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TRULY Taming the harmonics in spring-piston airguns

8/13/2018

19 Comments

 
Quite a few of you, my loyal and greatly esteemed readers, have written to me about why I have been "lazy" and about new work on the Walthers, some others are raring to see further work on the Stormrider. Sorry.
To say that I have been busy, is to put it mildly. With two little ones and an extended family trip (the family is the extended one, the trip was nowhere extended enough, LOL!), it has taken all of my time just to keep the company deliveries going.

BUT, let me give you a GLIMPSE of the things we've been up to. And, for that, let's divide this blog entry into two parts:
Part 1 will demonstrate once and for all that the DIANA Bullseye ZR Mounts WORK.
Part 2 will briefly show what some solid science can achieve where it counts: at the target.

​Let's get started!

Part 1.- Reducing the effects of harmonics in the scope:

To put everything in context, we need to start with an EMail requesting information about why the scopes break or loose zero.
The question came from a professional in the field of harmonics and vibrations, he analyzes issues from operator fatigue in the operation of heavy machinery, to structural elements' breakages that are (or are not) covered by insurance, so, to say that he KNOWS his stuff and that we hit it right off the bat, would be a silly and gross understatement. 
We spoke the same language, we understood things like Fourier Transformations and Differential Calculus, AND he became my hero because he has a LOT of toys.

What sort of toys?

Things like these:
Picture
And these
Picture
What you are seeing here is a dedicated system to evaluate the vibrations produced (in a three dimensional sense) by a machine.
There is a sensor that is attached to the Field Hardened PC that captures readings and these are sent to the PC that then uses a dedicated analysis software to produce a number of critical and important numbers:
​
- Natural frequency of vibration
- Fourier analysis of the extremely complex vibration patterns
- Maximum amplitude of the vibrations in each of the three axes (X, Y and Z)
- Maximum acceleration (in g's averaged over the sample period) suffered by different components in the system.

Airguns are just machines, as much as we may love them and even name them, they are just machines, and so, they can be analyzed using solid physics principles; and the software that applies to one machine can do a good job on another, as long as we know the restrictions and how to interpret the results.

This is the graph produced for an HW98 sensed at a solid mount, as in the first picture,  after the first shock wave has passed:
Picture
C1 axis is the axis that lies along the bore line.
C2 axis is the vertical axis that is perpendicular AND vertical to the boreline
C3 axis is the axis that is horizontal and perpendicular to the boreline.

Do note that the FIRST strong vibration to occur is in the C1 axis (as is logical, since from this axis all the impulse/energy for producing these vibrations gets sourced.
BUT the HIGHEST acceleration (after the shock wave, remember) comes in the C2 axis (in other words, it is a vertical jolt to the scope) and that the sensor, averaging over 100 samples a second (not nearly fast enough, we know, but we will procure a better sensor as time and monies permit), says it is 1g push.
Please do NOT get fixated on the VALUE, because we are measuring extremely fast phenomena with slow sensors. What will be important is what happens when a DIANA Bullseye mount is used, as in the second picture above:
Picture
Axes are the same, but take a closer look at the magnitude of the accelerations detected.
The vertical jolt to the scope is reduced to 0.021 g's, and that from the previous case of 1.00 g; that is 47.6 times smaller! Almost 50 times!

To put it in another way that should be understandable to all airgunners:
Using a DIANA Bullseye ZR mount reduces the vibrations FELT BY THE SCOPE, by 98%, or reduces it to 2% of the full recoil of the rifle.

If you have any doubt as to what vibrations can cause in things, just search YouTube for "Tacoma Narrows Bridge" and you will see what I mean.

A scope erector is not too unlike a suspension bridge. It is a structure that is suspended on a spring, whether it is a bridge or a tube suspended by cables, a coil, or a leaf spring, matters little, it just changes where in the frequency spectrum things start to go "wacky", but it does not change the basic phenomenon.
Part 2.- Reducing the Harmonics at the muzzle of an LGU:

​Now, we had NEVER had so much information, and my friend's help in interpreting the software's results has been invaluable.

My brain, being what it  is (sort of a maze of possibilities), immediately started to go in the sense of detecting which characteristics of a powerplant made the best and highest improvement in the reduction of harmonics, but my friend asked a very valid question:

¿Have you seen the oscillation reducers that are used in buildings?

