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Old 11-13-2010, 10:59 AM   #291 (permalink)
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Quote:
Originally Posted by discovery View Post
Wow 91.43 MPG at 56 MPH that is Wow
Hi Discovery,

And that 91 mpg was at a cooler air temperature.

The Insight as well as most of our cars like hotter temperatures for the best mileage.

If that were a 95°F day instead of 55°F or so, it would have probably been over 110 mpg or so. It's a guess but probably not too far off.

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Old 11-13-2010, 11:07 AM   #292 (permalink)
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Nice to see the increase in fuel economy, is that number the percentage additional MPG. I suppose I would have taken the amount of fuel and said I used 9x% or 8x% to go the same distance. Either way, excellent to see the results!

- Insight has limitation of display updating every 0.6 miles or so
No it doesn't. Press the FCD button twice, it will update every time, if I reset it and accelerate and coast it will update every second if I keep pressing the button. A CleanMPG'er drove my car to compare the fuel numbers on a well-known very easy to duplicate route and I thought my button was going to be worn out with how many times it was stabbed. I'm not complaining though.

What are you running for tire pressure, I think boosting that up is the next step if you don't already have it up there. Huge differences can be had with tire pressure.

"Wow 91.43 MPG at 56 MPH that is Wow"
This is pretty sweet for sure. I've gone 630.5 miles and got 70.2mpg on the FCD or 630.5/8.592 gallons =73.4MPG calculated going as fast as I could go in lean-burn. The car can hang out in lean-burn up to 78mph if you can control the throttle and watch LOD values and find the TPS limits for those RPMs. I've run most of that tank between 70-75mph and it sagged to 65mph sometimes with mostly flat inclines and more speed sag with hills. I'm curious what the tail would have brought it to in my same scenario. The key IMO is tire pressure if a non-modified car can't hold 75mph in lean-burn on flat smooth roads with no wind.

55mph is a very tough place to hold speed in lean-burn a little faster and the engine actually has more power and seems to be quite a bit more efficient at climbing hills when around the 60-65mph area. I've found 4th gear makes driving easier and better MPG going 50-55(if even up to 60)mph. It seems the engine is gutless at 2000RPM. I could hold 65-70mph easier than I can hold 55mph.

Awesome stuff, keep us posted!
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Old 11-13-2010, 11:21 AM   #293 (permalink)
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OK, let's take another look at the true aero efficiency increase in the Insight due to the tail extension.

Shown below are two sets of theoretical data based on real world gas consumption during a 1.3 mile run on a reasonably flat road, with the conditions shown in the previous post.

The group of data on the left side is without the tail and on the right, with the tail.

As before, we have assumed that the mix between rolling and aero drag is identical at a speed of 45 mph. So with this in mind, the Crr is arbitrarily set to 0.5 and the aero is also set to 0.5. At a speed of 45 mph, this gives us a total drag component of 1.0 when adding the Crr and Aero components.

Since the gas mileage test was run at 56 mph and not 45, we have identified this data in the blue row, as shown on the left. Notice that the total drag without the tail is indicated by the red box as 1.39...

Now we move to the data on the right side, and this is where the theoretical part begins.

If we take the total drag number without the tail at 1.39 and reduce it by 10.27%, which is the decrease in fuel consumption due to the tail, then we now have a target drag for the car with the tail added, which is 1.25....

This 1.25... number is again indicated by the red box, and this is our target total drag that we are looking for. So the Aero drag due to the tail is now reduced until we get the total drag to be 1.25... at 56 mph. Once we have reached this point by iteration, we now know exactly the mix of Crr and Aero it takes to get a reduction in total drag of 10.27%.

So how much of an Aero drag decrease did the tail make on the car?

The "Diff" column shows a consistent 18.5% decrease in Aero drag due to the tail.

So with this limited distance fuel consumption test, we tentatively can say the tail offered almost a 20% decrease in Aero drag.



Jim.
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Old 11-13-2010, 11:38 AM   #294 (permalink)
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Quote:
Originally Posted by MN Driver View Post
....It seems the engine is gutless at 2000RPM. I could hold 65-70mph easier than I can hold 55mph....

Awesome stuff, keep us posted!
Hi MN Driver,

First off I must mention that I've seen a lot of your posts over at IC, and enjoy reading your comments.

Did not know about about pushing the FCD button to update the display, but still would not mind finding a flat section of road that is about 5 miles long and doing the test again, and this time A-B-A if possible.

