moderator problem

[matt_hooks 188]

Come on then Rich, explain the transonic regime to us, and give us your learned thoughts on how it might affect flight of a free flying, unpowered projectile.

 

 

Edited to add, it is probably some of the rounds running slightly hot.

Edited March 17, 2012 by matt_hooks

[.338LM 10]

The destabilisation depends very much on the bullet; or for that matter any other projectile, its shape, CofG and the medium it is transiting through. Some bullets have more 'problem' then others.

 

As for Wiki, very good for general and sometimes misleading info but nothing really beats field trials, especially those using Doppler to validate theory.

 

Without stretching the thread too far of line, another area that is a can of misinformation 'worms' is the field of terminal ballistics.

[richmcgin 32]

Yes 338LM i think you are right, to a degree about the transonic effect. not sure how much has been done with doppler, have read the easily available stuff but not much more.

I know that the main ammo manufacturers, CCI and Federal Give very little thought to transonics as they dont think it has a relivent affect !. a theory i agree with.

[richmcgin 32]

Come on then Rich, explain the transonic regime to us, and give us your learned thoughts on how it might affect flight of a free flying, unpowered projectile.

 

 

Edited to add, it is probably some of the rounds running slightly hot.

Nob !!.

[matt_hooks 188]

It was a serious question. If you proclaim with such certainty that the transonic effect is imaginary, or at least negligible, then you must have some evidence to base this opinion on. If you do then I'd like to hear it, as it might help inform my opinions.

 

On the other hand, if it's a "I don't think it does" then I'll carry on with my opinion regarding transonic flow and the effects on a body flying through it.

[.338LM 10]

Yes 338LM i think you are right, to a degree about the transonic effect. not sure how much has been done with doppler, have read the easily available stuff but not much more.

I know that the main ammo manufacturers, CCI and Federal Give very little thought to transonics as they dont think it has a relivent affect !. a theory i agree with.

Lapua have done a good bit of work that is, I believe in the public domain. There is a lot of material that both the UK and US Governments have however, unfortunately it is not in the public domain. Doppler is also useful in matching Magnus effect theory and practical in long range work. Helps to marry up the 'comeup' charts.

[richmcgin 32]

Ok taking your post at face value, and being the kind of nice chap that iam here it is in brief:

Very little evidence exists to sugest that a bullet, not any projectile, a bullet is effected by influences it encounters during the transonic phase of flight, it is well known that the C of G and C of P change and the increase in BC, can have a destabilising effect, but to what degree? do your bullets tumble into the target? No they dont this is because of rotation which stabilizes bullets in flight, this is complicated by speed of rotation to weight but most people know what range of bullet weights they can use with their twist rate, with modern bullet design taken into account transonic flight problems become negligable.

[richmcgin 32]

Yes 338LM i think you are right, to a degree about the transonic effect. not sure how much has been done with doppler, have read the easily available stuff but not much more.

I know that the main ammo manufacturers, CCI and Federal Give very little thought to transonics as they dont think it has a relivent affect !. a theory i agree with.

Lapua have done a good bit of work that is, I believe in the public domain. There is a lot of material that both the UK and US Governments have however, unfortunately it is not in the public domain. Doppler is also useful in matching Magnus effect theory and practical in long range work. Helps to marry up the 'comeup' charts.

will have to have a look at that lot sounds interesting, i get sadder as i get older!!!!.

[matt_hooks 188]

Stability is not the problem. The problem is out of balance forces. (NOT the same thing)

 

Unless a bullet is perfectly balanced and symmetrical, parts of it will enter the transonic regime at different times. Air flow around some parts of the bullet will remain subsonic, whilst that around other parts will be supersonic. This coupled with gyroscopic precession can easily cause shot to shot variation. Now look at the difference in flow between supersonic and subsonic regimes. Subsonic flow is virtually incompressible, and a boundary layer can form reducing drag and helping keep flow laminar. In the supersonic region flow is compressible and there is no boundary layer formed, so drag is increased and a larger force is exerted on the bullet.

 

This doesn't necessarily lead to instability, but then again it isn't conducive to good accuracy. Any variable that cannot be controlled is bad for accuracy.

[richmcgin 32]

i have explained that before i seem to remember, and yes stability is the problem which is caused by the CP moving. to make it real simple the effect is like jamming the front brake of your bike on, the back end wants to over take the front. i seem to remember explaining about diff air speeds at diff points of a projectile, i think i was told i was talking bollocks.

It may be worth looking up what laupa have done in their tests. we can go on about it for ever and still disagree as their is no way of proving it either way, saying that i would find it easier on the range to disprove it than you would to prove it, Some time ago a bloke called deker was spouting some stuff about this regarding CCI Velocitor.22lr rounds, so i went out and did the long range tests and spoke to CCI, both disproved his theory. ( i think from memory he was try to say it only occurs during deceleration). and yes you mention shot to shot variation well i would accept that but not to any significant degree. dont forget that the transonic period is encountered for the first time in the barrel and the bullet is still being forced to spin at this point and will be well through the transonic period of flight before it is 3/4 up the barrel. the second encounter the bullet is naturally slowing due to air resistance and gravity and modern bullet design and rotation will help the bullet stay stable through the transonic period but the bullet will be slowed further causing the bullet to drop faster.

See what i mean could go on for ever, if you unwrap the sience from the problem and just use what you know and not what you just read up, things become clearer mate, unless you are fully conversant with physics i dont think you can argue the point to any conclusion, that just leaves me with what i know and what i have been told by those that in theory should know!. but i think you get closer to the reality of the transonic issue than Deker did.

[richmcgin 32]

just been reading something similar to this this subject which sort of backs me up but also backs transonic destailistion up too. it gets very complicated the further you dig in and the truth seems to be that no one knows for sure just what does happen, i still recon that for our purposes transonic destabilisation is negligable, even in a .22lr.

 

look up Mike larsen he worked at ATK for a while not sure what he is doing now but he knows his stuff, Hisham Halawi this guy knows every thing there is to know a bout balistics, he was a sniper master and Bryan Litz, who i have just been reading. will warn you though with the exception of Byran Litz they will all bore the socks off you.

[matt_hooks 188]

rich, I have a degree in aeronautical engineering, so yes, fairly conversant with the relevant physics. The transonic regime isn't that complicated!

 

And what you are saying about it is frankly wrong.

 

Transonic flow conditions can only occur when the bullet is travelling through the air, and whilst it is in the barrel it is in a confined state and therefore air flow exerts far less influence.

 

So the bullet is decelerating as soon as it leaves the barrel, so yes, the effect I am discussing occurs only when the bullet is decelerating.

 

Destabilisation is not the issue. Your phraseology is all wrong. The spin of the bullet causes three types of stability. positive, or converging, stability, neutral stability or negative/divergent stability.

 

Positive stability means that if an external force acts on the bullet, once the outside force is removed the bullet tends to converge back to the original path. Neutral stability means that if the bullet is diverted, it retains the diverted course. Negative stability obviously means that if a force acts and is removed, the bullet continues to diverge further and further from the path.

 

So, what we are talking about has nothing to do with stability.

 

If we were talking about an aerofoil then I would agree that as we approach compressible air flow, the centre of pressure moves rearwards, causing a nose down moment. However, we are discussing a cylindrical projectile, spin stabilised, so the C of P is irrelevant.

 

Drag actually decreases as the projectile slows, so the rate of deceleration is slower the slower the bullet travels.

 

I can see you've made your mind up, but I can tell you that the physics says that a transonic projectile will be of dubious accuracy. You might get lucky and get several shots in a row that behave the same, but that proves very little.

[richmcgin 32]

Well i cant argue with your education but phraseology is not the point and if you will forgive me i will still give the term destabilsation because i think it is a good description of something that becomes unstable!. and i bow my head to your knowledge of this subject but i completely disagree that the C of P is irrelevent. and i agree that there will be some effect but i can still disprove Transoic infulence in practice far easier than anyone can prove the theory in practice. as i mentioned i have already done it on the range and british army marksmen will also diprove it on a regular basis. Sure i know that the effect exists but i still think that the it is neglagable. Bryan Litz is a balistian you should look him up he has done quite a bit on this subject.

 

Just cheated and went into the text books and your way off the mark, as i thought the C of P is the main problem, it hink your degree in aeronautical engineering is possibly the wrong field of expertise, i dont doubt you have a good basic knowledge and prob better than mine. but iam going to stick with Ruprecht Nennstiel`s writtings.