Aerodynamics of tv-toad combos

Roamin Ovum · 03-05-2012, 02:24 PM

After getting 7.5 mpg on my last pull

I've wondered about improving the airflow over the trailer. Has anyone simulated, or seem a simulation of, wind tunnel testing of various combinations of open bed pickup, tonneau cover, low rise vs high rise camper shells? It would seem plausible that a "duck-tail" camper shell that directed airflow up over the top of the trailer would help improve mileage but I haven't yet found any data on the web. Air-tabs are reputed to help decrease drag by forming vortices on the trailing edge of the camper that smooth out the turbulence, but I've yet to see them on the highway or in a campground. My combo is a Ford F-150 Ecoboost short bed, 3.55 LS 4x4 and Tracer 230 with the Touring Edition cap.

Gary

crocus · 03-05-2012, 02:52 PM

I would think that a high-rise camper shell with a ducktail would certainly help, but I seriously doubt anyone has studied the issue.
Why are you getting such terrible gas mileage?

TURBS · 03-05-2012, 03:42 PM

To be honest I don't believe the effort and cost to benefit the gains if any imo

crocus · 03-05-2012, 03:52 PM

The camper shell should not only improve the fuel mileage somewhat, but also provides a secure and dry place to haul camping stuff. So the idea is not so easy to dismiss.

MtnGuy · 03-05-2012, 03:54 PM

Roamin Ovum, what speed are you pulling ??

I am not sure what can be done about the trailer airflow, but you might be on to something about the truck aerodynamics. On a trip last week, I noticed my soft tonneau cover really being whipped around.....I was carrying my canoe this trip. On trips without the canoe, it lays pretty still, so I contribute the cover being blown by the turbulent air of the canoe. Plus I had my bikes sitting over the bed, but I travel with them most times, and don't notice that kind of movement with the tonnaeu cover.

I have read several places that an open bed forms an air pocket, and doesn't affect the aerodynamics that much, but I prefer to think that a tonneau cover has to do a little in making the truck more aerodynamic. As far as a topper, I wonder if the more wind resistant stance would be countered by the extra weight.

This last trip, we decided to stay away from the interstate as much as possible. The slower speeds helped some with fuel mileage, but was countered some with some stop lights.

The 1st day we had 20 to 30 mpg sustained winds, with gusts to 50 mpg....there were all sorts of high wind warnings out. We were basically quartering into these winds (sometimes broadside, sometimes head-on) and my fuel mileage was 9.1 mpg that day....I think the canoe on top of my racks really hurt the mileage that day. The other fill-ups were much better, and I contribute that to the lower speeds using non-interstate speeds.

Roamin Ovum · 03-05-2012, 04:06 PM

I was towing at 62 - 68 mph into a head wind. I've gotten as high as 10 mpg on other trips. Tires were properly inflated - 42 front, 44 rear, and 50 in the trailer. There were quite a few stops this time, it seems all the lights were red. The trailer weighs 5000 lbs dry, maybe 5600 as loaded. The truck gets from 17 - 21 when not towing so no complaints there. The only factors affecting mileage are internal engine resistance (same towing or not) rolling resistance (much higher when towing - more weight, more tires) and wind resistance. Other than keeping the inflation pressures up to spec aero drag seems the only variable. I was hoping someone on the forum had taken a hit for the team and run the shell / no shell experiment

crocus · 03-05-2012, 04:08 PM

"I was towing at 62 - 68 mph into a head wind."
==============================
That would explain it!
Without the Ecobeast, you probably would have been gong 50!

depo · 03-05-2012, 04:11 PM

The Eco-Boost is a super high efficient Engine and get great Gas Mileage. There has been some road tests of guys getting up to 32 MPG on the truck with a light foot and etc...

What has been a massive complaint is because of the twin turbo. It takes a massive amount of energy for the engine to "Spool" up heavy hauling or towing, which in turn consumes a far higher quantity of fuel. To the point at which getting significantly lower fuel economy then some large displacement motors.

