Streamlining/aerodynamics

[DouglasW]

Hello I'm new to the forum and also the group of happy Toy owners. My question is has anyone had personal experience with the AirTab streamliner or air deflector system. It's a series of small plastic deflectors that are placed on the rear sides and top of the motorhome to deflect air and ease the back pressure created behind the rig, thus enhancing mileage [so say} They are placed three to a foot to create this airstream. Also, a bit related, has anyone ever tried a bug deflector [usually smoked plastic] add on to the hood front and also possibly to the overhang roof front to deflect air and aid mileage. Any thoughts. Thanks Doug on Gabriola Island, B.C.

[wistoy]

I looked into the tabs for my own toyhome. The payback was like 100,000 miles.

Also talked to my friend ( manager of trucking form a major manufacture), the products do work but payback is a long way off,

Bug shields on a pickup usualy cost 1mpg. in fuel because of the change in airodinamics.

When I used to run a trucking company we install a buble like product to the box over the cab, which saved about 1mpg.

Maybe a custome molded unit over the cab, and flares from the cab doors to the mh body?

[Derek up North]

Unless 'time is money', the best way to save on fuel bills is to slow down a bit. Resign yourself to life in the slow lane or pay the price.

[Vanman]

Derek up North

Unless 'time is money', the best way to save on fuel bills is to slow down a bit. Resign yourself to life in the slow lane or pay the price.

When the first gas crunch hit a van magazine tested all the products on the market at the time and found differences hard to measure with all of 'em. But they did find one thing that worked every time, removing the side mirrors!!! not legal but works.

vanman

[Derek up North]

I seem to remember that test. Might be illegal to drive with none, but no legal requirement for them to be huge, flat 6"x12' cookie sheet sized like we use. Not that I'd want to try driving without them!

[84TOYRV]

Removal of Air Maxx vent covers and the rooftop ac would improve aerodynamics. Also, a good coat of wax.

[Vanman]

Derek up North

I seem to remember that test. Might be illegal to drive with none, but no legal requirement for them to be huge, flat 6x12 cookie sheet sized like we use. Not that I'd want to try driving without them!

When I got the van in 1970 it came with what they called "West Coast Mirrors" which were required for towing, or if the center rear view mirror was blocked. I seem to remember when we first got this Toy someone telling me that standard also applied to RV's here. I don't know about RV laws but I do know towing laws vary from state to state. Wonder how having a full time wide view rear camera might affect the mirror regs.

vanman

[DouglasW]

Well, thanks for the responses re aerodynamics. Very interesting all but I've concluded the single most effective gas saver is a light right foot! However, through this site (http://www.gassavers.org/showthread.php?t=1482} I found D.I.Y. Airtabs. So for the price of a can of spray paint [i had the light weight alum kicking around] I have made and installed 65 Airtabs at the rear of my Toy (a 1991 Warrior, by the way). Will be a conversation piece if nothing else. I'm hoping they will at least disrupt the rear turbulence enough to keep the back of the Toy somewhat cleaner. Time will tell. of course. Fun, fun and more fun. I've also learned that my O2 sensor may be defective, causing low mileage. As soon as I jump the Inspection module terminal and get the codes to confirm I'll replace them. But that's another story. Just itching' for Spring. DougW on Gabriola Island.

[Derek up North]

Sorry to hear about the O2 sensor problem. That means we won't get accurate before/after results for your DIY AirTab experiment!

Did you glue them on?

[DouglasW]

Yeah the O2 thing kinda delays the experiment, but I'll eventually know. The small alum tabs are fixed in the rear sidewalls and roof using clear silicone and when properly cured I'm sure they will be secure. Am also thinking of installing a spoiler under the front bumper to clean up the under chassis airflow. Perhaps a bug deflector installed upside down. Have no specific tips on this but will continue to search forums etc. to get ideas. All in the name of fun, fun and more fun. You just never know DougW on Gabriola Island, B.C.

[waiter]

From my professional view, (I've designed, built, and fly airplanes)

I've stayed out of this so far because I knew I could spend hours talking about this.

Bottom line - I think we could see a noticeable increase (maybe 1/2 mpg) by installing air deflectors on the back, BIG deflectors, Don't waste time or money with tabs.

****** WARNING - TECHNICAL STUFF **********

You couldn't have done anything else to a Toyhouse to make it a perfect example of what not to do if your attempting to make an aerodynamic vehicle.

The vortex generator tabs in the link would help clean up turbulent airflow if we had a laminar airflow separation problem. However, after thinking about it for about three seconds, I can't think of anywhere on a toyhouse that I could envision the existence of laminar airflow, let alone separation. ( You've probably seen Automotive commercials where you see a car in a wind-tunnel and they have tiny smoke streams that blow across the car. It looks very nice, the smoke lines go over the hood, the windshield, across the back, and the smoke line doesn't break up. Then when it gets to the back you see the little smoke streams kind of start turning like little tornadoes. thats where the laminar airflow trips and we start introducing drag. Unfortunately, in a Toyhouse, this laminar flow gets tripped about three feet in front of the grill. (actually, it never exists to start with.

Our main problem is flat-plate drag (a barn door) If you put a barn door (or a Toyhouse) in a wind tunnel, what you'll see is a bow wave forms in front of the vehicle. There is very little airflow inside the bow wave. Air compresses as it hits this bow wave, flows around the bow wave and past the barn door, then you have this huge low pressure area behind the door as the air attempts to decompress and recombine, Its this low pressure area on the back side that creates the drag.

BOW WAVE

This applies to subsonic speeds, I hate to break it to you, a Toyhouse definitely falls into this category.

Ever notice how a passenger jet has a blunt nose, then they taper off very smoothly at the trailing edge. You can force air to seperate and compress (Front of vehicle), but you can't force it to de-compress and recombine (back of vehicle).

Whats interesting, a bow wave is actually clean and introduces little turbulence. Air flows around the bow wave and compresses as it passes over the vehicle (or barn door) . (On the airplanes, you try and design the nose so it will follow the contour of the bow wave, if you do a good job, the bow wave will be a laminar flow across the nose and create very little turbulence.

For you older people who remember the vent wing window, Notice you don't get a lot of air on a Toyhouse vent window,. Thats because its inside this bow wave, and there isn't a lot of airflow.

TRAILING EDGE

I've thought of doing something like this, just haven't gotten around to it. I believe it would have a measurable effect.

I said that you could not have built an aerodynamically dirtier vehicle if you tried, that's not exactly correct. The way the roof curves around to the back wall, helps reduce drag significantly but I bet that's not why they did it that way. The 90 degree angles where the sides meet the back are going to severely cut into efforts to clean up that airflow. (picture Airstream trailers)

The most bang for the buck would be achieved by redirecting airflow into that large cavity known as the back wall, the only problem is, if this is done incorrectly, you'll actually increase the drag instead of reducing it. If we were doing 250mph, I would say, don't do this without some tufting or wind tunnel testing, but at 60mph, probably going to be hard to aggravate the problem.

Large side deflectors mounted on the sides and top to redirect air would probably produce a noticeable difference, If I were going to guess, I would say if you took a 6ft long PVC pipe, maybe 24 inches in diameter, cut longwise into 1/3. This would give you three 120 deg deflectors that are 6 ft long. Mount two of them on the back so that they stick out the sides into the airstream about 6 inches, they will scoop that air, and turn it about 120 degrees and deflect it toward the center of the back wall.. Do the same for the roof with the third piece.

A quick calculation of static pressure gives you an idea of why the back wall is the problem and why speed has such a significant effect on mpg.

Drag goes up by the square of speed.

Static pressure

30 mph = 0.02psi

55mph = 0.06psi

65mph = 0.09psi

back wall is 6ft x 6ft or 5184 sq inches.

Multiply this by the pressure to see what the over all pressure (vacuum) is on the back wall . This is like a giant vacuum trying to hold you back, its an anchor.

