Motorhome Aerodynamics

[wannaclassc]

Originally Posted by TOM GUY

Larrikin, the AERODYNAMIC drag increases by a 40%, but the total drag is much lower. I agree that driving slower improves fuel mileage, but not as much as the "experts" say. As speed increases, so does the distance covered; your drag increases with the square of speed, but so does the ground covered.

The result is that mileage goes down linearly with the speed, but not with the square.

And rolling friction is much higher than aerodynamic drag.

Just a tote to clarify.

Tom

The experts? Like engineers and people who build vehicles for a living? you think they're wrong? You go from 65 in your RV to 75. That's 15% faster. You'll be burning a LOT more than 15% more fuel.



Rolling resistance matters a ton less at speed.

[Peacekeeper6]

Originally Posted by rickemo

Sitting here drinking my morning coffee and thinking back over our 1800 mile journey from Pennsylvania to South Padre Island Texas. We averaged 6.5 mpg in our 2020 FR3 30DS towing our Jeep Wrangler.
As a retired engineer I notice things such as architecture and the method other vehicles on the road are designed. The automobile industry including, the trucks that pull the 53 foot trailers, have made great strides in designing aerodynamic features into their product. Many 5th wheel trailers and Class C motorhomes are designed with aerodynamics in mind.
What about the Class A motorhome? There seems to be no effort by the RV industry to apply aerodynamics to these RVs. The majority are square flat front with little consideration to aerodynamics. In our age of computer simulation it seems to me the industry could put more effort into engineering the front of the Class A motorhome. Maybe an increase in fuel economy due to better aerodynamics would increase motorhome sales.
So now my coffee and thinking are done for today You all be safe and have a great day.

If you think there's a way to improve aerodynamics on a vehicle that puts a premium on usable living space, I've got some beachfront property in Kansas I'd like to sell you.

Really cheap too !!

[RVingNow]

Originally Posted by wolfe10

Interesting. At least Caterpillar would differ with that statement and supports it with data:


https://www.rvtechlibrary.com/engine...erformance.pdf

Nice reference. I was expecting a picture of a bulldozer with a spoiler.

[sibe]

Sad part is these studies and such have scientific data to support one way or the other and build arguments to support a specific research.. Physics and the laws are fact and that data is sometimes looked past..

The chassis design and aero is very much a factor.. RV is still a cube,, the old flat nosed conventional Tractor trailer combos back in the day just pushed air.. then they added a long nose with the same motors and even made the tractor longer sleeker and with the same power plants saw bigger increases in MPG..

Still without a proper designed motor for volumetric efficiency in a target rpm/speed range with proper power to weight...you are up craps creek...
You can go after the aero tweeks of spoilers and wheel covers once you have engine efficiency..

Funny how years back, bail out era,, GM, ford etc Pickups got 8-10 around town 12-14 on highyway beat.. some government cames and fuel/emission mandates or swaying lets say, within 2 years 12-15 around town , 18-21 on highway.. Same motors, same chassis, same weight.. Just tuned ..

blah blah,, RV deal with the mpg. enjoy

[Daveinet]

Originally Posted by wannaclassc

The experts? Like engineers and people who build vehicles for a living? you think they're wrong? You go from 65 in your RV to 75. That's 15% faster. You'll be burning a LOT more than 15% more fuel.

Not really. Not if the engine is tuned correctly. I took a 1000 miles round trip with my Revcon. On the way there, I was running late, late at night, pushing 85 mph+ sometimes over 90 mph. I got 8.2 mpg. On the way home I drove a leisurely 70 to 75 mph and got 8.4 mpg. Most engines don't have efficient exhaust flow at higher RPMs. My observation was that with a good free flowing exhaust, the mileage doesn't nose dive as badly.


The fact is, the engine itself is more efficient at higher RPMS. The wider you have the throttle open, the less pumping losses you have.

[Daveinet]

Originally Posted by Peacekeeper6

If you think there's a way to improve aerodynamics on a vehicle that puts a premium on usable living space, I've got some beachfront property in Kansas I'd like to sell you.

Really cheap too !!

Cheap is much more important than living space. You can radius corners without giving up storage, but it becomes much more expensive to build.

[Rob_M]

I’ve noticed that 5mph + or - on our DP makes very little difference (.5 or less) in avg mpg, UNLESS I’m going against a strong headwind. What I’m towing makes very little difference either unless I’m in steep hills / mountains.

On secondary roads, the weight I’m towing does make a difference since we’re making more stops and starts. I played with gear changes and found that keeping it in 5th instead of 6th in 55mph zones netted a slight avg mpg increase. Torque curve sweet spot? Banks tuning may play a part.