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Old January 12th, 2018, 05:51 PM   #31

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learned much from your posts.Thank you.
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Old January 16th, 2018, 10:27 PM   #32

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Replica crossbow builder Andreas Bichler made some very interesting comments today in his Great Horn Crossbow video:

Yes - the power of a composite bow varies depending of serveral factors (temperatur, air moisture). If its cold and dry the bow will be more powerful and it's able to store more pontential energy - so velcity and efficiency will increase. But an other problem is the "creeping deformation" of the bow - as longer it is stringed and used as "weaker" it will become. Compared to the steel bow the data of a composite bow varies permanent....

Compare this with what I translated from the Cui Wei Xain Sheng Bei Zheng Lu in post 30:

During the hot summer, when it’s raining and there’s steam, the horn [composite prod] should be easily taken off, and use a wooden [simple prod] crossbow. During the spring and winter, where there is wind and bitter cold, the wood (simple prod) is heavy and sluggish, and horn [composite prod] crossbows must be used.

You can also compare the 'creeping deformation' he mentioned to the Chu-Yen slips (
Slip 36.10) mentioned in the OP.

Andreas Bichler also gave the following information on two of his composite crossbows, to be found i
n the German journal: Jahrblatt der Interessengemeinschaft Historische Armbrust 2016 and 2017.

Great Crossbow (1270lb), shot at roughly +25 degrees Celsius
Powerstroke: 14.76 inches
Stored potential energy: 1276.9 Joule
155 g bolt – 67.96 m/s – 357.94 J - 28 % efficiency
260 g bolt – 57.74 m/s – 433.41 J - 34 % efficiency
348 g bolt – 52.92 m/s – 487.79 J - 38 % efficiency

Cranequin crossbow (1200lb),
shot at around -6 degrees Celsius
Powerstroke: 7.48 inches
Stored potential energy: 589.43 Joule
81.1 g bolt – 69.85 m/s – 197.84 J - 34 % efficiency
98.1 g bolt – 64.17 m/s – 201.98 J - 34 % efficiency
105.1 g bolt – 61.47 m/s – 198.56 J - 34 % efficiency

Same Cranequin crossbow (1200lb), shot at around +30 degrees Celsius
Powerstroke: 7.48 inches
Stored potential energy: 589.43 Joule
82 g bolt – 64 m/s – 167.94 J -
28 % efficiency

That last one came from Peter O. Stecher's video of Andreas Bichler shooting his 1200 lb cranequin crossbow in the middle of summer. Note that Andreas Bichler calculated stored potential energy using the actual stored potential energy, not the linear estimate "draw weight*powerstroke/2" equation that we had been using. This meant his stored potential energy includes the yellow area in the graph below:

Click the image to open in full size.

Using actual stored energy for composite bows is bigger than its linear estimate for stored energy (the opposite is true for steel bows). This would decrease efficiency but increase potential energy given the same draw weight and powerstroke. The resulting joules that gets transferred into the projectile would be the same because the bigger stored energy and lower efficiency would cancel each other out.


Now Bichler mentioned that the reason for increased velocity during the winter and decreased velocity during the summer is because draw weights of composite bows increase during dry/cold environments, and decrease in humid/hot environments. Now for the efficiencies listed, I am assuming that the draw weight was measured at room temperature for both crossbows. So under this assumption the efficiency for the 1270 lb crossbow shot at +30 degrees is lower than it should be, and that for the 1200 lb crossbow shot at -6 degrees is higher than it should be.

Edit: He just mentioned the following in terms of measuring draw weight of his crossbows:
For measure I put it for a short time outside but this dosen't matter because it needs several days to change its characteristics. A central heating system is perfect for keep it dry. At the other hand it varied like outside over the rest of the year.

Last edited by HackneyedScribe; January 16th, 2018 at 11:56 PM.
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Old January 17th, 2018, 10:02 PM   #33

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Andreas Bichler cleared it up by saying this:

I would not say so - the temperature is one part but the main part is air humidity. In winter the cranequin crossbow was not in use for several month and completely dry from the central heating at home. At the testing-day is lay about 15 hours in the cold car. I observed in other cases if I stored my crossbows at an event in my linen tent and the weather was rainy at the following days you can feel the power loss .
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Old February 4th, 2018, 02:34 PM   #34
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Fantastic thread

Please contribute to Three Kingdoms Total War. Will be wonderful to use crossbow pi formations against the Xiongnu
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Old March 16th, 2018, 08:27 PM   #35

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Since the vast majority of people simplify efficiency by calculating stored energy using a linear curve, the equation to calculate potential energy would be: Powerstroke*draw weight/2

The simplified method would result in the following (bolded parts are the numbers which changed due to switching to the more popular method):


Great Crossbow (1270lb), shot at roughly +25 degrees Celsius
Powerstroke: 14.76 inches
Stored potential energy: 1059 Joules
155 g bolt – 67.96 m/s – 357.94 J - 34 % efficiency
260 g bolt – 57.74 m/s – 433.41 J - 41 % efficiency
348 g bolt – 52.92 m/s – 487.79 J - 46 % efficiency

