Mk108 & MG151/20, two questions for Pyro and gun experts

[Fatty]

They do vary, per plane at least.  Take up the hurricane IID for an extreme example of this.

[MANDOBLE]

Verm, if we want to be purists then even pilot movements into the cockpit will affect the plane. The question is the grade of the shake. Minimal? Enormous? Only longitudinal vibrations? Vertical and side vibrations also? More lateral shake than four wing mounted Hispanos???? Only brake effect?

Pbirmingham, I've read several sources giving different reasons for the Mk108 replacement by Mg151/20 in the He162.
Efectively, several sources say it was due recoil effect, but they do not precisse whether it was due "brake" effect or due real shake effect. Other sources simpy say that two Mk108 with only 50 rounds each was insuficient weapon set being preferame a pair of MG151/20 with much more ammo and better ballistics, and other sources say that the He162 nose were too heavy with a pair of Mk108.

IMO, related to recoil effect, two MK108 mounted in the outer wings of a 190A8 would have much more negative effect than just two of them in the nose of a jet, and a pair of wing mounted Mk108 was considered a valid weapon set for a 190A8.

[hitech]

Mandable: Having spent my fare share of time using a jackhamer I can conclusivly say you are totaly incorect. If you debate it run this test find a spot just high enfo for a jack hammer and your hand on top of the jack hammer to fit between. Now squeeze the jack hammer lever, odds are you will not have many bones left in your hand. Newton explained it very simply for every action there is an = and oposit reaction.

The work required to make a bullet with mass xx and travel at yy speed  is equal to the work transmited to the plane.

You can dampen this force with a spring but the work done remains the same i.e. you can have a 10 lb force for 1 sec or a 5 lb force for 2 secs. But the basic effect is still the same on the plane.


As to the AH modling there are 2 recoil effects being used.

1. Produces the head shake, it its only a graphic effect and does not effect the balistics. Because the gunsight now stayes realitive to you head, it has no net effect other than the apearence of the cockpit shaking.

2. The real recoil effect calculated from the bullet. This is applied to the flight model and varies with every different gun position and with every different ammo type.

HiTech

[pbirmingham]

Originally posted by MANDOBLE
[
IMO, related to recoil effect, two MK108 mounted in the outer wings of a 190A8 would have much more negative effect than just two of them in the nose of a jet, and a pair of wing mounted Mk108 was considered a valid weapon set for a 190A8. [/B]

Again, the flavor of what I read was that the overriding recoil effect was damage to the wooden airframe of the Heinkel.  While wing-mounted MK108s would have a greater effect on the dynamics of the 190, its metal construction meant it wouldn't be damaged by the recoil of its guns.

That's not to say that the recoil was without problems.  Here's another citation  that seems to indicate that the recoil of the MK108 was quite considerable.  It says:

The Mk103 was initially devloped as a ground attack weapon but the RLM needed a weapon to fight the heavy bomber threat that was growing. When installed in a wing application, it proved to be a very powerful and very good weapon, but inaccurate due to the large amount of recoil that was associated with the firing of the weapon. Eventually, the weapon saw service in engine-mounted applications where the recoil wasn't as noticable.

Again, everything I can find on the web indicates that this weapon, far from being recoilless, actually packed quite a wallop in both directions.  I haven't read the sources you're reading, but I'd be glad to if you can point me to them.

[MANDOBLE]

pbirmingham, note that I was talking about Mk108, not about the much more powerful Mk103.

Hitech, agree totally with you, work done is work done. But there are a lot of mechanims to minimize the effect of applying a force every X milliseconds. To minimize that effect is just to "absorb" the effect using mobile parts, springs, pneumatic systems or whatever. OK Let me draw a bit, and beware, my drawings are ALWAYS the ugliests.

The following example implies a solid metal ball, a spring, a table and a paper ball:



The spring is absorbing the impact, and there is no "shake" effect in the paper ball.

[Raubvogel]

I think I had that game for Atari.

[Staga]

There is a reason why you should keep shotgun/rifle pressed against your shoulder when firing it. Recoil is same in both situations  

[-ammo-]

Originally posted by MANDOBLE
pbirmingham, note that I was talking about Mk108, not about the much more powerful Mk103.

Hitech, agree totally with you, work done is work done. But there are a lot of mechanims to minimize the effect of applying a force every X milliseconds. To minimize that effect is just to "absorb" the effect using mobile parts, springs, pneumatic systems or whatever. OK Let me draw a bit, and beware, my drawings are ALWAYS the ugliests.

The following example implies a solid metal ball, a spring, a table and a paper ball:



The spring is absorbing the impact, and there is no "shake" effect in the paper ball.

If you were to put a guage under the legs of that table, it would measure the same for both instances. The differences would the amount of time the force occured.

Think of this example of action/reaction.  Where I grew up folks get stuick in the mud and sand often.  Guys would carry chains and snatch straps to pull folks out of the mud/sand. If I was to attach a chain to the stuck vehicle and drive off with some momentum it would create damage considerable have a jarring effect.  But the result would be that I moved that vehicle. Now if I attached a flexible snatch strap, and tried the same thing, the strap would soften the blow but the same amount of energy would pull the vehicle out.

Another more appropriate example is the M16 Rifle which employs the same basic design as the Mk108 action..although on a much smaller scale. The M16 is a carbine, its bolt is a floating design that rotates around its axis when fired. Behind the bolt is a considerable spring. The 5.56 mm round does not have a considerable amount recoil at all when fired in semi-auto mode, but when in full auto the recoil is more noticeable simply because the rate of fire. The spring does not lessen the amount of recoil, but it does lengthen the amount of time in which the recoil is felt. This makes it much more managable. (the M16 is a gas operated wqeapon, hte Mk103 is a recoil , or blow back operated weapon)

[Pongo]

There are features to an API blowback action that would smooth out  the recoil vs other types of locked bolt firing weapons.
The round is fired befor it it fully seated in the chamber and the last action of the bolt is to seat it as it its fired. The bolt is not locked in place when the round is ignited. IF the firing cycle had the bolt travel suspended by the recoil spring short of the reciever wall then the recoil of the weapon might be dampend considerably.
I am not a scientist. But if the recoil is stored in a spring then expended gradually(relativly) reseating a new round and pushing the bolt forward. How much of the energy expended into the spring is disipated with the reload..that energy that reloads the weapon comes from somewhere...And it follows that if it comes from the recoil then it will not be applied to the airframe.

I guess how much recoil that the airframe is saved depends on how much it takes to reload the weapon.

but...

If we sat a non secured 108 on a table and fired a 5 round burst with it I think that we would all be suitibly impressed with its recoil.....Describing it as recoiless is incorrect. It might have very light recoil for a 30mm cannon but it has plenty of recoil I bet...

[pbirmingham]

Originally posted by MANDOBLE
pbirmingham, note that I was talking about Mk108, not about the much more powerful Mk103.

Whoops!  You're right.  The 8 and 3 looked too much alike to me.

In any case, yes, I understand what you are saying about the spring.  What I am saying is that you are overestimating the effect that the spring will have.  The spring serves to spread out the time over which the momentum is transferred, but my calculations and accounts we've both read seem to indicate that in the case of the MK108, this changes a tremendous force over a short period into a merely huge force over a longer period.

I'll get into this more, but I've got taxes to do.

[MANDOBLE]

Remember that this is not what "I say", it is what the mk108 description sais. The spring / reload mechanism absorbs the energy generated in the shoot. The energy is not vanished, just employed into doing some other work instead of just disipating it against the structure as a rearwards hit.

Resuming, there are mechanisms that will change the way you "feel" a force. Ammo, the example of the quake below the table ins unnecesary, just look at the "quake" in the table surface. In the firts example, that "quake" will make the paper ball to bounce and fall to the ground, but with the spring, the paper ball will "feel" that force in a different way, and it will not bounce a bit. Just imagine this paper ball as the pilot head/body or any other shaking part of the plane.

1. Produces the head shake, it its only a graphic effect and does not effect the balistics. Because the gunsight now stayes realitive to you head, it has no net effect other than the apearence of the cockpit shaking.


HiTech, remember that some of us do not use the sight to aim because of the pronounced bullet drop in some planes. In my case, I use a slightly elevated head poss, using the upper part of the gunsight mounting as a firing reference point. That means that if the head shaking is only an "eye candy" effect, it should be present only when the physics of the shoots imply that shaking.

[hitech]

MAN:

This statment:

just employed into doing some other work instead of just disipating it against the structure as a rearwards hit.

The whole point is there is NOT a dispation of work.The spring simple STORES the work, then the spring puts all that work  back into the plane structure. All work done is stll done to the structure, it's just done with less of a force over a slightly longer period of time. The componts holding the gun will not have to be as strong as without the spring, just as in your table example, That is because we changed the force*time balance but the total momentum transmited to the plane is still exactly the same.

It realy comes down to shooting a bullet forward with X momentum, you decresed the momentum of the plane by X.

There is no way around this other than to add energy to the plane by some other means, such as firing 2 bullets in oposit directions at the same time.

HiTech

[MANDOBLE]

Originally posted by hitech
The whole point is there is NOT a dispation of work.The spring simple STORES the work, then the spring puts all that work  back into the plane structure. All work done is stll done to the structure, it's just done with less of a force over a slightly longer period of time.

Very true, and because that, the paper ball doesn't shake in the second "ball" example with the spring. And that is just my point, If the mechanism minimized that shake effect then my head should keep mostly stable when firing. Just imagine that the pilot's head is the small paper ball, jumping in the first example but inmobile in the second one.

As far as I've understood of your previous explanations, there are two main effects modeled in AH when firing the guns:
1 - Graphical shake with a stable (fixed) gun sight (eye candy?).
2 - Real displacements applied to the airframe due shooting.

The first point affects your head possition, but your real head is stable in front of your monitor, as stable as the gunsight, so, no problem with this graphical effect... ...well, I disagree with that cause some of us dont use the sight as a referece to fire as I told before. If my reference point is the top of the sight mounting, and you are applying an imaginary and eyecandy shake to this, my entire amming is being ruined. Of course, if these simulated head shakes were accurately calculated, then I haven't had anything to complain about.


If we forget about springs mechanisms and so, and we do a crude comparation with hispano, the result is as follow (PlaneX vs PlaneY):

PlaneX, 1x30mm Mk108, 0.312 Kg per bullet with a muzzle vel of 500 m/s

PlaneY, 1x20 hispanos, 0.130 Kg per bullet with a muzzle vel of 880 m/s

If we use kinetic energy (1/2m*v^2) as an aproach to compare the shake probable effects for same place mounting guns:

PlaneX 39000
PlaneY 50336

Does that means that even forgetting about springs, etc, a Me262 should a more stable firing platform than a Typhoon?

[hitech]

Your head would not shake at all in any plane. But there is no other meens of feeling the fibration that your but would feel.

Therefore we add head shake for effect, debating weather its real or not is realy a moot point.

[lemur]

HT, does this mean you're finally going to add visible buffeting when you approach a stall?

~Lemur