Aerodynamic drag on the escape trailer?

[Hilola]

While I never could measure it, I assume drag coefficient was pretty good in our HiLo trailer.

[Brian B-P]

Originally Posted by EdColorado

And if you want to increase overall aerodynamic drag while towing, add a roof rack of some type to your tow vehicle and watch your mileage go down

Yes and no. We have a large Thule carrier and a 17-foot canoe. We have carried both (one at a time) on the van, with and without the trailer. When not towing, the aero effect is noticeable to the driver, but while towing it's not. These rooftop items both have a reasonable aerodynamic shape, and fit within the frontal area profile of the trailer.

The Consumer Reports article talks about fuel economy changes in miles per gallon from various causes, mostly without reference to the baseline fuel economy. In the rooftop section, the baseline is given for the Accord (the bike rack example), but not for the Camry (the carrier example). That doesn't make sense, because (for instance) a 5 MPG decrease in fuel economy is only a 50% increase of fuel consumption if you started at 15 MPG, a 100% of fuel consumption if you started at 10 MPG, and an 800% increase if you started at 6 MPG. The numbers without proper context aren't good for much.

In more useful terms, in their examples for a 2013 Honda  Accord @ 65 MPH:

• nothing on roof: 2.38 US gallons per hundred miles consumed
• empty bike rack: 13% increase (over nothing on roof) or an additional 0.32 US gallons per hundred miles
• empty bike rack with deflector: 20% increase or an additional 0.48 US gallons per hundred miles
• rack with bikes: 55% increase or an additional 1.32 US gallons per hundred miles

Bikes are pretty effective parachutes.

The practice in Canada (and Europe) of specifying fuel economy in consumption terms (litres burned per hundred kilometres driven), rather than in distance per unit of fuel, makes these comparisons easier.

If you look at the drag of your trailer the same way, you can see how much extra fuel it takes to haul it. Miles per gallon doesn't tell you that directly. Our van burns about 10 litres per hundred kilometres (L/100 km) on highway trips without the trailer, and about 16 L/100 km with it, so it costs us about 6 litres (about C$6 currently) to drag it a hundred kilometres.

[Brian B-P]

Originally Posted by Hilola

While I never could measure it, I assume drag coefficient was pretty good in our HiLo trailer.

I suspect that the drag coefficient is mediocre, but the frontal area is low so the total drag is not bad. It's largely in the "shadow" of the tow vehicle, but sticking out each side will be costly, in drag terms.

Total aerodynamic drag depends on the coefficient of drag and the frontal area (and the speed, and the properties of the fluid).

[Hilola]

Originally Posted by Brian B-P

I suspect that the drag coefficient is mediocre, but the frontal area is low so the total drag is not bad. It's largely in the "shadow" of the tow vehicle, but sticking out each side will be costly, in drag terms.

Total aerodynamic drag depends on the coefficient of drag and the frontal area (and the speed, and the properties of the fluid).

FWIW (which probably isn't much) HiLo stated in their brochures that a 22' HiLo trailer is 77% more efficient (fuel economy-wise) than a conventional 23' trailer. They state "this was proved in a fuel consumption test conducted by Transportation Research Center."

[Merlin]

Originally Posted by pc500

Does anyone have any data on the drag coefficient of a Escape trailer.

Aerodynamical drag is not always as it appears to the human eye. Some trailer designs are horrible and about as bad as a brick wall (IE: tab/teardrop style trailers). Others are fairly good (IE: Airstream, and one other brand I can't think of that made "bullet" looking trailers.).

Does anyone have any data on the escape?

A member of a teardrop site that I used to frequent had modeled aerodynamics of his and posted pics. (BTW, the folks on the site were obsessed with storage space (duh), weight (duh again) and aerodynamics for gas mileage (ironically) ).

The style suffered in three areas; the front where the air comes off the bed of his truck, the underside where about 1/2 of the air flow ends up on the teardrop and quite a bit on the rear where it tapers.

Having a teardrop in the past, I can say that it felt like just as much air resistance as other taller/wider/longer campers I have owned. Mileage was not much better either. Mine had a small fin in the back of the teardrop, presumably to help with aerodynamics.

Once towing in a heavy rain storm, I remember being amazed with how much turbulence was coming off of the front bottom, visible with the spray and what looked like a stream of water shooting off the corners. It looked to be shooting straight out sideways so plenty of trapped air coming out of there. Much less spray at bed level. And yes, the fenders were bad as well but the tires kicked up plenty of spay so it was hard to tell the two apart. Both fender and tire were bad for aerodynamics based on how much spray was shooting out.

[EscapeBoulder]

While purely subjective... Towing a Scamp '16'er behind a Chysler minivan - which was very sensitive to mileage with respect to weight & drag - for in the range of 35,000 miles in 10 yrs, I noticed no significant change in mileage between towing with and without two kayaks on the minivan's roof rack. So my guess is the kayaks slightly increased the aerodynamic efficiency (if you can call it that) of the system, offsetting the 200 to 300 extra pounds of kayak and ancillary equipment being carried. I picked up our new Escape 19'er in December, and look forward to seeing if things will remain the same regarding aerodynamic efficiency vs weight with it, and our Highlander tow vehicle.

[Brian B-P]

Originally Posted by Hilola

FWIW (which probably isn't much) HiLo stated in their brochures that a 22' HiLo trailer is 77% more efficient (fuel economy-wise) than a conventional 23' trailer. They state "this was proved in a fuel consumption test conducted by Transportation Research Center."

That makes sense, only because it doesn't stick up above the tow vehicle. The same would be true of essentially any random shape of that size, tucked in behind the tug.

[Brian B-P]

Originally Posted by Merlin

A member of a teardrop site that I used to frequent had modeled aerodynamics of his and posted pics. (BTW, the folks on the site were obsessed with storage space (duh), weight (duh again) and aerodynamics for gas mileage (ironically) ).

The style suffered in three areas; the front where the air comes off the bed of his truck, the underside where about 1/2 of the air flow ends up on the teardrop and quite a bit on the rear where it tapers.

Good confirmation of just what should be expected.

Originally Posted by Merlin

Having a teardrop in the past, I can say that it felt like just as much air resistance as other taller/wider/longer campers I have owned. Mileage was not much better either. Mine had a small fin in the back of the teardrop, presumably to help with aerodynamics.

The fin was probably intended for stability, but (unlike with a single vehicle) you don't want the centre of pressure due to sidewind to be rearward on a trailer - it might have been more stable without the fin.

Originally Posted by Merlin

Once towing in a heavy rain storm, I remember being amazed with how much turbulence was coming off of the front bottom, visible with the spray and what looked like a stream of water shooting off the corners. It looked to be shooting straight out sideways so plenty of trapped air coming out of there.

My guess is that this teardrop curved under at the bottom of the front (some end vertically at the floor level). This is design is terrible aerodynamically, forcing airflow where you don't want it, under the trailer.

[Merlin]

Originally Posted by Brian B-P

... My guess is that this teardrop curved under at the bottom of the front (some end vertically at the floor level). This is design is terrible aerodynamically, forcing airflow where you don't want it, under the trailer.

Yes, it had a slight curve at the bottom curving toward the underside. Most likely was pushing a lot of air down and under. Certainly was getting pushed out the sides of the bottom from the air pressure.

[Merlin]

Originally Posted by Brian B-P

The fin was probably intended for stability, but (unlike with a single vehicle) you don't want the centre of pressure due to sidewind to be rearward on a trailer - it might have been more stable without the fin.

I towed with a 1/2 ton and didn't notice any side wind issues. BTW, the thread was buzzing with better mileage talk and such, as it was a new feature compared to older ones. (which prompted the aero model I think). Everyone wanted to know what mpg new folks were getting .
And then much later posts talked about how to better seal the dang thing to keep water out of the window just below. It had a ton of screws holding it on.

[escape artist]

Originally Posted by sunrisetrucker

Excuse me for being picky and correct me if I'm wrong but shouldn't that be Imperial and not Canadian?

Hi: sunrisetrucker... I AM CANADIAN... but I don't do L. per 100 Km. Alf
escape artist N.S. of Lake Erie "Searchin' for my lost shaker of salt".

[sunrisetrucker]

Originally Posted by escape artist

Hi: sunrisetrucker... I AM CANADIAN... but I don't do L. per 100 Km. Alf
escape artist N.S. of Lake Erie "Searchin' for my lost shaker of salt".

Where's that maple leaf emoji when you need one.

Oh wait here it is 🍁

[emers382]

Originally Posted by escape artist

Hi: sunrisetrucker... I AM CANADIAN... but I don't do L. per 100 Km. Alf
escape artist N.S. of Lake Erie "Searchin' for my lost shaker of salt".

So Alf can you switch your readout in your RAM to miles per CANADIAN gallon from l. per 100km?

[ericw]

Originally Posted by pc500

Does anyone have any data on the drag coefficient of a Escape trailer.

I intend to do some relative experiments on drag this spring (after the snow is gone). It won't directly give the coefficient of drag, but it will tell you if changes make the situation better or worse. My friend suggested doing it by coasting on a flat road from point A-B while videotaping the speed and time on a stop watch. Do the same from B-A to cancel wind effects. We intend to start and 70+mph and coast to 40mph in neutral. He used this method in grad school to write a paper. You do have to pay attention to things like resolution and repeatability to understand your error, but I am going to at least give it a try to see how much bikes, kayaks, and air deflectors change things with my setup. FWIW.


We ended up with this after our conversation started with "I hate cleaning bugs off my trailer...."

[Brian B-P]

Originally Posted by ericw

I intend to do some relative experiments on drag this spring (after the snow is gone). It won't directly give the coefficient of drag, but it will tell you if changes make the situation better or worse. My friend suggested doing it by coasting on a flat road from point A-B while videotaping the speed and time on a stop watch. Do the same from B-A to cancel wind effects. We intend to start and 70+mph and coast to 40mph in neutral. He used this method in grad school to write a paper...

That's coast-down testing, as I mentioned earlier.
Running it in both directions helps cancel out the effect of a non-level road, as well. All you need is frontal area to get the drag coefficient from the results. Your friend should remember from his earlier work to do a quadratic fit to the data to separate the aero drag from the rolling drag.

[escape artist]

Hi: All... This thread is really a "Drag". Alf
escape artist N.S. of Lake Erie "Searchin' for my lost shaker of salt".

[escape artist]

Originally Posted by emers382

So Alf can you switch your readout in your RAM to miles per CANADIAN gallon from l. per 100km?

Hi: emers382...The male sheep does miles/ U.S. Gallon and "I AM CANADIAN" but don't drink the stuff. Alf
escape artist N.S. of Lake Erie "Searchin' for my lost shaker of salt".

[Iowa Dave]

And the kid says “That’s my Daaaaaaaad.”
Iowa Dave

[Joat]

I had 2007 Chevy truck 5.3L V8, 4 speed auto,
3.73 axle ratio and Leer topper with roof rack.
I added Thule wind deflector and set to rear of
topper. It increased gas mileage little over 1
mpg and I could tell the truck was pulling trailer
easier. Trailer 2007 Casita 17’. I was averaging
13.8 mpg went to 14.9 mpg over all and speed
always 65 mph or less. I have sold both.
Hope this helps
Good Luck to All

[fatehunter]

I'm late to this post, but will post what I've learned. (Amateur Pilot and Professional Mariner with a strong interest in this stuff)
Drag is not a strait-forward type of thing, and often misunderstood. Here's the basic principles to follow and some other info road vehicles.
- the air from the TV should be diverted around the trailer, in essence you want to deflect the air only once around your whole towing unit (TV and TT) - having the air coming off the TV hit the trailer behind it gets more drag out of the same air. So get a deflector on the back end of your tow vehicle, adjust it up until you get no more bugs hitting your trailer. Look at what semi-trailers do to make them one unit with regards to air-flow.
-Round fronts don't matter much, it's how the air hits it from the TV.
The back end is very important, you have two choices for least drag - 1. Make a very clean cut (square ends, like a semi), or a very gradual taper, like an airfoil. You are trying to either cut the air off clean, or have it stick to the shape all the way to the back. This does not appear logical, but it is true, therefore tear-drop trailers are some of the worst for drag, as the curve is enough to have air stick to it for a while, but not all the way to the back. If you want to get fancy you can step the shape down at the back with a smaller box shape attached to the end of the trailer - some semi trailers have a smaller box at the end of the trailer.
- anything sticking out into the airflow is bad - if it has a poor shape. Roof racks, Air-co, radio and tv antennas, but even worse is if air that has been defected off the front of the TV hits something before it gets to the back of the whole package - so open windows, open wheel wells, open areas under the TT, etc.