Telescoping frontal fuze for very large shells

[TheMarcksPlan]

Dunno if this is a "what if" or a technical question... I've never seen an example of the idea so I'm posting it here. Feel free to move as appropriate if, as so often happens, my utter ignorance is later exposed and this is a "didn't work" rather than a "what if."

I'm thinking primarily of naval bombardments by battleships, monitors, and the like - but also of railway guns and other superheavy artillery. You have a very large shell that will burrow into the ground quite a bit and dissipate much of its effect there. Sometimes that's good, such as against dug-in enemies. Many times it's bad - such as for counterbattery fire or against moving troop concentrations.

For the occasions when you want the large shell's explosion not to be buried underground, my idea/question regards the feasibility of a fuze mechanism that telescopes out of the shell body in flight, after a set number of seconds. If the telescoping fuze, once deployed, were 3 (or more) times the shell's body length then the fuze could feasibly be triggered 15 or more feet above ground (for high angles of fall) - thus perhaps giving some air burst effect or at least avoiding the large-shell drawback of digging too far into the ground.

The telescope mechanism would be simply a narrow tube running the shells' centerline, into which concentrically smaller tubes would fit and out of which they would deploy when triggered (by a spring mechanism?). Once deployed (during terminal shell trajectory), a small pressure on the telescope's tip would trigger the fuze.

Observe the dimensions of a 16in US naval shell:



...the astute will notice that this is actually an AP shell with a windscreen but there's no reason a windscreen can't go on an HE shell as well...

We have 6ft of length overall, so a telescoping fuze mechanism, where 3 telescopic fuzes emerge from the body in the final seconds of flight, could extend nearly 3x the length of the shell body - let's say 17ft.

To know the height above ground at which the fuze triggers, we need to look at angle of fall. I know the angle of fall for a max-range 16in super-heavy AP: 53.25 degrees. The HE's terminal trajectory will be steeper. Why? Because it has higher initial velocity but lower ballistic carrying power due to its lower mass. It slows down more than the AP, but the degree of difference is greater on the X than the Y axis (because its vertical component of velocity is stored as potential energy during ascent rather than expended as heat in friction). Does anyone know the terminal angle of fall for a max-range 16in/50 HE shot? Let's say 57 degrees.

Basic trigonometry [ cos ( 57deg ) * 17ft ] gives 9.3ft height when the telescopic fuze is triggered.

Besides triggering higher up, the telescopic fuze seems likely to be more instantaneous. Why? Because large-shell fuzes usually relied on a change of momentum. For a very large shell hitting relatively soft dirt, that change registers later - thus the heavier shell digs deeper underground. So the telescopic fuze may have something of an airburst effect on this very large shell, even if only by a few feet.

But what about accuracy and aerodynamics? Won't the telescoping fuze, once deployed, ruin these? Well yes, if it's deployed throughout the flight. Computing the time of flight within a second or so, however, isn't that difficult, and you'd use a timer to ensure the telescope deploys only the last second or so before impact. Any deviation in the final second of shell trajectory will have negligible and/or predictable impact on range.

At least one drawback:

The fuze will have to occupy some part of the shell reserved for bursting charge. Seems possible for this to be only a few % points, however, which seems a worthwhile tradeoff.

At least one open question:
Can the shell be structurally sound for firing with a small hole in its apex, to fit the telescoping fuze? Just an intuitive answer but seems likely. Versus a shell of ideal metal vs. filler weight, you'd have to shift somewhat metal-ward to compensate but, again, seems a worthwhile tradeoff if it means your giant shell explodes 5ft above the ground rather than 15ft below (when such shell behavior is desired - otherwise deactivate the telescope fuze or use another shell).

[thaddeus_c]

Dunno if this is a "what if" or a technical question... I've never seen an example of the idea so I'm posting it here. Feel free to move as appropriate if, as so often happens, my utter ignorance is later exposed and this is a "didn't work" rather than a "what if."

I'm thinking primarily of naval bombardments by battleships, monitors, and the like - but also of railway guns and other superheavy artillery. You have a very large shell that will burrow into the ground quite a bit and dissipate much of its effect there. Sometimes that's good, such as against dug-in enemies. Many times it's bad - such as for counterbattery fire or against moving troop concentrations.

