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Open Roads Forum  >  Travel Trailers

 > Hensley Arrow: How does it REALLY work?

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bettered

UpCountry SC

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Posted: 02/04/06 05:30am Link  |  Print  |  Notify Moderator

I'll not disagree with Ron, but maybe I can seek to clarify for those that may not be entirely familiar with the Hensley operation...

Ron says: "Because of the way the HA's linkage works, it is especially important to ensure a HA-equipped TT is not allowed to push on the TV."

To which I would suggest we append: "....in a cornering situation where one link has had a chance to go past the center position." I'm guessing this would be almost a 30 degree turn.

While the brake controller should always be active so that the TV's brakes do not supply the primary force stopping the TT, in a primarily straight line or slight turning situation, less than say 15 or 20 degrees, there is no reason to anticipate the Hensley will enhance anything other than a straight and true, fully undramatic stop, absent the uneven trailer braking situation being discussed here.

We could look more closely at the geometry to determine exactly what angles have the potential to become un-nerving, but in a panic situation, we won't have the option of chosing the specific conditions anyway.


BetterEd

DW + 2 grandkids + Mini Schnauzer
2005 Chev 3500 Crew D/A 6.6L LLY, 6 x 6 DRW, 3.73
Tru-Flow + Banks, 2005 Flagstaff 831FKSS
Hensley + Prodigy

"Genius may have its limitations...." E. Hubbard 1856 - 1915

Stressor

Whitefish Bay, Wisconsin

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Posted: 02/04/06 09:05am Link  |  Print  |  Notify Moderator

More nonsense.

All you have to do is take your Hensley Arrow equipped rig out on a vacant stretch of road, and turn down the gain on the brake controller. Then brake while steering. Merely changing lanes while braking hard will do the trick.

The tongue will move either left or right as the linkage collapses, the trailer will stay directly behind the tow vehicle for the simple reason that it can't go anywhere else under those conditions.

And none ever have. [emoticon]

The RGIH might work differently, but then, he don't sell many hitches.


Milton Findley (and Kerene)

A small piece of my mind...

bettered

UpCountry SC

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Posted: 02/04/06 09:43am Link  |  Print  |  Notify Moderator

Maybe Milt's comment should be appended with the phrase: "...up to the limits of adhesion." Under normal circumstances, most of us are not skidding down the road, but when either the TT or the TV start to skid, unusual things happen.

Milt, that's the realm we're in here. This recent discussion is all and only about "slippery conditions." The Hensley can only "hit the stop" when either the TV or TT (or both) is skidding. And I know there is no "stop." People who use this phrase are talking about what happens when the links interfere at their limits of travel.

You may be old and wise, but I've still got about 5 years on you.

Ed

Garfie|d

South-Western Ontario

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Posted: 02/04/06 11:56am Link  |  Print  |  Notify Moderator

6MISFITZ wrote:

Ron, On my thread, there was a story from what happened to Garfield in a corner with his trailer, so I do agree that the hitch won't save me from every law of physics or that of a ham fisted maneuver by the driver and that towing requires more attention - no matter what hitch.


Gee, I think I was just insulted!!! LOL! [emoticon][emoticon][emoticon] (Kidding Mike!) [emoticon]

Anyway, this thread extension appears to be focusing around an incident that I experienced last summer, so I thought I should clarify things, expecially because it underscores the need to ensure there's proper braking pressure to the trailer to control the Hensley even in situations where it may not be thought necessary.

I experienced a situation last summer where I was slowly coasting into an intersection to make a 90 degree left turn. I was in a small town and there was no traffic around and I had the whole intersection to myself. I rolled into the intersection doing 10-15 kph and quickly cranked on the wheel without applying the brakes. After pulling a long trailer for a while you get into the habit of pulling well into the intersection and turn sharply, and that's what I did.

