Why no Streamlining?

[BobMontgomer]

I love the look of modern class A motorhomes, but at the price of gasoline I have to wonder why manufactures do not make them more streamlined. Some of the older ones appeared to be. I would think at 60 mph it would make a a big difference..

Anyone know the history of this subject?

[Jake21]

I have often wondered that myself. I guess that the loss of living headroom and the cost in fuel savings is probably not worth the trouble. If my math is correct, and you could decrease fuel consumption by 25% you would probably only save 1600.00 per year based on 10,000 miles of travel.

Just a guess.

[nothermark]

Off hand the DP's would have a problem with the door in the front corner. Not so much of a problem with mid door common on gas units. As I recall the major factor is the cross section size in square whatevers. Streamlining like tilting the windshield back does not do much for that. What are you envisioning?

[Gary RVRoamer]

Would you lower the rig or make it narrower, to reduce the frontal area? Cause that's the primary factor in wind resistance. Much of the rest is all those nasty things like windows, roof top a/c's, tv & satellite antennas, ladders, and such that disturb the air flow around the coach. Would you eliminate those? And finally the suction at the rear, which can be addressed with those big folding wings you now see on the back of big trailers. Probably only a few thousand $ extra.

[BobMontgomer]

Originally Posted by Gary RVRoamer

Would you lower the rig or make it narrower, to reduce the frontal area? Cause that's the primary factor in wind resistance. Much of the rest is all those nasty things like windows, roof top a/c's, tv & satellite antennas, ladders, and such that disturb the air flow around the coach. Would you eliminate those? And finally the suction at the rear, which can be addressed with those big folding wings you now see on the back of big trailers. Probably only a few thousand $ extra.

What about the flat front end? See any cars made that way? Last one I remember was the VW Bus and it could hardly get out or it's own way on the freeway.

[Mekanic]

Originally Posted by BobMontgomer

I love the look of modern class A motorhomes, but at the price of gasoline I have to wonder why manufactures do not make them more streamlined. Some of the older ones appeared to be. I would think at 60 mph it would make a a big difference..

Anyone know the history of this subject?

My guess is this

On a survey of what people want in a RV

Good (or better) Fuel economy is NOT high on the list.

[wimpy]

Originally Posted by BobMontgomer

I love the look of modern class A motorhomes, but at the price of gasoline I have to wonder why manufactures do not make them more streamlined. Some of the older ones appeared to be. I would think at 60 mph it would make a a big difference..

Revcon, with the FWD Toronado Drive Train, which reduced the overall heighth of the light weight all-aluminum, steel chassis vehicle. In 1972, GM began production of their 1st RV, which would appear to have incorporated aerodynamics in its design. In 1978, Revcon also changed to a "slant-nose" aero look & using aluminum with fiberglas endcaps from 78 forward resulted in a fairly light weight MH.

Equipped with the 403/455 & then 454 engines, Revcons were billed as the 1st 100 mph motorhomes. Fuel mileage wasn't a concern and carbed versions delivered <10 mpg.

[Fiesta48]

On a 05 FW Fiesta gasser I added many light weight aerodynamic aids.
Front v shaped lower air dam
Smoothed out drag on 2 A/C
Many obstructions to things hanging out sides, top or bottom.
Windshield was slanted back.
Coach was about 14k lbs.
I ended up getting another mpg. 8.5 to 9.5
Was a lot of fun work, min. expense.
But as usual, I sold it before getting a return on my money.
Have a 35k DP now that gets 8.8, go figure...

[Waiter21]

At 60mph, not a huge difference. I'd guess 1 or 2% max.

The most gain would come from the trailing edges (the back end), taper would be perfect, but simple large radius (24 inch) on the corners would help. This is why you're now seeing the tail panels on 18 wheel trailers. These help the compressed air to slowly turn inward and start de-compressing slowly to fill in the large area behind the trailer.

The leading edge isn't as critical, The air compressing as it hits the front will tend to form its own rounded bow. But the air can only de-compress at a certain speed at the rear of the vehicle, if the air cannot de-compress fast enough to fill in the void, the vacuum now tends to hold the vehicle back (sucking it backwards)

Drag increases by the square of the speed. So the drag at 60 mph, is 4 times as great at 120 mph..

Slow down.. round the trailing edges.

[777 Driver]

Originally Posted by Waiter21

At 60mph, not a huge difference. I'd guess 1 or 2% max.

The most gain would come from the trailing edges (the back end), taper would be perfect, but simple large radius on the corners would help. This is why you're now seeing the tail panels on 18 wheel trailers. These help the compressed air to slowly turn inward and start de-compressing slowly to fill in the large area behind the trailer.

The leading edge isn't as critical, The air compressing as it hits the front will tend to form its own rounded bow. But the air can only de-compress at a certain speed at the rear of the vehicle, if the air cannot de-compress fast enough to fill in the void, the vacuum now tends to hold the vehicle back (sucking it backwards)

Drag increases by the square of the speed. So the drag at 60 mph, is 4 times as great at 120 mph..

Slow down.. round the trailing edges.

Check these out: http://www.airtab.com

Be sure to do due diligence before you buy.

Take care,
Stu

[RKins]

My '97 (and some of the '98 lineup) were the last year Newmar had some sort of aero-dynamics. Yes, I have a mid door entry on the curbside. I don't seem to get blown around by semis like the flat front models. I don't get exceptional fuel economy either. It's not tall like the newer coaches (it's under 12 ft).

[Waiter21]

Be sure to do due diligence before you buy.

I'd LOVE to see the wind tunnel data on these.. Personally, I don't believe the claims. Slap some tufts on the sides and rear and I doubt you would see any changes in air flow at 60 mph.. (here goes)

Real world testing would come in the form of the trucking industry. These tabs would be significantly less costly to install and maintain than the trailer tails. yet we don't see the tabs on the trailers. Even the trailer tails is a low improvement, but given the cost of fuel, miles driven, and the cost of the trailer tails, a 1% percent improvement would pay for itself in a year or two when driving 1/4 million miles a year.

RICK - Nice paint job....

[Waiter21]

Stu - Whats Mmo on a 777?

[777 Driver]

Originally Posted by Waiter21

I'd LOVE to see the wind tunnel data on these.. Personally, I don't believe the claims. Slap some tufts on the sides and rear and I doubt you would see any changes in air flow at 60 mph.. (here goes)

I have seen them in use a couple of times, even once on a passenger car. I don't recall many 'objective' favorable reviews.

Take care,
Stu