H
Harry Fuller
Guest
Analysis of Slow Motion all-of-flight videos; what can they tell us?
Pellet flight and spiral stats ... some observations from SM video
Ted from Madison introduced us to the camera and bracket hardware that fits to our scopes to allow through-the- scope video. Thanks again Ted. ... However most if not all such videos being shown on the internet only show the pellet in the last stages of flight.
I have been concentrating on developing the system to allow for all-of-range-flight depiction and analysis. The results have enabled me to get insights into some, or all, of the following analyses to the degree allowed by the quality of video made with a relatively cheap camera system in daylight.
A. Firstly some of the reference points of interest for me to note in the pellet's flight are:
1. The near zero where the pellet first crosses the line of sight
2. The far zero where the pellet again crosses the line of sight - (the shooter's zero)
3. The trajectory apogee where the pellet reaches the apparent highest point in its trajectory relative to the line of sight.
B. With reference to Dave's Chairgun CGBallistica each of these can be defined in terms of:
1. The time of flight.
2. The location of the pellet in flight between muzzle and target at any instant.
C. These in turn can be related to:
1. The extent of "clean" stable flight down range; and the point where it may become unstable.
2. The onset of spiral flight, if any, and its relationship to A1,2,3 and B1,2.
3. The number of spiraled flight rotations, if present; their direction, frequency per second and per unit distance; and relationship to initial pellet spin rpm .
4. Spiral flight's onset in relation to positive and negative acceleration due to gravity (climbing and descending).
5. Precession /oscillations in the absence of spiral flight (if light and camera settings allow that degree of definition).
Here is one example of flight, shown from the rifle to 71 yards, and some analysis to follow; MV 880 fps with a pellet that became unstable down range: Best viewed full screen (click bottom right corner of video):
http://smg.photobucket.com/albums/v...71ydrifletotargetslowmotionspiralfrom35yd.mp4
In our example we see the pellet first crosses the reticule cross hair at approx 10 yd and reaches the apogee at about 41 yards (distances derived in conjunction with Chairgun); it can then be seen in the video that spiral flight begins at around 35 yards/105 ft. Many pellets that apparently begin well and with stable flight, seem to lose it at about that range/ time of flight and we describe them as "25 or 30 yard pellets".
Approximately 5 left hand spirals from the right hand twist barrel in the last approx 36 yards of flight, can be counted in this example. Five spirals in the last 36 yards of flight equals an average of one spiral every 7+ yards ie., one every 21+ feet of forward travel.
Because the pellet takes about 0.146 seconds (Chairgun CGB) to travel the 36 yards from 35 yards to 71 yards, the rate of spiral would be approx 0.146/5 = one spiral per 0.0292 seconds. Say a rate of 34+ spirals per second, 2,040/min.
As this shot's pellet spin rate (from rifling) is approx 586 rev / sec, 34,800 rpm, (disregarding slight radial velocity decay) then the ratio of spin to spiral is approx 586:34 = 17+ pellet revolutions per each spiral.
Interesting to note that the direction of the spirals is always in oppositional rotation to the pellet's spin direction. Right twist equates with left spiral and vice versa. I have both L and R twist barrels and this always results. No, it has nothing to do with water and sink holes.
My slow motion videos do show that some pellets start spiraling right out of the barrel. The bullet-like old Sheridan .20 cal Bantam is an example which I have videoed numerous times.
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=SheridanBantams25yd-1.mp4
Contrast that with this from JSB .20 cal Exacts shot from the same Sheridan rifle:
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=SheridanJSB25yd-1.mp4
Further, some videos capture oscillations / precession without spiral (seemingly perhaps related to pellet centre of gravity where the forces acting upon the head are somehow counteracted by the drag at the rear), example: - Best viewed full screen:
http://smg.photobucket.com/albums/v...wMagnum25precessionwithoutspiralat51yards.mp4
The practical application of these analyses comes through correlating the above pellet flight quality/characteristics from such full flight slow motion video with:
* group size
* pellet muzzle velocity
* velocity decay rate - drag coefficient and ballistic coefficient BC (as tested for the particular rifle and pellet).
* points on the trajectory curve as they relate to positive and negative gravity to pellet trajectory vectors
* pellet head size and shape (pointed/round/hollow)
* wind direction (head/tail/lateral)
* air density/temperature/altitude.
* and interactions between the above.
To leave the reader with a positive visual impression of clean pellet flight barrel to target, and therefore an optimistic outlook, here is a barrel to target 71 yards pellet flight from a rare "pointed" pellet that does fly true - from a .22 BSA barrel even in a touch of breeze: 3 JSB .22 cal Stratons making a 1/4" / 6.3 mm group at 71 yards:
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=3JSBStratonsat71yd.mp4
And three .25 cal JSB Kings to 51 yards shot from a Swedish FX Smooth Twist barrel at a particular velocity, in a light breeze, making a group of about 0.10" / 2.5 mm and showing great stability:
http://smg.photobucket.com/albums/v...Elite3JSBKings51ydspigsilhouetteJan2012-1.mp4
Hope there is something of interest for everyone here who read this far.
Kind regards, Harry Fuller, Yrrah Down Under.
