Primitive Archer
Main Discussion Area => Bows => Topic started by: duffontap on May 03, 2007, 12:08:03 am
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Perhaps some of you aficionados of bow design and performance could explain how the piggy-back bow fattens up a f-d curve? I've been thinking about this for a while and I can't really figure it out. Is it just harder to brace? Does the little bow reverse the effect of string follow?
Curious.
J. D. Duff
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Josh
I made one a few years ago but did not find the performance increase that everyone says they are supposed to have. I made mine as close to an actual replica as I could, did use modern strings for it though. The FD curve gets moved around a bit but that's about it. The only advantage that I could see is that the small bow did seem to lessen set a bit.
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Its a tricky design to produce, thats for sure. You want the little bow bend early in the draw, and then as its string pulls tight to the back what you find is the big bow limbs get stressed more at mid-limb than it would without the little bow. So you're drawing two bows, and changing the stress on the big bow all at the same time. The hard part is figuring out what dimensions to make the little bow. You want some reflex because that will give you some amount of bending wood, and the relative length of little bow to big bow is going to change how soon you get to "full draw" on the little bow, at which point it sort of becomes a cable-type backing for the big bow. Plus you want the little bow to be fairly stiff, so it doesn't "max out" too easily. YOu want it to be pulling against you for most of your draw. Then you have to properly tiller the big bow so it has a decent bend, which I'm told comes down to making it stiff at mid-limb before you add the little bow.
I've never tried one, I personally think they look kind of clunky. But they do have interesting physics.
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Thanks guys,
Have you read the back-issue articles on the Penobscot bow? I think there are three. People keep talking like there's this amazing jump in performance but I don't see where the magic could be stored. I saw a F-D curve online the other day and it looked like it gained 3 lbs. per inch from 13-27" and gained 4 lbs. in the last inch. That doesn't seem revolutionary.
I thought it would be interesting to replicate one but if I'm facing the prospect of dozens of failures and average performance, I think I'll pass.
I would like to see a picture of your bow Marc.
J. D. Duff
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What the F/D curve doesn't tell you is how much wood it takes to make the poundage. It is likely that the poundage is being made with less limb mass, thus a greater increase in performance.
I read those articles, and spoke with a fellow out East that specializes in the things (I think he wrote one or more of the articles). I forget his monicker, it was ironwood or something with Iron in it. I was interested for awhile, but never enough to actually tackle the project. I just don't see myself shooting one.
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What the F/D curve doesn't tell you is how much wood it takes to make the poundage. It is likely that the poundage is being made with less limb mass, thus a greater increase in performance.
Good point. Did you see Lost last night?
J. D. Duff
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No, I've been busy packing stuff for our excursion down to the TN Classic archery tournament. I usually watch the show with the wife though. Did they have archery or something?
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Same for me Marc. My FD curve looked about the same as the ones from my standard bows, but the design does have it's advantages. My main bow pulled 48#s by it self, but with the back bow attached the weight could go up as far as 68#s. But no matter what that main bow's limbs are still only feeling 48#s of stress, which let them hold 1/2" of their original reflex once broken in. Pretty amazing to have a potential 68# bow that is just over an inch wide and only 62" long that can hold a decent reflex! But that's about the only huge upside to the design I could find, that and it's cool to have a bow with a wide weight range to it.
Dan
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Lennie,
Two guys with the alias 'Tom Sawyer' talk about how girls like the name. Ha, ha. Now I know why you chose it.
J. D. Duff
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Interesting Dan. Maybe I should try one. Could one of you guys post the replica you built?
J. D. Duff
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Oh yeah, chicks dig it.
I took it because I live in Hannibal though, and I specialize in getting other people to do my work.
I think I disagree that the 48lb bow is not feeling extra stress as a result of the back bow. It isn't feeling a full 68lb, but it is getting squeezed in a different way when the back bow is in place. Just how the stress is distributed, depends on the geometry during the draw.
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Lennie,
Would you say the back bow moves the neutral plane forward, putting the belly bow under more compression and less tension?
J. D. Duff
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Eh, whatever...just a cool bow design as far as I'm really concerned. I tend not to care why they work they way they do and simply focus on weather or not I'm happy with my latest baby. All I know is you can't build a normal bow that pulls 68#s at 28" an inch wide and 62" long and have it hold reflex like this.
Dan
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Nice bow! Thanks for posting, but I must say that deserves a separate thread. You should post it so it can be eligible for bow of the month.
