US 90 mm cannon

[Przezdzieblo]

bojan, there must be some mistake, M431 could not been delivered to Yugoslavia in 1956. In 1958 it was still in development phase as T300. I guess E59 variant was standarized as M431 not earlier than in 1960s.

 

The first 90 mm HEAT for US tank guns was T108, started in 1950. Orginally penetration of 5 inches armour at 60 degrees obliquity was required - no idea if ever . E40 variant was standarized as M348 but it proved to be inaccurate because of design and quality issues. Modified M348A1 (T108E46, circa 1957) was not very better. T300 was started in 1953, mainly because of problems with T108.

 

 

Old Tanker, maybe do you remember if those "special" HEAT-T rounds were spike-ended like one below?

[AdmiralB]

Does that diagram indicate a slip ring? Fin-stabilized, so I reckon there's some sort of spin control?

[Przezdzieblo]

M431 got nylon slip band. Do not know details about methods of spin control in case of T108 series, but guess might be similar.

[bojan]

bojan, there must be some mistake, M431 could not been delivered to Yugoslavia in 1956. In 1958 it was still in development phase as T300. I guess E59 variant was standarized as M431 not earlier than in 1960s.

 

I will double check it but I am pretty sure that first batch of 3200 (thats onlz 10/tank!), was delivered with some other armament soon after Soviets invasion of Hungary. Only doubt I have is that they were designated T431 in our documents... Which I assume (yeah I know ) to be M431 as there was no 90mm T431 HEAT. Could it be those were original T300 and designation somehow got f***ed up (would not be 1st time, one official document has "49mm Bofors"...?

BTW, HEAT ammo used in tests vs T-54 was definitely M431, so it was available in 1962 when those were done.

 

The first 90 mm HEAT for US tank guns was T108, started in 1950. Orginally penetration of 5 inches armour at 60 degrees obliquity was required - no idea if ever

5" @ 60deg is close to my tabellar 110mm @ 60deg for M348.

[Guest Jason L]

bojan, there must be some mistake, M431 could not been delivered to Yugoslavia in 1956. In 1958 it was still in development phase as T300. I guess E59 variant was standarized as M431 not earlier than in 1960s.

 

The first 90 mm HEAT for US tank guns was T108, started in 1950. Orginally penetration of 5 inches armour at 60 degrees obliquity was required - no idea if ever . E40 variant was standarized as M348 but it proved to be inaccurate because of design and quality issues. Modified M348A1 (T108E46, circa 1957) was not very better. T300 was started in 1953, mainly because of problems with T108.

 

 

Old Tanker, maybe do you remember if those "special" HEAT-T rounds were spike-ended like one below?

 

Gaah.....why does it have a square cavity at the cone apex? Square apex bad for optimal penetration.

Edited January 8, 2013 by Jason L

[Przezdzieblo]

Since when?

 

I mean, since when "we" know that square apex bad for optimal penetration? Guess it was not the "default" knowledge in shaped charge research history.

Edited January 8, 2013 by Przezdzieblo

[bojan]

Jason, IIRC it is not really square bottom is semi-hemisferical.

[Guest Jason L]

Since when?

 

I mean, since when "we" know that square apex bad for optimal penetration? Guess it was not the "default" knowledge in shaped charge research history.

 

That's a good question. There is a mix of flat apex and smooth, rounded apex weaponized shaped charge devices throughout the 40ies. However, I presume it was known fairly early, like in the mid-late 40ies, before the aerojet days in the US, that rounded bottom charges offered better jet coherency and consistency. That sort of square section at the apex is typically associated with interrupted shaped charge jet designs.

 

Jason, IIRC it is not really square bottom is semi-hemisferical.

 

Yeah, but is it smooth like a conventional conical liner or does it have a conical divot? Maybe they wanted the divot to throw a massive, somewhat incoherent jet tip ahead of the rest of the jet to bust through the fuse probe?

Edited January 9, 2013 by Jason L

[BabyOlifant]

OK, I gotta ask: What's the reasoning behind the "spike ended" HEAT ammo in the style of the above cartridge? It is clearly not designed with favorable aerodynamic properties in mind.

[Guest Jason L]

OK, I gotta ask: What's the reasoning behind the "spike ended" HEAT ammo in the style of the above cartridge? It is clearly not designed with favorable aerodynamic properties in mind.

 

It's a stand-off probe that contains the piezoelectric impact sensor that triggers the base fuse. You can make it more aero with an thin faring but not necessary.

[Przezdzieblo]

Spike-nose is not only for stand-off and anti-ricochet purposes, but also it is a method of stabilization of quite fast, fin stabilized projectiles. Presence of spike helps to reduce length of tail with fins - and vulnerability of tail, very prone to damages during firing and flight, were one of the reasons of failures in 90 mm HEAT-T T108 programme.

[bojan]

Spike-nose is not only for stand-off and anti-ricochet purposes...

 

Ironically spike nosed M431 worked up the 60deg, convencional nose BK-5M worked up the 65-70deg... More issue of fuse then nose shape.

 

...and vulnerability of tail, very prone to damages during firing and flight, were one of the reasons of failures in 90 mm HEAT-T T108 programme...

 

IIRC main culprit was muzzle break, hence the change in muzzle break shape at one moment. M438 was also not useable in 90mm M3A1 guns in M36 TD, even our local M74 HEAT required removal of it's muzzle breaks when it was introduced.

 

For comparing, 100mm M69, BK-5M (BK-5 is generally same but liner is steel and it lacks wave shaper) and 90mm M74:

 

 

BTW, all 3 have two shaped charges in warhead, spitback fuse is a miniature (less then 10mm diameter) semi-hemispherical shaped charge.

