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Old 11-14-2023, 04:38 AM   #61 (permalink)
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Quote:
Originally Posted by JacobLeSann View Post
aerohead,

I don’t understand fully what you’re saying about the cold/hot air temp mixing in the inram system. I’ll report back once I fully get it.

As for your second post…hmm…I suppose it is possible to cover it up. My main goal with this design is *not* to drill holes into the unibody, so I want to see how much I will end up covering up. If it is doable without much cost/effort, then I may just go ahead.

———————————————-

P.S.

I plan to make a large separation edge horizontally along the bottom of the rear bumper. I’ve noticed that on most ultra-aero cars that the rear diffuser doesn’t come out far from the bumper surface. Is the a pedestrian safety thing? Is it a pointless endeavour? I can provide images to better explain my question.
I believe the extended diffuser thing not being on most cars is simply styling. The Mercedes eqxx has a diffuser that sticks out at stick, and then at highway speeds it extends out even farther

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Old 11-16-2023, 11:53 AM   #62 (permalink)
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' drilling holes'

Perhaps, the holes used to mount the existing, narrow outboard belly panels, could be 'recycled', creating an attachment point for a 'new', single, full-width belly pan section which spans the entire width of the underbody, losing the two small panels in exchange this solitary single new panel. Section by section, front to rear.
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My CRX has a bunch of existing 'holes' underneath the car. I found that 1/4-20 RIV-NUTs fit these holes exactly. I cleaned these areas with 91% isopropyl alcohol , plus the RIV-NUTs, and wearing Nitrile gloves ( Harbor Freight Tools ), I applied a thin coat of J-B Weld epoxy before insertion, to help prevent 'spinning loose' when bolts were installed, or removed ( give the epoxy at least 24-hours to set, before using ).
I was able to pan then entire belly without ever drilling any new holes.
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Old 11-16-2023, 12:12 PM   #63 (permalink)
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' rear separation edge'

If you're not going to boat-tail the car, the 'end' of the diffuser will be your separation edge. Like with the VW XL1. It's inset enough from the bumper, that a pedestrian, snaking their way through a parking lot won't be apt to hit their shin on it accidentally.
And diffuser isn't going to do you much good unless the entire belly is paneled in 'upstream.'
And, if you can do the 'long, low-angle' diffuser, it will pay you higher dividends than a 'short, high-angle' diffuser.
The 2022 M-B EQXX was designed around the near-eight-inch diffuser extension, which also pinched its effective-diffuser-angle down by three-degrees, reaccelerating the flow velocity to match that of the top and sides of the car. This killed the vortex drag of the subby, high-sloped, sub-35-mph diffuser. A Cd 0.010 drag penalty.
Tuning the nose of the car with the diffuser extended allowed M-B to tailor the amount and direction of air going around the car, to achieve this non-vortex-forming 'matched' velocity at 35-mph and above.
By retracting it for low speed and parking, ground strike potential was eliminated, plus the pedestrian safety issue was resolved.
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Last edited by aerohead; 11-16-2023 at 12:14 PM.. Reason: add data
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Old 11-24-2023, 09:14 PM   #64 (permalink)
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900km Road Trip!

Recently took the car on a road trip 913km to the west. I had been carefully spending time building and testing until I ran out of time last minute. For the millionth instance; I built up several mods on the spot from scratch. Ran out of materials and had to call it a day before I could finish the diffuser.

Here are some pictures:













The result? Well…

Cooling is good. I added two strakes to help keep any large debris from getting sucked into the grille. The car held a constant and consistent 87-89 Celsius. I think it might have gotten a bit higher at one point in slow traffic, but I don’t recall fully.

Wind noise has been greatly reduced. Car is quieter for sure, and very enjoyable to travel in.

High speed stability is great! The car felt planted and very controllable at 170-200 km/h.

but…

The actual mileage wasn’t very good. Hm. Whereas before I was pushing towards 800km per tank, this time I could barely break 600km. Crappy!

There was black ice and heavy rain on the way out, but it did warm up. However, it was plagued with heavy winds. I noticed the worst gas mileage at this portion of the trip. After reaching my destination, the mileage was pretty good. When leaving, it was a bit worse yet again.

Temperatures varied from -14 to 6 degrees celsius, and wind speed varied from 5-35 km/h. I drove 100 km/h the whole way with very little deviation or any stops.

Is the lack of a good mileage a result of the elements or a failure in my prototype design? Have to see.

Hm..
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Old 11-24-2023, 09:27 PM   #65 (permalink)
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Aerohead, that is very good info. If a person is walking close enough to smack their ankle on the rear of my car, then they should back up! Haha. I do believe the OEM diffuser on my car has too steep an angle and *could* do better if it was less steep. I love the look of the EQXX and I think that could apply well to this car.

————————————————

On the topic of boat-tails…I may very well switch up on my own tastes and try one out. My biggest concern is how to tackle the issue of tail-lights and license plate lighting. I’ve designed the rear extensions on my car to keep the taillights “open”, which looks ugly and isn’t good for the aero. But I’ve done it to keep the car from being pulled over, as well as meet my design criteria.

My second concern is more about the aero. I don’t feel a boat tail is worth pursuing until I fix up the airflow ahead of it.

But yes, a boat tail has been crossing my mind.
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Old 11-25-2023, 12:11 AM   #66 (permalink)
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Put a trailer lights socket on the car and give the boat tail it's own lights?
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Old 11-25-2023, 12:37 PM   #67 (permalink)
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The aeromods look great ! ( functionally of course )
Great to see some bold modifications.
Thanks for sharing the actual results, rather than just sharing the good points.
Do you have a small video camera to do tuft tests with ?
I came across some small "dice" mini cameras for less than $15 that are small enough to even fit in an inner wheelwell.
At that price, you could have several to test multiple areas at once.
https://www.walmart.com/ip/Mini-Cube...mory/906337644

One other thing I came across that might be helpful is a 3d photogrametry app called KIRI.
I did an extremely crude test of my car with it, and it picked up quite a few detailed areas on the car.
It built a 3d model of my car in 10 minutes that would take 25 -30 hours to model in a 3d program.
Once the model is built, you could run a sim in Airshaper to see where your trouble areas are.

I'm thinking of investing in some pressure testers like Julian Edgar suggested using.

Keep the posts coming ! I'm really liking what you are doing witg the car !
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Old 11-25-2023, 06:38 PM   #68 (permalink)
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freebeard…. Yeah! Could do the trick if it’s easily removable. You had posted way earlier in the thread about mounting Volvo taillights and I think that’s an interesting idea. For the sake of cheapness I could use a pair of Chevy c\k 1500 pickup lights from a 90’s truck.

Cd, thank you! It’s important not to let bias ruin actual results; if you look at my earliest threads they are too optimistic and without proper research. That’s why I stress being realistic. That’s a pretty good idea with those little cameras, and maybe I’ll check that out. Ever consider a GoPro? I want to get one for Christmas.
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Old 11-25-2023, 08:59 PM   #69 (permalink)
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The light socket would then pair well with an actual hitch. That enables a hitch mounted box.

Then some nerf bars on the rear face and it can stand on it's end, like these Westfalia trailers:

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Old 11-26-2023, 12:07 AM   #70 (permalink)
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rear box cavity fins look pretty sick though


mileage was probably do to weather and winds

my car drops into the high 30s and low 40s for mpg with bad winds when its usually hanging around 60ish on the interstate

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