AHC: propose a technical design of most primitive yet effective SAM

Plausible construction of crudest (with roughly interwar tech) possible homing heads?


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trurle

Banned
A review of the various European groups and research is conducted and hydrogen peroxide, or more precisely high-test peroxide (HTP), catches their eye. Engines like de Havilland's Sprite were how several companies entered the field in our timeline IIRC. Development leads to the idea of adding kerosene to improve thrust and using silver mesh as a catalyst.
Hydrogen peroxide had generally marginal performance and handling problems. Its main advantage was actually high availability to developer, due to widespread civilian applications.

black power 70-90 sec
rocket candy 115-130 sec (when invented?)
H2O2 117-220 sec (largest number is for H2O2/kerosene deHavilland Sprite of 1951)
ethylene oxide 160-190 sec
nitromethane 190-230 sec
nitrocellulose 160-200 sec
asphalt/KClO4 ~180sec (developed in 1936-1942?)
Unrotated Projectiles and Rocket Projectile 3-inch (RP-3) rockets since IIRC that was the largest diameter solid they could produce at the time.
Mental inertia to blame i suspect. Soviets did have interwar an industrial capability for 1-inch solids only, yet they fielded 82mm and 132mm rocket motors, by bundling together 7 or 19 propellant rods in single case. Igniter was fitted to central rod only. Not good design for sustainer motor i suspect (burn speed, torques and center of mass are not well controlled), but it was good enough for booster.

Lubbock was off doing his own thing with Lizzie plus kerosene and oxygen was a very interesting field of research, if you approached Sedgfield and Bedford who were running Brakemine
Interesting. Brakemine was beam rider with 1944 tech level, fitting 2 control channels roughly in 25cm diameter case. It sets a good reference for understanding technology limitations.

Automatic Command to Line-Of-Sight (ACLOS) guidance is potentially even easier - stick beacon on the SAM so that it can be tracked accurately, the target is tracked by the radar, data on their locations and directions of travel is passed to a simple computer to work out the path needed for the missile to follow, and those instructions are transmitted to it.
Good idea. Keeping projectile simple is good for crude tech. The beacon on SAM can also double as radar proximity fuse, therefore you would not need an additional command channel for detonation. I would elaborate what oscillating fin/vane design (forgot OTL model name using it) will need only one radio control channel for spinning missile, alternating between pitch and yaw commands. You need to have a gyro in missile to make proper de-multiplexing of control inputs, but i remember it was initially lighter and more reliable tech compared to radio receivers. Or (just my wild idea) - make not-spinning missile with (airflow-spun) spinning antenna. The ground station will detect polarization of beacon and send pitch or yaw commands alternatively, while beacon antenna slip ring will control on missile which channel to control - pitch or yaw.
 
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Deleted member 1487

Why not passive homing? RAF and IIRC USAAF bomber formations put out vast amounts of radiation to jam German radars and communications. Launch a missile in the general direction of the bomber formation and then after a delay have it home in on the radio signals which with a big enough warhead (i.e. Wasserfall size) will take down several bombers nearby.
 

trurle

Banned
Why not passive homing? RAF and IIRC USAAF bomber formations put out vast amounts of radiation to jam German radars and communications. Launch a missile in the general direction of the bomber formation and then after a delay have it home in on the radio signals which with a big enough warhead (i.e. Wasserfall size) will take down several bombers nearby.
I am afraid the directivity of missile mounted antennas will be very bad, resulting in large direction errors. Also, in general you need very high speed and manoeuvrability of missile to successfully attack in this manner from any direction other than directly from front or rear. Finally, the enemy bombers would soon adapt to use frequencies not suitable for missile receiver, because they in general have less limitations on frequency selection.
 

Deleted member 1487

I am afraid the directivity of missile mounted antennas will be very bad, resulting in large direction errors. Also, in general you need very high speed and manoeuvrability of missile to successfully attack in this manner from any direction other than directly from front or rear. Finally, the enemy bombers would soon adapt to use frequencies not suitable for missile receiver, because they in general have less limitations on frequency selection.
They did mass jamming of frequencies, so it's not like they could simply switch frequencies. Also you don't need a special antennae:
http://www.luft46.com/missile/bv246.html
And you don't need something particularly special in the manueverability department for bomber boxes that were miles wide and had predictable paths.
 
