quest for better fuel mileage while pulling a travel trailer

[Frank Lee]

See? The wind is strong here.

[slowmover]

Tractor-Trailer Drag Distribution

25-35% Tractor Drag

An aerodynamic tractor only affects the flow over the trailer face!
70% of the drag of a tractor trailer is trailer drag.

65-75% Trailer Drag

- 30% Trailer Front Face
- 30% Trailer Base
- 30% Undercarriage
- 10% Side and Top Surfaces

Trailer Drag

Pressure Drag - normal to surface

• Hot Spots: front face, rear face, undercarriage
• Comprises more than 90% of total trailer drag

Friction Drag - tangential to surface

• Hot Spots: side and top surfaces
• Comprises less than 8% of total trailer drag

Roughness Drag - this is a pressure drag increment

• Hot Spots: side and top surfaces
• Comprises less than 2% of total trailer drag

Getting Better Fuel Mileage - Truckers' Trucking Forum | Largest CDL Truck Driver Message Board


(.pdf 5.8 Mb) PETERBILT WHITE PAPER ON AERODYNAMICS

Aerodynamics 101

According to Peterbilt Engineering Systems Manager Rick Mihelic, the truck engine must overcome five primary forces in order to move the truck down the road. They are:

• Rolling resistance, or the loss due to friction between the tires and the road;

• Mechanical losses, which result from friction inside the engine and the drivetrain;

• Accessory losses, which result from running alternators, air conditioners, fans, etc.;

• Grades, or changes in road elevation; and

• Aerodynamic drag.

http://www.peterbilt.com/eco/pdf/Aer...%20PAPER-2.pdf



(.pdf 3.2 Mb) KENWORTH WHITE PAPER ON FUEL ECONOMY

http://www.loadtrek.net/loadtrek_net...whitepaper.pdf


(ARTICLE) HEAVY DUTY TRUCKING

Hands-On Tips For Buying Fuel, Driving & Spec'ing For Better Economy


Tips For Drivers

Tips For Drivers

***** In a major study, The Technology and Maintenance Council of the American Trucking Assns. identified the major factors that most affect fuel economy. The top 10 are:
*****
1: Driver skills, then,

***** 2: Speed - especially with poor aerodynamics
***** 3: Cooling fan "on" time
***** 4: Electronic versus mechanical engines
***** 5: Using rib tires in every wheel position
***** 6: Cutting idling time
***** 7: Using single semi-trailers instead of doubles
***** 8: Using a roof fairing rather than a flat roof
***** 9: Using a roof fairing rather than a raised-roof sleeper
***** 10: Slowing down 5 mph


.

[aerohead]

Originally Posted by zoom

Thank you for all of your suggestions I will be working on my 1994 Ford F. 350 diesel crew cab long box with a flat toper and 30 ft. travel trailer not a fifth wheel. In all what you have said about tractor-trailers having an aerodynamic deflector on the cab. I'm wondering if a rack was made for the top of the truck and a light aluminum boat was put up on this rack upside-down with the bow to the front and the Stern close to the trailer but not in the way of turning and somehow filling the gap between the trailer and the boat and truck. I realize that will not gain a lot of and MPG in normal circumstances but with my truck the horsepower is only around 200 and when I pulled my trailer out to Montana from Wisconsin, it not only seems like an uphill drive all the way but it seems like your battling 20 to 30 mph Headwinds that would decrease my fuel mileage down to 7 mpg from 11MPH this is where the aerodynamics would really shine. By the way I have a pullright hitching system too. thanks again you all have great suggestions! Zoom

zoom,the boat idea is a good one.I have an article from the 1950s,where they've done this very thing and also closed in the sides above the rails.
If you can close the gap between truck and trailer with some kinda flexible seal you might pick up an additional 10% mpg.

[Clev]

I'm reading that fascinating thread that slowmover posted, and somebody posted an interesting data point:

Likewise, if you assume:
1) You run a constant 800 mile journey (at $1.30/mile)
2) You work 11 hours per business day, all year

Truck #1 goes 75mph and gets 5mpg will net about $64k
Truck #2 going 55mph and gets 7mpg will net about $92k.

Truck #2 will make 70 less trips, but the money saved overcomes the potential losses in work.

Interesting, and goes against everything truckers have said in rallying for the repeal of lower speed limits for trucks.

[slowmover]

Originally Posted by Clev

I'm reading that fascinating thread that slowmover posted, and somebody posted an interesting data point:

Interesting, and goes against everything truckers have said in rallying for the repeal of lower speed limits for trucks.

Don't be too quick on the gun. The world of four wheelers and big trucks only overlap in imagination. It is difficult to maintain a 50-mph headway in a big truck . . a 10" stop in a car can have, at equivalent, 30" or more in a heavily-laden big truck. Then, I have plenty of times not been able to re-gain 65-mph for more than 30" since departure as the truck is so heavy, the truck straining; hills, traffic, etc. At the end of a workday one's average speed is not very high. 70 mph allows one to keep speeds, overall, at a decent clip. One can trip plan for a 60 mph day in a car, but a big truck is 50 mph (industry average); this is all hours on the road.



