Air Speed Indicator

Since the biggest determinant of power consumption is wind resistance, a bit of thinking about Air Speed vs. Ground Speed is in order. With a headwind of 20mph, a ground speed of 60 would be consuming power at the 80mph rate. Conversely, with a tailwind of 20mph, a 70mph cruise speed would only be consuming the equivalent of 50mph rate.

These are significant factors. In a way, the driver of a limited-range EV is a brethren of an airplane pilot. When determining range, it is Air Speed that concerns us rather than Ground Speed.

In that light, an Airspeed indicator would seem to be an appropriate instrument to include on the Leaf. When trying to optimize range, the driver should have that information rather than trying to derive it from second-order information such as the power consumption, or "building trees".

Of course, one must remain legal and reasonable in terms of ground speed, and I imagine legal departments might cringe at the notion that an airspeed indicator might cause someone somewhere to speed or be confused with road speed. I'd hope those concerns could be worked out by proper design.

And a pitot tube would be a cool conversation starter, and more useful than the solar panel, imho.

Nubo said:

And a pitot tube would be a cool conversation starter, and more useful than the solar panel, imho.

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YES! And it would allow you to "optimize" your tracking distance while drafting (oops ... that would be a liability issue ... oh well, we'll have to wait for after market :twisted: )

Of course, for the best mileage, people would always want to travel with a tailwind.

No telling where they might end up, but they will get there having consumed less fuel!

Dav said:

Of course, for the best mileage, people would always want to travel with a tailwind.

No telling where they might end up, but they will get there having consumed less fuel!

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http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind/

http://skepticblog.org/2010/05/27/sailing-directly-downwind…-faster-than-the-wind/

Nubo said:

Since the biggest determinant of power consumption is wind resistance...

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Above 45mph...

Nubo said:

j...a bit of thinking about Air Speed vs. Ground Speed is in order. With a headwind of 20mph, a ground speed of 60 would be consuming power at the 80mph rate. Conversely, with a tailwind of 20mph, a 70mph cruise speed would only be consuming the equivalent of 50mph rate.

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Source: The New Electric Vehicles: A Clean & Quiet Revolution, Michael Hackleman, 1996, 0962958875

Well, if you have a pitot tube, then somewhere you need a static port. Imagine waxing over that little guy when you're trying to get the shine back into the paint... :lol:

Total load makes more sense to me though, as you can climb a hill with a tailwind and be in worse shape than going down a hill into a headwind.

That all being said, rigging up a pitot/static system wouldn't be that hard, especially if you mounted the gauges boy racer style on the A pillar.

Here we are - pitot and static in one assembly for $26.

http://www.aircraftspruce.com/catalog/inpages/pitot15144.php

Nissan needs to drop some new info fast, before we all go insane.

Bicster said:

Nissan needs to drop some new info fast, before we all go insane.

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You have to imagine that their marketing people must be as busy right now refining the messages as their engineers are finishing the car.

DeaneG said:

Bicster said:

Nissan needs to drop some new info fast, before we all go insane.

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You have to imagine that their marketing people must be as busy right now refining the messages as their engineers are finishing the car.

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My wife is a tech writer, so I imagine the marketing people and writers being frustrated with the engineers and managers constantly changing stuff that they've previously told them was set in stone. :lol:

Bicster said:

Nissan needs to drop some new info fast, before we all go insane.

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Aye, I thought it was just me.

Bicster said:

Nissan needs to drop some new info fast, before we all go insane.

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Haha! I suppose you're right!

I think an air speed indicator is a pretty silly idea since the only thing it is useful for is to tell you your power consumption, and there is already a gauge that does that. Even if you knew the air speed, that would only make a difference if it was high and steady in one direction, and you were driving a long distance in one direction more or less with or against the wind (not orthogonal), in which case you probably already know the prevailing wind direction. If you want one, though, have at it, but I would be astounded if Nissan puts one in. Having said that, it does make a difference in some cases, as I found out by personal experience. When my wife and I drove from the Bay Area to Santa Barbara down 101 a few years ago in her Acura TSX I kept a close eye on the mileage indicator and was able to keep it just over 30 MPG. Coming back in the same car, driving style (no rush), and route I couldn't. It stayed at about 28.5 max. The difference is that prevailing winds along the California coast come from the NW (tail wind going out, head wind coming back). For most of us most of the time, though, we are turning so often and the winds are shifting so often that it all averages out anyway.

Rat said:

I think an air speed indicator is a pretty silly idea since the only thing it is useful for is to tell you your power consumption, and there is already a gauge that does that. Even if you knew the air speed, that would only make a difference if it was high and steady in one direction, and you were driving a long distance in one direction more or less with or against the wind (not orthogonal), in which case you probably already know the prevailing wind direction. If you want one, though, have at it, but I would be astounded if Nissan puts one in. Having said that, it does make a difference in some cases, as I found out by personal experience. When my wife and I drove from the Bay Area to Santa Barbara down 101 a few years ago in her Acura TSX I kept a close eye on the mileage indicator and was able to keep it just over 30 MPG. Coming back in the same car, driving style (no rush), and route I couldn't. It stayed at about 28.5 max. The difference is that prevailing winds along the California coast come from the NW (tail wind going out, head wind coming back). For most of us most of the time, though, we are turning so often and the winds are shifting so often that it all averages out anyway.

