# Aussie solar car fastest in world - Page 2

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Re: Aussie solar car fastest in world

"David L. Jones"

Here is the actual theoretical graph

**  WTF does " actual theoretical " mean ??

It simply cannot be both things.

for the Sunswift car:
http://www.eevblog.com/images/projects/SunSwiftDragGraph.png
The rolling resistance and aerodynamic drag are equal at 60km/h
Drag is not a linear function of speed as you said. Rolling resistance
is linear.

** Rolling resistance is linear  -  in theory only.

Odds are it diminishes at high speeds since the tyres are subject to large G
forces thereby reducing contact area and hence loss of energy by deformation
PLUS  that solar array looks like a wing and so it must have some lift.

.....  Phil

Re: Aussie solar car fastest in world

I meant that this is the theoretical power requirement graph from the
actual Sunswift car used.

All the various external surfaces are aerofoil wings, mainly to reduce
drag and tail vortexes et.al. No lift figures are mentioned.
The graph is the theoretical power required to drive the car based on
total rolling resistance and aerodynamic drag figures. Presumably they
are using known measured test data for both of these, and it kind of
implies that in the document I have.
It is stated they have measured these parameters and use them in a
real-time simulator model to enable optimisation of the cars energy
consumption vs performance etc.

From the documentation it sounds like the rolling resistance is not
insignificant and is split into two components, tires and "bearings
etc".
In a formula provided, the tire rolling resistance and the wheels
bearing resistance are both included.
The tire rolling resistance term is: mass * gravity * rolling
coefficient
The bearing resistance term is: Number of Wheels * bearing coefficient
* velocity

Dave.

Re: Aussie solar car fastest in world

I doubt that has much effect actually, especially with the very high tyre
pressures used on this kind of vehicle.

Highly unlikely they've designed-in any lift. You can't get lift without
drag.  In fact the main figure of merit for sailplanes is L/D ratio,
because that tells you how much of your drag is actually producing lift.
It also happens to give you your sink angle.

Clifford Heath.

Re: Aussie solar car fastest in world

"Clifford Heath"
"Phil Allison"

** Really ??

90 psi is only 6 atmospheres.

88 kph results in about 250Gs on the surface of the tyres.

A  =  V squared / radius

G  =  A / 9.8

** Not unlikely at all.

Even a small amount of lift would reduce rolling resistance as much as
removing the batteries did.

...   Phil

Re: Aussie solar car fastest in world

From another post, the record attempt car weighed 140Kg.

The Michelin solar car competition tyres have a rolling resistance
coefficient of around 0.0025 - meaning the actual resistance force is
about 3.4N. To carry 140Kg across the three wheels at 88KPH requires

Estimating the total mass of each tyre at 250g, the diameter at about
60cm, and the width of the contact patch at 1cm, the mass of the tyre
in the contact patch is about 7.5 grams. At 250Gs, that's less than
20N - less than 5% of the 450N.

So you're proposing that the rotational speed at 88KPH can save about
4 watts. Big deal.

Michelin tyre data from <http://en.wikipedia.org/wiki/Rolling_resistance .

It would increase the aerodynamic drag by much more, especially considering
that the aerodynamic drag is costing (1200-80) watts, or 93% of the energy
budget.

Clifford Heath.

Re: Aussie solar car fastest in world

"Clifford Heath"

** The graph posted by DL Jones shows rolling resistance consumes about 350
watts.

http://www.eevblog.com/images/projects/SunSwiftDragGraph.png

Very little energy is lost in ( presumably) ball bearings - else they would
become very hot.

** Wrong.

Aerodynamic drag is more like 70 % of the budget -  as shown in the graph.

Any aerofoil section has drag, whether is produces lift or not. A simple
flat bottom, curved top aerofoil ( as appears in the pics) has lift even
with zero attack angle and so no additional drag.

.....  Phil

Re: Aussie solar car fastest in world

"Phil Allison"

http://bigpondnews.com/articles/Technology/2011/01/07/Aussie_car_breaks_a_world_speed_record_561319.html

** Oops -  the new record is 88 kph.

... Phil

Re: Aussie solar car fastest in world

It would have to be a lot less. This is why any serious human powered
vehicle speed attempt is undertaken by a bicycle(usually recumbent) with
fairings front and back if not a complete shell.

Re: Aussie solar car fastest in world

"terryc"

** Nonsense.

The speeds and input powers are similar.

Means the drag force must be too.

...  Phil

Re: Aussie solar car fastest in world

I sure hope your understanding of electrical matters isn't as poor.

Re: Aussie solar car fastest in world

[...]

Suspicion seems to be confirmed.

The actual data indicates the streamlining was almost 10x better than a
race bike. No wonder the total power was comparable to just the rolling
resistance of other electric cars. :)

--
[Specific learning difficulties:]

We've slightly trimmed the long signature. Click to see the full one.
Re: Kym is full of Horeshit and a raving NUT CASE

"fritz the fuckwit "
<

** Good grief.

The speed and input powers are both known.

