Coast down testing, 2000 Honda Insight (gen. 1)

[aerohead]

Originally Posted by aerohead

3-Wheeler,just catching your post.My CRX data are at home,I will try to remember for tomorrow.I'm trusting my memory less and less now so rather than shoot off my mouth with nonsense I'll get the written materials together for you.Catch you then.

3-Wheeler,these are the values that CAR and DRIVER's computer came up with for the coastdown tests at Chrysler.I was not given the raw data set from the 5th-wheel.
The report I got broke the numbers down into road horsepower at three different velocities.
Test conditions at Chrysler were 49-DBF,42-WBF,29.15"Hg baro.,Calm.

velocity,MPH HP ( friction and tires ) HP (aero ) Road-HP
30 1.76 1.21 2.97
50 2.94 5.61 8.55
70 4.12 15.38 19.50
BSFC @ 70----------------------------------- 0.3988 LB/HP-HR
The CRX test weight was 1,926-lbs + 183 for Don and his equipment.
Tire pressure was 35-psi all around.
Coastdown included the aero drag of the optical 5th-wheel,as it was mounted to the passenger door.To date,I've never received info on the drag contribution of the 5th-wheel.I've estimated it's composite frontal area and composite Cd and will address that in a separate thread.

[3-Wheeler]

Thanks for posting that information Aerohead,

Take a look at your data below. The data is curve fit with a second order polynomial so we can fill in more points.

The data shows several interesting things:

As expected, the aero portion of the drag is not linear, but rises sharply since it is a cube function (velocity ^3).

The road drag is linear and directly related to the velocity!! This means that my initial hunch about rolling friction of moving components in the drive train was correct. Apparently how this relates to my coast down testing was misinterpreted and needs to be looked at further. I did notice that the dV/T or deceleration while coasting was essentially a constant when it came to rolling friction. But did not tie this in with velocity at the time.

With this in mind, I will reword the apology about the Instructables posting regarding Crr in an earlier post.

Notice also the total drag at 55 mph. See that the aero portion consumes about 70% of the total drag. This very close to the data generated for the Insight, and essentially collaborates my coast down numbers. Apparently that old GPS unit doesn't do too bad of a job for this application.

This is also good news for anyone making aero mods to their vehicles, as it shows that the vast majority of drag is due to the air portion of the overall drag.

Yes, using low rolling resistance tires and such will help, but the low hanging fruit will continue to be anything related to smoothing the airflow over the body.





Thanks again Phil !!

Jim.

[aerohead]

Originally Posted by 3-Wheeler

Thanks for posting that information Aerohead,

Take a look at your data below. The data is curve fit with a second order polynomial so we can fill in more points.

The data shows several interesting things:

As expected, the aero portion of the drag is not linear, but rises sharply since it is a cube function (velocity ^3).

The road drag is linear and is directly related to the velocity!! This means that my initial hunch about rolling friction of moving components in the drive train was correct. Apparently how this relates to my coast down testing was misinterpreted and needs to be looked at further.

With this in mind, I will reword the apology about the Instructables posting regarding Crr in an earlier post.

Notice also the total drag at 55 mph. See that the aero portion consumes about 70% of the total drag. This very close to the data generated for the Insight, and essentially collaborates my coast down numbers. Apparently that old GPS unit doesn't do too bad of job for this application.

This is also good news for anyone making aero mods to their vehicles, as it shows that the vast majority of drag is due to the air portion of the overall drag.





Thanks again Phil !!

Jim.

Jim,you're scary-fast with data! That's great!
From your curve,at any slope-intercept,you can just "read" your power consumption.The beauty of curves!
I re-visited my SAE J1263 Recommended Practice for the coastdown.I get cross-eyed looking at it.
They're very specific in their methodology:
* Vehicle weight per axle,within 10-lb accuracy.
* Moment of inertia for wheel,tire,brake rotor or drum ( they do have an estimator for it).
* Drag coefficient dependence on yaw angle.
* Temp coefficient of rolling resistance.
* Vehicle test mass
* Effective mass of wheel,tire,brake components
* Total equivalent mass of drivetrain components
* Total effective vehicle mass
* Tire rolling radius
* Time,within 0.1% of coastdown interval
* Time,resolution 0.1 seconds
* Speed,accuracy plus or minus 0.25 mph(0.4 km/h)
* Speed,resolution 0.1 mph ( 0.2 km/h )
* Temp,resolution 2-degrees F or 1-degree C
* Temp,accuracy plus or minus 2-degree F or 1-degree C ( shielded from radiant sources)
* Atmospheric press. Baro with plus or minus 0.2"Hg or 0.7 kPa
* Wind: speed,direction,continuously monitored with plus or minus 1-mph or 1.6 km/h accuracy.
* Tire press plus or minus 0.5 psi or 4 kPa
TEST CONDITIONS:
* Temp 30 F( -1C ) and 90 F ( 32 C )
* Fog No!
* Wind: 10-mph max ( 16 km/h ) or 12.3 mph peak ( 20 km/h )
* Ave crosswind vector max 5 mph ( 8 km/h )
Road: dry,vlean,straight,must not exceed 0.5% grade,and if there is grade, grade must be constant.Concrete or rolled asphalt.
COASTDOWN SPEED RANGE
* 60mph-25 mph ( 100-40-km/h )
Frontal area can be estimated @
0.80 X H" X W"
--------------
144 " SQ per Ft-sq
WARM-UP
* 30 minutes of continuous driving @ 50 mph immediately prior to test.
Runs: 10-runs minimum in alternate directions
Procedure: Accelerate to 65 mph,start recording equip.,de-clutch,shift to neutral,re-engage clutch,coast.Repeat in opposite direction.
A root-mean-square deviation of 0.25 mph disqualifies the data and it must be discarded along with it's reverse direction paired run.
At least 3-sets must qualify or coastdown is invalid.
Al's closing at 4:00 so I'm about out of time.Hope these tidbits are of use.Keep us apprised of your monster numbers-crunching! See ya,Phil.

[RobertSmalls]

Somehow I missed this thread until now. Jim, did you come up with a CdA value for your Insight? How about a Crr value for your tires on that road at that temperature?

[3-Wheeler]

Hi Robert,

I'm still collecting coast down data.

There are several very flat roads, out in the boonies on the way to work. Very little traffic, so I can coast from 50 or so mph, all the way to down to zero.

I just turn on the GPS about two miles in advance and let it record data every two seconds.

About every two weeks, the GPS data is downloaded to the computer for archival in a spreadsheet.

Still coming up with good data smoothing methods, as the GPS is rather rough in it's output.

If I were better with microcontroller programming, I would get one of those bicycle magnetic/pickup assemblies, mount it to the rear brake drum, calibrate it with the GPS, then simply record the frequency coming off the pickup as the wheel turns when slowing down.

For now, the GPS will have to do.

I plan on continuing the recording process as the weather gets warmer this spring, and then we can see what develops. It's basically free as I do this on the way to work each morning.

Robert, when do you start on your tail extension for your car? I'd like to start the planning phase this month.

Jim.

[RobertSmalls]

I was hoping to get the aerodynamics of the tail nailed down in SolidWorks COSMOS FloWorks, which can illustrate streamlines but can't tell you overall drag. I plan to run a few variations on a model of the car to check for flow separation in parallel flow and in gentle crosswinds, then build one a little bit more conservative than what the simulation tells me I can get away with. Here's an old model that's similar to an Insight:


I could make a much better model by importing the side, top, and frontal views of the car, then adding detail where necessary.

For construction, I really have no idea what I'm doing. Maybe an Al frame with the bottom half of the skin coroplast, and the top half acrylic. I'm sure you'll be going with foam and fiberglass. Will that be on a wooden frame?

[3-Wheeler]

Hi Robert,

If you work up something in SolidWorks, please shoot me an email, because I am really interested in what you come up with.

For my design, I plan on using that "streamlining template" that AeroHead has already posted, and determine curvature of all sides based on that.

Whatever angles I end up with be based on the relative angle on the template for distance.

On the underside of the car, I will measure the angle on our driveway apron to determine what the maximum angle is as the drives in and out of the driveway. Some gas station driveways are slightly steeper, so I will design the tail to clear this ramp angle.

Hopefully, six degrees of slope on the underside will be enough for this clearance, as I really don't want to go steeper than this.

As you know, the Insight hatch back window is already at 18 degrees, so this angle will just about be the same across the length of the extension.

You are very observant, and yes, foam and fiberglass will be used. With a strong structure like this, there will be no need for any further framework of any kind. The fiberglass structure will be strong enough for you to sit on as mounted on the car, if you wish. It also has to be strong enough for someone pushing on the rear of car, when trying to move through snow in the winter.

As for strength in a rear end collision, the structure will disintegrate!! The mass of even a lightweight GeoMetro would be enough to pulverize any type of lightweight structure for this purpose.

The motorcycle fairing that was made 15 years ago was just strong enough to deflect birds if they hit it at speed, but I'll bet a little league player could drive a baseball through it. Again, the strength was just enough for the job, and the full size fairing weighs only 13 pounds. In comparison, an old Vetter fairing weighs about 40.

Keep me posted on your progress.

Jim.

[Christ]

Originally Posted by 3-Wheeler

The motorcycle fairing that was made 15 years ago was just strong enough to deflect birds if they hit it at speed, but I'll bet a little league player could drive a baseball through it. Again, the strength was just enough for the job, and the full size fairing weighs only 13 pounds. In comparison, an old Vetter fairing weighs about 40.

Keep me posted on your progress.

Jim.

I can vouch for the weight of Vetter fairings... having just mounted one a few days ago for a neighbor, I think I threw my back out. (I keed) No, but seriously, those things aren't light when you get the framework and lights and everything that goes with them.

It was an ancient WJIII I think.

[3-Wheeler]

And the styling of that original Windjammer was really pretty cool....

My uncle had one of the first fairings, and I spent a good portion of time just looking at the curves, and how it fit on the motorcycle. Very nice!!

Jim.

[Christ]

The one I mounted wasn't one of the originals, I don't think. I believe it was the 3rd iteration of the WJ fairing.

I'll see if I can find a pic on Vetter's site and post it back.



Yup, WJ3 it was.

Too bad the last few I've looked at online haven't been some of the earlier ones. People collect those things.

I bet more than a few true HD guys would like to find one of these in good shape: