Air Flow Deflectors

[RHasse]

We just had our TT out for the first time in a very long time, and are looking forward to getting it out more frequently here in 2021, with a least 1 long trip planned for this summer, but hoping to get a few shorter (3-4 day weekends) trips in as well.

But something came to mind recently, I recall seeing large wind deflectors on the tops of TV's years ago, some were just simple wings, others were more elaborate, like the large "spoilers" you might also see on top of the tractors of 18 wheelers. Almost all big rig tractors running line haul have some kind of wind deflector on top of the cab to direct air flow up and over/around the trailer.

So I did some internet searching and found surprisingly little information on this. There appears to be 2 main brands of air deflectors for TV's, Aero Shield and Aero Plus. The Aero Shield folds flat when not in use, but seems to be intended for larger vehicles than my Escape. The Aero Plus is intended to be mounted onto the stock roof racks on many SUV's like my Escape.

I did a search here on this forum expecting to find discussions on these, but didn't find anything. Just curious if anyone has any experience with these air deflectors, would like to hear it, positive or negative. I'm thinking they may cause a bit of wind noise, maybe cause aggressive wear on a roof rack not designed to carry that kind of force, and that maybe why I don't see a lot of information about them is because they don't work.

[BackOfThePack]

CavemanCharlie wrote:

BackOfThePack wrote:
The days trip plan trumps aero aids (any spending to save). It’s basic as to all stops planned, travel speed below the crowd on cruise control, and maximum vehicle separation while traveling. Zero idling.

“Trip plan” is a term used by truck drivers to account for all the days details — the how to — to maximize hours available at the best rate of speed (where speed is governed).

With RVs otherwise identical, your aero aids and my better trip plan will cause me to “win” the MPG game on a daily basis.

Once one understands how little time over the course of a full day one actually spends at cruise speed, the pieces fall into place.

I’m hardly against an aero rig, I spec’d both TV & TT for longest life with highest reliability at lowest cost of operation. Aero (plus a high compression engined TV) is central. But it has to be built-in at vehicle specification to be truly effective.

Average Speed (Engine Hours vs Odometer Miles) is related to Average MPG, directly. The aero wall is at 60-mph. No one gets better MPG above this. The rate of increase rises so rapidly above 65-mph that most big trucks are governed at 65-67/mph. “Time saved” no longer works past this (traffic volume and driver stress).

The RV lane in all this (Interstste) is from 62-64/mph. Not faster. No lane changes. No accel/decel events of any note. CONTROL of pre-planned stops and off-road minutes (driving, too) is major changes in AVERAGE mph & mpg. Which is the game.

I drove Chicago to Fort Worth in a rental identical to my sons car. He likes to run 70+. I eased along at 64-mph. His lower mpg meant he lost enough time for extra fuel that — on a trip just over 1,000-miles — his DRIVING time savings would have been 40-minutes (assuming he controlled time at pre-planned stops as well as I do. He doesn’t). He’d have burned 2/3 an extra tank of fuel to have done the same work. And likely arrived no earlier (is the point). As a transport-rated ex-military pilot he certainly understands all this.

So, you retired guys and budget-pinching Rvers pay attention: chasing pennies at a remote fuel stop WILL COST MORE. Risk, time and stress.

Save money during your commuter daily miles and it underwrites travel. Ten years ago when fuel was $4 and higher I figured out how to save enough annually in my daily driving to pay for 5,000-miles of “free” vacation fuel. You can too. Keep records of all gallons used and watch out for Average MPH. If yours is below 27-MPH as an average you’re a poor driver and abusive operator.

Apply a common sense attitude BEFORE you try spending money to save money.
Keep records and apply some discipline in ALL driving.

I think I understand and agree with most of your post. I don't understand the part you said " If yours is below 27-MPH as an average you’re a poor driver and abusive operator." That has me confused.

Most of what you are saying is to just plan you trip in advance, get on the highway, set the cruse control, and avoid starts /stops / idling etc. That all makes sense.


But, don't travel to much below the crowd speed. You are a hazard to traffic when everyone has to change lanes to go around you.

There are limits to this of course. If everyone is going 80 I'm not suggesting you should go 80! But, 65-70 is good towing speed on the interstate. If you want to go slower then that find a nice back road. One that is listed for 55-60 and enjoy the scenery. That is fun too and I often do that.

Average MPH = All Miles divided by Engine Hours.

