Heresy! Smooth Wheel Covers- Myth Busted!!!

[freebeard]

*Wolf H.Hucho basically said the same thing in 1987.For high-speed sports cars and race cars it was another matter.Especially open-wheeled race cars.

Open wheel is best wheel.

We could attack Julian for not employing laser-doppler-anemometry when compiling his pressure study data.If the results are the same,or within some standard deviation,do we want to go there?

Remember when we used to talk about Schlieren Flow Visualization?

[aerohead]

The 2016 Renault EOLAB concept incorporated active wheel covers,activated by built-in wheel temperature sensors, which would close off the brake-cooling vents when not needed,for lower drag. Michelin also designed tires specifically for EOLAB, which were honed for lower aero drag.
Re. http://www.car-engineer.com/renault-...mics-features/

[gumby79]

The rear is impressive as well. The active aero air- curtains to help rezolve the wake off the rear 145/70r17's w/active aero wheel covers.
---
Control?
Any theories on how they have mechanized the louvers in the wheel?

Some sort of a power generation mechanism harnessing centrifugal force, if it's electrical.
My mind went towards a purely mechanical mechanism. Simply using a bi-metal spring,(like a clutch fan or thermostatic stovepipe control mechanism used on carburetors) calibrate it on a safe operating temperature of the brake hardware. As demand for cooling increases the bi-metal gets hotter and opens further.
--
Another note from reading the article.
All their active Aero activates at 70 kph.(43mph) implying a simple lack of advantage below

Dream Big Chisel Down To Reality

[aerohead]

They didn't go into it,by intention,or by default.Ford Had a concept pickup that did the same thing.I don't recall an explanation for that as well.The Mercedes-Benz IAA has active wheels as well.
Power to the wheel thermosensor could be battery,through a slip-ring,or inductive coupling.
Electric or mechanical power to the louver mechanism itself could be imported through the hub or spindle.Whatever it is,it's pretty clever.

[freebeard]

Originally Posted by gumby79

My mind went towards a purely mechanical mechanism. Simply using a bi-metal spring.... As demand for cooling increases the bi-metal gets hotter and opens further.

Paired bi-metallic springs that work against each other. Maybe minimum of three pair?

Those trailing air curtains seem oddly familiar. They could also flare outward to make air brakes.

[California98Civic]

I had no idea the "heresy" conversation had become so interesting. Bimetalic springs seems brilliant, and that Renaut is beautiful.

[ptjones]

The nice thing about Hybrids is they use regen braking so brakes don't get hot, you can keep covers on all the time.

Paul

[freebeard]

Making something light and robust enough might benefit from solid, force-multiplying hinges:

https://www.youtube.com/watch?v=97t7Xj_iBv0

[ACEL]

Science is ever evolving. Until there is new knowledge, basic tenet holds and sometimes the knew knowledge seems like "heresy". In the past "general universal explanations" were developed and as long as no new facts and data became available, the "general universal explanation" figured as "the law". Today, science recognize that there are both the "general universal explanation" and many "particular solutions" applying to specific situations or devices. General universal solution" is often expressed in general terms and simple equation. The "truth" applying to one specific situation is much more detailed and vary somewhat from the "law". As an engineering professor said in my first year in university, "physics is an exact science as it describes a situation in general terms and then searches for the particular applications; engineering is the inexact science of applying the laws of physics to real applications; engineering solutions may be as far as 100 % from the truth but are narrowing the range around the exact solution through the years. e.g. see the heavy piston engines of the beginning of the 20th century (connecting rods especially) producing little power because of so much inertia compared to the actual piston engines.

So, the fine solution for some car is not necessarily the appropriate solution for my car. It saddens me for I have to search and experiment to confirm the solution that works for the situation at hand. This is also science.

Before to fabricate and install the "definitive" wheel covers on my 1999 Acura EL, two mock-up were tested. First was an open perimeter wheel cover. Second was an almost full wheel cover with the wheel center open (pics). Tape mock-up was installed on all four wheels to get aerodynamics information.

