kinda military

[binabik]

ok i just got done watching transformers and i did some research on the ac-130 and found out it was a real plane and it has a 105mm howitzer on it. i was wondering if you could take a plane of fighter plane size and put say a 120mm tank gun on it, though modify it to be recoiless maybe and what stresses it would put on the plane and weather it would be able to be done even. i am thinking for instance if you were to fire it going 400 miles per hour how much speed loss. this would be either a forward or backward facing gun. just wondering because that looks ausome. it would probably be backward so that the air to air gun would be in front.

[binabik]

addition, it would have to have an autoloading system

[jab2]

There are some factors which you need to understand to discuss your idea. I also suppose, from your mentioning of tankguns, your intended targets will be armor.

Firstly, no existing recoil gun or cannon design can be modified to be recoilless. There is no way of getting past Newton's law about action/reaction. You either have a gun that fire from a closed breach and the reaction force that balance the projectile is spend on momentum of a huge weight and buffers towards the back, where such weapons will have recoil, which is a function of projectile weight and speed, or the weapons is "breachless" and fire like a quasi rocket where the reaction force is the hot gas escaping to the rear like in a RPG. This weapon will be recoilless. The means of operation between the two is so different that one cannot be modified to work like the other.

The 105 on the AC-130 was, as I understand, mostly used with HE rounds for area effect in the anti personnel or soft vehicle role and not in the anti-amour role. The AC-130 was flown along a circular path round the aiming point by means of a sight in the side window of the pilot, as all the weapons fire at right angles to the flightpath on the port side. The target point was thus basically motionless or moved only slowly relative to the sight line of the weapons, thus making aiming relatively easy and stable.

In fast movers which is much smaller and lighter than the AC-130, off-axis forces would play havoc with the flight performance of the A/C. This would thus exclude any weapons not firing along the flight path and in fact along the center line of the A/C, as was found with the A-10 Warthog. In this fast moving environment stable aiming becomes a problem, and the platform move too much if long bursts of heavy weapons is fire. That is why the current weapons have a very high cyclic rate and are only made in the 25 - 30mm caliber range. Having seen the result of a burst from a A-10's 30mm GAU-8 Avenger at 3900rpm, and the fact that an A/C can hit ground vehicles through the thin top amour, not having to penetrate the full frontal armor as ground based anti-tank weapons does, I doubt whether your idea of a tank gun on an A/C will have much support amongst military hardware designers.

There is naturally the issue of weight as well. A 120mm gun with autoload will be one heavy mother.

See also GAU-12, Gait 30, GSh-6-30 and GSh-30-2.

[Moontanman]

I agree, the warthog pretty much has the whole fast mover anti-armor airplane thing covered. I see them fly around where I live regularly up and down the beach. Very impressive airplanes, they look like very no nonsense war planes. A friend from the Gulf War confirms this to be true. He says pilots describe a real recoil effect from their gun when it fires, not sure a bigger caliber gun, not firing from the line of flight, would even be possible much less any more effective.

[binabik]

OK, like i said saw it on transformers which looked ausome and looked it up and wondered, thanks

[CraigD]

Originally Posted by binabik

i was wondering if you could take a plane of fighter plane size and put say a 120mm tank gun on it, though modify it to be recoiless maybe and what stresses it would put on the plane and weather it would be able to be done even. i am thinking for instance if you were to fire it going 400 miles per hour how much speed loss. this would be either a forward or backward facing gun.

As Jab2 points out …

Originally Posted by jab2

Firstly, no existing recoil gun or cannon design can be modified to be recoilless.

… if you make a tank gun into a recoilless gun, it’s no longer really a gun, but a sort of missile. Otherwise, this is a pretty straightforward question.

A big, high velocity tank gun throws a 20 kg shell at about 2000 m/s. A small-ish jet fighter like an F-18 masses about 11200 kg empty. So a quick momentum calculation shows that, worst case, such a fighter firing such a gun would change speed by the speed of projectile * mass of projectile / mass of vehicle = 2000*20 /11200 = about 3.6 m/s = about 8 MPH. Note that this is a pretty simple formula, and can be applied to lots of similar questions. Also note that it doesn’t depend on the speed of the vehicle – parked with the brakes off or flying at high speed, the change in speed is the same.

The acceleration would be pretty severe: assuming uniform acceleration and a 6 m gun barrel, the change in speed would occur in 2*6/2000 = .006 seconds, equating to a 600 m/s/s, or 60 g, worst case jolt, tolerable is managed correctly. (The physics for this are just a little more complicated, coming from the formulae and and a little bit of algebra)

So I’d say you could fire a tank gun from a fighter aircraft. It’s rather silly, though, as the purpose of a tank gun is to fire a shell a long distance, the purpose of a gun on a plane is short-range armament, and a fighter aircraft can carry missiles more effective at killing a given target than a tank gun round.

Such silliness pales beside the silliness to be found in nearly every minute of the Transformers movie, however. To enjoy this or most any other sort of gundam animation, you pretty much have to leave your knowledge of science and common sense at the door, or take them out only when you want a good laugh or an exercise in “could that actually happen?”.

