Performance quest!

[Apex Predator]

Let me say that I am not a speed freak, by any means.  

I am building my third hybrid off the same form.  The first was 60", the second 62", and the third (current one) is 64" nock to nock.  The first used two bamboo and one action-boo lam.  The second had four hickory lams.  This third one has two action-boo and two osage lams.  All have .040 clear glass back and belly.  All lams have a .001 taper.  I liked the profile on the first two but decided to use power lams up the belly ramp on the third to force the mid limb to bend more.  Here is the full drawn profile on the first two.

 

 

I used a .060 red elm power lam under the belly lam running up each belly fade ramp.  The power lams are 12" long and extend into the limb 5" past the end of the riser fade out.  The end of the power lams fade from full thickness to nothing in the last 6". It really smoothed out the bend right off the fades.

 

My performance testing was done on a shooting chrony.  I was using a finger release with a big shot glove.  I was drawing to a 28" mark on the arrows, and an assistant telling me when to release.  All performance strings were built with 12 strands of D-97, and had padded loops.  I was shooting as close as I could get to 10 grains per pound.  The last bow (64") draws 52@28 and I was shooting a 519 grain CE Heritage arrow.

The first 60" bow shot 170 fps.  The second shot 175 fps.  The third averaged just over 180 fps.  It was 176 with a 12 strand B-50 string.

If I went with fewer strands of D-97, used a shooting machine, and a mech release, I'm sure it would be close to 190 fps.

Comments?

[PV]

Good work Apex!

Moving the working portion of the limb out picks up some speed.
Heres a couple of pic's of my WTT bow short version. My WTT bow was 64" and these are 58" losing abit of net reflex but what I'm trying to show and not hijack your thread is the effect of taper and riser lenght. The bow on top(walnut riser) is an 18" riser with 002 taper
The bow under is 20" riser with 003 taper
Both bows have the same 7"tip wedges and 22"power lam.
 
Braced
 
 
Drawn
 
 

Both these bows are shooting within 1 fps of each other @10 grpp finger release
Same glass 040 back and belly
002 lams walnut and maple
003 lams maple and lacewood
The 003 taper bends slightly further out than 002 but shoots the same speed.
My WTT bow is 002 taper and all things considered i think that is the optimum taper for my form. Shoots abit smoother and a few fps faster than the 003 taper.

Your results may vary...........


     

[Peckerwood]

Could you show some close ups of the power lam ?

I am a little confused on the term.

Thanks ... Bill

Nice Work both of you guys.

[Apex Predator]

Here are some close ups.  The first shot shows the .060 red elm just below my .060 osage belly lam.  This power lam is 12" long.  

 

My finger is at the end of the power lam.

 

Here you can see it running out past the end of the riser fadeout.

 

[TNstickn]

Man thats too cool. Great work Marty, thanks for sharing.  

[wihill]

Would an addition length of glass allow the same performance gain without the mass of the lam?  

I've always wondered about that, essentially doing the same thing that you are now with the added lam, but with glass.  Did you just pick up a couple tapers, or did you sand them down yourself?  

I DO like the way that turned out, you turn out some smart looking bows, Marty.   :D

[Frank]

It looks like your bow design in perfect for the power lams and your performance shows this.

But what do I know, I build selfbows. You start talking lams and thickness and I hear, lalalalalalalalal............I just get a piece of wood and whittle.

You do build nice bows.

[Apex Predator]

Wihill,

The glass weighs much more than the wood.  Weight is not a big issue at that position in the limb though.  I guess you could use glass.  I made these on my Rigid drum/belt sander combo.  After getting a uniform .060 parrallel, I taped one end to a squared piece of stock and feathered the end to nothing.

Frank,

I started with selfbows and all wood laminated bows.  I've built a few nice ones, but also made a lot of firewood.  All of my fiberglass ones have been shooters.  It's much easier for me.  I do have a nice osage stave that is calling me though!

[sulphur]

marty that last profile looks really good.  sounds like it performs really well too. did you pick up and handshock??  also how much did you adjust your stack thickness with the power lams??

[kennym]

COOL!!

[Dmaxshawn]

Interesting and pretty darn cool as Kenny said.  Marty that seems to allow you to build a heavier drawing bow without much more total weight gain on the bow itself. Does it take away from the performance of the bow or will it improve it?  Also could one use phenolic here inplace of power wood lams or glass?

thanks Shawn

[Apex Predator]

I didn't allow for the power lam in stack thickness, but figure it added 6-7# draw.  You could probably use any material for this type of power lam, but wood is the lightest and easiest to make.  This bow has the least shock of any I have built, and I attribute that to the limbs bending in a perfect arch, the tips remaining straight, and perfect limb timing.

[Jesse Peltan]

That looks way cool. 180fps at 10gpp with fingers is pretty good. That would be around 190 at 30in with 10gpp. 195 with a release and shooting machine. If you added a skinny d-97 or 8125 you might be close to 200. At amo specs with a skinny string you could get 205fps. If you are going to ATAR I can make you a 8125thin skinny string with padded loops. You have a very fast bow.

[TradBowyer]

Great job Marty. I"m trying something similar but just messing with the overall lam taper for right now adn see how that does. When I first started designing limb profiles, the line of thought was that the closer the limb bent to the riser, teh faster it would shoot heavy arrows. I'm not so sure that is true now with the testing i've done and others are doing. its amazing to see what is being done with longbow designs and the performance ratings.

[ChristopherO]

Marty,
I've alway liked your bows but you've just crossed the line to make me down right envious!  
Man, that is one excellent bow.  I love how it smoothed out the arch of the limbs in the full draw picture.  
When you first spoke of incorporating a power lam after building your second hybred I thought you meant adding a single, feathered on both ends, piece between the riser and the limb laminations that is so common.  I had to read your description above a couple of times to get the idea to sink in that they are actually lammed to the belly of the bow.  It looks perfect.  As you said about the handshock, that make sence as you no longer get the thump out of the limbs near the riser with this style.  
Again, excellent job and thanks for posting.

[No-sage]

Good idea.... and nice job on your fadeouts.  Glue lines look excellent.

I like the more rounded full draw profile too.

[deadpool]

man your bows look great and look great!
i always liked them
wish i could shoot one one of these days!!

[vermonster13]

Very nice Marty!

[Allen Ziebarth]

I have a question.
Couldn't you just extend the length of the riser to the same length where your power lams go to to get the same bend in the limbs?
I would think it would have the same effect.
Kinda like the long riser shorter working limb style of bow.
Nice bow by the way!

[Apex Predator]

I don't like the looks of an overly long riser, but I think you could use a longer one and get the same results.  The fades would need to be good and long.  18" riser blocks are very common though.  I would have much less selection of woods if going longer.