100 mph & 32 mpg

[ERTW]

If you haven't seen this already, it's a very well done piece on the absurdity of speed limits.

http://www.youtube.com/watch?v=2BKdb...t=HL1379516101

fact: germany has fewer fatalities per million miles driven than the USA.

fact: emotional people will always argue facts.

[320touring]

Originally Posted by ERTW

If you haven't seen this already, it's a very well done piece on the absurdity of speed limits.

fact: germany has fewer fatalities per million miles driven than the USA.

fact: emotional people will always argue facts.

Agree wholeheartedly, my argument in my last post is that the leap in public perception required to achieve the stated aim is huge

the real issue with raising speed limits is the behaviour of the drivers themselves.

I'm arguing that a better MPG output (say 55mpg) at a slightly lower speed (say 75mph) needing a much more mundane style of car would be more acceptable, and ultimately pave the way for acceptance of greater goals?

kind of like a stepping stone?

The general public like to be lead by the hand- "you NEED this iphone/dvdplayer/car/gnat/tube of toothpaste"

Over here (Europe) , the "MPG mantra" of diesels is making a killing in the markets- nothing to say that the petrol engine could not achieve the same in the US with similar aero to the "Bluemotion VW's" etc

[aerohead]

Originally Posted by ERTW

my thinking is: you run a car at a certain speed, a certain rpm, and load (which determines bsfc). reducing aero load simply gives the same load at a higher speed - with the same rpm and load on the engine (with appropriate gearing). so your 32 mpg at 100 mph is not the issue.

mechanical friction increases with the square of the speed. Reduced wind drag means mechanical friction is the significant loss to accordingly higher speeds. Wind drag increases with the cube of the speed, so there is a definite benefit to higher speed/lower drag.

I'm interested in seeing those SAE standards. I was under the impression that the fuel economy curve is an inverted bathtub...so at best l'd expect the plateau to extend higher...not climb drastically as you state.

Now you'll have to police drivers without appropriate licenses - and more importantly, the necessary skill to handle the car. how many new licenses will it take before the state drops millions of dollars to build a special lane? How do you police drivers from out of state? Driver training would have to be raised in the entire north america (way too low a standard). Germany's standards seem appropriate - 18+, $3000, graduated licensing, yearly car inspections, regular recert, know how to change your oil, etc).

The SAE papers I have give the mechanical power train losses as constants:
*A transmission would be 95% efficient (up to 6-speeds)
*A differential/rear axle would be 96%
*A propeller shaft,98%.
*An entire pickup truck power train is 92% efficient as measured between flywheel and road interface.
*I allowed 94% for the Honda Accord's transverse layout with either lockup torque converter or manual trans.
Since the 'Road Load' of the 100 mph car is identical to the 75 mph car,no efficiency variable exists.

A Gear Vendor (Doug Nash Racing Transmissions) unit uses a 1:1 output ratio for top gear in its 'overdrive' transmission.All gear-matching is done with the ring and pinion with no losses in the transmission itself.(something a 100 mph car might incorporate).
-------------------------------------------------------------------------
As far as the fuel economy goes,I'm using Honda's BSFC as a constant (which can be achieved with the gear-matching) and a fixed Road Load horsepower.
I've compensated for the higher rolling-resistance loss (read directly off Honda's power curve).
The difference in aero load which must make up the difference is solved for using the standard aerodynamic power equation with standard SAE barometric conditions,and yields the Cd 0.125 necessary to make the fit.
The power absorption coefficient is presumed constant with Z-rated rubber,held below standing wave velocity.
-------------------------------------------------------------------------
As for any fuel economy testing,you'd follow SAE on-road protocols for temps,wind,precipitation,road conditions,grade,curvature,and banking.
This has nothing to do with EPA certification lab testing.This is real world on road, steady-state highway cruise speed mpg.

[aerohead]

Originally Posted by 320touring

The real question should be more fundamental

"Why does modern life need us to be this fast?"

tele commuting would allow better communities (more folks able to use local services/shops as they're about when they are open) with a reduction in fuel consumption, and a corresponding drop in traffic density.

