Some possible reasons:

 

-- RLP systems are only advantageous for guns that use separate projectile and incremented propellant charges.  For NATO this would mostly be the 155mm systems. 

-- RLP is probably only usable on self propelled guns due to added weight, complexity, and power requirements.

-- None of the advantages you listed, either singularly or together, provides a 'show stopping' advantage.  And, unlike other changes in gun systems, RLP represents a significant change in the weapon itself, rather than an incremental improvement.  Hence it has the potential for actual failure, rather than just not living up to it's hype.  That can terrify a bureaucrat into indecision.

-- Reliability.  You are injecting a large amount of propellant very quickly into the combustion chamber at extremely high pressures while the gun is firing.  Nobody has any idea how it will stand up in actual use with field maintenance.

 

-- Competition.  RLP systems are only one of many concepts that are competing with each other for the next big thing in guns, including rail guns, electrothermal propulsion, various plasma enhanced combustion concepts, new propellants, and dual charge propulsion.  Currently no one design has a clear advantage over the others when all factors are taken into account.

Liquid propellant has seemed like an obvious good idea for the last 50 years or more, and has been proclaimed as coming real soon on several occasions.  The attraction is less propellant to carry around.  Originally Crusader was gpoing to use, in the event it was dropped during development IIRC.

 

One scientist working in the field said the problem in one word to me "oxidiser".

My layman's first thought is " What if it leaks?".. 

Until the rail-gun arrives (with its own problems), some of the major advantages of the RLPG would however seem to be substantial:  instant infinitely adjustable charge and easier transfer of propellant - just pump it.

 

 

 

The gun crew dies.

Are the chemicals which would be used in such a Liquid Propellant really that nasty?  As mentioned by Neutraliser UDLP initially envisioned the XM2001 Crusader as being a liquid propellant gun but after the third instance of "Energentic Venting" and "High Speed Dissassembly" on the ordnance test bed that approach was abandoned!!!!!

There isn't a hypergolic of which I know that isn't deadly in some "interesting" way. Not to mention, that pressure overburden is the classic way we produce fragmentation effects.

 

 

 

the propellant HAVE to be hypergolic?  Just asking...A fuel and an oxidizer, yes, but why not an external igniter, be it a hot wire, or a primer like artillery currently uses?

 

Liquid propellant has been a mil Sci-Fi staple for decades...and every year is "Next Year Jerusalem."

Are the chemicals which would be used in such a Liquid Propellant really that nasty?  As mentioned by Neutraliser UDLP initially envisioned the XM2001 Crusader as being a liquid propellant gun but after the third instance of "Energentic Venting" and "High Speed Dissassembly" on the ordnance test bed that approach was abandoned!!!!!

 

Liquid Propellants are supposed to have toxicity similar to ANFO for the mono-propellants.  The binary propellants would presumably be selected so as to be even less hazardous until mixed.  They are most definitely NOT hypergolic.

 

The big problem with any propellant is controlling the deflagration rate so as to not exceed the allowable pressure.  In solid propellants this is done by controlling the grain size and shape and using retardant coatings.  None of these are possible with a liquid propellant, so the only solution is to introduce it into liquid propellant into the firing chamber at a controlled rate while the gun is firing.  It's a bit like a diesel engine, except everything is much bigger, much faster, and at MUCH higher pressures.

 

Inject the propellant to fast, or fail to maintain a smooth rate, and you get "Energetic Venting" (cracked breach) and "High Speed Disassembly" (explosion). 

 

How difficult is that?  Well figure you are going to have to inject 60% to 80% of the total propellant mass into the combustion chamber at 80,000 psi in less than 0.002 seconds, while preventing the detonation wave from projecting up stream into wherever the uninjected portion of the propellant charge is located.

eliminate the oxidizer problem. As for the toxicity of the other compounds, CANCER DEATH from the fumes breathed in is no joke.

Herald

 

The developmental liquid propellant gun I saw being developed for the Crusader was huge and had too many moving parts.  If I remember correctly, there was also a major corrosion problem with an internal piston. There were several microcomputers that choreographed its firings.  There was a 'rats nest' of electrical cabling.

 

The developmental gun misfired causing damage with attendant delays while it was being repaired.  It was unlikely that cannon would ever receive a safety release. 

---  CHAS