HuntStand Hunting App
how much energy is lost
Elk
Contributors to this thread:
smurph 30-Aug-21
cnelk 30-Aug-21
tm 30-Aug-21
bigeasygator 30-Aug-21
Grey Ghost 30-Aug-21
HUNT MAN 30-Aug-21
cnelk 30-Aug-21
elknailer 30-Aug-21
cnelk 30-Aug-21
Grey Ghost 30-Aug-21
Jordanathome 30-Aug-21
JohnMC 30-Aug-21
GF 30-Aug-21
PAOH 30-Aug-21
Old Reb 30-Aug-21
cnelk 30-Aug-21
Tilzbow 30-Aug-21
Jordanathome 30-Aug-21
bad karma 30-Aug-21
HDE 31-Aug-21
DanaC 31-Aug-21
APauls 31-Aug-21
Rocky D 31-Aug-21
Grey Ghost 31-Aug-21
smurph 31-Aug-21
Firsty 31-Aug-21
flybyjohn 31-Aug-21
DanaC 31-Aug-21
Jordanathome 31-Aug-21
Tilzbow 31-Aug-21
cnelk 31-Aug-21
Treeline 31-Aug-21
GF 31-Aug-21
12yards 01-Sep-21
GF 01-Sep-21
DanaC 02-Sep-21
GF 03-Sep-21
Zap 03-Sep-21
From: smurph
30-Aug-21
I am wondering how much less energy an arrow possess when guys are shooting longer shots at elk. Say the arrow weight were about 450 grains at an initial speed of 280 fps. How do you estimate the K.E. at say 30, 50, 80 and 100 yards? Does this significantly affect penetration on an animal like and elk?

From: cnelk
30-Aug-21
A few years ago I shot thru my chronograph at 20 - 40yds. I can’t remember the statistics but it was informative

From: tm
30-Aug-21
Shooting thru a chronograph is the only way I could think of to get any idea. Otherwise too many variables.

From: bigeasygator
30-Aug-21
Not sure on the actual metrics, but arrow performance isn’t just based on velocity and KE. For example, often times at long ranges you get much better arrow flight as the arrow has much more time to stabilize. Perfect arrow flight can make up for a lot of that KE loss.

From: Grey Ghost
30-Aug-21
Well, how much math do you want to do? Here's the layman's version with out all the formulas.

Since KE is a function of velocity, and velocity slows down range due to the drag forces, you'd have to calculate the drag coefficient of your arrow first. Then use the drag coefficient to determine the deceleration of the arrow down range. With that you can calculate the velocity of the arrow at any specific distance down range. Once you know the velocity of the arrow at a specific distance, you can calculate the KE at that distance.

The drag coefficient is the most difficult to calculate. You can do it using fluid dynamics, or you can do it with a wind tunnel and force gauges.

I know there are online calculators that will calculate the KE of an arrow as it leaves the bow, but I've never seen one that calculates the KE down range, probably do to the complicated math involved.

Matt

From: HUNT MAN
30-Aug-21
Archery advantage computer program will tell you speed , drop and kinetic energy for every yard 0-100. Have to take a few measurements to get it right. Hunt

From: cnelk
30-Aug-21
Still more fun to shoot thru a chrono at 40yds

From: elknailer
30-Aug-21
yep, as long as its not yours!

From: cnelk
30-Aug-21
Man, if you can’t put an arrow above a chrono at 40yds it’s probably time to get off Bowsite and go practice some more

From: Grey Ghost
30-Aug-21
Yes, if you have access to a chrono that you can set up at any distance downrange, that would be the easiest way to determine KE at specific ranges.

Suffice to say, the KE of any standard weight arrow drops off significantly after about 50 yards. Heavier arrows will retain more KE down range at the expense of trajectory, so yardage estimations becomes more critical for accuracy.

Personally, I think any shot on an elk beyond 60 yards is asking for trouble, regardless of how accurate you are at longer distances.

Matt

From: Jordanathome
30-Aug-21
"I can’t remember the statistics but it was informative"

That is awesome! LOLOLOL

So informative you forkin forgot! LOLOLOL

From: JohnMC
30-Aug-21
How many guys out there would not attempt to shoot through a chronograph they paid good money for that would shoot at a animal at same distance? The hole is similar size to the vitals.

From: GF
30-Aug-21
It’ll probably just piss him off to have me say so, but I think John just asked a damn good question…

“ So informative you forkin forgot! LOLOLOL”

Obviously, the conclusion he came to was “Damn! Forget the whole thing!”

So he did.

You probably don’t need to have your angry ex-girlfriend’s phone number memorized to know that she isn’t interested in your companionship….

From: PAOH
30-Aug-21
Check out Ranch Fairy on YouTube. He did a show on this.

