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View Full Version : The effects of sideslip on gun trajectory and sighting.



AndyJWest
09-03-2009, 05:33 PM
I have seen it stated several times on this forum that any sideslip will cause fire from forward-facing guns to deviate from the direction indicated by the gunsight. It seemed to me that though in real life there might be a slight effect, it seemed unlikely to be noticable in normal conditions. I decided to experiment in IL-2 to see how marked it was. Flying a P-38 at about 2500m and 100% power, with 'unlimited ammunition' selected I first fired with no slip to confirm the sight was correctly aligned, then put in maximum rudder trim and adjusted the aileron trim to balance out the turning effects induced. Firing the guns again, I could see little evidence of devition from the sight line, though with this much slip it is difficult to hold a dead-straight course and any turn may make the trajectory appear to deviate slightly: you need to 'sight' at a cloud or other distant point to ensure a straight flightpath.

This suggests to me that this 'effect' if it is modelled in IL-2 at all, is unlikely to have any real consequences, but others seem to have formed other opinions. I wonder whether there are further experiments that would throw more light on this? Does anyone have any comments?

This does not of course mean that I think flying with sideslip is generally a good thing: it will increase drag and can make accelerated stalls more unpredictable too...

BillSwagger
09-03-2009, 07:55 PM
Assuming we are talking about a fixed gun platform, the guns trajectory would also shift with the nose of the plane.
This is how i aim with rudder.

I think the perception that sideslip changes trajectory has more to do with the fact that in Il2, more extreme side slip is actually turning the plane or shifting it to one side. So as the bullets travel they appear to veer off to one side, when its actually the plane moving away from its original line of site.

Bill

Waldo.Pepper
09-03-2009, 08:20 PM
If the game models reality accurately, and I hope will all think that it does this as accurately as possible. Then this is the situation in reality.

Taken from Kittyhawk Pilot by Wing Commander J.F. (Stocky) Edwards page 191

"Reflector and gyro gunsights were used in our aircraft," Eddie said, "but they were a complete nuisance in a dog-fight. First of all, one had to look at the sight to use it, and this was taboo. One had to have all of his concentration on the target and the sky around and behind. Except for a mark on the windshield which could be seen without having to look at it directly, everything else was confusing." Although the Kitty provided a stable platform to fire from when flying on a straight level at a given speed, it became a monster in rapid diving and climbing. In dog-fights when the speeds changed rapidly, the aircraft had a tendency to slip and skid. By checking a primary needle and ball instrument, situated beside the airspeed indicator and other primary instruments in the cockpit, the slipping could be eliminated. But it was fatal to look down, even for a split second. Eddie's initiative had groundcrew staff move the spirit ball part of the intrument to eye level below the gunsight. When he lined up his target, he could see that his aircraft was stable."

AndyJWest
09-04-2009, 07:08 AM
That is an interesting quote, Waldo. http://forums.ubi.com/images/smilies/25.gif

The only thing is, J. F. Edwards seems to be talking about the Kitty's tendency to 'slip and skid' in the sense of being directionally unstable. I'm talking about a situation when the aircraft is holding a fixed angle of sideslip. In these circumstances, I cannot see any evidence in IL-2 that the rounds deviate laterally from the sight trajectory. At the sideslip angles we are talking about, I'd be surprised if there was much deviation in real life either, as the only reason for it to occur that I can think of is aerodynamic drag resulting from the round not meeting the airflow head on.

This needs further investigation: I will report back when I've done a few more experiments...

Blutarski2004
09-04-2009, 08:49 AM
Originally posted by AndyJWest:
That is an interesting quote, Waldo. http://forums.ubi.com/images/smilies/25.gif

The only thing is, J. F. Edwards seems to be talking about the Kitty's tendency to 'slip and skid' in the sense of being directionally unstable. I'm talking about a situation when the aircraft is holding a fixed angle of sideslip. In these circumstances, I cannot see any evidence in IL-2 that the rounds deviate laterally from the sight trajectory. At the sideslip angles we are talking about, I'd be surprised if there was much deviation in real life either, as the only reason for it to occur that I can think of is aerodynamic drag resulting from the round not meeting the airflow head on.

This needs further investigation: I will report back when I've done a few more experiments...



..... This fits right in with the description of P40 trim characteristics posted earlier this week:


quote -

P-40

A major aspect of flying the P-40 series airplane was handling trim changes from power and speed changes. A veteran AAF pilot stated “The trim changes with speed were more than in other contemporary fighters.” Typical of many single engine propeller fighters, the vertical tail fin was slightly offset to counter propeller slipstream effect at cruising speed. In a dive, as speed increased, more and more left rudder had to be added; slowing down in a climb some right rudder was needed. One pilot said “—a drawback was having to virtually stand on the left rudder pedal to keep the ball centered—it could be a real handful in a loop” (where trim reversed from dive to climb and then back again). Although directional trim tab power was available to zero out pedal force, left rudder trim could not be rolled in fast enough with high dive acceleration. No matter what P-40 version was involved, it was the same: “In the air, the Tomahawk tended to yaw considerably with speed changes”, needing directional trim, and for the P-40E/H87A: “Every power and speed change brings an immediate trim change which the pilot must either counteract or trim out”. The H87 was, if anything, worse than the H81 Tomahawk.

- unquote

AndyJWest
09-04-2009, 09:05 AM
Undoubtedly true Blutarski, but I'm not sure it's that relevant to the OP except in as much as it will highlight another issue - when firing guns, recoil will slow the plane down, causing a change of trim - I'd imagine this will be less noticeable in the side-slipping P-38 I was testing than in a P-40 in similar conditions.

I've now done some tests of the extreme case: a gun fired at 90 degrees to the line of flight. I set up a B-25 on autopilot - level flight at 2000m & 300 km/h, and fired the top turret sideways. There IS an effect, and from external views it looks quite dramatic:
http://i958.photobucket.com/albums/ae65/ajv00987k/B-25gunfireexternal.jpg

Seen from the gunsight, it is much less noticeable though:
http://i958.photobucket.com/albums/ae65/ajv00987k/B-25gunfireturretsight1.jpg
http://i958.photobucket.com/albums/ae65/ajv00987k/B-25gunfireturretsight2.jpg

Most of the rearward deviation seems to be occurring at some distance from the turret, as the rounds lose forward velocity. At a distance you should be using guns, the effects are slight.

Choctaw111
09-04-2009, 09:11 AM
Il2 does model lateral drift of the bullets flight path.
I have tested many things regarding the ballistics in the sim and I have been very impressed.

Tully__
09-04-2009, 09:58 AM
Andy, try it using a ground target as your reference. I think you'll find it a more significant drift than you think at all but the shortest of ranges. I certainly notice it when I'm doing ground attack without trimming rudder.

AndyJWest
09-04-2009, 10:43 AM
Tully:
My first thoughts on reading your post were that if you've got significant sideslip when attacking ground targets, you will have to fly a curve to keep the target centred, and this is bound to throw your aim off, regardless of any other effects.

I tried the sideslipping P-38 against ground targets (a nice line of Zeros on the QMB Okinawa map), and the first thing you notice is just how much harder it is to hit anything at all. Any change of airspeed induces a yaw, as does a change in pitch - you have to really concentrate to keep the target centred (and not collide with it - it is easy to get 'just that bit closer' when you are almost hitting it). With properly centred rudder trim, the contra-rotating props make the P-38 a much more stable gun platform. All in all, I think this demonstrates that regardless of what sideslip does to gun trajectory, it is never a good thing.

horseback
09-04-2009, 11:00 AM
When in the sideslip condition, the bullets will still appear to go through the crosshairs; the problem is in getting your rounds to concentrate on a specific spot.

