Trajectory

[Jock Whisky]

Question on trajectory for you scientific wizards.

An archer is about to shoot an arrow at a target 25 yards away. The line from the arrow nock (when it is at full draw) to the target is perfectly level or horizontal. The arrow travels at 170fps.
During its flight the arrow will rise slightly and then drop into the target.

Given the above, how high above horizontal will the arrow rise? I am aware that there are other variables such as feathers vs vanes, arrow diameter, air density and friction etc but lets ignore them for the time being.

Is there a site that will calculate this for other distances?

[JimB]

I'm not a wizard but the arrow doesn't rise.It only drops.The fact that most of us anchor well below the eye,does make it intersect and go higher than our line of sight but it really isn't rising.

[Hermon]

The arrow will not be parallel to the line of sight.  It will be pointed up, and then drop into the target as stated.  So many variables I'm not smart enough to tell you how much the drop would be.  Maybe someone can.

[ChuckC]

Here is a wild ass guess.

The reason for the initial rise is due to aiming, your eye is above the arrow (or gun sight). As soon as the projectile leaves the string (or barrel) it starts to fall due to gravity.  The amount of "rise" is dependant upon aiming plane, where your anchor point is compared to your aim point.  In this case, is specified as starting off horizontal so there is likely no "rise", just fall.

Try using your point as an aim, on a target face, to determine your "point on" distance, and then find your very own trajectory pattern by then walking in toward your target and shooting.
ChuckC

[screamin]

According to the ballistics calculator on petewards website, if the arrow weighed 500grs, it is down 6" at 10 yards, 25" at 20 yards, and 58" at 30 yards.

[ChuckC]

Does the weight matter ?  I am guessing only the initial speed really matters.
ChuckC

[KSdan]

I would think you could test it for yourself.  Set a temporary site (like a toothpick on the riser).  Set the site for 2-3 yds. (fairly flat-line of site).  Then shoot at varied targets at small yardage increments with that pin out to 25-30 yds.  Plot the results.  Do the same thing again, but set the pin for 25 or 30yds.  Again shooting at various incremental targets.  You can plot the trajectory curve.

My 2C
Dan in KS

[old_goat2]

If I'm understanding my Archer's Advantage software correctly, it's about 9.5" @ 25yds and it shows 40" @ 50 yds. It's good software I bought when I shot wheels and wanted sight tapes. I still use it for figuring out arrows with trad bows.

[**DONOTDELETE**]

I did a bunch of testing along these lines to see the difference in how much the arch changes with different speed arrows and different weight arrows.

This can be kind of fun, and it teaches you what branch you can shoot under or over, or how big of window you need to shoot through the brush.

The easiest way to do this is to set up a frame at 10 yards from your target and put some butcher paper or card board across the frame or two stakes..... Now cut a 4" hole in the card board about 3' off the ground. and set your target up dead center  3' off the ground and put a fluorescent dot at the same height as the center of the hole you've cut..... Then drop back to 20 yards and shoot from your knees.

Then focus on the spot on your target through the hole and shoot until you hit that dot consistently..... You will be amazed at the difference in that short yardage between 170 fps and 190 FPS....Btw... your arrows will pass through the paper higher than the hole your are looking through and you can measure from center of hole to where the arrows are traveling through the paper above it to get the exact height of the arc at the apex of the cord 1/2 way to your target..

  It's a very good way to learn your trajectory at different yardages....and its kind of fun to try too....

[savage1]

My take on it is the arrow will rise "about" 20" at its high point. Based on 170 fps no matter the bow
weight or arrow combination.

The way I like to go about it is like Jimmy Blackmon explains on youtube. Just point at a dot at bottom of a bail and walk back 5 yds at a time always aiming at the same dot. The further you go back the more the arrow rises until it begins to fall. You can measure it for every yardage.

What I find aside of grains per pound is that arrows with extreme foc will dive faster.
20% is plenty for me. You can build your arrows to fly as you wish to a point.

