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Old 03-02-2019, 06:25 PM   #1
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Aerodynamic drag on the escape trailer?

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?
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Old 03-02-2019, 06:34 PM   #2
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I've never seen aerodynamical drag posted for any brand of trailer, so even if you can find data for Escape, you'd have nothing to compare it to.
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Old 03-02-2019, 06:46 PM   #3
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I suppose I can have a friend tow it with his Tesla and look at the energy consumption. It's not weight when it comes to the drivetrain efficiency on electric vehicles. For example, his 4,000# airstream gets better "mileage" than a 1,200# trailer with two dirt bikes and a "ramp". The ramp's the problem.
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Old 03-02-2019, 06:48 PM   #4
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Originally Posted by pc500 View Post
(IE: Airstream, and one other brand I can't think of that made "bullet" looking trailers.).
Are you thinking of the Bonair Oxygen?
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Old 03-02-2019, 07:04 PM   #5
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I have never seen actual drag coefficient data, but speaking to others and reading this forum for a couple of years, it appears that the newer escapes with the boxier front ends on the 19' and the 21' have more drag than the first generation models that were rounder.

I agree that drag has a significant impact on milage. I once drove all day westbound across Idaho against a stiff headwind and my normal 14-15 MPG dropped to 11 MPG. This was towing a 19' classic trailer with a Tacoma.

I'm guessing that the 5.0 will have less drag since a good portion of the frontal area is in the slipstream of the tow vehicle. Also the part of the 5.0 above the truck has a nice slope to it. But I don't know that from personal experience.
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Old 03-02-2019, 07:50 PM   #6
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Originally Posted by pc500 View Post
Some trailer designs are horrible and about as bad as a brick wall (IE: tab/teardrop style trailers)...
Oh, I don't know. When I towed my teardrop with my Honda Element it had a negligible effect on fuel mileage. The teardrop drafted in the path of the Element which had kind of a barn door aerodynamics.
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Old 03-02-2019, 08:06 PM   #7
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Drag

I don’t know much about measuring wind drag on the Escape but I did have a nice involved conversation with the owner of Tweety Bird once. Tweety bird is a Compact Junior. They are very square. He was towing with a Chrysler product minivan. He said it’s like towing a brick. So he had a bolt on spoiler from a previous tow vehicle that he mounted on the minivan and tilted it till the bugs quit hitting the upper front of the camper. He told me his mileage went up an honest three or four miles to the gallon. From like 11 to 15. I looked into buying a spoiler and mounting it on the Highlander but never did it. I think there’s probably a possibility for a
payback here.
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Old 03-02-2019, 10:00 PM   #8
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Originally Posted by pc500 View Post
I suppose I can have a friend tow it with his Tesla and look at the energy consumption. It's not weight when it comes to the drivetrain efficiency on electric vehicles. For example, his 4,000# airstream gets better "mileage" than a 1,200# trailer with two dirt bikes and a "ramp". The ramp's the problem.
Weight matters with an EV, too, but at constant speed weight isn't a big factor. Aero drag is always important, and any vehicle shows that ramps and protruding fenders are much more important than moderate differences in trailer weight.

The energy consumption per distance display on an EV could be handy for this purpose, although you would need drag at multiple speeds and non-towing baselines to get a reasonable idea of aero drag.
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Old 03-02-2019, 10:00 PM   #9
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Originally Posted by Donna D. View Post
Are you thinking of the Bonair Oxygen?
Or the Bowlus Road Chief?
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Old 03-02-2019, 10:39 PM   #10
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Originally Posted by pc500 View Post
Does anyone have any data on the drag coefficient of a Escape trailer.
Not me. I agree that aero data on trailers is rare, for multiple reasons:
  • Trailer manufacturers have nearly zero technical resources, to perform or even understand any kind of testing.
  • Trailer manufacturers have little reason to systematically consider drag, since it is not a requirement or a competitive differentiator; for the few buyers who really care, a trailer can be sold as "low drag" completely without objective basis, so there's no reason to test.
  • Trailers are only used in combination with a tow vehicle, and the total drag depends significantly on the tow vehicle's shape and size. With no "standard" tow vehicle, there's no reasonable way for the drag of a trailer to be definitively determined.

Quote:
Originally Posted by pc500 View Post
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.).
I agree that typical teardrops are horrible (despite the widely-held belief that they are ideal), both in the basic shape and in the tendency to use highly effective side-mounted airbrakes, which also cover the tires. The old "canned ham" shape with external fenders seems to have returned to popularity - it's truly horrible.

I suspect that Airstreams, my old Boler, and the really cool but failed Bonaire Oxygen are all pretty bad, too, because of their rounded tails. The Oxygen is a particularly frustrating example because it is as if someone put some serious effort into producing an excellent front end, then quit working and just popped another copy out of the mould and put it facing the other way on the back end. How often do you see an aircraft with identical nose and tail?

My guess is that the front corners of a conventional Escape (the 5.0TA is quite different) are usefully rounded, but the identical rounded rear corners do substantial harm. Like many trailers and most older motor vehicles, the underbody is a disaster; I don't know how much that matters in the aerodynamic mess behind a tow vehicle.

If anyone really wants to study this, they could do coast-down tests of various trailers behind the same tow vehicle, and maybe the same set again with a different style of tow vehicle for some insight into the effect of the tug. All you need is something to record speed versus time, and a flat place where you can shift to neutral and coast down from a reasonable highway speed to a significantly lower speed. Apparently there's even an SAE standard for coastdown testing: SAE J1263, “Road Load Measurement and Dynamometer Simulation using Coastdown Techniques”. If anyone does this, I'll note that to distinguish aero drag (force varies as square of velocity) from rolling drag (force approximately independent of speed), at least three data points (pairs of speed and elapsed coasting time) are needed so a quadratic fit can be done.
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