Aerocivic - how to drop your Cd from 0.31 to 0.17

[eco_generator]

It seems engine tuning for the McLaren and a econobox are being viewed as the same, eg: both just tune for stoichiometric with different engine sizes... If you hammer the McLaren engine it creates so much heat based on hp/liter that many things would be different from a very softly tuned engine.

In general, very high performance engines tune very rich under load so as to never blow up the engine with a simple hiccup, there is a safety margin for any leaning-out event. To operate at extreme hp/temps things like spark plug "temp" and gap are spec'd differently. The camshaft has to be profiled to match it's intended operating range, typically no where near economy revs. Some engines literally use un-burnt fuel to cool down the cylinder walls and keep internal temps in check. Some of these reasons are why you can see a fireball shoot out the exhaust at times. And we haven't even gotten into things like valve overlap, parasitic drag running coolant through 2+ radiators and on and on.

Hence, even piddling along for an entire trip would probably still result in lackluster fuel economy.

[aerohead]

Originally Posted by freebeard

Just being hard on the noob. [ ¯\_(ツ)_/¯ ] (sorry CeeforCitroen)

So you're saying.... we can both be right?

The most exacting conclusion is no.
Energy and entropy are entirely different animals, words; so, of course we'd expect different spellings.

[aerohead]

Originally Posted by CeeforCitroen

I did find a link you might find interesting based on the semi truck idea
www(dot)yankodesign.com/2017/12/13/hey-elon-heres-an-idea-for-your-semi-trucks
Interestingly I was looking up about the Tesla Semi, because electric power has often been a challenge for long range vehicles. I'm surprised it's still only a single speed transmission as well because while electric motors generally get away with less gear range, as vehicle weight increases, a choice of ratios generally come back into the picture which is why a semi generally has more gears than a motorcycle. (I've drafted a write up of the efficiency of electric motors at different loadings and come to the conclusion that motors with high DC resistance and low mechanical friction should be lightly loaded, and vice versa for low resistance but high mechanical friction). I would be interested to know how the motor performs towing 80,000 lb up a hill, compared to coming back to the dock empty, because I find it hard to believe you would get optimal range using the same gear ratio for each task.
As for McLaren F1 fuel economy, usually with supercars and hypercars the efficiency island for the "over sized" engine puts you well over most speed limits. At which case the air drag is more than optimal if you can't cruise at peak efficiency until over 100 mph. For most city driving it would be like using the engine to run an electric toothbrush. A McLaren F1 body with a Smart Fortwo engine would do rather well - if a little boring to drive on a track. The other factor is the speed range the two cars are generally used.

It would seem to me though as speeds head north (possibly beyond the top speed of the Smart) that the McLaren would drink less petrol. Also whether the low mpg figures of these cars are measured puttering to the shops of caning it round the Nurburg Ring. Perhaps one of these cars should have a tiny engine to putter along to the track day and then switch over to the large engine to have some fun!

I'm curious as to where the fuel goes in some of these cars because 15 mpg US (18 UK) is what my Citroen C2 would get if I put it in 3rd or 4th, pushed the pedal to the floor and also put my other foot partway on the brake (or drove up a hill) enough to stop the car from accelerating. I mean a McLaren isn't exactly a 4 ton 2 lane wide garden shed, so where does the fuel go? Is the engine fighting itself? If I was to tow one with my Citroen with the McLaren in gear would the engine braking of the large engine cause my car to consume the same fuel? I'm assuming the "waste fuel" in an uneconomical large engine just goes to moving itself round - just like a 7 litre V8 geared to move a scooter at 30 mph at 4000 rpm is mainly fighting its own resistance and a tiny bit is used to move the scooter.

1) with 100% torque available, from zero-to- full-rated rpm, the single, 10:1 ( just for for example) planetary gear set, behind an electric motor, gives virtually infinite 'gearing' with a BEV.
2) if you'll re-visit the Tesla Semi website, they spell out the performance comparison of the electric tractor pulling an 80,000-pound load up a grade, versus a conventional diesel-powered rig.
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3) any mpg figures published for the McLaren would be determined by the official testing protocol used. For those units sold in the USA, the numbers would come from the EPA procedure.
4) As to 'where' the fuel goes in the McLaren, it's the same as for any heat engine:
* internal friction
* pumping losses
* engine accessory losses
* heat flux from the cooling system
* heat flux out the exhaust
* actual road load at any moment
* inefficiency of transient engine loading on BSFC
* mechanical efficiency of the transmission
* mechanical efficiency of any universal joints, CVC-joints
* mechanical efficiency of the differential
* brake pad friction
* tire rolling resistance
* wet roads, other precipitation
* curve drag
* climbing losses
* traffic
* idling
* velocity
* local air density
* aerodynamic drag ( including all wind, gust spectra )

[aerohead]

Originally Posted by CeeforCitroen

I'm curious now as to whether a cyclist will go faster if they wear one of those on their back.
Here's a video of a lorry with one in action. It shouldn't be too hard for a fleet of trucks to save masses of diesel this way, though I have no idea what the savings will be at 55 mph

The world's fastest cyclist wears this on his head, back, arms, and legs.
In the Mercedes video, they're claiming a 20% improvement? 83 kmh used to be the speed limit in the EU for trucks.
Fachsenfelds' boat-tail of 1935 would provide a larger savings than the unit tested in the video.

