AA guns + rockets alternatives for 1935-45

[Zmauky]

So you'd have to steer it manually from the ground within to 45m of a bomber.

Well I wasn't completely clear. A rocket like the Enzian, but without guidance with a time fuze and a predictive aiming method like a regular 88mm AA shell.

 

[Shortround6]

So you'd have to steer it manually from the ground within to 45m of a bomber. I'm just not seeing how that could be any kind of effective system. Guided missiles were the future of heavy AA, but getting all the pieces of the puzzle together for such a system to see service during WWII is probably too much to ask.

You have hit the nail on the head with the very large hammer of reality.
It is one thing to control by ground observer using radio equipment a small airplane (or car/boat) that is within a few hundred ft or yds (but see You tube videos). It is also quite possible to control large slow airplanes at several thousand yds.

1. Trying to control a small missile (harder to see than the biplane) at 4-5 miles (slant range) at 20,000ft + (clouds-haze-smoke) that is flying at 4-600mph
and steer it to a close area to the enemy bomber/s is quite a trick.
2. Using the pretty much standard eyeball, Mark I, (even with binoculars or telescope) to judge the relative heights in addition to position the lateral plane calls for judging the relative heights to under 1%.
3. They were "working" on a terminal homing device, they didn't have one yet.
4. They were "working" on proximity so they wouldn't have to use the controllers thumb on a switch located how many miles away.
5. This assumes the rocket motors work as advertised when made in large numbers so an even minor failure rate is not lobbing 500kg warheads into German cities.

 

[Shortround6]

Well I wasn't completely clear. A rocket like the Enzian, but without guidance with a time fuze and a predictive aiming method like a regular 88mm AA shell.

And regular 88mm shells had a success rate of ?????? in 1000 at best?
Granted you may big up quite a bit with the bigger warhead. In in 100, 1 in 50?
What was the height judging accuracy of the German radar to assist in setting the fuses?
What is the accuracy of the un-guided rocket compared to the 88mm/105mm shells. Deviation from intended flight path.
Lets remember that the best German 88mm fired it's shells at darn close to Mach 3. Doesn't mean they were accurate but it does mean the time of flight was short.
Even a 620mph missile/aircraft is doing 910fps which is just under 1/3 the speed of the standard old 88mm shell, granted the artillery shells slow down but total time flight is still going to be a number of seconds shorter than the rocket/missile which increases the potential miss distance.

 

[tomo pauk]

Yes. But it was also a major consumer of resources such as nickel, which would have been sorely needed elsewhere.

Germans were using obscene amounts of war material just to kill one bomber, or to damage a few. Average went to 16 thousand (sixteen thousand) of heavy AA shells per a bomber killed by early 1944. Or, the production of heavy AA shells (vast majoprity being for the 88mm) went above 1.5 millions of shells per months in many wartime months; plans were to reach 2 millions, but that never happened.
The thing with having quad 20mm guns was that they were also burning through millions of shells like there is no tomorrow, and they still didn't have the range and ceiling that even the German 37mm guns had. Quad 20mm, when deployed to protect forward troops, or even those in occupied West Europe, can't have the PoW, teenagers and women as crews, these need to be well-trained men of military age.
Again, a bigger gun here is better, since it can provide the better coverage of the assets on the ground by employing less guns per area of terrain, and with less manpower. Making one 37-40mm shell will be cheaper and faster than making 3-4 20mm shells, especially since Germans never adopted the utterly simple air column fuse for their light guns.

And d@mn, was the 40mm Bofors one hell of a gun.

 

[Zmauky]

We'll never be sure, but 3x slower speed (i.e. accuracy compared to artillery shells) versus 5x the volume of destruction... and they don't even have to shoot down a single plane, it's enough to break the defense box.

 

[Shortround6]

The 20mm might have been a viable AA gun in the beginning of the war, or at least better than no AA guns or machine guns.
US did a study of the last year in Europe and estimated that they were firing 50,000 rounds of .50 cal ammo for each plane brought down compared to 500 rounds of 40mm ammo. This does skip over the 20mm but the 20mm needs to be an order of magnitude better than .50 to even get close to the 40mm.

Now several things skew the result here. The US was handing out .50 cal guns to just about everybody that wasn't a cook (granted a few cooks did rather well in a few emergencies).
Point is that there a lot of .50 cals being pointed into the air with gunners having not the best training or any resent training. US fire discipline was a little lacking?( supply was rarely a problem). Not saying that 20mm gunners were all experts but the proportions may not have been the same.
The Germans took a while but they were coming to same conclusions. A single late model 37 was worth more than the quad 20mm. How much more is subject to question but it had the advantages of less man power and greater effective range (could cover a wider area using the same number of mounts/guns).

