The science bit

MSR

Member
AIUK Saviour
Hello. I realised the other day just how big the gaps in my knowledge must be. I was thinking about why some bows are recurve, some are reflex, etc. and the physics that gives a recurve an advantage over a traditional longbow, for example. And I realised I could not describe the advantage, or why there was one!

I googled a bit and mostly discovered internet discussions. For once, Wikipedia had a good paragraph, but there is no specific reference for the text.

If a limb is 'straight' its effective length remains the same as the bow is drawn. That is, the string goes directly to the nock in the strung (braced) position. When the limb is recurved (tip of limb away from the archer), the string touches the limb before it gets to the nock. The effective length of the limb, as the draw commences, is therefore shorter. However, as the bow is drawn, the recurve 'unwinds', the limb becomes effectively longer, and the mechanical advantage of the archer increases.
https://en.wikipedia.org/wiki/Bow_shape#Design_factors

The references section on that page does list several volumes of The Traditional Bowyers Bible, but at around ?100 a copy, I'm not about to get my hands on one of those! What's annoying is the absence of an in-text reference for the paragraph, above, so that I'd at least know which volume and which chapter that reference was taken from, because it was clearly what I was looking for!

What I'm looking for are reputable sources, be they books or websites, that cover the science behind the bow! I'm not entirely ignorant: I can describe a lot of what is going on, but there are gaps and I want to fill them.

So, if you've got a personal favourite text or reference that you found illuminating, or know of a good resource, please do recommend it. Archery is such a complex subject, there's probably just as much that I don't know I don't know than I already know that I don't know to know!

:eek:ptimist:

Cheers
 

geoffretired

Supporter
Supporter
It is possible to propel an arrow with a string in three ways that I can think of.
One is to move the ends of the string forwards in the direction you want the arrow to go. The last part of the longbow power stroke has the limb tips moving forwards quite a lot, moving the ends of the string forwards, and just a little bit further apart from one another.
A second way is to move the ends of the string away from one another at right angle to the direction of the arrow. The string starts bent into a V like a fully drawn string on any bow. Pull the ends away from one another and the arrow is thrown forwards.
A third way is to start with a string in a V as in fully drawn bow, and wind the ends round a wheel at each end. As the string wraps round the wheels, the arrow is shot. Many parallel limb compounds wind string round cams and the cams rotate but don't move forwards much. They do move apart from one another a little, though.
The advantage in the recurve over a longbow seems to me to be the way it can pull the string from V to straight.It combines pulling the ends forwards and apart as does the longbow, but it adds the trick of wrapping some of the string round part of a wheel or round the recurve.
It also shortens its limbs as they return during the power stroke, as the recurve section curls up.
 

Rik

Supporter
Supporter
In some ways, thinking about the shape/type of limbs is a little beside the point. What's important is the draw force applied over distance/time. That defines the energy stored and the "feel".
How you get to the particular curve you want is the shape/design of the limbs. Compounds are the most flexible in that regard, longbows probably least so, with recurves in between.
Hmm. Imagine a compound cam designed to produce the same sort of profile as a longbow... :)
 

geoffretired

Supporter
Supporter
I think that the reasons why a recurve is faster than a longbow( if that is the advantage MSR is talking about) is down to how the V in the string at full draw, is pulled back into a straight line, as seen on the braced bow.
How, in the sense that, the shape seems to be the visible difference that might be the reason.What does the recurve shape do, that the longbow shape doesn't?
I guess some really smart cam designer could come up with a compound with the same profile as a longbow.Heehee
Then I would want to see his boss's face when he rushes in with the prototype cams on a bow.
Reinventing the wheel, springs to mind.
 

