Testing E Target Accuracy

[Jennb]

I don't understand all I know about this electronic scoring; has anyone put a camera in front of the target to record actual impact vs electronicly "derived" impact and check in real time?

At Nationals in Lodi, two years ago they displayed a paper target and a printed out electronic result target from one of the top open shooters. Looking at those side by side convinced me that I wanted to shoot electronics and could believe the results.

 

[Keith Glasscock]

The bigger problem with anecdotal evidence and testing on a small scale becomes apparent when we look at the goal of the testing.

In my mind, there are two goals:
1) Ensure that the Score of every shot fired is recorded accurately. That means that random error does not change the score of any shot, better or worse than actual.
2) Ensure that the system gives accurate feedback about impact location to the shooter. It is a closed-loop system, and bad information leads to bad decisions.

If only 0.1% of shots (this is not a statistic, but a made-up number) fall so close to the line that a system could have a random error large enough to cause a score change, and 33% of those actually change a score, then we have an issue to discuss. Competition is about determining who performs the best. Games of chance are a completely different animal.

 

[chkunz]

I found a math error in my previous post. It has been corrected in the post.

Thanks to Clyde for helping me find my error.

Keith, thanks for sending me the calculations. I was able to understand your assumptions and follow the calculations. However, I made different assumptions and got a smaller number. I am not saying my number is correct and yours is not, but it got me to thinking that it may take a more sophisticated analysis to get an answer that is close to reality. I have seen some great work done in this area by folks with PHDs and sophisticated computer programs. Unfortunately we do not have access to that type of analysis.

So here is what I would like to see. I would like to see someone set up a fan with an open sensor E target and actually get some test data. This would not be a difficult test to conduct and then we would know. I would enjoy doing this test myself, I could probably get access to a fan but we do not have power in our pits. Since some folks think this is a big potential problem with the open sensors targets I think this is critical information.

Again thanks for sharing your analysis.
Best wishes, Clyde

 

[Keith Glasscock]

Real world testing always trumps theoretical. That sounds like a great idea.

 

[GeoffR]

The variation in center location as a result of a change in wind across the face of the target isn't all that hard to rough estimate.

Thinking in 2 dimensions:
In a windless environment,a sound wave will propagate in a circle with a radius related to the speed of sound. The time to reach a sensor on the very corner of a 6 ft square target is close to .03771236 seconds from the center (using 1125 as the speed of sound).

If we insert a crosswind across the face, our nice, pretty circle becomes and egg shape. The sound is moving through the air at the same speed as before, but the air mass is also carrying the sound downwind with it.

If we calculate out the elliptical shapes (half upwind, taller than wide and half downwind, wider than tall), we can calculate the effective speed of arrival of the sound wave. In the case of a 5 mph wind, I guesstimate the change in geometric location would be roughly Correction - 0.235 inches at the water line. That number shrinks as the distance between sensors decreases. For a 3 ft square target, it is more like Correction - 0.12 inches.

The problem is that the effects of wind across the target face (even if my guesstimates are completely off) should be the same regardless of distance the bullet travels getting there. It should represent more noticeable effects as the range shortens because the error represents a larger percentage of a ring width.

I know that Adam has the math on this down to a science. Perhaps he will comment.

4/22/19, Corrected a math error.

Hi Keith,

For what it is worth my calculations coincide with yours. About 1/2" per 10 mph on a 6x6 target. Give or take a bit.

The distance traveled by the bullet has no bearing on this.

I think it would be very difficult to prove or at least quantify in the field. I found that the timing relationships at the sensors (TDOA's) were largely unaffected and I put that down to the entire target face being subjected to a uniform shifting air mass. This means no detectable numeric measurement error.

Someone else, independent to me but with greater ballistics knowledge than I have (not hard) as I recall, came up with the same number some time ago (perhaps a year) somewhere on this forum but I can't remember where or what the topic was at the time.

It sure would be nice to prove this theory one way or the other and quantify it!

Geoff.

 

[Keith Glasscock]

The real difficulty in testing this is getting the wind angle right. If the wind starts shifting toward a headwind, the airflow around the face of the target will turbulate and detach from the target face. It should happen at a surprisingly shallow angle.

 

[6BRinNZ]

The variation in center location as a result of a change in wind across the face of the target isn't all that hard to rough estimate.

Thinking in 2 dimensions:
In a windless environment,a sound wave will propagate in a circle with a radius related to the speed of sound. The time to reach a sensor on the very corner of a 6 ft square target is close to .03771236 seconds from the center (using 1125 as the speed of sound).

If we insert a crosswind across the face, our nice, pretty circle becomes and egg shape. The sound is moving through the air at the same speed as before, but the air mass is also carrying the sound downwind with it.

If we calculate out the elliptical shapes (half upwind, taller than wide and half downwind, wider than tall), we can calculate the effective speed of arrival of the sound wave. In the case of a 5 mph wind, I guesstimate the change in geometric location would be roughly Correction - 0.235 inches at the water line. That number shrinks as the distance between sensors decreases. For a 3 ft square target, it is more like Correction - 0.12 inches.