 

[Shortround6]

5x the volume of destruction

that 5x times the volume (actually 125 times, you need to cube it) is still a very small volume in space. This assumes that the bombers fly exactly on the estimated course and at the estimated speed and at the estimated altitude. Yes the estimates are based on radar information and optical rangefinders but those are not exact.
AA artillery was sometimes estimated to have an effective range/altitude equal to the distance/altitude that the gun could fire for 20 seconds to get off 4-6 shots and to have some chance of correcting fire for the last shell fired. Closer distances meant the guns increased in effectiveness quite a bit. But this brings time into the problem, the standard 88 needed close to 20 seconds to get to the mid 20,000ft range. Lobbing a missile that takes even 30 seconds to get to the same point in the sky also makes a huge difference to size of the possible target area, and that assumes the unguided rocket travels as predictable a flight path as the shell, unguided pretty much means fin guidance or at least basic gyros. Basic gyros do NOT steer the missile to the original point of aim, they steer the missile on the original heading. Cross winds, updrafts/down drafts and changes in expected density will shift the missiles flight to a course paralleling original course set on the gyros.

 

[tomo pauk]

The Germans took a while but they were coming to same conclusions. A single late model 37 was worth more than the quad 20mm. How much more is subject to question but it had the advantages of less man power and greater effective range (could cover a wider area using the same number of mounts/guns).

This document might be worth taking a look: link

One of graphs (pg. 57) shows that 9 hits by the 20mm is required for a 50% chance to kill the P-47 outright, while it will take two 37mm (from the US gun) or 3cm Mine shell to do the same. It will take perhaps 17-18 hits of the .60 API, while the no. of hits by the .50 is everyone's guess:

 

[z42]

Well I wasn't completely clear. A rocket like the Enzian, but without guidance with a time fuze and a predictive aiming method like a regular 88mm AA shell.

If we're talking about unguided rockets, maybe something like Taifun (rocket) - Wikipedia ? A (much!) smaller rocket with a contact fuze fired from a launcher array with 30-50 launch rails.

 

[z42]

But this brings time into the problem, the standard 88 needed close to 20 seconds to get to the mid 20,000ft range. Lobbing a missile that takes even 30 seconds to get to the same point in the sky also makes a huge difference to size of the possible target area, and that assumes the unguided rocket travels as predictable a flight path as the shell, unguided pretty much means fin guidance or at least basic gyros.

One advantage of rockets for AA vs cannons is that the rocket motor accelerates the rocket as it gains altitude and the atmosphere gets thinner, vs having the highest velocity directly at the muzzle where the air is at its densest. One of the reasons why these various orbital cannon projects for launching satellites have never really worked out. Maybe not a huge issue for reaching up to only about 25000ft that the WWII era bombers in Europe were flying at, but still.

That of course supposes you can economically mass-produce functioning rocket motors. Which apparently was one of the main reasons why the above mentioned Taifun project never reached operational status.

 

[Zmauky]

Ok if we insist there are some Greek letters in the formula about the volume of a sphere so it is not exactly 125 but yes ... 5 times the radius of destruction is not is not what I wrote (what I meant to say). So can we switch to my native language to better understand each other?


But the general idea is that 5000 -16000 shells and xy spare tubes and xy more crew costs less than ... 19 - 50 - 500 ? unguided but much more destructive missiles.

 

[Shortround6]

Good find Tomo.
So we have fire rates of the various guns of and just swapping German guns and American guns

Old 37mm.....................80 (?)rpm
Flak 43 37mm............180rpm
Flak 3cm.......................250rpm
Flak 30 20mm............120rpm
Flac 38 20mm..........180-220rpm
Quad 20mm............700-800rpm

and if we very optimistically assume we can get 2% hits
we need to fire
the old 37mm for 2.5 minutes to get the required 2 hits
the new 37mm needs 1.1 minutes
the 30mm can do it in about .75 minutes (46-47 seconds?)
The flak 18 20mm needs 3.75 minutes to get the required 9 hits
The Flak 38 needs 2.5 minutes
The Quad 20mm needs about 0.6 minutes.

A lower hit rates things start getting worse and the 37mm and 30mm guns have longer effective ranges. Parking your 20mm guns 2000 meters from the bridge may not do what you want. Germans used 3 or more sights on the 20mm guns of greater and lesser effectiveness. Later sights were often less effective (required less training, where cheaper, could actually be supplied?)

The US study showed 2 hours of continuous fire for the .50 cal for a kill (not a cripple) and 4 minutes for the 40mm but we can assume the 40mm Bofors shell is a bit more lethal than the German or American 37mm shells.

 

[Shortround6]

But the general idea is that 5000 -16000 shells and xy spare tubes and xy more crew costs less than ... 19 - 50 - 500 ? unguided but much more destructive missiles.

