|Check this helmet out||RutterMan|
Mar 13, 2002 12:31 PM
|Anybody have any comments on this helmet with the dimples? How can you get more aerobynamic than a smooth surface?? Imagine a 747 with dimples all over it.
Also, does his left leg look broken?
|let's try this again.||RutterMan|
Mar 13, 2002 12:33 PM
|Golf Ball Design||ms|
Mar 13, 2002 12:43 PM
|The top of the helmet looks like a golf ball. I am not a golfer, but I assume that the dimples on golf balls exist for aerodynamic reasons. (Why? -- I don't know -- maybe the science types on the board can explain).|
|What about a golf ball||Icefrk13|
Mar 13, 2002 12:44 PM
|Than why are golf balls dimppled? Hmmmm.|
|Golf Balls have dimples||AllUpHill|
Mar 13, 2002 12:40 PM
|because it makes them fly farther. Someone else will have to explain why this improves the aerodynamics, but it does. I can't imagine it offers much improvement at the speeds of a cyclist though...|
|Golf Balls have dimples||RutterMan|
Mar 13, 2002 12:50 PM
|I thought that golf balls had dimples, in part, due to the contact being better with the club rather than for aerodynamics.|
|GOLF BALL DIMPLES||MisJG|
Mar 14, 2002 7:07 AM
|The quick and dirty answer as to why golf balls have dimples; they fly farther with more accuracy. Every club in your bag (except the putter, for obvious reasons) is designed to put backward spin on the ball. A backwards spinning dimpled golf ball creates an area of low pressue above the ball (creating lift) while at the same time reducing drag. More lift + less drag = lots more distance. For those of you writing a term paper on the subject, see this link: |
When I hit the ball, I put sideways spin on the ball (also called 'slice') and my drive ends up in the next fairway. That's why I'd much rather bike in my precious little spare time. (One Wife + One 2.5 yr old Daughter = Not Much Spare Time)
|Why do you think they put dimples on golf balls?||bianchi|
Mar 13, 2002 12:42 PM
|Seems like I've heard that they improve aerodynamics or lift.|
|But golf balls spin!||mr_spin|
Mar 13, 2002 12:59 PM
|I can't explain the dimples, but I do know that golf balls spin as they travel through the air. Even if Axel Merckx (I think that is Axel) were possessed by the devil, his head wouldn't spin at the same rate as a golf ball.|
|The dimples assist in maintaining the spin . . .||morrison|
Mar 13, 2002 1:06 PM
|of the ball, which controlls the ACCURACY of the shot, but I don't think it helps the distance. (I could be wrong here.) I used to golf quite a bit, and I seem to recall reading that a ball without dimples would be more aerodynamic, but it would also be next to impossible to controll the direction of the ball with the same accuracy that you can with a dimpled ball.
So . . . maybe Merckx is trying to control the accuracy of his head? (Hey . . . don't scoff at this . . . if he were accidently decapitated at 40 mph, don't you think he'd want to be able to find his noggin?)
|As I understand it,||TJeanloz|
Mar 13, 2002 1:03 PM
|There are two kinds of aerodynamic drag in this world, surface and pressure drag. The higher the speed, the less important surface drag is and the more important pressure drag becomes. Surface drag is the result of friction between the air and the projectile, pressure drag results from the low pressure area formed behind the projectile which acts like a vacuum, pulling the projectile backwards.
I believe the dimples break up the airflow a little bit, which reduces the size of the low pressure area behind the ball/helmet, thus reducing pressure drag.
I recall that an MIT professor introduced a dimpled baseball bat a few years ago, which allowed for higher bat speeds- and provided more home runs. But in true Boston fashion, he announced that he would only supply them to the Red Sox, and MLB subsequently banned the design.
But somebody better at physics than me can probably provide a more scientific explaination.
|$hit. You just shot a whole in MY theory. Next time . . .||morrison|
Mar 13, 2002 1:07 PM
|there's a science question, post BEFORE those of us who have no idea what we're talking about.|
|right, and furthermore...||ET|
Mar 13, 2002 2:39 PM
|due to the complicated aerodynamics as speed increases, it is not obvious until tested how a moving object or material will behave at a given speed, and sometimes even which type of object will have the lower drag. (For further reading on the golf ball phenomenon and related topics, look up or do a search on "Reynolds number".)