Edited January 10, 2013 by bojan

[BabyOlifant]

But there's no reason that couldn't be covered with an aeroshell, which would help ballistic coefficient and hit probability significantly, I should think.

[Guest Jason L]

But there's no reason that couldn't be covered with an aeroshell, which would help ballistic coefficient and hit probability significantly, I should think.

 

Following what Przezdzieblo said, it's quite possible that the shoulder creates a desirable effect on the center of pressure from the perspective of quickly stabilizing precession of the round on leaving the muzzle. Never really thought about it before, but it makes sense.

 

Also, IIRC, the edge of the ring is an alternative sensor element as well, something not as successful if you put a fairing.

 

Of course you can make a round with a better aerodynamic front end. Multipurpose rounds with fusing/sensors more sophisticated than simple contact tend to encase them in a nose cone ahead of the liner and explosive. Note the changes in the A1 over the base M830.

[shep854]

The 'spike' looks awkward, but at supersonic speeds, won't the shock wave produced by the spike act as its own fairing?

[Guest Jason L]

The 'spike' looks awkward, but at supersonic speeds, won't the shock wave produced by the spike act as its own fairing?

 

Yes, in principle the bow shock off the spike will reduce the intensity of the shock/BL growth around the shoulder.

[shep854]

I believe at least one ejection seat used a similar principle to protect the user in the event of a supersonic ejection.

For a little further information, here's the Wiki:

http://en.wikipedia.org/wiki/Drag-resistant_aerospike

"A drag-reducing aerospike is a device used to reduce the forebody pressure drag of blunt bodies at supersonic speeds. The aerospike creates a detached shock ahead of the body. Between the shock and the forebody a zone of recirculating flow occurs which acts like a more streamlined forebody profile, reducing the drag."

[Guest Jason L]

I believe at least one ejection seat used a similar principle to protect the user in the event of a supersonic ejection.

For a little further information, here's the Wiki:

http://en.wikipedia....stant_aerospike

"A drag-reducing aerospike is a device used to reduce the forebody pressure drag of blunt bodies at supersonic speeds. The aerospike creates a detached shock ahead of the body. Between the shock and the forebody a zone of recirculating flow occurs which acts like a more streamlined forebody profile, reducing the drag."

 

The principle was also investigated to extend the use of thicker wings at higher speeds.

[DKTanker]

But there's no reason that couldn't be covered with an aeroshell, which would help ballistic coefficient and hit probability significantly, I should think.

My only experience is with 105mm and 120mm HEAT, both are very accurate. Something to keep in mind, as mentioned, the spike acts to bend the airflow back toward the small fins for stabilization and accuracy. If there is a ballistic cap the air will tend to spread away from the round neccessitating longer fins such as the folding types depicted in the drawings. Those longer fins present a much larger surface area thus degrading velocity. Though the aerodynamic round may retain more velocity, the tradeoff is a more complicated design. Edited January 9, 2013 by DKTanker

[BabyOlifant]

Huh. So it keeps the round shorter? Weird.

[Hakka]

I just read the Tankograd blog's article on the T-62 and they talked quite a lot about "shape stabilization". Apparently, it's about the pressure building up at the shoulders of the shell rather than the shockwave reducing the drag. A shell with a probe actually has 20% more drag than the usual sort.

 

https://thesovietarmourblog.blogspot.my/2015/12/t-62.html (skip to section on 3BK-15)

Edited January 17, 2017 by Hakka

[Ken Estes]

As far as the OP is concerned, the USMC briefed its tank battalions in mid-1970 that the 90mm was no longer effective vs. Russian tank armor, based upon the army's research of the 67 War. As I recall the study was termed MEXPO, but it was classified and I was not privy to the acronym nor its specifics. The faces fell in the room, especially those of the more grizzled SNCOs who could not believe we were going to give up the beloved Ninety.

Edited January 17, 2017 by Ken Estes

[GARGEAN]

As far as the OP is concerned, the USMC briefed its tank battalions in mid-1970 that the 90mm was no longer effective vs. Russian tank armor, based upon the army's research of the 67 War. As I recall the study was termed MEXPO, but it was classified and I was not privy to the acronym nor its specifics. The faces fell in the room, especially those of the more grizzled SNCOs who could not believe we were going to give up the beloved Ninety.

Hm, strange. Pretty... Late decision. mid 70's was time of T-64A and T-72, with T-64B not far away(may be not known for them, but first two should be). And 90mm wasn't absolutely perfect against T-55/62 already. Why they took so lond to make such conclusion?

[Ken Estes]

Sorry, I mean the middle of the year 1970. Don't forget most of the USMC was in Vietnam 1965-70 and the M48A3 suited us just fine, later beat the NVA T-55s in 1973 in ARVN hands. By 1974 we had the M60A1, but in 1980 had no 105mm ammo capable vs T-72 frontally [were perhaps trusting in army stocks].

[GARGEAN]

Sorry, I mean the middle of the year 1970. Don't forget most of the USMC was in Vietnam 1965-70 and the M48A3 suited us just fine, later beat the NVA T-55s in 1973 in ARVN hands. By 1974 we had the M60A1, but in 1980 had no 105mm ammo capable vs T-72 frontally [were perhaps trusting in army stocks].

Well, 1970 sounds much better) Just in time when T-64A started to become a real thing. About A3 against T-55 - as far as I can see most reliable was M431 round(or what they used at the moment?), cause HVAP has not perfect chances at range.