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File 138931942585.jpg - (69.54KB , 684x475 , electimefuze.jpg )
5423 No. 5423 ID: 5d922e
Because I'm in the mood.

Aircraft! Airpower. Air dominance. Modern war has changed in ways largely unrecognizable to our ancestors by the sheer virtue of this aspect alone. Ever since the days of the Red Baron shooting down Camels with a 12 gauge, militaries around the world have sought out a means of putting to an end that pesky happenstance of a fellow from the other side dropping bullets or bombs on them from a decidedly unfair position of three-dimensional advantage.

Welcome to the Acid Man SAM thread. You are, as always, invited to

>dealwithit.jpg.

In the early days of aerial warfare, when warplanes had evolved beyond a modestly useful curiosity and become one of the key defining aspects of victory (no ground victory without air supremacy!) we made do with large caliber guns and explosive, fragmenting warheads. "Flak." Explosive shells had timed fuses that would cause them to burst at the measured altitude of the slow moving enemy planes, with the resulting clouds of shrapnel, or flak, hopefully damaging critical systems and/or killing the crew of the aircraft.

Since this thread mostly concerns SAMs, we're only going to be looking at AAA in one real aspect that was carried over into missile development: The radar proximity fuse. Or as it was originally called for the purposes of counterintelligence, the VT, or "variable time" fuse.

Buckle up, OPchan. We're about to experience some turbulence. The SAM thread is GO!
Expand all images
>> No. 5424 ID: e5fb2b
FUCK YES FINALLY
>> No. 5427 ID: 5b9651
File 138945510539.jpg - (14.15KB , 292x160 , fig016.jpg )
5427
Fucking home sick with the flu. Good time to work on this thread I guess. Pardon the typos, my bedroom is a little spinny.

Alright, on the subject of the VT fuze. Lets have a little history:

>The shock of fire breaks a small glass vial filled with liquid electrolyte near the base of the fuse [which is the top part of the shell]. Centrifugal force in the rotating projectile causes the liquid to flow towards the outside of a cylindrical cell through a stack of thin, ring-shaped plates insulated from each other. Contact between the electrolyte and the plates instantly makes it an active wet battery [like your car battery], charging a firing condenser with electricity.

>This electricity activates a radio vacuum tube [a device that generates radio signals, a form of light well below what we can visibly see with our eyes on the electromagnetic spectrum], which sends a continuous radio frequency signal [away from the shell] at the speed of [light, or] 186,000 miles per second. This signal will be reflected back by any target that gives a radio reflection, such as airplanes, ships, or other metal objects, water, or earth.

>The reflected [radio] signal, received by an oscillator [a coil of wire that creates alternating current] interacts with the outgoing signal to create a "ripple pulse." When the projectile approaches within 70 feet of a reflecting object, the ripple pulse (amplified by audio tubes) becomes powerful enough to trigger a thyratron tube [which is a device that when it receives a poweful enough signal, sets off a trigger. ] This sets off a chain of reactions, all accomplished in a fraction of a second. Energy stored in the charged condenser is released, an electrical detonator exploded, an auxiliary ("booster") explosive charge set off, and finally the explosive filling in the projectile detonated [meaning the shell expoded].

>Since the shell is designed to explode on making radio contact with its target, what prevents it from bursting in the muzzle itself as a result of the nearness of the gun or the ship or the earth from which it was fired? The inventors took care of this danger by designing two safety switches, described below, which are not entirely released until the projectile has traveled about 400 yards at the appropriate rate of 2,600 feet per second. Only then is the projectile ready to detonate.


That's the basic mode of OPERATION for the original WW2 proximity fuse that the allies developed.

What are the basic principles of its operation? Thus:

A battery that sends current to an electrical oscillator.

The oscillator has an antenna that transmits a radio signal.

A receiving antenna, isolated from the transmitted, receives any reflected radio waves.

An oscillator connected to the receiving antenna converts any received waves back into current.

An amplifier is tuned to amplify that received current.

A thyratron (electrically operated switch) is tripped when the current from the amplifier reaches a certain level of power.

The thyraton is the switch that closes the detonator circuit on the warhead.

So you have a radio transmitter, a radio receiver with amplifier, a battery, and an electrically OPERATED switch. You select the detonation distance from the target by tuning the amplifier so that it puts out enough juice to close the thyratron switch when receiving an appropriate level of signal from the receiver.

The idea was retard-simple, even in the early days of RADAR. The hard part was building such a device that could fit in artillery shell, not blow up when unwanted, and could survive the shock of being fired out of a gun and that of typical military rough handling.

Some interesting excerpts from the patent history:

>Performance characteristics of radio-controlled proximity fuzes heretofore manufactured could not be predicted with certainty. It was not unusual for a large percentage of fuzes that had been stored for a few months in tropical climates to fail to fire. This failure to fire, or duddage, as well as premature detonations resulted from, among other reasons, both imperfect weatherproofing of and mechanical failure within the fuze. The hermetic sealing of the fuze casing was ineffective to entirely prevent entry of moisture, and under conditions of high humidity the plastic of nose tip of prior art fuzes transmitted sufiicient moisture to cause loss of sensitivity of the oscillator. The wax in which the electronic circuit assemblies were embedded had sufficiently high water absorption, and particularly water transmission through cracks, to cause both failure of the condensers of the amplifier and, in effect, overloading of the oscillator. This embedment material often softened sufiiciently at the temperature encountered within the fuze during the firing of a projectile to cause displacement of the electronic circuit components and their supports with consequent breakage of leads.

