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11-03-2016, 12:52 PM
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#1
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Senior Member
Name: alan
Trailer: looking
Colorado
Posts: 264
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Trailer Roof Shape And Tongue Weight
The current Trailer Frontal Area topic reminded me of an allied question that I’ve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of it’s roof was flat. The front half of the roof was also flat but was angled downward by (I’d guess) somewhat less than 30º. What I wonder about is what is the effect of roof shape on tongue weight at cruising speed? In this perhaps extreme case static measurements may indicate a safe tongue weight but at e.g. 60 MPH perhaps it becomes unsafe.
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11-03-2016, 06:30 PM
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#2
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Senior Member
Name: Kelly
Trailer: Trails West
Oregon
Posts: 3,047
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Quote:
Originally Posted by minke
The current Trailer Frontal Area topic reminded me of an allied question that I’ve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of it’s roof was flat. The front half of the roof was also flat but was angled downward by (I’d guess) somewhat less than 30º. What I wonder about is what is the effect of roof shape on tongue weight at cruising speed? In this perhaps extreme case static measurements may indicate a safe tongue weight but at e.g. 60 MPH perhaps it becomes unsafe.
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There are some CAD programs that can analyze wind tunnel effects, maybe you can locate someone to help test out your theory with basic building block shapes.
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11-03-2016, 11:19 PM
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#3
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Senior Member
Name: John
Trailer: Roamer 1
Smith Valley, Nevada
Posts: 2,880
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Quote:
Originally Posted by minke
The current Trailer Frontal Area topic reminded me of an allied question that I’ve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of it’s roof was flat. The front half of the roof was also flat but was angled downward by (I’d guess) somewhat less than 30º. What I wonder about is what is the effect of roof shape on tongue weight at cruising speed? In this perhaps extreme case static measurements may indicate a safe tongue weight but at e.g. 60 MPH perhaps it becomes unsafe.
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Interesting thought. But I suspect that if it went from "safe" to 'unsafe" at speed that is was too close to unsafe before starting out. There is a lot of talk about what TV will handle what trailer and it seems many TVs are near their max, or should I say, undersized for best safety to begin with.
It would be interesting to see some real test numbers on this.
__________________
I only exaggerate enough to compensate for being taken with a grain of salt.
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11-04-2016, 07:36 AM
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#4
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Senior Member
Name: Jon
Trailer: 2008 Scamp 13 S1
Arizona
Posts: 11,925
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I'm wondering if there is a natural lift effect that this shape is intended to counter?
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11-04-2016, 08:06 AM
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#5
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Senior Member
Name: alan
Trailer: looking
Colorado
Posts: 264
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Quote:
Originally Posted by Jon in AZ
I'm wondering if there is a natural lift effect that this shape is intended to counter?
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Good question. My only experience was from 60+ years ago when I'd stick my hand out of my parents car window (only if my mother wasn't there!) and change it's angle to the wind. Air at 60 MPH is a formidable force.
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11-04-2016, 12:06 PM
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#6
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Senior Member
Name: Kathleen (Kai: ai as in wait)
Trailer: Amerigo FG-16 1973 "Peanut"
Greater Seattle Metropolitan Area, Washington
Posts: 2,566
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Quote:
Originally Posted by minke
Good question. My only experience was from 60+ years ago when I'd stick my hand out of my parents car window (only if my mother wasn't there!) and change it's angle to the wind. Air at 60 MPH is a formidable force.
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I used to do that, too! It is, indeed, formidable! And back when I was a child (and pterodactyls darkened the skies,) we would drive 75 miles an hour--even more formidable! Both the lift up and the push down.
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11-04-2016, 12:26 PM
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#7
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Senior Member
Name: Dave W
Trailer: Escape 19 and Escape 15B
Alberta
Posts: 523
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Quote:
Originally Posted by minke
The current Trailer Frontal Area topic reminded me of an allied question that I’ve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of it’s roof was flat. The front half of the roof was also flat but was angled downward by (I’d guess) somewhat less than 30º. What I wonder about is what is the effect of roof shape on tongue weight at cruising speed? In this perhaps extreme case static measurements may indicate a safe tongue weight but at e.g. 60 MPH perhaps it becomes unsafe.
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Considering simple statics, the effect of wind on the "flat" front of a trailer will be to reduce the weight acting on the hitch (due to a moment acting about the wheels). An inclined front on a trailer reduces the unloading effect due to wind hitting the front of the trailer, but also adds a downward wind force component that actually puts additional load on the hitch. The overall effect of the inclined front on the hitch weight would be less than that of the flat front.
__________________
Dave W - 2013 Escape 19', 2013 Escape 15B and 2011 Toyota FJ Cruiser
"You've got to be very careful if you don't know where you are going, because you might not get there." - Yogi Berra
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11-04-2016, 12:49 PM
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#8
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Senior Member
Name: alan
Trailer: looking
Colorado
Posts: 264
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Assumption: trailer is a rectangular prism.
Quote:
Originally Posted by Ice-breaker
Considering simple statics, the effect of wind on the "flat" front of a trailer will be to reduce the weight acting on the hitch (due to a moment acting about the wheels)....
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I hadn't realized that. At cruising speed tongue weight is diminished.
Quote:
Originally Posted by Ice-breaker
... An inclined front on a trailer reduces the unloading effect due to wind hitting the front of the trailer, ...
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OK, the tongue weight won't be diminished quite as much with that wedge gone, but still less than static tongue weight.
Quote:
Originally Posted by Ice-breaker
... An inclined front on a trailer reduces the unloading effect due to wind hitting the front of the trailer, but also adds a downward wind force component that actually puts additional load on the hitch. ...
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My guess, based on a complete absence of facts and experience, is that the downward force from the inclined front roof would dominate the upward force on the tongue from the front surface.
Quote:
Originally Posted by Ice-breaker
... The overall effect of the inclined front on the hitch weight would be less than that of the flat front.
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Without anything but ignorance on my side I come to the opposite conclusion.
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11-04-2016, 01:59 PM
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#9
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Senior Member
Trailer: Scamp 16 ft Side Dinette
Posts: 1,279
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Dont blow a gasket on this one. Your tow vehicle breaks the wind enough that any effect on the trailer is negligible.
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11-04-2016, 02:45 PM
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#10
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Senior Member
Name: Dave
Trailer: Casita SD17 2006 "Missing Link"
California
Posts: 3,738
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Quote:
Originally Posted by Wayne Collins
Dont blow a gasket on this one. Your tow vehicle breaks the wind enough that any effect on the trailer is negligible.
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11-06-2016, 11:52 PM
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#11
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Member
Name: Randy
Trailer: In the Market
Oregon
Posts: 51
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Intresting
How about this...It Looks Cool..
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