SHOOTING MACHINE
Posted: Thu Oct 11, 2018 2:55 pm
I needed to build a shooting machine to generate the data to help a university undergraduate complete a paper.
With a little effort and a few dollars I was able to modify my force/draw setup viewtopic.php?f=34&t=11983 to a shooting machine.
I purchased a release aid on special for $23.00 which I could modify, the release aid enabling a consistent ‘clean’ loose.
To my surprise the shooting machine worked perfectly on the first test run.
A recurve and longbow each being 45lb@28” were used for the test once their stored energy was established.
Typically arrow velocity varied by .3% i.e. Red arrow longbow, 162.4, 162.6, 162.2 fps. Red arrow recurve, 174.5, 174.7, 174.2 fps. Stated accuracy of the chronograph was within .5%. The base for the shooting machine was a little unstable which may have added to the variations in velocity.
The chart below illustrates the fact that different arrow mass will have little impact on the efficiency value within the bow even though arrow velocity increases.
Although this fact has been accepted for many years it is rewarding to go through the process to verify it. Once a bowyer has this information he / she can make changes to limb design / configuration to make efficiency improvements.
I believe the longbow utilising a rock maple and black wattle core could be improved by shortening the n to n length to 68” resulting in a lower limb mass and increased limb recovery speed.
The following image is for a 40# longbow utilising a laminated bamboo core. Daryl.
With a little effort and a few dollars I was able to modify my force/draw setup viewtopic.php?f=34&t=11983 to a shooting machine.
I purchased a release aid on special for $23.00 which I could modify, the release aid enabling a consistent ‘clean’ loose.
To my surprise the shooting machine worked perfectly on the first test run.
A recurve and longbow each being 45lb@28” were used for the test once their stored energy was established.
Typically arrow velocity varied by .3% i.e. Red arrow longbow, 162.4, 162.6, 162.2 fps. Red arrow recurve, 174.5, 174.7, 174.2 fps. Stated accuracy of the chronograph was within .5%. The base for the shooting machine was a little unstable which may have added to the variations in velocity.
The chart below illustrates the fact that different arrow mass will have little impact on the efficiency value within the bow even though arrow velocity increases.
Although this fact has been accepted for many years it is rewarding to go through the process to verify it. Once a bowyer has this information he / she can make changes to limb design / configuration to make efficiency improvements.
I believe the longbow utilising a rock maple and black wattle core could be improved by shortening the n to n length to 68” resulting in a lower limb mass and increased limb recovery speed.
The following image is for a 40# longbow utilising a laminated bamboo core. Daryl.