Primitive Archer

32.2

I wanted to do a small study on reflex shapes—bow designs that can realistically be built in real life. Even though theory and practice don’t always align, we should remember that there is always theory behind practical results. Yes, the zero set, but it doesn’t matter, because all the bows are similar except for the side profile. The only purpose of this comparison is to examine how different side profiles affect bow performance (10 gr/# -arrow) in theory.

“mmattockx” mentioned the front profile — it’s quite standard, adjusted so that with a 0.008 taper rate the stresses are distributed as evenly as possible along the entire length of the limb. But again, that doesn’t matter here, because the main purpose is to compare how the reflexed side profile affects the performance of a bow.

Regarding energy storage, it’s true that high energy storage does not necessarily mean that a bow will be fast. However, in this comparison the fastest bow has the highest energy storage, and it also has the highest efficiency, and unfortunately it has also the highest strain values.

Remember, the main goal is to compare different models in an idealized situation. How they are actually built in reality is a different matter, and there are many other variables involved, such as stability, material properties, and so on. However, there is still one model (side profile) that clearly outperforms the others (at least in theory...).

So far, one “correct” answer.

I experimented with the VirtualBow program to search for an answer.......... optimized for even stress distribution along the limbs.

I am curious what your stress curve looks like. I posted about this earlier in
http://www.primitivearcher.com/smf/index.php/topic,72997.msg1024157.html#msg1024157
and would welcome any comments should you wish to reopen that thread.

* Identical front profile, optimized for even stress distribution along the limbs.
* Taper rate 0.008

Usually you have to adjust taper to suit the front profile and side profile of a bow. Keeping them constant isn't typically optimal between designs. What front profile did you use? I stuck with a pyramid profile as it was easiest to get the stresses even along the limb and it never needed as much taper as you have, I was always around 0.003"-0.004" to get everything even on stresses.

So, which shape is the best? By best, I mean the fastest and the one that stores the most energy. Why? Which design performs the worst, and why?

Best will most likely be whichever one has the highest string tension at brace. Worst would be the lowest tension at brace.

I never considered a side profile like #2, I mostly stuck with circular reflex similar to #3. How does #2 compare to #3 on an F-d chart? It would be much easier to build #2 the way I was doing it.

#5 gave the smoothest draw curve for me, with a lot of early weight and no stacking. How does it look in your model?

Building a selfbow and achieving the spec are a challenge to say the least.

Yes it is. You need to be within 0.005" on the thickness at worst and it is hard to do that on a stave or board bow, especially if there is much thickness taper.

Laminate bows would probably be much easier.

I found that it was. I still ended up over thickness a bit, but that is better than under.

I do think that if the properties are put into the computer and the builder matches the dimensions it will turn out as predicted.

That was my experience with the two I did based on a model.


Mark

Hadn't been hunting much with my shoulder problem but decided to go Saturday morning before the Doctors tell me not to :)Got to meet with him Wednesday so figured this might be my last chance. Cold morning and the deer were really moving, seen 14 in all, have done kill my bucks, so doe only. This one came in with a 4 others, 9 yards and made a good shot, double lung and top of heart, ran 60 yards and I seen her go down, all over in seconds, don't always go that way but has been a good year. 87 lb. doe, shot with my old trusty Osage, spruce arrow and 160 ace head. Freezer is filling up.
 Pappy