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Slowtwitch Forums: Triathlon Forum:
Aerodynamics of the Louis Garneau Superleggera

zebragonzo

Oct 7, 08 7:26

Post #1 of 10 (487 views)

Aerodynamics of the Louis Garneau Superleggera	Can't Post

This helmet seems to go against common sense when it comes to designing a helmet for aerodynamics. It's got lots of venting:

Quote

Louis Garneau's new Diamond road helmet boasts a whopping 40 vents in its in-molded microshell yet it's not so much the number of vents, but rather the type, that makes it so interesting.

It's got pointless dimples:

Quote

A dimpled front half is designed to reduce drag and an optional polycarbonate windscreen can also be added.

It's got sticky out bits on the surface (screw heads?):

I thought that the Louis Garneau helmets were meant to be aerodynamically good!?!

mrtrik

Oct 7, 08 7:44

Post #2 of 10 (467 views)

Re: Aerodynamics of the Louis Garneau Superleggera [zebragonzo] [In reply to]	Can't Post

40 vents? Where are they?

Pointless dimples? Well... depends on the numbers. They may not be pointless. Hell - look at golf balls. There's a reason for them, right?

tribreck

Oct 7, 08 7:58

Post #3 of 10 (447 views)

Re: Aerodynamics of the Louis Garneau Superleggera [mrtrik] [In reply to]	Can't Post

Did they mean to say four vents? No way there are 40 vents on the outside of that helmet. Are they talking about inside in the foam? If so, that's not a vent....

triguy42

Oct 7, 08 8:02

Post #4 of 10 (436 views)

Re: Aerodynamics of the Louis Garneau Superleggera [zebragonzo] [In reply to]	Can't Post

I don't know about 40 vents, my Air only has 2 in the front and either 1 or 3 in the back...can't remember offhand. They are probably talking about the channels inside or something...or it actually has 4 vents and someone made a typo. That NEVER happens when making marketing stuff, especially not for trade shows!!! Smile

(Ask me how I know...)

FWIW rumor has it the Air is slightly more aero than the regular Rocket, according to 2nd hand windtunnel results. I definitely like my Air just for the temperature of my head. Don't know about the weird dimples on that helmet. It helps golf balls because they are moving well over 100mph. With them being so huge I wonder what they actually do?

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nproximos

Oct 7, 08 8:38

Post #5 of 10 (392 views)

Re: Aerodynamics of the Louis Garneau Superleggera [mrtrik] [In reply to]	Can't Post

but golf balls and zipp wheels spin. this does not.

i highly doubt its better than a smooth helmet with no vents.

Joe Santos

Oct 7, 08 9:03

Post #6 of 10 (358 views)

Re: Aerodynamics of the Louis Garneau Superleggera [zebragonzo] [In reply to]	Can't Post

I think the LG helmet being referred to (regarding the 40 vents) is their new road offering - the Diamond. Not so sure the dimples on the new TT helmet, though.

____________________________________

-Joe S.

Davis Wheelworks
http://www.daviswheelworks.com
Davis, CA

The NorCal Tri, TT and Road Source For: Cervelo, Felt, Kuota, Scott, Cannondale, Look, Pinarello, Colnago, Time, Ridley, Seven. Zipp, Mavic, HED. Profile, X-Lab, Hydrotail.

Paul

Oct 7, 08 10:54

Post #7 of 10 (284 views)

Re: Aerodynamics of the Louis Garneau Superleggera [mrtrik] [In reply to]	Can't Post

I owned a Rocket Air and it has 5 vents. 2 up front, 3 towards the back top of the helmet.

A golf ball also spins in excess of 2900 rpm and flies over 130 mph. I doubt that the dimples help much, but then again, i was not there at the wind tunnel testing. So, unless they show some real data, i'll remain a skeptic.

Paul..

JAC

Oct 7, 08 10:59

Post #8 of 10 (272 views)

Re: Aerodynamics of the Louis Garneau Superleggera [zebragonzo] [In reply to]	Can't Post

It is pretty clear that the dimples on the helmet are for styling.

I'm sure many of you know this, so I am not trying to be obnoxious, but for those who don't, the velocity gradient in a turbulent boundary layer is much higher than in a laminar boundary layer, so when you have curvature causing an adverse pressure gradient, it is possible to reduce overall drag by tripping the flow (forcing a transition from laminar to turbulent, assuming it is laminar in the first place) right before separation would occur.

That said, they would have done better to figure out where separation normally occurs under a variety of conditions, and then place a trip strip right in front of it. If a golf ball didn't rotate, you could get away with a trip strip around ~70-80 degrees off of the horizontal instead of dimples. Tripping the flow early incurs a friction penalty (due to the increased velocity gradient).

And those front vents are really gonna mess with the aerodynamics anyway unless they get taped over.

The dimples are designed to make it look good. (I personally think it looks goofy.)

(This post was edited by JAC on Oct 7, 08 11:03)

mrtrik

Oct 7, 08 11:01

Post #9 of 10 (264 views)

Re: Aerodynamics of the Louis Garneau Superleggera [JAC] [In reply to]	Can't Post

You lost me between styling and goofy.

triguy42

Oct 7, 08 12:59

Post #10 of 10 (190 views)

Re: Aerodynamics of the Louis Garneau Superleggera [mrtrik] [In reply to]	Can't Post

In Reply To

You lost me between styling and goofy.

Now I don't care who you are, that there's funny! Smile

Just remember there's a big difference between a 130mph spinning golf ball and a 25mph helmet. This is one of the reasons I (as a Mechanical and Aerospace Engineer) and my brother (MAE with a PhD in Thermodynamics) are somewhat skeptical of the recent rash of dimples on bike parts. I think my brother said "pure marketing BS" at one point. There are certain things that are considered "rules of thumb" in aerodynamics, and most of the items with dimples don't pass the sniff test. Smile

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