I own a wooden longbow and over time I have learned some interesting things. I wish to share this information, particularly with people who do not own a bow but think they might be interested in archery. First thing is that when you order a longbow, you state your draw length and the draw poundage. Most woodbows go up to 50 lbs but I was able to special order mine for 65 lbs at a 31" draw length at woodbows.com for no extra charge. 65 lbs is near the maximum capacity of the red oak wood that is used in my bow. Yew wood would be much more expensive but is preferable. Initially I was going to get a 33" draw length but it turns out that standard arrows only go up to 31". Arrows are expensive enough without getting into custom stuff so I went with the 31 inch draw. 33 inches would also put the string behind my ear, and that is a fast way to loose your ear.
The arrows you purchase must be matched up to the draw length and poundage of your bow. Arrows are designed to spin through the air. This gives them lift. The feathers give the arrow the spin. You always use the feathers from the same wing side of the bird so the air flows in the same direction. The arrows also move through the air in a snake-like pattern with a slight side to side movement. This is why the arrows must be matched to the poundage of the bow. If they are too stiff or too soft for your bow, the arrows will not fly straight. If you want armor piercing heads they must be 600 to 700 grains, although a 200 grain arrow head will probably do a good job too. 125 grains is the standard for target practice heads.
Traditional military longbows had draw weights of 120 to 180 lbs. These were drawn by leaning forward and using the large back muscles to pull up to the ear in a circular motion. Shooting in a high arc the archer could gain excellent distance near a quarter of a mile. For precision targeting you can aim down the arrow shaft. Most archers only use 35 to 40 lb bows for this. I use a 65 lb bow but I can do bent over-rows with 225 lbs for 6 reps. I also do specialized cable exercises where I pull 100 lbs to the ear with one hand and hold it there while bracing against the pole as if holding a bow. Be careful not to get a bow that is too powerful or your technique will never develop properly. You must pull it back and be able to hold it there and aim. The key to good targeting is to draw and release the bow consistently. You must hold the bow the exact the same way and draw to the same exact spot on you face. You will then be able to see where your first arrow lands and adjust your aim slightly.
I have seen longbows going up to $400. I got mine for $88 from woodbows.com The one I got was unfinished. That means it was not waterproofed. You can waterproof a bow by covering it with Vaseline and then wiping it down after a few hours. Do this twice a year. I also took some clothesline rope and whipped it around the center of the bow to give it a nice grip initaily. I have since removed the whipping since the gloves I wear made the grip too thick. My longbow can be fired left handed or right handed. This is very convenient because my bow is so heavy. After a few shots I change arms. The arrow rests on the index finger while I aim.
I also bought my fist set of arrows from woodbows.com These are cheaper and poundage is slightly off. They only go up to 50 lbs. I decided to do this just to get started. One can expect to loose or destroy their first set of arrows quickly. The 12 arrows cost $58. They had a slight in-flight spin because of the underweight. The next set of arrows I got from rosecityarchery.com I got those on sale for $65. They are 60 to 65 lbs and have harder 125 grain heads. These fly much straighter.
Also keep in mind never to pull and release a bowstring unless it has an arrow in it to offset the force of the bow. If not, the string may snap, or the bow may even snap. Unstringing it will lengthen the life of the string and keep the bow at its full tension. Use a stringer to unstring a woodbow. The stringer applies the force evenly over the bow. If force is not applied evenly on a wooden bow it may break.
Shooting Medieval Style
For a long time I doubted people drawing 150 lb bows. Then I came across some pictures showing the Medieval method of pulling the bow. The common method of shooting a bow these days is the Victorian method. This is where you pull the bowstring back with the small, Rear Deltoid Muscle to the chin or eye and aim down the arrow-shaft. The main focus is accuracy. To pull a heavy bow you have to learn to shoot with the Medieval method. This method involves leaning forward in pulling the bowstring back with the larger Latissimus Dorsi Muscle while squatting down a bit for balance. As you straighten up your hand will naturally land by your ear-lobe. These are the same muscles you use to do a chin-up. So effectively you are doing a one handed chin-up into the bow.
In the Medieval method, the Latissimus Dorsi Muscles involved start under your
arm and go all the way down near your waist. This muscle group is much larger
then the pectoralis Muscles (chest). This muscle group is only second in size
to the Quadricep Muscles group (legs). The Latissimus Dorsi Muscles also have
a mechanical leverage advantage because of the way they are attached to the
arm. There is a good deal of space between the joint and where the attach to
the bone.
