GRA
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Re: How beneficial is drafting/slipstreaming?

Tue Oct 17, 2017 5:37 pm

Nubo wrote:It can be very effective. When I was 18 and stupid I drafted big trucks with my bicycle and could easily keep up with 40mph traffic. If you've ever tried to pedal a bicycle 40mph on level terrain you know it takes an immense amount of energy *without* slip-streaming.

There is, however, a downside to closely tailing this way. I have arthritis in my left wrist to prove it.

I think many people who saw the trailer drafting scene in "Breaking Away" attempted to replicate it when they were teenagers, and thus immortal ;) https://vimeo.com/50872582

From the bicycle records wiki:
Fred Rompelberg from Maastricht, Netherlands is the current holder of the motor-paced speed world record cycling with 268.831 km/h (166.9 mph) since 1995.[citation needed] He used a special bicycle behind a dragster of the Strasburg Drag Racing Team at the Bonneville Salt Flats.
https://en.wikipedia.org/wiki/List_of_cycling_records#History_of_motor-paced_records

Hopefully, most people here are old enough to realize that, as with rumors of Mark Twain's death, rumors of our immortality have been greatly exaggerated. :shock:
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

Supersleeper
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Re: How beneficial is drafting/slipstreaming?

Wed Oct 18, 2017 3:04 pm

LOL, you guys are funny. I'm not talking about riding a rig's bumper. I'm talking about maintaining a safe distance. I might be a little shy of 2 seconds, barely. It might not be as effective as if I were a car and 1/2 length behind, but it still registers wind speeds at under 50mph, which means it's still effective.

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Nubo
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Re: How beneficial is drafting/slipstreaming?

Wed Oct 18, 2017 8:20 pm

Supersleeper wrote:LOL, you guys are funny. I'm not talking about riding a rig's bumper. I'm talking about maintaining a safe distance. I might be a little shy of 2 seconds, barely. It might not be as effective as if I were a car and 1/2 length behind, but it still registers wind speeds at under 50mph, which means it's still effective.


Interesting. At that distance the slipstream is probably breaking up pretty badly. While the average for the anemometer may be lower than your ground speed, that result may not be conclusive evidence for lower energy requirements for the vehicle. The buffeting could be affecting the laminar flow over your vehicle and negatively affecting its aerodynamics.
I noticed you're still working with polymers.

Tsiah
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Re: How beneficial is drafting/slipstreaming?

Thu Oct 19, 2017 1:22 pm

They did this on myth busters. You'd have to be like 6-8 feet from the truck to have any useful effect to drafting.

GRA
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Re: How beneficial is drafting/slipstreaming?

Thu Oct 19, 2017 5:39 pm

Tsiah wrote:They did this on myth busters. You'd have to be like 6-8 feet from the truck to have any useful effect to drafting.

https://www.autoblog.com/2007/10/28/mythbusters-drafting-10-feet-behind-a-big-rig-will-improve-mile/

There's a table for 55 mph, showing drag reduction for distances of 100, 50, 20, 10 and 2 feet. As these are all much too close at 55 mph (100 feet back only gives you 1.25 seconds to react), I provide this for info only. For more info there's this, which is talking about red lights:

1.) Driver Reaction Times (tr)
Driver reaction time includes recognizing the light has changed, deciding to continue or brake, and if stopping engaging the brake (remove foot from accelerator and apply brake). Reaction times vary greatly with situation and from person to person between about 0.7 to 3 seconds (sec or s) or more. Some accident reconstruction specialists use 1.5 seconds. A controlled study in 2000 (IEA2000_ABS51.pdf) found average driver reaction brake time to be 2.3 seconds. The study included all driver types, test were conducted on a controlled track and in a driving simulator.

Driver Reaction Times
0.7 sec -- about as fast as it gets
1.0 sec -- old standard
1.5 sec -- common use
2.0 sec -- common use
2.3 sec -- AVERAGE
2.5 sec -- used in a few states
3.0 sec -- NSC and UK Standard

A few states, including California, have adopted a standard driver reaction time of 2.5 seconds. The United Kingdom's Highway Code and the Association of Chief Police Officers ACPO Code of Practice for Operational Use of Road Policing Enforcement Technology use 3.0 seconds for driver reaction time. The National Safety Council (NSC) recommends 3 seconds minimum spacing (3 second reaction time) between vehicles traveling in the same lane.

