Moon Caps - Any Value on 1st gen. Honda Insight? (A-B-A coastdown test)

[aerohead]

Originally Posted by jime57

Thanks Phil. Found it.

Quote,"1982,Pontiac Trans Am Firebird wind-tunnel studies show Larry Shinoda's trick aero wheel-covers trim 0.027 off drag coefficient,compared to a open wheel."

The baseline for this test seems to be an "open wheel." I seriously doubt that the improvement would be anywhere near that great if the Insight wheel were used as a reference. It is by no means "open."

Still, I like the moons and will give them a try. Already drilled and threaded my "worst" set of Insight wheels

Somewhere,I have a case study which summarizes the minutia of Shinoda's tests on the Firebird.I'll find it asap and report back.There were some other wheel configurations tested and you are very correct to think that the MOONs won't 'show' on the Insight like they might for the open wheel.

[jime57]

Well the very short answer is in the title.

A slightly longer version, after testing coastdown times from 70 to 50 MPH in bidirectional testing, one cannot discern any improvement or penalty in using Moon wheel covers.

The longer, data version. I selected an essentially level course of about 1.5 miles where I could find convenient turnarounds. I tested over a course of about 3 hours, beginning at 11 am. The data:

No Moons:
East 33.89sec
West 36.01sec
E 32.4 sec
W 38.56 sec
E 35.19 sec
W 37.33 sec
Ave 35.72

Moons
E 34.03
W 35.95
E 36.87
W 36.53
E 37.25
W 37.51
36.35

No Moons
W 38.5
E 36.10
W 37.67
E 35.48
W 38.81
E 35.84
AVE. 37.24

There was a fairly linear minor increase in coast down times as the day became warmer. Anyone who drives an Insight will be well familiar with the improving MPG with temperature. In this case this is entirely dure to the warming ambient temperature and NOT to car warm up, as the car was thoroughly warmed before all segments.

If one averages the first and last segments to take out the temperature gradient, one gets 36.49 sec, no Moons. The Moon cap time was 36.35.

I'm left with several conclusions:
1. Stable temperatures, like still winds would be nice if we could get god to cooperate.
2. The Insight loves warm temperatures.
3. When compared to stock Insight wheels, Moons are a wash - no better, no worse.

Lots of time invested for no improvement in the end, but then there are never any guarantees.

Moons MIGHT improve on the stock wheels at much higher speeds, but that is not the hypermiler's world

[MetroMPG]

Thanks for doing that test. Another collection of data for the pile doesn't hurt.

[jime57]

Originally Posted by MetroMPG

Thanks for doing that test. Another collection of data for the pile doesn't hurt.

Yes, that is very true and useful in itself. But we modders always hope we have found something

I think that if the test were against a different wheel on a different car, then the Moons might show improvements. It's just that on an Insight they seem to be a wash.

I still plan to do some tuft comparrisons when I can get my setup together and get the time and conditions. I'd be interesting if there is any reaction of the tufts.

The Moons look neat, so I'll probably keep them - since I don't seem to be paying a measurable penalty.

There is another issue which might actually be more important to us in the ecomodding community. High speed coast down tests seem to be so full of pitfalls that they may be unreliable in general. Hucho mentions one of the famous aerodynamists who got false results - forget which one. A thorough, honest, and well controlled A-B-A test is going to take 2-3 hours to conduct on any reasonable course with turn arounds, acceleration zones, stabalization zones, etc. During that time, there is a very high porobability that some of the environmental conditions will change, thereby "swamping" the small changes we are trying to gather. I think I learned my lesson.

[MetroMPG]

I agree, but would restate slightly to say the takeaway from this is that testing modifications with likely small effects is difficult.

The larger/more effective mods have a much better chance of showing up above the normal noise of variability in a set of runs.

[jime57]

Originally Posted by MetroMPG

I agree, but would restate slightly to say the takeaway from this is that testing modifications with likely small effects is difficult.

The larger/more effective mods have a much better chance of showing up above the normal noise of variability in a set of runs.

Yep, but you might still miss the true value even on the big ones. That is one reason that I "copy" the results of trend lines of multiple other testers when it comes to the Insight. (The Insight itself being practically impossible to test.) We know from many tests here that removing both mirrors is worth about 3%. It is sort of a Oracle of Delphi method of seeking the truth

The low fruit on the Insight is the boattail. How do I know? Several folks have built and tested boattails and gotten 12-15% improvement on Insights and other cars. The "trend" is to the 13.5% =/- range

[aerohead]

I dug out the info for the above cars.
*On the Firebird,the vented hubcap showed a 5.7% drag reduction
*The MOON-esque hubcap measured out at 7.6% reduction.
----------------------------------------------------------------------------
With the wind tunnel development of the Subaru XT,the final 'vented' production hubcap showed 0.008 delta-Cd (2.2% drag reduction)
*A completely sealed cover was good for 0.01 delta-Cd (2.75% drag reduction).
----------------------------------------------------------------------------
It would probably require a wind tunnel to discern the difference in performance between 'aspirated' and 'sealed' covers.
On-road testing with the slightest change in any parameter,might slew the scatter-plot enough to 'hide' the very data we were looking for.

[gone-ot]

Originally Posted by aerohead

On-road testing with the slightest change in any parameter,might slew the scatter-plot enough to 'hide' the very data we were looking for.

...true, but it's so much FUN picking the fly·$hjt out of the pepper .

[3-Wheeler]

Originally Posted by jime57

Well the very short answer is in the title....

A slightly longer version, after testing coastdown times from 70 to 50 MPH in bidirectional testing, one cannot discern any improvement or penalty in using Moon wheel covers.

Jim,

I read through the entire thread, and did not notice a detailed picture of your particular moons, as this *could* make a difference, depending on how well they are executed.

Jim.

[3-Wheeler]

Originally Posted by jime57

Yep, but you might still miss the true value even on the big ones. That is one reason that I "copy" the results of trend lines of multiple other testers when it comes to the Insight. (The Insight itself being practically impossible to test.) We know from many tests here that removing both mirrors is worth about 3%. It is sort of a Oracle of Delphi method of seeking the truth

The low fruit on the Insight is the boattail. How do I know? Several folks have built and tested boattails and gotten 12-15% improvement on Insights and other cars. The "trend" is to the 13.5% =/- range

Jim,

I think that simply stating that a tapered tail yields an aero improvement of 12 to 15% is over-simplifying the situation.

Why?

Yes, it's true that the Insight benefits from a tail by about 10% from a gas mileage standpoint, and about 18% from an aero standpoint.

However, we need to keep in mind that on the Insight, the hatchback of the car is already closing down in shape, and that the addition of the tail does not add that much aerodynamically than it would on a car body that does not close at all.

In that case the addition of a tail might be 20% gas and 35% aero, and even higher gains at highway speeds.

Jim.