J. D. Duff
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Lovely bow Bowmo my hats off to you , I have made two Penobscots admittedly bamboo backed and although both have been light draw weight 45 # and 35 # both needed to shoot arrows approx 15 pound above there draw weight whereas my selfbows usually need 15# under . The 35# has the best cast shoots a 550 grain arrow very well , the short bow was more reflexed . I theorised the back bow raises the neautral plane , in effect a raised cable backed bow . interrestingly the 35# bow is around an inch wide tapers to 1/4" nocks and took no set , seems to match your observations . Next penobscot I make will be useing your bow as a referance , I was awake to the big reflex required in the short bow but was not sure just how much , I am very impressed . regrds Perry
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Nice bow! Thanks for posting, but I must say that deserves a separate thread. You should post it so it can be eligible for bow of the month.
J. D. Duff
hi guys! - yes PE-LEEEAAAASE! - a penobscot-thread would be great; this thread already had new info about the design. thanks!
bowmo! - that's a really nice bow!
question: would this be considdered a 'selfbow' or a 'backed bow'?? 8)
frank
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Good question Frank, I think its a selfbow as long as both bows are one piece. If someone
makes the bows for instance boo backed then we have a backed bow.
Actually I think its really a type of early compound :o ::) :-[ :-\ :'(
DanaM
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Actually Dan's Penobscot was included in a BOM vote before, last year I believe.
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the performance comes from the compound action of a properly made penobscott. meaning if you had someone who is very good at math you could figure out the right geometry to make a bow that literally lets off something like a modern compound. i think this design is very complex and would take some r&d to make anywhere near potential. perhaps a penobscott with recurves that lift off just as the strings of the back bow start to wrap onto the limbs........ just a thought
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Is it possible for penobscot bow to be Perry reflex?
I do not mean by gluing 2 pieces of wood together to make the arcs, which of course can be done,
but by using the small arc to draw the long arc backwards when not pulled.
Or is this actually the normal way to make such a bow?
I mean this design is too complex for just making the bow narrower, a non bending handle is easier to make and to invent.
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I guess I was the one who got this Penobscot bow stuff started with my first article in Primitive Archer. It seems to me that I should explain how the bow works.
At brace height the string angle between the back bow and the main bow is very shallow. This means that there is little mechanical addvantage that the main bow has when drawn to bend the back bow. As the bow is drawn the tips of the main bow do not bend back very much at first. The string angle on the back bow forces the main bow to shorten putting strain (stored energy) on the lower and mid limb areas of the main bow. Once the main bow tips bend enough to create enough mechanical addvantage (String angle between the back bow and the main bow) the back bow will start to bend. It is at this time in the draw where the force draw curve will flatten out.
I am in the house not the shop now so I can not give you the issues of Primitive archer my articles on this bow were in however I will post them in the future. By the way if you read the articles ignore the tillering info there is a better way o do it that I will also explain.
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Thanks for reviving this thread. ;D
I've made one penobscot bow of ipe (both parts) for my nephew. Both parts are self bows and are D-bows with no reflex. The bow has a surprisingly long draw and the ipe does not seem to be stressed very much. I need to go back and take measurements....I made it back before I read the bowyer's bible series.
As far as I can tell, the originals were made of hickory with rawhide strings. And the smaller bow barely bends at all. I don't think it behaves like a cable-backed bow because those bows depend on the springiness of sinew.....rawhide is not nearly as springy.
When I built the bow, I noticed it could be left strung for long periods without loss of power. I think that is the main advantage....that and the fact that you can make the bow more narrow than a regular D-bow.
I'm going to build several more this next year (cross my fingers) and I should be able to give a more educamated opinion later. ;D
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i have wondered about this too. the neutral plane argument seems reasonable enough, but that would mean that the mini bow isnt adding anything that a thicker bow, or some other backing, wouldnt add. the design is certainly harder than a cable backing, so why not just use a cable backing?