>The nose of many fuzes heretofore manufactured was made of insulating material with an antenna in the form of an exterior conical metal cap, or nose piece, molded at the tip of the plastic nose to complete the ogival con tour of a projectile. The designation antenna will be used herein to refer to such a nose cap, although the casing of the projectile is in reality employed as an antenna with the radio frequency energy end-fed to the casing through the nose cap, i.e., currents are induced in the metal casing of the projectile causing it to radiate energy which combines with that from the nose cap to form the resulting pattern of energy in space.[b] It is necessary to make a wire connection to the antenna cap, and in fuzes heretofore manufactured the heat developed in the flight of a projectile due to air friction against the exterior cap was often suflicient to open this connection.

>Briefly, the nose portion of the casing of the fuze of my invention includes a hollowed conical nose tip formed of a suitable plastic, such as polytetrafluoroethylene, having high impact strength and substantially zero water absorption joined to [b]a hollowed, frustrum-shaped, metallic intermediate member by a crimp joint which is impenetrable by moisture. The amplifier and thyratron circuit assemblies of the fuze are completely encased in a metallic housing and potted with a suitable plastic,
such as polyethylene, having substantially zero water absorption and a sufficiently high melting point to prevent softening at the temperature encountered within the fuze during the firing of a projectile. The oscillator is mounted upon this metal housing and potted with a similar plastic in a suitable cavity so that the resulting oscillator-amplifier unit is adapted to fit snugly within the hollowed nose portion of the fuze. The rear end of the oscillator-amplifier unit is sealed across the front end of the sleeve portion of the fuze casing by a crimp joint to provide a completely impervious enclosure within the sleeve for the battery and rear fitting of the fuze. A thin-walled conical metallic antenna cap is fitted tightly over the front of the oscillator-amplifier unit, and when this unit is inserted into the hollowed nose portion of the fuze, softened plastic is fed into the space between the oscillator-amplifier unit and the plastic nose tip to make all the parts of the nose portion substantially integral and thusminimize premature detonations due to microphonics generated by internal vibration. A gasket squeezed between the front edge of the sleeve and the intermediate member when the sleeve and nose portions are solidly screwed together forms an imperviable joint which seals off the nose portion from entry of moisture and offers a second obstruction to the entry of moisture into the sleeve of the fuze.


Wonderful insight on the physical construction of the electronics, isn't it?

Now see pic related. Behold the schematic for the original VT radio proximity fuse, in all its ancient, low-resolution glory!
>> No. 5428 ID: 5b9651
File 138945600655.jpg - (45.21KB , 603x246 , fig022.jpg )
5428
And a schematic diagram of the amplifier circuit.

What was complicated in 1940 would be childs play today. Even my electronically illiterate ass can understand these.

Excerpted from the US Navy Technical Manual "VT Fuzes for Artillery and Spin-Stabilized Rockets":

>A schematic diagram of the amplifier circuit is shown in figure 22. The amplifier is connected, in effect, across the load resistor in the transmitter-receiver circuit. The output of the amplifier is connected to the input of the firing circuit and the wave-suppression circuit. Direct current from the wave-suppression circuit is fed back to the grid of the first amplifier tube through the grid resistor. The amplifier is connected electrically through the fuze body to the projectile body and by leads to the "A" and "B" batteries.

>The main purpose of the amplifier is to take the weak signal developed by the transmitter-receiver in the presence of a target, and to amplify it until it is capable of operating the firing circuit.

You could breadboard an equivalent circuit to this from Radio Shack shit in about fifteen minutes. Or just buy a prebuilt adjustable amplifier and be done with it.
>> No. 5429 ID: 5b9651
File 13894562574.jpg - (24.45KB , 282x304 , fig025.jpg )
5429
Now pic related is a component I find interesting. The "wave suppression circuit" as it was called, was installed in between the amplifier and the thyratron.

>As is pointed out above, the amplitude of a target signal increases rapidly as the projectile approaches. In contrast, other signals, such as those resulting when a projectile passes over ocean waves, have a nearly constant average amplitude. They are sometimes large enough so that the fuze would be operated by them, except for a wave-suppression circuit which decreases the sensitivity of the amplifier in the presence of steady signals. The curve in figure 24 shows how amplifier sensitivity is decreased as strength of signals increases.

So this little circuit blocks any large, unchanging radio return signals to make sure your shit doesn't blow up because of anything except a target. Like, say, the ground underneath it.

Good to know.
>> No. 5432 ID: e5fb2b
Your work needs to be collated and presented in neat booklet forms,A semi-professional 'Do/k/ument' maybe.

Ever considered contacting Paladin Press?
>> No. 5433 ID: d444df
>>5427

It uses the same tube as an oscillator AND heterodyne?

NEAT
>> No. 5435 ID: 0e6ce4
>>5429
>>5429

Sounds like it would go of if transported by aircraft, no?
>> No. 5436 ID: 5b9651
File 138955716148.jpg - (66.40KB , 800x600 , Proxy fuse 1.jpg )
5436
>>5435

No, the signal return would be steady since the reflections would be coming from the interior walls of the aircraft. They would be isolated from the ground.

