Teardrops n Tiny Travel Trailers

What difference if any does the shape of the front of the trailer make? Primarily on gas mileage and drag on your tow vehicle. How much does it help to have a pointed front and/or a dropped nose? Thanks. . .


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Not nearly as much as a lower height profile does.

But still significant.

Too many variables to put a MPG number on it, but I'm guessing a good 10-20% of the differential.

And more stable in high winds, less blown around by the semi's.

But then just backing off on your highway speeds accomplishes all those goals as well.

To a certain degree but other factors can out weigh it. Alone or in combination.
Go to the website ecomodder. They have a section on trailer design, airflow etc.
It is very enlightening, though can be difficult to read thru.
In a nutshell, typical teardrop trailer is not that aerodynamic though one would think so.
A round nose trailer is best.
A square back end that tapers top and sides, I think 12 degrees (?) helps a great deal.
Rounded top edges, think airstream, provide stability and aerodynamics.
Some there say a v nose trailer is good, but then catches more wind in a cross flow direction which thereby creates more drag.

It is a bit difficult to determine without a wind tunnel eg practical test.

The drag (a force resisting your motion) is

Fd = Cd * (1/2) * ρ * V**2 * A

where V is the velocity, A is cross sectional area, ρ is the density of the fluid, and Cd is the drag coefficient of the object.

The biggest issue is cross sectional area. The bigger the area, the more drag. To a large extend, the cross sectional area is the combination of the towing vehicle (TV) and the trailer. All things being equal, if the trailer is completely blocked by the TV, it presents no additional drag. If it is bigger, it is adding drag. Think Formula 1 race car versus an SUV/mini van. Bigger cross sectional area is more drag for any particular shape.

The next issue is the drag coefficient (Cd) of objects that your are hauling or ability of fluid to flow around an object. The lower the number, the better. A cube is worst ( Cd = 1). A round nose is better (Cd=0.5) A wing is optimal Cd=0.04; a half wing ( Cd=0.09). How much is saved by rounding the edges of a box can be debated. Again, Formula 1 - almost a wing versus a mini van - almost a cube. To a large extent this is also a combination of the TV and the trailer. Granted we are asking about how much more drag will be added by the trailer.

Another issue is drag due to turbulence. This would have to be the effects of the air flowing over and behind the TV; into/out of the tongue area; flow on to the front of the trailer from the TV; and flow under the vehicles which will create more drag, raise your Cd. Ideally, you want your TV and trailer to be one solid object, so air does not flow between the two vehicles.This is why semis have various panels to redirect/smooth the air flow. I have seen that these panel can reduce the effective Cd by half. I have no idea how one determines these numbers for a TV and trailer without a wind tunnel test or a computer modelling system or trial and error. It is possible that these loses could wipe out all other gains. In the extreme -- image a really long tongue length, your TV and trailer will behave like two separate vehicles, greatly increasing your drag. I have seen some attempts to add screening to smooth the flow from TV to trailer -- could not say that that works or helps.

Finally, there is the drag due to the end of your trailer. A flat boxy back increases your drag the most. A 30 degree slope can reduce this drag significantly. You see this best when following vehicles in the rain, the amount of spray as you pass. You can see a big difference with the semis with those tail panels.

A nice simple example at https://docs.lib.purdue.edu/cgi/viewcon ... techsummit

In case no one noticed, velocity increases the drag. Slowing down can greatly reduce your drag.

Awesome information. Thank you troubleScottie.

McDave

troubleScottie wrote:It is a bit difficult to determine without a wind tunnel eg practical test.

The drag (a force resisting your motion) is

Fd = Cd * (1/2) * ρ * V**2 * A

where V is the velocity, A is cross sectional area, ρ is the density of the fluid, and Cd is the drag coefficient of the object.

The biggest issue is cross sectional area. The bigger the area, the more drag. To a large extend, the cross sectional area is the combination of the towing vehicle (TV) and the trailer. All things being equal, if the trailer is completely blocked by the TV, it presents no additional drag. If it is bigger, it is adding drag. Think Formula 1 race car versus an SUV/mini van. Bigger cross sectional area is more drag for any particular shape.

The next issue is the drag coefficient (Cd) of objects that your are hauling or ability of fluid to flow around an object. The lower the number, the better. A cube is worst ( Cd = 1). A round nose is better (Cd=0.5) A wing is optimal Cd=0.04; a half wing ( Cd=0.09). How much is saved by rounding the edges of a box can be debated. Again, Formula 1 - almost a wing versus a mini van - almost a cube. To a large extent this is also a combination of the TV and the trailer. Granted we are asking about how much more drag will be added by the trailer.

Another issue is drag due to turbulence. This would have to be the effects of the air flowing over and behind the TV; into/out of the tongue area; flow on to the front of the trailer from the TV; and flow under the vehicles which will create more drag, raise your Cd. Ideally, you want your TV and trailer to be one solid object, so air does not flow between the two vehicles.This is why semis have various panels to redirect/smooth the air flow. I have seen that these panel can reduce the effective Cd by half. I have no idea how one determines these numbers for a TV and trailer without a wind tunnel test or a computer modelling system or trial and error. It is possible that these loses could wipe out all other gains. In the extreme -- image a really long tongue length, your TV and trailer will behave like two separate vehicles, greatly increasing your drag. I have seen some attempts to add screening to smooth the flow from TV to trailer -- could not say that that works or helps.

