Shooting pellets vs arrows

PLEASE HELP TO FUND ARCHERY INTERCHANGE

4d4m

Active member
Oh. Well yes we generally talk about airgun and bow "power" but mean kinetic energy of the projectile not power in physical terms. I'm just curious about what the divisor is to get a figure of actual "power" in terms of work done per unit time, and what purpose that measurement serves for devices like guns and bows.
 

Kernowlad

Supporter
Supporter
I have to admit I just stuck the numbers through this and stuck the factory FPS figure through it and weighed my arrows.

With the gun I have a chronograph so it’s calculated from that. Sadly it’s no good for arrows.
 

malbro

Instinctive Archer
Supporter
Oh. Well yes we generally talk about airgun and bow "power" but mean kinetic energy of the projectile not power in physical terms. I'm just curious about what the divisor is to get a figure of actual "power" in terms of work done per unit time, and what purpose that measurement serves for devices like guns and bows.
Power is measured in all sorts of units but from an archery point of view power can be measured in ft.lb/s ( no longer regarded as a standard measurement). This is mass measured in pounds multiplied by velocity in ft/s that is lb.ft/s so the instantaneous power at the point of release is the weight of the arrow multiplied by its speed. The only factor in the calculation is the conversion of grains to pounds. The calculation of energy in imperial units ft.lb can be calculated from the formula energy = mass multiplied by velocity squared multiplied by a constant that converts ft².lb/s² to ft.lb, so this constant has units of s²/ft (in other words an inverse of acceleration) and will also include a conversion from say grains to pounds.

I weighed my arrows in grains and used a chronograph to measure the arrow speed, positioned close to the bow to get the velocity leaving the bow, I took the average of three arrows both in terms of weight and speed. The chronograph works with an app where I can collect all the data and store it for each set of arrows.

I am in the middle of testing a series of arrows with different weights and also size of fletching to get a correlation of arrow weight, fletching size, speed and distance travelled, this lead me to consider the energy transfer from the bow to the arrow to get the best from the bow.
 
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English Bowman

Well-known member
I have to admit I just stuck the numbers through this and stuck the factory FPS figure through it and weighed my arrows.

With the gun I have a chronograph so it’s calculated from that. Sadly it’s no good for arrows.
The factory FPS is with very light arrows, to make the calculation work you need to measure the speed of the arrow that you are using. Can you not shoot your arrows through your chronograph?
 

Kernowlad

Supporter
Supporter
The factory FPS is with very light arrows, to make the calculation work you need to measure the speed of the arrow that you are using. Can you not shoot your arrows through your chronograph?
Nope; it’s a small one that fits on the end of the muzzle.
But I would say my Powerflights are very light..
 

AndyW

Well-known member
Approx 320fps and my XX75s weigh 30 grams so 462 grains. My Powerflights are a lot lighter; my ACGs a little more at around 360 grains.
Kernowlad, lol, I'm sure you meant to say exactly 300fps and not a fps more. You did swap to NFAS remember.
 

Kernowlad

Supporter
Supporter
I said approximately. Its three years old and almost certainly down on factory “power.” I’ll call it 300. I’ll also chrono it when I get the chance.
I'm also fairly sure it's for tournaments only - we haven't been in one since Autumn 2019.
 
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4d4m

Active member
@malbro
OK, it just seems a very odd metric on a projectile device: instantaneous "power" on the moment of release. I've never heard of it in 35 years of obsessing over air rifles and their science.

But your lb.ft/s is more useful as a measure of momentum (mass x velocity i.e pounds x feet per second), rather than power (pounds-feet per second) even though the unit is equivalent.

The typical constant for ballistic calcs with imperial units is 450240, derived from the 1/2 in the KE formula (e = 0.5 m.v^2), the number of grains in a pound (7000) and the acceleration due to gravity (32.16 ft.s^-2). You need the acceleration of gravity value to convert from pounds (mass) to pounds-force (lbsF). From velocity in fps and mass in grains this gives energy in ft.lbsF (and almost nobody includes the F, instead using the incorrect but generally accepted ft.lbs "foot-pounds"). Problem is gravity varies at different points on the Earth's surface, so you never truly accurately know your air rifle's power unless you measure gravity where you are when shooting! ;)

In SI you don't need to worry about this and can happily use metres, kilos and joules with the standard 0.5 m.v^2
I still use imperial by force of habit but generally switch to SI when things get complex.
 

