Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: MANDOBLE on February 03, 2002, 12:59:37 PM
-
Firing wing ROOT mounted MG151/20 produce a noticeable yaw side to side effect in the plane. Is that correct?
Firing Mk108 from a landed 262 I noticed a very pronounced shake in the plane, that means very poor aiming chances in flight.
Mk108 was famous for having no-recoil effect. Is that wrong?
-
Mandoble,
The "cockpit shake" is preset. All guns have exactly the same recoil effects in AH. I agree that it should vary based on the gun(s) being fired.
Take 4 20mm cannon on the Fw190A-5 and fire just the cannon, note the shake. Now fire just the 7.92mm guns. Its the same shake. This is true on all aircraft. The 4 .303s on the Mossie shake it just as much as the 4 20mms. The single 7.7mm on the A6M5b shakes it just as much as the 2 20mms.
The plane itself is not bouncing, just the head position.
-
My point is that if wing root mounted guns do not produce side to side movements nor shakes, and if Mk108 had no recoil effect, then those head shaking movements should not be present disturbing the aiming. In the other hand, IMO, these are real yaw movements instead just head bounces. If not, In any case, where is the cause of my head bouncing like that?
In the first case, outer 151/20 should have much more dispersion/shake than wing root ones. In the second case (Mk108) dispersion should be mainly due ballistics ahead 300 yards than just due gun shake.
-
My favorite is firing the 7.92mm on the Ju88 and having the plane shake.
-
Where did you get the idea that the Mk108 had no recoil effect?
Its basic physics guys.
For every action there is a reaction.
Unless your using some sort of "recoiless" cannon, which isn't really recoiless but you get the idea, your gonna have recoil. Muzzle brakes and such designs can minimize "recoil effects", but thats just redirecting some of the forces.
In general the more powerful the cannon, the more recoil your going to get.
-
Verm, read, for example that:
http://visi.net/~djohnson/armament/mk108.html
An interesting feature was that neither the barrel or receiver moved in recoil, the entire force of firing was absorbed by the rearward movement of the bolt against the driving springs, which buffered against the recoil.
It that is not enough for you, Mk108 was anything but a powerful cannon, their mine shells where powerful, the cannon not.
Here, in AH, the shake effect firing these recoiless guns is very very noticeable.
-
(Stupid American flubs up his SI units. Original conversion of Newtons to pounds was low by a factor of 2.2)
Originally posted by MANDOBLE
It that is not enough for you, Mk108 was anything but a powerful cannon, their mine shells where powerful, the cannon not.
Here, in AH, the shake effect firing these recoiless guns is very very noticeable.
You're reading too much into Tiff's description of the freely-moving bolt. The gun wasn't recoilless; what happened was that instead of the bolt being locked in the breech as with most guns, the bolt flew backwards against a spring. This turned the sharp shock of a normal recoil into more of a push, but it was still quite a push -- the 312 gram shell flew at 550 m/s, giving it a momentum of 157.6 kg-m/s. To stop the bolt in the 1/10 second of a firing cycle takes 1576N of force on the average -- about 354 pounds. The spring exerts this force on the gun, which will push back against the airframe. Consider that you didn't have the whole firing cycle available, and the force becomes (1) greater and (2) less continuous.
Also, while the MK108's shell was quite slow, it was also very heavy. It had as a result quite high momentum and, therefore, kick -- more than the Hispano Mk V, whose 840 m/s, 130 gram shell had 109 kg-m/s of momentum. In the areas relevant to this discussion, the MK108 was powerful indeed.
(gun data courtesy of Emmanuel Gustin at The Fighter Gun Debate (http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-pe.htm) )
-
The Mk108 in AH is great, nothing to complain about here.
-
So can we assume that this thread is a request for different level of gun recoil according to planes? :)
-
pbirmingham, what I've read is just that the ENTIRE recoil force was absorbed by the springs. That is, that force affects inmediately the initial part of the spring, and the spring compression will absorb all the impact, supposedly, in the interval between shots. If the final effect is, like you say, a small push, it may produce a minimal "brake" effect, but not a tremendous shake.
Pick up a 262, and, from the runaway, fire the four guns and check the effect ...
-
MANDOBLE, What absorbed the force on the other side of the spring?
HiTech
-
Originally posted by MANDOBLE
pbirmingham, what I've read is just that the ENTIRE recoil force was absorbed by the springs. That is, that force affects inmediately the initial part of the spring, and the spring compression will absorb all the impact, supposedly, in the interval between shots. If the final effect is, like you say, a small push, it may produce a minimal "brake" effect, but not a tremendous shake.
Pick up a 262, and, from the runaway, fire the four guns and check the effect ...
It's not a [I[small{/I] push. For four MK108s, the total force from recoil (unrealistically assuming that the force is constant over the entire firing cycle, which it won't be,) is 1415 pounds. Compare it to the thrust of the Junkers Jumo 004 at 1986 pounds each (http://www.soton.ac.uk/~genesis/Level2/Planes/Germany/Me262.htm) and you see that this "small" push is nearly half the available thrust on the airplane.