When you are sideslipping, your nose is not pointed in the same direction as the aircraft is going. Thus, when you fire your guns, the rounds are landing in a line off to the side of your axis of flight, mostly parallel to it, assuming the degree of sideslip is constant (which is rarely the case).

In the turret example above, the rounds are eventually going to land along a line paralleling the bomber's course, rather than in one spot: no concentration of fire, less destructive impact, rounds wasted.

Firing in a direction perpendicular to the line of flight also imparts a vector in the direction the aircraft is moving to go with the perceived direction of fire. The bullets actually land a bit ahead of the line the rounds are supposedly fired along; how much ahead is determined by the speed vector, muzzle velocity, and offset angle (or angles, if there is any elevation involved in your firing solution).

When you are firing at an aerial target, flying at or near a coordinated condition keeps the rounds consistantly landing where your crosshairs are placed. If you're shooting at a target under 200m away flying at 300kph, the issue is not as critical as it would be firing at one 400m away going 400kph.

cheers

horseback

K_Freddie
09-08-2009, 03:02 AM
Don't forget the bullet gyroscopic effects, and side-on wind resistances.. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

AndyJWest
09-08-2009, 03:44 AM
Originally posted by K_Freddie:
Don't forget the bullet gyroscopic effects, and side-on wind resistances.. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Well, the 'side-on wind resistances' are presumably what is responsible for the rearward deviation seen in the B-25 turret example, as least as I see it. As for gyroscopic effects, I've no idea what these would be: can anyone offer an explanation?

Kettenhunde
09-08-2009, 06:05 AM
As for gyroscopic effects, I've no idea what these would be: can anyone offer an explanation?

Any force applied to a spinning object will produce a resultant force 90 degree's to the application of that force in the plane of rotation.

Tully__
09-08-2009, 06:48 AM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> As for gyroscopic effects, I've no idea what these would be: can anyone offer an explanation?

Any force applied to a spinning object will produce a resultant force 90 degree's to the application of that force in the plane of rotation. </div></BLOCKQUOTE>

Any torque applied to a spinning object out of line with the axis of spin will produce a rotation at 90 degrees to that you would expect if the object were not spinning. If the force is applied through the centre of gravity of the spinning object it will do what you expect, if the force is applied not through the centre of gravity but at 90 degrees to the axis of spin it will simple increase or decrease the spin.

It's rare that I catch Kettenhunde in a technical error, I feel justified in nit-picking http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

The outcome will be that the bullet may have a tendency to tumble if the sideways aerodynamic forces don't act through the bullet's centre of gravity and are not square to the axis of spin or in line with the axis of spin. This will adversely affect accuracy and increase dispersion.

MD_Titus
09-08-2009, 01:29 PM
Originally posted by AndyJWest:
I have seen it stated several times on this forum that any sideslip will cause fire from forward-facing guns to deviate from the direction indicated by the gunsight. It seemed to me that though in real life there might be a slight effect, it seemed unlikely to be noticable in normal conditions. I decided to experiment in IL-2 to see how marked it was. Flying a P-38 at about 2500m and 100% power, with 'unlimited ammunition' selected I first fired with no slip to confirm the sight was correctly aligned, then put in maximum rudder trim and adjusted the aileron trim to balance out the turning effects induced. Firing the guns again, I could see little evidence of devition from the sight line, though with this much slip it is difficult to hold a dead-straight course and any turn may make the trajectory appear to deviate slightly: you need to 'sight' at a cloud or other distant point to ensure a straight flightpath.

This suggests to me that this 'effect' if it is modelled in IL-2 at all, is unlikely to have any real consequences, but others seem to have formed other opinions. I wonder whether there are further experiments that would throw more light on this? Does anyone have any comments?

This does not of course mean that I think flying with sideslip is generally a good thing: it will increase drag and can make accelerated stalls more unpredictable too...

digging in a lot of slip whilst doing head ons can mean that you are passing slightly to one side whilst pouring fire at your target. unintentional slipping will make it harder to track your target and keep your guns on him, but if you are on the outside of a turnign bomber can be useful for hittig along the flanks. it's not a huge effect, but it is there.

Kettenhunde
09-09-2009, 10:34 AM
will produce a rotation at 90 degrees to that you would expect if the object were not spinning.

That is what I said. You describe the motion of the resultant force.

I did not.

I described the force vectors that creates that motion. The force is applied in plane, the resultant force manifest 90 degrees in the plane of motion.


Any force applied to a spinning object will produce a resultant force 90 degree's to the application of that force in the plane of rotation.


http://www.cybercom.net/~copters/aero/gyro.html (http://www.cybercom.net/%7Ecopters/aero/gyro.html)

The reaction to the resultant force is equal and opposite the original force. If the force was applied out of the plane of motion, then our equal and opposite reaction will be out of the plane of motion.

It is a brain smoker.

http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

AndyJWest
09-09-2009, 11:29 AM
Originally posted by AndyJWest:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by K_Freddie:
Don't forget the bullet gyroscopic effects, and side-on wind resistances.. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Well, the 'side-on wind resistances' are presumably what is responsible for the rearward deviation seen in the B-25 turret example, as least as I see it. As for gyroscopic effects, I've no idea what these would be: can anyone offer an explanation? </div></BLOCKQUOTE>
Can I amend this to read 'can anyone offer an explanation that I can understand when I've just woken up after an afternoon nap?' My head is suffering from gyroscopic precession (I think). http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif

Kettenhunde
09-09-2009, 06:26 PM
Gravity pulls the bullet down.

The nose of the bullet angles towards the ground, the drag increases at the top of the bullet.

This drag is exerting a force and the opposite reaction occurs 90 degrees from the top in the direction the bullet is spinning. If the bullet spins to the right, the force will be exerted on the right hand side and our bullet will drift to the right.

Make sense?

Check out the Coriolis Effect on shooting, LOL. Your bullets will move based the direction they are fired because the earth is moving.

Your bullets weight changes too based on the altitude you fire it.

http://www.grc.nasa.gov/WWW/K-12/airplane/wteq.html

Isn’t physics fun?

Freiwillige
09-09-2009, 06:39 PM
When topics get a bit deep do what I do to help wrap your brain around it.

Step one. Pull out a hammer. (Ball pin works great)

Step two. think about the topic until you feel something short circuit upstairs.

Step three. Timing is critical! when you feel your brain start smoking repeatedly rap yourself in the head with the hammer until you have an epiphany! or lose consciousness.

Step four. If knocked out during step three wait until you can count at least five fingers and then repeat step three as necessary.

Eventually you will get it, or be so mentally traumatized that at least you will think you get it...or you wont think at all! http://forums.ubi.com/images/smilies/blink.gif

zardozid
09-09-2009, 07:10 PM
http://i238.photobucket.com/albums/ff22/proton45/page1.jpg
http://i238.photobucket.com/albums/ff22/proton45/page2.jpg

AndyJWest
09-09-2009, 07:29 PM
Erm, thanks guys. I'm now no less confused overall, but instead slightly less confused about slightly more things. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

I'd better read all this tomorrow (or read what BableFish makes of the German text...), when I'm a bit more with it.