The legal Interstate speed is a RANGE and usually from 45-70/mph. Traveling 60-62/mph is hardly a problem. One watches mirrors and dies his best to get traffic around.

The “danger” comes from those with ZERO regard for others. “Too fast for conditions” isn’t about weather, first, it’s about TRAFFIC VOLUME. Thoroughly illegal to use the left lane as a travel lane as a higher speed IS NOT a defense for screwing things up for others.

How many here understand that it is illegal to block entry to the passing lane?
YOU will be at fault, or overturned in the median, for such disregard.

Multiple vehicles in the left lane is a recent phenomenon (didn’t exist before late 1990s), AND DO NOT HAVE R.O.W. in any situation. “Passing” is one at a time.

Only the right lane is for travell, and ONLY the travel lane has Right-Of-Way. (Make your pass SHORT in duration; get on the throttle).

I’m coming up on someone slow my left turn signal comes on when I see a gap. That’s a sign to other drivers illegally in the passing lane. I’m not asking permission.

If one wants Fuel Economy, then that’s with (ideally) ZERO lane changes, ZERO braking or acceleration events (use terrain). If I can run 700-miles without passing anyone outside the city in a big truck at 62-mph, then can anyone. It’s not impossible to find those below 60, but they’re rare once away from metros. (Thry catch you by surprise, then you ain’t doing your job).

A combination RV is pretty much the worst handling/braking vehicle on the highway. “Stupid” is the guy in the left lane COMPLETELY surrounded with no way out of his dunderhead driving. (Tell us about your “skill”, we might need the laugh).

The game is to maintain the very greatest distance between self and others all day long. It’s not hard, it just needs new habits. Great rear view mirrors.

Safety & Fuel Economy track each other. The former always pre-empty the latter when it comes up.

Steady & Smooth. Year around. Solo or towing.

An air deflector may or may not show a difference. But until one has comprehensive records (cents-per-mile), “proving it” is quite another thing.

Average MPH below 27 is abuse. It’s not hard (again) to have better regard for the engine. Some new habits. The difference is right there on the annual fuel expenditure line. And even more so on the vehicle longevity calculation.

Engines have a maximum life in terms of gallons used as one way of tracking life. Miles aren’t as important.

“Spend to Save” world best in initial vehicle specification. Much harder later to recoup costs with magic gadgets. Those that work ONLY at aero-difficult speeds are LEAST likely to pay for themselves as time spent at steady-state cruise is so low.

Do the numbers. See for yourself.

.

[CavemanCharlie]

BackOfThePack wrote:
The days trip plan trumps aero aids (any spending to save). It’s basic as to all stops planned, travel speed below the crowd on cruise control, and maximum vehicle separation while traveling. Zero idling.

“Trip plan” is a term used by truck drivers to account for all the days details — the how to — to maximize hours available at the best rate of speed (where speed is governed).

With RVs otherwise identical, your aero aids and my better trip plan will cause me to “win” the MPG game on a daily basis.

Once one understands how little time over the course of a full day one actually spends at cruise speed, the pieces fall into place.

I’m hardly against an aero rig, I spec’d both TV & TT for longest life with highest reliability at lowest cost of operation. Aero (plus a high compression engined TV) is central. But it has to be built-in at vehicle specification to be truly effective.

Average Speed (Engine Hours vs Odometer Miles) is related to Average MPG, directly. The aero wall is at 60-mph. No one gets better MPG above this. The rate of increase rises so rapidly above 65-mph that most big trucks are governed at 65-67/mph. “Time saved” no longer works past this (traffic volume and driver stress).

The RV lane in all this (Interstste) is from 62-64/mph. Not faster. No lane changes. No accel/decel events of any note. CONTROL of pre-planned stops and off-road minutes (driving, too) is major changes in AVERAGE mph & mpg. Which is the game.

I drove Chicago to Fort Worth in a rental identical to my sons car. He likes to run 70+. I eased along at 64-mph. His lower mpg meant he lost enough time for extra fuel that — on a trip just over 1,000-miles — his DRIVING time savings would have been 40-minutes (assuming he controlled time at pre-planned stops as well as I do. He doesn’t). He’d have burned 2/3 an extra tank of fuel to have done the same work. And likely arrived no earlier (is the point). As a transport-rated ex-military pilot he certainly understands all this.

