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Old January 12th, 2018, 06:51 PM   #31

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learned much from your posts.Thank you.
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Old January 16th, 2018, 11:27 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; Yesterday at 12:56 AM.
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Old Yesterday, 11:02 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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