jkb

I know how to figure K E but is there a formula for figuring the speed I would drop by going a little heavier arrow.???????How much K E do I need to put arrow threw deer at 40 yards????

BGfisher

If you can shoot the bow after it is tuned well, and shoot a normal configuration of any modern compound bow/arrow setup with the bow peaking about 50# then you have enough for deer. Regardless of the Kinetic Energy. Don't you know???? Kinetic energy kills nothing. Well placed, very sharp braodheads are what does the killing.

Screamingeagle

And momentum = penetration.

PABowhntr

jkb,

Steve Jackson has a website with a variety of archery related "calculators" on there. That might help. www.bowjackson.com Also, I believe the general rule of thumb is 1 fps lost for every 3-4 grains of arrow weight added.

Hope this helps.

Gundigest

It only takes about 40 ft-lbs of kenetic energy for a pass threw on a deer, however shot placement is more important. The Gold Tip website has some calculations on it.

98Redline

One thing to remember when figuring out the change in arrow speed vs. a change in arrow weight......The KE developed is a function of the bow more than a function of the arrow. In mathmatical terms, the KE developed is the integrated area under the draw force curve for the bow, minus the bow inefficencies (friction, noise, etc....).

Given a bow with the same draw length and weight, the KE developed for a super light arrow will be nearly the same for a super heavy arrow. The light arrow will just be a ton faster.
There are some small gains for using a heavy arrow as the bow efficency tends to go up which will yield you slightly more KE, but this figure is normally < 1ft-lb.

Sylvan

KE = m/2 x (SE / (m + mv))**1/2

where:
SE = stored energy
KE = kinetic energy
m = mass of arrow
mv = virtual mass of the bow

Clearly, KE is a function of the mass of the arrow. If we use an example of a bow storing 90 ft/lbs that throws a 350 grain arrow at 300 ft/sec which is 70 ft/lbs and we assume virtual mass to be 100 grains then that same bow will propel a 600 grain arrow at 240.5 ft/sec which is 77.1 ft/lbs. This is a 7.1 ft/lb or 10.2% increase in KE. In my opinion this is a very significant increase. In terms of momentum the change is from .47 to .64 slug ft/sec or a 37.4% increase. Certainly, super light arrows will travel alot faster but its also true there is a price to be paid.

SA Techie

One other thing, mechanicals (If ure shooting them) will need a bit more KE than fixed blades. Spitfires and the like open at around 55# or so.