Motorhome Aerodynamics

[MRUSA14]

Originally Posted by 777 Driver

You can add these:
Attachment 312688


Looks like this installed:
Attachment 312689

For info: Airtab | Aerodynamic Fuel Savers | Welcome

To purchase at $2.75 each (black or white only): https://buyairtab.com/

You'll need 3 per lineal foot (~50 Airtabs) for ~$137.5. Advertised to save you 2% - 5% in fuel burn.

Take care,
Stu

I am willing to bet that the savings (if any) that those tabs provide would be so small as to be immeasurable.

[TexasJeff]

Agreed A's have progressed almost statically (ie no progression) on aerodynamics. They've improved in other areas such as lighter weight materials. But gone are the days of 6 gal per mile. I think they continue to improve but pretty darn slowly. I wonder if the hesitancy of redesigning the air flow body style might contribute to cost in a significant way and that's frightening the manufacturers who might think it's hard enough to sell at their current price points (these COVID days excepted).

[cinitall]

Originally Posted by TexasJeff

Agreed A's have progressed almost statically (ie no progression) on aerodynamics. They've improved in other areas such as lighter weight materials. But gone are the days of 6 gal per mile. I think they continue to improve but pretty darn slowly. I wonder if the hesitancy of redesigning the air flow body style might contribute to cost in a significant way and that's frightening the manufacturers who might think it's hard enough to sell at their current price points (these COVID days excepted).

Porsche Designs has been involved in the design of the front and rear caps and other design elements of Newells for many years. If there was a way to make one of these saltine boxes aerodynamic and still provide the room customers want, Porsche would have been able to do it I think.

[groswald]

Originally Posted by MRUSA14

I am willing to bet that the savings (if any) that those tabs provide would be so small as to be immeasurable.

The fact that long haul trucking companies haven’t adopted Air Tabs wholeheartedly tells you all you need to know about how effective they are. (Or aren’t)

Regards,

Randy

[Flyer15015]

I'm going to get one of these, and cheat the wind all the way to Florida.
But I'll have to tell the DW she can't take all her "stuff".

I wonder if I'll be traveling alone ?

Want a beer ?

Mike in Colorado

[n2zon]

Originally Posted by 777 Driver

If you don't want to slow down, maybe you'd like to try this concept described in a article (https://www.af.mil/News/Article-Disp...revolutionary/) published in 2012 that includes this description:

________________________________________________

SCOTT AIR FORCE BASE, Ill. (AFNS) -- Migrating birds, NASCAR drivers and Tour de France bicyclists already get it. And now the Air Force is thinking about flying gas-guzzling cargo aircraft in formation -- 'dragging' off one another -- on long-haul flights across the oceans.

Flight tests with C-17s "vortex surfing" at Edwards Air Force Base, Calif., Sept. 6 and Oct. 2, have demonstrated potentially large savings of fuel and money by doing what geese do naturally. Tests show that flying in formation might be smarter than flying alone for Airmen, and not just for birds.

As one effort in the Air Force drive to reduce its overall fuel consumption, vortex surfing may be the wave of the future.

"The concept, formally known as Surfing Aircraft Vortices for Energy, or $AVE, involves two or more aircraft flying together for a reduced drag effect like what you see with a flock of geese," said Dr. Donald Erbschloe, the Air Mobility Command chief scientist.

A series of test flights involving two aircraft at a time, allowed the trailing aircraft to "surf" the vortex of the lead aircraft, positioning itself in the updraft to get additional lift without burning extra fuel.

Early indications from the tests promise a reduction of fuel consumption by up to 10 percent for the duration of a flight. Over long distances and with even a small fraction of Air Mobility Command's average of more than 80,000 flights a year, the fuel and cost savings could reach into the millions of dollars, experts say.
________________________________________________

Air tabs, vortex surfing...woohoo!

Take care,
Stu

I used to have an airspeed indicator mounted in the Southwind. I found that the vortices from large trucks create multiple low-pressure zones (as shown by drops in airspeed). The third one is far enough back that you don't have to tailgate, but you can't stay in it by sight or feel; you really need instrumentation!

This thread has reminded me of that airspeed indicator sitting on the shelf in the garage...hmmm....I can make a pitot/static tube on my lathe....