Dumping some more schematics for various versions of the VT fuse. These are all from the book "Radio proximity fuses for fin-stabilized missiles" which I now REALLY want to find a copy of.
>> No. 5437 ID: 5b9651
File 138955717197.jpg - (69.13KB , 800x399 , Proxy fuse 2.jpg )
5437
>> No. 5438 ID: 5b9651
File 138955717959.jpg - (55.97KB , 800x378 , Proxy fuse 3.jpg )
5438
>> No. 5439 ID: 5b9651
File 138955718944.jpg - (79.59KB , 800x496 , Proxy fuse 4.jpg )
5439
>> No. 5440 ID: 5b9651
File 138955719758.jpg - (85.89KB , 800x509 , Proxy fuze 5.jpg )
5440
>> No. 5463 ID: 5b9651
File 139005820199.png - (8.13KB , 1098x1039 , laserproxy.png )
5463
In addition to the classic radio proximity fuse, there are also some analogues that use more modern technology.

Or none at all, in the case of the US military's Stinger MANPADS. Its designed to actually hit the target and embed itself inside before blowing up. One of only two in the world with enough accuracy to do that, and the reason why the Stinger is so coveted. And expensive.

First up we have the second most common type after radio: The Laser Proximity Fuze.

This one has proven more or less impossible to find pictures of, so forgive me for the absence of a detailed shot.

Basically this one sends out a cone of laser light from the nose of the warhead and has an array of photodetectors looking for the reflected beam. Same principle as the VT fuze:

>Emitter (laser in this case)
>Receiver (photocell)
>Amplifier
>Electrically operated switch

When the photodetectors are picking up enough reflected laser beam, meaning the target is close enough, the amplifier will put out enough power to close the detonation circuit.

>Optical sensing was developed in 1935, and patented in Great Britain in 1936, by a Swedish inventor, probably Edward W. Brandt, using a petoscope. It was first tested as a part of a detonation device for bombs that were to be dropped over bomber aircraft, part of the UK's Air Ministry's "bombs on bombers" concept. It was considered (and later patented by Brandt) for use with anti-aircraft missiles fired from the ground. It used then a toroidal lens, that concentrated all light out of a plane perpendicular to the missile's main axis onto a photo cell. When the cell current changed a certain amount in a certain time interval, the detonation was triggered.

>Some modern air-to-air missiles use lasers. They project narrow beams of laser light perpendicular to the flight of the missile. As the missile cruises towards the target the laser energy simply beams out into space. As the missile passes its target some of the energy strikes the target and is reflected back to the missile where detectors sense it and detonate the warhead.


Other proximity fuze methods have been tried, but these are the only two to remain in any sort of practical use.
>> No. 5471 ID: 5b9651
File 139025044552.jpg - (146.00KB , 800x530 , 800px-Egyptian_SA-2_SAM_JPEG.jpg )
5471
So now we know how the missile senses the target its approaching and detonates the warhead. Though that does beg the logical question of "what exactly are we detonating, anyway?"

Lets talk about the business end of our anti-air boomstickery next.

SAM warheads can generally be divided into one of four categories:

>Fragmentation (flak)
>Enhanced Blast Fragmentation (explodes on impact, has a shaped charge effect in the nose for more piercing damage as well as fragmentation)
>Annular Blast Fragmentation (explodes an expanding ring-shaped cloud of fragments with a much greater potential "hit" area than flak)
>Continuous Rod Penetrator (Launches an expanding, solid ring of metal that shears chunks off the target like a knife)

The first type is the oldest, being a direct derivative from the age of AAA preceding it. The SA-2 Guideline was a good example of a flak-warhead SAM. They just stuck a shit ton of explosives in a fragmenting nose on the missile, blew it up in the general area of the target, and hoped for the best. The typical payload size on the SA-2 was 430lbs of high explosive and fragmentation jacket, with a blast radius of over 800 feet at altitude.

The problem with the plain fragmentation warhead is, unlike flak which you're firing hundreds of rounds into the air, you're not firing hundreds of expensive, sophisticated missiles at one or two targets. So either the missiles need to be huge with huge flak warheads, or you're going to have dismally low kill ratios because you're not getting enough shrapnel in the air to kill the target. One solution to this was to make SAM's smaller but more accurate, but this was only half the problem. The other warhead ideas also rose up because of a desire to make sure that a SAM warhead of any size would have the maximum chance to damage the target even in the event of a miss, and that in the event of a hit, that enough destruction would occur to make sure the target was knocked down for good.
>> No. 5472 ID: 5b9651
File 139025974850.jpg - (151.44KB , 800x486 , 800px-S-25_KYm.jpg )
5472
>Enhanced Blast Fragmentation

The next type to be developed came after the first major advances in accuracy improvement. Specifically in the form of on-board radar (as opposed to the SA-2s ground-directed guidance) and the use of a "terminal maneuver" - a short range, last minute flight correction designed to actually impact the missile against the target instead of merely getting close to it.

The "enhanced" from the name comes from the use of a shaped charge in the nose of the warhead. Unlike a HEAT type shaped charge, this one doesn't compress and launch a liner ahead of the missile. Rather it is a shallow cavity that is filled with additional fragmentation material, that will be shot forward of the missile at the moment of detonation. Essentially a high-explosive powered shotgun blast.

For an aircraft unlucky enough to be struck by such a missile, it was all but a guaranteed kill as the point-blank explosion propelled the nose cavity shrapnel directly, and deeply, into the target. In the event of a near-miss, the normal fragmentation bursting from the sides of the detonating warhead still had a reasonable chance of impact as well. This type had the same chances of a fragmentation kill as the normal fragmentation, but greatly increased lethality in the event of impact. Not a bad deal. Unless you're the enemy pilot.
>> No. 5473 ID: 5b9651
File 139026065049.jpg - (400.86KB , 2668x2298 , 6817296-0-large.jpg )
5473
Annular Blast Fragmentation

This is undoubtedly the most common type in use today, although it is noteworthy that it's used by pretty much everyone other than the United States.

"Annular" means "ring shaped" if anyone was curious.

Essentially what this warhead is, is an "hourglass shaped" core of explosive surrounded by a thick jacket of pre-formed fragmentation material. 3/4" diameter tungsten balls usually. Sometimes this will also incorporate the shallow shaped charge and fragmentation material in the nose from the previous entry as well.

This type of warhead has greater lethality in the event of a near miss. The explosion creates a 360 degree shaped charge effect, propelling the fragmentation material out the sides of the warhead casing in the shape of an ever-expanding ring instead of the more typical spherical cloud. It has the advantage that, when combined with modern guidance systems of some accuracy, the very high speed of the expanding fragmentation cloud and comparatively high density of fragments grants a very, VERY high probability of hit.

The primary weakness of this design is that due to the shape of the explosive there is a limit on the amount of fragmentation material the warhead can carry. In practice, but particularly with the smaller warheads such as found on MANPADS, it is notable that even though some of the fragmentation does indeed strike and penetrate the target, it may not cause enough damage to ensure a kill. Very high probability of hit with a "meh" probability of kill is what characterizes this particular warhead type.

Solving that problem was what drove the United States to develop the most effective SAM warhead of them all: The Continuous Rod Warhead.
>> No. 5493 ID: 5b9651
File 139076594156.jpg - (34.37KB , 317x590 , image1048.jpg )
5493
The Continuous Rod Warhead was a product of old fashioned American ingenuity.

Basically the CRW is a solid piece of steel shrapnel that expands out to cover a large area, without fragmenting. The picture illustrates the concept:

A cylindrical core of explosive is surrounded by a continuous metal rod. The rod is made of many smaller rods, which have their ends welded together such that if spread out in a line they would make a zigzag pattern. This continuous rod is then rolled into a circle and the two main ends welded together. This final zigzagular cirlcle is then compressed down to make a "bundle" into which the explosive core is inserted.

When the explosive is detonated, it pushes the rods out the sides of the warhead, expanding the bundle back into a circle of zig-zagging rods. One that keeps expanding as it moves forward through the air much like the ring of shrapnel from the annular blast fragmentation warhead would. The rods with their metal ends bend under the explosive force, stretching out like a spring.

The end result is a ring of solid metal 20-50 feet in diameter that has enough mass and velocity behind it to literally slice through an airplane fuselage like a knife. Not like the weak penetrating damage of any of the fragmenting styles, the CRW can literally lop off entire wings, engines, or even chop an aircraft completely in two with a lucky hit. It has both high hit probability and extraordinary lethality.

>'Murrika.
>> No. 5494 ID: 5b9651
File 139076605954.jpg - (344.64KB , 1024x683 , Mk%2046%20CR%20warhead%201024%20C.jpg )
5494
>> No. 5495 ID: 5b9651
File 139076618894.jpg - (156.20KB , 634x1024 , CR%20warhead%20exploding%201024%20C.jpg )
5495
>> No. 5496 ID: 5b9651
File 139076633093.jpg - (136.79KB , 428x1024 , Fragmentation%20shell%201024%20C.jpg )
5496
>The development of the radio proximity fuze by Johns Hopkins University Applied Physics Laboratory (APL) during the war improved anti-aircraft accuracy greatly, causing the projectile to detonate when it came close to a target. However, fragmentation warheads had low lethality. During the war many airplanes returned from missions with dozens of holes caused by shrapnel and bullets, with no serious damage. Unless a piece of shrapnel hit a critical component, such as a crewman or an engine, all it did was punch a small hole in the aircraft skin.

>A major problem with fragmentation warheads is that the distance between fragments increases rapidly as they move outward from the explosion. At some distance the space between fragments is larger than the dimensions of the target and the chance that a fragment will hit the target is very small. To have a high probability of causing serious damage the shell must explode very close to the target where blast effects become significant. Further studies at APL in 1944 showed that for shrapnel to penetrate deep into a target it needed a velocity near 10,000 feet per second, much higher than the 3,000 to 4,000 feet per second common with anti-aircraft shells.