From: Old Reb
30-Aug-21
Jordonathome. Is that your handle because you live at home in your parents basement? LOLOLOL

From: cnelk
30-Aug-21

cnelk's Link
For you smart asses…. See link for my data shooting thru a chrono 7 years ago

From: Tilzbow
30-Aug-21
A compound shooting 280 FPS with 450 grains has way more energy at 80 yards than a nearly any recurve shooting 550 grains at 20 yards. I think we worry about stuff we shouldn’t worry about. That said, no way I’m shooting at an elk at 80 yards but the reason isn’t because I’m worried about penetration with a perfectly placed shot.

From: Jordanathome
30-Aug-21
Actually I moved my mom in with me so I can help take care of her as she has aged. Thx for asking.

From: bad karma
30-Aug-21
FYI, Cnelk is a long time contributor, and has provided a lot of useful info. I would cut him some slack. His info is good even when he can't remember the precise numbers.

From: HDE
31-Aug-21

HDE's embedded Photo
HDE's embedded Photo
I did a backyard experiment back in the days when I thought it really mattered, only to find out it matters more on what your downrange arrow flight looks like as beg mentioned in his post...

From: DanaC
31-Aug-21
You need to chrono at the distance, and square the remaining percent of initial velocity. Then subtract.

Lose ten percent of your initial velocity and you've lost 19% of your KE at launch. (90% = .9. ... .9x.9 = .81. ...100%-81% = 19% loss.)

Lose 20% of your initial velocity and you have lost 36%.

From: APauls
31-Aug-21
I'm with bigeasygator on this one. From personal experience longer shots have zero penetration issues. I've had more penetration issues up close. I've said it many times before that I think arrow stabilization comes into play. People have told me that an arrow stabilizes in like 10 yards so I am out to lunch. Sure, archers paradox or whatever it's called doesn't take long to stabilize but I think real life arrow flight in the air and some wind or whatever takes longer.

If 100% of the energy/momentum stored in the arrow gets pushed through the tip your results will be massively different than even 95%. So while math may or may not exactly explain it, personal experience has been such that I would never worry about penetration at longer distances with a full length arrow. I would worry about the time it takes the arrow to get there, and the other myriad of variables that can change in a long shot, but penetration with a "normal hunting weight arrow" shot out of a reasonably average compound is not one of them.

While it is true that the sample size is much smaller, my experience on penetration at 45-75 yards has been better than 0-45 yards. While I am not arguing that penetration is better at longer distances, it has led me to believe that it is not a worry. I have also only every taken long shots in absolutely perfect conditions. (wind etc.) A small gust of wind pushing the back end of an arrow over or imparting any broadside velocity to the arrow will significantly decrease penetration. That can happen at 20 yards. I've never had it happen on a far shot because I've never taken a far shot with any wind.

From: Rocky D
31-Aug-21
“ From personal experience longer shots have zero penetration issues. I've had more penetration issues up close. I've said it many times before that I think arrow stabilization comes into play.”

Truth, in my experience! It always amazes me at the amount of penetration that I get on longer shots.

From: Grey Ghost
31-Aug-21
Dana's example demonstrates a common misconception. A lot of guys think that a heavy arrow will produce a lot more KE than a light arrow when shot from the same bow. In reality the KE difference between a 350 and 500 gr arrow is only about 7% greater for the heavier arrow, with all else being equal (same bow, same poundage, same draw length). KE is more a function of the bow, not the arrow.

If you really want to drive yourself crazy, look into articles that discuss broad head Mechanical Advantage (MA) and Tissue Penetrating Index (TPI) combined with KE and momentum to determine the true penetrating ability of an arrow.

Like some of you, I was obsessed with understanding the physics of arrow flight, energy, and penetration early in my archery career. And also like some, I concluded that arrow flight was the most important factor. I saw this over and over when I competed in archery tournaments. Back then, there was a 280 ft/sec speed limit at the 3D shoots. Many of us were shooting the exact same bows, arrows, draw lengths, and poundage, at the max speed... The only variable was how well tuned each shooter and his bow was. If you watched closely, you could see which guys were shooting darts versus the guys with less than perfect arrow flight. Invariably, the arrows with the best flight out-penetrated the others...sometimes by a considerable amount.

Matt

From: smurph
31-Aug-21
Thanks everyone for your comments, very helpful.

From: Firsty
31-Aug-21
Well not sure but I dont think cnelk has a long enough draw to shoot a 450 grain arrow at 280!

From: flybyjohn
31-Aug-21
I shot a bull at 70 yards that was standing in a pond. I saw the arrow land in the water under the bulls belly. The bull flinched but didn't take any steps. I then shot a second arrow that hit a branch mid way and did a splash in the pond about 10 yards before getting to the bull. The bull took three steps to the shore and then I shot the third arrow quartering away and hit the heart. The bull stood there without taking a step and tipped over nose first.