What happend next I didn't foresee, although I should have. The short wheelbase Yukon turned very quickly as usual, but of course the trailer wanted to keep moving forward in a straight line, so it did. With no brakes to slow it down, it pushed against the Hensley which pivoted to the right and slammed against the stops with enough force to cause the rear wheels of my Yukon to lose traction and skid several feet towards the curb. As soon as I started sliding I instinctively hit the brakes which allowed the trailer to pull back on the Hensley and immediately halted the spin. If we were going much faster we easily could have jacknifed the whole rig.

As I see it there were three major factors that attibuted to this incident:

1. I didn't apply (even lightly) the brakes to help control the trailer in a decelerating change-in-direction manouver.

2. The intersection was wet as it had recently started to rain. It had also been very recently paved and was covered in a mixture of oily water.

3. The short wheelbase of my Yukon worked against me as it turns VERY quickly. A longer WB vehicle wouldn't have been able to turn as quickly and might have prevented this incident.

I consider myself a conservative driver (expecially when it comes to towing) but this incident really caught me by surprise because of the low speed involved. What I've learned from this is the need to apply the brakes in pretty well any decelerating speed manouver in order to ensure the Hensley is well behaved. It also convinced me that there is no way I will ever tow the trailer on snow or ice.

I hope this helps to clarify things.

* This post was edited 02/04/06 12:02pm by Garfie|d *


2001 Airstream Safari 25SS tugged by 2011 Chevy Traverse 3.6L AWD
Hensley Arrow • DirecLink • Mckesh
Set up by Can-Am RV

Ron Gratz

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Posted: 02/04/06 08:30pm Link  |  Print  |  Notify Moderator

Hey Will,

Your thread made it to Page 50.

bettered wrote:

Ron says: "Because of the way the HA's linkage works, it is especially important to ensure a HA-equipped TT is not allowed to push on the TV."

To which I would suggest we append: "....in a cornering situation where one link has had a chance to go past the center position." I'm guessing this would be almost a 30 degree turn.

Ed,

I have stated previously (and Tim Luxon has confirmed with his diagrams -- somewhere back around Page 6) that, due to the HA's linkage geometry, the VPP moves about 20" to the side of the TV's longitudinal centerline when the angle between the TV and TT is about 4 degrees.

This means that, even with a relatively small angle between TT and TV, any forward thrust from the TT will be acting over a "steering lever arm" of more that 1.5 feet. In other words, any forward thrust from the TT would have a tendency to steer the TV. This is why it is important not to allow a HA-equipped TT to push against the TV no matter what the angle -- especially if the HA is being used to compensate for a short wheelbase.

Ron

Ron Gratz

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Posted: 02/04/06 09:01pm Link  |  Print  |  Notify Moderator

bettered wrote:

---This recent discussion is all and only about "slippery conditions." The Hensley can only "hit the stop" when either the TV or TT (or both) is skidding.

Ed,

With this, I must respectfully disagree. The discussion, which includes several accounts other than Garfie|d's, is not all and only about "slippery conditions". In fact, even in Garfie|d's incident,

"With no brakes to slow it down, it pushed against the Hensley which pivoted to the right and slammed against the stops with enough force to cause the rear wheels of my Yukon to lose traction and skid several feet towards the curb.",

there is no indication that either the TV or the TT was skidding until after the Hensley "slammed against the stops".

Ron

* This post was edited 02/04/06 09:26pm by Ron Gratz *

Ron Gratz

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Posted: 02/04/06 09:24pm Link  |  Print  |  Notify Moderator

Quote:

All you have to do is take your Hensley Arrow equipped rig out on a vacant stretch of road, and turn down the gain on the brake controller. Then brake while steering. Merely changing lanes while braking hard will do the trick.

The tongue will move either left or right as the linkage collapses, the trailer will stay directly behind the tow vehicle for the simple reason that it can't go anywhere else under those conditions.

And none ever have.

I'm guessing that the person who posted, Hensley jackknife, would disagree with these assertions.

bettered

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Posted: 02/05/06 06:26am Link  |  Print  |  Notify Moderator

Ron Gratz wrote:


I have stated previously (and Tim Luxon has confirmed with his diagrams -- somewhere back around Page 6) that, due to the HA's linkage geometry, the VPP moves about 20" to the side of the TV's longitudinal centerline when the angle between the TV and TT is about 4 degrees.

