Arrow weight

[Buckskinbob]

I enjoyed reading the debate on arrow foc. I've got nothing to add as I would be just saying the same things as others over again, but it got me thinking about arrow weight.

Most people seem to say that as arrow weight increases you get a higher trajectory, which is true if you lose speed because the bow weight stays the same. But let's say you have two arrows with the only difference between them being that one arrows is 400 grains and the other is 700 grains.

Both arrows leave a bow at 200 fps.

The bow draw weights would be different, ofcourse.

Which arrow has a flatter trajectory?

 

[Mighty Mouse]

The heavier arrow would have a flatter trajectory.

 

[Buckskinbob]

So that means we can add arrow weight, while also adding some foc, then conteract the negatively impacted trajectory by upping bow weight.

How much would you need to go up? I'm not sure, but it's not necessarily a black and white trade off of arrow weight and trajectory like people worry that it is. Adding 15 to 20 pounds draw weight is more difficult than changing broadheads but very doable.

 

[Mighty Mouse]

So that means we can add arrow weight, while also adding some foc, then conteract the negatively impacted trajectory by upping bow weight.

How much would you need to go up? I'm not sure, but it's not necessarily a black and white trade off of arrow weight and trajectory like people worry that it is. Adding 15 to 20 pounds draw weight is more difficult than changing broadheads but very doable.

No one is going to dispute that adding draw weight helps trajectory. But increasing draw weight is not a trivial matter, and adding 15-20# is simply unrealistic for most archers. I comfortably shoot a 70# compound. Even if I could get comfortable with an extra 15-20#, I would be hard pressed to find a bow capable of achieving 85-90#.

 

[Redman]

No one is going to dispute that adding draw weight helps trajectory. But increasing draw weight is not a trivial matter, and adding 15-20# is simply unrealistic for most archers. I comfortably shoot a 70# compound. Even if I could get comfortable with an extra 15-20#, I would be hard pressed to find a bow capable of achieving 85-90#.

Yep and you would have to custom order and the price is higher for 80# and up. Not sure why? I have found that a very very sharp heavy one piece broadhead is more beneficial than trying to rip your shoulder out drawing heavy poundage. You give up having pins set close together unless you shoot traditional or no sights...but the whole point in archery hunting is the challenge of getting close.

 

[Buckskinbob]

I guess I'm not familiar with what weights that compounds come in. I tend to look at things through a traditional bow lense, which is where things can get messed up in discussion.

It's probably easier to get ahold of a 90 pound longbow than it is a 90 pound compound. But not to long ago seems that plenty of archers were just fine shooting heavier bows without their shoulders being ripped out.

All of it is something to think about, im not trying to convince someone to overbow themselves. you can have a heavy arrow that is fast if you want one.

 

[bisblue]

According to the folks that just put together the bow tuning course through the Push importance in arrow performance was something like.

1. Archer's form/ability
2. Quality of tune for the bow and arrow (these are limited by ability)
3. Broadhead sharpness
4. Then bow weight, arrow weight, FOC, broadhead design, etc....

 

[Buckskinbob]

According to the folks that just put together the bow tuning course through the Push importance in arrow performance was something like.

1. Archer's form/ability
2. Quality of tune for the bow and arrow (these are limited by ability)
3. Broadhead sharpness
4. Then bow weight, arrow weight, FOC, broadhead design, etc....

I just like watching em fly

 

[Ought Six]

The heavier arrow would have a flatter trajectory.

Why would the heavier arrow have a flatter trajectory? It would have more kinetic energy, but wouldn’t it fall off faster down range than the lighter one because of the higher mass being acted upon by gravity?

 

[Buckskinbob]

Why would the heavier arrow have a flatter trajectory? It would have more kinetic energy, but wouldn’t it fall off faster down range than the lighter one because of the higher mass being acted upon by gravity?

A heavier arrow is more resistant to the friction caused by flying through the air. Gravity acts on all things the same.

 

[sclancy27]

Why would the heavier arrow have a flatter trajectory? It would have more kinetic energy, but wouldn’t it fall off faster down range than the lighter one because of the higher mass being acted upon by gravity?

The acc of gravity is the same, regardless of mass. Gravity affects over time, not mass. So, if two arrows travel the same speed, they will be affected by gravity equally. The heavy arrow and light arrow (given the same geometry, fluid density, and obviously velocity) differ in the way that air resistance (drag force) affects them. Basically, deceleration of the arrow due to drag decreases as mass increases.

