physics and Ashby

[jnd1959]

I'd like to see the momentum calculation at distances. It may be in the thread but I skipped all the arguments. This is a balance of trajectory versus momentum at the target point. It is my understanding that a lower mass projectile will not conserve momentum at the same rate as a higher mass projectile. At some point in the distance, the momentums will be equal and a lower mass but higher speed projectile will likely penetrate further than a higher mass projectile. After that point, the penetration switches. But there are other effects on the trajectory. Wind, primarily.

Ashby's methods were stated as unscientific. But unless his results were skewed, there may be something else going on from a physical standpoint that effects the equation. Foam, it appears to me, is a relatively consistent medium. Animals are not. There are other considerations than the physics of ballistics at source. Terminal ballistics in projectiles should be our driving consideration, including projectile orientation on impact.

I'm not supporting or defending anyone and it has been years since I studied terminal ballistics. I am raising questions in a true scientific manner. As I get time I will go back and read the posts before this one and see if this is addressed.

[SJP51]

My rig seems to put broadheads into one lung and out the other on deer and hogs. Not sure what else matters. I don't think I'll be hunting elephants or rhinos any time soon.

[enewman]

My first question would be did you tune your bow or did you let the shop "tune" it?

since this data was from joel. no I did not tune my bow nor do I let a shop tune for me. hahaha

I use the HVPS tuning method. All my setups are tuned

[Throwin Darts]

I feel like I’ve read this thread before

[enewman]

I'd like to see the momentum calculation at distances. It may be in the thread but I skipped all the arguments. This is a balance of trajectory versus momentum at the target point. It is my understanding that a lower mass projectile will not conserve momentum at the same rate as a higher mass projectile. At some point in the distance, the momentums will be equal and a lower mass but higher speed projectile will likely penetrate further than a higher mass projectile. After that point, the penetration switches. But there are other effects on the trajectory. Wind, primarily.

Ashby's methods were stated as unscientific. But unless his results were skewed, there may be something else going on from a physical standpoint that effects the equation. Foam, it appears to me, is a relatively consistent medium. Animals are not. There are other considerations than the physics of ballistics at source. Terminal ballistics in projectiles should be our driving consideration, including projectile orientation on impact.

I'm not supporting or defending anyone and it has been years since I studied terminal ballistics. I am raising questions in a true scientific manner. As I get time I will go back and read the posts before this one and see if this is addressed.

miss read

[enewman]

I'd like to see the momentum calculation at distances. It may be in the thread but I skipped all the arguments. This is a balance of trajectory versus momentum at the target point. It is my understanding that a lower mass projectile will not conserve momentum at the same rate as a higher mass projectile. At some point in the distance, the momentums will be equal and a lower mass but higher speed projectile will likely penetrate further than a higher mass projectile. After that point, the penetration switches. But there are other effects on the trajectory. Wind, primarily.

Ashby's methods were stated as unscientific. But unless his results were skewed, there may be something else going on from a physical standpoint that effects the equation. Foam, it appears to me, is a relatively consistent medium. Animals are not. There are other considerations than the physics of ballistics at source. Terminal ballistics in projectiles should be our driving consideration, including projectile orientation on impact.

I'm not supporting or defending anyone and it has been years since I studied terminal ballistics. I am raising questions in a true scientific manner. As I get time I will go back and read the posts before this one and see if this is addressed.

here is the data you are asking about. I did this test out to 50 yards.

I show FPS. KE. momentum, time in flight.

[enewman]

I feel like I’ve read this thread before

you have. I just showed a way to look at momentum using the work energy.

You will be seeing a third time when I finish my test. then a fourth and maybe a fifth.

I will be added NEWTINOAN AND NON-NEWTONIAN into my testing.

[WItoTX]

OP, can you recreate Ashbys tests and get the same results? Or has anyone else in the industry recreated his results?

If you get the same results, that means he's not wrong (Not necessarily right as to why though either). If you get different results than him, that means he is wrong.

I guess what I am saying, the best way to support your position is to try and prove yourself wrong. And if the best way to do that is test Ashbys method. If you cannot recreate it, then there are variables that are un-quantified in his method that are creating outcomes he hasn't considered.

Regardless of all that, appreciate the info!

[txchuck]

A foam target does not represent the body of an animal. To get an answer you have to account for the increase in penetration resistance with speed of the projectile.

[Duckologist]

since this data was from joel. no I did not tune my bow nor do I let a shop tune for me. hahaha

I use the HVPS tuning method. All my setups are tuned

I wasn't asking you. Perhaps go back and read it again. I was saying your first question to the guy with poor penetration was what broadhead did he use. That is when I said, that would not be my first question

[enewman]

OP, can you recreate Ashbys tests and get the same results? Or has anyone else in the industry recreated his results?

If you get the same results, that means he's not wrong (Not necessarily right as to why though either). If you get different results than him, that means he is wrong.

I guess what I am saying, the best way to support your position is to try and prove yourself wrong. And if the best way to do that is test Ashbys method. If you cannot recreate it, then there are variables that are un-quantified in his method that are creating outcomes he hasn't considered.

Regardless of all that, appreciate the info!

no, nor can Ashby.

Has anyone ever done Ashby's study? no. I doubt it will ever be done again. the study was to show Africa we can kill with a bow. that is what the natal study was all about.

I am looking at testing some of Ashby's thoughts. Now the difference is I will be using test media I can control. Animals are not good test media when looking at physics. If we didn't care about physics and only animals then of course.

I'm still looking at a few other things include gel. but I don't think I want to spend the money.

The study that Ashby did was good. he showed that setups with low energy with a good mass and broadhead can kill animals.

I think the mechanical advantage Ashby shows is without a doubt great information.

But we do not need that kind of mass or broadhead with a compound bow. Or maybe I should say with a bow with high energy. as short draw people as myself and low draw weight would benefit from arrows like the ashby study.

[Duckologist]

A foam target does not represent the body of an animal. To get an answer you have to account for the increase in penetration resistance with speed of the projectile.

Correct. I think the results would be different if using an animal vs foam

[enewman]

I wasn't asking you. Perhaps go back and read it again. I was saying your first question to the guy with poor penetration was what broadhead did he use. That is when I said, that would not be my first question

I do apologize. Im reading fast so I can just answer.

[enewman]

A foam target does not represent the body of an animal. To get an answer you have to account for the increase in penetration resistance with speed of the projectile.

That is why a specifically state this is a physics test in a foam target. Let's not forget that physics quantified the test in the foam target.

How much do you think resistance comes into play? Ashby talks about the fluid drag formula. he only talks about one part of it. velocity. That will also be the only part I will look at so its a comparison.

HE talks about a 700gr arrow at 150fps and a391gr at 300fps. he talks about the double velocity gives quadrible resistance. now he only talks about it and never gives any test data. I will be doing this test. I will have double velocity. My arrow weight may not be the same. But as long as the velocity is doubled it will not matter.

[enewman]

Correct. I think the results would be different if using an animal vs foam

I do too.

this is was not what this test was about.