32us MPG at 100mph is a noble goal, but opens more issues than it solves (e.g. acceptance of radical aero designed cars (needed for the Cd's refered to in the blog) and also the issues surrounding energy transference at that sort of speed, should the worst happen)

good on you for getting the thinking going though- some good ideas in the blog and on this thread

It's Gilkison's blog and I'm not going to answer for him,but the EV community has range-anxiety issues with pure plug-in EVs and this blog was a way to illustrate how existing pack range might be extended simply by reducing the road load itself.
If you want to maintain a warmer home in winter,or cooler home during summer with no change in your utility bill,you can add more R-Factor to your homes floor,ceiling,walls,windows,and doors.
The higher R-Factor equates to a lower Coefficient of heat transfer (a drag coefficient for the house if you will) and your heater or air conditioner doesn't have to work any harder to maintain the new indoor temps.
-------------------------------------------------------------------------
Aerodynamic streamlining is a way to add R-Factor against the effects of air drag.The more you streamline,the higher the R-Factor,lower the Coefficient of Aerodynamic Drag,and the faster,cleaner, cheaper,or greater distance one can travel at no greater expense.
Maintain you regular speed and you've found the Lost Dutchman Mine.
If I drive a Nissan Leaf to the edge of town on holiday,and rent a gap-sealed,boat-tailed Battery range-extender trailer which cuts the Leaf's Cd from 0.28,to Cd 0.125,I've got a chance to extend the range of the original pack in the car,as well as have a second pack in the trailer to get the family to Grandma's and back.Something which would be otherwise impossible.

[christofoo]

Phil, is there a mistake in your 32MPG figure? I know you're using a formula I'm not familiar with, so I'm just asking you to double-check, but I think you should get more MPG with a 2.0L under that road load and speed. In principle, with a lean-burn and proper gearing or somesuch, the upper limit for Cd=.125 A=~20sqft should be a whopping 60+ MPG at 100 MPH.

More to the point, if you get 32MPG at 31BHP at 75MPH, you should get 43MPG at 31BHP at 100MPH, all other things being equal.

But maybe I just didn't follow along.

EDIT: I would totally pay a couple $k premium to get access to a 100MPH-rural-in-good-weather-and-daytime freeway system (and I would even drive that fast once in a while), knowing it would double as an ultra-MPG commuter. I think it's a slick policy angle for aerodynamics.

[aerohead]

Originally Posted by christofoo

Phil, is there a mistake in your 32MPG figure? I know you're using a formula I'm not familiar with, so I'm just asking you to double-check, but I think you should get more MPG with a 2.0L under that road load and speed. In principle, with a lean-burn and proper gearing or somesuch, the upper limit for Cd=.125 A=~20sqft should be a whopping 60+ MPG at 100 MPH.

More to the point, if you get 32MPG at 31BHP at 75MPH, you should get 43MPG at 31BHP at 100MPH, all other things being equal.

But maybe I just didn't follow along.

EDIT: I would totally pay a couple $k premium to get access to a 100MPH-rural-in-good-weather-and-daytime freeway system (and I would even drive that fast once in a while), knowing it would double as an ultra-MPG commuter. I think it's a slick policy angle for aerodynamics.

Yep,we can do much better,but the premise of the blog was that with 1996 engine and powertrain efficiency,aerodynamics alone could deliver the numbers.(this really was the whole point of the blog)
If you extrapolate the HONDA power curve for 75 mph,you can read the Road Load power directly.This is the 'baseline.'
Subtracting the Rolling-Resistance power component at 100 mph (read directly from the curve) from the 75 mph Road Load yields the remaining power available for aero.(with gear-matching,the engine will see an identical load as at 75 mph and will operate at the same BSFC and deliver the same economy)
Using this value,we solve for the Cd which can satisfy this condition.
Cd 0.125 falls out of the equation.
--------------------------------------------------------------------------
With Toyota's current Phase-II GDI-turbo-intercooled technology, with 43% thermal efficiency,we have the efficiency of a diesel engine,only lacking the extra 11% chemical energy which diesel packs into each gallon/liter.
Add 2013's improved low-rolling-resistance tires and we push the numbers even higher.
Dr.Paul MacCready estimated 400 mpg for the 1987 GM SunRaycer of same drag coefficient,of course with much smaller frontal area,greatly reduced mass,and 'normal' highway velocity.
This is the sort of thing which led to the idea for the 'Template,'which shares similar architecture with the SunRaycer.

[aerohead]

Phil Knox is relying way too much on memory(as if he had any left)with some of his replies rather than waiting and ferreting out info from home.
I've gone back to #43 permalink and edited out some of my 'wrong' data.
I deleted the whole part about powertrain efficiency as a function of load .
What's left,I think represents the values originally reported by SAE.
I apologize for any trouble.In the future I'll 'wait' until I'm sure,before popping off
with dubious numbers.
I appreciate your understanding.