How Much Mass Is Noticeable?

[mmattockx]

When we are talking about mass and taking mass off the outer limbs and tips, how much mass removal is needed to give a measurable performance increase?

I have two bow designs this relates to. Same length, draw weight, handle section, length of stiff tips, etc. One is a pyramid that has a straight(ish) taper from fades to tips. The other uses a pyramid style straight(ish) taper from the fades but ends in thin levers. Both bows store the same amount of energy. The pyramid bow will weigh 22oz while the lever bow will weigh 20oz, with almost all of that 2oz difference in the outer half of the limbs.

Is 2oz on the limbs considered a major difference and will it translate into significantly faster arrow speeds?


Thanks,
Mark

[Selfbowman]

Mark I’m going to say yes. But don’t know for sure. I would think 1/2 oz on each limb would matter guiet a bit. Arvin

[Del the cat]

I'd say the variation in limb shape, tiller, wood etc will make more difference... and how do you know for sure where the weight difference is? An unless you are shooting flight arrows you probably can't tell the difference... and if you can see a difference... how do you know what to attribute it to?
I hope that's cleared it up 
To put it another way... IMO it's virtually impossible to build two bows accurately enough to compare one one specific factor. I think the only way is to build one bow, test it and then make a change ... is it better/worse?
I reserve the right to be wrong!
Del

[bassman]

I just finished up a 68 inch white Oak long bow that came in at 30 ozs. It feels like the tree I made it out of. One ,and seven eighth's at the fades to five eighth's at the tips. What a horribly heavy bow. I may wack it to 60 inches ,and narrow ,and thin  the limbs to reduce mass. I don't care to even shoot it as it is.

[simk]

it matters less than one would think. i once removed 70gramms of mass from the tips of a 35# sinewbacked mollegabet. I gained only 5fps with 10gpp, from 169fps to 174fps. I was surprised it wasn't more. decrease of handshock was clearly noticeble.

[mmattockx]

Mark I’m going to say yes. But don’t know for sure. I would think 1/2 oz on each limb would matter guiet a bit. Arvin

That is the impression I get, but I was hoping those who have really tested this out in flight would speak up with all the experimentation done. 2oz seems like a lot to me and it is all well out on the limbs where it matters the most.

I'd say the variation in limb shape, tiller, wood etc will make more difference... and how do you know for sure where the weight difference is?

I agree tiller, etc. will make a difference, but I am comparing designs to see which one is the better way to go before cutting wood. I know where the weight is because the bow is designed in CAD and I can measure it very precisely.

An unless you are shooting flight arrows you probably can't tell the difference...

I have wondered about this as well. It may not matter much with heavier arrows. I am going to have to buy a chronograph next spring to do more accurate appraisal of the end results.

I think the only way is to build one bow, test it and then make a change ... is it better/worse?

This is what I am doing with my analysis. I change nothing but the one thing I want to look at and see what happens. That isolates the change, but only as far as the analysis can go. What I really want to know is how much will performance change by taking 1oz off each limb in the outer half. I just have no feel for how significant that is. I am building the pyramid design for my first lam bow (should be gluing that up over the next couple weeks) and will be following it at some point with the lever bow but it will be a while before I get it all done and can test out the designs side by side.


Mark

[simk]

further i'm still planning the before/after experiments with this bow

http://www.primitivearcher.com/smf/index.php/topic,64555.msg907466.html#msg907466

will remove the superstructures on the limbs and take chrony measurments before/after.

[RyanY]

If losing mass can improve performance than gaining mass can make it worse. Just test one bow and add mass to the tips with tape and extra wood for weight. I think this has been done before.

[Badger]

    A real simple test that has already been performed many times is to simply tape some weight to the outer limbs and see how much effect it has. You might want to figure out first exactly how much wood you would be dealing with such as 1 cubic inch for example and then add that much weight at a mid point on the outer limb to average it out.
1 cubic inch of osage would weight about 1/2 oz added to a point about 4" from the tip and see what it does.

[bownarra]

Just what I was about to say....add weight Fishing weights, melted airgun pellets etc

[mmattockx]

will remove the superstructures on the limbs and take chrony measurments before/after.

Cool, I look forward to that.

Just test one bow and add mass to the tips with tape and extra wood for weight.

A real simple test that has already been performed many times is to simply tape some weight to the outer limbs and see how much effect it has.

Doh, that was fairly obvious. I will work out some weights and give that a try on my current bow when the weather gets civilized enough to shoot outside again. I doubt I will be able to tell much without a chronograph but it doesn't cost anything to see.

Thanks for the idea, gentlemen.


Mark

[lonbow]

I have once tested this by taping two teaspoons to the tips. The distances I reached were about 10 yards shorter than before. Each teaspoon weighted 0.7 oz.

[willie]

I have wondered about this as well. It may not matter much with heavier arrows.

and with lighter arrows, the string weight becomes increasingly important also.

[DC]

It's strange. I've had bows that would gain 5 fps with just a little tip lightening and others that I reduced to scary with no gain at all. These are all much the same design, RD's with lots of reflex.

[Selfbowman]

Yes DC that’s why I never know how much to take off till it’s to late. Does not matter unless you are in dying to hit a certain weight! Oh well it’s good I like to build them. Arvin