Main Discussion Area > Flight Bows
Arrows to shoot a mile
avcase:
For each set of limbs, I measure the force-draw curve, and run chronograph tests with a range of draw lengths and at least a couple different arrow weights. The configuration I was shooting last year was giving me 640-680 fps with a 110 grain arrow. Stored energy was 160 ft-lb. This recurve design averages about 70% dynamic efficiency at 0.44 grains per pound, so a majority of the energy stored drawing the bow still makes it to the arrow. In other words, it isn’t even operating close to dry-fire conditions.
This isn’t the fastest I’ve tested. The fastest chrono readings were well over 700 fps a few years ago, but I was blowing up a string nearly every shot and the limbs would come apart after about a dozen shots. That was not a lot of fun. I didn’t achieve very good distances because of all the disruption caused by various components failing. As a result, I took a step back and focused on reliability and it really paid off. I am able to pay more attention to systematically tuning the system. Really interesting things happen at low ggp. Small tuning and design differences that may not even register a measurable speed difference on my target bow will easily gain or lose 30-50 fps with this footbow contraption shooting very light arrows. It is a real eye opener.
Now that I have a proven design that is reliable and very efficient, I am ramping up the launch speed again. I hope to be reliably shooting 110-125 grain arrows around 700-750 fps by this fall. I want to make it as challenging as possible for someone with a wheel-bow design to come along and do better!
Alan
burtonridr:
700 fps! Wow, thats getting pretty close to the sound barrier.... almost bumping into the low end of the transonic zone, Thats crazy! I had no idea that was possible with a recurve bow
Marc St Louis:
--- Quote from: avcase on January 27, 2021, 02:04:57 pm ---For each set of limbs, I measure the force-draw curve, and run chronograph tests with a range of draw lengths and at least a couple different arrow weights. The configuration I was shooting last year was giving me 640-680 fps with a 110 grain arrow. Stored energy was 160 ft-lb. This recurve design averages about 70% dynamic efficiency at 0.44 grains per pound, so a majority of the energy stored drawing the bow still makes it to the arrow. In other words, it isn’t even operating close to dry-fire conditions.
This isn’t the fastest I’ve tested. The fastest chrono readings were well over 700 fps a few years ago, but I was blowing up a string nearly every shot and the limbs would come apart after about a dozen shots. That was not a lot of fun. I didn’t achieve very good distances because of all the disruption caused by various components failing. As a result, I took a step back and focused on reliability and it really paid off. I am able to pay more attention to systematically tuning the system. Really interesting things happen at low ggp. Small tuning and design differences that may not even register a measurable speed difference on my target bow will easily gain or lose 30-50 fps with this footbow contraption shooting very light arrows. It is a real eye opener.
Now that I have a proven design that is reliable and very efficient, I am ramping up the launch speed again. I hope to be reliably shooting 110-125 grain arrows around 700-750 fps by this fall. I want to make it as challenging as possible for someone with a wheel-bow design to come along and do better!
Alan
--- End quote ---
Maybe heavier arrows would have taken some strain off all the components plus a high BC from the heavier arrows
avcase:
--- Quote from: Marc St Louis on January 28, 2021, 08:16:08 am ---Maybe heavier arrows would have taken some strain off all the components plus a high BC from the heavier arrows
--- End quote ---
Hello Marc,
I will try this out. Distance with a heavier arrow launched at the same velocity should go a little farther, and heavier arrows does help the bow and strings live longer. This balancing act is one area where there is no substitute for real trial and error shooting. A month prior to the flight events, I have been preparing a wide range of arrows and travel to the Alvord dry lake bed to test and tune the system. This is where durability of the bows are really critical. I set the bow in a shooting fixture and keep careful notes about the arrows used, setup of the bow, shot quality, and atmospheric conditions on every shot. A hundred shots later, the data starts to paint a clearer picture of what is and is not working. I’d go insane if I was blowing a string on every shot!
Alan
Del the cat:
@Alan:- Thanks, very interesting post.
I've long suspected that low gpp wasn't the evil that many postulated.
The acceleration from a bow is so high* (even from a "normal" bow) that it doesn't take much to present quite a high inertial load.
I dread to think what the acceleration from your bow is! :o
Del
(I recall doing a back of an envelope calculation showing the acceleration to be about 300g :) )
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