Lower draw weight and increased draw length?

[arwin]

Ok I just traded off my McCullough 52#@28 longbow for a Bob Lee T/D Hunter LB that is 46#@28. Now all my arrows are too short,LOL! I have gained an inch of draw length bringing me just a tad over 28 inch draw. Is there a significant advantage of having a longer draw at a lower weight over a shorter draw pulling more weight? I have heard that the power stroke of a longer draw is better even if your weight is lower. I'm sure everything will point to a positive, but I want to hear some scientific reasons of why. This may help in choosing some new arrows.

[smj]

Energy delivered to the arrow depends on the draw weight and draw length, true enough, and also the efficiency of the bow. In other words, how well does the bow transfer energy to the arrow. Obviously, materials make a lot of difference on this. Typically, a force curve is drawn for a given bow. The available energy is the integral of the area under the curve. Hence, if you look at draw weight, you are going to a higher point, one of more potential. Yet, with a longer draw length you accrue energy for a longer period of time. Which is better - take the integral of the area under the curve! Again, based on materials - the efficiency of the bow - one may have a greater gain than the other. Push a brief period of time with more force, or a longer period of time with less force. At some point, they come out the same. You are giving up 6 pounds at peak force, and gaining only an inch of draw length. You might see if you can dig up the force curves for each bow and plot them both in Excel - you could do some analysis with the data at that point. However, your arrow is an inch longer, a bit more mass as well. So this, too, must be considered in the final analysis... Probably the easy way to do this is to find the right arrow for the new bow and shoot it through a chrono. Borrow the old bow if you can at the shop and do the same. Weigh the arrows, see which one gives you the best energy... Biggest energy wins! With a couple of different weight arrows you can plot the efficiency of the bow in question. Start to plot the arrow mass, arrow speed, and energy put out - as you increase mass you will usually find that the energy goes up with the arrow mass. At some point, this will turn around. The speed will tank with mass increases - you need to pick which speed you want to shoot with. At some point, your arrows start to get to slow to be a whole lot of fun shooting past 12 yards! Now take a look at the force curve for the bow. This is the same no matter what arrow you put on it. Compare the KE on the different mass arrows with the force under the curve, see what % has transfered to the arrow. Plot this result, and you begin to understand the efficiency of your bow for given arrow masses. Then compare one bow to the other.

To better understand efficiency - look down the page on the below listed book -
www.archerylibrary.com/books/pope/chapter04_1.html

Pope and Young gathered bows from where ever they could, and shot a single arrow from each bow to see which worked better... Note that the Yana bow drew 48 pounds, and shot 205 yards. The Alaskan bow drew 80 pounds and only shot 180 yards. The Tartar bow drew 98 pounds, yet only shot 175 yards... Materials make a difference - although, with your bow exchange there may not be much difference at all material wise.

Hope that helps... Let me know if you need more!

[arwin]

Thanks man I appreciate it. Unfourtunatly I do not have access to the old bow. I will have to take a few arrows of different weights/spines and shoot them through a chrono then figure K.E. At this point without the old bow for comparison, I will have to choose the best arrow. I'm a sucker for heavy weight arrows and hopefully the added mass from length will be a help. I would like to have 10-12 grains per pound.