For the occasions when you want the large shell's explosion not to be buried underground, my idea/question regards the feasibility of a fuze mechanism that telescopes out of the shell body in flight, after a set number of seconds. If the telescoping fuze, once deployed, were 3 (or more) times the shell's body length then the fuze could feasibly be triggered 15 or more feet above ground (for high angles of fall) - thus perhaps giving some air burst effect or at least avoiding the large-shell drawback of digging too far into the ground.

The telescope mechanism would be simply a narrow tube running the shells' centerline, into which concentrically smaller tubes would fit and out of which they would deploy when triggered (by a spring mechanism?). Once deployed (during terminal shell trajectory), a small pressure on the telescope's tip would trigger the fuze.

recall the 15cm Nebelwerfer 41 tried to achieve something akin to what you are describing https://en.wikipedia.org/wiki/15_cm_Nebelwerfer_41 albeit not with the fuze

some of the Mistel aircraft had the "bomber" component with a pronounced nose, Idk whether that was to aid or prevent burying the wardead?

[Orwell1984]

The concept has been done in a way less complex and complicated form for years. The more moving parts you add the more can go wrong. Sometimes simpler is better. And easier to mass produce.

For bombs:

https://en.wikipedia.org/wiki/Daisy_cutter_(fuse)

https://www.lonesentry.com/articles/ttt ... n-rod.html



For shells/artillery

Check out airburst fusing which was used in artillery during WW2 after being fine tuned in WW1

Clockwork fusing was a known technology during WW2 and used by all major forces for exactly the reasons you describe above.

https://en.wikipedia.org/wiki/Artillery ... urst_fuzes

Replaced in the allied forces in later years by proximity fuses.

[TheMarcksPlan]

The concept has been done in a way less complex and complicated form for years. The more moving parts you add the more can go wrong. Sometimes simpler is better. And easier to mass produce.

For bombs:

https://en.wikipedia.org/wiki/Daisy_cutter_(fuse)

https://www.lonesentry.com/articles/ttt ... n-rod.html



For shells/artillery

Check out airburst fusing which was used in artillery during WW2 after being fine tuned in WW1

Clockwork fusing was a known technology during WW2 and used by all major forces for exactly the reasons you describe above.

https://en.wikipedia.org/wiki/Artillery ... urst_fuzes

Replaced in the allied forces in later years by proximity fuses.

Pre-proximity airburst fuses were unreliable though. With a shell travelling ~1,500 ft/s, any timing error - either aiming/trajectory or fuze manufacture - gets you a useless Flak burst or it hits the ground. This is why men like Patton considered the late-1944 proximity shell as having the potential to revolutionize warfare. Even the 1944 proximity shell isn't very reliable at exploding when you want it to for anti-ground airburst, IIRC.

Re the bomb with extended nose that's plainly nonviable for artillery shells, particularly when fired from a ship (no room in the shell cradle for a massive nose like that). Most importantly it ruins your trajectory and aiming.

[Carl Schwamberger]

Its been some 35 years, but I read something about experiments with this in the latter 19th Century. Sorry I can't recall any details. Through most of the 19th Century burning fuzes were used to achieve a airburst. Those of Black Powder or similar compounds were almost never accurate to less than a half second , which could vary the range error by several hundred meters. Add in the variables in the black powder type propellants, and the necessity to relay the cannon after each shot these were rather hit or miss. A common gunnery technique with these was to aim low and watch the shot bounce or roll into the target area.

As the 19th Century ran out 'better living through chemistry' (for bonus points ID that one). improved burning time fuzes & got more accurate bursts. However mechanical timed fuzes proved better & between 1900 & 1914 mechanical time came to dominate, tho it did not entirely replace the chemical or oxidizing fuse. The advent of recoil mechanisms for artillery in 1890s & precision - reliable air burst fuzes caused the field artillery in most armies to become infatuated with air burst or 'Shrapnell' type cannon ammunition. At this point the problem was not getting air bursts, it became seeing the need for for penetrating fuzes to collapse trenches, blow apart sandbagged and log structure, and European style masonry buildings. Such fuzes existed, but were not as common as the armies found necessary in 1914. By 1918 'Shrapnel' types of cannon projectiles, designed exclusively for airbursts were out of fashion & General Purpose ammunitions designed for penetration, surface, and airbursts became the development focus.

Along with the improvement in time fuzes came improvement in impact function fuses. Even on ordinary soils its was possible in 1905 to get a projectile detonation before full penetration.