Test out your reaction time by playing the PassMeFast Emergency Stop game.

http://copradar.com/redlight/factors/

Here's another: http://www.visualexpert.com/Resources/reactiontime.html

Personally, while the driver's ed books and films in California said a minimum of 2 seconds spacing, I've always used at least 3 whenever possible, as my truck driver father taught me. I've been very glad to have that extra second on a couple of occasions.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

Tsiah
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Re: How beneficial is drafting/slipstreaming?

Fri Oct 20, 2017 5:55 pm

GRA wrote: t-behind-a-big-rig-will-improve-mile/[/url]

There's a table for 55 mph, showing drag reduction for distances of 100, 50, 20, 10 and 2 feet. As these are all much too close at 55 mph (100 feet back only gives you 1.25 seconds to react), I provide this for info only.

Personally, while the driver's ed books and films in California said a minimum of 2 seconds spacing, I've always used at least 3 whenever possible, as my truck driver father taught me. I've been very glad to have that extra second on a couple of occasions.

Those distances are too close at 55mph and most of the time trucks are doing 65 or 75 on the freeway here. They frequently pass me like I'm sitting still in the Leaf!
I try to stay 2-3 seconds away at the very least. If I'm that close to another car I pass them or slow down a little more.

Graffi
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Re: How beneficial is drafting/slipstreaming?

Mon Oct 23, 2017 4:48 pm

As the Leaf is a local commuting vehicle any savings or economy would be very small, and therefore do not justify the risk. However, with the advent of long distance EV technology drafting could be of some help in the case of strong head-winds.

Also, I would not even dream of trying this without the Tesla or other Adaptive cruise control that will maintain the spacing.

On our cross country trip with our new Tesla in June we found ourselves in a situation that we needed to extend our range because of missing a Supercharger. In this case we slowed down from the 80mph that we were driving and tucked behind a semi travling 65mph. At the time we did have a 5-10mph head-wind. We set the follow distance at 1 car length and let auto-pilot do the rest. After a little over an hour we had gained sufficient reserve to make it to the next Supercharger. We still stayed behind the semi until it exited the freeway and continued on for a few miles to the Supercharger. Fortunately this was the only time we felt a need to do this but it worked great. just saying....
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GRA
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Re: How beneficial is drafting/slipstreaming?

Mon Oct 23, 2017 5:26 pm

Graffi wrote:As the Leaf is a local commuting vehicle any savings or economy would be very small, and therefore do not justify the risk. However, with the advent of long distance EV technology drafting could be of some help in the case of strong head-winds.

Also, I would not even dream of trying this without the Tesla or other Adaptive cruise control that will maintain the spacing.

On our cross country trip with our new Tesla in June we found ourselves in a situation that we needed to extend our range because of missing a Supercharger. In this case we slowed down from the 80mph that we were driving and tucked behind a semi travling 65mph. At the time we did have a 5-10mph head-wind. We set the follow distance at 1 car length and let auto-pilot do the rest. After a little over an hour we had gained sufficient reserve to make it to the next Supercharger. We still stayed behind the semi until it exited the freeway and continued on for a few miles to the Supercharger. Fortunately this was the only time we felt a need to do this but it worked great. just saying....

You've just shown why the Tesla was the wrong vehicle for the job, on that route at that time. You're being forced to trust your and your passengers' lives to some hardware/software of unproven reliability and effectiveness. Until BEVs and their charging infrastructure have improved to the point where no one will be forced to adopt such measures merely to get to their destination, they will remain an unsafe choice for any such trip.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

edatoakrun
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Re: How beneficial is drafting/slipstreaming?

Mon Oct 23, 2017 7:41 pm

Tailgating is both unsafe and illegal in a Tesla, but you will be seeing legal and safe tailgating soon:

Are those 80,000 pound trucks tailgating each other? Soon it may be perfectly normal - and safe

If you look to the next lane and see two 18-wheelers roar past at 70 mph with just 10 yards between them, you'll probably think they are dangerously close.

In this high-tech age, that may no longer be true. In fact, it might be just the opposite, and it might even end up saving you money...
no condition is permanent

jjeff
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Re: How beneficial is drafting/slipstreaming?

Tue Oct 24, 2017 5:22 am

.....what goes around, comes around......
Breaker 1 9, we got ourselves a convoy ;)
Back when gas prices were high in the 70s such long convoys of trucks were quite popular, and I never heard of too many people dying or having accidents. Oh and personally I would NOT use CC while drafting, even adaptive, eyes on the bumper of the vehicle in front you at all times and preferably the vehicle in front of that if possible(around corners etc.). Again a car will stop a heck of a lot faster than a 80,000 semi, if the driver of the car is paying attention....
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