Trailer Roof Shape And Tongue Weight - Fiberglass RV


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Old 11-03-2016, 12:52 PM   #1
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Trailer Roof Shape And Tongue Weight

The current Trailer Frontal Area topic reminded me of an allied question that Iíve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of itís roof was flat. The front half of the roof was also flat but was angled downward by (Iíd guess) somewhat less than 30ļ. 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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Old 11-03-2016, 06:30 PM   #2
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Originally Posted by minke View Post
The current Trailer Frontal Area topic reminded me of an allied question that Iíve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of itís roof was flat. The front half of the roof was also flat but was angled downward by (Iíd guess) somewhat less than 30ļ. 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.
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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Old 11-03-2016, 11:19 PM   #3
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Originally Posted by minke View Post
The current Trailer Frontal Area topic reminded me of an allied question that Iíve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of itís roof was flat. The front half of the roof was also flat but was angled downward by (Iíd guess) somewhat less than 30ļ. 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.
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.
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Old 11-04-2016, 07:36 AM   #4
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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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Old 11-04-2016, 08:06 AM   #5
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I'm wondering if there is a natural lift effect that this shape is intended to counter?
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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Old 11-04-2016, 12:06 PM   #6
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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.



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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Old 11-04-2016, 12:26 PM   #7
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Originally Posted by minke View Post
The current Trailer Frontal Area topic reminded me of an allied question that Iíve had for a while. This summer I noticed a particular stickie near home a few times. The rear half of itís roof was flat. The front half of the roof was also flat but was angled downward by (Iíd guess) somewhat less than 30ļ. 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.
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.
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Old 11-04-2016, 12:49 PM   #8
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Assumption: trailer is a rectangular prism.

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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)....
I hadn't realized that. At cruising speed tongue weight is diminished.


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... An inclined front on a trailer reduces the unloading effect due to wind hitting the front of the trailer, ...
OK, the tongue weight won't be diminished quite as much with that wedge gone, but still less than static tongue weight.


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... 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. ...
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.


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... The overall effect of the inclined front on the hitch weight would be less than that of the flat front.
Without anything but ignorance on my side I come to the opposite conclusion.
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Old 11-04-2016, 01:59 PM   #9
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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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Old 11-04-2016, 02:45 PM   #10
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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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Old 11-06-2016, 11:52 PM   #11
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Intresting

How about this...It Looks Cool..
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