So the total amount of drag force is known =  49N.

** The data shows that the amounts of drag are similar.

The Sunswift uses about 900 watts (or 1.2 hp) to overcome aerodynamic
rag  - see graph.

http://www.eevblog.com/images/projects/SunSwiftDragGraph.png

A good cyclist outputs about that same figure when sprinting.

.....  Phil

Re: Kym is full of Horeshit and a raving NUT CASE

Here we go again, the latent abusive, probably psychotic trait of Phil
emerges.....
Philly boy, you have serious psychological problems.
Why do you suddenly resort to calling me "fritz the fuckwit " when 99% of the
people on this
newsgroup would agree that YOU are the fuckwit, based on your previous posts ?

If you can't beat 'em, insult 'em is the Phil Allison way...........as
usual................

What is the CdA for the Sunswift and a racing bike ?
Please fill in the following ...

Racing bike CdA =
Sunswift CdA =

coefficient (Cd)

Cd,

Fill in the CdA table above...if you don't know how to do it then shut up.

see graph.

The subject is air drag, CdA, specifically comparing the CdA of a racing bike
to the Sunswift.

Re: Kym is full of Horeshit and a raving NUT CASE

My latest document for the Sunswift 4 does not say, but from a
document for Sunswift 3:
http://www.sunswift.com/documents/media/FastFacts_Jan09.pdf

CdA for Sunswift III is 0.11
You could assume Sunswift 4 would be the same or marginally better.

Optimised bikes seem to be typically around 0.7-0.8 at best?

Dave.

Re: Kym is full of Horeshit and a raving NUT CASE

My latest document for the Sunswift 4 does not say, but from a
document for Sunswift 3:
http://www.sunswift.com/documents/media/FastFacts_Jan09.pdf

-CdA for Sunswift III is 0.11
-You could assume Sunswift 4 would be the same or marginally better.

-Optimised bikes seem to be typically around 0.7-0.8 at best?

-Dave.

That's what I suspected.
Looks like philthy phil has egg all over his face, yet again.

Re: Aussie solar car fastest in world

Congrats to Irving and the rest of the Sunswift team, awesome effort.
Hopefully I'll be doing a video blog tour of the Sunswift racer at the
end of this month.
If anyone wants me to show any particular area in detail, or ask any
specific questions, then let me know.

For those interested in some details, at 90km/h the aerodynamic drag
accounts for over 70% of the driving power. The rest of the required
power is directly proportional to the mass of the car. The base
chassis weighs only 50kg.
Also, the breaks can stop it from 50km/h in under 10m.
The whole car weights 165kg, including the 25kg battery pack, so the
record attempt car weighed only 140kg.
The wheel motor is over 97% efficient.
The tires are inflated to 90psi and are easy to puncture, so are
usually changed every day.

Dave.

Re: Aussie solar car fastest in world

Congrats to Irving and the rest of the Sunswift team, awesome effort.
Hopefully I'll be doing a video blog tour of the Sunswift racer at the
end of this month.
If anyone wants me to show any particular area in detail, or ask any
specific questions, then let me know.

For those interested in some details, at 90km/h the aerodynamic drag
accounts for over 70% of the driving power. The rest of the required
power is directly proportional to the mass of the car. The base
chassis weighs only 50kg.
Also, the breaks can stop it from 50km/h in under 10m.
The whole car weights 165kg, including the 25kg battery pack, so the
record attempt car weighed only 140kg.
The wheel motor is over 97% efficient.
The tires are inflated to 90psi and are easy to puncture, so are
usually changed every day.

Dave.
----------------------------------------------------------------------------------------------------------

A couple of specific questions on the Sunswift..
What is the frontal area (A) of the car ?
What is the drag coefficient (Cd) of the car ?
How does the drag area (CdA) compare to a racing bicycle ?

Re: Aussie solar car fastest in world
...

...

So air resistence is equiv to 840 W.  The math then shows the
friction coeff is .05; an effective profile almost 10 times better
than my old electric kart project which was around that for a
bike + rider in race mode.

From the rough calcs before, it certainly seemed air resistance
was very low.

Rolling resistence around 360 W. My old formula with race tyres would
have it .05*m*v == .05*(165+80)*55  = 674 W.  The tyres used were
apparently 2x better than Michilin "solars". :)

Thanks for the details.

--
[...] I want you to acknowledge that AGW is only one possible reason
for temperature increase, out of a number of possible reasons.
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Re: Aussie solar car fastest in world

"David L. Jones"

For those interested in some details, at 90km/h the aerodynamic drag
accounts for over 70% of the driving power.

** Thanks for that confirmation of my original opinions.

The heretics here are seriously looney.

BTW

The actual drag force on the solar car from all sources at the record speed
( 88kph) amounts to no more than 5kg.

1200/24.4/9.8 = 5

....   Phil

Re: Aussie solar car fastest in world

Who the fuck cares?