Electric vehicles!

[McGizmo]

I used to have a handle on this. Apparent wind can be in excess of the actual wind if the boat or vehicle is very efficient. You really need to look at vector diagrams to get a good idea of what is happening. If you are in that car and it is stopped and the wind is hitting you one one side, the apparent wind is on the beam and the apparent wind speed is the same as the actual wind speed. If the car starts moving with the wind still directly on its side or beam, this would be called beam reaching, the apparent wind is the sum of the vector of the actual wind speed plus the vector of the car's speed. As the car speeds up but remains on the same course, the apparent wind increases and appears to be coming from not only the side but also somewhat forward. It's all foggy for me now but I don't believe a boat or vehicle can exceed the apparent wind speed and I don't know what the limit of the vessel's speed might be.

Ice boats which look like that wheeled boat but with skate runners instead of wheels can also haul ass and go faster than the actual wind speed.

[josey]

I'm still having trouble getting an intuitive feel for how this works. All I can think of is squeezing a slippery seed between your fingers until it shoots out. But my imagination is loving it.

If the top multiplier is 10, imagine taking your state-of-the-art rig out in a 50 mph wind. That would be a heady experience, providing everything holds together.

[McGizmo]

Josey,
A quick google found a wikipedia explaination. For a while, I did some sailing on some friends ultralight sailboats which could plane and were not limited to theoretical hull speed. The physics is really interesting and to get the most from a boat, sail trim is all about the apparent wind and understanding it.

When I used to sail sailboards, I am certain that I often had board speeds in excess of the wind speed. Speed is one thing but another critical consideration is VMG which is velocity made good and based on having a target direction or location to reach. With some of these very efficient craft, you might have a maximum VMG by bearing off and away from the rhumbline which is the shortest and true course to your destination; even if you can sail the rhumbline.

EDIT: in a related link, I found the statement that modern land sail craft can go 3 to 4 X the actual wind speed and this is based on Bernouli's Principle.

[josey]

Thanks, Don. I appreciate the link.

Actually, your post made my day by introducing me to the concept of VMG. I love that term/concept because it applies to so much of human endeavor. Humans can cover a lot of ground with cunning cleverness, great intellect and high energy, but often we're going fast in the wrong direction.

[McGizmo]

Josey,
I have found that a lot of sailing terminology has slipped into common day speech and thought. I also find that the whole concept of plotting a course towards a specific destination in which you simply can not go the direct route is a great lesson for life itself. I have learned a lot about life from surfing and sailing. There are lessons in physics that do carry over into situations that may not be governed by the same physics but subject to similar constraints and dynamics.

I have often heard the term "Try another tack." which no doubt comes from sailing into the wind where you have a favored tack for max VMG but should the wind shift one way or you sail too far, the other tack then becomes favored.

Probably the most obvious lesson to glean from being on the ocean either surfing, sailing, swimming or what have you is that there are forces present and always in flux that you simply have no control over nor can you prevail upon them with superior force. You have to flow with them and take vector gains at best.

Ha ha. Taking one of Darell's threads off topic seems rather poetic.

I'm patiently waiting for an EV to become available to me and I doubt the ideal one will be in the initial lot that get offered so I will have to determine from the choices available which will allow me the maximum VMG.

[josey]

Would it be possible to have a computer-adjustable fin on an EV that could take advantage of the wind, either to cut resistance or to leverage wind power into a forward assist, somewhat like wind boats and ice boats?

[Darell]

You'd sure have to watch the parking garages!

Thanks for swinging us (almost) back on topic, Josey!

I realize now that *I'm* the one who went off into wind cars anyway...

[josey]

Originally Posted by Darell

You'd sure have to watch the parking garages!

Actually, I'm being serious, Darell. I'm not talking about 20-foot sails, but 3- or 4-inch retractable spoilers and maybe a 1- or 2-foot adjustable fin to take advantage of wind and vehicle shape, based on readings of pressure sensors in the car body.

I don't expect EVs to sail down the road, but maybe they could get an extra 10 percent efficiency by adjusting spoilers and fins to take power out of the wind and reduce wind drag.

Old school was to pump cheap energy out of the ground and spray it into an inefficient IC engine like force feeding a goose to make foies gras. Pollution was simply dumped into the atmosphere.

New school is going to have to use technology to work smarter in a lot of small ways because we don't have a super abundant fuel with a high energy density.

I know in making my cabin energy efficient, the key is to do a 100 small things, rather rely on one big solution. I expect EVs are going to be similar.