[modest]

It is also probably worth noting that the special effects shown in that scene are not of a 105mm howitzer as they say verbally in the movie. The howitzer on a ac-130 is hand loaded and has a rate of fire nowhere near what is shown there.

YouTube - AC-130 Gunship and A-10 - Transformers

~modest

[binabik]

ok, been a while since I talked on this forum but let me say a couple things...

interesting about the speed calculation, was just wondering, i understand that planes are fairly short range and that there are better missiles this was just a just wondering situation. you know you talk about such silliness but i watched the movie cause i hadn't seen it before and i get my ideas from movies, i ask someone weather it is possible and then i think about it.i don't have as big of a knowlege of science at this moment but i feel i can figure out common sense fairly well. when i watch a movie like that i do leave science at the door and then after it i think about the movie and weather some of i could actually be real. and i can enjoy a movie even if i know in realality it is not like that. like worldwide quake movies, supervolcanos (though iheard yellowstone is a supervolcano), FTL travel (extremly hard and probably take thousands of years to develop it), and much more. but when i saw that they put a 105 mm howitzer on a giant plane i just got to thinking and asked if it was possible. it is like a earthquake specialist watching a movie and scrutinizing it instead of enjoying it, i don't have that problem.

modest i know it is not completely accurate with the rate of fire, but i did look at some videos and i think it is 6 to 10 seconds depending on the crew for the 105mm on that plane, plus the rate of fire on it if you don't include the smaller guns seems like it would be about 1 shot ever 3 second or so and that might just be 3 seconds the movie people cut out.

oh and craigd, i am not thinking this was feasable but lots of people are doing things just because they want to. for instance, someone might think i want to modify a train to have the biggest possible artilary piece ever on it so i am going to do it just because i can. i am refering to the Schwerer Gustav 800 mm gun which is the biggest artilary piece fired in anger by germany. but this time it was just a wondering and i was never planning on pursuing it.

[modest]

Originally Posted by binabik

modest i know it is not completely accurate with the rate of fire, but i did look at some videos and i think it is 6 to 10 seconds depending on the crew for the 105mm on that plane, plus the rate of fire on it if you don't include the smaller guns seems like it would be about 1 shot ever 3 second or so and that might just be 3 seconds the movie people cut out.

That's a very good point. That's easily what an AC-130 could look like if it were firing all its cannons including the 105. From this clip on future weapons,

YouTube - Future Weapons: AC-130 Spooky Gun Ship

it looks like the 40 mm might fire at about 1 shot per second and the 20 mm is, of course, much much faster

YouTube - M61 Vulcan shooting 40 dummy rounds

So I think you're spot on. The scene was showing the gunship with guns balls-to-the-walls and is therefore not necessarily wrong despite my insistence.

It's probably also noteworthy that fighter cannons in WW-2 were as large as 40 mm which worked well against bombers.

~modest

[CraigD]

Originally Posted by binabik

modest i know it is not completely accurate with the rate of fire, but i did look at some videos and i think it is 6 to 10 seconds depending on the crew for the 105mm on that plane, plus the rate of fire on it if you don't include the smaller guns seems like it would be about 1 shot ever 3 second or so and that might just be 3 seconds the movie people cut out.

Around 10 rounds per minute seems about right for big guns of various sizes. According to the wikipedia article “Autoloader”, human loaders have claimed rates of 15 rpm, while autoloaders on guns as big as 130 mm have rates as high as 40 rpm (1 shot every 1.5 sec), and the autoloaded 8-inch (203 mm) guns on the heavy cruiser USS Des Moines (CA-134) can fire as fast as 10 rpm.

Originally Posted by binabik

oh and craigd, i am not thinking this was feasable but lots of people are doing things just because they want to. for instance, someone might think i want to modify a train to have the biggest possible artilary piece ever on it so i am going to do it just because i can. i am refering to the Schwerer Gustav 800 mm gun which is the biggest artilary piece fired in anger by germany. but this time it was just a wondering and i was never planning on pursuing it.

I didn’t think you were building mecha in your garage, binabik! I agree toy robot-inspired cartoon-inspired CGI movies, Manga, anime, and other fictions are great fun, and food for thought.

I’m a fan of Battle Angel Alita, a 1990-95 manga known primarily for intense cypberpunk (fusion/confusion of biological organisms and machines) themes, but also for big weapons that look like and apparently are just scaled-up versions of semiauto handguns, butterfly knives, and the like. More of an excuse for its artist (Yukito Hishiro) to indulge a fascination with detailed realistic drawings of weapons (both fictional and recognizable, real) than intentionally serious science fiction, this peculiar art nonetheless provokes some interesting lines of speculation such as: how would you build a 200+ mm rifle that fired from an open breech?

If you enjoy fictionalized guns and related mechanical things, and/or cyberpunk graphic stories, I highly recommend Alita.

As for keeping a sense or reality via science, this practical engineering stuff is IMHO best served by a really sound grasp of the basic, 300 years old laws of motion. If you master these, you can unserstand practically any sort of situation involving ordinary or exotic machines, or which guns of various sorts are just special cases.