Long bow tweak- Test results in

[Kirkll]

I’ve been building these TD long bows for quite a few years using the same taper rate and wedge configurations with good end results, but like most bows, once you drop down in draw weight past 42# the performance starts tapering off…. All of my designs do this, and I think it’s the just the mass weight of the limb tip to preload ratio. Lower draw weight  = lower string tension.

So I’ve got this 40# bow going here that is only to be drawn 28”, and decided I’d like a bit more horsepower. I started out by using some higher yield core material and put a couple paduke cores in the stack. The outer cores are thinner bamboo lams. This paduke material always adds a bit of snap to your limbs.

The second thing I did was use an inch longer wedge to push that working portion out a bit and shorten it up….. I was a bit hesitant to do this at first, but judging by the way she’s bending, and the string angle, I’m pretty happy with the results. I definitely got a better string angle on this D shaped limb design.

This is a sneak preview of the first time on the tiller tree. She is within an 1/8” of even tiller, and about 8 pounds over weight here. Perfect draw weight for what I have in mind. I’m going to narrow up these limbs to deep core skinny whips to get my draw weight down to 40#.  I’m definitely going to get some test results on this one and log my numbers for future reference.

I did manage to get the tip overlays done and some profile reduction yesterday. More to come as she comes together.   Kirk

[Roy from Pa]

Those tip overlays are very sharp.....

 

[Stagmitis]

Hey kirk it makes sense that lower weights have lower preload- But why do bows submitted for speed testing always seem to hover at 50# and not higher?

[Kirkll]

I've tested 100's of bows over the years, and the highest yield bows per pound of draw weight seem to run from 53-57#s between 28-30" at 9 gpp and 10 gpp on my established limb designs without tweaking them. That's just using std cores like maple and bamboo combos.

 I can get higher speeds messing with cores and backing, and running deeper stacks with narrow profiles,  but i like the consistency of the maple /bamboo i get and also longevity, and i don't mess with carbon backing any more.  So i pretty much stick with the consistent stuff and standard width profile for the most part. Over 60# it doesn't improve, but dropping below 50# it always tapers off.


I think the higher performance at 53-57# and even up to 60# has a lot to do with mass weight of limb to preload ratio. But your mileage will vary a lot depending on your limb design/shape, taper rates, and wedge configuration.   Some designs perform much better at longer draw lengths than others too.

Manipulating where the energy is stored in the limb, and the length of the working portion storing that energy makes a huge difference on over all performance.  The preload that stops the string dead is what regulates how much of that stored energy gets transferred to the shaft. 

My strategy on this bow is to pick up some performance in a lighter draw weight at only 28".  This limb design typically puts out better #s at 30" draw length, but slows down a bit with the same GPI arrows at 28"..... So i shortened the working section, used stiffer core lams, with a deeper stack than needed to hit weight so i can cut mass weight off the limbs with a narrow limb profile.

  I'll let you knw how this one comes out.  I haven't done any testing in awhile. I'll have to blow the dust off my hooter shooter and replace the batteries in my Chrono.  LOL     Kirk


PS.... If you want to build a hot rod just using glass sometime, build a 53-55# long bow using .030 glass with a deep stack & narrow profile. I wouldn't advise this on a recurve design though unless you incorporate some bias weave carbon into the core... Stability is a huge issue with thin glass backing.... I haven't build hot rods in years, but it was fun blowing stuff up going for the gold. 

[Mad Max]

I like it

How thick are the Padauk parallels?
I bought some Padauk a few months back, the first overlay I cut at the band saw and bent it with my hands and it broke in the middle. 

[Kirkll]

Yup…. It’s pretty brittle material,Very similar to Wenge. But if placed in the core between a couple other lams it holds up fine if it isn’t drawn too far. I’ve got two core lams about .060 dead center with two of these fossilized bamboo lams belly and back about .064 . With  40/40  glass. Total stack is 308 at 10” from the butt. Or .348 at the butt.  .004 FT , 12” wedge, 8” tip wedge with about an inch clipped off the tip, and 1/2” clip off the butt coming out of the form.

