Drive Electric Day - Sat 4th Oct - National

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timpootle
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Postby timpootle » Sun Oct 05, 2008 10:43 pm

ChrisB wrote:Must admit if this is going to be a yearly event we do need to make sure we start advertising it a bit more than 4 days in advance :?


We did, Chris. It was 369 days in advance for DriveElectricDay 2009 :-D
Tim Crumpton

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MaryRCrumpton
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Postby MaryRCrumpton » Mon Oct 06, 2008 9:36 am

Yes, better advertising next year, definitely :-)

My illness came at just the wrong time.

Glad to have done something this year, albeit fairly low key.
Still a successful event, but hope for bigger and better in 2009 :-)

Mary.
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ex925
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Drive Electric Day 08, and "Lost range" - Ed. in P

Postby ex925 » Mon Oct 06, 2008 9:56 am

Many thanks for the advice, hadn't thought of rain raising rolling resistance. It makes good sense. The best range, 26miles, was achieved in August.

I wonder if there are other contributing factors as well?
I came up with eight ideas, four probables and four possibles.

1] I weigh half a stone more than at the time of the benchmark test.
2] The tyres were 10psi down, for wet grip.
3] A few drops of water emerged when I opened the controller casing.
4] Temp. was 14 degrees C. 041008, at least 18 degrees in August.

a] 20" wheels and tyres on the MkII. 26" on the MkI
b] 4-speed Shimano hub gear on the MkII. 6-speed Derailleur on the MkI
c] MkII has less suspension travel at both ends, a bumpier ride.
d] MkII has cup and cone wheel bearings. MkI has sealed separable units

(24v. motor, controller, 2x22a.h.12v. SLA batteries transferred, I to II)

All the best, from Ed.

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Joe T
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Postby Joe T » Mon Oct 06, 2008 1:19 pm

My day passed with the usual comments like "when are we going to see this ELECTRIC CAR then" :shock: I then point to the Berlingo. I then get the look of disbelief :? and normally the conversation ends there.
I don't normally get as far as explaining the BVS :cry: shame really.

I clocked up 52 miles on drive electric day :D despite the weather.

I am sort of at the tipping point of explaining the benefits of the Berlingo but then don't want the whole world to know as I might want another :oops:

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MaryRCrumpton
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Postby MaryRCrumpton » Mon Oct 06, 2008 3:19 pm

Great to hear you did 52 miles. People are always impressed with Berlingos I find. It's a great vehicle.

Mary.
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ChrisB
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Postby ChrisB » Mon Oct 06, 2008 3:31 pm

Joe T wrote:I am sort of at the tipping point of explaining the benefits of the Berlingo but then don't want the whole world to know as I might want another :oops:


Yeah thats the trouble I think somefolks dont understand, while its great that we have these EV's and they are fairly cheap, Tax Free and we are not charged for the road usage of the fuel we use 8) I cant help thinking that the more we jump up and down and shout about how fantastic EV's are we will lose all these lovely cheapy benifits and it will end up costing us the same as driving an ICE :cry:

ChrisB
I reject reality and substitute my own !!!!!!

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Jeremy
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Postby Jeremy » Mon Oct 06, 2008 4:37 pm

The weather has more effect on power usage than many realise.

Rain significantly increases rolling resistance, largely due to the energy needed to deflect surface water away from the tyre contact area. However, aerodynamic drag is lower when it's raining, as humid air is less dense than dry air.

Similarly, power usage in cold weather will be significantly greater than in warm weather, due largely to increased aerodynamic drag due to increased air density.

Jeremy

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qdos
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Postby qdos » Mon Oct 06, 2008 7:47 pm

Being a pilot Jeremy you ought to know a surface covered in water wreeks havoc with aerodynamics. My Hanglider is an all Mylar wing and if it's wet oh boy oh boy do you know about it!

Sky, fall out of.
Ground, rush up.
Deep skid marks.

eeeeek!

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Jeremy
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Postby Jeremy » Mon Oct 06, 2008 8:18 pm

Being a pilot Jeremy you ought to know a surface covered in water wreeks havoc with aerodynamics. My Hanglider is an all Mylar wing and if it's wet oh boy oh boy do you know about it!


Sometimes it can, but most often the effect is small, it depends on the aerofoil section used.

If the wing section is a laminar flow, or supercritical one, then water droplets can cause a significant reduction in L/D, due to the separation point moving forward and a greater area of the wing being subject to non-laminar flow. For bluff shapes, like most vehicles, there is either no negative effect or perhaps a slight reduction in drag. The latter is due to increased surface roughness from droplets actually reducing drag by producing a controlled thickness turbulent boundary layer that acts to "lubricate" the surface.

The other negative factor for flexible fabric aerofoils is that when they are wet they handle very differently than they do when dry. Although my old flexwing microlight still flies OK when wet, the handling, particularly in pitch, changes markedly. One factor is that the swept Rogallo wing planform means that the wing C of G shifts aft when it gets wet (there being more fabric behind the wing C of G than in front of it), which slows the HOT speed a bit.

Nowadays, most aircraft designers try to avoid aerofoil sections with excessive sensitivity to rain droplet (or dead fly) surface irregularities. The last big design error I know of was one of the early Rutan canard designs. To reduce drag he used a laminar flow section on the canard which caused massive loss of pitch control when it rained. The design was quickly changed when the problem became apparent (being based in the Mojave I doubt that Rutan ever flew the thing in the rain!) and subsequent versions have all used a non-critical aerofoil section that is relatively unnaffected by rain droplets.

My own designs use sections that actually work slightly better when a little bit "rough", as do most other modern designs of powered aircraft. As far as I know, it's really only hotship gliders that still stick with laminar flow sections that need to be kept very clean and shiny to work effectively.

Jeremy

ex925
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"Increased Drag Electric Day" from Ed. Gordon in P

Postby ex925 » Mon Oct 06, 2008 8:51 pm

Hi, guys, thanks for the input, learned a few things. Can't help noting that if I understand Jeremy correctly, - when I FINALLY get round to bodywork for the Junkyard Dog (or the larger TWEV still on the way...) - my notorious unskills at producing a smooth finish might be a blessing in disguise...

One final thought on "Rain-Reduced Range": what proportion of loss might be due to the effect of cold on the batteries, would it be negligible, a bit, quite a bit, rather a lot, lots, or a hell of a lot? [and how's that for a subjective / emotive / unscientific scale!]

All the best, from Ed.


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