Drawlength and powerstroke

[CoilSpring]

[Margly]

Originally posted by Bill Carlsen:
I know from my experience with DAS ILF limbs that the preload is more important than a given weight at a determined draw length. For example, my wife shoots 46#  @ 26". Two years ago she had trouble with her thyroid, lost strength and was unable to shoot 46#. I lowered the weight on the limbs to about 42# but the performance lost was significant because of the loss of pre load. I got a lower weight set of the same limbs, same length, and set them for 42# @ 26". Because the preload on the new limbs was increased  in order to get to 42# she was able to redeem the performance she lost with the same set of limbs, set at 42# but with much less preload. So, one set of limbs at 42# was significantly better performance-wise than the 42# limbs with less preload. I know that was redundant but I think limb design has a lot to do with performance and one bow of equal weight at 28" may actually outshoot a bow of equal weight at 31".

I agree Bill that preload has a lot to say, but what I'm thinking about is as follows:
If you and I use the same type of limbs on our DAS'es you pull 28" and I pull 31"
With the same preload what # would you use to get the same performance as I if I for example shoots with a 55#?
(we will use the same arrow)

[Margly]

Just read thru the thread again and there is a lot of good advises here  

[Flying Dutchman]

Hello, I draw between the 29 and 30 inch. What you gain in weight is dependent of the weight you start with. The rule of thumb is simple: add 5% per inch more. If you go from 28 to 31, you will gain 15%. For 55 lbs this is 8,25 lbs.
So at 31" you will end at 63,25 lbs with this bow.

[Javi]

I wonder if the English Longbowmen or Native Americans sat around the campfire wondering about the draw force curve of their bows…

[Troy Breeding]

Javi,,,

lmao.....

Most likely they were wondering where their next meal was coming from and if anyone saw them miss that deer earlier in the day..   :-)  :-)

Troy

[LimBender]

Deleted.

[Javi]

I can tell you that 50 odd years ago, I bought cedar shafts spined 5# more than my draw weight and hand straightened them, cut them to 28” cause that’s what the measurement was when I stuck a nock in the middle of my chest and held the arrow between my outstretched hands, tapered them, glued a nock and a 125 grain point on them, fletched them and went out and shot them…. I didn’t worry about tuning the bow other than nock point and brace height; I didn’t care how much the arrow weighed, or how much FOC it had. I worried about how sharp the broadhead was and how straight the shaft was… I couldn’t have told you if my arrows all weighed the same or if they were spined within 1#; all I knew was if one didn’t fly good and hit where I was looking it got burned in the stove for kindling come winter.. We didn’t know nothing about shooting off no point or gaping, drawforce curves, or skinny strings we just killed stuff with our bows, some of us even shot field archery with our hunting bows… had a bunch of fun….. oh….. did I say killed stuff with our bows…  :D

[Shawn Leonard]

Bill Carlsen has it right. A lot depends on the limbs and what poundage they were built for. As a rule they say 3#s per inch over 28"s but some limbs start to stack at 28"s and that can be up to 5#s an inch out to 30-31"s. My new Borders are very smooth and I beleive after 28"s they gain only 2-2.5#s an inch until you get out there past 31"s or so. I also do not know about sixbys post, I don't think it would make it like a 53# bow at 28"s, that 3 more inches of power stroke will increase FPS. I doubt all else being equal a 53# at 28" bow will be as quick as a 53# bow at 31"s. Shawn

[Shawn Leonard]

I also would say to marglys question that Bill would have to shoot a bow that is around 63-64#s at 28"s to get the same performance you would out of your bow at 55#s at 31"s. That 3"s of powerstroke is huge, just ask the guys who draw 26-27"s. Shawn

[Bill Carlsen]

Margly: There is  no doubt in my mind that draw length would improve bow performance with two bows, identical preload and one was X#'s at 28' and the other limbs were the same weight at 31". When the DAS bows first came out there was a great deal of discussion about this on other sites and that seemed to be the consensus. I do not know, however, if you could quantify  the dynamics simply because every bow is designed differently and the use of various materials, carbon for example, would all  have to be figured in in some way.