>Direct attack on an aircraft's airframe is the most effective method of destroying the target. The airframe is the largest component and cannot be protected. The effect of damaging the airframe may be immediate disintegration of the target. Experiments were conducted using larger fragments that might be sufficient to cut through structural elements in an aircraft. Artillery shells were machined with parallel grooves as shown in the picture.3 When the shells exploded they broke apart into long rods which were much more massive than small fragments, and were capable of cutting through heavier parts of an airplane. When they ripped through the aircraft skin the resulting gash often tore open in the airstream causing great damage. However, these shells produced a relatively small number of rods, and like ordinary fragmentation shells, these rods moved apart rapidly and the chance of hitting a target decreased with range. It was necessary to explode the shell very close to the target. Still, these shells were considerably more lethal than ordinary fragmentation rounds.
>> No. 5497 ID: 5b9651
File 139076671335.jpg - (12.83KB , 302x237 , controd3.jpg )
5497
>In 1952 an idea was proposed to connect many rods together to create a large circle. Each rod would be connected at one end to its neighbor on one side and at the other end to the opposite neighbor. The rods would be folded together into a compact package surrounding a cylindrical explosive charge. When the warhead exploded the rods would be blown outward, but still remain attached at the ends so they would expand into a circle. With no gaps between rods the probability of hitting a target would be 100% within the radius of the circle if the target was in the path of the rods, and the resulting damage would span the aircraft. This configuration was far more effective than a dispersed pattern of rods.

>The MK 46 warhead that was developed for the Unified Talos RIM-8E had two layers of 19.25 inch long 0.25 inch square rods surrounding a hollow cylinder of explosives. The outer diameter of the rod assembly was about 16.8 inches, and the inner diameter of the explosive was 8.7 inches. The warhead was 29.5 inches long and weighed 465 pounds, with 225 pounds of explosives.

The explosive was 75% TNT (cyclotol) and 25% RDX. The molten explosive was cast into a steel shell formed by the inner liner, a forward end plate and an outer shell. A thin silicone sponge liner inside the inner liner prevented the explosive from cracking as it cooled after casting. The 1/16 inch thick outer steel shell not only contained the explosives but it served as a filter, along with a surrounding 0.025 inch thick lead layer, to reduce the severe shock of the explosion on the rod assembly. Around the filter layers were the two layers of rods. Two end rings were welded to the steel filter to hold the rods in place, and a 0.035 inch thick steel stress skin fit over the rods and was welded to the end rings to provide structural rigidity.


>The safing and arming device contained an arming mechanism that was activated by the acceleration of launch. A proximity fuze with antennas arranged around the electronics compartment triggered a detonator charge located at the rear center of the explosive assembly. This detonated a booster charge that spread the explosion to the main explosive charge. The rod assembly was located forward a distance sufficient to allow the explosive shock to form and move evenly through the explosive cylinder to ensure fairly constant acceleration through the length of the rods.


>At the rear of the warhead was the safing and arming assembly composed of the safing and arming device, the detonator and a booster explosive charge. This assembly fit within the rear end of the steel inner liner. A heavy cover plate at the rear carried the warhead when it was mounted into the innerbody assembly. A steel support cone was welded to the rear end ring and mounted to the struts that attached the warhead to the missile airframe.

Bwahahahahaaaa!
>> No. 5508 ID: 5b9651
File 139119869020.jpg - (20.03KB , 250x400 , otragonscale.jpg )
5508
So you now have an explodey warhead and a way of setting it off near the target. Looking good so far. But suddenly, a problem arises! The bastard on the other side is cheating. He's flying his airplane up in the air, maybe thousands of feet above you! Suddenly your plan to mount the warhead to the nose of your Buick and ram it into the enemy is dashed upon the jagged rocks of military reality!

The olden minds grappled with this same problem. After a few years of experimenting, they gave up on the idea of making your Buick fly and settled on a few different options for propulsion systems for the early generation SAMs:

>Liquid fuelled rocket motors.
>Solid fuelled rocket motors.
>Ramjet engines with rocket boosters (limited use).

Its time to segue into the great old American field of Rocket Surgery!
>> No. 5516 ID: 5b9651
File 13913622786.jpg - (52.01KB , 597x800 , a-4-combustion-chamber-production-sm.jpg )
5516
Liquid Propellant Rockets:

These were actually the first type to be developed even though they seem, at a glance, to be much more complicated than solid fuel. For the solid fuel rockets there was tremendous difficulty in the early years in the aspects of chemistry - finding a fuel that would burn at the enormous pressures inside a rocket engine but not have risk of exploding, and physical engineering of the shape of the fuel to get a reliable and consistent burn characteristic. While liquid fuelled assemblies were far more physically complex, all the parts that went into them were well understood at the time.

We're going to go back in time and look at the first and move famous large-scale liquid rocket for our initial study example: The legendary V2. Then we're going to fastforward to 1970s Africa and look at a little rocket that did liquid-fuelled on the simple and cheap.
>> No. 5521 ID: 5b9651
File 139163597596.jpg - (255.72KB , 1475x1080 , combustion-chamber-cut-away-med.jpg )
5521
The Mighty V2.

We've all seen the WW2 documentary footage of the V2 rockets taking off and impacting targets in faraway London. Or at least the vicinity thereof. Sometimes. She wasn't the most accurate bird to ever fly.

But did you ever wonder what Werner Von Braun discovered that made him the world's foremost authority on rocket technology? The design secrets of the V2s engine?

Well here we go.

In order for a liquid fuelled rocket to work, you need a few specific things.

