The metal-less aeroengine - a favour and a challenge (also open breach armament)

[Avimimus]

Hello everyone,

I'm working on a project examining the development of aircraft by aliens during their 1920-1960s technologically equivalent phase.

My first question is: Is it possible to create an aeroengine (turbine, internal combustion etc.) which doesn't use significant amounts of metal? If so: What would be the design tradeoffs?

The other questions is: Are there any conditions where closed breach weapons above 12mm in calibre would be impossible to produce?
(ie. under what conditions would the development of military aircraft not include the development of automatic high-powered cannons, but be restricted to small caliber and larger recoilless weapons)

Any ideas? Anyone more knowledgeable and wiser than I in engineering?

Thanks,

 

[mz]

There's a ceramic rotary engine project by a UK team.
http://ceramicrotaryengines.com/

 

[Lauge]

The other questions is: Are there any conditions where closed breach weapons above 12mm in calibre would be impossible to produce?
(ie. under what conditions would the development of military aircraft not include the development of automatic high-powered cannons, but be restricted to small caliber and larger recoilless weapons)
Thanks,

I don't really see any engineering conditions that would fit your needs. If you can produce a 12mm closed/locked-breech automatic weapon (and a large-calibre recoilless gun), then ity should be entirely possible to build a 30mm closed/locked-breech automatic weapon.

If you want to avoid weapons like that in your fictional setting, you might be better off going a "political" route, e.g. conventions prohibiting the development, manufacturing, stockpiling and trading of automatic weapons above a certain calibre firing explosive shells?

Or if, for some reason, your aircraft have to be very light-weight (say, a relatively low-density atmosphere giving you less lift from a given wing surface), large-calibre automatic cannon and their ammunition might simply be to heavy to be practical.

Hope this helps.

Regards & all,

Thomas L. Nielsen
Luxembourg

 

[Avimimus]

Thanks for the replies,

The basic setting is a technologically stagnant, pre-literate society. A number of societies in antiquity or the feudal era attempted some regulation of arms - but it isn't easy with poor communication networks and there is always plenty of incentive to break the rules.

The planet has considerably rougher topography which makes air travel more significant. This would favour long range and short field performance in aircraft designs. This also allows for blending bombers and fighters into a variety of intermediate designs, as was expected by many 1930s experts. The problem is that high-powered, automatic cannons provide a sufficiently high rate of fire for aircraft use, along with a muzzle velocity and round weight that meant such weapons were deadly at range. This meant that by the start of the 1940s small size was increasingly important for aircraft survivability.

One possible factor being considered is to have the planet be metal-poor with only trace amounts of accessible iron (and other metals, basically anything with an atomic number over 20). One solution could simply be to lower the maximum chamber pressure in this way - effectively reducing firepower for all weapons (including autocannons). It should be possible to create airframes out of a mixture of composites and ceramics. Although, I'm not entirely certain that properly reinforced ceramics wouldn't be suitable for high-powered cannons.

My initial solution was to have an upper limit to chamber pressures. Of course, this doesn't really solve the problem as it would favour larger calibre automatic weapons (whose high-explosive payloads would compensate for lower muzzle velocities in the 20mm-40mm range). One alternative might be to have airframes be unable to take repeated high recoils without deforming - although I doubt that recoil forces would be great enough to prevent careful structural engineering and over-building to compensate into the 20mm-30mm calibre range.

Any ideas are most welcome.

I'm finding that this is becoming a very interesting challenge (I'm imagining ceramic engines glowing hot in the night, carefully insulated from the fuel supplies - I can't wait to get onto the airframe designs!).

edit - I'd previously been under the assumption that small calibre and recoilless weapons had much lower chamber pressures than intermediate calibre closed breach weapons.

 

[mz]

Guess the rotary engine works well with materials having less impact strength than metals.

Then there's the possibility for turbines as well. Steam turbines were invented in the late 1800s, and a gas turbine ran in the early 1900s, so it's not *that* different from internal combustion piston engines.

Though again, gear boxes are hard without metals. Maybe jets then directly?


With a less dense atmosphere, long range surface cannons work better while flying becomes harder.

Glass, boron, carbon and lava composites all avoid the brittleness by making the materials into thin fibres and then putting that into a slightly flexible plastic. Glass fiber was produced from the 1930s on.

 

[Nik]

Have you restricted use of metallic alumin(i)um ? You'll need ceramic liners, perhaps...

Uh, could discarding sabot cannon be made air-worthy using reinforced stand-offs & deflectors for weapon-pods ?? A system akin to plated propellors & WW1 machine guns before interrupter gears ??

