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Old 09-08-2008, 06:57 AM   #1 (permalink)
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sawtooth trailing edge

I'm inclined to think a spoiler with a sawtooth trailing edge might have advantages over a straight one.

here's how i arrived at the idea.

first of all vortex generators have the ability to reduce drag, while their effectiveness is debatable in some applications their fuctioning si quite well understood.
now when i compared vortex a vortex generator with a naca intake, the first thing you notice is they're very similar in shape, in fact a naca intake also uses vortexes to draw air into it's orifice, so basically a naca intake is an embedded vortex generator that draws air from outside in.

so what if we where to use a series of naca ducts in a lip spoiler. likely the naca intakes would draw air from the top of the lip to the bottom of it!
all of this would be a low drag affair, and no additional frontal area is generated.

one could simplify this setup by cutting of the rear of the naca duct leaving a trailing edges with a curvy sawtooth pattern, wich might even be further simplified to just real sawtooth, as are used on turbulator tape for example.

the whole idea starts to make even more sense, when you realize humpback whales have fins which rounded sawtooth like protrusions at the end, which in turn have been copied to design low drag blades for huge wind turbines.

so what do people with a better understanding of aerodynamics think? am i drawing the wrong conclusions or is there something there?

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Old 09-08-2008, 12:20 PM   #2 (permalink)
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Quote:
Originally Posted by lunarhighway View Post
I'm inclined to think a spoiler with a sawtooth trailing edge might have advantages over a straight one.

here's how i arrived at the idea.

first of all vortex generators have the ability to reduce drag, while their effectiveness is debatable in some applications their fuctioning is quite well understood.
now when i compared vortex a vortex generator with a naca intake, the first thing you notice is they're very similar in shape, in fact a naca intake also uses vortexes to draw air into it's orifice, so basically a naca intake is an embedded vortex generator that draws air from outside in.

so what if we where to use a series of naca ducts in a lip spoiler. likely the naca intakes would draw air from the top of the lip to the bottom of it!
all of this would be a low drag affair, and no additional frontal area is generated.

one could simplify this setup by cutting of the rear of the naca duct leaving a trailing edges with a curvy sawtooth pattern, wich might even be further simplified to just real sawtooth, as are used on turbulator tape for example.

the whole idea starts to make even more sense, when you realize humpback whales have fins which rounded sawtooth like protrusions at the end, which in turn have been copied to design low drag blades for huge wind turbines.

so what do people with a better understanding of aerodynamics think? am i drawing the wrong conclusions or is there something there?
Not to push you in the wrong direction, because I think you are onto something here, but these Austrian people design computer case fans with notches in them to keep them quiet and push more air:

Noctua Fans

Also this is (was a while ago anyway) a topic of discussion in this thread:

Whale Tubercles
This may assist in your venture. Good luck and keep us informed.
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Last edited by Funny; 09-08-2008 at 12:27 PM.. Reason: To add post from other thread.
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Old 09-08-2008, 12:33 PM   #3 (permalink)
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I think you may be onto something. Fab one up in fiberglass, tuft test it, and post the video here so we can all see! We're easily entertained!
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Old 09-08-2008, 03:45 PM   #4 (permalink)
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lunarhighway -

This sounds really neat. If you already had a spoiler on your car, then maybe you could extend some serrated coroplast to create the sawtooth shape.

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Old 09-08-2008, 11:03 PM   #5 (permalink)
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Trailing?

I'm looking at this stuff and thinking those teeth would work on the leading edge.
The way I understand the effects, is you can get a much higher
AOA before stalling the wing (whale fin).



I've been thinking about adding a sawtooth leading edge to one of my
Coroplas model airplanes to test out the AOA idea..



This type of pizza box wing design really doesn't have real lift, but is fun to
fly around real slow angled up about 45 degrees. (A good engine is a must).
I suspect that adding Whale Tech to the LE will improve the high AOA slow speed hovering ability a lot..

Now, I just have to figure out how to implement the idea..
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Old 09-09-2008, 04:25 PM   #6 (permalink)
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naca

I thought that the submerged NACA inlet provided the perfect teardrop taper curvature,both in elevation and plan, to allow the air to decelerate without vorticity,and provide the highest static pressure for ram effect to the heat-exchanger.Turbulence I can see,but I thought vorticity was always a "no-no".----------------------------- With regards to the "tubercules",would the upswept "kick" as GM has just modified into it's VOLT rear spoiler,provide the same effect as the "sawtooth"? If the wake is with turbulence but without vorticity,as a normal spoiler would create,would the sawtooth create a local interference drag adding to overall drag?
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Old 09-09-2008, 05:53 PM   #7 (permalink)
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Vortex generators increase induced drag, but have the potential to reduce from drag. The net effect can be positive, but lower overall drag would be very hard to achieve by trivial placement as even on airfoils, which are much easier to work with than the back of a car, the effectiveness of vortex generators is highly dependent on chord placement, vg angle of attack and vg density, and you would not position them at the same place wheter your goal is drag reduction or, as in the case of an airfoil, lift.

I don't see what good they could do right before the wake break point.
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Old 09-09-2008, 11:48 PM   #8 (permalink)
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The image I've attached is that of the engine of a 787 Dreamliner. The guy who worked on the sawtooth design wrote that it reduces noise. This means less energy wasted energizing air to produce that noise. I'd guess that there would be small vortices forming at each point on the trailing edge, but that all the vortices combined would take less energy to maintain than a possible single large one trailing from a smooth trailing edge.
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Old 09-10-2008, 12:41 AM   #9 (permalink)
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NASA has been studying serrated trailing edges, and serrated leading edges are of interest, too. Google for it. Also, check into Barred Owls, which have serrated feathers for ultra-quiet flight. Works.
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Old 09-10-2008, 03:13 AM   #10 (permalink)
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Sayyad -

Wow, that 787 engine also looks totally Batman!

CarloSW2

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