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It's just those type of highway cruise scenarios where maximizing range could be most important. Consider an EV will be more affected than an ICE, due to its inherent efficiency. ICE already wastes a lot of energy, so the impact of adverse winds is a smaller percentage of the total. See the charts presented elsewhere for range vs speed for EVs. ICE cars are influenced, but nowhere near to that degree.

Wind does not have to be direct in line of travel to have an influence. As a cyclist, I'm keenly aware of the difference that even a quartering wind can make. And I spent a week in May getting pushed southward by those wonderful coastal CA winds!

In terms of information, yes you do have power consumption, although from pictures of the display, the resolution of that information may be less than ideal. On the other hand, people tend to drive at a set speed. Knowing the nature of the wind influence would help to choose a better speed in a rational manner rather than reacting to increased power consumption whose cause (and therefore mitigation) may not be immediately apparent.

But the one thing I didn't think about is that, while planes are almost always traveling more or less directly into the relative wind, cars are not -- as you point out. What that means for my airspeed indicator fantasy is that the pitot tube would not be accurate for side winds.

Guess I can make due with a bit of string taped to the nose. :lol:

Nubo said:

But the one thing I didn't think about is that, while planes are almost always traveling more or less directly into the relative wind, cars are not -- as you point out. What that means for my airspeed indicator fantasy is that the pitot tube would not be accurate for side winds.

Guess I can make due with a bit of string taped to the nose. :lol:

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To be fair, an airplane on has a 1 in 360 chance of flying "directly" into the wind. Depending on your route of flight, it's common to never have a tailwind or a headwind. Only time you are generally going to have a headwind is on take off and landing. Everything else is fair game.

BrendanDolan said:

To be fair, an airplane on has a 1 in 360 chance of flying "directly" into the wind. Depending on your route of flight, it's common to never have a tailwind or a headwind. Only time you are generally going to have a headwind is on take off and landing. Everything else is fair game.

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And there's no guarantee that we'll have a headwind even during takeoff and landing - unless we're using a huge chunk of pavement, a beautiful grassy aerodrome, or an aircraft carrier.

Wind affects all vehicles regardless of what turns the wheels - so does cold weather. We don't notice the affect of the wind or cold as much in an ICE because most are seriously over-powered.

Since aero drag is probably the most significant user of power above 45mph, an airspeed input would allow a driver to decrease their road speed in a headwind to reduce energy use, and increase their road speed if they want to take advantage of a tailwind.

Geeky but useful for efficiency nuts.

AndyH said:

Since aero drag is probably the most significant user of power above 45mph, an airspeed input would allow a driver to decrease their road speed in a headwind to reduce energy use, and increase their road speed if they want to take advantage of a tailwind.

Geeky but useful for efficiency nuts.

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Why again to we need the airspeed indicator? We already have a speedometer and an amp-meter. If you are drawing more than normal amperage at a given road speed, then slow down because your either going uphill or there is a headwind. Inclinometer would probably be less expensive to implement and be more accurate. It might even be built into the car already. I just don't see what is gained by adding this instrument.

ps 1/360 chance of being within 1 degree of a perfect headwind...you have a 50/50 chance of being within 180 degrees of a perfect headwind.

Interesting discussion. I just finished a round trip from LA to San Francisco with beginning and ending locations at ~200’ elevation. Prevailing winds were 280@15G29 on the way up and 270@12 coming back. I added up used state of charge and difference was 7 % higher going North with a slower average speed.

The other thing to consider is elevation. Even with tail wind southbound on San Marcos pass into Santa Barbara, I was down to 5% remaining at the top of the pass. Back up to 15% 10 miles later in Santa Barbara. I found elevation costs me 4-5% /1000 feet of elevation. I’ll be interested to see if elevation is part of LEAF navigation system. Lakeview Terrace to Mount Wilson is only 30 miles, but it’s 5,000 vertical feet. Highland to Big Bear is 35 miles and 6,000 vertical feet. Suggest Quick Charger at Hwy 18 and 210 for the skiers.

palmermd said:

Why again to we need the airspeed indicator? We already have a speedometer and an amp-meter. If you are drawing more than normal amperage at a given road speed, then slow down because your either going uphill or there is a headwind. Inclinometer would probably be less expensive to implement and be more accurate. It might even be built into the car already. I just don't see what is gained by adding this instrument.

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Certainly - 'need' it's not. The inclinometer can go to sleep when driving in Kansas.

BrendanDolan said:

Nubo said:

But the one thing I didn't think about is that, while planes are almost always traveling more or less directly into the relative wind, cars are not -- as you point out.

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To be fair, an airplane on has a 1 in 360 chance of flying "directly" into the wind. Depending on your route of flight, it's common to never have a tailwind or a headwind. Only time you are generally going to have a headwind is on take off and landing. Everything else is fair game.

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Gee, Brendon, what Nubo said sounded right to me. I don't know much about wing aerodynamics, but I had the impression a plane would be in danger of crashing if there wasn't a net airflow from front to rear. In fact if your ground speed is 100 MPH and there is a 90 degree crosswind of 50 MPH, wouldn't you be flying only 30 degrees off from directly into the effective wind? I'd call that "more or less directly into the relative wind."