question about arrow weight and speed loss
08-25-2007, 05:24 PM
#1
Thread Starter
Join Date: Apr 2004
Location:
Posts: 2,981
question about arrow weight and speed loss
i was shooting thru the chrono w/ some 520 gr arrows at 240fps from point blank. my buddy was shooting 257fps w/ a 377 gr arrow at point blank. from 23 yards i was shooting 232 fps, he was shooting 243 fps. i lost 8, he lost 14fps. is this a percentage speed loss - or do heavier tipped (200 gr) and spined correctly arrows slow down - well, slower.
i didn't trust him to shoot thru the chrono from any further or we would have done that and i'd have some #'s.
i didn't trust him to shoot thru the chrono from any further or we would have done that and i'd have some #'s.
08-25-2007, 05:40 PM
#2
Nontypical Buck
Join Date: Aug 2006
Location: Southern MD
Posts: 2,520
RE: question about arrow weight and speed loss
I think it is that "momentum thing". The heavier arrows maintain more momentum over distances. Because they are heavier the "drag forces" don't slow them down as much.
08-26-2007, 07:38 AM
#5
Giant Nontypical
Join Date: Feb 2003
Posts: 9,175
RE: question about arrow weight and speed loss
I was going to relate this story to Aussie last weekend at the show, but we kept getting interrupted by folks wanting to look at bows. The nerve of some people!
I learned about this difference in downrange performance a long time ago. I'd decided I wanted flatter trajectory to make it easier to hit that 70 and 80 yard target (NFAA Bowhunter Freestyle Limited class), so I put on a 5" overdraw to shorten my arrow to 29", enough to get from 2216's to 2213's. This is obviously PC - pre carbon. [8D]
I cut down some of my 2216's to tide me over until my new arrows were ready. I did have to close in with my 50 and 60 pins a little, but I expected that because taking the length down lightened them some. Made sense, lighter arrows/flatter trajectory, right?
Took my 2213's out when I got 'em, made a couple of slight tuning adjustments and sighted them in. My pin gaps between 20-40 tightened up considerably. But there was a huge gap between 40 and 50.[:-] The distance between my 50 and 60 pin was wider than it had ever been before.
With the full length 2216's, my pins measured 1 1/16" from the 20 to the 60. With the short 2213's, they measured 1 1/2". Not what I'd expected. Lighter arrows, flatter trajectory???? Something's not right.
Went over to the 80 yard target, did my normal pin stacking to get my aim point and I was horrified. My arrow didn't hit the spot. Didn't even hit the target. It stuck in the dirt 2 yards short of the target. I shot another 3 arrows, just to make sure. I had a nice 4 arrow group in that spot, 2 yards in front of the target.
Went back to the truck and got my shortened 2216's and went right back to the 80. Didn't move the sights. First arrow cleared the top of the target by a good amount. Changed to my 70 yard gap. Arrow stuck in the top 4 ring. Changed to my 65 yard gap. Spot! Spot! Spot!
Went and gathered up all my arrows, hauled my buns to the practice range and re-tuned/re-sighted for the 2216's and put a For Sale sign for a dozen 2213's on the club house.
The heavier 2216's shot a lot flatter at 80 yards, where I needed the flatter trajectory. My pins measured an even inch after I'd sighted back in with them. They were also evenly spaced instead of being real close for the first 3 pins and real wide for the last 2. Eventually I took off the long overdraw because it was a little too critical to shoot well with fingers and settled on a 2" overdraw.
That little experience is what got me really into this arrow weight/momentum/downrange energy retention stuff.
I learned about this difference in downrange performance a long time ago. I'd decided I wanted flatter trajectory to make it easier to hit that 70 and 80 yard target (NFAA Bowhunter Freestyle Limited class), so I put on a 5" overdraw to shorten my arrow to 29", enough to get from 2216's to 2213's. This is obviously PC - pre carbon. [8D]
I cut down some of my 2216's to tide me over until my new arrows were ready. I did have to close in with my 50 and 60 pins a little, but I expected that because taking the length down lightened them some. Made sense, lighter arrows/flatter trajectory, right?
Took my 2213's out when I got 'em, made a couple of slight tuning adjustments and sighted them in. My pin gaps between 20-40 tightened up considerably. But there was a huge gap between 40 and 50.[:-] The distance between my 50 and 60 pin was wider than it had ever been before.
With the full length 2216's, my pins measured 1 1/16" from the 20 to the 60. With the short 2213's, they measured 1 1/2". Not what I'd expected. Lighter arrows, flatter trajectory???? Something's not right.
Went over to the 80 yard target, did my normal pin stacking to get my aim point and I was horrified. My arrow didn't hit the spot. Didn't even hit the target. It stuck in the dirt 2 yards short of the target. I shot another 3 arrows, just to make sure. I had a nice 4 arrow group in that spot, 2 yards in front of the target.
Went back to the truck and got my shortened 2216's and went right back to the 80. Didn't move the sights. First arrow cleared the top of the target by a good amount. Changed to my 70 yard gap. Arrow stuck in the top 4 ring. Changed to my 65 yard gap. Spot! Spot! Spot!
Went and gathered up all my arrows, hauled my buns to the practice range and re-tuned/re-sighted for the 2216's and put a For Sale sign for a dozen 2213's on the club house.
The heavier 2216's shot a lot flatter at 80 yards, where I needed the flatter trajectory. My pins measured an even inch after I'd sighted back in with them. They were also evenly spaced instead of being real close for the first 3 pins and real wide for the last 2. Eventually I took off the long overdraw because it was a little too critical to shoot well with fingers and settled on a 2" overdraw.
That little experience is what got me really into this arrow weight/momentum/downrange energy retention stuff.
08-26-2007, 09:39 AM
#6
Giant Nontypical
Join Date: Feb 2003
Location: HENDERSON KY USA
Posts: 6,634
RE: question about arrow weight and speed loss
You have alot more energy being transferred into your arrow and that will equate into flatter trajectory.He has 55 ft/lb and you have 66 ft/lb,I believe is what I figured.You either have a longer draw or more poundage than him,right?
Arrow weight plays a role but the amount of energy you put into the arrow will directly affect how flat it shoots.
That is why most of the 3-d pros use bows around 65# instead of 55#.(I even know of atleast 1 that uses 80# only)Sure they can match the arrow weight to the poundage and get the chrono speed at the bow but the higher energy setup will yield in flatter trajectory.
This is why I had to get away from fat shafts,I didn't have enough energy to be accurate with them downrange.They lose too much speed too fast and become unstable and float on me.Basically,my groups opened up at distance with them.[:-]
Yes,heavier arrows do retain more downrangespeed.The reason you saw so much difference was a combonation of the 2.
Arrow weight plays a role but the amount of energy you put into the arrow will directly affect how flat it shoots.
That is why most of the 3-d pros use bows around 65# instead of 55#.(I even know of atleast 1 that uses 80# only)Sure they can match the arrow weight to the poundage and get the chrono speed at the bow but the higher energy setup will yield in flatter trajectory.
This is why I had to get away from fat shafts,I didn't have enough energy to be accurate with them downrange.They lose too much speed too fast and become unstable and float on me.Basically,my groups opened up at distance with them.[:-]
Yes,heavier arrows do retain more downrangespeed.The reason you saw so much difference was a combonation of the 2.
08-27-2007, 05:01 AM
#7
Thread Starter
Join Date: Apr 2004
Location:
Posts: 2,981
RE: question about arrow weight and speed loss
i don't quite get that. w/ a chrono at pt blank we're dealing w/ an initial velocity - plain and simple right? the only acceleration we're dealing with is caused be gravity.by the timethe arrow is in the chrono there is no more horizontal acceleration. i don't believe it matters what the bow did, or if the arrows were thrown - i think bg's right - its harder to slow mine down. we're both shooting 29" draw, and our pounds were w/in 2. he had 4" fletchings on a slight offset and i had 2" blazers w/ helical and so offset the vanes are just barely on the shaft - and they won't quite get thru the nap 360 w/out one of the bases touching the launcher. (i over did it just a little.)
08-27-2007, 06:06 AM
#8
Giant Nontypical
Join Date: Feb 2003
Location: HENDERSON KY USA
Posts: 6,634
RE: question about arrow weight and speed loss
Higher energy equals more efficiency.You have heavier arrows and that equates to some of it but there is no way you will see that much difference in speed loss if you shot those same 2 arrows out of the same bow,not at 23 yards.
Think about it,he lost almost twice as much as you.
Try it,it won't happen.
Think about it,he lost almost twice as much as you.
Try it,it won't happen.
08-27-2007, 06:12 AM
#9
Nontypical Buck
Join Date: Feb 2003
Location: Middletown PA United States
Posts: 3,625
RE: question about arrow weight and speed loss
John,
In your case it doesn't matter what kind of vanes are on the arrow when checking the speed out of the bow as there isn't any time for "drag" to slow the arrow down. However, down range an arrow with longer vanes (more surface area) or more offset can certainly make a small difference. I don't think you'd see a whole lot out to 30 yards though unless you "overdo it".
The statement about "pure physics" also assumes that both arrows are using the same fletching at the same angle. There are just so many variables in all this stuff.
In your case it doesn't matter what kind of vanes are on the arrow when checking the speed out of the bow as there isn't any time for "drag" to slow the arrow down. However, down range an arrow with longer vanes (more surface area) or more offset can certainly make a small difference. I don't think you'd see a whole lot out to 30 yards though unless you "overdo it".
The statement about "pure physics" also assumes that both arrows are using the same fletching at the same angle. There are just so many variables in all this stuff.
08-27-2007, 07:13 AM
#10
Giant Nontypical
Join Date: Feb 2003
Posts: 9,175
RE: question about arrow weight and speed loss
The exact same thing would happen even if you did shoot the two arrows from the same bow. The lighter arrow would lose a significantly higher percentage if it's speed and energy than the heavy one would.
The lighter arrow is faster. Increase the speed, you increase wind resistance. Air resistance increases in proportion to the square of velocity. The heavy arrow is slower and has less wind resistance. It doesn't have to spend as much of it's energy cutting through the air as the light arrow. PLUS it's additional mass allows it to use even less of it's energy to cut through the air resistance.
As I've often pointed out, if light arrows can't even penetrate AIR as well as heavier ones, how could anyone think they penetrate as well on game? That's another side of the same issue.
Here's something to peek at for a bit of background on archery ballistics.
http://home.att.net/~sajackson/archery_physics.html
The lighter arrow is faster. Increase the speed, you increase wind resistance. Air resistance increases in proportion to the square of velocity. The heavy arrow is slower and has less wind resistance. It doesn't have to spend as much of it's energy cutting through the air as the light arrow. PLUS it's additional mass allows it to use even less of it's energy to cut through the air resistance.
As I've often pointed out, if light arrows can't even penetrate AIR as well as heavier ones, how could anyone think they penetrate as well on game? That's another side of the same issue.
Here's something to peek at for a bit of background on archery ballistics.
http://home.att.net/~sajackson/archery_physics.html