What has also been a concern is the "rumor" of engine failures due to those people that are using the truck as a "work" truck, towing and hauling heavy loads on a regular basis. What the rumor is a lot of scorching going on in the motors due to the quite higher temps that the motor runs at when using turbos. Causing scorched cylinders and valve issues.

My buddy who is a Mechanical Engineer and works on heavy duty agricultural equipment said to me if you are towing or hauling nothing will ever beat displacement. Especially a low torque high horsepower engine like the Eco Boost.

MtnGuy · 03-05-2012, 04:14 PM

That headwind hurts. It has been speculation on how the Eco will do while towing. When you have 6 cyls. pulling just the truck without a load, then that engine is just purring along. Getting to the available torque when needed for trailer towing by making the turbos work is gonna dip into the gas tank some. I am also wondering if the 3.55 gears may be helping the non-trailer towing fuel mileage, but hurting the towing mileage.

Sounds like you are doing all of the right things. No excessive speeds and tires inflated. The aero end of the equation is about all that is left.

**bikendan** · 03-05-2012, 04:14 PM

Quote:

Originally Posted by crocus

"I was towing at 62 - 68 mph into a head wind."
==============================
That would explain it!
Without the Ecobeast, you probably would have been gong 50!

agreed! don't know what you expected towing into a headwind.

we all get about the same gas mileage doing that. especially at those speeds.

you do know that you increase the wind resistance a lot, by driving that fast. and your tires are only rated to 65mph.
no wonder you got only 7mpg!

and i seriously doubt you'll see much of a gain in mpg, with a shell.
it'll take a lot of towing to recoup the money you'd spend for one.

crocus · 03-05-2012, 04:14 PM

Well depo, that sounds like a pile of hogwash to me. And who told you the Ecoboost was a "low torque" engine? Check the specs.

depo · 03-05-2012, 04:31 PM

Quote:

Originally Posted by crocus

Well depo, that sounds like a pile of hogwash to me. And who told you the Ecoboost was a "low torque" engine? Check the specs.

The specs are checked.... they claim 400 ft lbs, but check out how that is achieved.....

It is not hogwash if from an engineering stand point you understand that the stresses that are created on an engine under load with the use of turbos creates great internal challenges.

Also read the road testing of the vehicle by truck magazines.... Same thing I mentioned while it gets 20+ mpg unloaded the towing of comparable weight is equal to or well below that of a V8.

Go to a drag strip watch two cars race.....

a 400 HP muscle car and a 400 HP turbo 6, you will understand the difference.

For a 400 hp turbo 6 to achieve the exact same power at launch it must spool up to the RPM and Boost which create heat and work. a 400 HP muscle car achieves this at a much quicker rate. Then the point at which a turbo car reaches maximum amount of acceleration is well down the track, but comes on at a Massive rate. Whereas an engine in a larger displacement vehicle has that curve at a much earlier point of the pull.

I love the idea of having a 3.5 twin turbo putting 350+ hp, but

I will tell you when shopping for a truck I went to the ford dealership and they specifically told me if I was towing consistently that I was much better off with a V8 or a Diesel, but as the weekend warrior truck and a commute vehicle the Eco was a great option.

crocus · 03-05-2012, 04:35 PM

depo, you apparently do not understand how the Ecoboost functions, so no point in wasting space debating the issue.

Roamin Ovum · 03-05-2012, 05:04 PM

Quote:

Originally Posted by bikendan

agreed! don't know what you expected towing into a headwind.

we all get about the same gas mileage doing that. especially at those speeds.

you do know that you increase the wind resistance a lot, by driving that fast. and your tires are only rated to 65mph.
no wonder you got only 7mpg!

and i seriously doubt you'll see much of a gain in mpg, with a shell.
it'll take a lot of towing to recoup the money you'd spend for one.