30 mph = 0.02psi = 104 lbs

55mph = 0.06psi = 311 lbs

65mph = 0.09psi = 466 lbs

These numbers are by no means exact, and there's a lot of room for other factors, but this should give a basic idea on how/why speed and aerodynamcs play an important part in gas mileage.

Static Pressure Chart

Scroll down in the link above to see the speed/pressure chart.

NOTE - If your interested in making a manometer to check your LP gas pressure, This link points to how to build a manometer.

.

John Mc

88 Dolphin 4 Auto

[Derek up North]

... on Gabriola Island, B.C.

Not knowing where Gabriola Island is, I Googled it. Wow, you're not exactly in a good spot for doing mileage comparison testing! I'd guess you're a few days drive from the nearest straight, flat stretch of road. For just about every other purpose, it looks ideal!

[mulwyk]

My streamlining efforts have mostly been an attempt to reduce the frontal area. I figure, aerodynamically, my Sunrader looks like a 8' x 7' box trying to push through the air....56 sq. ft. of frontal area. I first removed two Maxxair vent covers (1.9 sq. ft) I replaced the original 1 flat mirror and 1 convex mirror on each side with a single flat mirror with a convex insert. (0.2 sq. ft.). Then I tried to further smooth the exterior: I removed the range vent hood outlet, the heater outlet, and shore power cord fitting. I removed the "luggage rack" and ladder (0.5 sq. ft.). I covered over all the holes with flat aluminum plates. I even removed the spare tire but I'm not sure if that had much effect.

Total: 2.6 sq. ft. reduction of frontal area...or about 5% less drag.

[waiter]

Mulwyk;

Obviously, anytime you can remove something from the airstream you've eliminate the flat plate drag.

Rounding 90 degree corners helps significantly, I see some car carriers that the back door has nicely rounded corners.

I've also seen several 18 wheelers that have retractable air dams (panels) on the back doors that point in about 30 degrees, these help a lot.

The company I work for has a patent on an inflatable bag that mounts to the rear doors (18 wheeler), nice rounded contours that sticks out about 4 ft behind the doors. This completely fills in the low pressure area behind the truck at 70 mph and tuft testing shows a very good laminar flow.

John Mc

88 Dolphin 4 Auto

[mulwyk]

That's interesting, John. I wonder what a boattail extension would do on a Sunrader? You could put a nice quarter round window seat back there...and pirate ship windows! AAARRR!

[DanAatTheCape]

Well, thanks for the responses re aerodynamics. Very interesting all but I've concluded the single most effective gas saver is a light right foot! However, through this site (http://www.gassavers...ead.php?t=1482} I found D.I.Y. Airtabs. So for the price of a can of spray paint [i had the light weight alum kicking around] I have made and installed 65 Airtabs at the rear of my Toy (a 1991 Warrior, by the way). Will be a conversation piece if nothing else. I'm hoping they will at least disrupt the rear turbulence enough to keep the back of the Toy somewhat cleaner. Time will tell. of course. Fun, fun and more fun. I've also learned that my O2 sensor may be defective, causing low mileage. As soon as I jump the Inspection module terminal and get the codes to confirm I'll replace them. But that's another story. Just itching' for Spring. DougW on Gabriola Island.

O2 sensor?? Been there done that. These units are Odb1 codes which are rather lacking on info, (Odb2 came out about '96) When you stick your jumper in be careful not to push the pin receptacles down (if you do you can unwrap the assembly I pop it apart to access the pin holes..

If you even suspect that you have an O2 issue I would just put it in -- there is only one & it is relatively easy access.

Check your mass flow too. When you look up the codes - I think I recall a "20" it covers a lot of stuff. Your MF is the module on your air cleaner -- make sure your wiring harness plug in to the F is not loose (probably not loose).

While troubleshooting my issue (low mileage) I found that one brand of diagnosing testers (can;t recall the mfg but they made many many machines in many shops) would tell you to "force a code" which amounts to puling the plug off of the O2 sensor & drive around a bit. Which I had done that about $500 dollars of labor sooner.

If I had it to do over again I would throw a new O2 sensor at it if I even suspected that it might be bad. 100-150 bucks. BTW, I gather that they do go bad - 20 years old & >50,000 miles - meets the criteria.

