So after installing my new upgraded axles and springs, my WD needed a little tweak as the TT sits a tad higher.While making the adjustment, I got to thinking...It is often advised to error on the side of tounge low... My thought that I have never seen discussed here is that,, If it is tounge low, then the roof of the TT will act like a large spoiler creating downforce... I know it's not much of an angle (usually) but it is a very lage surface, and wind speeds can easily exceed 100MPH when towing into the wind.So how much downforce would this add? Would it be enough to exceed the weight ratings of axles and tires? Especially since the industry tends to skimp on these components?This could perhaps explain some failures that were unexplainable in the past.Thoughts?

It's not a math question it's an aerodynamics question. Not that a brick has much aerodynamics but the front of the roof will be in a low pressure area which will decrease the tongue weight and then the air hitting the back of the trailer's roof will take even more weight off of the tongue.*Have you ever seen the rubber roof of a trailer ballooning up in the front as it's going down the road from the air off the front of the trailer? Based on the answer below it is obvious you are not a pilot.

Ivylog wrote:It's not a math question it's an aerodynamics question. Not that a brick has much aerodynamics but the front of the roof will be in a low pressure area which will decrease the tongue weight and then the air hitting the back of the trailer's roof will take even more weight off of the tongue.I am sure that the answer can be figured mathmatically.I am also sure that it will impart downforce.Just try sticking your hand out the window on the highway at different angles to see what effect the wind has on it.

It certainly can be figure out mathmatically, probably to about 10 decimal places but it won't mean much. The angle on the front of your trailer is relatively small meaning a direct horizontal wind force will impact very little of its force downward, most will be backwards... :-( As the previous poster indicated, the downward force will be counter by a "lack of force" over the lead edge of the roof... just like a aircraft wing... resulting in some lift. Hence, the difference will be minimal but certainly a good exercise for some engineering student to get bonus marks in a dynamics course.

I was taking aerodynamics in my younger years and the truth is that when it comes to air drag, the mathematics don't work. The subject is so tricky that only wind-tunnels with smoke nozzles and hours spend on observation can answer the question with not much doubt. Coming to trailer down or up forces, the rule is that air going with higher speed is having low density, than air going with low speed. So my first guess would be that air deflected on the roof of the trailer goes faster than air pushed under suspension. Meaning the trailer will get some aerodynamic lifting. Still 50 or even 100lb of lifting, or downforce is nothing to trailer weight. Nice spending of time do.

Huntindog wrote:So after installing my new upgraded axles and springs, my WD needed a little tweak as the TT sits a tad higher.While making the adjustment, I got to thinking...It is often advised to error on the side of tounge low... My thought that I have never seen discussed here is that,, If it is tounge low, then the roof of the TT will act like a large spoiler creating downforce... I know it's not much of an angle (usually) but it is a very lage surface, and wind speeds can easily exceed 100MPH when towing into the wind.So how much downforce would this add? Would it be enough to exceed the weight ratings of axles and tires? Especially since the industry tends to skimp on these components?This could perhaps explain some failures that were unexplainable in the past.Thoughts?It has nothing to do with "down force".But is DOES affect something called CENTER OF GRAVITY (COG).Lowering the tongue effectively moves the COG TOWARDS the tongue which can raise the weight slightly on the tongue. But it isn't all about tongue weight, with COG moving slightly forward of the axles tends to help make for a more stable tow.Raising the tongue effectively moves the COG towards the rear which will lower the weight slightly on the tongue. The downside is the COG will move closer to the axles and some cases on or over the axles making for a rather unstable and unpredictable tow.

Math question | Good Sam Community

Ivylog
Explorer III
Sep 02, 2015
It's not a math question it's an aerodynamics question. Not that a brick has much aerodynamics but the front of the roof will be in a low pressure area which will decrease the tongue weight and then the air hitting the back of the trailer's roof will take even more weight off of the tongue.

*Have you ever seen the rubber roof of a trailer ballooning up in the front as it's going down the road from the air off the front of the trailer? Based on the answer below it is obvious you are not a pilot.
Huntindog
Explorer
Sep 02, 2015
Ivylog wrote:
It's not a math question it's an aerodynamics question. Not that a brick has much aerodynamics but the front of the roof will be in a low pressure area which will decrease the tongue weight and then the air hitting the back of the trailer's roof will take even more weight off of the tongue.
I am sure that the answer can be figured mathmatically.
I am also sure that it will impart downforce.

