Whippy ends, tiller shapes etc.

[Badger]

   Every now and then the topic come up about whip ended bows. It all goes back to energy storage in the bow vs the efficiency of the bow. A typical mid length 50# pyramid bow with a circular tiller will store about 45# energy and be about 66% efficient. A typical slightly whip ended bow might store only about 40# and be about 75% efficient. That would give the two about the same speed. A flight shooter or someone shooting lighter arrows would favor the more efficient design because as arrow weight drops off efficiency drops off with it. If soeone was hunting elk and wanted to use heavier arrows he would lean toward the more energy storing design because his efficency would improve even more as his arrow weights went up. Short bows are the same way, they store less energy but are more efficent so they tend to be faster with lighter arrows,
    If you shoot a heavy enough arrow through any bow it wil come up to almost 100% efficiency regardless of how heavy the limbs are. If you were shooting 1# arrows the bow storing the most energy would always win. The closer the bend is to the handle and the stiffer the outer limbs the more energy it will store, and the more it bends in the outer limb the less energy it will store but the more efficient it will be. Shooting 10 grains per pound we are usually looking for that middle ground which is what most of our bows are typical of. Steve

[Ryano]

Interesting Steve. I would agree with that statement. 

[Jesse]

Makes sense to me. I think. I like a bow to be able to cast a heavy arrow for hunting. Maybe thats why I tend to favor the longer bows. Would you say that handshock is also a sign that for one reason or another the bow is not shooting efficiently?  after all else fails, adjusting brace height etc. that particular bow design is just better suited for a heavier arrow.

[Kegan]

Learn more everyday!

Steve, what do you think of a R/D pyramid bow? I'd really like your experienced input on this one

[sulphur]

its all a balancing act.  like most things.  I am learning an awful lot from your recent posts.  I hope NASA doesn't call you back in.

[Kviljo]

A good summary, Badger! Although I agree with the principles, I'm not sure at what arrow weight the more whip ended bow will be better. I think it may be pretty low, perhaps as low as 2-3 grains per pound. I tried both designs, and the stiff ended designs seems to work better even with light flight arrows. But the stiff-tipped design is really dependent on how light one can get the outer stiff section of the limbs, which of course is not an issug with the whipended design.


As for the geometry of "straight limbed" bows without contact recurves, I think the best design would be a pretty hefty reflex/deflex, where the limbs are straight at half draw. That would have the best string angle thoroughout the whole draw.

[sulphur]

this is also something i have kept in mind when making laminated bows.  the addition of the power lam and length of it moves the bending forces towards the tips.  

[Badger]

  Kavilllo, the stiff tip designs aren't really typical pyramids with arc of the circle bends. I prefer the stiff tips also. Was using the pyramid as a basic example. We can get our r/d shaped bows up over 80% now with the 500 grain arrows, stiff tips and tillered elyptical. Those same bows are pretty fast with light arrows as well. The fastest light arrow bows I have made were around 60" long stiff tips but tillered to bend in the outer limb right before the stiff tips. These same bows would not be as fast as a slightly longer bow shootng 500 grain arrows and tillered to bend slightly more in the inner limb. Not talking huge differences with the heavy arrows but once you get below 200 grains it really starts to show up
Kegan, The r/d pyramid is a decent bow but I prefer to make the limbs paralell for at least 1/2 the limb and work the mid limb a bit more. Steve

[Justin Snyder]

Great discussion Steve. This is exactly what I was referring to on the cherry bow thread.

I have been working on some R/D bows with the parallel going out just a little farther than half way. I have been tillering them with the deflex at midlimb bending just a little more than the rest so I needed the extra width to keep from stressing the wood. I think they should pick up a little more performance without being whip tillered since the tips are still stiff and the last 1/3 of the limb isn't bending so much. I haven't pushed them to full ellipse yet though. This whole discussion is why I don't care for ellipses to judge tiller, it varies depending on the relaxed profile and the bow layout.