[Wayne & Irene]

Hi Douglas

Good to learn we have another Islander close by. Not Vancouver Island, but close enough. Have a look under the ToyIns folder for info on an upcoming Vancouver Island event this summer. (2012). I'm in Crofton and will look after organizing this event if there is enough interest. Hope to see you there. Cheers, Wayne

[rraabe]

So, if air pressure is building up out front, wouldn't a ram air tube from the frontal area to the air cleaner (kind of like what K&N sells for some vehicles) give us more intake air like very slight turbo charging and help mileage? When I pulled a tall flat fronted fifth wheel with a 1987 Ford F250 diesel, i bought a plastic duct that pulled air to the filter from the cowl vents in front of the windshield. It did give me a bit more power (thing was a sled) but I used every bit of it to hold 62 MPH. With the Toy, I might be able to ease back on the foot throttle a bit?

[waiter]

rraabe;

Yes it will. The Ram air will contribute about 0.08psi to the air pressure (at sea level) So, of your starting with 14.7 psi, at 60mph you'll have 14.78psi. If you have the proper laboratory instramentation, you should be able to see approximately 0.5% increase in HP.

Note - On my plane I have an Aux Ram Air door that supplies the Fuel injection manifold, and at 250 mph, I see an increase of about 7%, and that 7% is very noticeable.

JOhn Mc

88 Dolphin 4 Auto

[rraabe]

Definitely not worth the work and expense, oh well, if you don't dream, you will never advance.

Since we are talking drag (slightly off topic) I'm planning to add two 4 foot top loaded cb antennas to my mirror brackets. Problem is, they do not extend out past the body up top. I'm planning to add a steel bar to top mirror bracket to extend and wonder how far out from the body those antennas need to be? OTOH, will the decrease in MPG just piss me off more than the benefit of having that communication make me happy?

[chefdave]

Hi

have just fitted a bull bar to my dolphin and it has made a huge postive difference to wind noise and ability to stay in overdrive. ummmm not what i was expecting. any theoys on why.

Thanks

dave

[waiter]

Don't know what a "bull bar" is??

That chrome bumper thing, OH Thats what they call them.. :-)

I wouldn't expect any noticeable difference, there so much frontal area, I'd like to put one of these in a wind tunnel and see what it looks like, but I have a good idea there is a huge bow wave about 2-3 feet in front of it and the air is stagnate around the hood. Maybe ill put some "tufts" on the hood and go for a drive. (those little yarn strings so you can see how the air is flowing over a surface)

JOhn Mc

88 Dolphin 4 Auto

[chefdave]

Hi

yes it is a chrome bumper goes full width of front. if someone can explain how to upload a photo, i will be able to show you. since fitted use a lighter throttle and 50+mph comes up when driving up a 1 in 10 hill for over a mile. thats on an auto box in overdrive and no over heating

[chefdave]

Also looking to remove air con unit on top and lose window/vent/skylight over cab area to reduce noise. over cab body thinking of fitting perspex and tinting it. to help lose a few kilos to aid stability and try and gain a couple of mpg. along with a service new ignition leads dizzy cap and rotor arm. as i live in uk and drive a pre 1992 vehicle i am legally allowed to remove cat from exhaust. this should make biggest difference.

[Skydancer2992]

Removing the cat may or may not help with gas mileage. If back pressure is too low, incoming fuel/air mixture is scavenged out the still open exhaust valve.

For gas mileage, I like the idea of a front air dam to divert air away from the draggy underside of the camper. I would probably pick up some bumper brackets at a junk yard and mount them upside down to hold the air dam.

[fred heath]

Definitely not worth the work and expense, oh well, if you don't dream, you will never advance.

Since we are talking drag (slightly off topic) I'm planning to add two 4 foot top loaded cb antennas to my mirror brackets. Problem is, they do not extend out past the body up top. I'm planning to add a steel bar to top mirror bracket to extend and wonder how far out from the body those antennas need to be? OTOH, will the decrease in MPG just piss me off more than the benefit of having that communication make me happy?