>A rocket fuel and oxidizer (Alcohol and liquid oxygen in the V2's case)
>A method of moving large quantities of the above at high pressure into the combustion chamber. (turbopump)
>A means of injecting the fuel and oxidizer into the chamber in a manner that facilitates an optimum mixture for combustion (injectors).
>A way of breaking up the shockwaves inside the combustion chamber so they don't interfere and cause flameouts or rupturing. (flame cups)
>A way to cool the combustion chamber from the tremendous heat of the motor running (film jacket).
>An exhaust nozzle that can compress and release the combustion gasses to ensure the maximum level of thrust is attained per unit of fuel/oxidizer mass (the rocket bell).
>> No. 5522 ID: 7e5f23
What happened to your driving thread and which board was it originally on? I didn't save it....
>> No. 5524 ID: 5b9651
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5524
Relevant history:

>A particular point of contention involved this engine's arrangements for injecting propellants into its combustion chamber. Early in the German rocket program, Walter Riedel, Von Braun's chief engine designer, had built a rocket motor with 3300 pounds of thrust with a cup-shaped injector at the top of the thrust chamber. For the V-2, a new chief of engine design, Walter Thiel, grouped 18 such cups to yield its 56,000 pounds. Unfortunately, this arrangement did not lend itself to a simple design wherein a single liquid-oxygen line [18] could be supplied to the cups. Instead, his "18-pot engine" required a separate oxygen line for each individual cup.53

>Thiel had pursued a simpler approach by constructing an injector plate, resembling a showerhead, pierced with numerous holes to permit the rapid inflow and mixing of the rocket propellants. By the end of World War II, Thiel's associates had succeedfully tested a version of the V-2 engine that incorporated this feature though it never reached production. 54 Bollay's rocket researchers, still working within the company parking lot, were upping their engines' thrust to 3000 pounds, and were using them to test various types of injector plates. 55 The best injector designs would be incorporated into the Phase III engine, bringing a welcome simplification and introducing an important feature that could carry over to larger engines with greater thrust. In September 1947, preliminary design of Phase III began, aiming at the thrust of the V-2 engine but with a weight reduction of 15 percent.

So basically the V2 used these hollow steel cups as small mixing stations for the fuel and oxidizer inside the combustion chamber. Eighteen of them for full thrust. As it turns out though, that is actually a very difficult way of doing things. Modern liquid fuelled missiles use an "injector plate." This is a thick disc of heat-resistant steel with orifice holes drilled in it and feed lines running to the holes. The holes are angled together so that the jets of high pressure fuel and oxidizer will collide in any of several various patterns, mixing thoroughly as they flood into the combustion camber.

To get an idea of what an injector plate looks like, here is the F-1 injector plate from the Saturn V's main booster.

That plate is like 20 feet across, mind you.

The rounded dividers you see on the face are the shock dampening baffles that were added to make the combustion more controllable. hey serve the same purpose as the V2's cups, but were much cheaper and easier to engineer.
>> No. 5558 ID: 5b9651
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5558
Some more details concerning injector plates:

The manifolds that deliver fuel and oxidizer to the orifices aren't simple hoses or tubes. You have to remember that the fuel components are being forced, by pressure or turbopump, at very high pressures and velocities.

To continue using the Saturn Vs F1 as an example, here is how the manifolds were set up:

The injector plate was backed by another thick steel plate (the "Feed Plate") which had deep holes drilled into it in a radial pattern from the outer edge to near the center. These holes wee the feed inputs for the fuel and oxidizer. The surface of the plate had holes drilled into it on one side that were machined to match up perfectly with the orifice holes in the injector plate that it was sandwiched on top of, and also in line with the respective fuel/oxidizer inlet holes coming in from the edge.

Fuel and oxidizer were pumped from the tanks into the outside edge of the feed plate, then travelled through the radial holes to near the center of the plate, flowed downward through the feed holes machined in the face of the plate that were connected to these feed holes, where it then flowed into the respective "jet" holes in the top of the injector plate and was forced into the combustion chamber by the injector plate jets.

This is a bit of a simplified description, as the actual F1 used a 2-part manifold. Only fuel came in from the radial edge and the oxidizer was delivered via holes drilled straight down through the plate, but it serves better to illustrate what is happening.
>> No. 5596 ID: 5b9651
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5596
How, as far as getting the fuel to the injector plates in a timely manner.

To give you an idea on gas mileage, the Satun V rocket got about .7 feet per gallon. This implies you need a shit ton of fuel for sustained burning - but also that you have to have a way of getting the fuel and oxidizer into the combustion chamber fast enough. Doing that requires that the injector flow be under very high pressure, and there's two main ways this is accomplished:

>Turbopumps
>Pressurized Inert Gas.

A turbopump is an interesting hybrid of an impeller pump and a jet engine. On the V2 rocket, the tubopump functioned thusly:

>The V-2 engine was both the world's first large liquid-propellant rocket engine and the first large rocket engine to use a turbopump. The engine and its turbopump were developed by the German army rocket group under Wernher von Braun. The turbopump was manufactured by WUMAG, Abteilung Maschinenbau.

>The turbopump drew propellants from the missile's tanks and injected them under pressure into the combustion chamber. It moved nearly 9,000 kilograms (20,000 pounds) of water alcohol and liquid oxygen during the 60-second burning time. Exhaust gases from a steam generator, which turned hydrogen peroxide into superheated steam and oxygen, drove the turbine wheels in the center of the pump. The turbine wheels in turn powered the pump impellers for the two propellants.

