Author Topic: How do you explain the penobscot bow's performance?  (Read 68354 times)

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duffontap

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How do you explain the penobscot bow's performance?
« on: May 03, 2007, 12:08:03 am »
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

Offline Marc St Louis

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Re: How do you explain the penobscot bow's performance?
« Reply #1 on: May 03, 2007, 10:36:53 am »
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. 
Home of heat-treating, Corbeil, On.  Canada

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Offline tom sawyer

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Re: How do you explain the penobscot bow's performance?
« Reply #2 on: May 03, 2007, 11:09:11 am »
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.
« Last Edit: May 03, 2007, 11:11:51 am by tom sawyer »
Lennie
Hannibal, MO

duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #3 on: May 03, 2007, 01:35:00 pm »
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

Offline tom sawyer

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Re: How do you explain the penobscot bow's performance?
« Reply #4 on: May 03, 2007, 01:49:41 pm »
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.
Lennie
Hannibal, MO

duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #5 on: May 03, 2007, 02:15:21 pm »
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

Offline tom sawyer

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Re: How do you explain the penobscot bow's performance?
« Reply #6 on: May 03, 2007, 03:44:32 pm »
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?
Lennie
Hannibal, MO

Offline bowmo

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Re: How do you explain the penobscot bow's performance?
« Reply #7 on: May 03, 2007, 04:01:19 pm »
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

duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #8 on: May 03, 2007, 04:33:40 pm »
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

duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #9 on: May 03, 2007, 04:35:17 pm »
Interesting Dan.  Maybe I should try one.  Could one of you guys post the replica you built?

             J. D. Duff

Offline tom sawyer

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Re: How do you explain the penobscot bow's performance?
« Reply #10 on: May 03, 2007, 05:51:43 pm »
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.
Lennie
Hannibal, MO

duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #11 on: May 03, 2007, 11:28:03 pm »
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

Offline bowmo

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Re: How do you explain the penobscot bow's performance?
« Reply #12 on: May 04, 2007, 01:28:24 am »
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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duffontap

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Re: How do you explain the penobscot bow's performance?
« Reply #13 on: May 04, 2007, 06:58:01 pm »
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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perry

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Re: How do you explain the penobscot bow's performance?
« Reply #14 on: May 04, 2007, 08:09:44 pm »
    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