Again I don't recall any details for the experiments, but one problem with such a long fuze would be destabilizing the projectile, making it more prone to tumble. At one time I knew the math for this. A set of formulas hat used in part the length to diameter ratio as the starting point for calculating stability of the projectile in flight. Counter intuitively high velocity is not a fix for this. The faster the projectile the more sensitive it is to certain changes in atmospheric conditions. Other changes not so much. For a more stable projectile the correct rotation and greater mass help. A couple other problems I can see from this chair and time are transport and ammo handling o such a awkward projectile. Then theres the question of how much of this sticks out of the muzzle of the cannon barrel which leads back around to the stability question.

I'd also note that with high velocity cannon, or relative short ranges the problem is not one of the projectile penetrating into the ground, but of ricochetting off the surface & not detonating at all. When you have a angle of impact at or below 270 mil or 15.7 degrees the proportion of richochettes rose rapidly as did fuze malfunctions. In training, or during range cleanups it was common to find duds caused by a low angle impact. There was actually a technique that took advantage of this to achieve airburst when air burst fuzes were absent. it was still on the books in the 1980s in the US artillery, tho we were not taught it in the classroom..

[TheMarcksPlan]

one problem with such a long fuze would be destabilizing the projectile, making it more prone to tumble.

Exactly, this is what I meant by destroying accuracy with a fixed long frontal probe. My intuition is that destabilization is a cumulative and iterative process - the shells starts oscillating about an axis due to asymmetric forces; that oscillation causes greater asymmetry of forces; the shell's oscillation increases; the forces increase; etc.

That iterative destabilization process doesn't have much time to get going if the telescope deploys in the last second of flight, however. And any trajectory deviation caused by the momentary destabilization is small in the last second of flight.

And realistically the telescope mechanism could deploy in the last 0.2 seconds of flight - that's probably within the margin of accuracy for time fuzes.

It's the smaller timing increments that make a good airburst more difficult. At 1,500 ft/s terminal velocity you need to be accurate to within 1/100th's of seconds to discriminate between a wasted Flak burst and a ground impact.

A couple other problems I can see from this chair and time are transport and ammo handling o such a awkward projectile. Then theres the question of how much of this sticks out of the muzzle of the cannon barrel which leads back around to the stability question.

Agreed. And as regards heavy naval shells, it's impossible/impractical to fit a shell with fixed frontal probe into the shell hoists and cradle.

I'd also note that with high velocity cannon, or relative short ranges the problem is not one of the projectile penetrating into the ground, but of ricochetting off the surface & not detonating at all.

Yes, my idea would only work with high angles of fall.

[Sheldrake]

I'm thinking primarily of naval bombardments by battleships, monitors, and the like - but also of railway guns and other superheavy artillery. You have a very large shell that will burrow into the ground quite a bit and dissipate much of its effect there. Sometimes that's good, such as against dug-in enemies. Many times it's bad - such as for counterbattery fire or against moving troop concentrations.

For the occasions when you want the large shell's explosion not to be buried underground, my idea/question regards the feasibility of a fuze mechanism that telescopes out of the shell body in flight, after a set number of seconds. If the telescoping fuze, once deployed, were 3 (or more) times the shell's body length then the fuze could feasibly be triggered 15 or more feet above ground (for high angles of fall) - thus perhaps giving some air burst effect or at least avoiding the large-shell drawback of digging too far into the ground.

The telescope mechanism would be simply a narrow tube running the shells' centerline, into which concentrically smaller tubes would fit and out of which they would deploy when triggered (by a spring mechanism?). Once deployed (during terminal shell trajectory), a small pressure on the telescope's tip would trigger the fuze.

Observe the dimensions of a 16in US naval shell:



...the astute will notice that this is actually an AP shell with a windscreen but there's no reason a windscreen can't go on an HE shell as well...

We have 6ft of length overall, so a telescoping fuze mechanism, where 3 telescopic fuzes emerge from the body in the final seconds of flight, could extend nearly 3x the length of the shell body - let's say 17ft.

To know the height above ground at which the fuze triggers, we need to look at angle of fall. I know the angle of fall for a max-range 16in super-heavy AP: 53.25 degrees. The HE's terminal trajectory will be steeper. Why? Because it has higher initial velocity but lower ballistic carrying power due to its lower mass. It slows down more than the AP, but the degree of difference is greater on the X than the Y axis (because its vertical component of velocity is stored as potential energy during ascent rather than expended as heat in friction). Does anyone know the terminal angle of fall for a max-range 16in/50 HE shot? Let's say 57 degrees.

Basic trigonometry [ cos ( 57deg ) * 17ft ] gives 9.3ft height when the telescopic fuze is triggered.

Besides triggering higher up, the telescopic fuze seems likely to be more instantaneous. Why? Because large-shell fuzes usually relied on a change of momentum. For a very large shell hitting relatively soft dirt, that change registers later - thus the heavier shell digs deeper underground. So the telescopic fuze may have something of an airburst effect on this very large shell, even if only by a few feet.

But what about accuracy and aerodynamics? Won't the telescoping fuze, once deployed, ruin these? Well yes, if it's deployed throughout the flight. Computing the time of flight within a second or so, however, isn't that difficult, and you'd use a timer to ensure the telescope deploys only the last second or so before impact. Any deviation in the final second of shell trajectory will have negligible and/or predictable impact on range.

At least one drawback:

The fuze will have to occupy some part of the shell reserved for bursting charge. Seems possible for this to be only a few % points, however, which seems a worthwhile tradeoff.

At least one open question:
Can the shell be structurally sound for firing with a small hole in its apex, to fit the telescoping fuze? Just an intuitive answer but seems likely. Versus a shell of ideal metal vs. filler weight, you'dT have to shift somewhat metal-ward to compensate but, again, seems a worthwhile tradeoff if it means your giant shell explodes 5ft above the ground rather than 15ft below (when such shell behavior is desired - otherwise deactivate the telescope fuze or use another shell).

This is an attempt to solve a problem which was real, but also largely solved by the introduction of super quick fuzes in 1916.

"Functioning time. The time required for a fuze to detonate after impact or a preset time.
Instantaneous (Br Superquick) . When the functioning time of a fuze is 0.0003 second or less.
Nondelay.(Br Quick) When the functioning time of a fuze is 0.0003 to 0.0005 second.
Delay. When the functioning time of a fuze is longer than 0.0005 second. "https://web.archive.org/web/20091210112 ... /fuzes.htm

Large calibre artillery shells were valuble for destroying hardened shelters and dugouts. The shock effect could collapse trenches and undermine the foundations of concrete emplacements. Concussion could kill the occupants of otherwise intact concrete shelters. Big fragments created by big HE shells were valuable for engaging artillery,
They were not the ideal weapons for use against troops on the move.

The protubing rods on Nebelwerfer and mortars did use long rods to deliver an above ground burst effect. But the forces on a mortar or rocket are very much less than those on a shell fired from large calibre gun.

From your description is a[ppears that the telescoping rod is going to push a firing pin into a detonator. This type of direct action fuze will only work at a steep angle of descent. There would be a lot of blinds at a shallow angle or striking a glancing blow at say, the edge of a bunker. It also assumed that the action fo striking the ground would push the rod back rather than distort or bend.

It looks a complicated way to do something that wasn't that necessary.

[Carl Schwamberger]

... And realistically the telescope mechanism could deploy in the last 0.2 seconds of flight - that's probably within the margin of accuracy for time fuzes. ...

If your can achieve that accuracy with high angle of impact you don't need the extension, your time fuze produces the same effect.

Note that high angle of impact flight paths maintain a higher velocity as gravity is a greater factor than wind resistance. At those velocities a couple tenths of a second produce a consider a room for error in calculating time of flight to point X. My experience with mechanical time fuzes & high angle fires were not good. Proximity fuzes had some difficulties as well.

[TheMarcksPlan]

If your can achieve that accuracy with high angle of impact you don't need the extension, your time fuze produces the same effect.

Of course but as I said upthread it's obvious that this level of accuracy wasn't viable in WW2 - else why go the trouble of using proximity fuses for airbursts later?

[TheMarcksPlan]

This is an attempt to solve a problem which was real, but also largely solved by the introduction of super quick fuzes in 1916.

A super quick fuze doesn't give you an airburst though. Having a giant shell explode 15ft above ground rather than even 1ft below creates a substantial fragment dispersion benefit.

They [huge shells] were not the ideal weapons for use against troops on the move.

They're not ideal for reasons of expense and logistics rather than effect. Obviously it's worse to have a 16in shell land amidst your platoon than a 3in shell. Problem is a 16in shell weighs/costs ~150x the 3in shell but has only ~25x the fragmentation effect due to square/cube dynamics (shell effects are in 3D; moving ground troops in 2D).

For naval gunfire support - where the critical action for this idea would lie - these factors are less prevalent.

First, the logistics of a shell fired from a ship are much simpler than a shell shipped, then unloaded, then reloaded on amphibious craft, then supplied to frontline units.

Second, the non-logistic cost of providing non-naval gunfire support to your landed forces is extremely high (assault craft) and can outweigh the inefficiency of using "too-large" shells for missions that smaller, cheaper shells could achieve. This is particularly true where, as with most NGFS, the non-shell expense is a sunk cost due to having a navy for other reasons.

Third, a larger shell/gun has longer range, ceteris paribus. The US 16in/50 can reach ~10mi farther than the USN 6in gun, for example.

Fourth, while shell metal/filler cost escalates with size, it's not likely that fuzes do. I.e. you're normally paying only marginally more the fuze on a 16in shell (of the same type) versus a 3in shell - but again you're using ~150x the metal/filler. If it's worth spending $1 on the 3in fuze then it's feasibly worth spending $150 on the 16in fuze. (I'm sure the 16in fuze costs more but not 150x more)

All this suggests that paying an abnormal amount to amplify the usefulness of an abnormally large/expensive shell should make sense.

From your description is a[ppears that the telescoping rod is going to push a firing pin into a detonator.

Electric impulse from tip to the detonating charge seems the better solution.

[Carl Schwamberger]

If your can achieve that accuracy with high angle of impact you don't need the extension, your time fuze produces the same effect.

Of course but as I said upthread it's obvious that this level of accuracy wasn't viable in WW2 - else why go the trouble of using proximity fuses for airbursts later?

Easier to set & use, Less calculation by the fire direction team. We still use them for illumination projectiles and some other rare high burst requirements & they are a pain when used for HE airbursts. To get a mechanical time fuze to detonate at the desired height necessitated a lot more fussy calculation and adjusting shots. Finding the optimal activation time for the proximity or VT fuze was a lot simpler and faster.

That level of accuracy was viable in WWII, or in 1914, one just needed a reason to reach for it & do the work calculating the actual time of flight and firing adjusting rounds. Since shrapnel rounds were en vogue battery commanders became involved in the question of fuze time setting and finding the range to targets. French artillery batteries were expected to have accurate shrapnel fires (airbursts) on target in a few minutes from start of occupation of a position. They'd been pleased to have a easier to use VT fuze, but accurate fires were possible, you just had to be trained to work with a finicky tool.

[TheMarcksPlan]

To get a mechanical time fuze to detonate at the desired height necessitated a lot more fussy calculation and adjusting shots.

I.e. they're less accurate, less useful. Even years after WW2 (assuming you aren't 100yo). All due respect to your artillerist brethren but I doubt that much policy was based on making things easy for you guys.

[Carl Schwamberger]

To get a mechanical time fuze to detonate at the desired height necessitated a lot more fussy calculation and adjusting shots.

I.e. they're less accurate, less useful. All due respect to your artillerist brethren but I doubt that much policy was based on making things easy for you guys.

Your first statement is wrong in that respect. & the second part is based on direct knowledge or research?

Those were rhetorical questions, no need to answer. I've tried to convey some actual information & you are responding with what look like guesses & ?

[TheMarcksPlan]

I've tried to convey some actual information & you are responding with what look like guesses & ?

I'm responding with reasoning based on first principles. The fact that adjusting shots were needed for your timed shells at all implies they'd be less accurate than my notional shell (assuming it's possible - I haven't so concluded yet) because the notional shell always detonates when the long nose hits the ground.

[Sheldrake]

I've tried to convey some actual information & you are responding with what look like guesses & ?

I'm responding with reasoning based on first principles. (1) The fact that adjusting shots were needed for your timed shells at all implies they'd be less accurate than my notional shell (assuming it's possible - I haven't so concluded yet) because the notional shell (2) always detonates when the long nose hits the ground.

Re 1`. The adjusting shots will be needed to take account of variations in wind strength and direction at different the altitudes. Youn need the adjusting shots to hit the target.

Re 2. Only if.

#1 the telescoping extenbded as envisaged bit works
#2 the electrical bits function as intended.
#3 the electrical fuze does not go off prematurely e.g through ionised rain clouds .

This will still require some form of mechanical time fuze to arm the device. So we have a fuze which is part mechanical - the extending nose, part clockwork (The timer to arm) and part electrical - to action the fuze. This is starting to look more complicated than a proximity fuze.