Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 09-07-2020, 05:12 PM   #21 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
Quote:
Originally Posted by GreenTDI View Post
Can we see a picture of the underside? Or is that irrelevant?
My guess is that it will take off at highway speed
I haven't been able to find a pic but I assume it's fairly flat.

__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
aerohead (09-09-2020)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 09-07-2020, 05:18 PM   #22 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
Quote:
Originally Posted by Stubby79 View Post
To expand on my guess, without editing my post...

I would assume that downforce would work out to mean more rolling resistance, as the vehicle would behave as if it's heavier the faster you go...

Therefore neutral would be better for FE, presumably. And no loss of traction at speed. Of course, if it only weights 50lbs, you might want downforce at speed to keep you grounded. Bad things might happen when you catch air, though...

If it's heavy, they might have designed it for a bit of lift, to reduce RR the faster it goes.

Too much lift sounds like a bad idea in general.

Of course, if it only goes 30km/hr, lift and the Cd are both pretty moot points...

YMMV.
Car had calculated 160 km/h (~100 mph) top speed and averaged 89.76 km/h (55.77 mph) in the actual race.
__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
aerohead (09-09-2020)
Old 09-07-2020, 06:22 PM   #23 (permalink)
Rat Racer
 
Fat Charlie's Avatar
 
Join Date: May 2011
Location: Route 16
Posts: 3,944

Al the Third, year four - '13 Honda Fit Base
Team Honda
90 day: 42.9 mpg (US)
Thanks: 1,653
Thanked 1,787 Times in 1,156 Posts
Without seeing the underbody, I'd assume 1: Downforce.
__________________

Quote:
Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

  Reply With Quote
Old 09-07-2020, 08:51 PM   #24 (permalink)
Tyrant-at-large
 
Vman455's Avatar
 
Join Date: Feb 2012
Location: Champaign, IL
Posts: 1,641

Little Red - retired - '05 Honda Civic EX
90 day: 49.03 mpg (US)

Pope Pious the Prius - '13 Toyota Prius Two
Team Toyota
SUV
90 day: 59.03 mpg (US)
Thanks: 176
Thanked 1,436 Times in 755 Posts
Quote:
Originally Posted by GreenTDI View Post
Can we see a picture of the underside? Or is that irrelevant?
It has a slightly concave underside:
__________________

  Reply With Quote
The Following 6 Users Say Thank You to Vman455 For This Useful Post:
aerohead (09-09-2020), California98Civic (09-08-2020), Fat Charlie (09-08-2020), freebeard (09-07-2020), JulianEdgar (09-07-2020), RedDevil (09-08-2020)
Old 09-08-2020, 06:18 AM   #25 (permalink)
Rat Racer
 
Fat Charlie's Avatar
 
Join Date: May 2011
Location: Route 16
Posts: 3,944

Al the Third, year four - '13 Honda Fit Base
Team Honda
90 day: 42.9 mpg (US)
Thanks: 1,653
Thanked 1,787 Times in 1,156 Posts
It looks like they didn't do anything to increase downforce, but I'd expect some.
__________________

Quote:
Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

  Reply With Quote
Old 09-08-2020, 06:33 AM   #26 (permalink)
In the fasting lane
 
RedDevil's Avatar
 
Join Date: Dec 2012
Location: Nieuwegein, the Netherlands
Posts: 3,747

Red Devil - '11 Honda Insight Elegance
Team Honda
90 day: 55.71 mpg (US)

It - '09 Hyundai I10 Active Cool
Team Hyundai
90 day: 29.19 mpg (US)
Thanks: 1,517
Thanked 2,055 Times in 1,322 Posts
The wheel covers create a tunnel under the car so anything is possible. I'll say 2 - neutral just to have a vote.

I would expect the area around the canopy and the canopy itself to produce lift, but that would be compensated slightly on the front and the long tail. The underbody should provide downforce.
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.16 Gmeter or 0.1 Mmile.



COVID-19: Some people just don't get it.
  Reply With Quote
Old 09-08-2020, 06:02 PM   #27 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
So final guesses are:


(1) Downforce
(2) Neither lift nor downforce
(3) A small amount of lift
(4) A lot of lift


California98Civic - 5 (I assume therefore 4)

Redpoint5 - 3

Jakobnev - 3.5

Oil pan 4 - 3

Jimhs - 4

Green TDI - 3-4

Freebeard - 1

Ksa8907 - 1-2

Stubby79 - 1-2

Fat Charlie - 1

RedDevil - 2

Average score - 2.5, so somewhere between 'neither lift nor downforce' to 'a small amount of lift'.
__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
aerohead (09-09-2020)
Old 09-08-2020, 06:27 PM   #28 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
Here is the first part of the answer:



The line with red boxes shows overall lift coefficient (CL). It's at around 0.05 (low lift) until about 100 km/h, whereupon it starts to rise, reaching about 0.16 at 140 km/h. That's a fair bit of lift.

The line with yellow diamonds show front lift coefficient (CLf). It is about 0.13 (a fair amount of lift) until 100 km/h, and then rises to 0.25 at 140 km/h. That is a lot of lift.

The line with the black diamonds shows the rear coefficient of lift (CLr) having small/medium downforce (about -0.09) at all speeds.

The amount of aero lift the car experienced in zero yaw was enough to increase the height of the front of the car, causing the further worsening of the front lift values. Note: this was not desired by Honda - they said: "Future research and development will be required to refine the suspension and/or front lift coefficient in order to further increase the cruising speed."

So overall, this most streamlined of cars has, at zero yaw, quite a lot of lift. As Honda said: "The overall body shape was designed like the cross section of an airplane wing, resulting in a large CLf (front lift coefficient). The front part of the body would therefore receive more upward force at a higher speed."

Interesting, and the story actually gets considerably worse in crosswinds (next post).
__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics

Last edited by JulianEdgar; 09-08-2020 at 06:49 PM..
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
aerohead (09-09-2020)
Old 09-08-2020, 06:40 PM   #29 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
Here is the second part of the answer:



So what happens when there is a yaw (crosswind) component to the airflow? Not good things!

The CLf (yellow diamonds) doesn't change much - in fact, it actually improves (gets lower).

But the CLr (black diamonds) increases massively, going positive (into lift) at only about 4-5 degrees of yaw, and then reaching a stunning 0.53 at 15 degrees of yaw. That's the highest CLr I've ever seen.

As a result of that, the overall CL (red squares) goes to well over 0.6(!!) at 15 degrees yaw.

Frontal area of the car was 0.999 square metres and mass was 330kg - I'll let someone else do the maths for the effective weight of the car at 60 km/h - let alone at 15 degrees of yaw and 140 km/h (obviously, in those conditions the car would have been impossible to drive).

So, next time you read someone saying confidently that, well of course, streamlined cars have low lift, you can say: "You're dreaming!".
__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics
  Reply With Quote
The Following 3 Users Say Thank You to JulianEdgar For This Useful Post:
aerohead (09-09-2020), COcyclist (09-16-2020), Ecky (09-15-2020)
Old 09-08-2020, 06:48 PM   #30 (permalink)
Master EcoModder
 
Join Date: Nov 2017
Location: Australia
Posts: 773
Thanks: 53
Thanked 742 Times in 465 Posts
And if you're wondering at the incredible amount of rear lift with yawed airflow, look at the shape presented to the partly sideways airflow by the rear half of the car:



A huge area for the airflow to wrap around that upper curve, while lateral undercar airflow is largely blocked.

__________________
Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics
  Reply With Quote
The Following User Says Thank You to JulianEdgar For This Useful Post:
Ecky (09-15-2020)
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com