I’ve cut the working portion down about 1.5” in length and pushed the fade tips out almost 2”. I like the way she.s bending, and she’s lean and mean. This 64” bow is going to stack at 31” and could blow up at 33”. But…. It’s designed for a 28” draw.

I’ve got her balanced out at about 41 @ 28” right now, and have the full overlay portion going on the riser right now. Tomorrow she comes together and gets shaped for shooting. I’ll test this thing prior to finish sanding and spraying clear coat so as not to ding it up.    Kirk

[Mad Max]

Cool

[Kirkll]

One other thing I forgot to mention…. When you spend time with an in-line scale measuring preload tension at brace, the tension increases as the brace height lowers. But you can only lower a brace height so much before it becomes a problem with that string hitting your arm.   This is why when you are prototyping limbs, you should do it with an unshaped riser block, or and adjustable riser, and then measure the deepest part of the grip from the string and mark the riser at 7”.
This gives you a bit of room for brace adjustment from 6 3/4 - 7 1/4” and plenty of arm clearance.

With this full overlay design, I can get a 5/8” lower brace and better preload on the limbs because I’m moving the grip forward the thickness of the overlays that give me the flush limb pockets. This is going to help out boosting performance on this lighter draw weight bow.   I’ll brace this at 6 3/4” most likely.

  Kirk

[Shredd]

What was the average performance of your 50 plus lb. bows and what is the performance of your 40 lb. bows with the same exact layup...  What is the goal to reach speed wise for your 40 lb. bows??

[Stagmitis]

Gotcha, so its the mass limb weight in higher poundage bows that begins to limit performance-So when you say narrower profile and deeper cores what width at the fades are you talking about?

[Kirkll]

This particular long bow design has always tested a bit faster at 30” draw than 28” and shows a bit more horsepower at about 52-53#. Conservatively speaking I’d say an average of about 188-192 at 10 GPP. But occasionally I’ll get a hot one that that would go 194-196 that came in over weight, and had a lot of sanding and trapping to lower the draw weight. You can typically add about 5 FPS with 9 GPP arrows. The only way I could ring the 200 FPS bell with this design was using uni carbon backing. But I have come close a few times just using glass with zebra wood, paduke , hickory, and Wenge core materials. All of these materials have a stiff brittle nature and should be avoided in recurve limb designs with shorter working limbs, and never used on the belly side next to the glass. The D shaped long bows do not stress the core materials as much and the compression is distributed differently.

When you push one to its limits until she blows, it’s typically a delamination between the glass/carbon on the belly side due to compression failure of the belly lam. That’s why rock hard maple rules for belly lams.

But with that being said….. you can, and will get different results building identical bows. That is one I never could comprehend.

This one has an 1 3/8” riser pad width and is about 1.20” at the fades with a straight taper to 1/2” tips. The belly side is trapped by eyeball at  about 5 degrees from the riser to the tips and the edges eased over with sand paper.

What I’m hoping for is that between the shorter working limb length, the stiffer light weight cores, and narrow limb profile reducing mass weight….. I’ll get a higher performance at a lighter draw weight.



Kirk

[Shredd]

You said , "a bit faster at 30" draw than 28" draw"...  I assume the 188 to 192 fps is at 10 gpp at 28" draw...  Is that correct??  If so those are hot numbers and hard to touch with a longbow...

[Kirkll]

My hybrid long bow has done pretty well over the years. This little film clip is 10 years old. This is a 60” Sasquatch hybrid LB

   

[Longcruise]

My hybrid long bow has done pretty well over the years. This little film clip is 10 years old. This is a 60” Sasquatch hybrid LB

   

Ok, let me clarify first off, In fact emphatically clarify, that im not in any way pooh poohing your bow.  But it would be more meaningful,  at least to me, if it were a 10 GPP arrow at 28".  OTOH,  it appears that the vid was made for a specific customer and shot as they would shoot it so it's completely appropriate.