 

[bisblue]

I just like watching em fly

One thing I love about traditional is watching an arrow drop into a target at 30 or so

 

[Mighty Mouse]

Why would the heavier arrow have a flatter trajectory? It would have more kinetic energy, but wouldn’t it fall off faster down range than the lighter one because of the higher mass being acted upon by gravity?

As @Buckskinbob and @sclancy27 pointed out, gravity would cause these two hypothetical arrows identical in every regard except weight to fall at (very nearly*) the same rate. However, the drag forces opposing the forward motion of the arrow would cause the lighter arrow to slow down more quickly, thus increasing its total flight time and giving it more time to fall than the heavier arrow. Within the realm of practical arrow weights/speeds and shot distances, this difference in total drop would likely be very small though.

Out of curiosity, I plugged the hypothetical 400 gr and 700 gr arrows launched at 200 fps into the trajectory calculator included with my copy of an obscure reference book called Archery Calculations by Tom Liston. The calculator predicts flight times to a 30 yd target of 0.462 and 0.457 seconds, respectively, which equates to the lighter arrow hitting 0.55" lower than the heavier arrow (if both were launched at the same angle).

*In a vacuum, rate of drop due to gravity would be exactly the same regardless of object weight. In air, the effects of friction (aka, drag) and buoyancy cause a heavier object to fall faster than a lighter object, even if the two objects are of the exact same size/shape. So yes, the effect of gravity does cause the heavier arrow to fall faster than the (otherwise identical) lighter arrow. However, the effect of drag (acting in the horizontal plane along the flight path) is the dominant factor in these arrows' overall trajectories and will affect the heavier arrow to a lesser degree.

 

[Buckskinbob]

As @Buckskinbob and @sclancy27 pointed out, gravity would cause these two hypothetical arrows identical in every regard except weight to fall at (very nearly*) the same rate. However, the drag forces opposing the forward motion of the arrow would cause the lighter arrow to slow down more quickly, thus increasing its total flight time and giving it more time to fall than the heavier arrow. Within the realm of practical arrow weights/speeds and shot distances, this difference in total drop would likely be very small though.

Out of curiosity, I plugged the hypothetical 400 gr and 700 gr arrows launched at 200 fps into the trajectory calculator included with my copy of an obscure reference book called Archery Calculations by Tom Liston. The calculator predicts flight times to a 30 yd target of 0.462 and 0.457 seconds, respectively, which equates to the lighter arrow hitting 0.55" lower than the heavier arrow (if both were launched at the same angle).View attachment 263298

*In a vacuum, rate of drop due to gravity would be exactly the same regardless of object weight. In air, the effects of friction (aka, drag) and buoyancy cause a heavier object to fall faster than a lighter object, even if the two objects are of the exact same size/shape. So yes, the effect of gravity does cause the heavier arrow to fall faster than the (otherwise identical) lighter arrow. However, the effect of drag (acting in the horizontal plane along the flight path) is the dominant factor in these arrows' overall trajectories and will affect the heavier arrow to a lesser degree.

I think the loss in speed is interesting over just 30 yards. Would it be double the loss of speed at 60 yards? Or does it start to compound after the speed initially falls off?

 

[Mighty Mouse]

I think the loss in speed is interesting over just 30 yards. Would it be double the loss of speed at 60 yards? Or does it start to compound after the speed initially falls off?

I would expect the rate of speed loss to decrease slightly with distance because drag force is proportional to speed, so the drag effect should lessen as the arrow travels further and slows down. I think a constant speed loss assumption would give a very close estimate of downrange speed though.

Below are predicted speeds for a 400 gr arrow launched at 200 fps from 0 to 60 yds using the same calculator as before. It predicts initial speed loss of 0.36 fps/yd and 0.34 fps/yd at 60 yds.


For a real world comparison, below is a plot of actual speed vs. distance data collected by John Stallone. The speed trends are roughly linear at an average loss rate of 0.35 fps/yd, and most of the trends show a modest flattening toward the end.

 

[grizzly63]

F the speed "accuracy is final"

 

[Buckskinbob]

F the speed "accuracy is final"

I think that is the argument though, speed is going to help you be more accurate.

 

[grizzly63]

Only if you're shooting too far to begin with.

 

[Buckskinbob]

Only if you're shooting too far to begin with.

Your not wrong

 

[Buckskinbob]

But also, how far is too far?