Power stroke?

[knightd]

I will just have to agree to disagree..

[Marc St Louis]

 

Here is a FD curve that shows what I am talking about.  This is not one of my bows but rather it's a FD of a horn bow that I copied from another site.  As you can see this bow pulls 80# @ 25" and the guy has overlapped 2 brace heights, a 6" brace and a 7" brace.  Peak draw weight is still the same at both the 6" and the 7" brace height but at the lower brace height draw weight builds faster then tapers off while the 7" brace height climbs at a steady pace till both merge at 80# @ 25".  The higher draw weight at the beginning of the draw boosted performance.  The same principle would apply with a bow that pulls the same draw weight but a lower draw length.

[attachment deleted by admin]

[Kegan]

Thanks for the visual aid Marc

[Marc St Louis]

David
I see from your deleted post that you still don't understand the way the energy is moved around through brace height and design.  I have said before that to be able to see more clearly you need to look at some extremes.  That 27" draw bow is very close to a 28" draw bow so the differences are very small therefore harder to see.  If you were to take that 22" draw bow I mentioned above and make it so that you could shoot it with a zero brace height, this would give you the same power stroke as a 28" draw bow with a 6" brace height, then you would see a considerable boost in performance.  That jump is due to the fact that the bow has to make the same draw weight inside a 22" draw, the draw curve has a much steeper climb than a 28" draw bow.

How would such a bow's force draw look like?  The first inch of draw would show a tremendous jump in weight which would then level off for a few inches before starting to slowly climb again at a steady rate.  I know this because I have done the test to prove it.  This is how the 22" draw bow would make use of the stored energy in the limbs that is usually lost bracing the bow.  In essence that 22" draw bow would behave much like a 70# @ 28" bow because the projected draw weight of this bow at 28" would be approximately 70#, figuring 2.5#/".  A 55# @ 28" just can't compete with a 70# bow, everything else being equal

If you don't believe me then do the tests.  It's not that hard to do

[knightd]

It's not hard at all to do the test and I have on over 100 bows and 15 to 20 different designs.. On the subject of power stroke  if you take the chart you posted and use the lower brace height but hit 80# at 24" this will change the curve to be the same as the higher braced bow at the 1" longer draw..giving the designs being the same
 If you have done the test then you should also know that if you have 2 bows with same brace height and design with 1 reaching 50# at 27" and the other reaching 50# at 28" it is impossible for the shorter drawn bow to store the same or more energy than the longer drawn bow..
 I know there are others who share the knowledge and have done testing.. That see your side and some who see my side..But if we didn't test and try new things we would we never move ahead..
 
P.S. I deleted the post because I was willing to Agree to Disagree..But a healthy debate is good sometimes..

[Badbill]

Wow, You read the guys deleted post! Then used it in your post, to argue after he agreed to disagree, and let it go. I thought that the reason to delete a post was because you decided to NOT post that, and wanted to retract it, for whatever reason. Its kind of disturbing that you can read the deleted posts at all. Are p.m.'s really private messages?

[Hillbilly]

Y'all are making my little pea-sized brain hurt. If power stroke is so important, why do we stop at 28"? We could all learn to draw 36" and have better F/D curves. I think we already determined that 26" is probably a more realistic average draw length. My draw length is what it is, so I just try to make decent bows that shoot good for me and shoot them how I shoot them and don't worry about it too much. 

[Kegan]

David
I see from your deleted post that you still don't understand the way the energy is moved around through brace height and design.  I have said before that to be able to see more clearly you need to look at some extremes.  That 27" draw bow is very close to a 28" draw bow so the differences are very small therefore harder to see.  If you were to take that 22" draw bow I mentioned above and make it so that you could shoot it with a zero brace height, this would give you the same power stroke as a 28" draw bow with a 6" brace height, then you would see a considerable boost in performance.  That jump is due to the fact that the bow has to make the same draw weight inside a 22" draw, the draw curve has a much steeper climb than a 28" draw bow.