Finally, there is the drag due to the end of your trailer. A flat boxy back increases your drag the most. A 30 degree slope can reduce this drag significantly. You see this best when following vehicles in the rain, the amount of spray as you pass. You can see a big difference with the semis with those tail panels.

A nice simple example at https://docs.lib.purdue.edu/cgi/viewcon ... xt=polytec
In case no one noticed, velocity increases the drag. Slowing down can greatly reduce your drag.

_+1 0n slowing down if we are going to live in these things and carry our toys they are never going to be anywhere near aerodynamic.You can study physics till your blue in the face but your still going to get 12 mpg if your lucky

The formula for aerodynamic drag is for "clean" air. A trailer will be in turbulent air behind the tow vehicle. The turbulent air can make the Cd less relevant and the cross-sectional area more relevant.

Airstream trailers do get (a little) better gas mileage than "typical" travel trailers. The better mileage is attributable somewhat to the lower Cd of the "bullet shape" front, but is more attributable the decrease in cross-sectional area by removing the "corners" of the cross-section. (A typical travel trailer has a rectangular cross-section; Airstreams have an ovoid shape.)

So not really a lot of difference?


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Hit-n-Miss wrote:So not really a lot of difference?

Right, not much difference.
Probably easily detectible by engineers at a test track, but not likely anything you would notice at the gas pump unless you keep pretty careful records over thousands of miles of towing.

I'm told that the rear of the trailer has a big factor in efficiency..If it's straight flat at the back can cause a type of suction from the way the wind exits the trailer. That's why you'll see many trailer with what are called vortex generators

al

troubleScottie wrote:It is a bit difficult to determine without a wind tunnel eg practical test.

The drag (a force resisting your motion) is

Fd = Cd * (1/2) * ρ * V**2 * A

where V is the velocity, A is cross sectional area, ρ is the density of the fluid, and Cd is the drag coefficient of the object.

The biggest issue is cross sectional area. The bigger the area, the more drag. To a large extend, the cross sectional area is the combination of the towing vehicle (TV) and the trailer. All things being equal, if the trailer is completely blocked by the TV, it presents no additional drag. If it is bigger, it is adding drag. Think Formula 1 race car versus an SUV/mini van. Bigger cross sectional area is more drag for any particular shape.

The next issue is the drag coefficient (Cd) of objects that your are hauling or ability of fluid to flow around an object. The lower the number, the better. A cube is worst ( Cd = 1). A round nose is better (Cd=0.5) A wing is optimal Cd=0.04; a half wing ( Cd=0.09). How much is saved by rounding the edges of a box can be debated. Again, Formula 1 - almost a wing versus a mini van - almost a cube. To a large extent this is also a combination of the TV and the trailer. Granted we are asking about how much more drag will be added by the trailer.

Another issue is drag due to turbulence. This would have to be the effects of the air flowing over and behind the TV; into/out of the tongue area; flow on to the front of the trailer from the TV; and flow under the vehicles which will create more drag, raise your Cd. Ideally, you want your TV and trailer to be one solid object, so air does not flow between the two vehicles.This is why semis have various panels to redirect/smooth the air flow. I have seen that these panel can reduce the effective Cd by half. I have no idea how one determines these numbers for a TV and trailer without a wind tunnel test or a computer modelling system or trial and error. It is possible that these loses could wipe out all other gains. In the extreme -- image a really long tongue length, your TV and trailer will behave like two separate vehicles, greatly increasing your drag. I have seen some attempts to add screening to smooth the flow from TV to trailer -- could not say that that works or helps.

Finally, there is the drag due to the end of your trailer. A flat boxy back increases your drag the most. A 30 degree slope can reduce this drag significantly. You see this best when following vehicles in the rain, the amount of spray as you pass. You can see a big difference with the semis with those tail panels.

A nice simple example at https://docs.lib.purdue.edu/cgi/viewcon ... techsummit

In case no one noticed, velocity increases the drag. Slowing down can greatly reduce your drag.

Good post! I discussed this exact topic with a Ford engineer the other day and you are spot on. We came to similar conclusions. However- he was emphatic that rounding the front corners of the CT would be noticeably significant) we were discussing my slant nose v with square corners at the time.

Also- thinking back on historical aero work; there are two ways to study aero without a wind tunnel; one is a length of tube with a fluid inside that can act as a mono meter; tape it to different areas to study the pressure of the air at the tube end. This sounds like a colossal PITA, however, so here is the better way— tape small strings in a grid pattern across the area you want to understand; you can learn a great deal by watching how they act, which way they sail, etc as you drive.

Howdy All;

I used to drive Over the Road, and sometimes pulled a flatbed trailer.
The company that I drove for was adding a 6" steel plate to the front of
these. They were the type with a front wall. Well, the result was my fuel
mileage went down by 3 mpg with nothing on the trailer except that 6"
chunk of steel. It was supposed to be something like an Air Dam for the
containers that we were going to haul. After seeing the loss in mpg numbers
they had them cut off. Surprising how even a small thing can effect overall
performance.

By-the-way, 3 mpg in the mid 1990's was effectively cutting my mpg's in half
at that time.

hank

Least trailer wind resistance is the small airstream 2 person camper.
Look at its design.