I have prepared two small 350 k videos showing the Medieval Method of loosing a bow. Note that in the other pictures on this webpage I am loosing in the Victorian Method.
Things to notice:
1. I start in a low squat position. I need balance for this maneuver that swings
the upper body.
2. The bow starts out pointed down.
3. The elbow swings back over the head to the ear.
4. The bow tilts up so that it is in line with my elbow as the elbow back.
The first video better illustrates the squat stance. The second video better illustrates the arm/waist action.
Physics of a Bow
Now I will go into some of the physics involved in how the bow and arrow works. As you would expect, in order for the arrow to hit a target at a distance and penetrate it, it must hit the target with considerable momentum. That is it the mass of the arrow multiplied by velocity. Momentum = Mass x Velocity. The mass of the arrow is easy enough to calculate, but how does the tension of the bow generate Velocity to the arrow?
This is the exact formula to calculate the exit velocity.
v = (eFx/m)^1/2
v = The exit velocity.
e = The efficiency (all force applied in the same direction). We can assume
it will be 70% for most medieval bows. Modern bows are close to 1. If the value
is 1 is has no effect in the equation.
F= The force to draw the bow fully, commonly known as draw-weight. Keep if mind
that for every inch you underdraw a 50 lb bow, you loose 3 lbs of force or 6%.
m= Mass of the arrow. This will vary based on the arrowhead and length.
x= This is the distance that the string will travel from its rest position to
its fully drawn position. This is equally important to the draw-weight. If you
underdraw you arrow this factor will deminish. Also remember that for every
inch you underdraw a 50 lb bow, you loose 3 lbs of force or 6%.
Note: The ^1/2 in the formula is the same as taking the square root of (eFx/m).
Another factor to keep in mind is that the bow string will stretch over time. I have observed that I loose 5 lbs for every inch the sting stretches.
The main changing variables above are the force and the distance the force is applied over. Lets only consider these variables to see the effect. Let us assume the mass of the arrow will be the same. A medieval crossbow while having a greater draw-weight is drawn a smaller distance. Observe the changing effects of distance and force.
crossbow 200 lb x 8 inch = 1600
crossbow 200 lb x 10 inch = 2000
longbow 80 lb x 25 inch = 2000
longbow 100 lb x 25 inch = 2500
The results of these multiplication have no meaning unless you do the whole equation, but given that I am holding all those other factors equal this gives us a quick view to the importance of variable "x" above (the distance the force is applied over).
Once the arrow exits the bow we must now consider the effects of air resistance and drag on the arrow. The variable of drag is hard to calculate without a windtunnel, specialized equipment and training.
One less significant factor is the kinetic energy of the bow. Part of the energy from the release moves the bow slightly forward. This detracts slightly for the energy pushing the arrow. The equation acquires an new "K" component. The value of "K" is approximately .05 . It is likely that the scales used to measure draw-weight and the exact draw length will not be so precise to warrant factoring in "K". The equation with "K" is as follows.
v = ( eFx / (m + kM))^1/2
Just to give you and idea. If the arrow is shot at a 45 degree angle and there
is no drag (air resistance). Gravity is the only factor and the formula for
range is:
range = v^2/g
So you take the velocity and square it, then divide result by gravity (9.8m/s). This is main part of the equation which must be adjusted for drag.
Once you factor in "drag" the equation becomes a
very complicated.
range = v^2/g ( 1 + cv^2/mg)^-0.74
c = a constant number specific to each individual arrow that allows for the effect of drag.
Sorry I can't do any better then that in explaining the effect of drag, but
at least now we all know all the issues involved and how they relate to one
another.
Let us go back now are consider the effect of efficiency on the formula. For comparison purposes let us consider the following and assume the same draw-weight. The longbow will naturally have a longer power stroke since the recurve has that deep curve. I will assume 70% efficiency for the longbow and 80% efficiency for the recurve.
longbow .70 (25x100) = 1750
recurve .80 (21x100) = 1680
Naturally the efficiency rates here are a best guess based on reproductions following traditional methods. Modern high-end bows have a "e" factor close to 100%. Few bows have survived 600 years and those that have, have lost their original properties of springiness and flexibility, so it is hard to tell with certainty what the historical "e" factors were. We can assume that there was some variation from region to region and from craftsman to craftsman. We have significant evidence to suggest that the recurve was slightly more efficient then the longbow. This is inherent in the recurve's shape and design. We can also see from the formula that the longbow makes up for its small inefficiency with a longer power stroke.
If you have any questions feel free to email me at: tsafa@aol.com