Quote:
Originally Posted by euromodder
...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....
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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.
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