[aerohead]

Originally Posted by eco_generator

It seems engine tuning for the McLaren and a econobox are being viewed as the same, eg: both just tune for stoichiometric with different engine sizes... If you hammer the McLaren engine it creates so much heat based on hp/liter that many things would be different from a very softly tuned engine.

In general, very high performance engines tune very rich under load so as to never blow up the engine with a simple hiccup, there is a safety margin for any leaning-out event. To operate at extreme hp/temps things like spark plug "temp" and gap are spec'd differently. The camshaft has to be profiled to match it's intended operating range, typically no where near economy revs. Some engines literally use un-burnt fuel to cool down the cylinder walls and keep internal temps in check. Some of these reasons are why you can see a fireball shoot out the exhaust at times. And we haven't even gotten into things like valve overlap, parasitic drag running coolant through 2+ radiators and on and on.

Hence, even piddling along for an entire trip would probably still result in lackluster fuel economy.

Cylinder deactivation is allowing some V-8s to run on as few as 2-cylinders, depending on load. Modern Corvettes are returning Chevy Volt-II highway ( 37-mpg ) fuel economy. They selected the 8-cyl because the V-6 wasn't capable of this function.
This compares very favorably with a 1968 Stingray, which on a good day couldn't break past 12-mpg.

[CeeforCitroen]

I'm wondering whether with cylinder deactivation, you could actually install some sort of clutch plate in the crank shaft so the rest of the cylinders didn't even move. Then with a controlled slip, the timing is lined up with a locking pin so all the cylinders have the correct timing. The problem is the engine is designed to run balanced as a unit, so there could be vibration issues when dividing up into individual V2 groups.

[aerohead]

Originally Posted by CeeforCitroen

I'm wondering whether with cylinder deactivation, you could actually install some sort of clutch plate in the crank shaft so the rest of the cylinders didn't even move. Then with a controlled slip, the timing is lined up with a locking pin so all the cylinders have the correct timing. The problem is the engine is designed to run balanced as a unit, so there could be vibration issues when dividing up into individual V2 groups.

If sections of the crank were isolated mechanically via clutches, there could be situations where only the rearmost section was actually able to transmit power.
Also, to engineer enough clearance inside the block, might make for an unacceptably long engine. Synchronization of the crank elements would be problematic, and the individual clutches would have to withstand different degrees of torque, requiring more mass as you near the flywheel.
The cost and complexity would be astronomical.

[basjoos]

Anybody interested in adopting the aerocivic? I’m retired now and don’t do a lot of driving anymore, mostly local trips and rarely make those long interstate trips where the aerocivic mileage really shines. I have several other cars (minivan, pickup, 4-door sedan), so the aerocivic doesn’t get much use. I drive it every couple of weeks to keep everything running, but my wife keeps bugging me to donate it to the NPR car donation program since she thinks we have too many cars. The engine and transmission are in good condition with about 100,000 miles on each and a new timing belt installed less than 1000 miles ago. It needs new tires since the rubber is over 10 years old. To get it back up to its original specs (73 mpg at 70 mph) it will need to have a new smooth underpanel installed. I had to remove the original to track down and repair a fuel line leak. The rear Lexan polycarbonate glazing needs to be polished in the manner of headlight restoration to restore its transparency. The only other quibble is that the LED rear turn signals are somewhat weak. The LEDs are good, it’s likely a poor connection in the tap splice electrical connector on the stock rear turn signal wires.

The way things look right now, gas prices aren’t going to go anywhere but up, putting a hurting on anybody with a long highway commute. I’ll donate the aerocivic and spare parts to anybody who wants to continue with the experiment. Its one of the least expensive to operate commuter cars out there. There aren’t many cars out there that will give you an honest 70+ mpg at 70 mph.

[MetroMPG]

Wow, what a generous offer.

I hope someone here jumps at the chance to take over stewardship of one of the most iconic vehicles on the forum.

If I lived in your neck of the woods, I'd go for it.

[aerohead]

Only in my mind, exists a museum which would preserve your work for future generations. Aerocivic really stands out as a singular accomplishment. 'glad I was around to know about it. Thank you just doesn't seem to cut it.