Aero RV (custom boat tail for '95 Ford E-350 Class C motorhome)

[JasonG]

Awesome !
Never thought of fairing my AC units. Cool.

The belly pan on the fiver netted around 1MPG for me. (That's nearly 3%)
The biggest benefit is (so it seems) is less sway in cross winds. I'm guessing from the wind pushing on the I beams.

I have to figure a way to make a Kamm clear the ramp door though..........

Can't wait to see V2 !!

[orbywan]

Originally Posted by JasonG

Awesome !
Never thought of fairing my AC units. Cool.

The belly pan on the fiver netted around 1MPG for me. (That's nearly 3%)
The biggest benefit is (so it seems) is less sway in cross winds. I'm guessing from the wind pushing on the I beams.

I have to figure a way to make a Kamm clear the ramp door though..........

Can't wait to see V2 !!

I should have tested it before and after with the A/C fairing but according to the tell tails the air is flowing perfectly over the rear upper section, in spite of the steep angle. I think the A/C fairing is mostly responsible for that.

If you can figure out a way to Kamm the back, I'd love to see the results mileage-wise. I've never seen it done on a 5th wheel before. Never saw it done on an RV before either. To be honest I didn't think it would make such a big difference, but I kept looking at the huge abrupt drop off (for the air) area at the back and figured if it worked for NASA (referring to the Dryden AFB tests), I'll give it a shot. Completing the belly pan is next.

[aerohead]

Originally Posted by orbywan

I should have tested it before and after with the A/C fairing but according to the tell tails the air is flowing perfectly over the rear upper section, in spite of the steep angle. I think the A/C fairing is mostly responsible for that.

If you can figure out a way to Kamm the back, I'd love to see the results mileage-wise. I've never seen it done on a 5th wheel before. Never saw it done on an RV before either. To be honest I didn't think it would make such a big difference, but I kept looking at the huge abrupt drop off (for the air) area at the back and figured if it worked for NASA (referring to the Dryden AFB tests), I'll give it a shot. Completing the belly pan is next.

I don't know if a 1970 VW Westfalia Campmobile qualifies as an RV,but the 18-inch boat tail,with Breer/Fachsenfeld/Kamm-chop that I put on it in 1980 was good for almost 4 mpg by itself.
The radiused tail of the VW allowed more lead in curvature,so in essence,the virtual boat tail was more like 2-feet in length.
The tail curved into a maximum 20-degree angle,top and sides.No bottom.
With spare tire cover( on nose),full bellypan,rear wheel skirts,and tail,the van was capable of as high as 35 mpg @ 55 mph,up from 27 mpg.

[orbywan]

Originally Posted by aerohead

I don't know if a 1970 VW Westfalia Campmobile qualifies as an RV,but the 18-inch boat tail,with Breer/Fachsenfeld/Kamm-chop that I put on it in 1980 was good for almost 4 mpg by itself.
The radiused tail of the VW allowed more lead in curvature,so in essence,the virtual boat tail was more like 2-feet in length.
The tail curved into a maximum 20-degree angle,top and sides.No bottom.
With spare tire cover( on nose),full bellypan,rear wheel skirts,and tail,the van was capable of as high as 35 mpg @ 55 mph,up from 27 mpg.

I didn't mean it's never been done before, I've just never seen one on an RV, except in PhotoShop. An 18" boat tail seems really short, but it was a short vehicle, goes to show how much they make a difference I guess.

Doing a belly pan on this RV is going to be a pain but I kind of have to finish it. If I put a full pan on it, should I also make a front air damn?

[shorttimer]

Super pro work! If you do as good of a job for an under belly, I'll bet you pick up another nice 'reward'. Keep it up!

[bondo]

That is some very impressive work. Enjoy the extra money you will save that you don't spend on fuel.

Bondo

[slowmover]

I have to get the A/C to work with the fairing in place.

I admire this. Have been saving pics of aircraft wheel fairings and turbine engine air inlets to someday streamline a roof A/C on an aluminum trailer (looks & performance).

[cleanspeed1]

Excellent job on the aeromods! You should give Jody a call at dpTuner for an economy tune since you have a PSD. Will still pick up a little power, optimize the shift points in the transmission. If you haven't done the exhaust yet, Hypermax has a good system with a downpipe ( the stock downpipe is crushed from the factory to fit the chassis ) that doesn't cost an arm and a leg. And switch to Evans Coolant.

[thatguitarguy]

Putting this in the perspective of fuel savings, if you drove 100,000 miles in your rig at 15.97 MPG over 13.1 you'd save about 1372 gallons of fuel.

Some of us are really pleased with ourselves - me included - when we can take our 50 MPG and bump it up to 60 MPG. but over 100,000 miles, that's only saving 333 gallons of fuel.

Most people don't use motorhomes as daily drivers, but if you travel a lot, your aerodynamic improvements will net you HUGE savings!!!

[orbywan]

Originally Posted by thatguitarguy

Putting this in the perspective of fuel savings, if you drove 100,000 miles in your rig at 15.97 MPG over 13.1 you'd save about 1372 gallons of fuel.

Some of us are really pleased with ourselves - me included - when we can take our 50 MPG and bump it up to 60 MPG. but over 100,000 miles, that's only saving 333 gallons of fuel.

Most people don't use motorhomes as daily drivers, but if you travel a lot, your aerodynamic improvements will net you HUGE savings!!!

I don't drive it much now but it's good knowing it's efficient for it's size. I still have to finish the A/C unit, skin the undercarriage (that's going to be serious fun) and do some mods to the front so I'm hoping there's better numbers ahead. Time will tell.

I was surprised the Dryden tests didn't show better numbers for rounding off the front, so I went after the tail first. I found another chart on a truck products company's web site, which I can't find at the moment, that shows rounding a brick shape object in the front reduces Cd by 50%, which I think is the way the average Joe thinks, including me until I tried the boat tail.

Anyway, I'm going to try several things up front, there's serious room for improvement there also.