Shark Fin Antennas

[MetroMPG]

Wow - talk about splitting hairs. I like it.

I'd say if the trailing face (as intended to be mounted) is sufficiently round, I'd mount it backwards.

That said, how tall is this thing? The turbulent boundary layer thickness at the rear of a normal sized car's roof is about 20-30 mm thick. So the shape of stuff that's entirely within that layer isn't going to matter as much as stuff that's sticking up into free flow.

That's my amateur opinion anyway.

[winkosmosis]

Originally Posted by Drive Stick

Oh, and by the way my brother put one on his new 08 Altima... the radio no longer works.

Everything is installed properly, it simply can't compete with a stock antenna it doesn't even pick up local stations (with in 15 miles) that's pretty sad.

Shark fins are supposed to house horizontal antennas that pick up signals from satellites, either GPS or satellite radio... exactly what you don't need for radio stations.

[alohaspirit]

it looks pretty good by itself

maybe you could modify 2 of them back to back




but seriously, wth
V
V
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[Christ]

Wal-Mart "modding".. is the only explanation for that stupid little wing-antenna.

You can thank Sam Walton for that.

As far as the antenna, you can just bend the stupid thing over and keep it isolated from the chassis of the vehicle, and it will still work just as well, and won't interfere with flow as much.

Keeping your antenna isolated from the chassis is the most important part, because your vehicle is a giant grounding point, i.e. electrical field, i.e. electrical interference. That's why the antenna and it's wire are never in contact with the chassis. The mounting point has rubber in it to keep it isolated.

[davidgrey50]

I seem to recall that mid-1970's Mitsubishi/Dodge Colts used the ungrounded (plastic insulators in the hinges) trunk lid as the radio antenna. Dunno if it worked, though. Anyone out there ever own one of these and have a tale to tell?

[Christ]

I very briefly, and as an adolescent, thought of isolating the grounding system of cars to a few key points, making the entire car essentially an antenna, for cell-phone/radio/CB/etc transmissions.

I quickly realized how expensive this proposition could be, both with materials and working-time per model, and literally the planning and development to enter such a new structure into the traditional automotive model.

Apparently, running a few extra wires is a huge burden, basically.

[trikkonceptz]

In the end I may remove the antenna and base from the car completely and remount them inside the car at the front of the dash closest to the windshield. The stem part of the antenna adjusts to any angle and would still have clear shot to the sky due to the size and angle of the windshield.

Besides, I rarely listen to radio anymore, it's Ipod city for me now a days except for once a week when I tune in to NPR.

[Matt Herring]

Sirius Satellite radio is my choice for music, news, etc. And...the antenna is a flat disc magnet mounted on the hood so it's already modded (you do have to hard wire into the AM jack on the stock radio though so an all-together antenna delete is not possible). If you don't hard wire into the stock radio reception is "iffy" at best.

[Shawn D.]

Originally Posted by hummingbird

But it is not the teardrop tapering OUTLINE that is important, it is the overall cross section profile area that needs to taper to be better aerodynamically.

The theories & logic some of Y'all come up with are pretty hilarious -- do not mount it backwards. Mounting it backwards will not only look ridiculous, you'll be creating a stagnation area all along the upright edge that is not there when mounted properly.

Originally Posted by hummingbird

It is due to this reason that some early fast fighter aircraft fuselages had a strange 'dimple' at the point where wings met the fuselage The wings added a sudden additional area when cross section is considered. That prevented the aircrafts to overcome drag particularly flying close to Mach1 figure. the trick designers used there was to give a 'dimple' in the fuselage, that reduced sudden increase in the cross-section area. This helped push aircrafts to higher speeds.

Originally Posted by vtec-e

Whoaaaa!!! There's a random nugget of knowlege! Thanks!

Unfortunately, that nugget is taken out of context and is merely iron pyrite, not the gold it seems. The transonic area rule has nothing whatsoever to do with the subject of this antenna -- a normal roadgoing car way down low in the incompressible flow region.

[hummingbird]

Although I posted out of memory, I think the essence of the 'area rule' is pretty much captured. I never asked the antenna to be mounted reversed.

The antenna is really fat and chopped flat at the trailing face. this is not really good aerodynamically. If that face were smooth rounded, it would indeed be better to mount it backwards. That is demonstrated clearly in this thread by Craig Vetter, the motorcycle aeromodder. The thread initiator did not just pull that question out of his hat.

It is good to note that the 'compressibility' factor that makes the real difference about applicability of the area rule though. Thanks for pointing it out.

So the slow moving down to earth car should really be moving through a compressible fluid, rather than incompressible, right? Its the shockwave that makes it incompressible.