Compound bow - set up question

Reply Subscribe

Thread Tools

07-29-2008, 11:02 AM

#51

GMMAT

Dominant Buck

Thread Starter

Join Date: Oct 2005

Location:

Posts: 21,043

RE: Compound bow - set up question

Quote:

I would think a physics book, and a chapter on projectile motion should clear things up in a hurry. As opposed to relying on 15 "mr wizards" who slept in a holiday inn last night

You likely have a point, there, Ryan. Thanks for the advice.

Heeded.

Quote:

There is one spot, but it is below the straight line you draw from nock to tip.

Quote:

The only level I am familiar with is the one on my sight, and it only reads plumb/level in one plane...a different plane than the arrow flight travels on. Do you have a level for each of the 3 planes involved?

I'm talking about the levels on a t-square that some use to set their center shot.

Quote:

WHY can't the sight line line (from eye to target) and the arrow line intersect and then reconnect at 20 yds.

They do...always.

Thank you.

Quote:

If the target is below that one magical spot that I mentionedfirst in this post, then the arrow will not rise. Ifthe targetis anywhere above that spot, then the arrow will rise.

Thanks, again.

07-29-2008, 11:08 AM

#52

Rob/PA Bowyer

Boone & Crockett

Join Date: Oct 1998

Location: Hughesville, PA USA

Posts: 18,322

RE: Compound bow - set up question

Quote:

ORIGINAL: GMMAT

Quote:

The arrows elevation on the bow at rest is set in readings that are 90 degrees to the string. The string however would not be perpendicular to the ground if you were shooting at a target 20 yards out shoulder high. The arrow would also not be parellel to the ground.

The string can't be perpendicular to the ground when you're at full draw

. Gotcha. And really.....my original question was more from the set-up. But for S's and G's.......why couldn't your arrow be level .....shooting at a 20yd target? Is there nowhere that target could be that would find your arrow level (parallel) to the gorund?

Rob said....

Quote:

The bow/arrow is set up at level/plumb/center in a vice, not when your holding it. That is designed for the arrow to come out of the bow as straight as possible. Then you pick up the bow, and your raising it to shoot down range.

Tell that to the bubbles on your level

They won't read plumb/level if the bowstring/arrow isn't/aren't.

And this....

Quote:

Think about this Jeff, when you shoot 40 yards, do you not raise your bow? If you were to shoot 60 yards, do you not raise your bow higher? If you put your bow in a shooting machine, plumbed and leveled it so the arrow is level and shot it, it would not make the spot on the 20 yard target. It would not arch up, it would come straight out of the bow and start to drop immediately.

NOW you're going where I wanted you to go. I'm simply "asking"......WHY can't the sight line line (from eye to target) and the arrow line intersect and then reconnect at 20 yds. What I'm saying is the bottome or "arrow" line......isn't a line, at all. "I" theorizing they meet at 8 or so yds (per Matt/PA).....and from there the "arrow" line is above the sight line......and it arches to meet the sight line....at 20yds. I believe it DOES start to drop fairly "immediately".....crosses the other line.....then arches to the target.

I'm not sure it "rises", though......unless someone can explain to me why it has to be set up UNlevel.

Quote:

When your shooting 20 yards, your not holding the arrow level, your bow is level side to side not front to back.

It certainly "could" be. BUT.....This will help illustrate what I'm saying.....

What if your arrow was perfectly level.......on a parallel line with a line coming from your 20yd target. Now....."I" think your arrow line would be above your 20yd target line.....and the fact that you're looking down from your sight line would make this compensation.

Heck I'm gonna draw it.....I know this is confusing...

No kidding it could be if the target is lower than the shooter but I didn't think we were talking in could be's.

I was explaining as if both shooter and target are on the same level ground at the same elevation.

07-29-2008, 11:10 AM

#53

GMMAT

Dominant Buck

Thread Starter

Join Date: Oct 2005

Location:

Posts: 21,043

RE: Compound bow - set up question

Quote:

I was explaining as if both shooter and target are on the same level ground at the same elevation.

I'm emailing you a PDF.

07-29-2008, 12:14 PM

#54

GMMAT

Dominant Buck

Thread Starter

Join Date: Oct 2005

Location:

Posts: 21,043

RE: Compound bow - set up question

Is there anything wrong with this sketch?

No deductions for drawing skills (or lack, thereof) please.

07-29-2008, 12:19 PM

#55

brucelanthier

Nontypical Buck

Join Date: Aug 2006

Location: Southern MD

Posts: 2,520

RE: Compound bow - set up question

Where are the anchor points for the shooter? From the looks of that the anchor points need to be around the shooter's waist.

07-29-2008, 12:21 PM

#56

GMMAT

Dominant Buck

Thread Starter

Join Date: Oct 2005

Location:

Posts: 21,043

RE: Compound bow - set up question

I can alter the sketch......to show the lines closer together.....but the end result will be the same (in my mind and on paper). It'll just look "different".

07-29-2008, 12:24 PM

#57

brucelanthier

Nontypical Buck

Join Date: Aug 2006

Location: Southern MD

Posts: 2,520

RE: Compound bow - set up question

But the peep sight would have to be at a 45degree angle to the bow sight on full draw and that is not realistic.

07-29-2008, 12:26 PM

#58

Critr-Gitr

Join Date: Sep 2005

Location: TX Panhandle

Posts: 620

RE: Compound bow - set up question

If all thisREALLY matters to you, there is areally good book by Robert Rinker called "Understanding Firearms Ballistics." It is one of the most definitive works on projectile ballistics I have seen. And while it was wriiten about firearms, the principiles are the same as what you are describing here.

The arrow, as it leaves the bow, does NOT travel a straight line. It travels in a parabolic curve, whose rate of fall increases as range increases. This is due to the fact that acceleration due to gravity is not a linear function, but a squared function (acceleration due to gravity = 32 feet per second SQUARED). The arrow starts falling the instant it comes out of the bow, so we must aim the bow upwards (via our sights/line of sight/which IS a straight line) to make this curve that the arrow is traveling intersect with the staight line that our sight follows. The projectile will cross the line of sight twice in any normal setup. It might be possible to set a bow up where you could have the line of sight just barely kiss the tangent of the curve of the parabolic flight of the arrow, but i think it would be too unwieldy to use. And you can launch an arrow perfectly parallel to surface of the earth, it just depends where your target is.