I kept the speed lower on the secondary roads, but on I 45 in Texas going south from Dallas the traffic is probably doing 85. That was where I was doing 65-68. Your observation about the time to recoup the cost of the shell is apt. So far 90% of my miles on the truck are non towing. But, all these factors were the same when I was getting 10 mpg on one trip. Go figure.

depo · 03-05-2012, 05:08 PM

Quote:

Originally Posted by crocus

depo, you apparently do not understand how the Ecoboost functions, so no point in wasting space debating the issue.

Nope.... me big dummy

padave65 · 03-05-2012, 05:48 PM

[What has also been a concern is the "rumor" of engine failures due to those people that are using the truck as a "work" truck, towing and hauling heavy loads on a regular basis. What the rumor is a lot of scorching going on in the motors due to the quite higher temps that the motor runs at when using turbos. Causing scorched cylinders and valve issues.

My buddy who is a Mechanical Engineer and works on heavy duty agricultural equipment said to me if you are towing or hauling nothing will ever beat displacement. Especially a low torque high horsepower engine like the Eco Boost.[/QUOTE]

I have not heard of any failures to "work". Some people have experienced gate issues on the turbos and coil issues. I have read countless blogs on F150 forums and I have not read anything about burnt cylinders..The black soot is coil problems not burnt cylinders...... Low torque???? 420ft-lbs is far from low torque. The 3.55 rearend is not great for towing. The 3.73 will provide better towing mpgs. The 3.55 will bog down the engine and decrease mpgs. The higher rearend will give better mpgs on the highway though.....

depo · 03-05-2012, 07:02 PM

I do not mean to offend....

Sorry I did write low torque.... I thought I corrected that in my original post....

The torque is insane on the motor, but at a very limited RPM range and drops of quickly and takes a while to to get there. Now mind you it is right at the RPM range you want to be at which is 1200 to 2000 RPM when you are rambling down the highway. But in theory you want that torque at initial start and all the way across, which is not what the EB does on an engine dyno or at the rear wheel.

As I said, I think the engine is a create concept, I hope that they come up with a durable long lasting Eco engine that gets 35 MPG.....

But my concern is that they have torn some motors down and have found some odd wearing that they usually do not see on other motors. The other issue is that they have under load consistently shown lower then average gas mileage then other half ton trucks with V8s.

This is not a bash on the motor at all..... it is something to watch for as this motor progresses.

Roamin Ovum · 03-05-2012, 09:45 PM

2011 Ford F 150 Tourque Photo 70

Here is a graph of Ford's engines available for the F-150. The Ecoboost looks good compared to the others

I will tell you when shopping for a truck I went to the ford dealership and they specifically told me if I was towing consistently that I was much better off with a V8 or a Diesel, but as the weekend warrior truck and a commute vehicle the Eco was a great option.[/QUOTE]

That describes mine exactly. I just dragged some huge chunks of concrete around my property, actually pulling the smaller piece at idle in 4 low. I had to tap the gas a little for the big pieces

Roamin Ovum · 03-05-2012, 09:55 PM

[QUOTE=bikendan;166924]agreed! don't know what you expected towing into a headwind.

The headwind was pretty tame at 10 -15 off the right front quarter

we all get about the same gas mileage doing that. especially at those speeds.

you do know that you increase the wind resistance a lot, by driving that fast. and your tires are only rated to 65mph.

I kept reminding the DW about that, but she kept saying faster, faster. One must obey the captain

You're right, I didn't know what to expect - I've camped exactly 8 days in the Tracer

so I'm a newb at this. I was hoping for better, but this may be the norm. What mpg do the rest of you get towing, at what speed?

F and E Damp · 03-05-2012, 09:57 PM

Many years ago, my boss had a big Ford truck (It would be an F-350 in today's parlance) with a 12' slide-in camper. I think the truck had a 429 engine. Running with just the camper, he got a consistent 6.5 mpg. When he towed his sailing dinghy behind, it improved to almost 8.5. He figured the boat and trailer broke up what aerodyamicists call "bluff body drag", caused by a bubble of negative pressure air behind the vertical rear surface of the big box.

Even if they were'nt going to use the boat, he always towed it.

You may also like: