Plunging shot weirdness - need help

Russ Mitchell · Post by **Russ Mitchell** » Sun Nov 19, 2006 3:46 am

Hello gents,

Was out at the levee shooting this afternoon (yes, I *finally* have a place to shoot), and just for giggles, decided to do some high-angle shots.

I don't have chrono equipment or anything like that, so what comes next is going to be weird.

I put out a target and shot the arrows up, trying to have them land on my target (a plastic bag with an arrow through it to keep it from blowing away). These were generic arrows with the typical freaking huge American fletchings, so they got all over the place by the wind, and my shooting isn't all that great to begin with.

But when, at about 80 paces, I tried to calculate the speed of the arrow, I waited to the stall point, and counted until they hit the ground. The average was almost exactly four seconds.

4s*32.5 ft/s^2 = 130 fps or 4s*9.8m/s^2 = 39.2m/s^2.

Now, I was shooting, again, ye olde typical wood arrow with a target point, which weighs, as close as I can tell on my wife's kitchen scale, about an ounce/437gr.

Now, here's the weird thing. I was shooting one of Grozer's "Scythian" bows (the "Sacytha" jobbie off his site is what he's calling it now)... but I specifically picked a bow that my wife and her girlfriend could shoot.

I know these bows are more efficient than longbows, and the the Turkish bow tests really get up there in speed... but 130 fps, from a 22lb bow?

Now, I realize that this ain't hitting with a lot of force (.028kg)*39.2m/s^2 = 1.1N ... but isn't that awfully fast for a bow *that* weak?

Can somebody help me out here?
tnx...

Adam Karpowicz · Post by **Adam Karpowicz** » Sun Nov 19, 2006 5:17 pm

I recall the formula for frictionless (no air drag) flight straight up is: V = tg/2. The time t is counted from the moment of launch till the arrow hits the ground. I imagine air drag would change that, so the time of arrow going up would be less which shortens the max elevation. Less elevation = shorter falling time (unless it is a parachute-like flu-flu). This will give you shorter t, and smaller V.

It is possible the fall time of the arrow is made longer due to air drag. Maybe you can repeat the test with no fletching on the arrow?

Adam

Russ Mitchell · Post by **Russ Mitchell** » Mon Nov 20, 2006 3:02 am

Will do. Was shooting at 75-80 deg, rather than straight up. What's "g" stand for, and what's the units in said equation? t or tg in seconds?

Adam Karpowicz · Post by **Adam Karpowicz** » Mon Nov 20, 2006 11:42 pm

I am sorry, g is acceleration of gravity (32ft/s^2), t is time from launch to fall in seconds, V is velocity in fps. As you wrote, g in metric is 9.8m/s^2.

V = t * g / 2

Adam

Russ Mitchell · Post by **Russ Mitchell** » Mon Dec 04, 2006 6:15 pm

Thanks. I should get out to shoot on Wednesday after my last lecture.

jonR · Post by **jonR** » Mon Dec 11, 2006 4:28 am

Rus
get hold of a copy of David F Butler's book "The New Archery" Theres more pure math related to archery in it thsn any archer really needs.

You may have to seach on Bookfiners as the copy I have was printed in 1968.
JonR

Russ Mitchell · Post by **Russ Mitchell** » Mon Dec 11, 2006 3:49 pm

Thanks. Life has happened, so I haven't gotten back out to shoot... maybe *this* Wednesday...

jonR · Post by **jonR** » Tue Dec 12, 2006 3:11 am

Russ
I know the feeling. Keep trying