real bullet behaviour

[MemphisBelle]

hello guys,

 

I´ve just a simple question.

 

What happens to the speed of a bullet, if a jet is firing his cannon while flying supersonic speed, may be mach 2.

 

Would the speed of the projectile been influenced while leaving the barrel, says the total speed is slowlier? Or would the speed of the projectile be not effected and be the same as a bullet which is fired on ground?

 

Thanks,

 

Memphis

[topdog]

The speed of the bullet would be relative to the speed and angle of the gun it is fired from (clarification: to anybody except the shooter), so firing ahead would increase the speed of the bullet (it would already be going as fast as the jet, now it's propelled and will travel faster), firing behind would decrease it and the bullet would appear to be travelling slower than normal. Though - turbulence/friction/other matters aside - if fired from the front and the back simultaneously, both bullets would pretty much be moving away from the jet at equal rates from the point of view of the jet/shooter.

 

Firing from some angle at the sides would be the equivalent to firing it whilst stationary.

Edited August 2, 2010 by topdog

[Yo-Yo]

hello guys,

 

I´ve just a simple question.

 

What happens to the speed of a bullet, if a jet is firing his cannon while flying supersonic speed, may be mach 2.

 

Would the speed of the projectile been influenced while leaving the barrel, says the total speed is slowlier? Or would the speed of the projectile be not effected and be the same as a bullet which is fired on ground?

 

Thanks,

 

Memphis

 

As the pressure of the powder gases is much more than dynamic pressure you can presume that at the muzzle the bullet will have the same speed relative t the barrel. When it is in the world it starts its movement with the speed that is a vector sum of the carrier and bullet velocities.

Edited August 2, 2010 by Yo-Yo

[MemphisBelle]

Thanks for your replies, that helps me a lot.

[Moa]

However, at Mach 2 the shells slow slow down rapidly once they leave the barrel since the drag on the shell is higher at the combined aircraft plus muzzle velocity of Mach 3 than if the shell was fired from stationary (Mach 1).

 

I believe there is a historical case where a Canadian aircraft in a dive fired and overrun its own bullets/shells - shooting it self down (engine ingested them I guess). Crazy Canucks.

 

Never ask a physicist whether firing stuff from the front and back of an aircraft makes those objects move at the same speed (clearly not 'velocity' since that is directional). They would answer the speeds are approximately the same, but some infinitesimal difference due to relativistic effects. If an 'aircraft' was firing lasers and was also moving near the speed of light the forward laser would still travel at the speed of light (not twice the speed of light). One of the funky consequences of relativity. Now glad you didn't ask a physicist? :)

[IvanK]

There are many cases of aircraft hitting themselves on Strafing passes (Ball ammo) either from a direct ricochet (i.e. a round they fired) or an indirect ricochet that is a dead ball round in the butts being picked up by a fired round. I know of at least 6 cases in the Mirage (me being one). This ricochet risk is what determines (in peacetime ranges) minimum firing range.

 

The idea being to ceasefire at such a range that the aircraft recovery will clear the known richochet envelope. Push the ceasefire range and you will penetrate the known ricochet envelope. Minimum cease fire range in the RAAF for 20mm and 30mm is around 2200feet Slant range on 10 degree strafe.

 

The diagrams below are from a French study on DEFA 30mm ricochets using ball rounds.

 

Edited August 2, 2010 by IvanK

[Avilator]

I believe there is a historical case where a Canadian aircraft in a dive fired and overrun its own bullets/shells - shooting it self down (engine ingested them I guess). Crazy Canucks.

I've read that the airplane was flying level, fired the cannon, then entered a dive and accelerated. The path of the plane and the falling bullets intersected with predictable results.

[MemphisBelle]

Thanks for all those replies guys,

so basically you say that the speed of an aircraft increases a direct effect of the speed of a bullet one it left the muzzle, right?

[asparagin]

Thanks for all those replies guys,

so basically you say that the speed of an aircraft increases a direct effect of the speed of a bullet one it left the muzzle, right?

 

The speed doesn't increase the effect, it has an effect.

[MemphisBelle]

The speed doesn't increase the effect, it has an effect.

 

OK, thanks for the correction :thumbup:

[bumfire]

There are many cases of aircraft hitting themselves on Strafing passes (Ball ammo) either from a direct ricochet (i.e. a round they fired) or an indirect ricochet that is a dead ball round in the butts being picked up by a fired round. I know of at least 6 cases in the Mirage (me being one). This ricochet risk is what determines (in peacetime ranges) minimum firing range.

 

The idea being to ceasefire at such a range that the aircraft recovery will clear the known richochet envelope. Push the ceasefire range and you will penetrate the known ricochet envelope. Minimum cease fire range in the RAAF for 20mm and 30mm is around 2200feet Slant range on 10 degree strafe.

 

The diagrams below are from a French study on DEFA 30mm ricochets using ball rounds.

 

 

 

Are you a pilot on real life and caught a ricochet to your aircraft ?

