What kind of MPGs would a brick wall get?
 

https://jalopnik.com/what-kind-of-fu...1839901794/amp

Despite some inaccuracies and bad comparisons I noticed in the article, it explains well that engine efficiency plays just an important part in fuel economy as coefficient of drag does. So some cars that are shaped like bricks (my Jeep) can still get good FE without making too many concessions to aerodynamics. Not something too many ecomodders consider as most cars here have small engines and have a fairly low cd already.

@ what speed? Near zero, brick wall aero isn't all that bad. Supersonic, it sucks.

Provided you handicap the more aerodynamic vehicle with a less efficient engine.

Consider a brick with radiused edges.

The author of the article calculated that a brick wall with a Prius engine would still get 29 mpg at 50 mph.

So I went back and read the article. Instead of a brick,he is using a flat plate as analogous. A brick, on it's long axis would have better fineness ratio, like a truck van.

His starting point was imagining his lifted SUV as having little brick walls all over it. Not a bad article, except for

A wall is worse than a cube as well right? Basically holding up a sheet of plywood is worse. As pointed out it's all about speed. I can hold up that sheet and walk with it and not notice the aero drag but try an old it up in the back of a pickup on the highway and there will be an injury involved. I'm glad he mentioned the size as well because while I couldn't hold a sheet of plywood up at speed I could hold a playing card up which both have the same Cd.

They used .22 as an engine efficiency in the caculator while claiming a .4 engine efficiency in the article. 40% must be "peak" efficiency not seen at 50 mph.

I was going to try and see how reducing engine efficiency while leaving the aero good to see what effect that had compared to the aero. You have to take efficiency down to .105 to get 29 mpg. I don't know of any properly functioning ICE that is quite that bad. Take the speed up to 70 and run the same numbers and the aero is now a 40% worse penality than thermal efficiency.

The efficient USE of a vehicle is second consideration. MPG is far down the list as to what matters

1). How many family members? Must fit all persons aboard (with luggage).

2). Distances for necessities. Not work or school.

Etcetera

Where one lives in relation to necessary re-supply is prime as to the convenience of personal transportation. Overrides all others, as it’s a desire NOT a necessity to own a car.

A 5-mpg motorhome gets “better” fuel economy than a Prius with a roof rack tent.

Be sure you’ve defined, what is mpg?

It’s work performed against an energy input. One or two people being transported ISN'T work, per se. Its waste. Where’s the income offset or addition? Every single trip.

As to shape, the volume that encloses the most space in the most compact form is the winner.

How much space is mostly a function of how many children in your family.

An unmarried man, like an unmarried woman, is pretty well a drone. Not necessary; limited usefulness before disadvantages outweighs other.

More to the point, again, FE not being central, aero should impose no penalty first (as above), second, it should maximize safe operation (crosswinds, etc).

A drivetrain that can maintain 60-mph in rolling terrain is adequate for a loaded vehicle (as empty operation is proscribed). Thus, it’s more about the transmission & drive ratio than engine size or fuel.

The small Ford Transit van with passenger outfit, is close enough.

.

The counterpoint is the external shape the volume must squeeze through. Generally 8.5x14x∞.

Within reason. Slapping an efficient engine in an SUV doesn't also add a more efficient drivetrain, lower weight or lower rolling resistance.

wall
 

I've never heard of a comparison with a wall,only a brick,which would be Cd 0.85.
Members mentioned a flat plate,that would be Cd 1.11.
All ICE engines, whether gas or diesel will have an engine map,on which there will exist an island of lowest BSFC.Engineers might shoot for gearing which would hold the engine load,at cruise velocity,near the optimum BSFC on level road.
The CVT(Van Dorne) transmission is designed to maximize BSFC,keeping the engine in its 'sweet-spot' under all transient conditions.One reason why hybrids with the Atkinson-cycle engine do so well.Their gutless as far as torque goes,but they've got the motor to compensate.
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Since,on the open road,at constant speed,aerodynamic drag is 80-90% of load,it remains the greatest impediment to efficiency.And why all Tesla cars,Prius,Insight,and Hyundai Ioniq,etc.,can clean the best ICE car's clock in efficiency (119-130 mpge).
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A early 1970s JEEP CJ would get 33.5% better fuel economy with the body of a Prius ( all other factors held constant). With air-suspension it could probably 'go' where a CJ goes.I've no idea what a person could get with a GDI-turbo ICE engine or TDI diesel in a standard JEEP body.

29
 

I came up with,around 22.5 mpg at 62-mph.It would be a little better at 50.

https://ecomodder.com/forum/member-f...7-12-29-57.png
My favorite what-if would be a Prius with a Dasher 5-speed, 36hp VW and Porsche cooling fan. The donor vehicle got 40mpg with a 0.41 Cd. The Prius would loose hundreds of pounds of weight. I estimate equal economy and less acceleration.

air-cooled,5-speed,Prius-Dasher
 

A Dasher with a Prius body,and tires,if the same frontal area and weight would be 47.8-mph HWY.The air-cooled engine though,would knock the BSFC into the dirt.Without liquid-cooling,there's no way to operate it at temperatures high enough to achieve the thermal efficiency of the Dasher engine.You could lose 15%,ending up at around 41.5 mpg,not a great incentive for all the work.
Also,at 36-bhp,you'd have to get a run at every hill,entering the grade at top speed,just to have a chance to crest at any speed at all and not impeding other traffic.It's the only way I could operate my '64 Ghia,with the 40-horse,1,200 cc.Even rowing down through the extra gear,she'd still find it hard to climb.:p

The Dasher gets 45mpg with [approx. 0.32 Cd?] so not much gain there. You're prolly right about the BSFC.

My panel van had a 1600 with dual Solexes and weighed (empty) about as much as a Beetle (worse Cd). It topped out at 80 on I-5 and topped the Coast Range at 75.

The Type II is sort of a pebble-ized brick end-on, so it's back to ontopic. :thumbup:
I baked a few air-cooled engines trying. :)

Put the wall on its side :D

A person riding a commuter bicycle might have a Cd of 0.6 and there is hope of fairing it to get a Cd of 0.3 as usable daily rider.

the Best i have ever done with a 40 cell Prius battery and 6.0L engine was 28.7 MPG combined 31City/26.4hwy
4x the power of a prius
but only get 25.5MPG on average not too bad for a 6.0l 364Ci engine



not too bad for a 6 foot 6 foot brick wall?

what would you rather drive a v8 6.0l SUV or a 2.7l V6 Chrysler 300? which both get 25mpg?