Aeromodifications for large motorhome

[orbywan]

Originally Posted by aerohead

If the vehicle has completely flat sides,you'd apply the same curvature from the
'Template' as you're using on the roof,as the sides permit.
If the vehicle is taller than it is wide,just use the 'Template' for the width,then copy that curvature for the top.
The 2011 Prius boat-tail trailer illustrates the first condition.
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By using the same curvature,top and bottom,it's a way to help prevent longitudinal vortices which have enormous drag.And it avoids the tight turn you mention which would trigger separation right there.

OK, thanks, I'll keep the sides and top curvature the same, and try the make the bottom curvature the same also, although it may be a little off, there's a lot going on down there. I'll probably remove the rear bumper to make the transition from the bottom a little cleaner.

[winkosmosis]

Start at 0 degrees, end at 15 degrees (or 12 or 10 or whatever) and eyeball the curve between. You don't need a template.

[CrazyLee]

Originally Posted by crmears

My situation is not one typically discussed here but the phyics of fuel economy are the same. My 2008 Class A diesel motorhome gets 8 mpg at 65 mph. I have a goal of getting a solid 11 mpg. It is 26,000 lbs, 8 by 13 feet for a frontal area of 104 sq. ft. It is shaped like a brick (front and rear) with rounded corners. It has 2 large ac units on top and a couple of vents stickins up also. The engine is a Cummins 360 hp, 8.3 liters, variable blade twin turbo, computer controled fuel injection and computer controled transmission.
My assumption is 70% of energy is used to overcome aerodynamic drag so that should be my focus. I own a body shop have the means to create a front end that looks like a Japanese bullet train with a remote controlled liftable air dam 3 inches from the pavement. I could also modify the rear to look like the rear of the bullet train.
Would this be enough to gain the desired 3 mpg? Or could it even give me more gain? Any other ideas.
Thanks,
Randy

I am in the ecomodder mode with my rig. It has a Chevy 454 engine w/ TBI and automatic transmission. I have hooked an MPGuino to it and I have gained a lot of info on how to drive it. First, accelerate briskly, letting the tranny up shift as soon as possible. Each time it shifts up I gained fuel economy. I found that max economy was from 45 mph to 53 mph. Later I discovered I lost 3 mpg running at 53 to 54 mph. The brick wall effect is very pronounced. I settled on 50 mph and my last fuel check showed 16.4 mpg!

Here is a clip from my "blog post"

We got fuel in Westlake, Ohio. I again put $100 in the tank and since the price per gallon was $3.659 the gallons were 27.33. the miles driven was 450, that makes it 16.4 MPG. This is the best I have seen on the motor home so far. Slowing down 1-2 mph did the trick. Although 50 mph seems so slow, I enjoy it, since the driving is easier.

You can read it all here.
crazycomputers dot com/Fleetwood_Flair_26/]1993 Fleetwood Flair

My fuel saving tips are on this blog as well.

Cheers for saving fuel

[crmears]

It is fairly well understood that driving slower will give an increase in mpg. One guy put up a charge showing 7 mpg at 70, 8 at 65, 9 at 55 and 10 at 45. Your rig was 16 k which is light for a class A. The 454 is not know for getting such good fuel economy and I am not clear on how you calculated it. When you put in $100 worth of fuel was it just a coincidence that it took $100 to fill it? Or were you not filling it and just making an estimate based on the gauge level?

Motorhomes often have 100 gal tanks and it is really difficult to fill them to the same level. It is very easy for me to be off 5 to 10 gallons on a fill up.

Best wishes,
Randy

[crmears]

Just read an article from Cummins. It was 32 pages long and discribed the critical factors in getting better mileage from a truck with a Cummins engine. Their main point was that below 50 mph there is more rolling resistance that aero drag. Above 50 mph the air drag is a greater source of restance. Worn tires get better mileage. Ribbed tires get better mileage than cross treads. It is essential to inflate the tires to the safe maximum as every 10 psi low can cost a 1% loss in economy. The best truck drivers get 30% better mileage than the worse drivers. Just use the cruise control and you will beat the average.

Randy

[CrazyLee]

Originally Posted by crmears

Just read an article from Cummins. It was 32 pages long and discribed the critical factors in getting better mileage from a truck with a Cummins engine. Their main point was that below 50 mph there is more rolling resistance that aero drag. Above 50 mph the air drag is a greater source of restance. Worn tires get better mileage. Ribbed tires get better mileage than cross treads. It is essential to inflate the tires to the safe maximum as every 10 psi low can cost a 1% loss in economy. The best truck drivers get 30% better mileage than the worse drivers. Just use the cruise control and you will beat the average.

Randy

Thanks Randy,

I know how hard it is to figure fuel mileage for a big RV. I went from fill up to fill up, 1/2 tank to full (my RV has another 1/4 to go to actual full). The $100 is what the pump took out of my credit card and shut off. The previous fill up was about exactly the same. I used the miles driven and fuel used to calculate the mpg from my last run. The difference between the previous fill and the best results was 100 miles more travel, 350 miles vs 450 miles.
I'm not sure what affected the lower mpg but ethanol may be the culprit

My MPGuino was not working right, the data was trashed by a lightening strike! So I couldn't get those results.
I had it re-flashed and I found the bad data yesterday. I hope to check it out today for correct mpg.

Cheers, Lee

I ran the RV today, 6-10-2011 and the MPGuino responded well. The temperature was 60 deg. and it had rained today so the humidity was high.
My fuel mileage reading was 13.8 mpg at the highest.

I'll have to run another mileage test once the gas price drops to $3.50 or so. I'll have to fork over $200 to fill it. Ouch.