[Flyer15015]

When you calculate the fuel cost savings from drafting, don't forget to add back the cost of a windshield and getting the nose repainted.
I don't think it will work out in the long run.
Just saying...........


Mike in Colorado

[tderonne]

NASA has spent a lot of time over the years studying truck aerodynamics.

Back in the '70's they made what they called the "Shoebox". It was a square box that they modified and measured the aero affects.

The base square box (the proverbial brick) had a drag coefficient of .89, bad.

Just rounding the front and rear corners dropped it to .41, half the base drag!

Just rounding the front, and cleaning up the underbody dropped it to .365.

The shoebox appears in lots of NASA reports. Here's one There's a Shoebox summary on page 14.



Here's a summary of some other NASA papers.
(Motorhomes are even mentioned when talking about the Roadrunner project on pages 63-66. It seems that project was never completed.)

Lots of interesting reading out there.

[tderonne]

Originally Posted by n2zon

I used to have an airspeed indicator mounted in the Southwind. I found that the vortices from large trucks create multiple low-pressure zones (as shown by drops in airspeed). The third one is far enough back that you don't have to tailgate, but you can't stay in it by sight or feel; you really need instrumentation!

This thread has reminded me of that airspeed indicator sitting on the shelf in the garage...hmmm....I can make a pitot/static tube on my lathe....

What did you have for an indicator before? What pieces do you have now? I'd love to have one on the motorhome. Thought of just sticking an anemometer on the roof. Give me some real data as to what I was driving against relative to the wind.

[rickemo]

Originally Posted by rollondown

My opinion....(Brought to you by a guy that hauls his 24000lb 46' long 5th wheel with a class 8 semi truck).... If you can afford the Class A price tag, the fuel bill should be a non issue.....

So, I did a bit of figuring and rollondown is spot on.
If you purchased a new Class A and drove it 50,000 miles over a 5 year period at an average price of $2.00 per gallon, your fuel costs would be:
At 6.5mpg - $15,385
At 8.5mpg - $11,765 ($3,620 savings over 5 years, $724 per year)
At 10.5mpg - $9,524 ($5,861 savings over 5 years, $1,172 per year)
Even an improvement of 4mpg from 6.5 to 10.5 is only a savings of $1,172 per year. And for those of us living in high gas tax states like PA, where the cost per gallon is around $2.50 the cost would on add $293 per year.

[n2zon]

Originally Posted by tderonne

What did you have for an indicator before? What pieces do you have now? I'd love to have one on the motorhome. Thought of just sticking an anemometer on the roof. Give me some real data as to what I was driving against relative to the wind.

It's an airspeed indicator from an airplane. It's complete, but it requires a dynamic pressure source (pitot tube) and a static pressure source (static tube). The pitot and static tubes can be combined in a single assembly or separate. The pitot tube faces forward and projects into clear air, while the static tube is at right angles to the airflow.

A picture of my airspeed indicator is below.

[LarryinID]

Keep your speed under 65 and you should get 7.5 mpg. Towing my Cherokee has no noticeable affect on mpg.

Head winds cause the biggest impact. Slow to 55 in headwind. Enjoy the scenery. That’s what Class A windshields are for.

[Calson]

The single greatest factor in truck fuel economy is the person behind the wheel. The exact same rig pulling the same load over the same route with one driver can average 6 mpg and a different driver it can average 9 mpg. The fleet operators know this and put most of their attention on hiring "9 mpg" drivers.

I found this to be true even with the Toyota Prius. Anyone can get 45 mpg with one of these cars but there are competitive types how get 60 mpg with them with lots of tricks.

A big problem with a RV is that any improvements to reduce air drag is going to make for a 3 foot longer coach. Not to many people would accept the trade-off.

The simple truth is that gas and diesel are too cheap in the USA for most people to care about driving to minimize fuel consumption. It is very rare for me to see people driving at the speed limit whether they are driving a motohome or pulling a trailer. Routine for people to blast pass me at 80 mph and then pull immediately into the right lane and hit the brakes so they can slow down enough to take the next exit.

[F4Gary]

A couple of years ago you used to see those foldable airflow smoothers on the back of semi trailers. Don't see them much anymore so I guess they weren't cost effective.


Gas prices will most likely be going up....a bunch.