As to streamlining pickup truck and travel trailer, the "rule" is 24-30" for a gap that can be faired. On my rig, the distance from TV (tow vehicle) tailgate to TT (travel trailer) front was 60". Among the above quotes was this:

At distances over 24" inches between the trailer and the tractor, drag goes up considerable. By 48" you have the drag of TWO FULL FRONTAL AREAS. Might as well have the trailer beside the truck!


I think it's important to note two things about trailers: the one used for pleasure, and the one used for business. The first may only be pulled, say, 5,000-miles/year. The second is the one on which to pay special attention (going for length to cut height; reduced width, etc) as it may travel 10X as far. In which case going to FEATHERLITE to custom-spec a trailer would be, IMO, worthwhile.

This is the way I wrote it in an email to another guy:

Were I in a position to spec a cargo trailer I would do my best to keep height and width to a minimum, about 6'H and 6'W for purposes of fuel economy. It wouldn't be higher than my truck and certainly not wider. I would rather have an extra ten feet in length (well, five feet plus) than another one foot in heighth or width. An 8'H x 8'W x 20'L trailer could be 6'H x 7'W x 30'L if cubic capacity had to be identical. (Which I doubt). Here are the words of an expert:

"I would rather tow a trailer that is 6 feet longer and 2000 lbs. heavier than one-foot taller."

The difference between the two trailers is 64 sq/ft frontal area versus 42 sq/ft frontal area; a reduction of one-third.

All corners and edges should be greatly radiused. My nine-and-half-foot tall 34' travel trailer had such, and wind just rolled off of it, instead of piling up against -- and pushing against -- the trailer wall edges and corners. I haven't found the source, but have seen quoted numerous times that a square box versus a rounded/aero trailer had road horsepower differences for the same speed of 50HP and 30HP respectively. AIRSTREAM maintains that their trailers take 20% less fuel to tow, all other things the same.


The best travel trailer is an aerodynamic, all-aluminum, independently-suspended one. AIRSTREAM is the only survivor of that era. I averaged 13 on the backroads with my SILVER STREAK, and 15 mpg Interstate at 63 mph/ 1,850-rpm. Had I reduced to my current solo speed of 58-9 mph, I would (I believe) have broken 16-mpg (34' trailer). I am not alone at this. The "best" mpg appears to be, currently, with European turbodiesel SUV's pulling AIRSTREAM trailers at 16-mpg and better.

V8 diesels do poorly compared to 6's, but both benefit from many, many details related to hitch rigging, alignment, tires, etc, etc.

[KamperBob]

Originally Posted by slowmover

All corners and edges should be greatly radiused. My nine-and-half-foot tall 34' travel trailer had such, and wind just rolled off of it, instead of piling up against -- and pushing against -- the trailer wall edges and corners. I haven't found the source, but have seen quoted numerous times that a square box versus a rounded/aero trailer had road horsepower differences for the same speed of 50HP and 30HP respectively. AIRSTREAM maintains that their trailers take 20% less fuel to tow, all other things the same.
[/I]

The best travel trailer is an aerodynamic, all-aluminum, independently-suspended one. AIRSTREAM is the only survivor of that era. I averaged 13 on the backroads with my SILVER STREAK, and 15 mpg Interstate at 63 mph/ 1,850-rpm. Had I reduced to my current solo speed of 58-9 mph, I would (I believe) have broken 16-mpg (34' trailer). I am not alone at this. The "best" mpg appears to be, currently, with European turbodiesel SUV's pulling AIRSTREAM trailers at 16-mpg and better.

V8 diesels do poorly compared to 6's, but both benefit from many, many details related to hitch rigging, alignment, tires, etc, etc.

There is also a thriving breed of molded fiberglass trailers designed for towing by small vehicles. You can learn more here.
Egg Central

It depends on driving conditions and habits of course but I get anywhere from 15 to 18 mpg towing my 19' Scamp fifth wheel with a 4.7L 4WD Tundra for example.


Cheers
KB

[Angmaar]

Add a boat tail and under belly pan.

[Bajascoob]

Originally Posted by ECONORAM

Zoom, I am currently working on streamlining my Quad cab. Have not tried with a trailer yet. However, I think my mods would work. I am going to wire in my MPGuino and see what results I get...

http://ecomodder.com/forum/showthrea...cap-12573.html

[Domman56]

How bout skirt and a big spoiler on the top of the truck

[slowmover]

I get anywhere from 15 to 18 mpg towing my 19' Scamp fifth wheel with a 4.7L 4WD Tundra

I'd enjoy seeing some interior shots of that. That's a cool rig (from a guy who really dislikes 5'ers).

Have you ever calculated storage space (cubic foot enclosed storage of cabinets/closets)? Have seen CASITA and SCAMP and some other "oddballs" but not ever heard about trade-offs (am familiar with aluminum trailer so-called "deficiencies" [primarily psychological IMO]) in "living".

I looked at the company website, but have trouble believing any of them in re weight, so, as a "hypermiler" I figure you have a short stack of weight scale tickets:

What is dry weight as well as GVWR?

What is the GCW on that rig as pictured?

Pin weight?

How does it do on a scale reading per axle?

Is the roof a solid cap, or a multi-piece "rubber roof"?

What are fresh and waste water capacities?

What is your impression of how long they last (time and miles)?

Thanks.