TJ: Bug Shield testing
 

For starters, while I know adding a bug shield should be a given MPG penalty on any kind of vehicle, but considering the aerodynamics of a TJ (two completely vertical/flat surfaces; the grill and the windshield) I figured it might just help. So I had a bug shield I had bought a while back and I figured why not.

I used the route from my house to school as my test route. Tests were performed over 3 days. Run A is going to school, B is heading back, a trip distance of 12.3 miles. Engine was cold for all runs. I go in around 10, leave around 7. Run A temps were 64F-66F, Run B temps were around 66F-68F Cruise control was set at 65 mph.

Run A
Shield on: 19.6
Shield off: 20.3
Shield on: 19.8

Run B
Shield on: 17.9
Shield off: 16.2
Shield on: 17.3

Now my question is that, going in, there appears to be a small hit in FE but it could be almost neglibile, but going back there is a descent gain in FE with it on, why is that? I'd have figured a penalty on both trips

Look at differences between runs... you'd need more samples to conclude anything that small.

^^ ditto

Your environment factors are too large to easily see a result ;)

Do you have consistent wind conditions - that is, do all run B tests have a headwind (explaining lower overall results and potentially increasing an mpg/aero change).

If you're going to collect data over time... Collect a lot more, but also record all of the temp/wind conditions for every test. That's what sucks about long term testing - it's more difficult to control variables :/

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Can you experiment with different attack angles? Or is it a molded one-shape only type of thing?

Kewl, I'll keep on going.

treb, I'll double check the wind info I have, don't recall the direction. B is worse, FE wise since its mostly uphill, while A is mostly down hill.

It is a molded one piece thing, I was hoping that the collected data would be bad enough to warrent me chopping it up some. I'll post up a picture of it tomorrow.

I wonder if the bug shield could be mounted at the base of the windshield? I was thinking of doing something similar to my car. It should reduce the high pressure area that builds up at the hood/ windshield junction.

I?ve seen cowl covers for sale in JC Whitney before for trucks that would basically do the same thing you are looking for I believe.

So some pics of what it looks like

https://astralfoundry.com/linkgfx/FE ...J/IMG_0216.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0220.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0221.gif

And some simulated "air flow" testing with a hose.

https://astralfoundry.com/linkgfx/FE ...J/IMG_0208.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0209.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0210.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0211.gif
https://astralfoundry.com/linkgfx/FE ...J/IMG_0213.gif

I've got next Friday off so I am going to try another set of runs inside a smaller time frame.

Man, that's a steep angle of attack - I'll bet it has to be to change the velocity of flow above it :p

The best question as far as overall performance of it is... Does it actually work? If it doesn't do a decent job - and decreases mileage... Sell it on fleaBay :p

It pretty much sends anything small to the moon :D

Honestly when I ran it way back when I didn't notice much of a change. Tried selling it then, no takers, figured I'd try to quantify what it exactly did before I try to sell it again.

If you have a hill without much traffic see if you can come up with some sort of coast down test. Start at a spot on the hill at a fixed speed and let it coast in N as far as it will roll, to a terminal velocity where it stays at a constant speed down the hill, or to a spot at the bottom of the hill where you can see it's speed at that point. Usually I have good luck with coasting tests and they are pretty consistent as long as the air temp and wind temp are the same and the car is at a consistent warm up state. Here the wind always blows the same direction in each place so wind is almost never an issue.

I have never been able to see a mileage difference with the small rear spoiler on my car but a coast down test shows a tiny improvement. So I leave it on there on the premise that every little bit helps. One hill on my commute if I put the car in N at a road sign at the top of the hill at 60mph it will always cross the 55mph mark on the speedo at a certain sign at the bottom of the hill. Without the spoiler it crosses the 55mph mark about a car length before the sign. I typically use this hill on my way home to make sure there isn't anything wrong with the car's rolling ability. If I pass a large truck I don't get a good coast though so traffic has to also be consistent.

Finding a good hill and practice coasting on it on your normal commute till you figure out your variables and get it consistent. It is very handy to be able to do a mod and figure out over the next few commutes whether it helps your aero or not.

Coyote X,
With the Jeep I can't really coast worth anything @ speeds greater then 45 MPH, speed drops like a rock when I put it into neutral on the highway. One of the lots at school is fairly steep, I could use that but I doubt I'd get faster then 30-35 MPH before running out of road.

So here are the results from todays test. 10 mile trip, elevation delta -112ft, Jeep was at operating temp, closed loop, cruise control set to 65 MPH. Weather is slightly crappy right now, 64F no wind.

w/out BS: 25.2 MPG
w/ BS: 21.5 MPG
w/out BS: 24.9 MPG

A delta of 3.55 MPG or difference of 14% using the "w/outs" as a baseline.

So I think I'm gonna put it up for sale again. If it doesn't get sold this time around, I think I will chop it up some, see what would happen if I change the curvature.

maybe it would fetch a nice trade-in on new or used hybrid?

opens the HOV lanes for you Californian solo pilots...

and any vehicle gets poor mileage stopped ;-)

Bah, I'll be lucky to get 20 bucks....

If actually really low in value as you suggest, maybe keep it as the occasional fun go anywhere just not quickly vehicle... would it hurt the wallet badly as a 2nd vehicle to insure?

I agree with jellybean... If the value isn't too high, and you can afford to store it... Hold on to it until you go on a more extended trip.... I don't recall bugs being that big of a problem during my summer stay in the Bay Area, but I have no idea about the surrounding areas....

Ahhh I completely misunderstood your post 2ton. I wasn't going to sell the Jeep by the end of this test, I was planning on selling the bug shield. Insurance on this sucker is fairly cheap though, considering a 20 yr old owns it; 50 bucks monthly. Which would probably drop some if I classed it as a recreational vehicle.

eh, in most of the places I've driven to in CA, bugs aren't anything worth a shield. I had originally bought it because some claimed it cut down on the wind noise, but a small roll of electrical tape did a much better job.

If I did sell it, getting a Mazda3 hatch would be pretty fun.:D

*hangs head*

I so misunderstood that!!! LOL

Nice area... We have good friends in the Pittsburg (without an H along the Delta), and I love cycling up Diablo... well except that ramp at the summit. :eek:

Any further mileage results to post? Thanks, Jim

When I bought Rusty, he had one of those large, flat plexiglass bugshields on him. (Similar to this one)
https://www.dynamicd.biz/images/steve...0bugshield.jpg
I took it off and got an extra 2-3 MPG. I don't know if the modern curved "areo" bugshields have the same MPG penalty though.

-Jay

I always figured they'd be more effective for aero if they went from about half to 2/3 back along the hood. Not on vehicles with decent windshield rake though. In your mind you might think Marvin or an S-10 blazer was 100% bricklike, but they are not really. Most mid 80s up trucks and vans aren't too bad for that really. We had a 2.5 van in the family, it came with a bug deflector on, the owner liked it... she got more bugs hit than Marvin did and got 19mpg while Marvin was getting 21 with the V6. When it cracked up and broke off she started getting 22-23mpg.

I have a bugshield put away, it's probably going on top of the bumper on Marvin as an aerodynamic grille block.

judging from the way the water jets up so harshly, I would think it might help get some air up and over that big flat wind shield. maybe if you can find one that has a less harsh angle and maybe a little bigger, it could actually help get the air around that wind shield, rather than taking it off all together.

Red,
Any further mileage results to post? Thanks, Jim

there are a lot of inactive members here, many i really miss. try email or PM, it might get a response.

If in fact he is gone or inactive, that would be a shame. We need active members who follow up, so that we can all improve. Thanks for your time, Jim.