Request for those who are starting a new bow.

[Badger]

   Ben, if the formula was right on then your 28" shot would match your second 24" shot. I think my formula might be closer based on string travel. This would have also made your 1st 24" shot a bit faster for an even bigger difference.

[sleek]

Ben, that looks like a good test and is consistent with the tests I have done on pretty well made bows, it demonstrates the loss due to hysteresis that occurred during the last few inches of tillering. Good Job. 

  Dc,  Woodbear is 24/28     mine is 18/22  somewhere inbetween seems to work out best but I do think Woodbears is a bit closer than the one I was using.

Shoukd we do an average if the two formula? Add the two formula then devide by 2? So it would be 21/25.

[DC]

OK 24/28 first
40#@24"=184fps   348grains  should be 342

40#@26.5=185fps   400grains   correct weight

33#@24"=180fps   294grains   should be 282


now 18/22
40#@24"=189  322 grains  should be 327

40#@26.5=185fps   400grains  correct weight

33#@24"=180fps  294grains  should be 270

I included as many numbers as I could think of so you could check my work. The bow is a Maple backed Yew with a bit of Perry reflex. This one didn't gain any reflex while tillering. It took about an inch of set but most of it happened in the first half of tillering, whatever that means.

[Selfbowman]

Ok y'all know backwards Tex. I did something a bit different. I tillered the bow to 24" . Usualy at this point there is very little tiller work left. The bow weighed in at 41.24 at 24".  I then pulled the bow to 26" .the bow weighed in at 45.94.  I then weighed the bow in at 24" again weight 40.76 so does this mean.48 loss due to whaaaat.  That should get you guys laughing for a bit. I have 5 bows that are at tiller stage . 4 Osage and one hickory. So call me badger and tell me better what you want. I could be some of the worst but that means I have more room for improvement.  I am having fun.
Arvin

[avcase]

This is an interesting thread. Ignore this if it has already been answered, but the only places on the bow that should be used to scale something based on draw length is the places where your hands touch the bow. The deepest part of the grip is a good point on the bow itself, and the point where the fingers connect to the string.

So, a 28” draw is really 26-1/4”.  A 24” draw is actually 22-1/4”.

Equivalent ggp at 24” draw is found by multiplying 10ggp by the ratio of (22-1/4) / (26-1/4”) = 8.48 ggp.

The logic in this:
Take an perfect design for 28” draw and scale it for 24” draw. The length of the 24” draw bow will be proportionally shorter, the brace height of the 24” bow will be proportionally a little less, and the amount of set of the 24” draw bow will be proportional to the draw length ratio also.

This may not work

[DC]

Why not the power stroke like Steve is doing? That's what actually does the work.

[Selfbowman]

D.C. I just did that to See if it would change. It should work on any bow . I will test some of my finished bows and see if they change. Thinking out loud here D.C. If it does change then there has to be a cause. The dreaded H word maybe! Now what if anything can we do to change that number to even every time. Still thinking out loud. Arvin

[Selfbowman]

Alan I was measuring from the throats of the nock to a women's hair tie at desired lengths on the arrrow. Measured to the back of the bow. That's as close to the same as I am capable of right now.
Arvin 

[Bayou Ben]

Thanks Badger.  I was wondering about why the last 24" shot was less.  It looks to be pretty consistent with the other numbers DC and Leonwood provided. 

And after reading avcase's response, it got me thinking.....Wouldn't you want to scale the power stroke ratio's? not the artificial 24" / 28" values? 
So the powerstroke of the bow is how much it is actually being pulled back, so if you use AMO draw length, and you have a 6" brace height throughout, the power stroke at 24" would be 24"-1.75"-6"= 16.25" ,  and at 28", 28"-1.75"-6"= 20.25".  Using this ratio, 16.25/20.25, you get .802 as opposed to 24/28 which is .857. 

5.5% different could be why we are dropping off in speed at the 2nd 24" test.  I guess that's what you were trying to tell me.  Sorry, I'm just picking this up. 


 

[willie]

this mean.48 loss due to whaaaat.

Arvin, due to "permanently" compacting the cells when you drew it  to 26 for the first time. I would be happy with 1/2 lb loss over the last 2". I bet Steve doesn't do much better with his no set method.

permanently is in quotes because the bow may recover at rest unstrung some, so if you try the test tomorrow, you may see some of the same thing, but probably not as much as the full .48 lb.

[PatM]

What is the end goal of this? Certainly everyone isn't going to start drawing their bows 24 inches and shooting underweight arrows to flatter speed.

 The bottom line is that the longer draw delivers more all around, even if the wood is broken down.  It's a net gain scenario.

[Bayou Ben]

I would think Badger is trying to find a formula to level the playing field in the flight shooting world for people with different draw lengths.  Just a guess.

[willie]

Ben, I think that this test is a good overall comparision, but when it comes to splitting hairs, there are a few details that will "gotcha"

one is that the test assumes a straight  line force draw curve, so each inch in the powerstroke adds the same weight increase, but his is not always the case. more over the force draw curve can lie to us if the bow is stacking some at the end of the draw. the test really assumes that efficiency is the same through out the range of test draw lengths.

Put another way, this test may work well on a practical basis for two close  numbers, ie 24" & 26" & 28", but the formulas will all have problems if the spread is too much or the bow too short

[DC]

I got fairly different results for the two tests I did. The first one I pulled to 28" and probably got some set and the numbers kind of spread out. The second test I only wanted to pull to my draw length, 26.5". What surprised me was how close the first 24" pull was to the 28" pull. Granted I was using a lighter arrow but in a half-assed way that 4" didn't do much. It is possible that the whole test was designed around those two pulls and that's the reason they match.From what I gather the test was to hopefully level the playing field for short draw length archers. I don't think it got close enough to make everyone happy but then nothing does. I had been thinking the same as Alan with the scaled bow bow but that kind of lead nowhere except to make me think there is no way to level the field. Maybe if we measured the length of each archers elbow to fingertip(a Cubit)or some appropriate body part and use that to calibrate the scaling.

[Badger]

  The test was not to level the playing field exactly. More so to demonstrate that in most cases the 24" draw bow would be more efficient if it had never been drawn past 24".