Would that be more or less useful than Newtons?
Why does this type of banter not happen in any of the Fantasy Football forums?
there are fantasy sports forums that get pretty damn nerdy.
hell it was through some of them that some of the math behind ‘moneyball’ was born.
much more useful
.
Good point jack just statistics versus physics i guess.
Good point jack just statistics versus physics i guess.
what I mean is that people remember from high school or general “guy stuff” that drag goes up more than linearly with speed.
and they remember that spinning masses have inertia due to their rotating motion
and then people miss subtleties like time over a fixed distance not sharing the same relationship as drag vs speed, and assume that the rotational inertia is much larger than it is etc etc
Tom
sorry to bother but I would love to see this tech presentation, if you ever find it.
ta
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
interesting i didn’t know that although i was merely pointing out why CdA is a better metric than drag force for assessing the “aeroness” of gear.
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
True that.
Basically, I’m wondering if “grams” of drag is even a real thing. That would be like measuring distance in “light” instead of “light-years.”
Grams simply aren’t a unit of force, so I don’t understand how they can represent drag. I’ve done a couple wind tunnel tests myself, and never had the occasion to represent drag in grams.
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
Humidity is not accounted for in any tunnels to my knowledge. I have pondered this and tried to find the answer. Temperature is only taken into consideration to calculate density altitude. Is it because the water content in the air, does not make up the air? So my question is: what would be the effect on an object at 30mph, let’s say at sea level, 59 degrees, 10% humidity, to that same object at 30mph, sea level, 59 degrees and 70% humidity? I cannot find this answer but would love to know.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
Humidity is not accounted for in any tunnels to my knowledge. I have pondered this and tried to find the answer. Temperature is only taken into consideration to calculate density altitude. Is it because the water content in the air, does not make up the air? So my question is: what would be the effect on an object at 30mph, let’s say at sea level, 59 degrees, 10% humidity, to that same object at 30mph, sea level, 59 degrees and 70% humidity? I cannot find this answer but would love to know.
I thought most (good) tunnels varied the speed on the fly to hold a fixed normalized air pressure. I.e., they aren’t really using 30mph but are changing the speed automatically to say 29.X or 30.X mph on the fly so that air pressure is held at some fixed level. This allows comparisons across different dates/times. Wouldn’t this implicitly account for both temperature and pressure differences? (Also once they do this there’s no need to normalize the data other than to account for beta.)
What he said above. In my tunnel experience, we never directly measured wind speed. We measured dynamic pressure and backed out the wind speed using static temperature and pressure readings. That being said, we didn’t account for humidity because it is such a minor impact compared to the other factors and probably falls well within the noise of the measurement data. But it is interesting to note that humid air is less dense that dry air.
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
Humidity is not accounted for in any tunnels to my knowledge. I have pondered this and tried to find the answer. Temperature is only taken into consideration to calculate density altitude. Is it because the water content in the air, does not make up the air? So my question is: what would be the effect on an object at 30mph, let’s say at sea level, 59 degrees, 10% humidity, to that same object at 30mph, sea level, 59 degrees and 70% humidity? I cannot find this answer but would love to know.
http://wahiduddin.net/calc/calc_da_rh.htm
Looks to me to be ~0.3% difference in air density for those 2 conditions you stated above. So yeah…it’s not a very big effect.
Even so, reporting CdA is STILL in my opinion the most useful way of reporting tunnel data. There’s no need to ask about test speeds, air densities, etc…and you can then use it however you desire.
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
Humidity is not accounted for in any tunnels to my knowledge. I have pondered this and tried to find the answer. Temperature is only taken into consideration to calculate density altitude. Is it because the water content in the air, does not make up the air? So my question is: what would be the effect on an object at 30mph, let’s say at sea level, 59 degrees, 10% humidity, to that same object at 30mph, sea level, 59 degrees and 70% humidity? I cannot find this answer but would love to know.
http://wahiduddin.net/calc/calc_da_rh.htm
Looks to me to be ~0.3% difference in air density for those 2 conditions you stated above. So yeah…it’s not a very big effect.
Even so, reporting CdA is STILL in my opinion the most useful way of reporting tunnel data. There’s no need to ask about test speeds, air densities, etc…and you can then use it however you desire.
Thanks Tom. That is better than an E6B.
So can we now declare on ST that humidity has no real effect on drag?
I can put a chart together from our wind tunnel tests showing the CdA and send it to you if you care to see how our hydration products stacked up.
Hans
Would that be more or less useful than Newtons?
I also think grams of drag is stupid since drag is a force. But CdA is better than Newtons since it is theoretically air independent and thus a function of the object only. Different wind speeds have different drags. Different air temperatures also would have different drag forces since drag force is a function of the dynamic viscosity/density of the fluid.
Yes but most wind tunnels normalize the data to 59 degrees and a barometer of 29.92. So the results should always be the same regardless of temperature.
But, not necessarily to the same speed (hence the reason everyone always questions the 30mph test speeds). Also, do they take into account humidity? That too affects air density.
Humidity is not accounted for in any tunnels to my knowledge. I have pondered this and tried to find the answer. Temperature is only taken into consideration to calculate density altitude. Is it because the water content in the air, does not make up the air? So my question is: what would be the effect on an object at 30mph, let’s say at sea level, 59 degrees, 10% humidity, to that same object at 30mph, sea level, 59 degrees and 70% humidity? I cannot find this answer but would love to know.
http://wahiduddin.net/calc/calc_da_rh.htm
Looks to me to be ~0.3% difference in air density for those 2 conditions you stated above. So yeah…it’s not a very big effect.
Even so, reporting CdA is STILL in my opinion the most useful way of reporting tunnel data. There’s no need to ask about test speeds, air densities, etc…and you can then use it however you desire.
Thanks Tom. That is better than an E6B.
So can we now declare on ST that humidity has no real effect on drag?
I can put a chart together from our wind tunnel tests showing the CdA and send it to you if you care to see how our hydration products stacked up.
Hans
Sure…for some reason I was under the impression the effect was greater…hmmm…
No need to make a special chart on my account if you already have it in grams of drag and at (or normalized to) a specific tunnel speed 
Yeah, you think it would make a difference but it does not. I think at 100% humidity with visible moisture (fog) it would make a difference though.
And yes, all of our aero data is normalized at 30mph. But we have all the CdA values as well if anyone ever wants to scrutinize those.
Yeah, you think it would make a difference but it does not. I think at 100% humidity with visible moisture (fog) it would make a difference though.
Yeah…I did a TT at Fiesta Island earlier this year that had condensation on every leading edge. So much so that I could watch the rivulets of water stream back in the air flow…the bonus, I guess, being that it was “nature supplied” flow vis I could watch during the TT to take my mind off the pain