So an autocatalyzing reaction of Hydrogen Peroxide generated a powerful steam jet (same principle that the rocket engine of the H2O2 powered Bell rocket belt used, btw) that was directed into a small turbine. This turbine drove a shaft connected to the impeller pumps for the fuel and oxidizer. While fairly simple in theory, the actual machining and construction of the turbopumps was a major problem with V2 development. Considering the complex fluid dynamics going on inside the impellers, the pump system was probably the most complex part of the V2s design.
>> No. 5762 ID: 5b9651
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5762
Coming back to this briefly because I'm having a shitty morning.

Ready for some math?

I was going to post excerpts from the book "How to Design, Build, and Test Small-Scale Liquid Fuelled Rocket Engines" by the Rocket Laboratory from China Lake.

Then I realized "aint nobody got time for dat."

So here's the whole fucking book. Enjoy!

http://www.operatorchan.org/z/src/rocket.zip


Now a few things to touch on. In the case of the injector plate nozzles, they can be configured to spray their fuel and oxidizer streams in any number of various configurations. The two big ones being "like on like", meaning 2 oxidizer streams colliding together before mixing with an adjacent fuel stream. Or "like on other", meaning an oxidizer stream colliding directly with a fuel stream 1:1. This will be important later.

Here are some highlights from the book.

Popular combinations of fuels and oxidizers:

Propellant Combination Oxidizer/Fuel Combustion Pressure, psi Mixture Ratio Flame Temp (degF) Isp, sec
Liquid Oxygen & gasoline 300 2.5 5470 242
Gaseous Oxygen & gasoline 300 2.5 5742 261
Gaseous Oxygen & gasoline 500 2.5 5862 279
Liquid Oxygen & JP-4 (jet fuel) 500 2.2 5880 255
Liquid Oxygen & methyl alcohol 300 1.25 5180 238
Gaseous Oxygen & methyl alcohol 300 1.2 5220 248
Liquid Oxygen & hydrogen 500 3.5 4500 363
Red fuming nitric acid & JP-4 500 4.1 5150 238

Bold is the easiest for our purposes, not messing with cryogenic oxidizer.

>Combustion Chamber

A parameter describing the chamber volume required for complete combustion is the characteristic chamber length, L*, which is given by

L* = Vc/At


where Vc is the chamber volume (including the converging section of the nozzle), in cubic inches, and At is the nozzle throat area (in2). For gaseous oxygen/hydrocarbon fuels, an L* of 50 to 100 inches is appropriate. L* is really a substitute for determining the chamber residence time of the reacting propellants.

To reduce losses due to flow velocity of gases within the chamber, the combustion chamber cross sectional area should be at least three times the nozzle throat area. This ratio is known as "contraction ratio".

The combustion chamber cross-sectional area is given by

Ac = (pi)Dc^2/4


The chamber volume is given by

Vc = AcLc + convergent volume


For small combustion chambers the convergent volume is about 1/10 the volume of the cylinrical portion of the chamber, so that

Vc = 1.1 (AcLc)


The chamber diameter for small combustion chambers (thrust level less than 75 lbs) should be three to five times the nozzle throat diameter so the injector will have usable face area.

>The math in the book actually isnt that complicated, though I can imagine the nightmare that it was to experimentally derive all those formulae.
>> No. 5763 ID: 5b9651
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5763
That book will give you good info to chew on for a while.

Just for practice, try scaling it up to make a rocket with 100lbs of thrust and then do the math to figure out the dimensions for the nozzle and combustion chamber.

>Anyhoo, continuing from where I left off 2 posts ago.

The next method of fuel and oxidizer delivery is also the simplest and cheapest - pressurizing the fuel and oxy tanks directly using an inert gas.

Systems like this are very robust and actually quite simple to manufacture, but theyre also less used because rocket systems always have a propriety on available weight. And in order to pressurize the tanks to a high enough level to have adequate flow to the combustion chamber, the fuel and oxy tanks have to have thicker walls and sturdy fixtures, which results in a significant weight increase.

A few examples of pressurized-tank rockets are the Bell X1 rocket plane (nitrogen), the Apollo Lunar Module main engine and thrusters (helium), and the second stage of the Delta II rocket (nitrogen).

A pressure fed engine can carry less usable weight and has poorer performance than other engine types at low altitude. But their design and construction is so ridiculously simple than they are the preferred choice for almost any amateur designer.

>The pressure-fed engine is a class of rocket engine designs. A separate gas supply, usually helium, pressurizes the propellant tanks to force fuel and oxidizer to the combustion chamber. To maintain adequate flow, the tank pressures must exceed the combustion chamber pressure.

>Pressure fed engines have simple plumbing and lack complex and often unreliable turbopumps. A typical startup procedure begins with opening a valve, often a one-shot pyrotechnic device, to allow the pressurizing gas to flow through check valves into the propellant tanks. Then the propellant valves in the engine itself are opened. If the fuel and oxidizer are hypergolic, they burn on contact; non-hypergolic fuels require an igniter. Multiple burns can be conducted by merely opening and closing the propellant valves as needed. They can be operated electrically, or by gas pressure controlled by smaller electrically operated valves.

>Care must be taken, especially during long burns, to avoid excessive cooling of the pressurizing gas due to adiabatic expansion. Cold helium won't liquify, but it could freeze a propellant, decrease tank pressures, or damage components not designed for low temperatures. The Apollo Lunar Module Descent Propulsion System was unusual in storing its helium in a supercritical but very cold state. It was warmed as it was withdrawn through a heat exchanger from the ambient temperature fuel.[1]
>> No. 5801 ID: 96d59a
Gona be on so many lovely lists thanks to this thread. :)
Btw check out "Ignition! an informal history of liquid rocket propellants" to learn about various challenges when dealing with liquid propellants.
Solid fuel is decades easier for the amateur/hobbyist.
There is also a reason why MANPADS and air-to-air missiles use solidfuel.