How would such a bow's force draw look like?  The first inch of draw would show a tremendous jump in weight which would then level off for a few inches before starting to slowly climb again at a steady rate.  I know this because I have done the test to prove it.  This is how the 22" draw bow would make use of the stored energy in the limbs that is usually lost bracing the bow.  In essence that 22" draw bow would behave much like a 70# @ 28" bow because the projected draw weight of this bow at 28" would be approximately 70#, figuring 2.5#/".  A 55# @ 28" just can't compete with a 70# bow, everything else being equal

If you don't believe me then do the tests.  It's not that hard to do

Marc, would the leverage of the limbs explain some of that early build up for lower brace bows (as in, the stirng has to pull the limbs from striaght- more leverage than having to pull on already bent limb tips)?

[Marc St Louis]

It's not hard at all to do the test and I have on over 100 bows and 15 to 20 different designs.. On the subject of power stroke  if you take the chart you posted and use the lower brace height but hit 80# at 24" this will change the curve to be the same as the higher braced bow at the 1" longer draw..giving the designs being the same
 If you have done the test then you should also know that if you have 2 bows with same brace height and design with 1 reaching 50# at 27" and the other reaching 50# at 28" it is impossible for the shorter drawn bow to store the same or more energy than the longer drawn bow..
 I know there are others who share the knowledge and have done testing.. That see your side and some who see my side..But if we didn't test and try new things we would we never move ahead..
 
P.S. I deleted the post because I was willing to Agree to Disagree..But a healthy debate is good sometimes..

David
Much easier to move the higher braced curve over to a 26" draw at the same draw weight.  Wouldn't prove very much though because the whole curve would be affected, as in depressed.  Still if you do that you would see that the lower braced bow would have a fatter FD curve but it wouldn't be by much.

But we aren't talking about 2 bows with the same brace height.  We are talking about bows with the same power stroke.  That's why I used the 22" draw bow with a zero brace height as an example.

Debate can be good

Bill
I don't know if a PM can be read by a mod.  All deleted post can be read though as they are temporarily stored and a post can be read by anyone before it is deleted as well. 

Kegan
Good question.  Possibly.  On the other hand a bow limb that is already bent has energy stored in it so it will be harder to bend it more.

Anyway I can see that this debate seems to be disturbing to some so I won't make anymore commenst on it.

[Hillbilly]

Bill-no, PMs cannot be read by moderators.

[billy]

POWER STROKE???  Well hell, I've got an osage longbow that's 42 inches long....and I draw that little booger 32 inches!!  It pulls about 45 tons.  Talk about a power stroke!  James Parker, The CIA, even President Obama are constantly calling my cell phone trying to see it so they can buy it off me.  Hell no I say!  I use it to shoot at the space shuttle when it comes in for landing, or jetliners that are cruising by at 30,000 feet.  Obama doesn't like it when I send arrows screaming by the cockpit of Air Force One....cause my arrows are flying Mach 32,000 and the shock wave always cracks the plane's windshield.

One time I shot it at an oak tree....the tree instantly vanished cause my super warp speed arrows turned it into powder...instantly!  I can't shoot at deer cause it vaporizes them.  One time the neighbors below me were raising all kinds of hell, making noise, partying, and smoking the funny stuff.  Well, I'd had enough so I just shot an arrow down through the floor, it exploded when it got below my floor and all the people who were making noise suddenly disappeared...no blood, no fingerprints..nothing.  Just VAPORIZED THEM!!   The feds could never get me for homicide cause there was absolutely no evidence.  Yeah, that's right ya govt yo-yo's...ya'll couldn't get me and you never will!  Hahaha   

[DanaM]

This is a good debate guys, I can't contribute to it but I am learning from it especially since a I have a short 24" draw which
makes it tough to build a bow matching the performance of a longer draw.

billy thats funny but somehow I think someone will find it offensive Go figure eh

[DCM]

Marc, and others, have helped me through being entrenched in horribly muddled thinking on a number of topics.  And I would hope my comments over the years have helped foliks see things from a different perspective.  It's very difficult sometimes to really entertain a topic thoroughly and objectively while trying to support an opposing view at the same time.  Usually a break from it for days or weeks can break the log jam.

Such things as the physics of the bow and arrow in this context need not be based upon conjecture, and certainly not by popular vote or "who is right."  There's only one "right" answer, from the scientific pov, but unfortunately infinite ways to describe it in laymans terms. 

More often than not when discussions go on for days and days something is being missed, one side or both aren't actually commuinicating to the other.  In such cases it's pointless to keep drumming away.  Better to hang up and dial back later, perhaps securing a better "connection."