I understand the general ideas of separation, pressure, etc…
Is it because the shield is effectively ‘blocking’ the air, instead of letting it find its way through the helmet via the paths of least resistance?
I really prefer a visor over glasses, but I’m getting the impression visor vs. no visor is not position/person dependant, it’s sounding more & more like a universal truth.
Educate me.
My basic understanding is that you are correct in your explanation. The visor forces the air around the helmet instead of letting it go through the helmet. And it seems like it’s a trend that visors are bad. Although IIRC there was a post here that said the Selector may be the exception and be better with a visor.
See a specialized engineer here:
Hey guys,
I don’t want to jump into this discussion except to clarify the direct questions about our shield research. I’ve been MIA recently due to a busy few months so if I miss anything that I may be able to chime in on, just PM me to take a look and I’ll get on it!
Anyways, what we have found is that a head is a fairly poor aerodynamic shape because it is a pretty good approximation of a sphere. Spheres are bad because (at the Reynolds numbers associated with the size of a human head and bicycle speeds) they tend to separate nearly at the point of max width/diameter and create a large wake region, resulting in high drag. Wearing a good aerodynamic helmet is actually faster than wearing no helmet since they shape the head into more of an ellipsoid than a sphere. Why do I bring this up? Because with the way visors are typically executed, the visor/helmet front end becomes closer to a sphere (by creating a smooth round surface from the front of the face onto the helmet surface) and separation migrates back out to the wide point - again, resulting in higher drag. We’ve found this in nearly every visor/helmet combination that we tested. In a way, it can be worse than wearing no helmet since we’ve created a sphere that is bigger than your head.
Now, to the point of why some helmets may contradict this and test better with a visor than without: The catch with not having a visor is that you have to manage the airflow inside and out the back of the helmet. With an open front, no matter how tight you wrap the sides of the helmet to the head, flow will enter. Unless the helmet has been designed to effectively evacuate this flow, this can result in higher drag. With some helmets, drag from internal flow stagnating can be higher than drag from adding a visor, so the net result is a visor is faster in that particular system.
Finally, specifically with the S-Works+McLaren helmet: the fastest configuration is with no eyewear. We realize almost no one rides without something over their eyes, but we wanted to be upfront about what the fastest configuration is. Next fastest is with sunglasses (this one depends on which model exactly with no real rule of thumb - but I don’t recall testing a sunglass model that was slower than a visor on this helmet). Next is with a visor.
Sorry for the long winded response, but I like to get these things right/clear and with aerodynamics it’s hard to be brief. Hope that helps, and again sorry for barging in on this particular thread!
From here: http://forum.slowtwitch.com/gforum.cgi?post=4404496;search_string=mclaren%20visor;#4404496
I know you didn’t write this, but I don’t know that we have a ‘tagging’ feature.
So if you could trip this boundary layer earlier (maybe a few holes in the visor, or have visor that doesn’t sit flush with the helmet like the LG vorttice) would you then have a smaller wake region/smaller pressure differential resulting in lower drag? And could this small turbulent boundary layer have less overall drag due to the fact that there are no more high pressure zones where the helmet face cutout meets your face?
The new LG P09 has a visor, but it appears to sit somewhat inside the contour of the helmet and allows flow through the helmet. I don’t quite get why they don’t change the shape of the visor so the front of the helmet is les spherical.
Soon we’ll be finding out Supercycle Hooligans are more aero than shivs.
I understand the general ideas of separation, pressure, etc…
Is it because the shield is effectively ‘blocking’ the air, instead of letting it find its way through the helmet via the paths of least resistance?
I really prefer a visor over glasses, but I’m getting the impression visor vs. no visor is not position/person dependant, it’s sounding more & more like a universal truth.
Educate me.
one needs to distinguish between testing of a helmet and testing of a rider with a helmet. the reason i believe this is important is because a visor may (or may not) enable an athlete to achieve a more aerodynamic functional position (=can still see as much as they need to based on the demands of the event) than the same helmet run with sunglasses. with some sunglasses, for example, one must hold their head slightly higher. (higher could actually be more aero, so careful testing would need to be done.)
it’s a small point but, i believe, an important one.
Guess I’ll be taking the visor off the Bell Javelin this year and using glasses. I would rather get rid of it anyway as the helmet is hot as hell with it on…
Just so you guys know, not every helmet tests faster without the visor, some helmets test faster with vs without.
Brian is correct. In fact, the Javelin is typically better with the visor, as is the Giro Selector and Lazer Wasp. The P09 is better without.
Jim - Any info on the new Rudy Wing57? Have you had the opportunity to test it? Am sure you cannot give specifics… but any broad insight on it would be greatly appreciated! Have not been able to find any kind of testing info on it except what Rudy Project released…
Once data from the aerocamp last weekend at ERO starts to circulate you might see some data on the Wing57. It’s up to everyone individually to post there data, but I think most are planning on it. Think about half or maybe just under that tested it.
Once data from the aerocamp last weekend at ERO starts to circulate you might see some data on the Wing57. It’s up to everyone individually to post there data, but I think most are planning on it. Think about half or maybe just under that tested it.
I’ll leave the Wing 57 numbers to the campers. The star of the show was the Louis Garneau P09.
Is the P09 availible for sale yet?
The star of the show was the Louis Garneau P09.
Massive +1
.
Once data from the aerocamp last weekend at ERO starts to circulate you might see some data on the Wing57. It’s up to everyone individually to post there data, but I think most are planning on it. Think about half or maybe just under that tested it.
I’ll leave the Wing 57 numbers to the campers. The star of the show was the Louis Garneau P09.
I’ve started a Aero Camp post here:
Hopefully we can get all the questions into one place.
Is the P09 availible for sale yet?
not yet, it seems.
From the LG site:
P-09 HELMETUSD$ 349.991405362
THIS ITEM IS NOT AVAILABLE AT THIS TIME BUT CAN BE PREORDERED NOW!
NOTE: PREORDERED ITEMS WILL BE SHIPPED AS A SEPARATE SHIPMENT WHEN THE ITEM BECOMES AVAILABLE
I understand the general ideas of separation, pressure, etc…
Is it because the shield is effectively ‘blocking’ the air, instead of letting it find its way through the helmet via the paths of least resistance?
Yes, basically.
I really prefer a visor over glasses, but I’m getting the impression visor vs. no visor is not position/person dependant, it’s sounding more & more like a universal truth.
Educate me.
There are some successful visor/helmet designs, under some conditions. But closing off the front of a blunt object like a helmet does seem to hurt the aerodynamics somewhat, yes.
The star of the show was the Louis Garneau P09.
But did I understand correctly that it tested best without the visor as well? And can you give a relative idea how meaningful the difference was with vs. without? Also, plugged or unplugged (front vent)?
It seems unlikely that the uncovered part where your face and glasses are is more aero than a smooth part. But I guess science proves me wrong. Nobody answered your question why manufacturers keep making the helmets with visors though. But it makes me doubt the wind tunnel data that keeps popping up.
I have a LG vortice, and taped the visor on the sides, so it is not all round in the front but kind of pointy in the middle. Also this helmet has a hole in the forehead, so I wonder if this helps the letting the air flow through, as in more aero. I love this helmet and will wear it only with visor, because it is awesome which makes me feel awesome and hence 10% faster over an ironman bike leg. I tested this without visor and I don’t feel as awesome then, so I was like meh. With visor I was more in the direction of zoofff or swoosh.