For example, I have in front of me some results from a research article measuring the total mean drag on a cycling leg with various coverings in a wind tunnel. It turns out that, compared to a bare (shaven) leg, a leg covered in fine wool actually is better(!), with a decreased drag of -0.6% (take that, you effeminate leg shavers :-)). A suprising second was tight-fitting cotton jersey (+0.2%), beating out even rubber-coated nylon-spandex (+0.4%). Leg with hair came in at +2.6%. (Note: that does not mean you are slower by 2.6%, just that the drag is worse by that percent, and then the drag must be inserted into other formulas (assuming the variables are known or can be reasonably estimated) to figure lost time, and it's nowhere close to one-to-one, but ceteris paribus--i.e. ignoring things like you might sweat more in wool and so that might slow you down--lower drag does mean faster times.) The worst two tested were cotton crew sock (+12.4%) and (no surprise here) loose-fitting cotton (+15.0%).
On the same general topic, an article claimed that for sprinters, a shirt with a vertically-ribbed pattern may be superior to a plain one (hey, if it buys you a few hundredths of second in the 100 meters, that can be huge).
|oops, I left out the speed of the cycling leg||ET|
Mar 13, 2002 2:46 PM
|It was 32 km/hr, or 8.89 meters/sec. But wait! We're not allowed to use metric measurements on this board. :-)|
|As I understand it,||yeah right|
Mar 13, 2002 8:03 PM
|TJean is really close, and the person below who talked about Reynold numbers is on the right path.
When a fluid flows over any object, there is a boundary layer, in which the velocity of the flow goes from zero at the edge of the object, to the full velocity of the fluid stream a distance away from the object. In certain (ie low) reynolds number regimes, laminar flow can occur. Laminar flow has very low skin friction, much lower than turbulent flow, but it is also much more likely of detaching from the object as well. When a flow detaches from an object, eddies and currents form behind the object, and suddenly the pressure is lower behind the object than in front of it. The pressure difference translates to a drag force.
So, you'd be better off with all laminar flow, if you were ideally streamlined, but since most objects aren't, turbulent flow can be your friend. Even some times when designing wings, aeronautical engineers add turbulators to make the flow turbulent so the flow won't detach.
Hope that helps.
|Laminar Flow - dimples on a 747||tz|
Mar 13, 2002 1:05 PM
|I think that the dimples on this guy's helmet are just a fashion statement. There had been, however, attempts to control turbulent airflows over aircraft wings by making holes in them. Below are a couple of links, if anyone is interested. Links have nothing to do with bikes, though...
Laminar Flow Control research:
Here's why golf balls have dimples:
|a few surfboard manuf. have also tried this principle...||Spirito di Finocchio|
Mar 13, 2002 1:12 PM
|on the bottom or fin side of the board.
their theory had many supporters. the claim was that a smooth surface was in fact still high in drag (something to do with surface tension) and that a dimpled bottom was thought to create some ruffles and make the board looser and a little less sticky.
then again surfboard design isnt exactly the last word on integrity and scientific basis.....
Mar 13, 2002 1:14 PM
|so.......bad acne and warts will make us faster cyclists? ;-) NM||Spirito di Finocchio|
Mar 13, 2002 1:18 PM
|The real reason ...||bianchi|
Mar 13, 2002 1:21 PM
|If you look closely at his helmet, you'll see a MaxFli logo. So he's probably being paid to wear a helmet that looks like a golf ball. Isn't that how the pros choose all their gear? :)|
|Maybe Axel has...||Pedal Jockey|
Mar 13, 2002 1:26 PM
|the "I'd rather be driving a Titleist" bumper sticker on the back of his saddle.
|I think Lance's TT bike is dimpled||CRM|
Mar 13, 2002 1:32 PM
|I think I recall reading that Lance's Trek TT bike had a dimpled head tube or something to assist with aerodynamics. Does anybody else know about that?|
|his leg is covered in slime||ishmael|
Mar 13, 2002 4:20 PM
|its all oily...what is that stuff and how much does it help|
|Been around for a few years.||Sintesi at home|
Mar 13, 2002 4:21 PM
|Apparently to no real benefit for Domo, although, didn't Gonchar (sp?)use this style at the worlds in ' 00?|
|what about the olympics?||slow-ron|
Mar 14, 2002 7:30 AM
|I remember the speed skaters during this years Olympics wearing Nike outfits with dimples built into the fabric for the same air flow characteristics as mentioned above. Newsweek had a special on it.
Just a matter of time before all the weight & speed weenies are wearing dimpled spandex around the block.
|And the swimmers||TJeanloz|
Mar 14, 2002 7:40 AM
|Swimmers in the 2000 games had some fancy suits that used the same principles.|| |