Calculating angle compensation

[muleyapprentice]

I shot a buck yesterday and want to know the non angle compensated range. It was 86 yards with 100 feet elevation loss. Is there a formula for this? Is it rangefinder specific? I’m guessing I could take the approximate slope of the hill, but once I know what the angle of the shot was now what?

 

[BBob]

Is there a formula for this?

Yes, it’s called trigonometry. Mby you’ve heard of it before?

Edit: If the 86yds was a compensated distance from a rangefinder then the true distance to the target was 92yds.

cos 21°= .9335804 so 92•.9335804 = 85.9

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[BBob]

The way we did this in the field back in the late 80’s early 90’s was with an angle finder, Casio calculator watch and a trig table. Take the cosine of the angle, multiply that by the true distance to the target and the result is the horizontal distance you would shoot for. That was cumbersome to me so I calculated a bunch of distances with various angles. I then typed out a chart, laminated it and carried it with the range finder and angle finder. I still have that old cut chart.

 

[Mighty Mouse]

 

[muleyapprentice]

Incredible. What I did not understand is that the angle compensated range is true horizontal distances? Is this true to extreme angle of 50 degrees?

 

[BBob]

What I did not understand is that the angle compensated range is true horizontal distances?

Yes

 

[muleyapprentice]

Yes

Care to poke at why that is? I would think the time in the air affects trajectory more than horizontal distance traveled. Why does vertical travel not affect trajectory?

 

[Harvey_NW]

Care to poke at why that is? I would think the time in the air affects trajectory more than horizontal distance traveled. Why does vertical travel not affect trajectory?

It does. With a 50° downward shot angle the horizontal distance would be 86 yards, but line of sight would be ~112 yards and time of flight would need to be accounted and solved for. That's why there's an arrow velocity input in the software of the Sig Kilo archery mode. No different than a ballistic solution for a rifle.

 

[Zac]

I think you’re just posting this to brag, even if so well done sir that’s an amazing shot. I shot a doe at a very steep incline, and my RF read 100. I didn’t even think to cut and ended up shooting her right through the jugular.

 

[Mighty Mouse]

Incredible. What I did not understand is that the angle compensated range is true horizontal distances? Is this true to extreme angle of 50 degrees?

The typical method of angle compensation used in rangefinders is simple trigonometry based on line of sight distance (the hypotenuse of the triangle) and angle. The laser provides LOS distance and a built-in inclinometer provides the angle. Using those two numbers, the rangefinder calculates and displays the horizontal distance (i.e., the angle-compensated distance). This method works well enough in most situations, but it is subject to some amount of error because it doesn't account for the effect of increased air resistance (due to longer flight path) when taking an angled shot vs. a horizontal shot. There are some newer, more sophisticated rangefinders (Leupold Full Draw, Sig Kilo) that claim they account for this discrepancy and provide a more accurate angle-compensated range.

 

[BBob]

Care to poke at why that is? I would think the time in the air affects trajectory more than horizontal distance traveled. Why does vertical travel not affect trajectory?

Basically with the short ranges in archery the affects of the air resistance don't amount to much or not enough to matter. It will start to show up eventually at the extremes but those extreme shots rarely if ever show up in real life. It's been way too long since we all tested this that I honestly don't remember where the discrepancies started or where they started to matter. They did show but I concluded that I'll never take a shot at those extremes so I flushed it memory wise. I'm not sure I have those notes anymore. They might be tucked away in an archery file somewhere.

 

[muleyapprentice]

Outside of air resistance, are there any factors that affect trajectory on steep cuts? Is that the only added factor compared to a flat shot?

 

[Mighty Mouse]

Outside of air resistance, are there any factors that affect trajectory on steep cuts? Is that the only added factor compared to a flat shot?

Parallax caused by the distance between the peep sight and arrow can also be a factor with very short and steep shots.

 

[roadrunner]

Care to poke at why that is? I would think the time in the air affects trajectory more than horizontal distance traveled. Why does vertical travel not affect trajectory?

Gravity works the same whether the shot is along flat (horizontal) ground or inclined.

Always aim for true horizontal (flat) distance.

 

[muleyapprentice]

I’m surprised that horizontal distance is the constant with gravity and not air time. This is obviously true because wether I’m shooting uphill or down hill at the same incline my cut will be the same, where I would expect it to be different.

 

[BBob]

where I would expect it to be different.

If you want to get very deep in the weeds it’s not exactly the same up and down but in reality it doesn’t matter one bit archery or rifle distances and angles. It’s so small in our world you’d never see it.

 

[dkime]

If you want to get very deep in the weeds it’s not exactly the same up and down but in reality it doesn’t matter one bit archery or rifle distances and angles. It’s so small in our world you’d never see it.

^^^^^ truth

Head to archersadvantage if you want a great explanation of all of it

https://www.archersadvantage.com/index.php?option=com_content&view=article&id=10&Itemid=3

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