The problem is that the effects of wind across the target face (even if my guesstimates are completely off) should be the same regardless of distance the bullet travels getting there. It should represent more noticeable effects as the range shortens because the error represents a larger percentage of a ring width.

I know that Adam has the math on this down to a science. Perhaps he will comment.

4/22/19, Corrected a math error.

help me out here - if there is a complete wind reversal is the potential difference between acoustic centres ~.24" for a 3 foot sensor position and ~.47" for a 6 foot sensor position for a 5 mph wind? I assume this wind has to be directly across the target face?
To any that might reply.
This isn't bashing. I just want to understand and there is nothing wrong with trying to understand!
If you can't constructively reply to this post please don't.

 

[GSS]

The real difficulty in testing this is getting the wind angle right. If the wind starts shifting toward a headwind, the airflow around the face of the target will turbulate and detach from the target face. It should happen at a surprisingly shallow angle.

I / many feel;
no matter the wind or other conditions on any given range on any given day the saving grace is what shows up on the monitors of all E targets on the range that day they will all have shot in the same conditions with any slight real or perceived E Target discrepancies included equally for all.

This could be near impossible to quantify and many are just rolling with it and enjoying the benefits E targets bring to our game.

G-

 

[GeoffR]

I / many feel;
no matter the wind or other conditions on any given range on any given day the saving grace is what shows up on the monitors of all E targets on the range that day they will all have shot in the same conditions with any slight real or perceived E Target discrepancies included equally for all.

This could be near impossible to quantify and many are just rolling with it and enjoying the benefits E targets bring to our game.

G-

I can't resist.

So what happened to the .25" accuracy requirement? Or is that off the table now?

So what measurement standards really apply in reality? Especially when contemplating high stake prizes and records? (I am not talking "personal systems" but rather those used in serious competition.

George... this problem (and others) go away with closed targets that don't necessarily have to cost $1000's of dollars.

A while back I shot at 800 metres in a competition on manual targets. Eight or nine shooters per target. Those at the start of the series had hellish conditions with a thunderstorm that passed through that whipped up a real flurry of wind. Scores were abysmal for those guys - some of the best in Australia. By the time I got to shoot (maybe 1/2 hour later) we were in gallery conditions - no wind at all. I got up with a 50.9 and as I recall won the range prize.

I guess my point is that it is not correct to state that everyone shoots in the same conditions on any day and that the best shot wins. I was certainly not the best shot on that range that day! The weather is not something any of us can control - other than to not shoot in such conditions. Do we accept the same rationale when it comes to technology that we do have some control over?

I'm sorry but I simply do not accept what you have just said.

Geoff.

 

[GSS]

I can't resist.

So what happened to the .25" accuracy requirement? Or is that off the table now?

So what measurement standards really apply in reality? Especially when contemplating high stake prizes and records? (I am not talking "personal systems" but rather those used in serious competition.

George... this problem (and others) go away with closed targets that don't necessarily have to cost $1000's of dollars.

A while back I shot at 800 metres in a competition on manual targets. Eight or nine shooters per target. Those at the start of the series had hellish conditions with a thunderstorm that passed through that whipped up a real flurry of wind. Scores were abysmal for those guys - some of the best in Australia. By the time I got to shoot (maybe 1/2 hour later) we were in gallery conditions - no wind at all. I got up with a 50.9 and as I recall won the range prize.

I guess my point is that it is not correct to state that everyone shoots in the same conditions on any day and that the best shot wins. I was certainly not the best shot on that range that day! The weather is not something any of us can control - other than to not shoot in such conditions. Do we accept the same rationale when it comes to technology that we do have some control over?

I'm sorry but I simply do not accept what you have just said.

Geoff.

Pretty much the same response that has been stated and accepted by many in all the other threads this question comes up....

You would have won that day regardless if it were electronic targets or paper targets with wet wrinkled paper and pasters falling off in the rain on the early poor weather conditions.

 

[Keith Glasscock]

help me out here - if there is a complete wind reversal is the potential difference between acoustic centres ~.24" for a 3 foot sensor position and ~.47" for a 6 foot sensor position for a 5 mph wind? I assume this wind has to be directly across the target face?
To any that might reply.
This isn't bashing. I just want to understand and there is nothing wrong with trying to understand!
If you can't constructively reply to this post please don't.

Please note that I updated the numbers for my calculations yesterday.

If I understand your question correctly, you are asking if a 5 mph direct crosswind, left to right, suddenly became a 5 mph direct crosswind, right to left what would happen to the acoustic poi?

I believe that 0.47" change is correct for that scenario. Mathematically, it works. The next step is to investigate it in the real world and see if the math holds up.

 

[Keith Glasscock]

I / many feel;
no matter the wind or other conditions on any given range on any given day the saving grace is what shows up on the monitors of all E targets on the range that day they will all have shot in the same conditions with any slight real or perceived E Target discrepancies included equally for all.

This could be near impossible to quantify and many are just rolling with it and enjoying the benefits E targets bring to our game.