[McGizmo]

Josey,
The problem with trying to harness any added power from the wind is that you need sail area and the sail needs to be trimmed appropriately. A vehicle will most likely have apparent wind right on the nose most of the time and in this point of sail, you can't get any lift or aid from the wind. The efficient body styles take into consideration drag and are based on apparent wind being straight ahead. When you do have a cross wind of significance, I would guess that some designs are more forgiving and retain better slip than others. Any real wind that is aft of abeam (somewhat behind you) reduces your speed relative to the apparent wind and thus you are not pushing as much air out of the way (less friction) but your apparent wind is still forward of you so any sail area would have to be tuned accordingly. This sail area would typically just be added surface area causing drag most of the time.

I am assuming that vehicle speed would typically be well in excess of true wind speed.

I don't think there is any gain here.

[josey]

You're probably right, Don. It sounds like it. But don't race cars adjust spoilers for track and speed conditions? I should stick to stuff I know about.

[idleprocess]

Originally Posted by josey

You're probably right, Don. It sounds like it. But don't race cars adjust spoilers for track and speed conditions? I should stick to stuff I know about.

Race cars that can adjust wings/spoilers do it to regulate downforce so they can maintain traction and take corners at speed. I gather that - depending on the corner - there is a gap between the maximum low speed and minimum high speed cornering where the vehicle will probably spin out. At low speeds, the aero effects don't do much and the car has to rely on friction to make a corner. At high speeds, the downforce from the aero effects greatly increases friction so the car can snap through the corner - without slowing down too much.

Some vehicles also adjust their aerodynamic surfaces to increase braking at high speeds where drag can produce more deceleration than braking (and also prevent the brake fluid from boiling off).

It's difficult to imagine enough surface area to harness adequate energy to be useful without simply introducing additional drag. The surface area to mass ratio on a car of practical dimensions will be pathetic relative to a sailboat.

[Darell]

My concern is that most of the time any sort of "sail" would just add drag. You can't tap the manufactured wind (the wind created by consuming power to shove the car through the air) for any extra energy gain, so you could only get an advantage with a sail if there were other prevailing wind. What do you do with the contraption the rest of the time? I don't mean to dump on your idea. I LOVE stuff like this. Makes me think. Don's point that the car is damn-near ALWAYS going faster than prevailing wind is an important one to remember.

Spoilers and wings on race cars achieve a couple of things. One is down force to keep the car connected to the ground at high speed. The other is to tune the airflow over, under and around the car. You want to avoid air going under the car (this can create a partial vacuum, thus aiding the down force) and you want to spoil the vacuum that is always caused at the rear of a car. "Spoilers" tumble the air coming off the back to fill in the void that always forms there. Some of these things cause more drag, but allow the car to go faster due to more traction, etc....

I'd like to see more races that are more dependent on limited fuel supply.

[josey]

I’ve always thought that EVs need to pay more attention to vehicle weight and aerodynamics than regular cars because their energy source is more tenuous. At highway speed, roughly 60 percent of the energy needed to power the vehicle is spent overcoming wind drag. And, EVs have some advantages over IC cars, such as being able to have a flat under pan to move the air along.

The Volt, from what I’ve read, has a Cd of somewhere around 0.3, in the aerodynamic range of a good, but not great passenger car. The Prius has a Cd of 0.26, so it is much slicker.

A big weakness in my idea is that most of the drag is a function of speed, which is squared.

Force = Cd (slickness) x frontal area profile x air density x speed²

There are some efforts to change vehicle shape to improve drag, including raising spoilers and turbulators and trimming air dams at certain speeds, but the complication is at the moment not worth the effort, when so many other factors play a bigger role. My guess is that EVs well become increasingly refined and adjustable aerodynamics will become important.

I don’t know how to address Don’s point about small, retractable/trimable sails being useless when the car is going faster than wind speed. If the wind vehicle Darell posted is going 120 mph, it has to be using the wind to go faster than the wind, so can’t a car raise a small fin to reduce the power it needs to go faster than the wind, at least in some situations where wind direction is favorable?

I found this cool link on aerodynamics. They improved the aerodynamics on a Nissan Maxima and improved the mpg from 26 to 34. That’s huge.
http://www.recumbents.com/car_aerodynamics/

Toward the bottom of the page are some incredibly aerodynamic concept cars.

There is another link at the bottom of the page on “mechanical engineering smooth body,” which is about older GM efforts to get an EV1’s Cd down to 0.163.

[Darell]

I swear that I didn't see Idle's post before I put mine in... very odd.