At what cost? A 10.5cm shell held 1.5kg of explosive and about 5.6kg of propellent but used a crap load of steel. That 500kg charge in the rocket is 333time more expensive in explosive.
How much propellent does each rocket use up? How many hundreds of KG?
Wooden air frame materials are cheap, labor is not even slave labor might be better employed doing something else.
Shells don't use gyros and servo controls to flight surfaces.

 

[Shortround6]

One advantage of rockets for AA vs cannons is that the rocket motor accelerates the rocket as it gains altitude and the atmosphere gets thinner, vs having the highest velocity directly at the muzzle where the air is at its densest.

Quite true but lets look at the Wiki specs again.
Max speed 2100mph = 3080fps
Better than the old 88mm, a bit better than the 10.5cm not as good as the long 88mm (but that didn't built in huge numbers)
However the motor burned out in 2.5 seconds which means that even under 7,700ft the rocket has started to coast. It does have a good advantage over the artillery shells but it is not going through 10,000ft- 20,000ft airspace at 3000fps either.

What is unknown in the common articles is what was the dispersion at 22-25,000ft? how big an area of the sky were these things going into?

 

[tomo pauk]

A lower hit rates things start getting worse and the 37mm and 30mm guns have longer effective ranges. Parking your 20mm guns 2000 meters from the bridge may not do what you want. Germans used 3 or more sights on the 20mm guns of greater and lesser effectiveness. Later sights were often less effective (required less training, where cheaper, could actually be supplied?)

We can also take a look at the twin 30mm, even if it is not as fancy a gun as the Kugelblitz was supposed to be. Per your numbers, it should be needing under 0.4 sec to do the job. It should be a far easier to install the two of either MK 101 or 103 on the quad 20mm mount than it was to install 4 of the 103s as the Germans were musing with.
So basically there is a lower time required to kill a sturdy aircraft than even the best of the lot, while offering the much improved ceiling and range.

A twin 30mm on the mount for the single 37mm would've also made sense. The single 30mm would've fit on the tracked, wheeled and half-tracked vehicles where the quad 20mm or the single 37mm does not fit, while a single 20mm is too small a gun for the vehicle.

Similar math (if not better) would've been for a light 37mm gun that is a spin-off from the MK 101/103, that fires a 500-550g Mine shell as it's primary shell.

 

[z42]

Quite true but lets look at the Wiki specs again.
Max speed 2100mph = 3080fps
Better than the old 88mm, a bit better than the 10.5cm not as good as the long 88mm (but that didn't built in huge numbers)
However the motor burned out in 2.5 seconds which means that even under 7,700ft the rocket has started to coast. It does have a good advantage over the artillery shells but it is not going through 10,000ft- 20,000ft airspace at 3000fps either.

Simple high school Newtonian physics assuming constant acceleration (ignoring air resistance and propellant burnup) gives me a burnout altitude of 1145m assuming a vertical launch. At that altitude the air density has dropped only about 10% or so, so not particularly significant.

What is unknown in the common articles is what was the dispersion at 22-25,000ft? how big an area of the sky were these things going into?

Does it matter if you can't get the rocket motors to work reliably in the first place?

 

[ThomasP]

FWIW

A bit I posted elsewhere on the forum:

"What if the Germans had radar proximity fused AA shells?"

I have wondered how well a developed land-based vehicle mounted system would have worked. Maybe something like a multiple (20+) tube 2" version mounted on a quickly trainable mount (like the small naval Mk V gun mount) fitted on the back of a truck or trailer of some sort. Not as versatile as a cannon, but it would have to be rather discombobulating for the pilot to suddenly have 20+ parachute mines popping up in front of him - knowing that each aerial mine had enough HE to blow a wing, tail, or engine right off of your aircraft.

 

[Zmauky]

Looking at the Nuts & Bolts Experimental Flak Weapons bookazine later light AA (experimental) systems were geared towards getting as many shells (bullets) in as little time as possible. Mostly 6-8 barrel systems which is repeated in the handheld "Fliegerfaust". Which makes sense - how many times will you have a chance to shoot planes flying over you from one point and with a salvo you cover a larger cone of fire. This reminds me of the alternative weapon for Bachem Ba 349 Natter, a bunch of 30mm barrels with one grenade each. Kind of like a shotgun, only bigger and with explosive charges. And the Natter is not far from my idea of big unguided rockets (eject the pilot, add explosives...)

 

[Shortround6]

Natter substituted human pilot for electronics as the guidance system and/or aiming/terminal homing system.

The real problem was not the propusion system. It is what do you do when the "weapon" gets in general area of the target.

 

[tomo pauk]

One tidbit about the German production of the 37mm Flak 18 and 36 in 1940: monthly production of 54 pieces through several months sunk to 36 in July and remained as such through at least October because Rh-B was also trying to make the 3 cm weapon (ie. MK 101) for the needs of Luftwaffe in these months.