G-

You are a bit out of context. My post was in response to the notion of testing the effect.

 

[GSS]

You are a bit out of context. My post was in response to the notion of testing the effect.

Sorry, Clarification,
Testing the effect is what I was referring to as "near impossible to quantify".

I'm thinking nearly impossible to definitively, precisely test or measure and get any conclusive meaningful results out of.

Would take 100 pages in a thread like this, or have NASA or Massachusetts Institute of Technology design and perform all the tests it would require. Even then I doubt the results would be precise, decisive, conclusive, definitive in a way that would satisfy everyone.

 

[chkunz]

Keith and GGS, I believe it is possible to learn a lot with a simple test that would be feasible do. There are a lot of opinions that say that the wind is an important factor with estimates of tenths of an inch in the 5 to 10 mph wind range. We do not have to have a precise answer to 0.01 inches, just a test to tell us if our opinions and calculations are in the right ball park.

 

[6BRinNZ]

Please note that I updated the numbers for my calculations yesterday.

If I understand your question correctly, you are asking if a 5 mph direct crosswind, left to right, suddenly became a 5 mph direct crosswind, right to left what would happen to the acoustic poi?

I believe that 0.47" change is correct for that scenario. Mathematically, it works. The next step is to investigate it in the real world and see if the math holds up.

Thanks Keith.

I think this answers some theoretical discussion where the acoustic centre is offset (windage) by 1 moa and a complete reversal happens. In the discussion it was assumed you would now need to allow up to 2 MOA (as an example) but what we can see here is that a complete reversal would still only require a 1 moa correction. The group on paper would look terrible but the score would be correct based on the correct wind judgement.

 

[Keith Glasscock]

Yet, knowing exactly what to expect as to center shift might be the difference between winning and losing.

It is much like learning the effects of mirage. Those that understand it tend to score better than those who do not.

 

[chkunz]

No difference in the results with a stationary frame of reference or reference frame moving with constant speed.

Steve, I have been thinking about this and the basic difference is that when the bullet moves thru the air at some Mach number the stagnation temperature and stagnation pressure used in the compressible fluid flow equations are the ambient conditions. When air is moved over bullet that is held stationary (as in a wind tunnel), to achieve the same Mach number the stagnation temperature and stagnation pressure that are used in the compressible fluid flow equations must be high enough that when the gas is expanded the Mach same number is achieved.

 

[243Mendoza]

Steve, I have been thinking about this and the basic difference is that when the bullet moves thru the air at some Mach number the stagnation temperature and stagnation pressure used in the compressible fluid flow equations are the ambient conditions. When air is moved over bullet that is held stationary (as in a wind tunnel), to achieve the same Mach number the stagnation temperature and stagnation pressure that are used in the compressible fluid flow equations must be high enough that when the gas is expanded the Mach same number is achieved.

The stagnation pressure when a bullet is moving through air is Pstag=Patmosphere*(1+0.2Mach)**3.5

For wind tunnels where a reservoir feeds the test section, the stagnation pressure is the pressure in the reservoir.

Another way to look at it, the SR71 skin heat up because it reaches the stagnation temperature of air.

Also for wind tunnels, it may be required to heat the air in the reservoir to avoid condensation and liquefaction of air (if the speed is high enough).

 

[SWRichmond]

I / many feel;
no matter the wind or other conditions on any given range on any given day the saving grace is what shows up on the monitors of all E targets on the range that day they will all have shot in the same conditions with any slight real or perceived E Target discrepancies included equally for all.

This could be near impossible to quantify and many are just rolling with it and enjoying the benefits E targets bring to our game.

G-

The bolded part of your statement is obviously false. The wind on the face of each target is not the same. It is very very different across the range. This means the accuracy of displayed shot result is not the same for all shooters, or even from shot to shot.

Is this what you want me to "roll with" and enjoy tje benefits of? The fact that it is impossible to quantify the differences is not a recommendation for electronic scoring devices.

Fix this and I might consider them viable for high level competition.

 

[GSS]

The bolded part of your statement is obviously false. The wind on the face of each target is not the same. It is very very different across the range. This means the accuracy of displayed shot result is not the same for all shooters, or even from shot to shot.

Is this what you want me to "roll with" and enjoy tje benefits of? The fact that it is impossible to quantify the differences is not a recommendation for electronic scoring devices.

Fix this and I might consider them viable for high level competition.

Personally I believe the current affordable systems available do all we need them to do.

There will be those trying to sell high priced systems that will always work to cast doubt on their competition and some that will just plain never trust E targets period.

We'll have to get NASA to figure out the details on IF OR HOW it effects every target from every swirling wind angle. Even if they did there will always be doubters and nay sayers. So I won't waste bandwidth debating it.

It's really very simple,
If you don't like or don't trust E targets. Support ranges that still use paper and pull pits. When there are no ranges that still use paper near you,,,, there is always golf, fishing or square dancing...

Those of us that like and Trust E targets will be shooting on and supporting ranges with E targets.

Simple as that...
Happy Shooting to you,
George