Ron


Wow! Thanks for the clarification Ron. At risk of re-opening the thread on a technical level, I'm wondering if the geometry/resultant force issue becomes critical as a result of the VPP's lateral travel reaching its extreme OR if it becomes significant when "hitting the stop" (collapse of one of the two links) occurs, causing a "jerk" load on the TV's rear wheels as was Garfield's experience. My expectation (not my experience) would be that the latter would be a more likely LOC event.

6MISFITZ

Fort Erie, ON, CANADA

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Posted: 02/05/06 09:05am Link  |  Print  |  Notify Moderator

Garfie|d wrote:

6MISFITZ wrote:

Ron, On my thread, there was a story from what happened to Garfield in a corner with his trailer, so I do agree that the hitch won't save me from every law of physics or that of a ham fisted maneuver by the driver and that towing requires more attention - no matter what hitch.


Gee, I think I was just insulted!!! LOL! [emoticon][emoticon][emoticon] (Kidding Mike!) [emoticon]
........
I consider myself a conservative driver (expecially when it comes to towing) but this incident really caught me by surprise because of the low speed involved. What I've learned from this is the need to apply the brakes in pretty well any decelerating speed manouver in order to ensure the Hensley is well behaved. It also convinced me that there is no way I will ever tow the trailer on snow or ice.

I hope this helps to clarify things.


Sorry Garfield, I assure you that comment was not directed at you and in retrospect, I should have written that sentence more carefully [emoticon].

We were not towing at the time but behind a trailer going through the narrow concrete gates (bollards) at the Peace Bridge 2 years back and that driver very unfortunately turned the tow vehicle too early causing the back of the trailer to swing wide into the concrete bollard and do some very significant damage to the side and back wall of the TT. In defense of that driver, it is a sharp right turn to make the 190 highway ramp once past the Peace Bridge bollard I was talking about.
So far it has not happened to me but I am very conscious of it every time I have to do a sharp turn and if in doubt, I use a spotter!

Mike.


Mom, Dad, 4 kids, 2 Camping Dogs
Express 2500 LS (135"WB) 6.0L, 4.10, G80, PYO wheels, HENSLEY & McKesh
--------------------
MISFITZ RACING
MFCC Member
Rallies Attended 4, 7 Un-Rallies


Ron Gratz

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Posted: 02/05/06 01:52pm Link  |  Print  |  Notify Moderator

bettered wrote:

---At risk of re-opening the thread on a technical level, I'm wondering if the geometry/resultant force issue becomes critical as a result of the VPP's lateral travel reaching its extreme OR if it becomes significant when "hitting the stop" (collapse of one of the two links) occurs, causing a "jerk" load on the TV's rear wheels as was Garfield's experience. My expectation (not my experience) would be that the latter would be a more likely LOC event.

Ed,

BOTH situations can result in jackknife forces and moments being applied to the TV if there is sufficient deceleration of the TV and the TT is not being braked sufficiently.

At an articulation of only a few degrees with the VPP at or close to its lateral extreme, TT thrust will tend to steer the TV. If the thrust is great enough or the TV has too short a wheelbase, a jackknife might result. This situation might be the more dangerous because an articulation of a few degrees can exist at or near highway speeds. This HA phenomenon could explain how the "Hensley jackknife" occurred.

The other phenomenon (which you have called, "hitting the stop") is likely to occur only at lower speeds because it requires an articulation angle of 15 degrees or more. At an articulation of more than 10 degrees, the HA's VPP has moved rearward close to the location of the ball coupler. This means the HA now is acting pretty much like a conventional hitch -- TT forces are being applied very close to the ball coupler. Except, there is one very important difference. If the TT is pushing against the HA and if there is "collapse" of the linkage, the "hitting the stop" will cause an impact load which can be considerably greater than the static push from the TT. It sounds very much as though this second HA phenomenon is what Garfie|d experienced.

Ron

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