this is just a thought, i have not made nor have i studied any of these bows myself. however, i was thinking that based on microscopic reversibility, the micro steps you take to get from A to B are the opposite of the steps from B to A-what goes up comes back down in a symmetrical fashion. The mini-bow flattens out against the big bow early in the draw, and at that point it can add weight but it seems liek it would be stacking weight-in other words it shouldnt add much in energy storage. the big bow doesnt start to bend at all from the tips until relatively late in teh draw. this means that the bow tips of the big bow would stop moving early in the release as well. as the opposites all happen, the tips would hit home well before the string is finished moving forward thrusting the arrow. the little bow now starts to pull off the big bow and snaps the string taut using the long bow tips as leverage. it would be the energy storage benefits of a short bow with a longbows mechanical advantage-same idea as a holmegaard. the energy curve would be steep early in the draw as you pull the short bow into stacking mode but that would be translated over a longbows length, so late in the release you should have the same steepness of energy released. SOM
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wow you guys rule if someone would get me in the right direction i can get halp from my math teacher and physics teacher and we could form a hypothetical model of the best way to make a "recurve compound." i think it would be sweet
will someone make a flash video/slideshow of how the draw is supose to work like how son of massey described it. that would be way cool and a easy to grasp. i want to make one >:D >:D >:D >:D >:D >:D
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If you people want to read the articles I wrote on the Penobscot bow for Primitive Archer they are in volume 3 issue 4,volume 5 issue1, volume 5 issue 4, volume7 issue 1.
Did you know that there are six distinst variations of the Penobscot bow which should in reality be called the Abnaki bow as the basic design was found with all the members of the Abnaki Confederacy. Probably the most distinctive variation was with the Micmacs, this is also the only Penobscot variation that was specifically a war bow. (If you go to Web shots you will find pictures of these bows) Reasearching these bows has been lots of fun and shooting them even more. One hint that I have found is to tiller the main bow to what ever you want for a final draw weight. After you have done this then add the back bow and retiller until you get back to your desired draw eight.
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From what I understand...
The main bow is about 10-20# less than the bow's final weight. It doesn't feel all the extra stress because the smaller back bow does. It is, in effect- well overbuilt without all the extra mass. Which Comstock and Baker and anyone using Osage has discovered. The smaller back bow is pretty heavy and should be highly reflexed or stiff (to give it lots of power), to give it the desired weight. If it's wayyyyyy too overbuilt, it doesn't matter so much, because it's jsut a weight-adder, and only functions in small movements. It's close to the handle, and therefore doesn't have to slow the arrow.
What all this adds up to is a bow with the phsycial weight of just slightly more than, say, 40#, but shooting with the power of, say, a 60# bow. It's mroe of a primitive sort of fiberglass than a primitive compound (which is why it shoots heavy arrows better- all that extra energy with less mass, instead of just mechanical leverage without storing mroe energy).
DANG IT- NOW I WANT TO BUILD ONE!!!! ;D
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As to why this design was used, could it be because of the wood/materials they had to use ie...poor quality wood in tension? Or compression? Just curious, maybe it wasnt to build a better performance bow...but just a bow that would survive..just thinkin out loud...maybe we should build this bow from willow or doug fur and see what happens ;)....Brian
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As to why this design was used, could it be because of the wood/materials they had to use ie...poor quality wood in tension? Or compression? Just curious, maybe it wasnt to build a better performance bow...but just a bow that would survive..just thinkin out loud...maybe we should build this bow from willow or doug fur and see what happens ;)....Brian
Hickory in the North East. The semi- green hickory would have pretty poor compression strength by comparison. Which would be a perfect example of my delusional ramblings ;D.
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;D Sorry, aint familiar with the history of the P. bow...I just remove wood till it bends or breaks,lol....Brian
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so would it be possible to have a super heavy mini bow and a light say 35 pound bow and reach a weight of like 60 with very little mass on the large bow and it is all on the small one. i guess what i am asking is what are the limits to this cool design and does anyone have some good web pages on this stuff.
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so would it be possible to have a super heavy mini bow and a light say 35 pound bow and reach a weight of like 60 with very little mass on the large bow and it is all on the small one. i guess what i am asking is what are the limits to this cool design and does anyone have some good web pages on this stuff.
I built one when I started into archery. I built a recuirved D bow that bent WAY too much in the handle, and only drew about 40#. Well, I jsut attached a little bow to the back and bount it all together. Jumped up to a sweet little 60# flinger. I was pleased as punch :).
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The people who built the Penobscot bows seemed to under stand "Bowology" It appears apparent that they knew that there are two to make a bow shoot "harder". One way of course, is to increase draw weight. This is the route that the English took with their long bow with weights reaching as high as 150 pounds. The second way is to make you work harder drawing the bow during early and mid draw with the final draw weight remaining the same. This is the idea behind the modern compound bow and it seems that the members of the Wabanaki confederacy realized this over 1000 years ago.
