Aero Crosstour- Squeezing blood from a stone

[Chonk_Master]

Drilled lugnuts today. There's very little material for threading, even though I was able to cut one and insert a bolt.

Then I found this:


Steel ties it is!

[Chonk_Master]

Moderate to Large Update:

So, first off, HUGE shout out to Daox for helping me finish the side mirror mounting plate. He used a photo with measurements to create the final version (probably) of the mounting plate:

I never thought to use a drawing to create a sketch in CAD but it seems obvious now. I will definitely be learning this trick.

Also, finally got coastdown times. It took a while, since Central Texas is nothing but hills, but I managed to knock it out after work; we're out in the sticks and it's a little flatter here.

You can definitely see the hills at work with the coastdown times. I started at 50 mph and went down to 25 mph (before running out of road). This A-run was done with a full tank and an empty car, which will be the standard for the B-A tests moving on.

My graph and trials:



Author's graphs and trial:



With a little math, I figured my average deacceleration was .1597 m/s^2 versus the author's, which was .2103 m/s^2. Looks like momentum kept my coastdown time up, compared to the author's, but this is just to satisfy my curiosity. Obviously, I'll only be comparing to myself from here on out.

I'll start printing another prototpye side mirror plate to check fit tonight and, if everything looks right, I'll start the final product's print Saturday morning. I'll set it up for 4mm wall thickness and 25% infill. After baking it, it should be plenty hard enough to stand up to the outdoors.

[miro]

I'm kinda late to the party re: frontal area.
Perhaps a old school planimeter might be useful to estimate the ratio of the frontal area between the Crosstour and a known Honda vehicle ( Insight ? ).
Maybe it's too old school, - I use it to estimate HP from pressure- volume curves on old stationary engines.

[Chonk_Master]

So, I think it was aerohead that mentioned it somewhere: the few times that Honda has released cross sectional frontal surface area, it fell to within 75%(?) of absolute height x width.

The Crosstour is tall-ish, compared to it's width, but I don't think it's ~50% tall. It's not that rectangular. Of course, without more Hondas to check against, it might not be crazy far off. Also, holy ****, the planimeter! TIL.

Anyways, small update: still tackling side mirror design. The fact is, I'm teaching my self CAD on FreeCAD, two things that do not make for fast, efficient production. I've also toyed with other manufacturing methods (like making a mold of the factory mount, sans mirror, with a vacuum former and filling that mold with high strength epoxy) but it's looking like a CADded, 3D printed version would be most efficient. I'm also thinking I'll be vastly simplifying the design versus OEM, since the prototype doesn't need to mount the same way. More on that later.

MPG is now sitting just under 22 MPG (21.54). It was just under 23 but I had a weird drop, tank before last, down to 19 MPG, so that definitely dragged the local average down.

[ACEL]

To continuously measure mileage for cheap:
OBDII - Bluetooth adapter from Amazon, ELM327 chip or else, below 20 $, mine was 10$
+
your smartphone or tablet, iPhone or Android, even an old Android 4 will do
+
Torque App for free or better Torque Pro App (6-8 US$)

With these you get instant reading of the actual mileage from the car ECU : Engine Control Unit. The mileage might need to be calibrated after entering car weight, engine size, tire size, published drag coefficient Cd and else.

Basic free Torque App can do some data acquisition on a few parameters (time, GPS Speed, Coolant temperature, Instant Mileage, Long Term mileage). Recording the actual time with thousands of second precision may be useful for coast down testing.

As coast down testing may be somewhat misleading to measure drag reduction realized with a modification, I prefer to use Julian Edgar method shown on YouTube, "Throttle-stop speed testing of aerodynamic drag" and "Measuring changes in car drag". Julian Edgar compares methods for measuring drag like 20 K miles mileage, coast down, and his Throttle-stop speed testing. The later is like "fast prototyping" as you can quickly evaluate a modification and even test more mods the same day. Whatever your preferred method for measuring improvement, the continuous data acquisition of speed, actual mileage, time of reading is a must. You can transfer the data set to your preferred EXCEL, LibreOffice CALC or else for analysis.

I know from experience that the mileage recorded on a long and repeated drive between tank fill ups vary because of climate factors like wind intensity and direction, temperature and other factors.

The best of success with your mileage improvement project,

Acel

[caeaves]

Drag coefficient (Cw-Wert):


Cd claimed:


Cd estimated by a-c:

0.36

https://www.automobile-catalog.com/c...sstour_ex.html

[caeaves]

Frontal area A estimated by a-c:

2.63 m2

Drag area CdA claimed:


Drag area CdA estimated by a-c:

0.946 m2