 

If so that must of been hella scary to see your fired rounds coming back up in your direction.

[IvanK]

Yes now in the airlines, many moons ago in the Military.

 

In my case I never knew it happened until I had shut down and was walking away from the aeroplane. One of the maintenance guys saw it. A Ball 30mm round had penetrated the lower wing surface and was still embedded in it with about 3 cm of the round still exposed. I believe in my case it was an indirect ricochet. Viewing the cine film of the last pass did show I had "pushed the min range" a bit so I guess I was asking for it .... my stuff up.

[IvanK]

Here is an image of the repair patch. Colour is a bit lurid as its scanned from a 29 year old 35mm colour slide.

 

[GGTharos]

Good tale IvanK :D

 

Good thing it didn't do any more damage!

[bumfire]

Crazy Stuff Ivan, real crazy, I bet you are glad you walked away from that one, as it could of easily ended up in disaster depending on where the round struck.

 

The patch job looks a fair size, those 30mm rounds must make quite a mess.

 

May I ask what kind of Mirage it was you were in ?

[IvanK]

Mirage IIIO serial A3-15 on 15 Aug 1981 at Saltash Air weapons range 10 degree strafe.

[IvanK]

Another image that shows a little more perspective as to where the hit occurred.

 

[GGTharos]

Looks like it had a pick of engine or taileron if it went a little here or a little there ...

[bumfire]

I cant believe how lucky you are

 

1, for actually getting to fly a fast fighter jet, which the majority of us can only dream of doing, and 2, lucky that you never shot yourself down :pilotfly:

 

I can see the headlines now, "Fighter Pilot Scores his First Air to Air Kill by Shooting Himself Down".

 

You know what the media is like, they would have a field day with something like that.

 

Is the canopy amoured ? does it have a bullet resistant plate at the front ?, so that if you were to be shot at head on, either from the ground during strafing or from a plane, you would be kinda safe ?

 

Basically what i am asking is, if that ricochet had bounced back up and went straight for your face, slap, bang in the middle of the canopy head on, just infront of where the HUD is, do you think it would it of penetrated ? or is their protection there to minimise the danger ?

 

I know 30mm has got a fair amount of kinetic energy behind it plus whatever type of filling the ammo has, but do you think it could of been stopped if it had struck your canopy head on or any part of the canopy for that matter ?

 

I ask, because I saw a video of a su25 takin 23mm shots to the sides and front, and come away mostly unscathed except for a few dents ( no holes ) and powder burns, and I was wondering if it would be the same for the mirage.

 

Regardless if it could or not, you are still a lucky bugger for getting to fly a jet fighter :thumbup:

 

EDIT:

 

Your post about your self inflicted damage due to ricochet reminds me about a uk TV series about Tornados, it was either made by the BBC or ITV and it was all about the life of a fictional Tornado Squadron. One of the episodes had your exact problem shown, they were doing strafing tests somewhere and the pilot was warned not to go too low and to watch the angle that the plane attacked from, needless to say when the Tonka opened up, you saw the tracers hit the deck and come bouncing back up and lodge in the pilot or navigators ejector seat, I think it was the pilots? cant exactly recall as its a good 15 years since I saw it.

 

The pilot had to do a smooth landing incase the jolt made the seat go off, once landed the pilot had to ever so slowly climb out of the seat/plane and just as he got down from the plane and with no one in the pit, the seat fired due to the round lodged somewhere on said seat.

 

For the life of me I cant recall the name of the tv series, apart from a few aerial shots of tonkas earning their bread and butter by flying lowlevel, it wasnt that good of a tv programme.

Edited August 4, 2010 by bumfire

[IvanK]

The Mirage III being a child of the 50's had a three panel windscreen. The centre section was armoured. Ok for small calibre stuff but that would be about it. There was no armour anywhere else on the airframe. 23mm hits on a Mirage would chew it to pieces.

 

Most peacetime strafing practice is done with Ball ammo. In most cases the ricochets are indirect but even in the case of a direct ricochet the round has lost a lot of its energy still enough though to bring an aeroplane down if it hits something vital or goes down an engine etc.

 

Yes I have been very fortunate and owe a lot to all those that helped me along the way.

Edited August 4, 2010 by IvanK

[bumfire]

For your plane to have no armour, save for the small windscreen, for you to then get hit by a 30mm round and not know anything about it til you landed was nuts, but I suppose it would be quite hard hearing external noises when you have all the normal noises of a jet to put up with.

 

Then with your helmet/earphones on top which must obscure alot of the remaining noise that you can readily hear, plus your pulling the trigger ontop of all that which must produce a fair bit of noise and vibration, so it is very understandable that you never heard/noticed anything wrong.

 

But, saying that, it is a 50's plane, things back then were built to last, so I presume the Mirage III is a solid piece of kit and took the hit in its stride ? I say presume, as I dont know anything about the Mirage III.

 

Mucho Respect, not because you shot yourself :music_whistling:, but cause you flew a jet fighter which many of us on this board aspire to :thumbup: