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# Air Pressure and Golf Ball Distance - Page 3

Quote:
Originally Posted by limoric

I fully expect to get an arguement from you without a single attempt to prove your possition...

Yeah, because that wouldn't be a waste of my time at all.    I think I'll pass. Have fun with your thread.

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Quote:
Originally Posted by sacm3bill

Yeah, because that wouldn't be a waste of my time at all.    I think I'll pass. Have fun with your thread.

Sorry to say, you waisted your time when you suggested a calculation that would see air pressure fall to a level that is not possible. You could have chosen to put what I was trying to say into context or ask for clarification if you really wanted to be helpful; instead of trying to teach me how to calculate a percentage which was irrelevant to the query.

Nope, you'd rather argue, adamantly state I'm wrong and then offer no evidence to the contrary.

Your departure will not be missed...cheers.

What a waist of thread... Do we have a winner?

Quote:
Originally Posted by limoric

The percentage change doesn't matter and I don't care what it is. I'm after the percentage change in air density or the percentage change that an object is affected by when passing through that air density. It's the point of the whole thread, you could have chosen to look at it a different way, despite how you understood my description..

I mentioned this earlier, but it may have been missed....

It seems to me that what you're looking for is a way to calculate the difference between a "normal" day at your course, and the conditions of any other day either at that course or another course that you may have traveled to.

The best way I can think to do that is by calculating the density altitude in the same manner that pilots do in determining operating performance for their aircraft.  If the density altitude on any given day is significantly lower than whatever your baseline day is, you'll see a reduction in distance.  If it's higher, you'll see an increase in what you're used to.   The RELATIVE DENSITY is what you're looking for, but not as calculated, because that's calculated from sea level standard conditions of 15* C and 29.92 inches of mercury for temp and pressure.   So you'll want to start by calculating the density altitude for your "normal" day at your location, then run it again for the current day.  That will allow you to see the difference in the actual air density for both and you can calculate the relative difference between the two.  Should give you a good point of departure for the day as to how those factors will affect your ball flight.

http://wahiduddin.net/calc/calc_da.htm

Yes, I saw it and I just now followed the link. Very cool! I'm going to play around with it when I get to a pc. Also I know a pilot who's brain I'm going to pick, he flies small planes. I'll ask him if there's areas of the lower main land that consistently have Lower or higher air density...

Thanks!

Maybe we can add this to the "how far you hit your driver" thread as a factor prior to distance as a disclaimer...

Quote:
Originally Posted by limoric

Yes, I saw it and I just now followed the link. Very cool! I'm going to play around with it when I get to a pc. Also I know a pilot who's brain I'm going to pick, he flies small planes. I'll ask him if there's areas of the lower main land that consistently have Lower or higher air density...
Thanks!

Higher altitude (mountains) or higher average temperature = lower density.

Lower altitude (coast) or lower average temperature = higher density

The important thing though would be to identify your own "standard baseline" day where you play most. Then you can compare any other day or any other location to that to get a relative comparison.

David,

As a pilot, do you know of any calculations for change in drag coefficient with temperature and altitude?  We are assuming that the effect of ball flight distance is directly proportional to the air density.  But are there other factors that change?  Does drag change with humidity and temperature?  Pilot training may help us here.

I haven't found anything decent with web searches.  The problem with searching the web is you get a lot of anecdotal information.  All my text books deal with fluid flow of liquids mostly (Chem E).

Quote:
Originally Posted by boogielicious

David,

As a pilot, do you know of any calculations for change in drag coefficient with temperature and altitude?  We are assuming that the effect of ball flight distance is directly proportional to the air density.  But are there other factors that change?  Does drag change with humidity and temperature?  Pilot training may help us here.

I haven't found anything decent with web searches.  The problem with searching the web is you get a lot of anecdotal information.  All my text books deal with fluid flow of liquids mostly (Chem E).

Drag varies based on the density of the air (or viscosity of fluid). Air density varies based on actual geographic altitude, temperature, and humidity. Lower altitude, lower temperature, and lower humidity all contribute to higher air density.

What I don't know is whether the delta in drag is in direct proportion to the change in air density. If air density increases by 5%, does that correlate to a 5% increase in drag and therefore a 5% decrease in carry..... We know there's a correlation. I don't know exactly what that correlation is.

Someone out there smarter than me, or with stronger Google fu may know.....

These guys are smart.

http://www.grc.nasa.gov/WWW/k-12/airplane/dragco.html

But do they golf?

I found this calculator for the properties of air.  Quick calculation between 760 and 745 mmHg shows a very small change in viscosity <0.1%.

http://www.peacesoftware.de/einigewerte/luft_e.html

So it looks like drag is directly proportional to density as well and the viscosity of air doesn't change that much.  So we are back to only a 2% change in distance with a change from 760 to 745 mmHg barometric pressure.

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