[Archie]

I draw 31", and shoot a 48# @ 31" longbow.  This thread is of great interest to me, as I have wondered the same:  Can I have the identical "confidence" in the "knockdown power" of my setup as a guy shooting, say, 55# @ 28"???  (All other variables being equal.)  I shoot heavier bows, too, but the 48-pounder is just so pleasant to shoot...

Archie

[Margly]

Originally posted by Bill Carlsen:
Margly: There is  no doubt in my mind that draw length would improve bow performance with two bows, identical preload and one was X#'s at 28' and the other limbs were the same weight at 31". When the DAS bows first came out there was a great deal of discussion about this on other sites and that seemed to be the consensus. I do not know, however, if you could quantify  the dynamics simply because every bow is designed differently and the use of various materials, carbon for example, would all  have to be figured in in some way.

Hi Bill!
I have the same thoughts and is curious about the difference in performance, I do have a Firefly longbow 66" 43@30 and acces to a same in 46@28 and will give it a try and see how it goes:)

Of course it is a lot of unknown factos but this will give me a clue of what we are talking about!

Take care:)

Ronny

[Margly]

NB Will post the results after some chrono testing:)

[Sixby]

Shawn, I guess I worded that wrong and good catch. I meant that the bow would probably pull about 53 lb at 31 in draw.
 I believe what I was trying to say is that if the bow still pulled 44 lb when drawn to 31 inches then it would shoot much harder that the same 44 lb pull drawn only to 26 inches.
 We are attempting to analyze how much is gained by adding inches, not lbs but we have to have a lb per inch figure to do that.
With my analysis, (right or wrong) agree or disagree. The 44 lb pull at 31 inches would shoot like you had added 8 or nine lbs more weight over the same 44 lbs pulled to 28 inches. I believe this is harmonious to what you are saying but I did not make myself very clear nor am I completely sure that the figures are exact. The added three inches of string time definately does add considerably to the performance without having to add poundage.
Now as to preload. The limbs can be built to have preload without having a high brace. You gain on the bottom end or brace end extra string time instead of tacking it on with a long draw. This increases the efficiency of the bow without adding extra poundage. It really helps all draw lengths but especially the shorter draws. A person with a bow with a brace of 7inches compared to the same poundage bow with a brace of say 9 inches , that has a draw of 26 inches will be able to have the performance that they normally would have to draw 28 inches to get.

God bless you, Steve

[Lee Robinson .]

As far as how much weight the bow gains per inch of draw...that would depend upon a few things...

1. Design (recurve, longbow, r/d hybrid, amount of backset/string follow, tip angle, etc),
2. core to width ratio
3. carbon or not
4. trap style (IME a rev trap draws smoother than the typical belly trap),
5. bow length, and
6. riser length

All that said, most bows of that pull weight would gain between 2.5# to 3.5# per inch with the better ones being on the lower side.

Now, that said...let's say your bow is 55#@28 and 64#@31", you are going to get way more velocity than a bow of the same design that is 64#@28" draw. I suspect this is where the 1" of extra draw equals about 5# of extra draw weight at the same draw comment comes from...although I would venture to say it would be equal to even more than that.

[Troy Breeding]

You can bet for sure that if you had two shooters with different draw lengths shooting the same weight the longer draw would be faster.

Longer powerstroke is a big advantage.

Troy

[buckeye_hunter]

Cool.

I always wondered if I would be better off getting a set of 45 pound limbs @ a true 29in  vs 53# limbs drawn to 28inches....

[jamesh76]

pretty interesting thread, but it has too many variables and gives me a headache thinking about.

[Ray Lyon]

I believe that the technical answer is going to be different with each bow and that you have to look at the "area" of increase under the force draw curve for the additional stored energy under the draw force curve for each inch of draw. As noted above, this is going to be different for each bow and the draw length for that bow. If you look at the graph that's in Blacky's bow report article in each TBM issue, you'll see what I mean. I wonder if Blacky has an average that he could share with the class?