M_Gunz
09-10-2009, 09:29 AM
From the top:

You are flying along at 360kph with 5 degrees of slip and fire at some object 300m away centered in your gunsight.
You bullet has a sideways motion of 100m/sec x sin(5) due to your forward motion being 5 degrees off your direction
of aim. Sin(5) = .0872, in one full second the bullet will be about 9m off to the side towards the direction of
flight. 300m takes more like 1/3rd of a second to reach.
IF the target is flying parallel to our plane at the same speed then he will move to the side at the same speed as
the shots do or just a tiny bit faster -- he will appear to stay directly in your sights while your shots appear
to be curving slightly away from your pipper.
IF the target is flying straight away from your sight, 5 degrees off parallel to your course then your shots will
miss by a meter or more.
IF the target is coming at you then the drift of your shots will be opposite to his drift, miss by more.

This is simple geometry. When geometry is unreal then check your assumptions again.

The longer the range, the greater the gap to deal with. At under 100m the bullet speed makes the difference very
small, by 200m you might not hit the part of the plane you aimed for, at 300m+ it's easy to miss a target.

If you are flying along and see an enemy plane close to the pipper then rudder over to center it, you are probably
in slip right then. Just know it and deal with it, the shot does not go where the pointed at the moment the shot
was made. Your speed, the bullet speed and the angle of slip have everything to do with it even before looking at
a target.

Believing that your shots all go where the pipper pointed is the dweeb mistake not to make. They don't.

Add in that ruddering the pipper over adds yaw which makes one wing go up and the other go down as well as gets
some nose up or down (tiny shifts depending on the rudder use) and in general, wobbles the nose of the plane.
Oh but that's supposed to be a modeling problem! Is it a pilot problem? Tiny nose shift = pipper moved 1+ tics!

Just to shake you all up, there's the vertical equivalent of slip as well. When I am flying slow my AOA must be
higher to generate the lift I need to follow my path. When I am flying fast my AOA must be lower. That moves
my sight up and down relative to my path. At some speed it's probably right but yeah there's vertical slip.

Pigeon_
09-11-2009, 04:57 AM
Originally posted by Kettenhunde:

Your bullets weight changes too based on the altitude you fire it.

http://www.grc.nasa.gov/WWW/K-12/airplane/wteq.html

Isn’t physics fun?

This confused me for a minute, as I was thinking about the bullet's mass, instead of it's weight. I was already beginning to think about relativity and time travel until I clicked the link and had a 'd'oh!-moment'... http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Now, for this gyroscopic effect.

"The nose of the bullet angles towards the ground, the drag increases at the top of the bullet."

Is the drag at the top really that much greater than the drag at the bottom? And isn't the nose angling downwards caused by more drag at the bottom? And, is this effect really worth mentioning at all? I think it only makes a difference on very large distances, way beyond the effective gunrange in IL-2.

And, apart from that, are the bullets fired from the guns of a warplane even rotating? Of course, this depends on the gun the bullet was fired from, but I'm no expert on warbird guns. And even if the bullets do rotate, I doubt this is effect is modelled in IL-2.

Anyway, back on topic...

I made a little picture to give some insight into the situation:

http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/bulletslip.jpg

I think your test with the B-25 was very interesting, but it would be even better to have a (preferably small) aircraft flying next to the B-25 on a parallel flight path and at the same speed. This way you can see how far ahead you need to aim to hit the aircraft. You can test this for multiple distances to get a real insight into the effect.

AndyJWest
09-11-2009, 06:12 AM
Hm, yes Pigeon, that sounds like a good way to test the effect. It might be possible to do this with the FMB. It would be worth trying at different airspeeds too. Maybe I'll try this out sometime.

Your diagram is a bit misleading, I think. To hit the target, you'd need to aim ahead anyway (deflection shooting), though if you are flying parallel, with a more realistic sideslip angle, the deflection needed would be slight, and the error due to drag would be smaller too. Still, It illustrates the effect well.

Unless someone can offer solid evidence that factors like bullet spin and diminishing weight with height are actually modelled in IL-2, I'm inclined to assume that the drag effect is all we need to take into account when aiming.

Pigeon_
09-11-2009, 07:33 AM
Originally posted by AndyJWest:
Hm, yes Pigeon, that sounds like a good way to test the effect. It might be possible to do this with the FMB. It would be worth trying at different airspeeds too. Maybe I'll try this out sometime.

Your diagram is a bit misleading, I think. To hit the target, you'd need to aim ahead anyway (deflection shooting), though if you are flying parallel, with a more realistic sideslip angle, the deflection needed would be slight, and the error due to drag would be smaller too. Still, It illustrates the effect well.


Actually (when talking about the no drag situation), if both planes are travelling at the same speed, there is no need for deflection. If you are going faster than your opponent you would even need to aim behind him!

M_Gunz
09-11-2009, 09:20 AM
Changing weight due to altitude... Earth diameter is about 6,000 km. Difference in gravity at altitude is Earth dia squared
divided by Earth dia plus plane height sum squared. 10 km alt, 6000^2 / 6010^2 = .9967498~ so you lose about .32% weight.

It is more important that drag on everything including bullets is less with increased altitude. Make tracks of very long single
shots that hit at below 1km alt and around 10km alt where the IL2 atmosphere model stops changing. See if there's a difference
in how long for the shot to hit and you will know.

A 50 cal barrel has 1 twist in 15 inches (381mm). IL2 muzzle velocity is supposed to be 870 m/s. 870000/381 = 137008 rpm!
Omitting the ones with muzzle wobble, what's going to change the orientation of that bullet until it slows the spin wayyy down?
Even with wobble the nose circles the flight path insanely fast and tight, the orientation of that dynamic should hold for a
good long while. Fire one in space to stay in orbit and halfway round the planet the nose would be pointing backward....

Pigeon, in that one picture where you have bullet without drag and bullet with, sorry but take the bullet without drag path
and add the sideways vector from the forward motion and slip, that's where the shot is headed at that instant. Since you are
moving forward though the bullet path should appear to curve off to the left but not due to bullet drag at all. The slip
sideways vector on the bullet is not high enough to see noticeable drag effects along that direction. The apparent curve is
only your forward motion being greater than the component of the bullet's motion in the same direction. Draw planes and
bullets at intervals and these things become more clear.

What's a half meter difference make when aiming at the cockpit? You might end up taking his radio out, or hitting fuel!
You just won't get the pilot.

AndyJWest
09-11-2009, 09:26 AM
Oops, absolutely right Pigeon, well spotted - that gives me one more excuse for not being able to hit a barn door from 100 ft.

Actually, my aim seems to be improving: took the wing off a Pe-8 with one quick burst with high deflecton from about 800m the other day. Would have been better still if I hadn't been flying a La-5 at the time, and mistaken it for a Ju 88 - perfect team kill. http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif

(Apologies repeated to the Pe-8 pilot, whoever he was - I know I'm a ******* sometimes)

M_Gunz, I think that Pigeon's diagram is correct, in that the path of the bullet as it leaves the gun will not initally be in the direction the barrel is pointing at that instant, but the sum of the along-barrel vector and the motion-of-the-aircraft vector. This should thus be aligned with the gunsight, which also effectively factors in the aircraft motion when sideslipping.

M_Gunz
09-11-2009, 10:09 AM
At the instant a nose gun bullet leaves the muzzle the path will be along the gunsight plus a sideways vector due to the
motion of the plane being to the side of where the gunsight is pointing. If you fire at a stationary target then you
will know, it will always miss the mark.

This whole business of how it appears to move from my position behind the gunsight in the moving plane after the shot is
made is just extra and I can tell it confuses a lot of people, maybe more than rise and drop of bullets relative to the
sight line does. That gets to be real fun when firing up or downwards.

ADD: Here is an example of slip mechanics not working out for you. The target is flying along a path at an angle to yours,
off to the left. He is going straight away from your gunsight but appears to be drifting left. You swing the nose over and
let off a burst at 200m with the pipper leading his apparent motion. Will you hit or should you have added some more lead
to cover for the slip?

AndyJWest
09-11-2009, 10:24 AM
Originally posted by M_Gunz:
At the instant a nose gun bullet leaves the muzzle the path will be along the gunsight plus a sideways vector due to the
motion of the plane being to the side of where the gunsight is pointing. If you fire at a stationary target then you
will know, it will always miss the mark.
...

Yes, but Pigeon's diagram shows two aircraft moving on parallel paths. As he says, whether you need to aim behind, on target or ahead will depend on your relative speeds. If you allow for the drag component, you then have to adjust your aim forward.

M_Gunz
09-11-2009, 11:47 AM
Well I guess that's as much as there must be to shooting with slip then. I give up, you guys know it all.

Kettenhunde
09-11-2009, 05:07 PM
Now, for this gyroscopic effect.

"The nose of the bullet angles towards the ground, the drag increases at the top of the bullet."

Is the drag at the top really that much greater than the drag at the bottom?

Yes. It is enough to impart a resultant side force 90 degrees in the directions and plane of spin from the top.

We see that side force as it is manifested equal and opposite the original force vector.


And isn't the nose angling downwards caused by more drag at the bottom?

It is gravity that pulls the bullet towards the earth.


And, is this effect really worth mentioning at all? I think it only makes a difference on very large distances, way beyond the effective gunrange in IL-2.


A 7.62mm bullet requires one 1/2 mil to the left at 600 meters. The effect is only noticeable at long ranges.

Now the application to your game was not the question asked or answered. I don't play IL2 and anything doing with what should or should not be in your game is not something I will participate in. I highly doubt your game models Coriolis Effect either or the effect of altitude on weight.

I just explained the physics behind gyroscopic procession and how it affects the flight of a bullet.

All the best,

Crumpp

AndyJWest
09-11-2009, 07:34 PM
Now the application to your game was not the question asked or answered. I don't play IL2 and anything doing with what should or should not be in your game is not something I will participate in. I highly doubt your game models Coriolis Effect either or the effect of altitude on weight.
I'd have thought from reading my original posting it was evident that what I was talking about was the effect as simulated in IL-2: Of course what happens in real life is interesting, but may or may not be relevant, depending on how much these minor factors are actually modelled.

Anyway, thanks everyone for your input. I think we've probably gone as far as we usefully can without doing some more experiments.

jermin122
09-11-2009, 08:12 PM
Originally posted by Blutarski2004:

A major aspect of flying the P-40 series airplane was handling trim changes from power and speed changes. A veteran AAF pilot stated “The trim changes with speed were more than in other contemporary fighters.” Typical of many single engine propeller fighters, the vertical tail fin was slightly offset to counter propeller slipstream effect at cruising speed. In a dive, as speed increased, more and more left rudder had to be added; slowing down in a climb some right rudder was needed. One pilot said “—a drawback was having to virtually stand on the left rudder pedal to keep the ball centered—it could be a real handful in a loop” (where trim reversed from dive to climb and then back again). Although directional trim tab power was available to zero out pedal force, left rudder trim could not be rolled in fast enough with high dive acceleration. No matter what P-40 version was involved, it was the same: “In the air, the Tomahawk tended to yaw considerably with speed changes”, needing directional trim, and for the P-40E/H87A: “Every power and speed change brings an immediate trim change which the pilot must either counteract or trim out”. The H87 was, if anything, worse than the H81 Tomahawk.



This sounds like the exact feeling I am getting when flying Bf-109s in the game.

jermin122
09-11-2009, 08:31 PM
It is much more difficult for us to keep the slipball centered when dogfighting in front of the computer. In a real flying aircraft, you can feel the slip if you are slipping, just like sitting in a drifting car. Expierenceed pilots are able to feel the slip precisely without seeing the slipball. This will help them concentrate on the target ahead. Unfortunately, this is something that simulator can not simulate. And this is the primary cause for low hit rates of online pilots.

Waldo.Pepper
09-11-2009, 10:33 PM
Originally posted by jermin122:
In a real flying aircraft, you can feel the slip if you are slipping, just like sitting in a drifting car.

I understand what you are getting at. The game is the game and reality is reality. But no actually you can't feel side slipping in reality as easily as you are suggesting. This is precisely the reason that Stocky Edwards felt the need to mod his Kittyhawk (read my first post in this thread.)

This is rather on (the minor) topic about bullets traveling along the line of flight. It is from a wartime pamphlet called "Air Gunner - Get that fighter!"

http://img.photobucket.com/albums/v516/WaldoPepper/Air%20Gunner%20GTF%20Excerpt/Untitled-09.jpg

Kettenhunde
09-12-2009, 05:46 AM
I'd have thought from reading my original posting it was evident that what I was talking about was the effect as simulated in IL-2:

Your question about gyroscopic procession was about real life or at least worded in such that the obvious conclusion was you did not know the effects as they should be simulated in your game. You further reinforced this conclusion by posting about not understanding the concepts and how it gave you a headache.

The other folks such as Tully helped to make a very difficult to understand concept much clearer.

Just thank the contributors and move on, there is no need to try and justify your question.

http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

AndyJWest
09-12-2009, 07:25 AM
Kettenhunde:

Just thank the contributors and move on, there is no need to try and justify your question.
I've already thanked the contributors, see my last posting.

I think most of the regulars on this forum will read my comments on the dificulty of understanding some of the points made in the spirit they were intended, as a joke.

Waldo.Pepper:
Nice find http://forums.ubi.com/images/smilies/25.gif
Any chance of a link to the pamphlet?

As a more general point, I think that topics can often get confusing when some people are talking about how actual aircraft perform, some talk about the IL-2 simulation, and others don't really make clear which they are referring to - I'm probably guilty of this myself on occasion, as Kettenhunde suggests. Perhaps we all need to be a bit more careful about making this clear. On the other hand, we could do worse: I've just seen a comment on YouTube about P-51s being able to outturn Bf 109s, based on the performance of the planes in the WW2 online simulation. http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif

Kettenhunde
09-12-2009, 10:29 AM
M_Gunz, I think that Pigeon's diagram is correct,

Actually M_Gunz is correct.

The bullet does not care when it leaves the barrel where the airplane goes, it only cares about the orientation of the barrel or the "gun target line" as it left.

Pigeons’ diagram is not even close. Both aircraft are moving and the bullets move behind the target as they are not longer in a moving frame of reference.

You probably already know that and are just joking some more.

All the best,

Crumpp

Waldo.Pepper
09-12-2009, 12:37 PM
Waldo.Pepper:
Nice find Thumbs Up
Any chance of a link to the pamphlet?

Will do. But I can do even better than that! Check PM (either later today or tomorrow.)

M_Gunz
09-12-2009, 04:06 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> M_Gunz, I think that Pigeon's diagram is correct,

Actually M_Gunz is correct.

The bullet does not care when it leaves the barrel where the airplane goes, it only cares about the orientation of the barrel or the "gun target line" as it left.

