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Old 12-17-2010, 04:10 PM   #321 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Hi Jim,

I'm sure a main page post (or full article!) could be updated with "finished" photos?
Hi Neil,

I would certainly be open to a post with the tail "as is" and come up with a "full article" for it.

For inspiration, I would just go to Mike's (AeroCivic's) page, start reading, and let the creative juices commence flowing.

We should let Darin catch up first!

Jim.

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Old 12-17-2010, 04:19 PM   #322 (permalink)
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For long threads like this one, it's useful to go back to the first post and update it with a view of providing an overview & "index" to the project to date. Possibly with links to significant milestones within the thread.

This is helpful if it's linked from the home page and you get a lot of "new" readers.

See the Metro boat tail prototype thread first post for example: http://ecomodder.com/forum/showthrea...mpg-10691.html
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Old 12-17-2010, 04:33 PM   #323 (permalink)
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Quote:
Originally Posted by euromodder View Post
...It'd add a lot of area for a sidewind to work on and cause additional stress on the boattail's structure.
Same goes for the additional weight of a vertical fin....
The added stress of the sidewinds on the tail structure is certainly something that kept me from pondering this much beyond an initial thought.

The foam/fiberglass so far has held up very well under some extreme conditions, but who is to say how much more force could be applied before "something" happens.

If a fin were to be added, obviously it would advantageous to make it very thin, probably 1 inch wide or less. However the mechanical advantage of the wind over an object that is let's say a foot or more high, and only secured over a 1 inch wide base means a 10:1 ratio of force at the base.

Now imagine a side-ways wind force that exerts 100 pounds across the surface of fin, the base would then be subjected in the neighborhood of 1000 pounds.

This force would easily over come the strength of the fiberglass and fold it over like a potato chip.

If the fin were to be made strong enough to handle this force, then the construction of the top surface of the tail would need to be strengthened considerably to compensate for the extra air loads there.

The base of the fin would probably grow in width to at least two inches, which would decrease the mechanical loading during side winds, but then also increase the Cd of the car in this area.

The foam core would not withstand the high localized stresses in the area, and honeycomb core would have to be added since this is commonly used in high strength composite structures.

Summing up, yes a tail could be fashioned that would help create more neutral steering in sidewinds, but would require cutting out a large section of foam, rebuilding with honeycomb core and then adding the tail on top of that.

Could it be done?

Sure.

Do I want to fix a small inconvenience in handling in high sidewind conditions by redesigning/reengineering the top portion of the extension?

Not really.

And remember that this high-wind event is a 1% day. It only happens 1 or 2 days of the year!! (1)

The weight of this would probably grow to at least five pounds, maybe even 10 because honeycomb core would also be needed at the base of the fin as well since the foam core would be no match for the high localized forces there.

The weight of the extension is currently 30.5 lbs without extra Bondo and paint. The tail would surely grow this to 40 lbs or so, and give a slight edge in handling sidewinds.

Then when driving the car I would always be wondering just how more force it could take on a high sidewind day.

Moving the COP of the car rearward due to tire spats is a whole other matter since they are mounted as the same width of the tires, which are close to 8 inches or so. No problems with side wind strength there!!

The base of the spats is at this point in time, makes the base almost as wide as they are in "height" when viewed upside-down. This high mechanical advantage means that foam core can still be used, keep the additional weight to a minimum and make them reasonably easy to fashion into shape.

(1) This is similar to one that pilots a 4-wheel drive vehicle all year long with the intent of a safer drive let's say three days of the year during heavy snowfall. Three days of the year is only 1% of yearly travel, but the gas consumption remains high for 99% of the year for this convenience.

I can certainly live with gas savings 99% of year, and struggle through 3 days of heavy snow conditions with only two wheels propelling the car.


Jim.

Last edited by 3-Wheeler; 12-18-2010 at 08:57 AM.. Reason: Gas consumption.
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Old 12-17-2010, 05:01 PM   #324 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
For long threads like this one, it's useful to go back to the first post and update it with a view of providing an overview & "index" to the project to date. Possibly with links to significant milestones within the thread.

This is helpful if it's linked from the home page and you get a lot of "new" readers.

See the Metro boat tail prototype thread first post for example: http://ecomodder.com/forum/showthrea...mpg-10691.html
Darin,

I just checked your summary page, and it looks great!!

Thanks for the idea, and I will have to start working on that! Great idea and it makes perfect sense to have links and such as well. Should make it much easier for others to follow the progress...

EDIT on 12-19-10

The EDIT button for this first post is no longer available, so at this point in time at least, I can no longer make changes to the page. Sorry.

Jim.

Last edited by 3-Wheeler; 12-19-2010 at 08:48 AM..
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Old 12-22-2010, 05:33 PM   #325 (permalink)
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Hi Jim -

You should have an edit button in post 1 now.

Darin
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Old 12-23-2010, 08:24 AM   #326 (permalink)
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Excellent I look forward to the mail order kit!

Keep the numbers comming.
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Old 12-23-2010, 03:44 PM   #327 (permalink)
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fin

Quote:
Originally Posted by euromodder View Post
If we start from the basic Insight, then adding a tail extension (i.e. more area at the rear) surely is going to shift the resulting pressure point for a sidewind further aft.
Fortunately, the design of the extension is such that the wind can't get too much hold on it.
The CoG is also slightly moving aft by adding more weight at the rear, so the effect of having more area at the rear is at least partly compensated for.

The extreme situation would be adding so much area to the rear, that the car starts to severely weathercock and would become undriveable.
This is a situation where one might end up by adding a vertical fin to the extension.
It'd add a lot of area for a sidewind to work on and cause additional stress on the boattail's structure.
Same goes for the additional weight of a vertical fin.

I wouldn't do it.
The reason I threw a caution flag out on the play, was that Jim was already reporting that the front was 'going first' on the ice,something indicative of forward COP.
It has been reported by others that it's virtually impossible to ascertain the position of COP without a wind tunnel,so it's an especially tricky issue for us amateurs.
Since fins have often been used as a palliative in these situations,and since Morreli has demonstrated that behind-the-wheel fairings can perform the fin function killing two birds with one stone,it might be a talking point.
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Old 12-23-2010, 08:54 PM   #328 (permalink)
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It might be instructive to take a drive on a windless day when it is lightly snowing and watch how the the snowflakes flow around and behind the car as it moves through them. It would make an interesting video and would visualize the airflows around the car. When I drive my car under these conditions, the snowflakes are smoothly lifted up in front of the car and then just as smoothly set back down behind it with no turbulence visible such as you see behind most cars. It is as if they are momentarily displaced as the car passes through and then continue quietly falling after the car has past as if the car had never been there. Completely unlike the mad swirl of snow you see trailing behind most cars and trucks.
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Old 12-23-2010, 09:41 PM   #329 (permalink)
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Quote:
Originally Posted by retepsnikrep View Post
Excellent I look forward to the mail order kit!

Keep the numbers coming.
LOL!!

The shipping container only costs $5 to build, weighs only 5 pounds, and according to FedEx costs only $10 to ship cross-country!

Jim.
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Old 12-23-2010, 10:08 PM   #330 (permalink)
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if duplicates of this tail was being sold

id actually think about buying an insight just to put it on

so i could educate people when they see me driving with a boattail

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