Rambling Thoughts on Land Speed Racing....

[Sumner]

My two cents.....
.....2) Vortex Generators ~ again I quote from Wiki:

"The purpose of the generators is to stick out of the stagnant air near the surface of the wing, and into the freely moving air outside the boundary layer. This layer is typically quite thin, but dramatically reduces speed of the airflow towards the rear of the wing. The generators mix the free stream with the stagnant air to get it moving again, providing considerably more airflow at the rear of the wing and thereby providing the control surfaces with more power. This process is typically referred to as re-energizing the boundary layer."

(Me again) In lsr I would think that having a tidy airflow at the back of the car would be as important as the front. I've seen vortex generators on only a few race cars, an old Indy Eagle, and on the back deck of one John Force's floppers.

Maybe these two concepts provide not enough gain for the trouble, or wind tunnel $ is best spent on other bigger issues. For interest, I found a picture of a shark's skin; it's vortex generating surface results in a more slippery body that I would guess needs less energy to go through the water...

www.filmstream.com.au/ extraordinary.html

Thanks for enduring my own ramblings ... 

You might want to check this link and the products they have:

http://www.wingsandwheels.com/page29.htm

Products like these are allowed as far as I know on streamliners and lakesters, but you have to be careful on other cars to see what is allowed with regards to streamlining.

You might also want to check the links I have on Aero on my links page:

http://purplesagetradingpost.com/sumner/bvillecar/bvillelinks.htm#Aerodynamics

c ya,

Sum

[Greyboy]

.. and I thought I was cool because I knew about helicopter tape ..

A lot to digest on your links page ~ will be back on the thread after lookin' thru it (exit stage left).. Thanks

[Greyboy]

PS: to see that shark skin picture you have to click the line of type that says:

"The Extraordinary Nature of Water Video"

[Greyboy]

Two cents...

Also of aero-interest are golf balls and their dimples. My fire lit by a fellow Landracing poster, Roadtrip, I looked up a little on the subject. Unfortunately I majored in arts not sciences so I can only offer cursory info:

A roughed-up golfball travels farther than a smooth one, dimples being a practical manufacturable solution to roughing up a sphere evenly across it's surface. This caused the accepted golf ball of the day, the smooth "gutta-percha" ball to all but be replaced by the dimpled version by 1930. Today development goes on refining the number and arrangement and even the shape of dimples. For example hexagonal dimples have been found to be superior to the round.

So the rough surface is aerodynamically superior to the smooth surface in terms of lessening drag (keeping the flow attached longer). So why are all these cars and bikes smooth and polished? Wouldn't texturized, dimpled or even scratched be better? OK, that's three cents worth already...

Roger, alas, a non-scientist

[Seldom Seen Slim]

Somebody refresh my memory -- what about the Corbin bike that ran at Bville a couple of years ago?  It was covered with dimples (or at least the tailsection was, right?).  Did they ever arrive at any demonstrable conclusions about the value of the dimples?  I don't even have a photo of the bike, but I remember. . .

[Sumner]

Two cents..................So why are all these cars and bikes smooth and polished? Wouldn't texturized, dimpled or even scratched be better? OK, that's three cents worth already...

Roger, alas, a non-scientist

Rex is better on this than I am, but you want smooth on the front of the car for sure then further back where the air can start to separate, talking lakesters/streamliners, you might want to do what you are talking about and that is what that "z-zag" tape and other products do that were mentioned in the other post.

Of course to really see what is happening you almost need wind tunnel time.  Me I'll make the whole thing smooth and then go from there.  Kent did some work on this on the salt with I think WD-40 and was it chalk Kent?  Hope he jumps in here as I probably have this wrong and can't find where I saved it on the computer.

c ya,

Sum

[jb2]

Too many factors in the golf ball to mention.  spin, lift, speed etc....
The rotation of the ball is the main reason a dimpled ball goes futher than a smooth one.

Tour De France racers now wear some textured suits in certain areas to affect their aero "envelope".

Jim

[Greyboy]

Two cents ..

So if the idea is to make the wake of a vehicle smaller, would vents girdling the rear of the body shape that sucked air into the car (pulling the stream back in) and expelled it somewhere else that was helpful, like further forward, help out aero?

Broke now ..

[Rex Schimmer]

I think that if you are going to "dimple" the body work on your landspeed car it really only has an affect in transitional areas which are typically where the body is beginning to taper at the rear of the car. The dimples help hold the turbulent, but attached, air to remain attached as the body shape tapers. You can also use the small vortex generators which will also assist the air to remain attached in the transition area. I would not think that dimples on the front of the car would be an advantage. If you look at the BUB and the EZY Hook streamliner bikes you will note that if you look at them in the plan view they have no sections of the body that are straight lines, i.e. the shape starts at the front to expand out to the maximum width and then at that point the body begins to narrow to a very thin tail section and all of the transitions are very,very smooth. My guess is that neither of these two vehicles would find an advantage from dimples as I would bet a plot of the pressure gradiant on both would show a very long negative gradiant, which keeps the air attached, and a very smooth transition to a very slight positive gradiant to the rear of the "bikes". This is what  make them so aero. I would bet that the Wheelers "bike" is some NACA symetrical wing section design. Manning claims that his "bike" is designed after a salmon, and I have now idea what the flow characteristics of a salmon is.

Rex

[Greyboy]

Hmm,

Maybe fish ARE to be considered in aero-think. Even the megabuck Mercedes corporatistas seem convinced that there is worth in the shapes of our scaled friends... the following is press from MB "Bionic Car" from 2005...

"Despite its boxy, cube-shaped body, this tropical fish is in fact outstandingly streamlined and therefore represents an aerodynamic ideal. With an accurately constructed model of the boxfish the engineers in Stuttgart were able to achieve a wind drag coefficient of just 0.06 in the wind tunnel."

.o6? well here's a pic of it:

http://www.carpages.co.uk/mercedes_benz/mercedes-benz-world-17-11-05.asp

[John Burk]

Golf ball dimples help high drag shapes like spheres but they have found surfaces like vvvvvvvvvvvv lower skin friction 5% . They call them riblets . There are lots of sites on this . From what I saw lengthwise riblets help smooth objects but crossways riblets help irregular shapes . 3M makes adhesive back riblet film .

[RidgeRunner]

     Increasing water table vs wind tunnel research, sucessful Salmon shape liner, and now Mercedes Boxfish Bionic car.

     He may have left us and the garage torn down but Henry Y's advice about going down to the stream to observe the flow around the stones is proving more valid than ever. 

[mtkawboy]

Didnt Richard Petty try a vinyl roof in the late 60's or early 70's to see if there was an advantage to it? Never did hear how it worked or whether Nascar didnt like it

[Greyboy]

Chrysler Corporation was playing for keeps too and they also pulled out all the stops to take back the "Daytona 500" with the new design long sleek Plymouth Fury and Dodge Charger.  Keep in mind that in 1967 Richard Petty won 27 NASCAR (it was called the Grand National series back then) races on the way to his second season championship. Petty's 1968 Daytona Plymouth featured a vinyl roof with a surface like a golf ball. Petty claimed the reason for the unusual innovation was because the dimpled vinyl roof was expected to help the blue number 43 move through the air with less resistance - like a golf ball. 

[RidgeRunner]

Didnt Richard Petty try a vinyl roof in the late 60's or early 70's to see if there was an advantage to it? Never did hear how it worked or whether Nascar didnt like it

     Part of a big picture theory used by many over the years [including politicians]; to keep eyes from looking where you don't want them to stir up something very visible elsewhere? 

     Only the originators know the whole story for sure until they decide to tell all.