Pigeons’ diagram is not even close. Both aircraft are moving and the bullets move behind the target as they are not longer in a moving frame of reference.

You probably already know that and are just joking some more.

All the best,

Crumpp </div></BLOCKQUOTE>

I've given up trying to explain and now that I read it was all a <insert adjective here> joke I care even less.
I've tried for how long now to get it through a bunch of gamers that coordinated flight has real advantages in IL2?

When enough players show that they want modeling arcaded more than now (through unreal critiques and demands) then
we'll stop getting more realism, but with extra helpings of eye (and ear) candy that will surely make up for that.

M_Gunz
09-12-2009, 04:21 PM
Originally posted by AndyJWest:
On the other hand, we could do worse: I've just seen a comment on YouTube about P-51s being able to outturn Bf 109s, based on the performance of the planes in the WW2 online simulation. http://forums.ubi.com/groupee_common/emoticons/icon_eek.gif

Under the right circumstances of speed, altitude or both the Mustang was able to turn inside the Bf 109. Of course that does
include the 109 coming in at higher speed to bounce the P-51, certainly the case in at least one account but at very high alts
when the 109 is not a high alt version then lack of power in the 109 takes away what differences in airframe and weight between
that 109 and your average Merlin-engined P-51 (the by-far majority of P-51's?) -- of course adding caveats about fuel and other
loading and equal pilots experienced enough to get near the best out of their planes, nobody too surprised, etc, etc, that you
won't find in 90+% of combat stories. In other words, not always just that it's possible and it did happen occasionally.

IRL there were times when 109E's did cut inside the turns of Spitfires during the BoB as well. IRL above 12,000 ft the 109E
could easily out-turn a BoB Hurricane yet below 4,000 ft the situation reversed according to at least one BoB pilot, I have
the account where he says that's what they were told in training and then how it worked that way for him in combat.

There are very few true blanket statements in aerial combat. You see one then start looking for the exceptions.

Kettenhunde
09-12-2009, 07:12 PM
Under the right circumstances of speed, altitude or both the Mustang

At the same velocity sustained level turn, the Bf-109 will win except at high speeds. Most Bf-109's were greatly superior to the Merlin Mustang in low speed and middle of the curve sustained turns.

I wouldn't want to get into a low speed turn fight flying a Mustang against any model Bf-109.

All the best,

Crumpp

Kettenhunde
09-12-2009, 07:55 PM
I've given up trying to explain and now that I read it was all a <insert adjective here> joke I care even less.


I don't think for a second it was a "joke". You can gauge the amount of understanding just by looking at the posted homemade chart and the agreement it got.

M_Gunz
09-12-2009, 08:08 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Under the right circumstances of speed, altitude or both the Mustang

At the same velocity sustained level turn, the Bf-109 will win except at high speeds. Most Bf-109's were greatly superior to the Merlin Mustang in low speed and middle of the curve sustained turns.

I wouldn't want to get into a low speed turn fight flying a Mustang against any model Bf-109.

All the best,

Crumpp </div></BLOCKQUOTE>

*At the same velocity* being the catch when high enough that the 109's engine cannot make the same speed while turning.
Look at it the same way you would ceiling? At some height any of these planes can't make more than 2 G sustained turn
while holding altitude so... if another plane with higher ceiling can sustain 2.5 or 3 G's at that alt then who is likely
to win the turnfight? Of course the P-51 has to go faster to turn with the same G's so it must be able to sustain the
higher G's and not even close to equal G's let alone equal speed.

That's the fair contest. In Bud Anderson's bio, the chapter shown online has his 4 group jumped from above by 109-G's
at greater speed and very high altitude. They broke into a turn that the 109's went wide of and were soon able to get
behind the 109's. The mistake the 109 leader made was in staying in that fight instead of running when they missed
that first pass. He shoulda read up on Hartmann; hit or miss, get out of Dodge after the first pass.

doraemil
09-12-2009, 08:19 PM
Originally posted by Waldo.Pepper:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Waldo.Pepper:
Nice find Thumbs Up
Any chance of a link to the pamphlet?

Will do. But I can do even better than that! Check PM (either later today or tomorrow.) </div></BLOCKQUOTE>

hey any chance of sending me / posting the link also?

I loved the bag the hun and it really helped me understand IL 2 aerial gunnery.

thanks ahead of time.



------



I'm not skilled enough to do Richard Candelaria History Channel side slip rudder gunnery shot

http://www.youtube.com/watch?v=mdCm5z2RpI8


however I do notice if I'm line up a shot, and the ball is centered, rate of climb / dive and throttle are constant, I'll hit where the pipper is pointing.


No sideslip and its more accurate.



I tend to to use sideslip to get the nose to point where I want it to, then center and line up a shot.

M_Gunz
09-12-2009, 08:21 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> I've given up trying to explain and now that I read it was all a <insert adjective here> joke I care even less.


I don't think for a second it was a "joke". You can gauge the amount of understanding just by looking at the posted homemade chart and the agreement it got. </div></BLOCKQUOTE>

I *think* that diagram is supposed to be two planes in motion with the bullet paths being relative to the shooter, in which
case he does have it right though I'd say the straight line is for close shots and the curved is for long ones. It took me
a while to think of it but as the shots slow down then so does their forward vector and for sure the path would appear curved.

IOW, I *think* you have it right Pigeon and for the right reasons! It's just not so easy to be sure if what I think you mean
is what you actually meant! C'mon back!

WTE_Galway
09-12-2009, 09:11 PM
Originally posted by AndyJWest:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Now the application to your game was not the question asked or answered. I don't play IL2 and anything doing with what should or should not be in your game is not something I will participate in. I highly doubt your game models Coriolis Effect either or the effect of altitude on weight.
I'd have thought from reading my original posting it was evident that what I was talking about was the effect as simulated in IL-2: Of course what happens in real life is interesting, but may or may not be relevant, depending on how much these minor factors are actually modelled.
</div></BLOCKQUOTE>


To be honest what happens in real life is way more interesting to know than what happens in what is afterall just a game http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

AndyJWest
09-13-2009, 05:11 AM
To be honest what happens in real life is way more interesting to know than what happens in what is afterall just a game
I think that what happens in real life is interesting, and useful to me too from a practical point of view if IL-2 simulates it. As I said in my original posting. people have suggested that in IL-2, sideslip affects gun trajectory. I wanted to know how marked the effect was. Clearly, how marked it is in real life has got to be relevant to this, but only to the extent that it is accurately modelled by IL-2. As several people have suggested, relatively minor factors like reduction in gravitational force with altitude, gyroscopic and corolis effects and the like are quite likely not simulated, though how much practical difference this makes is unclear to me. I'm fairly certain that aerodynamic drag is simulated, as my B-25 experiment seemed to show.

I think I'll try another experiment or two with the B-25 firing sideways, because if aerodynamic drag is modelled accurately, the deviation in projectile path ought to vary with aircraft airspeed, and with altitude. If I have any meaningful results, I'll get back with them.

(As an aside: M_Gunz, I never intended the topic to be taken as 'a joke', I merely tried to suggest that my comments about some of the explanations giving me a headache was meant in a light-hearted way, and was commenting on my own lack of understanding, not suggesting that I wasn't taking the comments seriously. The effects of sideslip are evidently not as straightforward a question as it might at first seem, and premature 'understanding' may even be misleading, so an acknowledgement of ones own possible misinterpretation may even make the truth easier to arrive at. Or that's my take on it anyway)

Kettenhunde
09-13-2009, 06:15 AM
the path would appear curved.


Yes it appears curved from the frame of reference of the pilot. It is an illusion however resulting from the fact the bullets have dropped out of the moving frame of reference and our eyes have not.

http://www.av8n.com/how/htm/mo...#sec-just-centrifuge (http://www.av8n.com/how/htm/motion.html#sec-just-centrifuge)

All the best,

Crumpp

Kettenhunde
09-13-2009, 06:21 AM
I'm not skilled enough to do Richard Candelaria History Channel side slip rudder gunnery shot

WTF was that????? I think the History channel has botched another one.

Bremspropeller
09-13-2009, 06:32 AM
Earth diameter is about 6,000 km.

Fairly small Earth, you're living on http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Kettenhunde
09-13-2009, 06:53 AM
*At the same velocity* being the catch

Exactly!

M_Gunz
09-13-2009, 12:27 PM
Originally posted by Bremspropeller:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Earth diameter is about 6,000 km.

Fairly small Earth, you're living on http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

I shoulda said RADIUS seeing as how that's how I did the math.

AndyJWest
09-13-2009, 12:58 PM
I've tried some more experiments with aerodynamic drag effects on gun trajectory, using the B-25 turret, but am getting a weird bug with a .ntrk replay not showing what originally occurred. Unless anyone knows a work-around, this will make things difficult. I'll do a forum search on this and see if there is a fix...

I was online earlier, and I don't think my aim has improved due to all this extra knowledge, but it wasn't the ideal place to try it out, as I seemed always to be outnumbered and got shot down every time. Still practice, practice...

M_Gunz
09-13-2009, 01:08 PM
Originally posted by AndyJWest:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">To be honest what happens in real life is way more interesting to know than what happens in what is afterall just a game
I think that what happens in real life is interesting, and useful to me too from a practical point of view if IL-2 simulates it. As I said in my original posting. people have suggested that in IL-2, sideslip affects gun trajectory. I wanted to know how marked the effect was. Clearly, how marked it is in real life has got to be relevant to this, but only to the extent that it is accurately modelled by IL-2. As several people have suggested, relatively minor factors like reduction in gravitational force with altitude, gyroscopic and corolis effects and the like are quite likely not simulated, though how much practical difference this makes is unclear to me. I'm fairly certain that aerodynamic drag is simulated, as my B-25 experiment seemed to show. </div></BLOCKQUOTE>

There's drag, gravity and then the tiny things all lumped into the random scatter we do have. Not match-target-rifle close
but then we're not concerned with a few mm to cm difference.


I think I'll try another experiment or two with the B-25 firing sideways, because if aerodynamic drag is modelled accurately, the deviation in projectile path ought to vary with aircraft airspeed, and with altitude. If I have any meaningful results, I'll get back with them.

I'd like to know if you see difference with alt and what your test setup is. It's possible in FMB to set up lights and
cameras even up high so you can set up known distances and markers to know when and where to shoot as well as see the
results from different places/angles.


(As an aside: M_Gunz, I never intended the topic to be taken as 'a joke', I merely tried to suggest that my comments about some of the explanations giving me a headache was meant in a light-hearted way, and was commenting on my own lack of understanding, not suggesting that I wasn't taking the comments seriously.

Sorry I didn't get it that way... NP, you're cool!


The effects of sideslip are evidently not as straightforward a question as it might at first seem, and premature 'understanding' may even be misleading, so an acknowledgement of ones own possible misinterpretation may even make the truth easier to arrive at. Or that's my take on it anyway)

In your example of shooter and target flying parallel paths, the motion of the target *is* the same difference as the
deviation due to the slip and at close enough range the bullet doesn't lose enough to drag to make any more difference.

Honestly the angle-off from firing in slip is dead simple in principle. Knowing the angles and distances then incorporating
all the rest is the hard part! Once things are no longer a mystery all it does for me is make my guesses less random is all.
I do slip shooting and if the range isn't far I get some hits between a stream of bullets and a target moving into them,
automatic weapons make all that fiddly sniper business moot in about a quarter second or less anyway! Make a guess, fire,
and if it wasn't a snap-shot opportunity then correct and fire again. Just don't hang on the trigger and hose until you
have a solid lock on the enemy.

Lot of people post here about the guns effectiveness that once it gets down to it turns out to be aiming problems or online
lag and packet loss. My posts about slip are to take the mystery out of that one aspect alone and get players who don't
use the rudder and aren't even aware of slip to have incentive to find out and deal with it. You not only shoot better but
fly better too, might cut down on the "my plane's too slow" posts -- something has, you should have seen this board 4+ years
ago but IMO those who didn't learn either quit the game, quit posting, or actually learned something.
I don't mind "hey, what's wrong?" posts, it's the "this game is wrong!" ones that drop all kind of clues that the problem
is closer to the keyboard than the mobo that gets to me. At least you don't play that, so you're cool.

Pigeon_
09-13-2009, 04:05 PM
Is it just me, or is the atmosphere getting a bit tense here? That would really be a shame, because I find this topic very interesting and it would be very undesirable to see this all end in a flame war. Personally, I participate here to learn and to help others in the best way I can. I don't see any reason to start acting hostile to others and be impolite, so let's keep it civilized. Please.


Anyways, back on topic... (well, sort of http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif)

I have been thinking about the things mentioned in this thread for a long time, and the more I think about it, the more I see that the situation is far more complicated than I had expected. Also, there are a lot of things I would like to address. This combination will, I'm afraid, result in a quite long post. I would like to apologies in advance for my writing style, which undoubtedly will be a bit chaotic. And, since English is not my primary language, it is sometimes hard to transfer my thoughts into words. However, I will try my best to tie everything together in a smooth, readable way.

First of all, though, I would like to state that I am NOT an expert on the subject matter. Unfortunately, I only have basic understanding of physics. I try to understand and explain things with the limited knowledge I posses. So, if you encounter an error in my reasoning, please do point it out to me, preferably along with a good explanation of what I did wrong.

From the subsequent posts to my post containing the diagram it has become clear to me that the diagram was not understood in the way I intended it to be understood. I apologize for not being more clear in the initial post.

Here is the diagram again:

http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/bulletslip.jpg
Diagram 1. Firing in a slip condition while traveling in the same direction at the same velocity.


Depicted here are two aircraft (a Messerschmitt Bf-109 and a Curtiss P-40 Warhawk) flying in the same direction at the same velocity. The P-40 is in a left sideslip to get his guns on the 109.

The orange line indicates the path of the bullets in a situation without drag. In this situation the aircraft can be thought of as static objects (for the sake of simplicity), because they are flying in the same direction at the same velocity and are not moving relative to each other. Consequently, the bullets will travel in the direction the guns are pointed and in a straight line.

The blue line indicates the path of the bullets in a situation with drag factored in. The aircraft can still be thought of as static objects, as they are still not moving relative to each other. However, in this case, a strong stream of air (wind) should be added to the equation. The direction of this wind should be opposed to the 'direction of flight' in the diagram. In this situation the bullets will be "blown" from their initial path and follow a curved path.

That is how I intended the diagram. I now understand that it might be too simple, as I did not account for the drag which results from the bullet's forward motion (forward motion being movement towards the direction the bullet is pointed), which brings me to the following:


Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> the path would appear curved.