Cranequin crossbow (1200lb),
shot at around -6 degrees Celsius
Powerstroke: 7.48 inches
Potential energy (linear): 507.12 Joules
81.1 g bolt – 69.85 m/s – 197.84 J - 39 % efficiency
98.1 g bolt – 64.17 m/s – 201.98 J - 40 % efficiency
105.1 g bolt – 61.47 m/s – 198.56 J - 39 % efficiency

Same Cranequin crossbow (1200lb), shot at around +30 degrees Celsius
Powerstroke: 7.48 inches
Stored potential energy:
507.12 Joules
82 g bolt – 64 m/s – 167.94 J -
33 % efficiency
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Old March 17th, 2018, 08:35 AM   #36

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We can gauge Qin crossbow draw weight by looking at thickness and width of the limbs, length of the prod, and powerstroke. Generally speaking, under an all else being equal scenario (same material in prod construction, same thickness/width/prod length/powerstroke):

Thickness: Increasing thickness by twice will cube the draw weight
Width: Increasing width by twice increases draw weight by twice
Prod Length: A longer prod length decreases draw weight if thickness/width/powerstroke remains the same
Powerstroke: A longer powerstroke increases draw weight if thickness/width/powerstroke remains the same

In "History of the Qin Army" 秦军事史, pg 591-592:

There are (as of the book's publishing date) over 130 crossbow prod remains in Qin Shi Huang's Terracotta army. From these we can determine:

Prod length: 1.3-1.44 meters
String length: 1.08-1.24 meters
Stock length: 70-76 cm
Grip diameter: 3-5 cm
Tip diameter: 2-3 cm

After adjusting to real size, the Qin excavated bronze crossbow was determined to represent a crossbow with prod diameter of 2.6 x 4.6 cm.

Usually I would say that the dimensions of the grip isn't relevant because the grip doesn't contribute to the moving parts of the bow, but the dimensions of the mid limb look to be around the same as that of the grip, and then the width/limbs peters off towards the tips.

Click the image to open in full size.
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Old March 17th, 2018, 12:25 PM   #37

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Given what's said above, and compared with the composite bow stats below with their estimated draw weights, I'd say Qin crossbow prods (say, 2.6 cm thick and 4.6 cm wide at mid-limb for a light one) were in the range of 200-400 lbs. Some authors speculated that Qin crossbows were just hand bows mounted on a stock, but given the great thickness of the bow limbs combined with the short prod length (for composite bows), I'm just not seeing this.

http://mandarinmansion.com/tigers-tail-patterned-composite-bow

shows 70-80 lb bow, length 1.79 meters, 1.8 cm x 3.4 cm

http://mandarinmansion.com/heavy-manchu-war-or-strength-bow

shows 160-200 lb bow, length 1.85 meters, 2.5 cm x 5 cm

Mughal composite bow, kaman | Mandarin Mansion

Mughal bow, >150 lbs, 1.5 meters long, 1.6 cm thick, 5.25 cm wide at midlimb

Again, from the post above:
-Increasing the limb thickness by twice will increase draw weight a LOT more than increasing width by twice.
-A longer prod means you need to increase thickness or width or powerstroke in order to maintain the same draw weight.


Also compare this with post 30, in which a Song document (Cui Wei Xain Sheng Bei Zheng Lu) was setting limits on the draw weight and draw length of crossbows because some crossbow draw lengths were getting so long that soldiers were drawing the string up to near their chest, and such a distance limits the amount of muscle power a crossbowman could use to draw the string. The resulting long draw length also caused crossbow prods to become too long, hampering ergonomics. It puts the desirable draw length at 1.6 meters and 1.9 meters (I presume the former is for composite prods and the latter is for pure wooden prods) and considered draw weights of 264 lbs - 397 lbs to be desirable: At present day we want to use crossbows with draw strength of 2 stone to 3 stone (~264 lbs to ~397 lbs)

Last edited by HackneyedScribe; March 17th, 2018 at 12:51 PM.
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Old March 18th, 2018, 08:56 AM   #38
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How late were crossbows used by Chinese military forces? Considering the other archaic weapons I've seen used by the Qing during the Opium Wars I thought I'd ask.
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Old March 18th, 2018, 09:29 AM   #39

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You'd have to ask the future, because for the present....

Click the image to open in full size.

But if you're asking when they dropped crossbows from use as the most popular ranged weaponry, I'd say the end of the Song dynasty.

Last edited by HackneyedScribe; March 18th, 2018 at 10:04 AM.
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Old March 18th, 2018, 01:56 PM   #40
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Quote:
Originally Posted by HackneyedScribe View Post
You'd have to ask the future, because for the present....
That's a fairly recent re-emergence of the weapon though isn't it? I'm not aware of prior Chinese armies like the KMT issuing crossbows to their troops in any significant numbers...

Quote:
Originally Posted by HackneyedScribe View Post
But if you're asking when they dropped crossbows from use as the most popular ranged weaponry, I'd say the end of the Song dynasty.
Huh, that's earlier than I expected, considering the Song dynasty ended in the 13th century and muskets wouldn't start to challenge bow weapons in China until the 16th at the earliest. Any reason for Chinese troops under dynasties after the Song not using crossbows in significant numbers anymore?

Last edited by Komi; March 18th, 2018 at 01:59 PM.
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