[Kirkll]

I’m not sure where the 10 GPP @ 28” testing standard really came from. Does anyone here really know?  Years ago it was 9 gpp at 30” draw if I’m not mistaken. 

When I test a bow these days,  it’s typically at the draw length my customer has.
Funny thing is …. In the last year or so I’ve built more bows with a 30-32” draw requirement than 28”.

I’m curious why it would be more meaningful  to you at 10 gpp @  28”?

Kirk

[Mad Max]

I always thought 10GPP@28" was standard so that comparing was the same

[Stagmitis]

Kirk not sure when it started but I think WTT solidified the standard using 10gpp @ 28" as a measure for testing-Not sure I have seen any bow go over Kens 199fps @ 28" and 10Gpp since then.

From that event forward it has been meaningful to me to compare each others bows using that standard.

I remember years ago chasing speed in my hills- I built a 56# bow with 3/4 backset that shot 196 fps consistently but i used a VERY light arrow....Today that speed i meaningless to me..

All that being said I don't care much for 10gpp arrows and prefer anywhere from 8.5-9 gpp. Thats just a personal thing.

[Longcruise]

I’m curious why it would be more meaningful  to you at 10 gpp @  28”?

Same reason as Max and stag.  But, testing to the customer's specs makes a lot of sense too.  Most customers are probably not able to test it themselves.

I test at 28"/10gpp just for consistency in my own record keeping.

Come Sept 2 though I'll be holding 45# and shooting 645 grains.

[Kirkll]

I was just curious if anyone knew where they came up with that standard. WWT was a fun event. I remember getting stuck at the airport coming home in Milwaukee Wi due to a massive thunderstorm. They shut the airport down.

The chronograph is a valuable tool for bowyers prototyping limbs and tweaking a design. But the dad burn things can cause problems with customer’s expectations too. The lighting itself can cause different readings outdoors, and measuring exact draw weights and arrow weights can creat misleading results. Using a shooting machine with a light kit and never using fluorescent lights indoors make a big difference too in consistency. The biggest issue I’ve seen over the years is people getting different results shooting by hand. 3 different guys shooting the same exact bow will get 3 different numbers…

After getting my bow designs established years ago, I got away from doing much testing. And I got tired of the thrill of victory and agony of defeat routine building hot rod carbon backed bows after awhile. Ringing the 200 FPS bell is tough to do at 10 gpp 28” draw length, but I’ve had a few bows do it at 30-32”  just using glass.

About 10 years ago, Steve Tallant and I played with some excellent grade bias weave carbon with foam cores on recurve designs. That’s when I came up with my SS recurve design btw…. We both came up with some crazy fast bows doing that, but the longevity of those hot rods just were not there, and those foam core bows were loud. I think the glass spheres broke down over time after thousands of shots.

But it’s kind of fun going into mad scientist mode now and then seeing what you can come up with if ya have the time.

We had a 110 weather yesterday here, and the shop was an easy bake oven even with the big fan blasting…needless to say I didn’t get much done.     Kirk

[Shredd]

   I'm kinda lost here, Kirk...  Seems that you skipped over my question and got a video up of a hybrid bow speed test with numbers that most of us are not familiar with... I thought we were discussing improving performance on your longbow?? I asked those questions to get a simple baseline as to where you are starting from and where you want to end up...  I thought my question was important as to have a solid starting point...  So I will ask the questions again... You don't have to but if you want most of us to understand where you are going please use the 10 gpp @ 28" draw method otherwise the numbers you post won't have any value to most of us...

What is the average arrow speed of your 50 plus lb. bows @ 10 gpp and at 28" draw and what is the arrow speed of your 40 lb. bows @ 10gpp and at 28" draw with the same exact layup??  What is the goal to reach speed wise for your 40 lb. bows??