Well, yes, enormous pendula (pendulums?) suspended from the top of buildings that help reduce the oscillations created by wind, or earthquakes, and in at least one case, tides.
Further research also showed that there are now machine tools utilizing some of these principles, and so the idea was born to make a device that could actually and TRULY reduce the muzzle vibrations of an airgun.

In the past, we had concentrated on TUNING the exit of the pellet to the point of maximum excursion of the muzzle's vibrations, at that point, the muzzle has reached the limit of the oscillation and is starting to return, so, therefore, at that point, the transverse velocity of the muzzle is zero, or very, very, low.
We have talked about controlling the harmonics in another entry. But now, we had the information and the means of actually REDUCING the harmonics where it matters.
​
And so, we decided to start with the requested LGU. Not only was this the rifle that my friend wanted, it was also a rifle that was known to produce very high levels of C2 axis vibration and shock OoB.
As they are issued, the rifles "jump" upwards. A simple result of the different axes on which the action and buttstock have been located.
They are easy to tune and the jump is greatly diminished by the use of a tight top-hat because then the rebound of the piston slows down the vertical jump. It becomes sort of a push-pull toy. You can read more about what can be done to the LGU here.

The rifle was procured from the Netherlands, and after a couple of hundred rounds had been shot as a "run-in", a benchmark target was shot at 35 yards to have an idea of which pellets were the preferred ones by the barrel.
Picture
These are 10 shot groups, but as you can see, apart from the groups shot using the JSB 8.44/4.53's no other pellet shoots reasonably well.

So the quest was on for a device that would suspend a weight, but still offer some resistance to the movement of the muzzle up to the maximum deflections we had found through the vibrational analysis.
We started with complex arrangements, but in the end, we settled for the simplest design that would do the job.

Here we are starting the machining of the element.
Picture
I cannot publicly publish the dimensions, or weight, or materials, that go into the finished product, but perhaps a similar test target, shot under similar circumstances to the one posted above will give you an idea of what was achieved:
Picture
You can see now that the gun shoots quite well not only the original JSB 8.44/4.53 pellets, but ALSO the Baracuda FT.

The Baracuda FT is, so far, an experimental pellet produced by H&N using a similar die to the Baracuda Match, but using a different base punch that yields a total weight of 9.57 grs.
That one rifle CAN shoot accurately pellets that differ so much in weight (more than 13%), is a HUGE result. It means that the harmonics reducer is TRULY doing its job,

Hopefully, H&N will progress from "on test" to "in production" soon, as it is indeed a good pellet (it could be better, but we're in talks about that) and it adds another option to those that enjoy accurate airguns.
As to what happened with the LGU? well it got shipped recently:
Picture
​In store for the future is, of course, analyzing some scopes to find what is their NVF (Natural Vibration Frequency), analyzing other airguns, as well as coming up with a design for a Harmonics reducer that can be fitted to other rifles. There is much to be done and very little time. There is now more and better tools that give us information to confirm, or refute, our theories.
Come, stay tuned, the best is yet to come!

Thanks to those that wrote to me, thanks for the good wishes, and above all, thanks for reading this humble Blog.

Keep well and shoot straight!





​HM
19 Comments

    Hector Medina

    2012 US National WFTF Spring Piston Champion
    2012 WFTF Spring Piston Grand Prix Winner
    2013 World's WFTF Spring Piston 7th place
    2014 Texas State WFTF Piston Champion
    2014 World's WFTF Spring Piston 5th place.
    2015 Maine State Champion WFTF Piston
    2015 Massachusetts State Champion WFTF Piston
    2015 New York State Champion WFTF Piston
    2015 US National WFTF Piston 2nd Place
    2016 Canadian WFTF Piston Champion
    2016 Pyramyd Air Cup WFTF Piston 1st Place
    2017 US Nationals Open Piston 3rd Place
    2018 WFTC's Member of Team USA Champion Springers
    2018 WFTC's 4th place Veteran Springer
    2020 Puerto Rico GP Piston First Place
    2020 NC State Championships 1st Place Piston
    2022 Maryland State Champion WFTF 
    2022 WFTC's Italy Member of TEAM USA 2nd place Springers
    2022 WFTC's Italy
    2nd Place Veteran Springers

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