When drawing a properly designed Penobscot bow one will find that the draw weight climbs very fast until a bit after half draw, then the weight climbs very slowly up to full draw. On my reflex deflex bow from 20" to the full draw of 28" it gains only two pounds per inch. When Dean Torges tried my static recurve Penobscot in Coudersport, he asked me what it gained as he drew the bow several times. Not sure what he meant I asked him and he replied. "From about half draw on it feels almost as if it has let off like a compound." I was very pleased that he had noticed the same thing about these bows as I had and it was not all in my head!
Going to that Penn. shoot was one of the highlights of Barb's and my life. Steve Hulsey invited us to set up at their tables with Primitive Archer Magazine and we got to meet so many great people such as Gary Ellis, Dean Torges and so many others. Thank you again Primitive Archer for the opportunity.
The following year I came down with R.A. and it was 8 months before I could even dress myself. Archery was out of the question and my weight dropped from 165 to 130. Thanks to Remicade and great doctor I am once again able to shoot a bow and get back to doing the research I love on the Penobscot Bow. But I can't post a dam picture, help what am I doing wrong? However all the pictures and force draw curves are at webshots under my name so you can still see them if you want.
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If this picture comes out it will show 3 variations of the Penobscot bow. Top is a static recurve next a reflex deflex and the lower one a slight recurve, this is the bow that was on the cover of Primitive Archer Magazine. The silencers on the top bow are Turkey feathers striped and wound onto the string.
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/3variationsofthebow-1.jpg)
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Judson, I had thought of the turkey feather thing, and put them on a string, but didn't know if they would work. I guess they do, huh? ;D
Sean
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beautiful bows judson. now why are the mini bows not recurved i thought that was part of the design.
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When the bow is not strung there is some recurve to The back bow. The Micmac variation of these bows is very highly recurved to the point of lookinc sort of like a "C" when unstrung. On thing sort of intresting about the Micmac bow is that unlike the rest of the Penobscot bows where the draw weight climbs very fast thenlevels out the Micmac version is different. The Micmac bow has no stack or drop off in the draw weight. For example on my bow the draw weight gains 3 pounds per inch from brace height up to full draw and 65 pounds of weight. This is the bow I am talking about I will try to post a picture of it un strung.
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/IMG_0131.jpg)
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/IMG_0135.jpg)
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This is a force draw curve graph comparing several different bows the two solid lines are from a static recurve Penobscot bow set at 60 pounds and at 65 pounds. The dotted lines show the force draw curve for a 55 pound flat bow and the one that drops off is the curve for a Martin Warthog 60 pound compound. As you can see from the graph the Penobscot bow stores the most energy. The numbers to the right of the graph are the # of squares below each line representing stored energy.
(http://thumb8.webshots.net/s/thumb1/5/92/84/72559284GeGAmA_th.jpg) (http://home-and-garden.webshots.com/photo/1072559284045906888GeGAmA)
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Here are a few more pictures of the Micmac bow. This is the only version of the Penobscot bow to be specifically a war bow it is also the most recent design. This is the bow at full draw
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/MicMacBow.jpg)
Details of the upper nock carved as a wolf's head.
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/IMG_0133.jpg)
This the gliding nock on the back bow I was told that these were of moose antler but I used deer since no body seemed to want to let me cut up their moose antlers. The next picture is of the horn nock down by the grip. Sinue was used to hold these in place on the origional bows. On this bow I used "A" thread which is the thread used to wrape guides on fly rods.
(http://i543.photobucket.com/albums/gg465/Judson127/Penobscot%20Bows/IMG_0134.jpg)
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Haven't tried one of those yet Hmmm. ;)
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This is a force draw curve graph comparing several different bows the two solid lines are from a static recurve Penobscot bow set at 60 pounds and at 65 pounds. The dotted lines show the force draw curve for a 55 pound flat bow and the one that drops off is the curve for a Martin Warthog 60 pound compound. As you can see from the graph the Penobscot bow stores the most energy. The numbers to the right of the graph are the # of squares below each line representing stored energy.
(http://thumb8.webshots.net/s/thumb1/5/92/84/72559284GeGAmA_th.jpg) (http://home-and-garden.webshots.com/photo/1072559284045906888GeGAmA)
Hello! Sorry for digging up an old thread, but I would be really interested to the draw force curves, wondering if you could possibly upload them again? It looks like they disappeared somehow. (tried pm:ing but it wouldn't let me)
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He's not a member on here anymore.