Overshoot requirements on sloping ground.

geoffretired

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Does anyone know how to calculate the extra overshoot required when an archery field has a slope behind the target line?
 


KidCurry

Well-known member
Really 🤓 This will give you a heads up for distance 'X' over a given slope, but make sure you have a cup of tea and some biscuits. And skip the first 30 seconds.

 


geoffretired

Supporter
Supporter
Heehe beautiful in its simplicity. heehee
I worded my post badly, sorry. I wonder if there is a chart of some sort, with results such as drop in level x requires extra overshoot=Y
Or simpler still, every drop of 1 foot requires extra x feet overshoot.
 


KidCurry

Well-known member
Heehe beautiful in its simplicity. heehee
I worded my post badly, sorry. I wonder if there is a chart of some sort, with results such as drop in level x requires extra overshoot=Y
Or simpler still, every drop of 1 foot requires extra x feet overshoot.
The problem you have is the number of variables. You could use excel to calculate the distances for every variable but what you are after is a projection for every arrow speed and every initial trajectory. You could probably then just extend the curves using a french curve approximation but it's a lot of work. And I'm not sure why you need it. I don't know how they came up with 150yds. What arrow speed was used and what initial trajectory was used and why?
 


geoffretired

Supporter
Supporter
Thanks for that.
I wondered if assessors of archery fields used a chart that would show how much needs adding for a drop of let's say 1m in 20m. Or some other simple to apply formula.
 


KidCurry

Well-known member
Thanks for that.
I wondered if assessors of archery fields used a chart that would show how much needs adding for a drop of let's say 1m in 20m. Or some other simple to apply formula.
They might, or must have. I hope they didn't just guess :), but they may well have the above equations punched in already, then all they need to do is set initial trajectory and velocity and slope angle. Punching that stuff into Excel is not difficult but probably a 3 cup of tea job at least :)
 


Kernowlad

Active member
Fairly simple trigonometry would estimate it.
But I suspect it’s mostly worked out by old fashioned “shoot in the air and see where it lands.”

And I also suspect that if anything went legal, it would still be 150 yards whatever the topography.
 


geoffretired

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Supporter
Imagine a level field and a 150y line is marked on it. An arrow lands on the line.
Imagine, next that the ground either side of that line is excavated and a wide 1foot deep trench is cut out parallel to the line.
An arrow that would have landed on the line will now travel further. How much further depends on the flight path of the arrow.
I would imagine that an estimated flight path would be used to work out a reasonable extra amount to be added to the 150 in such a situation.
The drop in height is easier to estimate, I would imagine. It might be quite simple to measure, too.
Arrows landing just short of the line will give an idea of flightpath, I think. BUT is that correct? Does the angle of the arrow in the ground match the angle of approach?
 


KidCurry

Well-known member
Imagine a level field and a 150y line is marked on it. An arrow lands on the line.
Imagine, next that the ground either side of that line is excavated and a wide 1foot deep trench is cut out parallel to the line.
An arrow that would have landed on the line will now travel further. How much further depends on the flight path of the arrow.
Okay... because the base of the trench is at a given depth the solution to the distance traveled is just the addition of an initial height to the starting equations for a flat field.
Because the base of the trench is flat the change in height is known. If the whole field behind the target is the same height but at a lower level than the archer it is still the same calculation. However, if the ground behind the target slopes you have to two variables, the change in height as the distance changes. Now you have to factor in the functon for slope angle. This is easier for a constant slope from the archer, trickier if the slope starts behind the target. Both solutions are beyond my level of motivation :)

And a compound arrow's parabola will be flatter than a longbower's.
Assuming the compound is faster than the longbow :)
 


Kernowlad

Active member
Every archer shoots with a different flight path, every arrow has a very slightly maximum range; add the variations in slope shape and it’s potentially very complex.

So just make it simple.
 


ArcheryFox

Member
We're getting into the hypotheticals here, but my suggestion would be:
1 - Select your bow speed and arrow type. I would suggest picking a worst case scenario here, so a modern 60lb compound.
2 - Calculate the angle of inclination required to hit the ground at 150 yds
3 - Keeping this angle add in inclination to the ground and see where the arrow now lands

I have a code that will calculate arrow trajectories and here are the results for my bow:
1 - Launch velocity 285 fps, 330 grn arrow.
2 - 6.16 degrees above horizontal will allow my arrow to land at 150 yds on the flat.
3 - A downward slope of 5 degrees, an 8.7 yd drop over 100 yds - more than I have ever seen on a target field, the arrow will land at 176.5 yds.
Your new overshoot is somewhere around 175 yds.

More realistically a slope of 2 degrees (3.5 yd drop over 100 yds) gives a new overshoot of 162.5 yds.

Given the 150 yd figure was probably plucked out of someone's rear a few years ago, hopefully has a reasonable factor of safety applied, and assumes that people are not shooting like morons (look at flight results - many bows could shoot beyond 150yds if they tried) I would not be too worried about needing excess overshoot on even the most sloping grounds I have shot at *cough Targetcraft cough*.

As KidCurry says, this is beyond the level of effort the worry inspires, and I'm only doing it because I have a code I made earlier that can be used!
 


geoffretired

Supporter
Supporter
Hi Folks, thanks for all the help.
The reason I ask is that we shoot on a field that is level out to 120y then slopes down to the boundary at 170y.
We restrict our shooting to 80y giving an overshoot requirement of 130y. ( compounds 150y)
The slope has recently cropped up in conversations about the overshoot. I was trying to find out what guidance there is about that.
 


ArcheryFox

Member
I would argue that you don't (really) need to worry about where the slope starts if you are only concerned with where the arrow might land at a certain distance away.

For the same scenario above, my arrow's trajectory would have it land 7.5 yds below horizontal at 170 yds if I shot off a cliff.

This would represent an angle of 2.7 degrees down the entire field, or, perhaps more useful to you, the boundary at 170 yds being 7.5 yds below the level of your shooting line.

Hopefully the drop on your field is less than this. You'd have to check, but if so I would have no concerns shooting 100yds.
If in doubt you could always request a range assessment from AGB.

Edit: I have never seen any official more detailed guidance, and like I say I doubt there was ever any use of charts or calculations, just a 'what sounds reasonable if people follow the rules, try and hit the target rather than shoot like idiots, and then we round up with a decent factor of safety?'. These calculations, and searching when I occasionally miss at 100 yds 😂 , make me comfortable that 150 yds is still a reasonable overshoot distance on most target fields though.

As a side note, given the compound overshoot is 150 yds whatever the target distance if you are happy to have compounds on your field at all then you should also be happy to shoot 100yds.
 


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Kernowlad

Active member
We had an 80 yarder over a lake at my last shoot; I shot slightly low and despite good netting, my arrow found a way through. And there it was, splitting a lone sapling of barely arrow width, clean in half but just enough to catch it. Had it gone anywhere else, it was a 20ft drop into a field of long grass; another ACG would have been lost! Such a lucky fluke!
 


KidCurry

Well-known member
I have a code that will calculate arrow trajectories and here are the results for my bow:
1 - Launch velocity 285 fps, 330 grn arrow.
2 - 6.16 degrees above horizontal will allow my arrow to land at 150 yds on the flat.
I'm guessing you must be using a coefficient for drag, which I don't use.
 


ArcheryFox

Member
Perhaps of further interest: PressReader.com - Zeitungen aus der ganzen Welt
Worth noting the overshoot in field is 140m from line or 102m behind the 60m target (total of 148 yds).
At least for AGB...; IFAA used to have 26 yds behind a 20 yd bunny as being deemed safe 😂😂😂.

The article also highlights that there are a few factors at play and that common sense should be exercised and that as much effort as reasonably possible put in to make ranges safe.
To me 150 yds does not guarantee an arrow will never leave the safety zone, but that the probability of it doing so is so small that the risk is negligible when balanced with finding suitable fields to shoot on. Risk assessments are built upon the combination of severity and probability, not just severity.

Kernowlad - which course was the lake target at?, it sounds like an amazing shot!

I'm guessing you must be using a coefficient for drag, which I don't use.
Yes, 2.5*pi/4.0 as suggested by Park (2011) - EDIT: actually Miyazaki et al (2013), apologies.
Works reasonably well when I generate sight marks and tapes.
 


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geoffretired

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Supporter
Thanks ArcheryFox.
It is strange how we can be shooting on the same field for 18 years and suddenly start doubting things that we have assumed to be safe all that time.
 


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