[George Tsoukalas]

I hope you don't mind some disagreement. Steve, how did you measure all of the data you presented in your first post? Well I'm not hopping on just yet as I really dislike whip ended bows. Keep in mind I'm not a flight shooter but a hunter and long bows are not for me. I like 62-64 ntn bows for my 26 in draw bows with stiff handles with the bend starting at the end of the fades  or with limbs that bend through the fades and into the handle. Got some questions because 75% efficiency seems high for a whippy bow unless they are really long. Short whippy bows would  stack and would that not decrease efficiency?  Then of you are comparing a pyramid  bow to a Mear heath style whippy longer bow you've introduced other variables which could affect data. I'm wicha with heavy arrows increasing efficiency though. Jawge

[sulphur]

One thing we haven't mentioned is accuracy.  That cherry bow, although fast, was all over the place.  I am not a great shot but i feel i can hold my own, and half the time i had no idea where the arrow was going.  speed is great, but how does it affect stability and accuracy.

[Badger]

   Jawge, when I said slightly whippy ended I just mean tillered to bend more in the outboard limb. Those particular figures are just examples but pretty typical of stuff I have measured. A true whippy end is probably not much good for anything. Whole point I was making was that high energy storage is not always the best bet and neither is super high efficiency, even though they both could have their place in a specialized type circumstance. Middle of the road seems to fit us the best for a plain bow.
    One thing I did last year as I wasn't building any bows was to pull a stack out of the garage and just test a bunch of different things, I never write anything down of course. Testing a lot of bows I was looking for time savers. One of the time savers I found to determine stored energy was just to make an extremely heavy arrow, like fill an aluminum arrow with dirt or bb's. nails etc and then fill with glue. The arrow was so heavy it would travel slow but give me near 100% readings of stored energy. This would save me the trouble of plotting a graph by measuring every 1" etc. Probably at least as accurate anyway. Then I could shoot the test arrows and calculate the efficiency at different weights.
    A common test was to find where a broadhead bow and a flight bow were to shoot the same speed. A braodhead self bow might hit in the mid 170's with a 10 grain arrow but only hit about 225 fps with 200 grains where the flight bow might hit 168 with 10 grain arrows but hit 240's with a 200 grain arrow. They might shoo t about the same speed with a 325 grain arrow for instance. I never really test for accurate data, just looking for patterns and things to kind of help me with the understanding. Exact data is kind of useless unless you make a perfect bow of each type. Getting back into building now, did a couple of plum bows this week, one is only 39" long. I have to wait for sinew to dry before I draw it all the way out but did some testing with it at very short draws and 100 grain arrows and it was holding very high efficiency. Steve


 

[George Tsoukalas]

Thanks, Steve. Jawge

[half eye]

Hey Steve,
       What are your thoughts on efficiency VS longevity? What I'm asking is : Generally speaking; as something approaches 100% efficiency the more it is on the verge of self destruction ( like rebuilding 2000HP AA Fuel Dragster motors between @ run) Like wise it would not be desireable to build a "dog" just because it would be a dog for a long time, that's not good either.
       So is there some "compromise point" between efficiency and longevity? What is your opinion please.
Half eye

[Badger]

     Half, I think redlinning a bow is a recipe for a very short life as you might expect from a flight bow. But just designing in efficiency based on sound principles such as equal limb stresses and having enough wood in the right places extends the life of a bow. Aside from having a flaw in the wood most bows fail because one part of the bow is weaker than the other parts.
     Making a bow super dry will increase the efficiency greatly but also put the bow at high risk of sudden failure. about 8 to 10% humidity as Jawge often recomends is probably a good safe number for minimal set and good longevity.
   About 5 years ago I was trying to build some super fast light arrow bows, anything over 260 fps with light arrows would usually blow in less than 3 shots. It will still fun kind of like building race cars.
   The R/d designs are very efficient and we have been seeing a lot more of them lately, I started making mine a bit wider and using a bit more limb bending, I gave up about 5 fps but they are more reliable now I feel. Steve