The goals are :
1. Find the most appropriate wheel cover for this 1999 Acura EL car in terms of actual fuel economy and aerodynamics behavior.
2. Determine which wheel cover will allow brakes heat to escape.
3. Aesthetic constraint: the final wheel covers have to look good on the car and not disfigure the good looking wheels (wifey requirement)

To measure the parameters to satisfy goal 1, Torque Pro App was used to log : throttle opening (%), acceleration (x), mileage instant, RPM, Speed GPS. The data series were logged every half second.

To satisfy goal 2, simple observation and "touch feeling" were used

Goal 3 is satisfied when "wifey" says it looks good. She did. See pics.

Testing of the mock-ups were conducted "back-to-back" on the same morning and road segment. The previous day, on the same road and similar conditions a series of runs without any cover were done in order to obtain a baseline data for comparison.

The metrics for comparison were the top speed achieved at a constant throttle opening according to the "throttle stop" method proposed by Julian Edgar on Youtube. The instant mileage averages over the few seconds that the speed remained constant at the said throttle opening were also compared.

Tests were conducted in the following order:
0. Baseline test, no covers (32 Celsius)
1. Open perimeter mock-up (17 to 20 Celsius)
2. No perimeter mock-up (17 to 20 Celsius)
3. Final wheel cover installed

Results and observations:

1. Open perimeter mock-up : allowed a top speed increase of 1 to 3 % over the base line even though the air temperature was lower by more than 10 degrees Celsius.

Revised data and results on July 12: Top speed increase 7 % at 111-112 Km/h (60 mph); no significative difference over baseline result in top speed at 122-124 Km/h (76 mph) - Fuel consumption decreased 4 % at 111-112 Km/h and 3 % at 122-124 Km/h (20% throttle opening) .

2. No perimeter mock-up : REVISED DATA : ALLOWED THE SAME TOP SPEED INCREASE OF 7 % at the same speed of 111 Km/h but a top speed decrease of 2 % for the same throttle opening of 20 % (119-121 Km/h)). (Previously reported:"did not allow an increase in top speed as the open perimeter did. On the contrary, it decreased the top speed obtained by the open perimeter mock-up by at least 13 %"). REVISED DATA Allowed a fuel consumption decrease of less than 1 % at 111 Km/h but of 9 % at 122-124 Km/h.

Also, the tape on the wheel perimeter felt hot to the touch on one front (disc) and one rear (drum) wheels. For mileage, the open perimeter mock-up used at least 7 % less fuel than the full perimeter blocked wheels. The final wheel covers will be with an open perimeter like the Tesla "aero" wheel covers and the design will have to match the underlying wheel.

3. Final wheel covers (17 Celsius : same road): Projected wheel covers fabricated with aluminum pizza pans and decorated with back sticking lettering vinyl was okay’ed for aesthetic.

These final wheel covers did not allow for a significative increase in top speed for a given throttle opening over the mock-up open perimeter wheel covers (increase of 1 - 3 Km/h in 120 - 125 Km/h range and 20 % throttle opening). On the other hand, fuel economy was improved by 2 to 5 % in the same speed range over the said mock-up. No particular heat accumulation was felt on the perimeter of the aluminum pizza pans.

Conclusions

Cheap modification mock-up is a good way to test various alternatives to orient the search for the appropriate modification.

Definitive wheel covers design retained are appropriate to the 1999 Acura EL and are proved to be a worthy modification that saves fuel.

[California98Civic]

Thanks again for your testing and your detailed reports. You mention that the torque app logged throttle % and RPM and such. Do you still have that data to report? Because the radical difference between your outcomes for open perimeter and covered perimeter mock ups seems to indicate possible variables sneaking into your results. Also, am I right to think the pictures show your final cover is fully covered in the middle of the wheel and only open at the perimeter?

EDIT: I am totally persuaded that your test shows the final covers work, by the way. I am just wondering how to explain the wild variation between the two mockups.