Arrow flight and air density

[shoeshineman]

All other variables being equal, what happens when someone has their arrow dialed in at 60/80/100 yards at sea level and then go to 14K feet?

I figure at sea level, the higher air density would push the arrow around (and the vanes would have a lot to push against to keep flight corrected).

I figure at 14K, the lower air density would allow the arrow to fly faster, but the same vane size would allow the arrow to move around more.

Would the extra speed at 14K offset any "squirreliness?"

Am I thinking about nonsense or drinking too much coffee?

 

[joshdidthis]

I'm also interested to see if anyone has had experiences with this.

 

[Don Qui Puncher]

My 60 yard pin sighted in a sea level was spot on at 60 around 9000 feet

 

[Btaylor]

My 60 yard pin sighted in a sea level was spot on at 60 around 9000 feet

Same for me. Have not seen any difference in POI out to 60. Havent shot further than that at altitude.

 

[notchfir3]

OK I am going to show my science teacher side. The more water vapor in the air the lighter the air. Water vapor molecules have an atomic mass of approximately 18 but Oxygen gas molecules and Nitrogen gas molecules, the two most common gases in Earth's atmosphere, have approximate atomic masses of 32 and 28 . So the more water vapor in the air the more you will feel the humidity and the lighter the air. This air will rise. Will it affect arrow flight? I do not know if it is a significant enough to notice, I would be more concerned about wind speed. Maybe a physics person or engineer can add to this. I will also add that the warmer the air the more water vapor it can hold so maybe temperature combined with humidity will have some effect. I do not know.​

 

[TBarron]

Somebody call Bill Nye


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[Beendare]

Yeah, I've seen a difference at 10,000'.....FWIW, I've never hunted anything over 12,000'.

IME, the faster lighter the arrow....the more you see a difference.


Easy solution; back your limb bolts out a touch....1/4 turn to 1/2 turn should do it....and it doesn't affect your tune.

..

 

[OR Archer]

I live at around 500ft sea level and normally elk hunt between 6500-8000 with zero difference in point of impact. When I hunted in Colorado a few years back I checked my sights and also had zero change at 11.5k at the trail head. However changes can occur so it’s vital you check it when you get there.

 

[Super 91]

I live around 1000' above sea level, and went we camp at 10,000 and hunt up to 12,500 in CO, I typically see a little difference in POI. It depends more on the weight of the arrow it seems to me, but I have noticed a difference at times. Some years it is very small to none, others it seems I am off a couple inches at 60 yards or so.

 

[Blockcaver]

I remember reading this a long time ago, and as usual Randy Ulmer is thorough and easily understood. I found this on Archery Talk:

Here is Randy Ulmers take on the subject as well as a quick fix while in camp.

At high elevation the air is thinner and gravity loses a small percentage of its pull. Every projectile slows more gradually and takes a flatter line. While baseball’s power hitters love the thin air of Denver’s Coors Field and professional golfers enjoy 10% more distance at Castle Pines just south of the city, this phenomenon is not a bowhunter’s friend. Sure, elevation flattens trajectory, reducing the effects of misjudged shot range, but all too often the knowledge comes as a surprise to the hunter at just the wrong time. If you hunt more than two thousand feet above the elevation where your bow was sighted in you will begin to notice that your arrows impact higher than normal. This can be a serious problem for bowhunters heading for the timberline from eastern states.

The difference can be fairly large, several inches for arrows fletched with vanes and even more for arrows decked with feathers. Left unchecked, such a built-in accuracy bias can produce an outright miss, or worse.

Of course the real key to remedying the problem is first understanding that it exists. After that, the physical solution is simple. Because the gap between the pins is affected, you can’t simply gang-adjust your entire sight head upward to account for the flatter trajectory. And, resetting every pin individually is too problematic in the constraints of most hunting camps. Instead, focus on one of your longest pin settings. Assuming it is 40 or 50 yards, set out a target at that distance and shoot until you are comfortable that you are executing good shots. Then simply turn your limb bolts out (reducing draw weight) in small increments until you are hitting dead-on at this range. Make sure to turn both bolts an equal amount in order to preserve the bow’s tiller setting.

After making these adjustments move up and check your shorter-range pins just to be sure everything is still tracking. Your 20-yard impact point may be slightly below the intended target, but the difference will be so small that it is insignificant.

Not only is elevation an important consideration when preparing yourself physically for the mountain hunt of a lifetime, it must also be considered when preparing your bow. Adjusting your draw weight is a
step that can make a big difference in the outcome of the hunt.

Caption: Hunting at altitude will affect your arrow’s point of impact. A small adjustment to your draw weight can quickly fix the problem.​

​

 

[Topo_trekker]

Tim Gillingham has talked about it before as well and changes his sight tapes accordingly.


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[jdubrr]

Same for me. Have not seen any difference in POI out to 60. Havent shot further than that at altitude.

Same here. I thought it was going to change the POI so I shot my bow at the truck before hiking out and no change

 

[Billy Goat]

I always expected to see a difference at altitude but can't remember that I ever did. I can remember shooting to 75 yards in camp and don't remember needing to adjust anything. I was shooting decent as I was collecting money from anyone who thought I couldn't hit a beer can.

Definitely seems you would hold more velocity further away with thinner air. I'm at 1245' where my range is setup. Camp while hunting was at 9500'.

 

[IdahoHntr]

Hot and cold can also effect point of impact. Hotter air has less drag than colder air. For the guys not changing point of impact at elevation, its possible the higher temperature low elevation air is offsetting the most likely colder temperature high altitude air? Just a thought. The physics of it says elevations should change impact, but there could be other factors offsetting that as well as the changes just could be to miniscule to matter in the real world.