I just made a bow and arrow out of a rule, a rubber band and a pencil, but its not flying straight?

Question

i got really bored. any ideas on how to fix this problem, the pencil is coming out all wobbly

Answer 1

Wear safety glasses and don't shoot it at or near anyone else. Yes, stabilize the pencil.

Answer 2

Yep, fletching would help, but you really haven't made a bow.  The force from a bow is from the wood or whatever it's made of, springing back to it's original shape.  The string doesn't stretch.  What you've made is sort of a slingshot.

Answer 3

Well, I don't know what kind of rubber band you're using, but your average sized pencil is much too stiff for the average rubber band.  

Warning! archery science content.  

Say a rubber band has a pull of only a few ounces, maybe a pound if you draw it back far enough.  A pencil on the other hand has a static stiffness of about .3, this means if you take 28" of that material and you hang a 2lbs weight in the middle of the span it'll only flex about 0.3".  An arrow shaft with a 0.300 spine is usually shot from a 70lbs bow.

Now, that was static spine, meaning all data is assuming you're shooting a 28" projectile.  But when shooting, the spine that is in effect is the dynamic spine.  The dynamic spine of that pencil is probably much greater than .300, in fact it probably approaches 0.100 or stiffer.  This is due to the fact that the pencil has no pile, it doesn't have a heavy tip in the front to force it to flex, and it's so short.  Arrows flex because it has a metal point in the front, when shot the rear of the arrow moves faster than the front, causing it to bend.  This bending of the arrow, called the archer's paradox, is in fact what allows the arrow to fly straight.  In other words, unless you find a 150lbs rubber band, that pencil will always be wobbly.

Fletching do mask the effects of out of spine arrows.  But in this case, the pencil is just out of spine by way too far.  In the case of a real bow and arrow, the spine can be off by 3 sizes and still be correctable by large feathers, this means shooting a 500 spine shaft out of a 30lbs bow for example.  But this pencil is out of spine by a good 20 sizes or so.  Fletching in this case will result in clearance issues more than solving the spine issue.  My suggestion is to find a better arrow, something more bendy.

Answer 4

Projectile stabilization is done by fin or spin.  If you dont put fletchings on the rear, try notching the pencil, twist and pull back.

Answer 5

whittle the back of the pencil and fold some paper real finely and stick it in the notches you made and glue it or tape it then make a notch in your rule for the arrow t rest in also try using the thinkest rubber band that you have i hope this helps

Answer 6

Fletching (feathers on the pencil)  would probalby help- as would a straighter path out of the bow. With a ruler you're shooting the pencil sideways more then straight, you're not going to get a real accurate shot.

Basically, you need a better bow and a better arrow. So you're probably doing about as good with what you have.  The problem is the whole concept of a ruler bow and pencil arrow, probalby not implementation.