Rockets ??

Given the short/rough field requirements, perhaps auto-gyros and flying-flap-jacks will find a slot...

I'm also wondering if valve-less pulse-jets may have their place in the twin-sun-light...

 

[Abraham Gubler]

If you want to promote both flight and demote larger caliber shells in your alien world just make the atmosphere thicker. A thicker atmosphere would mean a wing can produce more lift for its size and that wider shells would generate more drag.

 

[Justo Miranda]

Why not rocket shells?
...please see http://pwencycl.kgbudge.com/J/a/Japanese_40mm_Ho-301_gun.htm

 

[Avimimus]

Thanks for all the input. Short field performance and long range / multi-purpose uses for aircraft as planned requirements - keeping sizes larger, handling better and speeds lower. One can certainly imagine air-combat with such aircraft developed alongside autocannons. The problem is that turret mounted, high velocity 20mm-30mm weapons would be desirable as they would remain effective at longer ranges and allow the aircraft to change course periodically. Air combat would focus on concentrating fire-power and tactics would be closer to surface combatant naval combat (but at higher speeds and only a few hundred metres).

However, this would be quite a bit different from 1930s projections of future aircombat (anyone read the original book by Alexander de Seversky: Victory Through Airpower?) - which I was trying to partially make use of for this project.

The real problem is with any medium calibre weapon that has a sustained high rate of fire. A secondary goal would be to increase weapon weight and decrease muzzle velocities.

Why not rocket shells?
...please see http://pwencycl.kgbudge.com/J/a/Japanese_40mm_Ho-301_gun.htm

Regarding the Ho-301 - it is certainly in line with the types of weapons planned. I wasn't aware that it used such shells and it is a very good suggestion (although its rate of fire might be a bit high if it could be modified for longer bursts).

Under consideration were machine gun calibre volley (or Nordenfelt) guns, semi-automatic medium calibre recoilless (or low-pressure) weapons and high calibre recoilless rifles (proximity fused shells). The latter would be supplemented by rocket projectiles and barrel launched rocket projectiles (some of which could have magazines). The exotics would be single shot fuselage mounted batteries and occasional use of extensible rams (used for prestige - similar to coup sticks). I also considered the inclusion of small calibre squeeze-bore weapons (ie. AT rifles) - but their feasibility depends on the solution used to remove autocannons.

If you want to promote both flight and demote larger caliber shells in your alien world just make the atmosphere thicker. A thicker atmosphere would mean a wing can produce more lift for its size and that wider shells would generate more drag.

It may not be so straightforward as it initially seems. I was thinking about this and it occurred to me that there would be a further degradation in the performance of low velocity cannons. However, if my observation is correct the lower surface area to mass ratio in a larger shell would tend to work in the favour of larger calibres (at least during the terminal stages of flight). So, smaller calibre weapons might lose effectiveness faster (at least for longer range work). Thanks for the idea, though.

Any other ideas on how to lower sustained rate of fire or muzzle velocity (or for alien pre-1950s technology aircraft in general)?

 

[riggerrob]

I am picturing a chain of volcanic islands ...

The biggest disadvantage of no metals is having to avoid the shock loads of piston engines. Even a Wankel or Liquid piston would substantially reduce torsional shocks to the drive train.
Liquid Piston is an experimental engine that looks like a reverse-Wankel inside, with a triangular combustion chamber, but an oval rotor.
With turbines or rotary (Wankel) you only need to build hot engine parts from ceramics. You can side-step many precision machining steps by rotating semi-hardened parts together until bearing surfaces are a close fit.
Given the different types of soils and clays on the different volcanic islands, different tribes could specialize in making pots, ceramic knives, ceramic arrow points, wind mill components, etc.

Can dense carbon transmit electrical currents?

The rest of the air frame can be built with wood and textiles.

As for firearms ... what is the precursor?
Remember that most projectile weapons were originally designed to kill food the size of deer or birds. Your imaginary world would need much larger, armoured prey before large caliber, explosive weapons were needed ... say giant turtles or armored whales.
Forget about squeeze bore as it was only briefly fashionable during WW 2. After that everyone went to sabots which allow you to use a wide base/low pressures, but still focus all the terminal energy on a tiny point for deeper penetration.
If you want to use a recoil-less gun, how about punting the ceramic cartridge casing out the back end of the gun. That will help balance recoil and if your ceramic cartridge case disintegrates into a cloud of clay dust ... so much the better!

 

[riggerrob]

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