Anyway... yes the sail car in the article I posted does go faster than the wind. But remember that to get those speeds he gets to go in whatever direction makes the most sense... and he does it where there is good, useful wind. He uses a GIANT sail, and tiny vehicle. If you're stuck going wherever the road goes, and you are plowing along at high speed, the wind isn't coming from many other directions than straight ahead. And any reasonable amount of sail that you're going to put up will be useless, I'm afraid - and affected by the turbulence of the vehicle. If the wind comes from straight ahead, there's no help that it can give you.

If you haven't seen the underpan of the EV1, here's mine:
http://evnut.com/images/ev1/ev1_gall..._underbody.jpg

The holes were for unbolting the battery tray.

[McGizmo]

When you are sailing, you do what ever you can to avoid "dirty air" which is the turbulence and wind shadows created by other boats or possibly fixed obstructions. A vehicle on the road with other vehicles traveling with and against its flow create all kinds of dirty air. I understand many race cars will "draft" behind another car and this can significantly reduce the required energy for them to maintain their present speed. Any kind of sail integrated on a vehicle would be subjected to all kinds of disturbances I would imagine and be a hinder more than help in unanticipated and unpredictable ways. I suspect that reducing the air friction of the car in its direction of travel is the most significant aerodynamic consideration in terms of efficiency. Any foiled surfaces designed to convert lift to forward propulsion would probably cause more drag and net a loss in terms of efficiency.

[jtr1962]

Edit: I meant to post this is the other thread about mpg as a function of mph. Somehow it ended up here. I also posted it in the other thread but I think I'll leave it here also as it's definitely relevant to EVs.

I saw lots of equations for vehicle resistance in a transportation planning course I took in college. For autos the equation was:

R = 0.01T + 0.0001TV + 0.0024CAV²

V is in mph, T and R are in pounds, and A is in square feet. The first term is obviously static rolling resistance. This is typically about 0.01 times the vehicle's weight but can vary from 0.006 (LRR tires) to 0.015 (SUV tires). The second term contains both tire flex and first order aerodynamic components (mostly the former). The first order aero components aren't too important for cars but they are very important in trains where most of the aero drag is side friction. The third term is aero drag. Horsepower needed to maintain any given speed is:

P = RV/375

So yes, the power needed to overcome aero drag goes up with the cube of the speed.

Food for thought:

Why do we even make vehicles with high drag coefficient? For any given size vehicle there exists a shape which will give the minimal amount of drag. Sometimes practical constraints dictate that we deviate from this shape slightly. That's fine, but why the boxes? No good functional or other reason for those. IMO they look ugly besides. Aero shapes seem like a no-brainer as far as saving eenrgy (whether it's an EV or an ICE). Once made, the shape saves money for the life of the car with no additional cost or maintenance. I don't get it. Even nature doesn't design that way. Just look at fish and birds. They're not boxy.

Thought this might be of interest here. It's an MS Word documentation for an MS Train Simulator friction calculator I made a while back. It has loads of train resistance equations in the appendix.

[McGizmo]

Originally Posted by jtr1962

..... Sometimes practical constraints dictate that we deviate from this shape slightly. That's fine, but why the boxes? No good functional or other reason for those. ...

I suppose it is relative and a question of what you mean by box but I presently drive a GMC Safari van that I would guess one would classify as a box. I beg to differ in there there is no good functional reason for this. The function I enjoy is interior storage and cargo space. Granted, the exterior form could be optimized for drag and still leave me with some room inside but I am guessing not without some compromise?!? Obviously trucks and delivery vehicles need to address capacity as a significant priority.

I have a deposit in on an Aptera and should it actually become available before any other full EV that I could purchase, I will probably go ahead with it but I think it has gone too far in terms of aerodynamics with significant compromise in what I need from it; the utility of carrying stuff besides myself.

[Darell]

Yeah... it is true that nothing beats a box for carrying crap! But what you also bring up is true as well - there are many ways to create a box inside without so much drag on the outside. And it doesn't have to be a losing compromise. They're just starting to do this with the big rigs now in a serious way. There were several little things done before like a big cone on the cab or front of the first trailer. Now they're starting to fill the gap between the cab and the box. Smooth out the grille. Rake the windshield. Dam the front, even fair the wheels a bit. A box is a pretty easy thing to move through the air as long as you break the wind appropriately, and recombine it appropriately. And those things don't infringe on the box benefits.

Here's an irony to ponder. My Rav4EV is considered a small SUV, and for all intents and purposes, it is a box. My Prius on the other hand is optimized (only compared to most other cars) for aero. Which one can haul four full-sized bikes inside with all the doors closed? Yeah... the Prius. I can only fit two in the Rav. So the moral here is that useful cargo and good aero are not mutually exclusive. The Prius may be an ugly example - but for practicality you can do a LOT worse. Oh... and I find the Rav even uglier than the Prius!