Upon looking at the hole through the lungs of the bull and looking at my arrow fleching floating in the water, I concluded that the first arrow passed through the bull and landed on the other side of the elk in the water. The second arrow of course didn't make contact with anything except a stick and the water and the third arrow punctured the heart and the broadhead was just below the hide on the oppossite side front shoulder. So a 375 grain arrow leaving the bow at 304 fps will pass though an elk at 70 yards no problem. It also will burry itself up to the fletching on a quartering away shot after piercing the heart.

From: DanaC
31-Aug-21
Grey Ghost, I noted only KE. 'Momentum' is _resistance_ to velocity loss. An arrow with more momentum slows down more slowly, both in the air and in tissue.

Both momentum and KE are a combination of mass and velocity, but KE depends on the square of velocity, so faster is more impressive.

And as noted above, 'penetration' depends on other factors as well. I've yet to see an equation that takes all factors into account and _predicts_ penetration.

From: Jordanathome
31-Aug-21
Well Heck....I thought Brad's sentence was funny as hell and just commented to poke fun at him not to offend or get the BS'ers all riled up to defend him. Yes I can't remember chit from 7 days ago much less 7 years ago....so my apologies to you Brad. I hope you understood it was posted in good natured jest and not to offend or do harm. :(

From: Tilzbow
31-Aug-21
To my earlier point, the setup I’m using this year starts out at 287 FPS with a 480 grain arrow and 87.7 KE ft/lbs and .61 slug of momentum. At 100 yards this drops to 255 FPS and 69 KE ft/lbs and .54 slug. Still way more than needed. This is with field points and I’m pretty sure a broadhead tipped arrow would slow a little more but would still have plenty of energy.

My 56# Habu hybrid triple carbon longbow shoots a 565 grain arrow 190 FPS. I have a 31” draw…. I don’t think anyone would doubt the capability of that setup but in comparison to my compound it’s only producing 45 KE ft/lbs and .45 slug at the bow.

I realize with my draw length my numbers are high but it still makes for a good comparison and highlights the fact that modern compounds way more capable than needed.

This is the first time I’ve looked at these numbers in year and to the point others made I think tuning and working on a torque free grip to ensure perfect arrow flight is way more important than the other numbers.

One more thing I like to do is use the stiffest arrow possible for my compound, while still getting a perfect tune, to reduce arrow flex at impact. Not sure if it helps but it seems like it should. I yet to find an arrow that’s too stiff to tune so it also comes down to a balance between spine and total arrow weight.

From: cnelk
31-Aug-21
@Firsty “ Well not sure but I dont think cnelk has a long enough draw to shoot a 450 grain arrow at 280!”

Shoot a PSE and welcome to the wild side.

From: Treeline
31-Aug-21
Pretty sure I wouldn’t want to try the cnelk 40 yard challenge with my chrono… but I can get a 450 grain arrow to blaze out of my bow at 180 FPS!

From: GF
31-Aug-21
I can’t vouch for the calibration of the chrono involved, but I did once put 3 shots through a chrono and got a buck eighty-ish at about 8.1 GPP. Which seems pretty near respectable with a Dacron string. 9.5 GPP came down to about 165. Then the damn thing had a (NON)-impact-related conniption and we gave up.

I wonder how far a 500 grain arrow needs to go to scrub from 280 all the way down to 165 feeps???

And I agree that an arrow fully settled in flight will outpenetrate one that’s a lot faster, but still snaking and flying cock-eyed from a poor tune.

Also agree that a stiffer shaft should out-pen a flexier one because arrows flex twice on every shot - at the beginning and the end; flexing can store some energy on launch (still less efficient than zero flex) but flex robs and misdirects “energy” on impact. Bad Juju.

But not as bad as bad Tune….

From: 12yards
01-Sep-21
I suppose a very hard helical on feather fletched arrows might slow it down more at distance. However, It may still have enough momentum to pierce both lungs.

From: GF
01-Sep-21
We Sticky-dudes tend to use way too much feather because they’re purty. And a lot of us because they can't tune their rigs adequately.

But even a straight-fletched, 2” vane creates a huge amount of drag compared to a bare shaft; plenty enough that Todd was able to put a relatively large (by modern standards) BH and shoot it through that B&C moose with just 2-inchers… and a #39 recurve…

Think about it…. At 180 fps, my arrows should strike a 60-yard target 1 second off the string… but it feels more like about 3 and is probably closer to 2 than 1.

From: DanaC
02-Sep-21
" At 180 fps, my arrows should strike a 60-yard target 1 second off the string"

Only in vacuum ;-)

From: GF
03-Sep-21
Precisely.

Arrows slow down way faster than many seem to believe. And the lighter/faster they are, the faster they shed KE.

But I’ll tell ya…. Even though I would be surprised to learn that my #[email protected]“My DL” longbow is generating 175 feeps with a 480 grain arrow right off of the string… I’d sure as hell hate to be standing in the wrong spot when one of those missiles dropped out of the sky from 80 yards out. Even if I was #800 of rutted-up Angry.

From: Zap
03-Sep-21
Dopplar will tell you what you want to know.

Zap

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