Yes it appears curved from the frame of reference of the pilot. It is an illusion however resulting from the fact the bullets have dropped out of the moving frame of reference and our eyes have not.

http://www.av8n.com/how/htm/mo...#sec-just-centrifuge (http://www.av8n.com/how/htm/motion.html#sec-just-centrifuge)

All the best,

Crumpp </div></BLOCKQUOTE>

So, you claim that the bullets will fly in a straight line, instead of a curve? Bullets flying in a straight line sounds pretty straight forward, but is it really the case? For instance, think about standing in a field with a ball and imagine there's a strong wind. Now, throw the ball in a direction 90 degrees to the wind direction. In this situation, the ball would follow a curve, instead of a straight line in the horizontal plane of movement.

However, comparing a ball to a bullet is like comparing apples and pears. So, what would actually happen to a bullet fired from a gun? This question has got me really wondering and so I decided to draw another picture.

http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/90degdrag.jpg
Diagram 2. Bullet fired from a sideways moving gun.


Here you see a diagram of a bullet that was fired from a moving gun. The direction of aim is 90 degrees to the direction the gun platform is traveling in. If the bullet is to travel in a straight line, the total drag component of the bullet should be 180 degrees to the initial bullet movement direction (as depicted in the diagram). If this is not the case, one could imagine that the resulting force would make the bullet veer off it's linear path and follow a curved path instead. A deviation from the relation as depicted between the 'drag from forward movement' component and 'drag from sideways movement' component (i.e. the 'drag from sideways movement' component is increased while the 'drag from forward movement' component stays the same) would result in the total drag component of the bullet not being 180 degrees to the initial bullet movement direction.

A bullet is a lot less aerodynamic when met by air from the side than it is when met by air from the front. This suggests that the 'drag from sideways movement' component should be larger than the 'drag from forward movement' component. However, the forwards speed of the bullet is far greater than the sideways speed, resulting in a far greater 'drag from forward movement' component. The exact relation between both components is unknown to me. However, I think it’s safe to assume that the sideways motion stops sooner than the forward motion. This indicates that the bullet follows a curved path, at least at the beginning of it’s journey through the air (please note that the value of the components will change as speed changes). However, in the above reasoning the bullet’s orientation does not change. In reality, the bullet will probably rotate because of the airflow, resulting in a deviating path. More on this later. For now the only conclusion I can make is that I’m not sure about the path the bullet will follow. It could be a curved path, it could be a straight line, or partially curved and partially straight.

Now, apart from the shape of the blue line, I don’t see any other flaws in the first picture I posted (diagram 1), and I’m not even sure if the shape of the blue line is flawed. Kettenhunde, you wrote that diagram 1 is flawed.


Originally posted by Kettenhunde:

Pigeons’ diagram is not even close. Both aircraft are moving and the bullets move behind the target as they are not longer in a moving frame of reference.

I do not understand your explanation as to why my diagram is wrong. Could you please elaborate?


On to my next point…

So far, I’ve only discussed aircraft flying on parallel paths. Now, what would happen if they didn’t travel on parallel paths (as you often see in practice)? Two situations are depicted below. Please don’t worry too much about the shape of the blue lines, as I made these diagrams before I thought about the things I discussed above. Suffice it to say that the bullets in the drag condition will fall behind the bullets in the non-drag condition.

http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/anglein.jpg
Diagram 3. Firing in a slip condition while traveling at the same velocity and flying towards each other.


http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/angleoff.jpg
Diagram 4. Firing in a slip condition while traveling at the same velocity and flying away from each other.


As you can see in these diagrams you need to adjust your aim if your target is flying slightly towards you or slightly away from you. If he is flying towards you (diagram 3), you need to adjust your aim to be more in front of him compared to the situation in diagram 1. If he is flying away from you (diagram 4), you need to adjust your aim closer to him compared to the situation in diagram 1.

Having stated all this, I doubt knowing it will do you much good while playing the game. Of course, a basic understanding of aerial gunnery is desirable, but in a dogfight you don’t have the time to make well thought out calculations. Think about it. The situations I have discussed so far are already very complex and need a lot of ‘brain power’ to grasp. However, this is nothing compared to the complexity of the situations you will encounter in the game. For instance, are you really able to perform an absolutely stable slip? And how often do you encounter an enemy that is flying in a straight line at the same altitude and at a constant speed while you are engaging him?

The bottom line is… you can’t rationally calculate where to aim in a dogfight. There simply is too much going on in too little time for your brain to cope with this. You just have to know where to aim. The only way to gain this knowledge is from experience: practice, practice, practice! And even then, merely knowing where to aim is not enough. You have to get your crosshairs at that exact point. Not an easy task, be sure! (http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif)

There still are some other issues I would like to address (one of them being the change in bullet orientation), but for now I’m going to leave it at this. Methinks I’ve done enough typing for today! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

I hope this text will be useful to somebody. If you have any questions, please don’t hesitate to ask.

Kettenhunde
09-13-2009, 05:15 PM
So, you claim that the bullets will fly in a straight line, instead of a curve?

As straight as any other bullet path, just like Denker explains on his website in link I provided.

The bullet is a seperate object that leaves the rotational frame of reference. It does not continue to travel forward with the momentum of the aircraft like you think.

It appears that way from the pilots POV inside the rotational frame of reference.


Consider our point of view as we ride in the centrifuge. At point A, the tennis ball has no velocity relative to us. For the first instant, it moves along with us, but then gradually it starts moving away.

The bullet is outide the rotational frame of reference once it leaves the barrel:


Consider the point of view of a bystander (not riding in the centrifuge). The dropped tennis ball moves in a straight line, according to the first law of motion.

Now read this part carefully:


Einstein’s principle of equivalence guarantees that our viewpoint and the bystander’s viewpoint are equally valid.

That means your diagram is correct from the viewpoint of inside the rotational framework as M_Gunz points out. Where you make the mistake though is in trying to explain the forces on the bullet from that rotational framework. You cannot mix them together. The bullet is not in the rotation when it is fired.

http://www.av8n.com/how/htm/mo...html#fig-centri-newt (http://www.av8n.com/how/htm/motion.html#fig-centri-newt)



Diagram 2. Bullet fired from a sideways moving gun.



On an unrelated note:

Do you understand gyroscopic precession, pigeon?

If you do answer the question:

If we applied a side force of drag on the bullet in your diagram where would the equal and opposite reaction manifest itself if we have a right hand spin?

Now look at your force vector array in diagram 2 and your error should jump right out at you.

Not to confuse the subject though. The bullet just is not in a moving frame of reference once it leaves the barrel. Denker's site explains this well.

All the best,

Crumpp

edited because I mispelled precession

M_Gunz
09-13-2009, 05:29 PM
Something you should consider is that 720 kph, pretty fast for these planes, is 200 m/s while muzzle velocity of a 50 cal
in IL2 is 870 m/s.

That's why I make the case of the 'without drag' straight line you show above being very close at short range. There isn't
enough deviation to matter. At very close ranges like 100m the error from 5 or 10 degrees of slip is also very small.

When you see the shots curve away after firing 90 deg to the side that does show side-force drag in IL2. The shots have
to go a good ways out before it's apparent though. If you fire say 45 to the left of forward then even the drag in the
aimed direction on the bullet will add to the perceived curvature since it slows the velocity along the path your plane
is moving but just how that would appear due to relative plane:bullet speeds --- IMO less curve than fired at 90 deg.