Actually, the force on the spring is not even -- it increases as the spring is compressed by the bolt, and as HiTech and I are telling you, ultimately that force is transmitted to the airframe.
Consider that according to this account of the He 162 (http://www.csd.uwo.ca/~pettypi/elevon/baugher_other/he162_mm.html) the Salamander was equipped with MG 151/20 cannons because the recoil of the originally-planned MK108 was too great (look under "Prototypes.") Obviously this gun taxed the airframe greatly.
This was not a recoilless gun. It exerted forces on the Me262 that were significant relative to the other forces on the plane. While I don't know what a realistic amount of shake is (I've only seen one 262, at the Deutsches Museum. They didn't let me fly it, or even shoot the guns on the ground. Bastards.) I don't think any of us have enough information to say that it's too much now.
-
Hitech and Pbirmingham, the working principle is just like a modern pneumatic "ground flatter" or pneumatic hammer. The device is applying tremendous forces able to break big rocks while being manned confortably by a single human worker. These modern devices have a ratio of hit similar to the Mk108 or even higher. Basically, the spring system is converting the recoil shock into more or less smooth push. The "sinusoidal push" graph would not cause the shake effect of the "digital violent hit" graph. In the other hand, these pushes go directly towards the GC of the plane from the nose, paralel to the flying course, so there is no explanations for lateral neither vertical bouncing shakes. IMO, the effect of a Mk108 burst should be as a constant and soft brake, not just like hitting an asteroids field.
-
Originally posted by MANDOBLE
Hitech and Pbirmingham, the working principle is just like a modern pneumatic "ground flatter" or pneumatic hammer. The device is applying tremendous forces able to break big rocks while being manned confortably by a single human worker. These modern devices have a ratio of hit similar to the Mk108 or even higher. Basically, the spring system is converting the recoil shock into more or less smooth push. The "sinusoidal push" graph would not cause the shake effect of the "digital violent hit" graph. In the other hand, these pushes go directly towards the GC of the plane from the nose, paralel to the flying course, so there is no explanations for lateral neither vertical bouncing shakes. IMO, the effect of a Mk108 burst should be as a constant and soft brake, not just like hitting an asteroids field.
If your opinion were correct, why did the Heinkel engineers decide that the He 162 airframe could not handle the recoil of two MK108s? From the above-cited account:
The V2 was the prototype for the A-1 variant and was fitted with the two 30mm MK108 cannons, and it became clear that even with these low velocity guns the recoil was too much for the plywood nose area to handle.
In other words, they didn;t use the MK108 because it would tear up the plane.
Your pneumatic hammer (jackhammer) analogy is an interesting one, but flawed. The problem with it is that the forces involved are MUCH greater when you impart 157 kg-m/s momentum to ten shells a second. This takes an average force, for four guns, of three quarters of a TON.
Breaking rocks, by comparison, is much easier. A person can do it with a twelve-pound hammer -- the jackhammer is used because it can strike more frequently, doesn't use the worker's muscle power, and often is designed so that the part that hits the rocks is pointed, increasing the pressure at the point of contact so less force is needed. So, I dispute any implication that the forces are anywhere near equal.
Finally, do not forget that the jackhammer's own weight assists the operator in holding it down. In watching the construction on Wacker Drive here in Chicago, I've never seen a jackhammer being operated in a position far from the vertical, with the exception of the big crane-mounted ones they use for the serious rock-breaking.
-
It just doesn't work like that Mandoble.
True, the spring would work as a dampener, but it would not have the effect your describing.
For it to work that way, each gun would have to be precisely located off the aircraft centerline in relation to one another to counteract the other gun, and then each gun would have to fire precisely at the same moment as the counteracting weapon, and the aircraft has to be perfectly homogenous and perfectly balanced.
I'm talking nuclear weapons grade machine work, and weapon timing firing mechanism. And THEN each gun would have to have the exact same amount of powder, exact same shell weight, and be chemically identical to the other shells powder to something on the order of 99.999999 %
Take a basic Mechanical Engineering Statics course (no not statistics, statics ) and you will rapidly see that what your describing is literally impossible.
-
They do vary, per plane at least. Take up the hurricane IID for an extreme example of this.
-
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.
-
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
-
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 (http://home.earthlink.net/~poole124/weapons/mk103.htm) 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.
-
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:
(http://www.terra.es/personal2/matias.s/muelle.jpg)
The spring is absorbing the impact, and there is no "shake" effect in the paper ball.
-
I think I had that game for Atari.
-
There is a reason why you should keep shotgun/rifle pressed against your shoulder when firing it. Recoil is same in both situations :)
-
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:
(http://www.terra.es/personal2/matias.s/muelle.jpg)
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)
-
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...
-
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. :mad:
-
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.
-
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
-
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?
-
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.
-
HT, does this mean you're finally going to add visible buffeting when you approach a stall? :D
~Lemur
-
Originally posted by hitech
Your head would not shake at all... ...But there is no other meens of feeling the vibration that your but would feel.
ROFLOL!!!!!! HiTech, this is an historic post :D :D :D
Hope StSanta is not following this thread just reading it in a LIFO mode ;)