So, you retired guys and budget-pinching Rvers pay attention: chasing pennies at a remote fuel stop WILL COST MORE. Risk, time and stress.

Save money during your commuter daily miles and it underwrites travel. Ten years ago when fuel was $4 and higher I figured out how to save enough annually in my daily driving to pay for 5,000-miles of “free” vacation fuel. You can too. Keep records of all gallons used and watch out for Average MPH. If yours is below 27-MPH as an average you’re a poor driver and abusive operator.

Apply a common sense attitude BEFORE you try spending money to save money.
Keep records and apply some discipline in ALL driving.

I think I understand and agree with most of your post. I don't understand the part you said " If yours is below 27-MPH as an average you’re a poor driver and abusive operator." That has me confused.

Most of what you are saying is to just plan you trip in advance, get on the highway, set the cruse control, and avoid starts /stops / idling etc. That all makes sense.


But, don't travel to much below the crowd speed. You are a hazard to traffic when everyone has to change lanes to go around you.

There are limits to this of course. If everyone is going 80 I'm not suggesting you should go 80! But, 65-70 is good towing speed on the interstate. If you want to go slower then that find a nice back road. One that is listed for 55-60 and enjoy the scenery. That is fun too and I often do that.

[mr_andyj]

There is a BIG reason the big rigs have these same air deflectors....

The issues, looking at the red truck above, with most is that the deflector is too far in front of the trailer. Having the minimum gap between is critical. Though the red truck still has benefit with such a large gap, a smaller gap would produce better results.

WIth gaps between the truck and trailer you experience the full front of the trailer hitting oncoming air. The closer the trailer can be to the truck the better.
The closer the air shield is to the trailer the better.

Ideally for the red truck the shield should be hanging over the back of the truck and should be taller, closer to matching the height of the trailer.
The problem for that trailer is that it is bricked shaped. Manufacturers do not consider aerodynamics when building trailers, only how the interior will look when the wife is shopping for one.
More air hits the two side corners of the trailer than the top roof corner. The sides need more attention than the roof. A trailer with nice rounded front walls will be more aero than with rounded roof.

Consider making aerodynamic improvements to the front of the trailer rather than to the vehicle.

The back of the trailer is a very good place to increase aerodynamics, but will be more difficult.

[BackOfThePack]

The days trip plan trumps aero aids (any spending to save). It’s basic as to all stops planned, travel speed below the crowd on cruise control, and maximum vehicle separation while traveling. Zero idling.

“Trip plan” is a term used by truck drivers to account for all the days details — the how to — to maximize hours available at the best rate of speed (where speed is governed).

With RVs otherwise identical, your aero aids and my better trip plan will cause me to “win” the MPG game on a daily basis.

Once one understands how little time over the course of a full day one actually spends at cruise speed, the pieces fall into place.

I’m hardly against an aero rig, I spec’d both TV & TT for longest life with highest reliability at lowest cost of operation. Aero (plus a high compression engined TV) is central. But it has to be built-in at vehicle specification to be truly effective.

Average Speed (Engine Hours vs Odometer Miles) is related to Average MPG, directly. The aero wall is at 60-mph. No one gets better MPG above this. The rate of increase rises so rapidly above 65-mph that most big trucks are governed at 65-67/mph. “Time saved” no longer works past this (traffic volume and driver stress).

The RV lane in all this (Interstste) is from 62-64/mph. Not faster. No lane changes. No accel/decel events of any note. CONTROL of pre-planned stops and off-road minutes (driving, too) is major changes in AVERAGE mph & mpg. Which is the game.

I drove Chicago to Fort Worth in a rental identical to my sons car. He likes to run 70+. I eased along at 64-mph. His lower mpg meant he lost enough time for extra fuel that — on a trip just over 1,000-miles — his DRIVING time savings would have been 40-minutes (assuming he controlled time at pre-planned stops as well as I do. He doesn’t). He’d have burned 2/3 an extra tank of fuel to have done the same work. And likely arrived no earlier (is the point). As a transport-rated ex-military pilot he certainly understands all this.

So, you retired guys and budget-pinching Rvers pay attention: chasing pennies at a remote fuel stop WILL COST MORE. Risk, time and stress.

Save money during your commuter daily miles and it underwrites travel. Ten years ago when fuel was $4 and higher I figured out how to save enough annually in my daily driving to pay for 5,000-miles of “free” vacation fuel. You can too. Keep records of all gallons used and watch out for Average MPH. If yours is below 27-MPH as an average you’re a poor driver and abusive operator.

