Some LabRadar Data from Nick Nielsen

[rsterne]

Nick has his new LabRadar, and sent me a bunch of raw data today.... One of the things he did was try and see how far away it would track a 25.4 gr JSB King.... It made it out to about 150 yards several times.... Here is a plot of the Velocity and Distance vs Time....



You can see that the Velocity data starts to spread out past about 80 yards.... but that the Distance curve tracks nicely right out until it lost contact at about 150 yards.... although after 120 yards it started missing the occasional return.... I have two different ways I am analyzing the data at the moment (it's a work in progress).... Here is the plot using the Distance data, smoothed by the trendline equation in Excel.... and then using time and distance increments to calculate the velocity and acceleration....



The data is good out to about 100 yards, and then starts to break down because of the gaps in the data.... The other method I am using is to use the 1st Derivative of the trendline equation for the Velocity and the 2nd Derivative for the Acceleration.... It gives a nice smooth curve for the Cd....



I'm not so sure I trust the data out past 100 yards (ie below ~ 650 fps).... but the processing methods certainly show promise....

Bob

[rsterne]

Here is the Derived Cd compared to the G1 Drag Model for a Form Factor of 1.5.... That would give a BC of 2/3rd of the SD....



From 650-950 fps they aren't too far apart.... The SD of the 25.4 gr. King is 0.0581, which at a FF of 1.5 would be a BC of 0.0344.... Here is what I got for the G1 BC from the Cd data for the King....

950 fps - 0.037
900 fps - 0.034
850 fps - 0.033
800 fps - 0.034
750 fps - 0.038
700 fps - 0.040
650 fps - 0.033
600 fps - 0.023 (data suspect)

Averaging the BC over the entire 150 yards flight I calculated a BC of 0.035.... I'm looking forward to getting some data for 900-1200 fps and also for 500-700 fps to get a more accurate idea of what the complete drag curve looks like.... but the LabRadar is looking like an invaluable tool already....

Bob

[rgb1]

Bob, is the raw data "shareable" ??  I would like
to try a few things in the way of processing......
especially with multiple shots.

                                                         Ron

[nielsenammo]

Bob, is the raw data "shareable" ??  I would like
to try a few things in the way of processing......
especially with multiple shots.

                                                         Ron

I don't have a problem sharing the data. 

I think it would be a good scenario to use the same pellet in multiple guns, different twists and powers to see how the data changes or stays consistent.  Do it all on the same day so conditions are as close as possible.

A less windy day would be good as well, we had a pretty good wind for this shooting.

Nick

[rsterne]

Ron, I would suggest you get the data directly from Nick, as I have already corrupted some of it with my manipulations.... The LadRadar files are .lbr which I can't open.... but the summary (string) files and the individual shot files are .csv files you can open with Excel and then manipulate to your heart's content....

One thing that needs to be done is to record the atmospheric conditions at the time of the test, or the data cannot be converted back to ICAO or NTP conditions.... Without doing that, data from one test won't mesh with other tests by other people or on different days.... The data required is the temperature, altitude and barometric pressure.... and the relative humidity if you can, although it has a much smaller effect.... The temperature is critical to get the speed of sound, as all calulations are done in relationship to Mach number, and then converted to velocity afterwards.... For the pressure, you can either use the altitude PLUS the corrected (sea level) pressure.... OR you can use the absolute pressure at your location.... as those numbers can be easily converted to the atmospheric density, which is the number required to determine the Cd and hence the BC.... The more accurate the weight, and OD of the fired projectile, the more accurate the results, of course....

I should mention that I did not have the atmospheric conditions for the data above, so the Cd and BC data may well be in error by 10% or more.... Ron, do you work with ICAO or NTP, and which would you suggest and why?....

Bob

[rgb1]

Bob,  my preference is for ICAO, if for no other reason than the
ballistics community adopted it exclusively years ago. Those
institutions doing heavy duty research, such as ARL, made the
switch in the 60's. And anyone involved in aviation was using
it long before then........which may have had something to do
with that switch. But as long as information pertaining to the standard
is included with data meant for interdisciplinary sharing, then
all is well. Until approximately a year ago, I had never heard
of NTP. If the explanation I found was correct, it was configured
for use by the fan industry........which I find puzzling. How did
it find its way into ballistics work?

Nick, would you kindly send what was given to Bob, my email
is listed in the profile. And thanks much.

                                                                        Ron

[nielsenammo]

I don't see an email when I go to your profile...

[rsterne]

I sent it to you, Nick....

Bob

[rgb1]

I don't see an email when I go to your profile...

I was assuming that because I can see it, along with other info,
that members could also........and apparently that's wrong.

                 rnburne@aol.com

[nielsenammo]

Thanks Bob.

Ron I sent an email so you can access a Dropbox, I will put the files in that folder.