If you see how far the shots from 90 deg take to curve and never shoot that far then you'll avoid the worst of it.
Just be going as fast as possible in the bomber when checking it, shallow dive time and all that. Too bad the Mossies
can't have side guns. http://forums.ubi.com/images/smilies/16x16_smiley-tongue.gif They sure have the speed. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

The thing about where the target is going.. you have that when you aren't shooting with slip. But with slip you get
situations where that relative (in the one case, lack of) motion can either negate or worsen the error. It's good to
know.

Yeah all this is to help judge about where to aim that first burst or have any chance of making a snap shot. It's hard
enough to judge distances and speeds in IL2 let alone be doing mental trig while in motion. That's why we have machineguns.
On snap shots I aim a bit ahead and hold the trigger for up to 1/2 second, wasteful as that is.

M_Gunz
09-13-2009, 05:40 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> So, you claim that the bullets will fly in a straight line, instead of a curve?

Yes, just like Denker explains on his website in link I provided. </div></BLOCKQUOTE>

Nice, but that's not a moving centrifuge with the bullet leaving perpendicular to that movement.


If we applied a side force of drag on the bullet in your diagram where would the equal and opposite reaction manifest itself if we have a right hand spin?

More drop?


Not to confuse the subject though. The bullet just is not in a moving frame of reference once it leaves the barrel.

Even with the side-motion component imparted by the movement of the plane? I'll have to look at that page again.

Kettenhunde
09-13-2009, 05:43 PM
Nice, but that's not a moving centrifuge with the bullet leaving perpendicular to that movement.

It works the same M_Gunz.

Read the first sentence in Denkers explaination:


To get a better understanding of the balance of forces in a turning and/or slipping airplane,

http://www.av8n.com/how/htm/mo...#sec-just-centrifuge (http://www.av8n.com/how/htm/motion.html#sec-just-centrifuge)


More drop?


Bingo! We have a winner. http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

The fact we are in a yaw, we can divide the force vector into two components. A top vector we have already figured out and a direct side force vector.

The direct side force vector will induce a tilting force and cause it to corkscrew about the axis of rotation.

Guess what the dynamic pressure effects of a side velocity would cause it to do with a right hand spin?

This is getting fun. Good Stuff Pigeon.

All the best,

Crumpp

M_Gunz
09-13-2009, 06:00 PM
Yeah okay the bullet fired 90 degrees to the side actually moves in a straight line as seen from a stationary observer
but that line is angled forward of the aim due to the vector added by the motion of the gun/plane. You're right.

Kettenhunde
09-13-2009, 06:44 PM
due to the vector added by the motion of the gun/plane


There is no vector added at all. The gyroscopic precession question was purely hypothetical.

We know from that an imaginary side force vector would not even produce any force to turn bullet left or right.


When the tennis ball departs the centrifuge, it once again travels in a purely easterly direction, but this time it also accelerates downward under the influence of gravity.


http://www.av8n.com/how/htm/mo...c-centrifuge-gravity (http://www.av8n.com/how/htm/motion.html#sec-centrifuge-gravity)

Now if the airplane is in accelerated flight then our bullet will act under the influence of that acceleration for a short period. It does not care whether the load factor comes from the earth’s gravity or the airplanes motion.

That is why shooting in WWII under a load factor was so difficult. Our gunsight is zero'd for 1G. An asymmetric loading situation is near impossible to shoot accurately.

M_Gunz
09-13-2009, 07:18 PM
Shooting while in slip, the bullets do not go where they are aimed. Yes they have a side vector added due to the forward
motion of the plane not being aligned with the direction the gun is pointing and that can be seen from outside in a
stationary frame.

Denker's example there serves to set up terms and understandings of the forces involved in the text below the example.
The centrifuge there is not moving and from reading the whole thing it describes releasing balls from a turning plane
though the principles also apply to slip. It does not describe a thrown ball but rather a released ball which gives
us the direction of the added vector and not the gun shot.

http://forums.ubi.com/images/smilies/winky.gif

Kettenhunde
09-13-2009, 07:59 PM
The relative wind will change the velocity of the round. This can cause trajectory shift because our sight is not set up for the change in velocity.

In this case, although our bullet path only appears to have changed once again due to frame of reference. Another reason why WWII pilots got in close to shoot.

If the aircraft is accelerated, the bullet will yaw due to gyroscopic precession as soon as it leaves the barrel causing projectile jump.

The path of the bullet will be the same as if fired on the ground however along the new trajectory.

In this case you are correct but it requires the aircraft to be acelerated which is not the conditions we are discussing.

Slipping on a straight vector does not impart an acceleration on the aircraft.

M_Gunz
09-13-2009, 11:01 PM
It imparts motion to the gun and bullet in the gun to the side of where the gun is aimed, which is not where the plane is going.
Motion vector, not acceleration.
When the bullet leaves the barrel it does so with both that motion and the motion imparted from being fired, two components.
It also applies to firing from moving ground vehicles or even throwing beer bottles at telephone poles from the back of a
moving truck, in my experience, and yeah the bottle paths appear curved from the back of the truck.

I really thought we had that down already. The shots do not go where they are aimed when firing from slip. It is most easily
seen when firing at stationary targets such as buildings on the ground.

Skoshi Tiger
09-14-2009, 01:15 AM
So help me get this straight.

I have to add my Schieberichtung to my Flugzeugochse and Visterrichtung to determine my GeschoBrichtung?

Hmmm! I see! it's easy when you start off with the basics!

WTE_Galway
09-14-2009, 01:32 AM
Originally posted by Skoshi Tiger:
So help me get this straight.

I have to add my Schieberichtung to my Flugzeugochse and Visterrichtung to determine my GeschoBrichtung?

Hmmm! I see! it's easy when you start off with the basics!

Just remember which way is left and which way is right

.. now all sing together the links rechts song !!!

"Schiebst Du von links nacht rechts -
dann links halten
Schiebst Du von rechts nacht links -
dann rechts halten "

Kettenhunde
09-14-2009, 04:11 AM
Motion vector, not acceleration.


It is most easily seen when firing at stationary targets such as buildings on the ground.


That is yet another frame of reference.

Otherwise in the same frame of reference as the bullet, it is acceleration.

Bremspropeller
09-14-2009, 04:21 AM
Shooting while in slip, the bullets do not go where they are aimed.

Mine do that even without slipping http://forums.ubi.com/images/smilies/bigtears.gif http://forums.ubi.com/images/smilies/compsmash.gif

Kettenhunde
09-14-2009, 06:34 AM
I have to add my Schieberichtung to my Flugzeugochse and Visterrichtung to determine my GeschoBrichtung?

We are looking at the conditions in Pigeons diagram. The shooting aircraft is in a one G slip on a parallel course.

If those conditions are not met, then the difference in vectors becomes part of the equation. Just like trying to hit a ground target.

All the best,

Crumpp

Pigeon_
09-14-2009, 10:11 AM
One G slip? What do you mean by that?

Are we understanding each other correctly? I am talking about a steady slip (as in picture 19.7 from av8n.com: http://www.av8n.com/how/htm/mo...fig-slip-plane-ball) (http://www.av8n.com/how/htm/motion.html#fig-slip-plane-ball)). The aircraft's orientation does not change (does not turn).

M_Gunz
09-14-2009, 03:04 PM
Flying straight and level is 1 G flight, slip or not. In a level turn it would be more than 1 G.

Pigeon_
09-14-2009, 03:55 PM
Of course! Thanks M_Gunz http://forums.ubi.com/images/smilies/25.gif