Sun 7 Mar, 2010
Here is a quick vid in real time of the terminal results of today’s shot. The chalk circle is where my esoteric calculations had predicted the bolt would exit. Range is 50 yards. 20100307132756(1) ………….. So much for my powers of divination.
As for the data from this shot, I find myself hesitant to post today’s results until I can get some independent confirmation of my what my eyeballs are seeing on the chronograph. However, it has always been customary for me to post any data the same day it is gathered, and so I can see no reason not to post the following numbers: bolt weight 6996 grains, bolt length 33 1/2″, draw length 45″, draw weight 4500 lbs., ……….. now here comes the part that is rocking my world……. velocity 401.8 fps, energy 2507 foot lbs. (3400 Joules). There isn’t time to attempt a duplicate of this shot today. Also, I am going to need to get another chronograph to verify the instrumentation. This level of performance (if it can be positively repeated) puts Firefly’s power potential far beyond what I ever dreamed possible. All my efforts must now be directed to confirm or debunk this data. Naturally if some kind of chronograph error is generating these results, I will make an immediate and grovelling retraction.
The draw length was increased from 40 1/4″ on Friday, to 45″ today. Perhaps that explains the possible jump in performance. Past experience with the Gallwey ballista has shown that it takes a dozen or so shots after the washers have been rotated to a new station, for the bundles to settle down and start producing consistent velocities. That the draw weight was 200 lbs. less than Friday, even though today’s draw length was longer, is a natural consequence of the bundles becoming accustomed to their work and losing some of their initial vitality. That we should see such a large increase in velocity does leave me a tad skeptical. On the other hand, the shot certainly appeared fast.
The new larger fins on the bolt resolved all the wobble issues we observed on the previous shots. Here is a photo of what the bolt looked like before heading out on its suicide mission down to the dreaded archery backstop.
I sure hope today’s results are for real. If they are not, I fully expect a severe spanking from the Catapult Gods.
A quick addendum for the day: somewhere I found the energy to assemble another bolt and try for another world land speed record. Stats are: bolt weight 7515 grains, draw length 45″, draw weight 4700 lbs, velocity 351 fps, energy 2055 foot lbs. (2768 Joules). The velocity was down on this shot partly because the bolt used was 519 grains heavier. The energy was also down from the last shot by 452 foot lbs. I do not have an explanation for this phenomena. At this point all I can do is be rigorously methodical and find a way to verify what the chronograph is telling us.
Gareth Gwillim says:
Hi, great work so far, absolutely superb build!
Looking at the timing of the release and the impact, it looks to be about half a second, so 400 fps doesn’t sound too far out, thats only a rough estimate but if it’s right thats a very good result.
Gareth