Straight bow, optimal tiller profile (VirtualBow)?

[Tuomo]

Primitive archery is a great practical hobby – I have just finished a bow. However, it is also nice sometimes to be more theoretical and play with a computer and VirtualBow…

Here is a small comparison: just a straight bow with a very optimized front profile. I simulated nine different constant taper rates (from −0.006 to 0.010) to see how they affect the bow’s stress and performance. In your opinion, what is the "best" and most optimal full-draw profile? How would you tiller your bow?

[Threy Cameron]

Interesting question.

I'd have to go with number 3 as I'm not a fan of whip tillering at all, really dislike how it looks and feels.
I've found stiffer outer limbs especially when Eiffel towered like in your depiction are much better when left stiffer and barely working.
Additionally I've found whip tillered tips to reduce early draw weight and lower performance and arrow speed though this is with my limited testing
and admittedly biased perspective.

The performance aside durability wise it'd be safer to have the widest part of the bow bending more and storing the most energy. 

I'm sure there are situations like the deflexed willow bow tips in some native American tribes where whip tillering is more advantageous
but for hunting use I believe they'd only be a negative.

That's a great program you've used for simulating the bows draw, would you mind sharing what program you used?

Cheers

[Tuomo]

Great thoughts! You clearly know what you’re talking about. I’m using this program—it’s free and still being actively developed (current version 0.9.1, version 0.10 is coming soon and maybe the final version 1.0 is coming next year).

https://www.virtualbow.org/

[Del the cat]

A thousand Quatloos on number 4!
Del

[Pappy]

3 or 4 for me, probable prefer 3. Both are how I try to tiller mine. don't always come out that way because of the character of the wood I most of the time am using but that is what I am going for. 
 Pappy

[bjrogg]

I’m with pappy. I prefer 3 but if I need a little more draw I usually end up with 4.

Bjrogg

[Lehtis]

3 and 4 look the best for me too.

[Selfbowman]

Has anyone other than me took the force draw and labeled the numbers marked on your bend profile chart or plan. Then tiller to force draw at each bend profile. This can double check  your wood properties possibly. It would be after the fact but possibly teach you something. When I did that it was pretty amassing to me how accurate the design was. Doing that in a selfbow is a real challenge. Because of the unknown crown. But tillering to force draw and bend profile is the answer to the unknown in my opinion. Please correct me if I’m wrong.

[Tuomo]

Has anyone other than me took the force draw and labeled the numbers marked on your bend profile chart or plan. Then tiller to force draw at each bend profile. This can double check  your wood properties possibly. It would be after the fact but possibly teach you something. When I did that it was pretty amassing to me how accurate the design was. Doing that in a selfbow is a real challenge. Because of the unknown crown. But tillering to force draw and bend profile is the answer to the unknown in my opinion. Please correct me if I’m wrong.

I am not sure if I understand you correctly. Could you please give an example? I am not sure how the draw-force curve can be involved, because the bow is overweighted during the tillering process?

[Badger]

 I would say #5. But I would stop the taper about 10" before the tip

[Zugul]

I'd say 4 or 5, even tho all my experience comes from reading this forum, watching bowyers on youtube and 10-ish broken bows   

[simk]

I'd maybe lengthen that powerlam by 6" and start a reverse taper 7" from the tip - then recheck 

[willie]

what is the "best" and most optimal full-draw profile?

the one that delivers the best theoretical arrowspeed at a stress level that does not compact the wood too much

How would you tiller your bow?

by the numbers

[Tuomo]

Here are clearly very experienced bowyers (and I already knew that…)! Number 4 is the best!

Here are the results I got from the program. It is clearly shown that the closer the bend is to the handle, the more energy the bow stores. Also, the more whip-tillered the bow is, the more efficient it becomes (the reason here being lower tip mass). Very interestingly, the speed is almost the same, independent of the tiller shape! It would be possible to say that every taper rate from −0.006 to 0.002 is good, so in that sense it does not really matter how you tiller.

[Aussie Yeoman]

That's a really interesting result. Thank you for putting in the legwork and plotting it all out. I wonder how it would go comparing across different lengths of bow for the same draw force.

For me, I like anything from 1-5, with 3 or 4 being the sweet spot(s).