[rgb1]

Here are the results from a series of shots provided by Nick that were
processed in order to look at data scatter. While Bob's method uses
time as independent variable, mine uses distance.......in exactly the
same manner when evaluating Chrony data. The two were compared
for differences and found to be within .5% of each other. Practically
speaking they're identical and if anyone wants details I can provide
them. Since neither of us had an air density value, the magnitude of Cd
is automatically wrong. Just look instead at the band of values and
consider extracting an average curve from it. While for a given velocity
it's possible to calculate an arithmetic average, that approach would
give too much weight to those few curves that are, in a loose sense
of the word, outside the group. Ultimately, we may find that the best
approach will be to simply hand draw a best fit curve while exercising
a good deal of personal judgement.
Nick, is it possible to get another batch of numbers........for instance
the higher speed stuff like Bob's? This is fun.

                                                                                     Ron

[rsterne]

Fun, yes, but you got totally different results than I did for the Cd.... *pout*.... Not for the JSB Kings, right?....

I don't understand how you can use distance as the independent variable, when it is a function of time.... perhaps you could explain that?....

I agree that the scatter looks scary....

Bob

[nielsenammo]

I can get you more data next time I go shooting.  I don't usually shoot on weekends so I will go middle of the week next week, we have rain coming Sunday/Monday and range is closed Tuesdays.

I gave you and Bob the same data so you should have all the same files.

[rgb1]

I can get you more data next time I go shooting.  I don't usually shoot on weekends so I will go middle of the week next week, we have rain coming Sunday/Monday and range is closed Tuesdays.

I gave you and Bob the same data so you should have all the same files.

Just went back to the dropbox website and found altogether different files
available for download. In the words of Sgt Schultz (Hogan's Heroes).......
 "I know nothing"

                                                                          Ron

[nielsenammo]

If you want more data when I go shooting again it is still no problem.  I hope we can all learn from the data, that was the whole reason for buying it.  I just ask you share your findings with us (or at least me  )

[rgb1]

I don't understand how you can use distance as the independent variable, when it is a function of time.... perhaps you could explain that?....

Bob

Sometimes it's easier to write it out and take a pic

[rsterne]

Yep, you lost me.... *LOL*.... I hate Calculus.... I'll take your word for it....

Bob

[rgb1]

Here are the five high speed shots, four of them group together rather
nicely.....don't you agree? (they were truncated where the data got fuzzy)
Curve A is based on the same string of numbers  as curve 1 but has been
processed using Bob's method, where a fourth order polynomial is used to
represent distance vs time. At 900 f/s they differ by only .5%. My method
evaluates over a small distance interval while Bob's calculates instantaneous
values.........which is potentially more accurate. I will most likely continue to
use both which serves as a cross check and if/when I buy one of these units
will switch to the other method. Each seem to have their respective pluses
and minuses when it comes to sitting at a keyboard.
Bob, in order to figure out the discrepancy in our graphs, I will work thru
one shot showing all steps and email it. You can look it over and note
any differences.......I'm confident we can resolve it without much difficulty.

                                                                                 Ron

[rsterne]

Looks pretty good, Ron.... I assume that is the JSB Kings?.... Your Cd seems to be a bit lower than mine, but then I only did one.... Once adjusted for atmospheric conditions they look VERY close....

Bob

[rsterne]

I spent the day today working on my spreadsheet  for analyzing the Labadar data.... I have decided to use the trendline for the Distance readings for the data string, and then use the 1st Deriviative for the Velocity and the 2nd Deriviative for the Acceleration.... I have revised the spreadsheet to Imperial measurements instead of metric, because most guys in North American will have their LabRadar set up for fps and yards.... I did the same set of shots as Ron did above, and here are the results....



The individual shots are above, and then I combined all the datapoints for all 5 shots into one set and had Excel draw the trendline.... below you can see all 750+ datapoints and the average Cd curve....



My data goes to slightly lower velocity than Ron used.... One of the outputs of the LabRadar is a Signal to Noise ratio.... I used all the data until the first point where the S/N dropped below 10:1.... That took me down to about 680 fps on one shot, and 700 on another.... whereas Ron stopped his data at about 750 fps.... I haven't compared them side my side, but they look to be VERY close....

My spreadsheet also does an average BC(G1) calculation over the entire shot.... The results are very close, the values for shots 1-5, in order, are 0.037, 0.039, 0.038, 0.036, and 0.037, with the average being 0.037 at an average velocity of 825 fps.... All these numbers assumed that the data was collected at sea level, in ICAO conditions.... which I have since found out is incorrect, the altitude was ~ 2100'.... so in fact the Cd is higher and the BC lower than shown by about 7%.... The average BC(G1) at sea level is roughly 0.035....

Bob