Kernowlad

Supporter
Supporter
@malbro
OK, it just seems a very odd metric on a projectile device: instantaneous "power" on the moment of release. I've never heard of it in 35 years of obsessing over air rifles and their science.

But your lb.ft/s is more useful as a measure of momentum (mass x velocity i.e pounds x feet per second), rather than power (pounds-feet per second) even though the unit is equivalent.

The typical constant for ballistic calcs with imperial units is 450240, derived from the 1/2 in the KE formula (e = 0.5 m.v^2), the number of grains in a pound (7000) and the acceleration due to gravity (32.16 ft.s^-2). You need the acceleration of gravity value to convert from pounds (mass) to pounds-force (lbsF). From velocity in fps and mass in grains this gives energy in ft.lbsF (and almost nobody includes the F, instead using the incorrect but generally accepted ft.lbs "foot-pounds"). Problem is gravity varies at different points on the Earth's surface, so you never truly accurately know your air rifle's power unless you measure gravity where you are when shooting! ;)

In SI you don't need to worry about this and can happily use metres, kilos and joules with the standard 0.5 m.v^2
I still use imperial by force of habit but generally switch to SI when things get complex.
Interesting; I had been wondering why muzzle energy had the same units as torque. Now I know why!
 

AndyW

Well-known member
I said approximately. Its three years old and almost certainly down on factory “power.” I’ll call it 300. I’ll also chrono it when I get the chance.
I'm also fairly sure it's for tournaments only - we haven't been in one since Autumn 2019.
It is 300fps whenever you type anything, these posts never die.
 

little-else

Supporter
Supporter
AIUK Saviour
dont forget that your altitude affects the velocity of the projectile as well as needing to adjust for gravity anomalies. Cornwall is full of those, all of the mining activity and granite's fault.
 

FernbankArcher

New member
Coriolis effect yet another excuse
Just had a happy hour reading all of this thread. Tempted to chip in many times on different topics (did it ramble a bit?). I'll have to gather my thoughts first, though, before making any contribution.

My background? I've been shooting recurve (i.e. Olympic discipline) for nearly six decades (just for information). I have shot field (just another form of target), tried compound, longbow etc. but these differing equipment types just never appealed to me so were never pursued. Field was enjoyable but limited rather due to lack of accessible facilities.

I was interested in the comparisons (?) between archery and air weapons. I suffered some minor (but inconvenient) shoulder issues and did consider switching to "air" weapons. Licensing in Scotland put paid to that thought.
One advantage of archery is that it is (so far) licence free.

The two disciplines (air & bow) are physically very different but, psychologically, very similar. The physical differences affecting shot repeatability coupled with the difference in projectile energy, shooting practices, customary target distance and effective range would appear to render sharing facilities (outdoor at least) problematic. Air weapons don't, in my very limited experience, need 170yd shooting grounds.
 

Kernowlad

Supporter
Supporter
Sadly the main airgun forum seems to openly support a very old fashioned, racist, homophobic and medieval old boys network.
Archery may be a bit behind in some ways but at least this forum manages to keep sensible.
 

4d4m

Active member
Sadly the main airgun forum seems to openly support a very old fashioned, racist, homophobic and medieval old boys network.
Archery may be a bit behind in some ways but at least this forum manages to keep sensible.
I know the forum you mean, and at least one other in a similar vein. I must say some of the posters don’t do themselves or the sport many favours. However the one I frequent most (more geared to airgun target shooting) has a better vibe.
 

Kernowlad

Supporter
Supporter
I know the forum you mean, and at least one other in a similar vein. I must say some of the posters don’t do themselves or the sport many favours. However the one I frequent most (more geared to airgun target shooting) has a better vibe.
Which one is it if you don’t mind me asking? I’m on a couple of FB groups but I hate the way even closed group messages seem to end up on every FB friends news feed.
 
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