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Old 11-14-2010, 06:23 PM   #301 (permalink)
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Oh that is a labor of love.... excellent.


Quote:
Originally Posted by MetroMPG View Post
Yup, and the workmanship is equally as impressive as the tail:

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

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Old 12-12-2010, 05:08 PM   #302 (permalink)
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Center of Air Pressure

Hi,

Just wanted to post another driving observation with the long tail on the Insight.

As you may know, we are in the midst of a winter blizzard with 30 and 40 mph winds.

My sister needed help snow blowing her driveway, and it was necessary for me to help.

After finishing her driveway I was headed north on an open stretch of road that allowed the 40 mph westward winds to hit the car from the left side. The roads were also very icy from the plows earlier in the day.

In one spot on the road it was glare ice and the wind was bursting to 40 mph. I could feel the car slide sideways from the wind pressure, and similar to before (in an earlier post), the front end gave way first. The car literally moved to the right about two feet during this fierce wind. Traction was minimal.

The center-of-pressure is still toward the front end even with a tail that is over three feet long in the back. If the pressure was toward the rear, the steering would remain neutral or even over-steer slightly, but this is certainly not the case, even on glare ice!

Other's should feel free to add their own tail without concern upsetting for the steering balance of the car during these events.

Jim.
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Old 12-12-2010, 05:12 PM   #303 (permalink)
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Pretty extreme conditions. Thanks for the update! (And hope you get yourselves dug out soon.)
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Old 12-12-2010, 05:17 PM   #304 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Pretty extreme conditions. Thanks for the update! (And hope you get yourselves dug out soon.)
Thanks Metro,

My sister got a new (for her) snowblower, and really appreciated someone showing her the ropes since she had never run one before. We took it easy to give the engine a nice break-in run.

Hopefully the snow season is being kind to you as well, being in Canada and all.

Jim.
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Old 12-12-2010, 06:10 PM   #305 (permalink)
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The Avatar looks great !
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Old 12-15-2010, 06:30 AM   #306 (permalink)
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Quote:
The center-of-pressure is still toward the front end even with a tail that is over three feet long in the back. If the pressure was toward the rear, the steering would remain neutral or even over-steer slightly, but this is certainly not the case, even on glare ice!
have you considdered experimenting with a dorsal fin? if i interpret your view of the situation correctly you assume the cars handling has remained stock even with the tail and therefore not an issue to be adressed, however perhaps there's a chance here to couple reduced drag with improved handling as well by adding a central finlet to the back of the tail (above and below perhaps). It would also be interesting to know how the tail effects the front and rear lift, as a change herein could bring about all sorts of handling and traction changes under certain circomstances

for example if the tail would produce some downforce behind the rear axle under side wind conditions this might actually "lift" the front axle, causing a reduction of traction, especially if the sidewind passing over the hood also produces lift (i think it might as fender finlets where fitted to some rally cars to counter this effect as the moved sideways drifting trough a corner)

Perhaps a small finlet at the rear might improve overall handling and make the car more stable without compromising any FE gains
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Old 12-15-2010, 08:47 AM   #307 (permalink)
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Quote:
Originally Posted by lunarhighway View Post
have you considdered experimenting with a dorsal fin?
Why would Jim consider adding area to the rear, while the centre of pressure is obviously still forward enough not to cause handling issues in sidewind conditions ?
A fin wouldn't cure an aft shift in CoP, it'd make it worse.

If not perfectly symmetrical to eliminate "lift", a vertical tail surface would add a permanent resultant sideways force working on the vehicle.

A fin also adds to the frontal area, and thus to the aerodynamic drag, the reduction of which is why the tail extension was built in the first place.
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Old 12-15-2010, 09:26 AM   #308 (permalink)
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3 wheeler be careful or you may end up in the ditch during your under-steer moments.
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Old 12-15-2010, 10:38 AM   #309 (permalink)
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Quote:
Why would Jim consider adding area to the rear, while the centre of pressure is obviously still forward enough not to cause handling issues in sidewind conditions ?
A tail wouldn't cure an aft shift in CoP, it'd make it worse.
first of i'm no expert so i might be wrong about any number of things, and i'm just trowing in an idea for what it's worth and to perhaps learn what such mods would actually do in reality to both handling and FE.


But it's my understanding that a forward Cop is bad for sidewind handling, since the front will be pushed out more than the back, sidewinds effectively "steering" the vehicle of the road, where a more aft COP, as can be achieved with adding a rear fin, will cause the rear of the vehicle to be pushed out more than the front, thus "steering" the vehicle into the wind, countering the outward force. as long as this fin does not projects above or below the vehicle no frontal area is added although the fin can change the Cd.

looking at the shape if the tail i'm wondering if it isn't perhaps produceing downforce behind the rear axle, esicially when the air is passing over it sideways and the elitical cross section starts looking a lot like an (inverted in the case of downforce)airfoil to the airflow. if this is the case this could unload the front tires and cause more oversteer (especially in conditions where traction is at it's limit) a fin underneath the tail (or above, this is speculation) could have a dual function, shifting the center of pressure back, but also working as a spoiler when the airflow becomes more sideways and thus canceling any undesirable downfoce that might exist. thus putting more waight on the front wheels and curing understreer

again, i'm mostely interested in actual experiments because airflow is so complex that some things are really counter intuitive, and as stated above i'm no expert
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aer·o·dy·nam·ics: the science of passing gass

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Old 12-15-2010, 06:05 PM   #310 (permalink)
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At any rate, getting out in that kind of weather is dangerous! Best of luck 3-Wheeler.

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