About a week ago I posted a question regarding a Craft top that seemed to catch and inflate with air until it was dry after the swim. Several people replied that they had a similar issue with their clothing tops. So the question that I have now is:
Once a race top has filled with air such that it is NOT flapping, but rather, it is just ‘inflated’, would this cause a decrease in drag. My thoughts are that the inflated top would act as a solid body once inflated, and deflect the wind like a solid body. There would possibly be some increase in frontal area; however, the surface would be smoothed out as a result of inflation, which would lead to lower turbulance and lower drag. Is there any merit to this, or is it just ramblings of a crazy man?
If this does indeed decrease drag, then could it possibly be taken one step farther where you design a garment to have ‘pouched areas’ that fill up with air and fill the spaces that are normally occupied by lower pressure when you are on the aerobars (I would think that they would also have to have some sort of semi-porous coating that would help to keep it inflated on these areas)?
I also need to make the note that I never had this happen with a skinsuit (I really love DeSoto’s stuff), and did not have it happen when the tri top was dry, or damp in training, or once off the aerobars.
Seems to me the problem is that it’s inflating at all. That means it’s catching air, and when it’s full, it’s acting like a parachute, regardless of whether it’s dry or wet. I seriously doubt you’re better off with it full, even if it looks smooth.
Maybe it’s sagging when wet, which is opening up something, allowing it to catch air.
Seems to me the problem is that it’s inflating at all. That means it’s catching air, and when it’s full, it’s acting like a parachute, regardless of whether it’s dry or wet. I seriously doubt you’re better off with it full, even if it looks smooth.
Maybe it’s sagging when wet, which is opening up something, allowing it to catch air.
I dont quite think so. I think that a better analgy would be a hollow point bullet without wrinkles to a rounded bullet with wrinkles. The material was not sagging; it was a size small, and I am not a tiny guy (6’1").
Once it inflates, it still requires more air to keep it inflated or else it will just deflate. The analogy of the parachute is correct.
I dont think so. Im pretty sure that all it requires is force which comes from moving. Yes, there will be some air mixing, but there will not be a stream of air going through it that one might think…Or I could be totally wrong. My limited knowledge in this area is limited to some fluid dynamics with liquids that are more viscous than air (and Dammit Jim, Im a molecular biologist, not an engineer). If you have some experience with this type of effect and the forces involved using air, then I would consider the arguement closed, and feel really bad that I am wearing something that is costing me time.
Why does a parachute work? As it moves through the air (down), the air it displaces is moved out of the way, which takes energy. Whether it goes into the 'chute itself or merely around it doesn’t matter. The parallel with your shirt is exact.
Why does a parachute work? As it moves through the air (down), the air it displaces is moved out of the way, which takes energy. Whether it goes into the 'chute itself or merely around it doesn’t matter. The parallel with your shirt is exact.
Not exactly. It is more like comparing a parachute with a nose cone, but wrinkled, and one that once it inflates, it has no wrinkles, but this analogy just falls apart here. If we were to use this logic, then wind deflectors and fairings would also be a waste of time and cause more drag…but they dont because it is the end result of a COMPLETE SYSTEM that we are analyzing, not the individual components.
Please dont give up on me here. I really want to hear a good convincing arguement to set me straight. To answer the last point about drag suits:
Because they increase the area significantly. In the example of the tri top, the frontal area is not increased sigificantly, but the smoothness of the surface is increased with the addition of air inflation. I may be totally off my rocker, but I have not seen the light that you are trying to shine on me.
I think that a better analgy would be a hollow point bullet without wrinkles to a rounded bullet with wrinkles.
Ah yes, the old “rigid, supersonic cyclist” approximation…
I think that a better analgy would be a hollow point bullet without wrinkles to a rounded bullet with wrinkles.
Ah yes, the old “rigid, supersonic cyclist” approximation…
Yea, I guess that pretty much describes me; only slightly less fast, and slightly more flaccid.
If a piece of clothing is puffed up and full, then it is taking energy or airflow to do so. Your material is somewhat porous, so it requires constant airflow into it to keep it’s shape. This is then acting like a parachute. The analogy is correct. And yes I am an engineer. Find a top that fits you better.
If a piece of clothing is puffed up and full, then it is taking energy or airflow to do so. Your material is somewhat porous, so it requires constant airflow into it to keep it’s shape. This is then acting like a parachute. The analogy is correct. And yes I am an engineer. Find a top that fits you better.
Here is a simple way of looking at it. It takes a small amount of pressure to “inflate” your shirt. This pressure is created by the pressure drop from before the air hits your shirt to after the air hits your shirt. The shirt will not stay inflated without this pressure. Once you acknowledge that there is pressure underneath your shirt, then you are acknowledging that a certain amount of energy is being scrubbed off to created the energy to keep your shirt full. Then we get into, “high velocity air has low pressure, low velocity air has high pressure”. Higher pressure means you have lower velocity, which means you’re wasting energy (a la parachute theory) - E
maybe I just reiterated what others have said, but the bottom line is, YOU HAVE A PARACHUTE!
no comment on the pink shoes and matching race belt as they dont increase speed, but I am interested in the illegal aerobars as this dude has beaten me a couple of times
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Hey dope, think before you post. It is absolutely legal. As for the shoes and race belt, as soon as you spring for new ones in a different color, Ill start wearing those. So I guess by your arguement a soda bottle held into the wind is a parachute as well; or a hot air baloon is a parachute (which is why they NEVER crash). I appreciate the folks that have put up some thought into this. It is an exercise that I have not read a convincing arguement that finds any support in physics, engineering, science (anything other than ‘I think it is this). Now you can call me lots of things; it doesnt really bother me, but dont call me a cheater. Thems fightin’ words.