[Darell]

Originally Posted by jtr1962

Even nature doesn't design that way. Just look at fish and birds. They're not boxy.

Box Fish are!
http://www.militaryphotos.net/forums...&pictureid=626

See, the thing is, fish and birds don't carry SCUBA equipment or kayaks or bikes or tents or food or dogs or four other family members. For that you need a good bike.
http://farm4.static.flickr.com/3566/...c2de427e87.jpg

Here's Darell on vacation. When was the last time you saw a fish taking his sporting goods and beer cooler along with him?

[McGizmo]

Box fish are boxy but they aspire for better hydrodynamics like some larger inflatable kin:



(I love going off topic in one of Darell's threads! )

[Darell]

Obviously what we need are big thorny spikes!

[josey]

Those are not spikes. Those are turbulators. That box can move when it wants, at least after it gives birth.

[McGizmo]

Originally Posted by Darell

Obviously what we need are big thorny spikes!

Certainly give you more elbow room on the roads! (at the expense of some drag of course)

[Darell]

Dunno. They're finding that fish-like scales really help with aero. Maybe spikes are the next big thing!

Turbulators... yup!

[McGizmo]

I wondered about surface texture and shape for aerodynamics. They found that the weird bumps in the leading edge of the Humpback's pectoral fins actually improved on hydrodynamics. I recall some article on a rudder or keel done in such a matter being better performing than a smooth foil.

Looking to nature is not a bad idea as it has had a lot more time to sort things out than we have! It's actually probably pretentious to assume that we can improve on nature without much effort.

Heck, nature has been creating life with alternative energy sources and impressive efficiencies and complexities before we entered the scene. No EV's to be certain but inherent bio-mechanical mobility stock on all sorts of platforms and scales!

Back on track, I read where Mexico City is now implementing a fleet of EV Taxis. I wonder if they could share their technology with their neighbors to the north.

[Darell]

Yeah, the swimsuit technology in the summer olympics was pretty impressive. It is true that the more we emulate what's evolved for millions of years, the better we seem to do. Want to swim faster, check out how the fish are doing it. Want to fly more efficienty? Check out the birds. Want to destroy the environment for just about every living thing? Check out the... uh... humans?

[McGizmo]

He he. We deny our own evolution and not only make the world around us a better place but improve our design as well! We can enhance ourselves in so many meaningful ways!

After watching the film, "A Beautiful Truth", one thought that came to my mind was that of the potential errors of deviating from our natural heritage in terms of food and environment. Some of man's improvements are actually questionable in terms of value and health. Financial gain for some might actually be at the expense of health and well being of others.

But back to those EV's!

[Darell]

Continuing completely off topic since if we started a new topical thread, it would never be this interesting....

I recently discovered that I've been condeming my poor dog to an early grave and increased suffereing - by feeding him what we humans think is the proper ballance of diseased meat product, ground up feathers and fur, a bunch of salt and flavorings topped off with that unmistakable putrid smell. Yes, I'm talking about commercial dog food. When I finally realized what X (fill in the type of meat) meal means, I realized that we've decided not to feed our dogs what they were programmed to eat, but what we think they'll survive with. This whole pet food thing reminds me of the baby formula fiasco back in my parent's generation (meaning when I was brought up!) No breast milk! We can make a more nutritious meal for that little guy!

So anyway, in the past 1.5 years, my dog has had two toes amputated, has had two cancers removed, his fur is dull and falling out. He itched everywhere. He wouldn't heal from his last cancer surgery. One month ago, I started making his food in a way that truly emulates what he was programmed to eat. Nothing is processed (except by me shoving the fruits and veggies through the Vita mix!) and nothing is cooked.

You likely won't believe it unless you experienced it, but honestly - I have a new dog. Wounds are healed, there is no indication of any cancer, he has boundless energy, he does not scratch and his coat is shiny and staying on him instead of ending up in the vacuum. Where it looked like we'd lose him to disease, it now looks like he'll make it to a ripe old age!

[josey]

At this time of year, my garden is full, and what I like to do is fill a huge pot half full of water and then boil all kinds of greens and veggies in a huge soup. My dogs love it, and they do seem to be happier. Me too. Good food counts.

[idleprocess]

Maybe I'll just let the cat catch his own food - he sure seems excited by the prospect judging by how intently he stares out the window and occasionally lunges at it! It's not like there are enough predators in the 'burbs to properly regulate the starling, grackle, rat, and mouse population, the cries of the Audubon Society notwithstanding...