And yes, I have also noticed how poochy the Insight engine gets at 2000 rpm. And it's due to the intake resonator null at that point. The engine is perky at 1600 and again at 2300 or so, but drops off at 2000 rpm.

Someday that null will have to be "engineered" out by modifying intake circuit.

Tire pressure is 55 psi.

Jim.

Last edited by 3-Wheeler; 11-13-2010 at 11:51 AM.. Reason: add tire pressure
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Old 11-13-2010, 01:48 PM   #295 (permalink)
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Jim,

A 20% improvement in aero drag would be great news! I need a ~17% improvement in CdA to hit lean burn at 74mph on flat land in warm weather. It would suggest a Cd reduction of about 0.04, I figure.
Quote:
Originally Posted by 3-Wheeler View Post
As before, we have assumed that the mix between rolling and aero drag is identical at a speed of 45 mph. So with this in mind, the Crr is arbitrarily set to 0.5 and the aero is also set to 0.5.
I think 35mph would be more accurate for a stock Insight, or around 38mph for a lightly modded one:

Calculator
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Old 11-13-2010, 04:39 PM   #296 (permalink)
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20.54% delta CdA

Based on the delta-mpg and your velocity,under steady-state driving conditions,GM Aero Lab would tell you that the Cd is down 20.54%.
If this was the only mod,the drag coefficient would be in the vicinity of 0.19.
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Old 11-13-2010, 10:17 PM   #297 (permalink)
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Quote:
Originally Posted by Varn View Post
Hi Donee
The biggest parts that I have made with vacuum bagging is probably on the order of 20-30 square feet with 20 oz of material. The fun begins when you can't get a vacuum because of leak. For the larger parts such as this, I would use a slow or ultra slow set epoxy. The trick I have found is to spray glue the reinforcement cloth to the mold. I have only had one time where I couldn't get vacuum and my part, a recumbent bicycle seat came out with too much epoxy.

If I were doing some production work vacuum infusion might be an advantage but thought it to be unnecessary for the size of and thickness of parts that were being made. Perhaps you might share some of your projects.

Hi Varn,

Oh, I am hardly a composites professional. I have only done some stressed skined plate vacuum bagging for a completely off-topic project.

One great help with Vacuum Bagging is to make a Vacuum Resoviour. Its easy, just use a pressure tank, with a valve. The quick application of Vacuum will help seal allot of small leaks.

I also made a control box for a Gast 1/2 HP vacuum pump I have. It used a vacuum pressure switch to maintain at least 10 PSI of vacuum.

But, the vacuum bagging table, and pump are all in storage. I needed the room in the kitchen for the 3 axis CNC project (which has been up and working for several years now) ;-)....
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Old 11-13-2010, 10:30 PM   #298 (permalink)
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Some smooth wheel covers (like those Robert Smalls made for his Insight) and add the rear wheel strakes, add side video mirrors, and I think you will be down to ~0.17! :-)

Remind me -- do you already have a full bellypan on this car?
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Old 11-13-2010, 11:28 PM   #299 (permalink)
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That is a good idea having a vacuum tank. With only 15 pounds of ambient pressure not sure how much help it would give but surely some.

I too have not been doing too much with composites. except what I can do outside. I am recovering from surgery to repair my sinuses from chronic asthma and allergies brought on by dust.

I probably should put this in an OT thread but the photos show some of the projects that I have built. Apologies to 3wheeler.

and recumbent seats

Quote:
Originally Posted by donee View Post
Hi Varn,

Oh, I am hardly a composites professional. I have only done some stressed skined plate vacuum bagging for a completely off-topic project.

One great help with Vacuum Bagging is to make a Vacuum Resoviour. Its easy, just use a pressure tank, with a valve. The quick application of Vacuum will help seal allot of small leaks.

I also made a control box for a Gast 1/2 HP vacuum pump I have. It used a vacuum pressure switch to maintain at least 10 PSI of vacuum.

But, the vacuum bagging table, and pump are all in storage. I needed the room in the kitchen for the 3 axis CNC project (which has been up and working for several years now) ;-)....
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Old 11-14-2010, 05:29 PM   #300 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Remind me -- do you already have a full bellypan on this car?
Yup, and the workmanship is equally as impressive as the tail:

http://ecomodder.com/forum/showthrea...els-10638.html

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