Ron Gratz
full time RVer
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Joined: 12/27/2003
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Willald wrote:I did read through all your numbers, Ron, and most of it did sound accurate. However, I think that given all the wind resistance a trailer has, tire friction, weight, etc., the 'pulling' affect we've described, MUST account for considerably more than a .07% or 1# increase/improvement. I don't pretend to be able to prove such, though, except to say the following:
Think about when you're pulling your trailer down the road, all the pulling/resistance it puts on the tow vehicle. Enough, to typically drop your mileage in half! Imagine how much force it'd take, for you to pull the trailer forward .5" closer to the truck (assuming there was enough 'slack' in your hitch to allow such). That would take a LOT of force, seems like a good bit more than any 1# or .07%.
I'm sure I'm missing some technical detail, though, which Ron will bring up. Soooo, have at it, Ron
Will, I don't need to imagine how much force it would take -- I can calculate how much.
The technical detail you are missing is the fact that the additional force require to move the TT closer to the TV has nothing to do with the drag forces on the TT. The additional force only depends on the mass of the TT and the magnitude of the acceleration needed to get it to move closer to the TV. The key word is "additional". The baseline drag force depends on speed and remains constant. The additional force is equal to mass (of the TT) times its acceleration.
Lets assume a swing of 1 degree and a TT weighing 6440#. The mass (mass = weight/gravity) of the TT is 6440# / 32.2ft/sec/sec = 200 slugs. Now assume this mass is moved at constant acceleration so that it moves forward 0.1 foot in 1 second. The required acceleration is 0.2 ft/sec/sec. The required force (force = mass * acceleration) is 200 * 0.2 = 40#.
Now, remember, the 40# is the increase in the longitudinal component of tongue load. The corresponding increase in the lateral component of force is 40 * tangent(1 degree) = 0.7# (I was generous when I rounded it to 1#.)
Will, if the increase in longitudinal force due to the forward movement of the TT relative to the TV is anywhere near as large as you seem to think it is, it would cause the TV to decelerate and you could feel it (even if you are driving an Excursion).
You can check out what I'm saying by getting something heavy (concrete block, bucket of water, etc.) and standing on a scale with it. Lets assume the added weight is 32.2# (1 slug). If you stand on the scale without raising the weight, the scale will read your weight plus 32.2#. Assume you raise the weight 1 foot in 1 second at constant acceleration. The acceleration is 2 ft/sec/sec. The added force is 1 slug * 2 ft/sec/sec = 2#. The scale, if accurate enough, would read your weight + 32.2 + 2 lbs. Please note, this acceleration is ten times greater than the acceleration of the TT which moves ahead 1.2" in 1 second.
And, I don't know what else to say.
Ron
* This post was
edited 09/06/05 06:41pm by Ron Gratz *
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bettered
UpCountry SC
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Joined: 07/26/2004
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TeryT wrote: Still would like to see that trailer mock-up on dollies - I'd buy the beer!
Oh brother. The two guys who are interested in putting casters under the the TT wheels and pushing it sideways are on the east coast and TeryT wants to buy us beer in Scottsdale. Thanks, Tery, but I'm no fan of warm beer..
Yuk, yuk
But I'm skeptical. I want to believe this would work, but Ron's analysis is making me think I'd prove myself to be too emotionally involved with my hitch.
Ed
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
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jdwhittaker
York, SC
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Joined: 06/01/2005
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bettered wrote:TeryT wrote: Still would like to see that trailer mock-up on dollies - I'd buy the beer!
Oh brother. The two guys who are interested in putting casters under the the TT wheels and pushing it sideways are on the east coast and TeryT wants to buy us beer in Scottsdale. Thanks, Tery, but I'm no fan of warm beer..
Yuk, yuk
But I'm skeptical. I want to believe this would work, but Ron's analysis is making me think I'd prove myself to be too emotionally involved with my hitch.
Ed
Wow, everyone's been busy.
Ed, I'll buy the beer...if you have any idea where to get the dollies. I'm quite sure that the swiveling dollies will work providing that they roll freely enough to push around a 3 ton TT by hand.
The video that Tim posted of me swinging my hitch through it's range of motion while mounted only to my stinger is the only way that the hitch can move. Doesn't matter if it has a come along pulling on it...doesn't matter if it has nothing mounted to it, and doesn't matter if it has a trailer mounted to it, if it is to move it must move the way that video shows. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile") It's resistance to sway comes from the unusual path of motion that it must follow, and the fact that the TT's tires resist that type of motion, because it's basically a sideways skidding motion for the TT.
Speaking of come alongs... where's Milt? Hope he didn't get mad and leave.
The promo mockup video from Hensley is an accurate depiction of the HA's motion as well, except for the fact that it is a mockup, and it shows the hitch very favorably due to it's geometry. Notice the direction that the guy is pushing...down, nearly as much as sideways. The downward force puts enough friction on the rear TV and TT casters (which I would bet are fixed, not swiveling), that they can't slide sideways.
Dave
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TnAnFLA
Nokomis FL
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Joined: 02/18/2005
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Quote:BTW, some of the most useful parts of this thread are found back on those pages. I found it extremely helpful to review that part of the thread last week.
I think Tim is exactly right. I also went back and have reviewed darn near this whole thread in the last couple of days (ok, I'm a glutton for punishment). That includes a review of the Hensley pantent documents.
After all that review, I'm convinced that, video clips notwithstanding, Ron & Tim have this thng down cold. The key, for me at least, is the drastic reduction in the moment applied to the TV via the Hensley vice what's felt by the TV with a conventional hitch. And it's all due to the difference in the length of the "lever arm" provided by the linkage. Which, in my view isn't and can't be "locked". Some of the later discussion on the thread ( the 1# or so difference in forces) ends up being in the noise compared to the effect of the shift in pivot point.
Since Ron & I went around a bit about the way the struts are "tightened" (compressed vs. tensioned), and the patent documents, upon review, clear imply they are under tension, I went down to the trailer this afternoon to see if anything else had changed vis-a- vis the patent. Nothing else has.
By the way, if you try to read the Feb. 2005 patent document to figure out how the Hensley works, you'll waste your time. The hitch descibed in that patent is a whole different beast than what they currently sell.
Andy
31' Itasca Impulse
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bettered
UpCountry SC
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Joined: 07/26/2004
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Don't want to be argumentative Andy (I've read the entire thread too) but the strut bars are in compression. You increase the pressure against the head until it's square to the TT centerline. Both bars are pushing toward the head.
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Ron Gratz
full time RVer
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Joined: 12/27/2003
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Ed,
Andy did not say the struts are in tension. He has been saying all along that they are in compression.
His comment about the struts being in tension pertains to what the patent document implies. The patent document describes the struts as a kind of turnbuckle. The real struts are different from those described in the patent document.
Ron
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smthbros
WI
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Joined: 02/15/2004
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So if we used the Hensley "marketing video" as a guide and performed the same demonstration using a Pulrite, would it also appear to be locked from the TT end? Jim Smith
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Ron Gratz
full time RVer
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Joined: 12/27/2003
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Yes, if the PR's pivot point were in line with the "TV's" rear wheels, the result would be the same.
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drfife
Dallas, Texas, USA
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Joined: 11/02/2002
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Ron Gratz wrote:...Andy did not say the struts are in tension. He has been saying all along that they are in compression.
His comment about the struts being in tension pertains to what the patent document implies. The patent document describes the struts as a kind of turnbuckle. The real struts are different from those described in the patent document...
Ron, actually the struts are static if the hitch is not towing.
The struts can be in tension or compression while towing depending on the direction of the applied forces.
The struts are nothing more than fixed length rods.
Yes, you snug them up during installation, but they should not be forced into compression.
Russell
'12 GMC Sierra 3500HD SRW
'13 Excel Winslow 34IKE
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TeryT
Scottsdale AZ
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Joined: 07/04/2003
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OK, I've probably heard enough. I know it's only been 47 pages, but I think I caught the drift (not to be confused with sway) of the conversation.
I know you-all will miss me, but . . . (let me know if you want me to buy the "warm" beer for the demo)
Mighty 4Runner Sport V8 4x4 - over 200k
Hensley Hitch
McKesh Mirrors, Geolandar G015 Tires
Hopkins Insight Brake Controller
Tranny: Hayden Cooler/Fan & CyberDyne Gauge
Mobil 1 Full Synthetic fluids everywhere!
Rockwood 2502 Ultralight TT (3600 lb. dry)!
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