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]

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

Maybe heavier arrows would have taken some strain off all the components plus a high BC from the heavier arrows

[avcase]

Maybe heavier arrows would have taken some strain off all the components plus a high BC from the heavier arrows

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! 
Del
(I recall doing a back of an envelope calculation showing the acceleration to be about 300g )

[Tuomo]

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.
Alan

May I ask, what is this recurve design? Would it also be possible to use that design in primitive bows? Or is it specific to foot bows or is it material dependent?

[avcase]

May I ask, what is this recurve design? Would it also be possible to use that design in primitive bows? Or is it specific to foot bows or is it material dependent?

This is an interesting thought. Yes, I believe it could be adapted to all natural materials. I follow many of the exact same ideas we discuss here with the primitive flight bows. It is a mild static recurve. Each limb is 20” long.  A majority of the bending takes place over 2-3” of the limb, and the wood core is very thin in that area to accommodate the bend without taking on damage or internal set.  The limb gradually transitions to very rigid levers and more stiff materials.

I think a modified version of this optimized for sinew-wood-horn composite with natural string would be an interesting project.  It would be like making a crossbow prod. I could make very similar arrows out of solid high density Tonkin split cane with water buffalo vanes. I bet 1300 yards is possible. It would pop the string on every shot.

Arvin Weaver made an amazing crossbow a few months back with bamboo back and water buffalo horn belly. I mounted the limbs from that crossbow in my footbow because he wanted to know what it would do. Unfortunately, the bamboo in one of the limbs sheared apart before I could find out. I felt pretty bad about that, but I was able to repair it and will try again.

Alan

[sleek]

May I ask, what is this recurve design? Would it also be possible to use that design in primitive bows? Or is it specific to foot bows or is it material dependent?

This is an interesting thought. Yes, I believe it could be adapted to all natural materials. I follow many of the exact same ideas we discuss here with the primitive flight bows. It is a mild static recurve. Each limb is 20” long.  A majority of the bending takes place over 2-3” of the limb, and the wood core is very thin in that area to accommodate the bend without taking on damage or internal set.  The limb gradually transitions to very rigid levers and more stiff materials.

I think a modified version of this optimized for sinew-wood-horn composite with natural string would be an interesting project.  It would be like making a crossbow prod. I could make very similar arrows out of solid high density Tonkin split cane with water buffalo vanes. I bet 1300 yards is possible. It would pop the string on every shot.

Arvin Weaver made an amazing crossbow a few months back with bamboo back and water buffalo horn belly. I mounted the limbs from that crossbow in my footbow because he wanted to know what it would do. Unfortunately, the bamboo in one of the limbs sheared apart before I could find out. I felt pretty bad about that, but I was able to repair it and will try again.

Alan

Is there a category for all wood self bow for the foot bow?

[avcase]

Is there a category for all wood self bow for the foot bow?

No, there isn’t a primitive-specific footbow category. But please don’t let this stop you!  Any information you provide about your bow, arrows, and strings on the equipment registration form will be transferred to the detailed shoot results. So there will be a permanent record of what you shot, and how far it was shot that can always be referenced in the future.  There are times where someone does make an exceptional shot with equipment that does not quite fit in the existing categories.  I was thinking of collecting some of these in a document for those who are curious. For example, Bede Dwyer once shot a round using a modern materials bow with a Historical Korean overdraw “Tongah” made from a split length of bamboo or grooved wood.  It allowed him to shoot these very short arrows at full draw. He also shot similar full length arrows from the same bow for comparison. This didn’t fit in any existing category, but the results were officially measured and recorded for anyone who is curious.

Alan