On TV part, the problems with the image quality of aircraft-borne TV transmitter were such what of 20 B-17 drones of Project Aphrodite in 1944, only 1 has hit assigned ground target, the rest either losing control, been shot down or missing targets. I think the TV technology was too immature.
It was, but seems to have been far more successful in the Pacific with the now near forgotten Interstate TDR drones in 1944
Interstate_TDR-1.jpg

for an example of 'State of the Art'
 
Candidate sketch

trurle

Banned
Here the one possible design inspired by suggestions by Simon:
sketch_hypothetical_primitive_SAM_1.jpg
The approximate characteristics:
Body diameter: 0.15-0.18m
Body length: 1-2m
Weight: 40-100kg
Sustained speed: 900 km/h at sea level,
Operating envelope: 12 km altitude at range 8km
Flight time until engine burnout: 30 sec
Guidance: automatic or manual command at line-of-sight, input data are feed from radar and 3 radio direction finder units.

This would be initially sold to Army as division-level weapon shooting down enemy high-altitude recon planes. Would be more responsive than having interceptor squadrons.

Also, will be simplified (no rotating band,ACLOC receiver antennas, and no boost motors) wire-controlled variant with wire bobbin in place of booster motors. It will have maximal control range of ~2km, to be used against land targets and low-flying aircraft with visual instead of radar direction.
 
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trurle

Banned
It was, but seems to have been far more successful in the Pacific with the now near forgotten Interstate TDR drones in 1944
for an example of 'State of the Art'
Thanks, this is an interesting development. 62% hit ratio against naval targets is not bad even by modern standards. The similarly controlled (therefore oversized) SAM design would be likely too expensive for economical SAM role though, except if used for protection of highest-value areas.
 
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my view what could be incorporated into their existing flak operations (and also what did they have ability to construct) so favor the Enzian of simple wood material and employing the flak 88 gun carriage http://www.warbirdsresourcegroup.org/LRG/enzian.html

used with (what we are told not to mention) sub-caliber tracer rounds, which have dual purpose of illumination, and photodiode(?) since they had some experience employing that with ME-163.
 

trurle

Banned
my view what could be incorporated into their existing flak operations (and also what did they have ability to construct) so favor the Enzian of simple wood material and employing the flak 88 gun carriage http://www.warbirdsresourcegroup.org/LRG/enzian.html

used with (what we are told not to mention) sub-caliber tracer rounds, which have dual purpose of illumination, and photodiode(?) since they had some experience employing that with ME-163.
Seems the most critical tech for SAM was radio control.
German technology of 1944 allowed roughly 130 kg per control channel, while British technology while been far less operational (Brakemine and Stooge designs) was closer to 50 kg per channel (may be due revolutionary EF50 vacuum tubes available in England?)
Or more likely British had slightly better amplidynes (equivalent to modern power amplifiers) or synchro/selsyns.
https://en.wikipedia.org/wiki/Amplidyne
https://en.wikipedia.org/wiki/Synchro

Does anybody know about servo-mechanisms state-of-art in US or Japan during WWII?
I remember Japanese had a problem supplying enough of servo-motors even for their 25mm AA installations though.
 
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Too slow to be considered useful in any sense of the word. This was a missile that could be intercepted relatively easily by fighters of the day.

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took 8 times as many sortie to bring down V-I since they could manage 400mph @ 1km altitude, which was unheard of in its day. The next gen model was ready year after the first with 495mph @ 1km altitude. Don't even think jets could manage that @ 1km altitude.

best option for WW-II tech would be ASM & hit shipping.
 
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Next best option for LW, was mounting several wire guided X-4 AA missiles with the acoustic fuse on a 2-seater fighter plane or 'Bomber Zerstroer' : either that or pair of longer range HS-117 AAM [similar guidance?].
 
Conclusion

trurle

Banned
Next best option for LW, was mounting several wire guided X-4 AA missiles with the acoustic fuse on a 2-seater fighter plane or 'Bomber Zerstroer' : either that or pair of longer range HS-117 AAM [similar guidance?].
Ruhrstahl X-4 has an interesting (although far from universal) acoustic proximity fuse. Other features and parameters seems to be nearly identical to my proposal of MCLOS (simplified) version of initial SAM.

Therefore, conclusion:
Initial crudest-tech yet effective SAM would be a 2-stage solid-fueled, ground-launched or ship-launched equivalent of Ruhrstahl X-4.
It feature wire-guide, time-domain multiplexed pitch&yaw MCLOS and acoustic proximity detonator, with effective range of 3km and hit rate of 10%.

Roughly in installation weight and effective range SAM is equivalent to the contemporary 20-25mm automatic AA gun.
The 25mm AA gun (Hotchkiss/Type96) would spend in average 300kg of ammunition (1500 shells) and 12 minutes to shoot down one aircraft.
Proposed SAM design in 1940-1941 will need initially 600kg of ammunition and 5 minutes per aircraft. (assuming 10% hit ratio and 2 RPM launch rate).

Initial SAM performance is barely enough to justify deployment, but SAM would have a better growth potential in range and hit ratio (evolving ultimately to automatically radar-controlled rockets with wireless control links, capable to bring down strategic bombers in single shot), making gradually difference as war is unfolding.
 
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