At Batsford we had some interesting talk about bow strings in relation to warbows. I wonder what your thoughts are to the following rambling thoughts?
It is understandable that someone who has invested a lot of money in buying a warbow or someone who may have invested a lot of time into making one will err on the safety side when making up a bow string. Bowyers may well advise on the side of safety for the sake of their reputations and insurance. No one wants a broken string and a broken bow and when faced with a monster bow of 100lb, 150lb and over a mega strong string suddenly seems like a good idea!
An interesting question would be what basic string type and mass/strength is the best compromise between performance and durability?
Some at Batsford thought that string mass had little influence on a heavy bow, the limiting factors being limb speed and limb mass, arrow mass etc. Basically along the lines of what works on normal bows doesn't apply to warbows.
Some build very strong strings, with 22 or so strands of Fastflight, feeling that this maybe is safer and that the stronger string may give a better push to the arrow.
All this has got me thinking. I wondered if anyone has done tests, looking at how the string (usually overlooked!) affects range with warbows and military and flight arrows?
So much of what we think is fact in archery isn't actually fact! Not long ago the perceived wisdom was that you couldn't use fastflight with wooden bows, now this is almost the norm. What one person is told just can't be done, someone else is doing, not having heard this FACT! A lot of what we hear is plain bulls--t or like 95%statistics is made up on the spur of the moment
So far I have noticed that the "laws" of physics are pretty fair, and generally apply to everyone. You don't live to long if you get to thinking you're immune to Newtons principles of equal and opposite reactions (though many pedestrians in London appear to be testing this!). It appears sensible to me that the basic physics that works for flight archery also will work for scaled up warbows.
Flight archery is more extreme, the Formula 1 racing equivalent, where performance at the expense of durability is worth the risk, but surely the same basic principles apply? As I understand it the distance you can get with ANY bow is limited by the initial speed you can give an arrow. This applies to both heavy military arrows or lighter flight arrows. In a nutshell distance is limited by arrow speed. Other factors in the arrow itself will decide how far that arrow goes, but if it ain't going fast it ain't going far!
What limits speed?
1) Bow speed. Arrow speed increases with bow limb speed or really bow tip speed. Really the power of the bow doesn't matter, just the speed. A really fast low draw weight bow will shoot a light optimal efficiency arrow further than a slower higher draw weight bow shooting a heavier optimal efficiency arrow. So a fast bow is a good idea.
2) The speed with which the limb tips move is transfered to the string. The string is a critical element that is usually ignored. While people may talk about their bows and envy each others arrows, we almost never talk about strings! It seems obvious that a lighter string will better transfer this speed. A string with infinitely low mass would take no energy out of the limbs, and a string with infinitely high mass would take all the energy out of the limbs. With an infinatly heavy string the bow limbs wouldn't be able to move at all! Extreme but perhaps shows that string mass must have an effect. So a string as light as possible is good for distance.
3) A low stretch string will better transfer the force to the arrow, give it that last final whip effect as the limbs slam forward. A stretchy string will instead itself absorb the energy of the bow. With an infinately stretchy string the arrow wouldn't leave the bow as none of that energy would transfer! So a string that stretches as little as possible on the shot is a good idea.
That is about it as far as I can see. Obviously there are other factors, like technique in the loose, draw length etc. The arrow itself is a huge factor. An arrow that is optimal weight is good. There is a limit with each bow at which there is no point in reducing arrow weight any further. The arrow will go no further and more shock will be taken by the bow and string leading to possible failure. Other factors like how well matched the arrow is to the bow, drag due to shape and fletching, balance point will have an influence on how well this energy is used after the arrow leave the bow.
What I think is generally overlooked is the string.
I think a string that is made light and not too stretchy but within acceptable limits of durability would help many people get quite a lot more distance.
Dacron is in my opinion terrible stuff. It stretches too much and is quite weak with a breaking strain of around 35lbs per strand. You have to strain too much to get the string on the bow, only to watch it strtetch like toffee a good 4 inches on the bow and god knows how much on the a shot
Fastflight and other equivalents have very little stretch and very high strand strength. Fastflight has a strand strength of 100lbs. 450 plus has a strand strength of 155lbs! Using the four times bow strength rule generally seen as "safe" a 35lb bow could use just one strand of 450 plus! Obviously it is very easy to overbuild a bow string using these materials.
A 22 strand fastflight string has a breaking strain in excess of 2200lbs! Using the 4 times bow strength guide this would be OK for a bow of 550lbs! It is possible that such a string could break a bow because it is simply too strong, when it was used in the first place to try to stop the bow breaking due to string breakage!
A 120lb bow could have a string with 5 strand of fastflight, giving a breaking strain of 500lb which is actually over strong! If this makes you wince too much, why not double up and have a 10 strand string over twice as strong as it really needs to be. Surely this would be a good enough safety margin for a seasons shooting?
Personally I like 450 plus, this has a strand strength of 155lbs per strand. A six strand string does look skinny, but at 930lbs breaking strain is really very strong, strong enough for a 265lb bow! As I have yet to pull such a monster bow I reckon it is more that strong enough for my bows until I do.
A double loop string made to match the bow strength (4 times bow strength and no more) may gve good flight distances and do so quite safely. Make a new one every six months or so and you should have no problems.
A somewhat overbuilt flemish twist string (8 times bow strength) may compensate for being too strong by the extra stretch the flemsih construction gives and again would be quite safe and being modestly overbuilt should last a long time. It is easy to make a new one and adjust brace height.
I think we are used to seeing bow strings of a certain diameter, these fit the nocks on our arrows and "feel" right. Much of this comes from target archery for whoom these plastic nocks are made, for whoom bow shock is not a problem, who want the stablity of a massive string, and durability for hundreds or thousands of repetitive shots before they go out and buy another string because they want it to match their fletchings! I think the truth is that most wooden bows and most warbows bows have got massively overbuilt strings and may shoot further and safer if we looked at it again.
Mark in England