Apply a common sense attitude BEFORE you try spending money to save money.
Keep records and apply some discipline in ALL driving.

[dodge_guy]

As I said on the 1st page. The deflector alone mounted as far back as possible on my Excursion gave me a .5mpg increase. And the added benefit of all the bug splatter gone from the front of the trailer. Also, my TT was 11.5ft tall. People with shorter height trailers may not notice much of a difference.

[LVJJJ]

The rear of the trailer is the place to take care of aerodynamics. I used to have a deflector on top of my Chevy Van and Suburban, didn't feel like they did anything. Flat back trailers are the worst design ever, they don't allow the air flow to detach from the trailer, so there is a vacuum behind the TT that tries to suck it backwards. I now have a 2005 Trail Cruiser that is very aerodynamic, a very laid back front that curves up from the bottom the slants way back above the propane tanks. The rear of the roof curves down and the bottom is angled in so air comes up from the sealed underside and is routed up to break the vacuum. It's also very low the the ground, which I prefer. When i had flat backs, I built a rear deflector that directed the air coming off of the roof straight down the back to break up the vacuum, the difference it made was noticeable also kept the rear end clean. So don't bother with a front air deflector

[hussbuss]

I have both Air Tabs and air deflector. Deflector used on headache rack on long box dually with golf cart with long top on cart. Up, over, and around front of airodinimac travel trailer. Haven't washed any bugs off in 20 years and 2 trailers. The Air Tabs really eliminate the bow wave from passing semi's. No push as they come around you. Also keep the back of your trailer clean as the vaccumn doesn't come back together until about 20 feet behind your trailer. Happy with both products. I keep my units for a long time, so worth the expense for me.

[Gdetrailer]

RHasse wrote:
This isn't very scientific (or not scientific at all), but intuitively it seems that if they reduce the amount of bug splatter on the front of the trailer they must be doing some good in directing air flow over and/or around the trailer.

Yes and no..

Deflectors must be placed close as possible to the next taller object to be helpful in the mileage department.

Too far away from the taller object and you now get drag behind the deflector caused by the vacuum created behind the deflector..

Found a informative website that may help explain it better than I can..

HERE

I think you will find the "jury" is out on whether they are really effective for improving mileage or not. Some folks insist they get much better mileage, some folks ignore and side step that question which also says a lot.

I think they are in the "maybe" category and if they did improve the mileage, it will not result in a large significant improvement and may not be enough savings in fuel to pay for the deflector unless you are racking up tens of thousands of miles towing per yr.

My Dad had one for his 5th, never heard him bragging about it improving his mileage (and trust me, he ALWAYS bragged about everything he modified to improve his fuel mileage but this was not one of those items), he did however spend less time removing bugs.

[RHasse]

This isn't very scientific (or not scientific at all), but intuitively it seems that if they reduce the amount of bug splatter on the front of the trailer they must be doing some good in directing air flow over and/or around the trailer.

[Star_Gazer]

I made one for my truck years ago when I pulled a full profile travel trailer. I keep good records and over 40k or so miles it maybe helped mpg by 1/2-1mpg. But what it did do good was keep most of the bugs off the front of the trailer 😉

[IAMICHABOD]

Speaking of airtabs, I have AIRTABS on my Class C.

They really help on a cross wind situation,no more sudden buffeting. It has stopped the sideways push when being passed or passing a large truck.

They are a vortex generator that produce a counter rotating air trail several feet behind the vehicle, This airflow alteration improves vehicle stability. As far a mileage it may helped some but the stability they provided is amazing.

[marpel]

Just found them (and boy was I wrong on the name).

You can find them at airtab.com

Marv

[marpel]

A few years back, I read up on a product that is affixed (with a double-sided adhesive tape like substance) to the back edge of each side of the trailer/fifth wheel (vertical strips placed right at the corner on each side). They are designed to break the airflow and reduce drag and the vortex that a trailer being pulled through air causes. It's been a few years so can't recall full details but they are named something like "sharks teeth" (could be way wrong on that). New product at the time, but do recall some positive reviews. Supposed to be better than traditional wind deflectors. Don't know if they are still around but google should be able to find them.

Marv

[RHasse]

Thanks for the replies, I appreciate it. I welcome any other comments, positive or negative.