Lou

[2bird]

Yep Jimmy Blackmon's video "method to the madness" is what you want to watch. Knowing the trajectory of your arrow and understanding that within normal shooting ranges the arch can be very minimal is why gap shooter can become so accurate.

There are or were calculators on the web that get pretty close but personal results vary with each archer (draw length, anchor points, arrow length etc).

Like said above, put a dot on a target and put your point on the dot, shoot from 5 to whatever yardage you want and record your dope. For me I have a 5" window between 5 and 25 yards, I think a lot of people will discover that they have a 2-4" window of arch between 10-20 yards which is great for hunting because there will be no thought to how high or low you will have to aim to get into the vitals.

Also raising and lowering your nocking point with increase or shrink your gaps (trajectory) and of course the higher you anchor on your face the smaller your gaps will be and vise versa, When I started gap shooting I was putting my index finger in the corner of my mouth and my arrow would impact 18" above the dot at 20 yards then I switched to my middle finger in the corner of my mouth and the arrow impacted 4" above the dot at 20 yards. Just food for though...

And no i'm not trying to say my way is better then anyone else's I was just explaining how trajectory relates to me...

[McDave]

If the only variable were initial arrow velocity, trajectory would be fairly easy to calculate.  However, the other important variable is friction loss due to air resistance.  There are a number of variables that affect friction loss, such as fletching, arrow mass, and shaft flexing.  Imagine the difference in trajectory between a perfectly tuned bare shaft and a flu flu, both fired at the same initial velocity!

Arrow weight doesn't directly affect trajectory, assuming the initial velocity is equal, as Newton proved when he dropped an apple and a cannon ball off the leaning tower of Pizza.  (At least I think that's what he did; at least they were two things of similar size but different weights).  But weight does affect momentum, which helps an arrow overcome the effects of air resistance.  Imagine the difference in trajectory of shooting a soda straw and a wood arrow shaft, both with the same initial velocity.  The difference would be even more if you shot a soda straw and a steel rod, but it would be hard to get a steel rod up to the same initial velocity as an arrow shaft out of a bow.

Because of the many variables in wind resistance, it is really just easier to do some kind of real life testing, as Kirk suggests.  Or even just skip that and measure the gap at the target, as in Jummy Blackmon's, Rod Jenkins's, or Byron Ferguson's videos.

[stonewall]

It's like throwing a baseball from center field to the infield you put an arc on it to get it to the target. Your fighting gravity, as soon as you release gravity is already pulling it down. gravity does not give it a break and let it rise a little bit, your brain is doing that. I could be wrong , Just ask my teen age boys.

[Jason R. Wesbrock]

Originally posted by Jock Whisky:

Given the above, how high above horizontal will the arrow rise?  

Rig up a temporary sight and set it for 25 yards. Shoot the same sight setting at 12.5 yards. Measure how far above the spot your arrow impacts.

[Chuck from Texas]

Don't forgetFeathers nake a big difference here. they are basically a parachute on the back of your arrow.

[katman]

savage1 "What I find aside of grains per pound is that arrows with extreme foc will dive faster"

Not my findings at all, I find equal mass arrows fly same trajectory even with large differences in foc.

Lots of good points mentioned, need to work it out for you and your setup.

[savage1]

You are quite right with the eaqual mass. We are blessed with a variety of shafts and components that allow us to build many configurations.
My builds usually net me heavier arrows as I increase foc.
I am at 20% which puts me in extreme foc according to Asbey's chart where he states 19% to 30%.

Lou

[gringol]

Originally posted by ChuckC:
Does the weight matter ?  I am guessing only the initial speed really matters.
ChuckC

Yes and no.  If you ignore wind resistance, no weight does not matter.  In a vacuum, only the speed will be in play.  However, in the real world more weight will translate to more momentum and the heavier arrow will be slowed less by wind resistance.  this can all get pretty geeky so i just like to watch em fly...