[Charles7a]

Hi Lee,

Are the MPGuino settings on your webpage the current settings you are using for your motor-home? I have a similar motor-home and have just received my MPGuino in the mail.

My motor-home is a 28' Class A 1995 Winnebago Warrior w/ a TBI 454. I have been using a netbook, TunerPro, and an ADL cable to get instant MPG for my motor-home. The MPGuino will be a simpler setup.

Modifications so far:
AquaTune AquaThrust Plus HB
AirTabs
Synthetic engine oil
Fabricated cold air intake
Fabricated front air dam
Accel Super Coil
8.5 MM Spark Plug Wires
K&N air filter
All 6 tires inflated to 90PSI

I am curious to find out if your fabricated wheel well covers/skirts made a difference. In my previous motor-home I used AirTabs in front of the wheel wells to redirect the airflow around the wheel wells. I also had AirTabs in front of the large truck style mirrors and at the rear of the roof-top A/C. I was aiming for "the ugliest motor-home on the road" since that motor-home was ugly to begin with. My current motor-home only has AirTabs at the rear of the motor-home. For now...

My fabricated air dam wraps around to the front wheel wells and goes down to ~5" above ground. It is flexible enough to withstand "eating curbs".

Charles

[ChazInMT]

Charles, give up on the airtabs, they're crap. Build fairing for your roof AC and something on the back to make it more aerodynamic there, you'll see the biggest gains. Read Orbywans thread and you should gather volumes of info from it. Ask questions there. Trust me, putting something on back to help the aero will keep you in the running for Ugly RV, but it'll put a big ol smirk on your face when the darn thing actually helps you out.

[orbywan]

[QUOTE=Charles7a;253731]Hi Lee,

"Are the MPGuino settings on your webpage the current settings you are using for your motor-home? I have a similar motor-home and have just received my MPGuino in the mail..."


Charles where did you get your MPGuino from? Does anyone know if those will work with diesel injectors?

Chas is right, vortex generators and most of that other stuff will net you minor amounts (or nada) compared to a boat tail, a belly pan, A/C fairings, etc. Not as easy as sticking on vg's but...

As for ugly, beauty is in the eye of the beholder. I think my RV looks way better with the boat tail. If the early results of a 25% improvement turn out to be accurate, I don't care what it looks like!

[CrazyLee]

Hi Charles,

I have found that the MPGuino seems to work but it presently shows more mpg than I atually get. The difference is about 1 mpg more than what the RV gets by fuel mpg calculations. I haven't recalculated the mpg to reset it. I just got back from a 5300 mile trip to Vancouver WA from Muskegon, MI. Actual total mpg was 10.49. This included a lot of hot 100 degree driving and mountains too. The A/C only showed -.2 mpg for the cooler air. We ran it continuously. Not bad. The headlights showed a -.1 mpg This I was surprised to see. Usually the MPGuino showed 12 mpg or 11.9. at 50 to 55 mph. It didn't vary much. My driving speed started at 50 mph and later went to 55 mph. 50 is just too slow! I do know that 50 mph will get a solid 12-13 mpg.

I think the Pulse and Hold injectors on the 454 GM engine messes up the MPGuino's readings. I read all the posts on this problem but I haven't tried their ideas yet. I will soon, and also try an Operation Amplifier to square up the wave form for a true pulse with modulated signal.

The wheel skirts were a toss up. I ran with them off and on. Maybe a -.2 mpg loss! I put them on on the way home. I think they just look neat. LOL
At 55 mph the wind resistance is not that great. If you drive like I see all the big RV's (at 70 mph) are going maybe the wheel skirts would help. I think that RV manufactures have probably ruled them out by now anyway.

My settings on the MPGuino are what I ran. I played around with the VSS delay and set it lower to 7. the I had a problem with reading @ 60 mph fuel use since the reading would go down to 1.5 mpg! Now the mpg stays about 10-12. Still too high, I think 8 mpg would be better @ 60.

Stay tuned for the MPGuino injector tests later this summer, or maybe September.

I have a OBDI plug on this rig. Maybe it had an ODBII inside the ECM with a ODBI connector. Some Corvettes had this arrangement. I forgot that question when my auto tech hooked up his scanner. I couldn't read the ECM with my ALDL cable and laptop hooked to the ECM.

If I have this I wouldn't need the MPGuino, just read the computer screen.
No messing with computer parameters, wires and stuff.

Cheers, Lee

Originally Posted by Charles7a

Hi Lee,

Are the MPGuino settings on your webpage the current settings you are using for your motor-home? I have a similar motor-home and have just received my MPGuino in the mail.

My motor-home is a 28' Class A 1995 Winnebago Warrior w/ a TBI 454. I have been using a netbook, TunerPro, and an ADL cable to get instant MPG for my motor-home. The MPGuino will be a simpler setup.

Modifications so far:
AquaTune AquaThrust Plus HB
AirTabs
Synthetic engine oil
Fabricated cold air intake
Fabricated front air dam
Accel Super Coil
8.5 MM Spark Plug Wires
K&N air filter
All 6 tires inflated to 90PSI

I am curious to find out if your fabricated wheel well covers/skirts made a difference. In my previous motor-home I used AirTabs in front of the wheel wells to redirect the airflow around the wheel wells. I also had AirTabs in front of the large truck style mirrors and at the rear of the roof-top A/C. I was aiming for "the ugliest motor-home on the road" since that motor-home was ugly to begin with. My current motor-home only has AirTabs at the rear of the motor-home. For now...

My fabricated air dam wraps around to the front wheel wells and goes down to ~5" above ground. It is flexible enough to withstand "eating curbs".

Charles