If your mirrors are like mine they're mounted to the outside door skin and window frame (jr west coast). The door skin is made of very thin sheet metal. Adding a 4'cb antenna could very easily rip the whole thing off in wind or if hit.

I mounted my CB antenna to the side of the coach body by the front overhang. I added a 4 bolt backing plate behind the fiberglass for strength. Then ran the cable down the side and into the cab. Works great. Very little cable shows on the outside.

[86rader]

i highly recommend ecomodder.com . There are a few threads about RV aero mods. Thre is a guy that does a few things with a ford powerstroke powered C class, including a boat tail. I believe he was able to get close to 20 mpg. he also made fairings for roof AC and a front airdam. There is a guy that had a V-6 dolphin, I think. He did a front air dam and maybe a few other things. mainly, I think he just used hypermiling techniques and was able to get into the low 20s.

[86rader]

here is the thread. he goes from 14 to 17 mpg with the boat tail. check out the roof AC fairing. a real work of art.

I would like to get a shorty sunrader and get it as smooth as possible on the roof and add a similar boat tail. It could double as a nice bike holder.

[Maineah]

I would work on directing air away from the over hanging bed area above the wind shield. Maybe a wing across the back to break up the turbulence behind the flat back end.

[86rader]

another vehicle to consider is the lesharo. it came with a renault diesel, later turbo diesel. these things make our toy houses look fast. due to horrific reliability, many have been repowered to mopar 3.3 fwd setups. these reportedly can break 20 mpg and have reasonably performance.

the succesor to the lesharo is the vw van based rialta. these came with the vr6. not sure what they do mieage wise, but, i suspect similar to toyhomes. Would love to have one of these with a 6 speed tdi drivetrain.

[chefdave]

Hi

love my v6 engine but for mpg improvement think i would go with a nissan terrano (not sure of name in usa). Had a terrano and got 35 mpg on a 2.7 turbo diesel engine is bullet proof and tunable on intercooler version. extra 25 bhp not sure of torque increase but can tow 2.8 tons legally in untuned form. sheds loads of torque from tick over to 3000rpm. had 2+ ton of caravan and fully loaded boot over motorway speed limit with no sign of stress. must make it a suitable doner engine.

[chefdave]

Hi

wrnt on to air tabs uk. they went to usa air tabs and answer i received was a little unexpected. not worth doing as my dolphin has rounded edge at rear and my sides are corrugated. have noticed most dirt collects on cab side windows not back of toy. obvious conculsion would be to improve air flow around cab. to reduce air flow underneath have looked into lorry spary control brushes. similar to a very long elongated paint brush. these would slow air flow under toy. i would fit under front bumper along cab sills and under where the motorhome body extends past cab. if what internet says is right it will push air around body create low pressure area behind rad also with these spary control brushes no worries about them bresking off if you accidental hit dips sleeping policemen etc

[chefdave]

Hi

been doing some research on aerodyamics by looking at new to 3 years old vehicles (anything from a car to a 50 seater coach. most seem to have a spoiler that is level with roof and jutts out to the rear by 6-8 inches. even cars with sloped back window has one. Was thinking of buying a spoiler (from any vehicle that i think will fit eith little modifaction) for the back and trying it out. any views either way would be appericated

[waiter]

Anything would help, Rounded corners help a lot. The idea is to fill that rear end with air and do it as cleanly and with the least amount of turbulence.

There you learned in two sentences what too me 6 years to learn.

There isn't a lot structurally to mount stuff to, so look at that before you go to far.

How much would you gain?? If you were able to put large deflectors on the sides and top, I believe you could see a 10% increase in MPG at 60 mph. That rear end accounts for a lot of drag, and drag goes up by the square of speed ( twice as fast, 4 times the drag)

John Mc

88 Dolphin 4 Auto

[chefdave]

Hi john

what would the deflectors look like and how large. Would it possiable to post a picture or rough sketch of what deflectors would need to look like.good point about mounting spoiler. 10% increase in mpg would nice provided the cost does not make pay back take years to recup.

thanks

dave