The best shape for a reflexed bow?

[sleek]

Ive done a lot of study and thought on why short bows shoot light arrows better than long bows and can answer that one with certainty. The answer is horsepower vs torque.  Short bows have high horsepower and long bows have higher torque.  Small little 4 cylinder cars that are light weight can go super fast but a truck with an inline 6 can pull large weight uphill.

The answer is in the engine, and specifically has a lot to do with connecting rod length. The longer the connecting rod the more torque and slower the engine will rotate, vs a short stroke engine that will wrap up fast with a blip of the throttle. The shorter rods ( limbs ) allow for higher rotational speeds and more horsepower which a light load ( arrow ) can be accelerated from. The heavier the load the more torque required to motivate it.

Some comparisons can also be made to the draw length, which is why a longer draw will return at a slower rate than a shorter draw, but deliver more torque. An English longbow takes advantage of both situations. A short bow can be made to draw a long distance but the longer the draw the slower it will shoot a light arrow after a certain point. 22 to 23 inch draw seems to be the peak for super light weight arrow speed, and the arrows weight increases, so too should the draw length to gain the extra torque to speed that arrow up.

[simk]

 to not confuse the thread we might stay a bit closer to the topic. The simple ( ) question actually seems: How and why does the sideprofile affect energy storage? 

[Badger]

to not confuse the thread we might stay a bit closer to the topic. The simple ( ) question actually seems: How and why does the sideprofile affect energy storage?

  Lower string angles and preload from reflex is the simple answer. The entire limb responds to it's relative position to the string. Lower string angles allow for more weight up front because they build weight slower during the draw.

[RyanY]

I think a common issue with the R/d design versus a recurve is that they’re much harder to tiller. I assume this results in less even strain and a slower bow. Recurves are simple in comparison which may explain the difference by wood bow makers on average. I think it’s also easier to get more total reflex from a recurve than with a r/d bow. Seems like Fiberglass bows that can be designed so close to perfect are closer to what we’d see in a model versus real world averages.

[willie]

Here is small comparison made with VirtualBow-program, of short and long bow. Straight, normal front profile, taper rate 0.004 (evenly distributed stess).

I am using version 9.1 and do not recall seeing outputs for strain. Are you using a development version to get your strain values?
When I see such a difference between back and belly strains in your table, I suspect you are using different moe values or thicknesses for the back and belly layers, however the back and belly layers dont appear to be much different in thickness in the pics.
If modeling for basic shape/profile principles, why not just use a single layer?

[willie]

@ ryan, virtualbow outputs a graphic view as if on the tiller tree that one can reference for any stage of the draw when making tillering adjustments.  Selfbowman had acess to a 36" printer and we once worked on enlarging Virtualbow plots to put behind bow when on the tiller tree.

[Tuomo]

I am using version 9.1 and do not recall seeing outputs for strain. Are you using a development version to get your strain values?

Yes, I am using a development version 0.10. It has strain-values as an output, and you can give an fixed grains per pound -value for the arrow. It seems that it is also more accurate. Version 0.9.1 gives a bit skewed results.