Desgeegee's Build Thread Ford Focus
 

Hi to everyone!
First of all, i'm apologize for my english (i'm italian), and i hope this is the right section.
I've got a Ford Focus 2016 hatchback diesel and despite it's very thrifty in consumption i wanted to improve aerodynamic.
The first thing that i did, was to look down the underside of tha car and what i saw scaried me a lot. there weren't panels or anything else except a little diffuser, two mini panels near the rear wheels, four spats and, of course, an undertray.
Here the underside of my car (photo by google):
[IMG]https://ecomodder.com/forum/member-d...825-cybm6r.jpg[/IMG]

So the first thing that i did after that thrilling vision, was to search what ford did in the "Econetic" version about aerodynamics mods, that is to add a paneling to the underside and equipped the steel wheels with a smooth hubcaps. I bought these panels and i mounted them.
https://ecomodder.com/forum/member-d...4-18-53-15.jpg

Here there is a photos of a Focus with all panels (photo by google):
https://ecomodder.com/forum/member-d...download-1.jpg
In the middle of multilink structure, you can see a little cover of it. It's very very little.
I decided to create a carbon sheet to cover all suspension structure that then, will work with a new diffuser, more wide. i was started with making a cardboard mock-up, and this is the final result:
https://ecomodder.com/forum/member-d...4-18-56-15.jpg

I'm sorry but i don't have the photo of the underside of the car with this panels, but i made a very poor photoshop :turtle:
https://ecomodder.com/forum/member-d...6-cybm6r11.jpg


What do you thing about this underside?
Soon i will project a right diffuser :thumbup:

Focus underbody
 

Everything you cleanup under there will only pay dividends down the road. It's a good investment! Looking good! :thumbup:

Looking good.

I've been spending some time recently under my car not as bad as most cars.

Nice improvements you have made.

Thank you guys.
Last month i read some papers about the efficiency of a rear diffuser in a sedan, wagon and hatchback. In the first two types, a proper diffuser actually reduces drag but not for the hatchback.
So my question is (hoping for your knowledge): is most effective to make a simple diffuser following the shape of the original "diffuser" with the plus of cover the holes between the bumper and tyres o make a diffuser with a different inclination size etc?

I would suggest you to slightly increase the surface of the one you proposed. Eventually if you can mount on the lower arms BMW deflectors.
And close the back according to the model of the central fairing.

most effective
 

We might presume that Ford actually 'tuned' the OEM diffuser for the peculiarities of the Focus' rear flow.
Some hatchbacks ended up with a 'raked', slanted chop to the roofline, and slope angles in the 'forbidden' 28-degree- to- 32-degree range, producing bi-stable flow and 'booming' as the flow jumps back and forth between fastback and squareback flow. Plastic roof extensions were added as a palliative to atone for the original sin.
I know of one variety of Focus hatchback with Cd 0.297. This suggests that Ford designers paid some 'thought' to the car.
Without a laboratory it's hard to 'accurize' modifications, and in your case, by mimicking Ford's original diffuser profile, it might have a better probability of success. Only testing will tell.

For Ironick: yes i need to "close" the holes between the oem little panels and my "suspension cover", it's in the list of things to do. For the lower arms covers, i thing it's hard to do properly an so i want to concentrate first on a modify the diffuser.

For Aerohead: Ok, i will try to follow the original diffuser and then test it.

Thank you for your answer

Hi guys, i'm back with some little news:
- i made a cardboard prototype of the right part of the diffuser (in black)
https://ecomodder.com/forum/member-d...14-27-29-3.jpg
-i used this prototype like matrix for create the final glass-fiber panel
-i used a sheet metal with C profile with the scope of fix the panel at the spar
https://ecomodder.com/forum/member-d...2-00-08-49.jpg

And this is the final result:
https://ecomodder.com/forum/member-d...23-00-03-3.jpg
https://ecomodder.com/forum/member-d...1-23-00-03.jpg

Now i'm testing this panel on the road (bend, twist, vibration ecc) and after that i need to putty it and paint it matte black.
:turtle::turtle:

Looks good! It will hide away nicely painted black.

Of course! I also use a round head screws (shich will be painted in matte black) to hide them

This is the final result! I'm sorry for the bad quality of this photo but it's a several days it's has been raining all days and i haven't been able to take a good photo with a good light.
However the panel is quite invisible and so are the screws.

https://ecomodder.com/forum/member-d...9-13-03-14.jpg

Yesterday i tried to do the Coast Down Test for Cd evaluation:
-7 test from 180kph* (about 112 mph) to 90/80Kph* (about 56/50 mph). *Speed from speedometer. ( 7 test, 4 in one direction and 3 in the opposite direction, because the trial road isn't very flat)
- I use elm 327 interface + Forscan to record all data (time, fuel, real speed)
- Several months ago I found an excel file that models the experiment for the evaluation of Cd and the resistance rolling coefficient, by inserting some characteristics of your car like mass, frontal area, etc plus the insertion of the actual speed that you find.

I edited this file because i don't like playing with two variables to minimize the error between the model speed and the actual speed, so i modeled the Crr with the Stuttgart rolling resistance coefficient which depends on Speed and Tire pressure.

The results are:
Cd= 0.272 ( i think it's quite reliable)

Error= 0.37 ( i think it's acceptable)

https://ecomodder.com/forum/member-d...s-attempt1.jpg

What do you think about it? Any suggestions?

After finish the diffuser, i'll try again of course!

Is the error factor larger than the actual results?

I think it is impossible to accurately calculate Cd* by coastdown tests, without very sophisticated data gathering (including real time wind/yaw) and very good modelling (including all rotational inertias).

Given the high speeds you are using, it might be possible to measure some relative changes in drag. Do the tests again with windows up / windows down and see how much consistent difference in speeds you can record after 50 seconds.

(* let alone to three decimal places!!)

After trying coast down testing several times this summer, I agree with all of this. It was just about impossible to get data consistent enough to show a change in drag with the windows up versus down, let alone try to calculate the cD with that spreadsheet (which I tried the first time. It came up with a radically different cR and higher cD with windows up than down!).

I wish there was anywhere here that I could do 100+ mph legally.

Yes it is and this is the data that gives me doubts. If you see the table, this error factor depends mostly by the difference between Vactual and Vmodel of 30 and 50 seconds.

30s: I've 107,6-107,4-109,1-103,2-104,2-106,4-108,2
Vmodel: 107,9 kph
I think that the only way to fix this "problem" is to collect more data and
do more test.
50s:Here there aren't some data due the traffic that forced me to brake..

What about to consider the mode and not the average(statistic mean(?))?

I need to do again this test in a major proper way of course

Yes this test isn't intended to find the real Cd but to find a "good" method (or refine and fix it for a better estimate)
to estimate it and make relative comparisons with the various upgrade made
I will do the Windows Up/Down test. I promise :cool:

You will be wasting your time unless you do a basic test of a change that does alter drag - eg windows up / windows down - and ensure you can measure it. Chasing imaginary changes is no fun.

I think is quite impossible to calculate the Cr without all coefficients and data of tyre and tarmac.. i used the formula that at least considers pressure and speed but i know there is an approximation error