Mythbusters tests "golf ball" dimples

[Nathan jones]

It depends on your average speeds, dimple size, orientation, depth and distance between dimples. Too close or deep and they create more turbulence or other mean negative forces. Each vortice has to operate indvidually

[aerohead]

Originally Posted by Piotrsko

All these years I have believed the main purpose of VG's were to keep the airflow attached, typically at sub critical Reynolds numbers because when your flow becomes detached you fall out of the sky stalled, at any speed. I also understand that at some distance from the surface, the airflow returns to being laminar so I suspect dimples or divots are just keeping the surface from stalling (detached airflow) which for wings in flight is the highest drag point.

* Once flow reaches the first minimum pressure on a wing it automatically transitions to a turbulent boundary layer ( TBL ).
* A TBL can withstand some degree of adverse pressure gradient ( pressure rise ), whereas, a laminar boundary cannot tolerate any of it!
* The angle of attack determines whether or not the flow will remain attached or not.
* On a Clark-Y for instance, the drag of the wing varies by 2,659%, depending on A-O-A.
* Zero lift occurs at -5.6-degrees cord.
* Trimmed cruise is at 12-degrees AOA.
* Max lift occurs at 15.6-degrees AOA.
* The wing begins to get mushy at 17-degrees AOA.
* At 19-degrees AOA the top of the wing is at 30-degrees and full stall.
* Max wing drag occurs at 22.8-degrees AOA. You're already falling. If you have enough altitude you just take your hands and feet off all controls, and the plane will recover in three spins.
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If you're forced into an emergency short field landing and must slip the plane to burn speed @ full flaps, VGs can help maintain aileron, rudder, and elevator authority, especially in crosswind or gusts.
At that point it's not about Reynolds number ( you've got that covered ), but tricking the flow into remaining attached when it would otherwise be separating along a contour of too radical a rising pressure gradient.
freebeard's Coanda-nozzles would be a big help just about then.

[Xist]

Has anyone seen wind tunnel results from cars with VGs on the trailing edge?

(assuming they were placed by an engineer in a wind tunnel)

[Piotrsko]

Originally Posted by aerohead

*
If you're forced into an emergency short field landing and must slip the plane to burn speed @ full flaps, VGs can help maintain aileron, rudder, and elevator authority, especially in crosswind or gusts.
At that point it's not about Reynolds number ( you've got that covered ), but tricking the flow into remaining attached when it would otherwise be separating along a contour of too radical a rising pressure gradient.
freebeard's Coanda-nozzles would be a big help just about then.

Only on Cessna brands of spamcans. No such requirement on other brands.

In the pacer, I practiced being at pattern altitude over the numbers and making my flair at midfield for a 2500ft runway by looking forward out the passenger window in a monster side slip

[aerohead]

Originally Posted by Xist

Has anyone seen wind tunnel results from cars with VGs on the trailing edge?

(assuming they were placed by an engineer in a wind tunnel)

I've only seen a yarn- wand image by Gary Wheeler, inventor of 'Air-Tabs' VG's, on his own Honda Accord notchback.
Gary's an aeronautical engineer, and one might presume that he knew something about the technology.

[Nathan jones]

..

N.b And I'm not a Master ecomodder, who changes this??!!

[freebeard]

Needs context.

Plan or elevation? Rotated 90 degrees? Source???

[Xist]

Originally Posted by Nathan jones

..

N.b And I'm not a Master ecomodder, who changes this??!!

Tap on User CP on the top right corner, Edit Your Details on the top left, and then Custom User Title under "Optional Information."

Under that it gives contact information for ICQ, AIM, MSN, and Yahoo Messengers.

How do I use any of those?

[Nathan jones]

Thanks yes I don't need that other stuff

In the study I used it was noted that with deep dimples even though the downforce overall increased drag dimples weigh less than spoliers so efficiency for performance vehicles was increased.

For my car however that's not neccasary. It was not easy, there is only a narrow band of increased efficiency but mine were designed for a descent starting yield of 38mph, my average speed. Much below this and especially below 25mph and they become almost of no benefit. I decided that in a real world enviroment despite crosswinds that it would help. Even below 25 sometimes you will have headwinds and there are no negative effects at any speed.

I did not test my car before and after as I cannot achieve exact similar testing, I just create what makes sense with the information I have. Comparing my nearly 20 year old gen 2 to a hired new 'eco car' however I'm doing something right

[Nathan jones]

Title change
It won't let me change it or reset
Says..
A required field called What's your main area of interest in vehicle efficiency? is missing or has an invalid value.

Or I will have to fill out forms like everything else