point quickly moves back close to the location of the ball coupler.
The location of the pivot point is of little or no consequence in determining whether the wind can cause the trailer to swing. An important factor is the distance between the TT axles and the center of pressure of the wind force. For a typical TT, having the pivot point farther forward means that the axles and wind force would be relatively closer together. This would make it somewhat easier for the wind to swing the TT. This means that, if anything, the HA would give a slight disadvantage relative to a conventional hitch.
Ron
Will responded with:
I do NOT for the life of me follow you on that one, but even if such is true, the HUGE advantage the Hensley gives in that the trailer is forced to pivot such that it cannot influence the tow vehicle as much, FAR outweighs any slight disadvantage that (may or may not exist) regarding wind. And, I have way too much experience towing with the Hensley in windy situations, to believe your suggestion here, anyway. I think you dreamed that one up.
No, Will, I did not dream that one up.
Consider a TT having a body length of 30 ft. Assume the axles are located according to a 60/40 rule putting the axles center at 18 ft behind the front of the body. Assume the center of a wind force of 1000# acts at the midpoint of the body, 15 ft behind the front. Assume the ball coupler is 4 ft ahead of the front of the body.
For a TT which pivots at the ball coupler, the tires would have to exert a force of 1000x(15+4)/(18+4) = 864# to achieve equilibrium.
If the TT had a Hensley hitch, the "straight ahead" pivot point location would be about 8 ft ahead of the front of the body. In this case, the tires would have to exert a force of 1000x(15+8)/(18+8) = 885#.
Therefore, the added effective tongue length, resulting from the use of the HA would be a slight disadvantage as regards the ability of a cross wind to swing the TT.
Please keep in mind that my example deals with how the HA affects the TT's ability to be swung by the wind and not how the HA affects the lateral forces imposed by the TT on the TV. As I explained in a previous post, if the TT swings more than 10-15 degrees, the HA also is at a disadvantage regarding the TT's steering effect on the TV.
Ron
Will,
The HA does not force the trailer to pivot similar to a 5th wheel in the first 15 degrees. When the TV and TT are aligned straight ahead, the HA moves the pivot point ahead about 47" and not all the way to the TV's rear axle as a 5th wheel does. Also, at an angle of about 4 degrees, the pivot point is only moved forward about 24". Beyond 4 degrees, the pivot point quickly moves back close to the location of the ball coupler.
The location of the pivot point is of little or no consequence in determining whether the wind can cause the trailer to swing. An important factor is the distance between the TT axles and the center of pressure of the wind force. For a typical TT, having the pivot point farther forward means that the axles and wind force would be relatively closer together. This would make it somewhat easier for the wind to swing the TT. This means that, if anything, the HA would give a slight disadvantage relative to a conventional hitch.
Ron
Will responded with:
I do NOT for the life of me follow you on that one, but even if such is true, the HUGE advantage the Hensley gives in that the trailer is forced to pivot such that it cannot influence the tow vehicle as much, FAR outweighs any slight disadvantage that (may or may not exist) regarding wind. And, I have way too much experience towing with the Hensley in windy situations, to believe your suggestion here, anyway. I think you dreamed that one up.
No, Will, I did not dream that one up.
Consider a TT having a body length of 30 ft. Assume the axles are located according to a 60/40 rule putting the axles center at 18 ft behind the front of the body. Assume the center of a wind force of 1000# acts at the midpoint of the body, 15 ft behind the front. Assume the ball coupler is 4 ft ahead of the front of the body.
For a TT which pivots at the ball coupler, the tires would have to exert a force of 1000x(15+4)/(18+4) = 864# to achieve equilibrium.
If the TT had a Hensley hitch, the "straight ahead" pivot point location would be about 8 ft ahead of the front of the body. In this case, the tires would have to exert a force of 1000x(15+8)/(18+8) = 885#.
Therefore, the added effective tongue length, resulting from the use of the HA would be a slight disadvantage as regards the ability of a cross wind to swing the TT.
Please keep in mind that my example deals with how the HA affects the TT's ability to be swung by the wind and not how the HA affects the lateral forces imposed by the TT on the TV. As I explained in a previous post, if the TT swings more than 10-15 degrees, the HA also is at a disadvantage regarding the TT's steering effect on the TV.
Ron