Just try sticking your hand out the window on the highway at different angles to see what effect the wind has on it.
budwich
Explorer
Sep 02, 2015
It certainly can be figure out mathmatically, probably to about 10 decimal places but it won't mean much. The angle on the front of your trailer is relatively small meaning a direct horizontal wind force will impact very little of its force downward, most will be backwards... :-( As the previous poster indicated, the downward force will be counter by a "lack of force" over the lead edge of the roof... just like a aircraft wing... resulting in some lift. Hence, the difference will be minimal but certainly a good exercise for some engineering student to get bonus marks in a dynamics course.
Kayteg1
Explorer II
Sep 02, 2015
I was taking aerodynamics in my younger years and the truth is that when it comes to air drag, the mathematics don't work.
The subject is so tricky that only wind-tunnels with smoke nozzles and hours spend on observation can answer the question with not much doubt.
Coming to trailer down or up forces, the rule is that air going with higher speed is having low density, than air going with low speed.
So my first guess would be that air deflected on the roof of the trailer goes faster than air pushed under suspension.
Meaning the trailer will get some aerodynamic lifting.
Still 50 or even 100lb of lifting, or downforce is nothing to trailer weight.
Nice spending of time do.
Gdetrailer
Explorer III
Sep 02, 2015
Huntindog wrote:
So after installing my new upgraded axles and springs, my WD needed a little tweak as the TT sits a tad higher.
While making the adjustment, I got to thinking...
It is often advised to error on the side of tounge low... My thought that I have never seen discussed here is that,, If it is tounge low, then the roof of the TT will act like a large spoiler creating downforce... I know it's not much of an angle (usually) but it is a very lage surface, and wind speeds can easily exceed 100MPH when towing into the wind.

So how much downforce would this add? Would it be enough to exceed the weight ratings of axles and tires? Especially since the industry tends to skimp on these components?

This could perhaps explain some failures that were unexplainable in the past.

Thoughts?

It has nothing to do with "down force".

But is DOES affect something called CENTER OF GRAVITY (COG).

Lowering the tongue effectively moves the COG TOWARDS the tongue which can raise the weight slightly on the tongue. But it isn't all about tongue weight, with COG moving slightly forward of the axles tends to help make for a more stable tow.

Raising the tongue effectively moves the COG towards the rear which will lower the weight slightly on the tongue. The downside is the COG will move closer to the axles and some cases on or over the axles making for a rather unstable and unpredictable tow.
Kayteg1
Explorer II
Sep 02, 2015
Now this can be a math.
Roughly center of gravity of the trailer is maybe a foot, maybe 2 above pivoting point.
Depends on the length of the trailer, moving the tongue up or down by 2-4 inches will move center of gravity 1/4" to 1/2" horizontally.
How much difference that 1/4" makes?
TomG2
Explorer
Sep 02, 2015
I wonder if a real aerodynamic engineer will come on here and explain the forces involved and the nonsense put forth so far. The wind tunnel is the answer and I don't know anyone who has one at their disposal. Kayteg is on the right track.
Huntindog
Explorer
Sep 02, 2015
I really didn't want a disscussion on the aerodymanics of TTs.
Most TTs are not shaped anything like a wing, so I am not sure what the thinking is there.

But if aerodynamics must be considered, I want to make this observation.
Most TVs nowdays have spoilers or air dams to keep the air passing under them to a minimum. Most TTs will have a lot more ground clearance th than the TV towing them. I would think that this would create a low pressure area under the TT that would ten to increase downforce,,, But it probably doesn't because the sides of the TT allow air to get in, filling the low pressure area. At any rate, I do not buy the wing theory. And the underside of a TT is often pretty dirty as far as airflow.
Of course if the lifting of the TT is right, then that means that the 1/2 fans can tow even more! :B

I haven't tried this yet, But if I were to take a rectangular box, and hold it out the window on the highway in different positions, then that would be a pretty good test of my thoughts. I think I know what will happen
TomG2
Explorer
Sep 02, 2015
The effect you are asking about is totally about aerodynamics and the application of Bernoulli's principle. I am thinking that there would be a slight amount of lift involved with a lowered front face, just as there is in an airplane wing. The kicker is that the drag associated with towing a travel trailer makes looking for other changes tiny in comparison.
GrandpaKip
Explorer II
Sep 02, 2015
Look up the Bernoulli Principle or Bernoulli Effect. Unless the angle presented to the wind is very severe, there should be a certain amount of lift, though because an RV is not smooth top or bottom, it is probably negligible.
Lots of fun and interesting experiments can be found to demonstrate this.
Huntingdog, my guess is the box would fly out of your hands at highway speeds.;-) that big sail will make most other forces insignificant.