Pellet flight and spiral stats ... some observations from SM video
Ted from Madison introduced us to the camera and bracket hardware that fits to our scopes to allow through-the- scope video. Thanks again Ted. ... However most if not all such videos being shown on the internet only show the pellet in the last stages of flight.
I have been concentrating on developing the system to allow for all-of-range-flight depiction and analysis. The results have enabled me to get insights into some, or all, of the following analyses to the degree allowed by the quality of video made with a relatively cheap camera system in daylight.
A. Firstly some of the reference points of interest for me to note in the pellet's flight are:
1. The near zero where the pellet first crosses the line of sight
2. The far zero where the pellet again crosses the line of sight - (the shooter's zero)
3. The trajectory apogee where the pellet reaches the apparent highest point in its trajectory relative to the line of sight.
B. With reference to Dave's Chairgun CGBallistica each of these can be defined in terms of:
1. The time of flight.
2. The location of the pellet in flight between muzzle and target at any instant.
C. These in turn can be related to:
1. The extent of "clean" stable flight down range; and the point where it may become unstable.
2. The onset of spiral flight, if any, and its relationship to A1,2,3 and B1,2.
3. The number of spiraled flight rotations, if present; their direction, frequency per second and per unit distance; and relationship to initial pellet spin rpm .
4. Spiral flight's onset in relation to positive and negative acceleration due to gravity (climbing and descending).
5. Precession /oscillations in the absence of spiral flight (if light and camera settings allow that degree of definition).
Here is one example of flight, shown from the rifle to 71 yards, and some analysis to follow; MV 880 fps with a pellet that became unstable down range: Best viewed full screen (click bottom right corner of video):
http://smg.photobucket.com/albums/v...71ydrifletotargetslowmotionspiralfrom35yd.mp4
In our example we see the pellet first crosses the reticule cross hair at approx 10 yd and reaches the apogee at about 41 yards (distances derived in conjunction with Chairgun); it can then be seen in the video that spiral flight begins at around 35 yards/105 ft. Many pellets that apparently begin well and with stable flight, seem to lose it at about that range/ time of flight and we describe them as "25 or 30 yard pellets".
Approximately 5 left hand spirals from the right hand twist barrel in the last approx 36 yards of flight, can be counted in this example. Five spirals in the last 36 yards of flight equals an average of one spiral every 7+ yards ie., one every 21+ feet of forward travel.
Because the pellet takes about 0.146 seconds (Chairgun CGB) to travel the 36 yards from 35 yards to 71 yards, the rate of spiral would be approx 0.146/5 = one spiral per 0.0292 seconds. Say a rate of 34+ spirals per second, 2,040/min.
As this shot's pellet spin rate (from rifling) is approx 586 rev / sec, 34,800 rpm, (disregarding slight radial velocity decay) then the ratio of spin to spiral is approx 586:34 = 17+ pellet revolutions per each spiral.
Interesting to note that the direction of the spirals is always in oppositional rotation to the pellet's spin direction. Right twist equates with left spiral and vice versa. I have both L and R twist barrels and this always results. No, it has nothing to do with water and sink holes.
My slow motion videos do show that some pellets start spiraling right out of the barrel. The bullet-like old Sheridan .20 cal Bantam is an example which I have videoed numerous times.
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=SheridanBantams25yd-1.mp4
Contrast that with this from JSB .20 cal Exacts shot from the same Sheridan rifle:
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=SheridanJSB25yd-1.mp4
Further, some videos capture oscillations / precession without spiral (seemingly perhaps related to pellet centre of gravity where the forces acting upon the head are somehow counteracted by the drag at the rear), example: - Best viewed full screen:
http://smg.photobucket.com/albums/v...wMagnum25precessionwithoutspiralat51yards.mp4
The practical application of these analyses comes through correlating the above pellet flight quality/characteristics from such full flight slow motion video with:
* group size
* pellet muzzle velocity
* velocity decay rate - drag coefficient and ballistic coefficient BC (as tested for the particular rifle and pellet).
* points on the trajectory curve as they relate to positive and negative gravity to pellet trajectory vectors
* pellet head size and shape (pointed/round/hollow)
* wind direction (head/tail/lateral)
* air density/temperature/altitude.
* and interactions between the above.
To leave the reader with a positive visual impression of clean pellet flight barrel to target, and therefore an optimistic outlook, here is a barrel to target 71 yards pellet flight from a rare "pointed" pellet that does fly true - from a .22 BSA barrel even in a touch of breeze: 3 JSB .22 cal Stratons making a 1/4" / 6.3 mm group at 71 yards:
http://smg.photobucket.com/albums/v392/Kyogle/?action=view¤t=3JSBStratonsat71yd.mp4
And three .25 cal JSB Kings to 51 yards shot from a Swedish FX Smooth Twist barrel at a particular velocity, in a light breeze, making a group of about 0.10" / 2.5 mm and showing great stability:
http://smg.photobucket.com/albums/v...Elite3JSBKings51ydspigsilhouetteJan2012-1.mp4
Hope there is something of interest for everyone here who read this far.
Kind regards, Harry Fuller, Yrrah Down Under.