Raven's_Eye

Active member
Ironman
I think that the reasons why a recurve is faster than a longbow( if that is the advantage MSR is talking about) is down to how the V in the string at full draw, is pulled back into a straight line, as seen on the braced bow.
How, in the sense that, the shape seems to be the visible difference that might be the reason.What does the recurve shape do, that the longbow shape doesn't?
I guess some really smart cam designer could come up with a compound with the same profile as a longbow.Heehee
Then I would want to see his boss's face when he rushes in with the prototype cams on a bow.
Reinventing the wheel, springs to mind.
The advantage that the recurve has over the longbow comes from the recurved tips. The string for the longbow always remains the same length, but with a recurve, once it contacts the "belly" side of the recurved limbs, the string is effectively shortened to allow for more speed. Same principle for the shelves on some horsebows.
 

chuffalump

Well-known member
The advantage that the recurve has over the longbow comes from the recurved tips. The string for the longbow always remains the same length, but with a recurve, once it contacts the "belly" side of the recurved limbs, the string is effectively shortened to allow for more speed. Same principle for the shelves on some horsebows.
I imagine the same theory holds at the start of stroke too. The recurves, being short, snap round quickly, giving a boost at release.
 

geoffretired

Supporter
Supporter
The advantage in the recurve over a longbow seems to me to be the way it can pull the string from V to straight.It combines pulling the ends forwards and apart as does the longbow, but it adds the trick of wrapping some of the string round part of a wheel or round the recurve.
It also shortens its limbs as they return during the power stroke, as the recurve section curls up.

Hi Raven's_ Eye The piece above is the real post I made a couple of posts ago. The post you have quoted from is just a summary for Rik in a way.
I guess in our own words we are agreeing with each other.heeheeh
 

Rik

Supporter
Supporter
I'd be interested in seeing how the draw curve of an ACS longbow compares to a budget recurve...
 

MSR

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AIUK Saviour
Wow. Ask and ye shall receive! Whether ye thought ye wanted it or not!

I have some reading to do :eye-poppi

Will there be a test at the end of term? :indiffere

I've had a quick look and spotted the V-bar program on TOPICS ON ARCHERY MECHANICS which describes itself, thus:
This is a program to illustrate how moment of inertia varies with the geometry/weights of a V-bar/long rod assembly.
That's it, then. Hours of my life will now disappear as I analyse and agonise over different stab configurations. I was already in the market for an angled beiter v-bar, preferably one of the 30 degree ones, not the 17. I have a notion of fitting it to the lower half of the riser, while keeping the long rod in the usual place.
 

MSR

Member
AIUK Saviour
Yes, and it's called the Kobayashi Maru....
If it's anything like getting to the end of a round and discovering that you need to shoot a 6 gold end to achieve your classification by one point, but you're tired, you're struggling to pull through the clicker, you're thinking about lunch, and it's just started to rain, then I am deeply familiar with the concept of the Kobayashi Maru...

Or, to paraphrase Spock: the statistical likelihood that your plan will succeed is less than 4.3%.

Me: Never tell me the odds!
 

Rik

Supporter
Supporter
If it's anything like getting to the end of a round and discovering that you need to shoot a 6 gold end to achieve your classification by one point, but you're tired, you're struggling to pull through the clicker, you're thinking about lunch, and it's just started to rain, then I am deeply familiar with the concept of the Kobayashi Maru...

Or, to paraphrase Spock: the statistical likelihood that your plan will succeed is less than 4.3%.

Me: Never tell me the odds!
Are you sure that was Spock? I thought it was Dumbledore...
 

MSR

Member
AIUK Saviour
No that was C3-PO and Han Solo, wasn't it ?
Rumbled :)

After reading the Shoot or Fire an arrow? thread about pedantry over terminology I was inspired to mix my Star Trek and Star Wars references. It often gets some scifi nerd frothing, just like when referring to the gold as the yellow bit in the company of 'serious' archers.
 

Rik

Supporter
Supporter
Rumbled :)

After reading the Shoot or Fire an arrow? thread about pedantry over terminology I was inspired to mix my Star Trek and Star Wars references. It often gets some scifi nerd frothing, just like when referring to the gold as the yellow bit in the company of 'serious' archers.
https://youtu.be/JADiBzni5-4
Dead Ringers got there a few years back...
 

Rik

Supporter
Supporter
I will never cease to be amazed at a world in which you can get kicked off your degree course for plagiarism, while exactly the same behaviour in the entertainment industry nets you billions and makes you a beloved household name!
I think we hold a special place in our hearts for the wickedly sarcastic...
 
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