I enjoyed the info on older radar fuses fascinating stuff.
I'll have to experiment with something like that some lovely day. Do note that old russian (still perfectly ok) tubes related to the short lifespan radar munition tubes are very available on ebay. But even eighties semiconductors are significantly more robust.
>> No. 5807 ID: 5b9651
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5807
>>5801

>Solid fuel is decades easier for the amateur/hobbyist.
There is also a reason why MANPADS and air-to-air missiles use solidfuel.

GOOD solid fuels are not available to the amateur. Military grade solid fuels use things like RDX explosive in special combustible binders. Even the oldest were still specially extruded combinations of nitroglycerine and nitrocellulose. Even the "large model rocket" hobbyists use pre-purchased ammonium perchlorate composite fuels.

The best amateur stuff I've ever found is probably Nakka Rocketry's potassium nitrate/epoxy composites and they're still very expensive for the amount of thrust they produce.
>> No. 5809 ID: f59923
Think you can make something out of gunpowder?
>> No. 5828 ID: 5b5c75
>>5807
>GOOD solid fuels are not available to the amateur. Military grade solid fuels use things like RDX explosive in special combustible binders

And that's where your other thread comes in, isn't it? I think of "amateur" rocketry is to advance, the propellants used have to as well.
>> No. 5840 ID: 96d59a
>5807
Care to link to references about RDX or NC+NG composite rocket propellant used in military munitions as the propellant?
Ammonium perchlorate composites are used in modern munitions, including air-to-air missiles.
Do include more info. This stuff is interesting.
I'll have to take a better look at those radar triggers. Sounds surprisingly simple.
>> No. 5852 ID: 5b9651
>>5840

I've lost the original links in my mountain of sources, but here's some stuff from some text files I saved.

>Higher-performance solid rocket propellants are used in large strategic missiles (as opposed to commercial launch vehicles). HMX, C4H8N4(NO2)4, a nitramine with greater energy than ammonium perchlorate, is the main ingredient in NEPE-75 propellant used in the Trident II D-5 Fleet Ballistic Missile.[12] It is because of explosive hazard that the higher energy military solid propellants are not used in commercial launch vehicles except when the LV is an adapted ballistic missile already containing HMX propellant (example: Minotaur IV and V based on retired Peacekeeper ICBMs).[13] The Naval Air Weapons Station at China Lake, CA developed a new compound, C6H6N6(NO2)6, called simply CL-20 (China Lake compound #20). Compared to HMX, CL-20 has 14% more energy per mass, 20% more energy per volume, and a higher oxygen-to-fuel ratio.[14] One of the motivations for development of these very high energy density military solid propellants is to achieve mid-course exo-atmospheric ABM capability from missiles small enough to fit in existing ship-based below-deck vertical launch tubes and air-mobile truck-mounted launch tubes. CL-20 propellant compliant with Congress' 2004 insensitive munitions (IM) law has been demonstrated and may, as its cost comes down, be suitable for use in commercial launch vehicles, with a very significant increase in performance compared with the currently favored APCP solid propellants.

Just google "high energy composite propellant". That's what my stuff is all filed under. There was some fancy ATGM that has RDX in the motor, too. Javelin maybe.
>> No. 5856 ID: 5b9651
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5856
So. We now have an idea of how we get our missile to detonate near its target, what kind of warhead it should use and how selfsame is constructed, and how to propel it all the way up there.

But how the fuck do you:

>A: Know where the targets even ARE?
>B: Steer the missile up there TO it?

This is the most technically complex part of the whole shebang, and the part that I've spent the most time researching. I'm not an electronics guy by nature, and most of this stuff started at a level well over my head.

We're going to start with the basic concepts.

>How do you spot a target aircraft?

This is a problem almost as old as flying itself, and one that has gotten much harder as aircraft technology has advanced. As airspeeds get faster and flight ceilings get higher, detection technology has to keep up. Else by the time you've spotted him and reacted, he's already bombed/droned you and flown off in some other merry direction.

Aircraft detection falls under a few categories:

>Visual detection.
>Enhanced visual detection.
>Audio detection.
>RADAR detection.
>Passive radio detection.

Then once you've found the bastard, sitting up there at ten miles and twenty thousand feet, taking bong hits around his oxygen mask and jerking off to the cover of The Weekly Hitler, you have to somehow manage to steer your missile up there to get to him. Systems for this also fall into a handful of categories:

>Manual Guidance
>Passive Homing
>Active Homing
>Radio Beam Riding
>Laser Beam Riding
>RADAR Ground-Directed

Furthermore, there are three "algorithms" that are employed in the guidance system, basically to make sure your missile is "leading" the target correctly.

>Line-of-Sight
>Proportional Navigation
>Dog Homing

We'll start breaking all these down next.
>> No. 6708 ID: 5b9651
Bump. This thread isn't done yet, just been preoccupied.
>> No. 7084 ID: bdc075
>>6708
update? :(

I need more of these for bed time readings.
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