Μilitary Questions & Answers

I suspect ramjet propulsion was caught up in many cases by solid fuel rocket propulsion, which turned out to be less bulky and offered higher peak speeds and better acceleration... remember ramjets require rockets and ramjets.

When scramjet technology is mastered I suspect a shift back to scramjet technology, but there are penalties for ramjet designs including large internal areas for piping and airflow and combustion. In missiles like SA-6 and Kh-31 and Onyx the large empty space is taken up by the solid fuelled rocket used to accelerate the missile to a speed where the ramjet can be started and operated efficiently.

For air to air missiles having terminal manouvering performance is much more important than for many other types of missile because aerial targets can manouver in 3D space making interception more complicated.

For anti ship missiles solid fuel simply doesn't allow the range needed for a decent anti ship missile, so if you want supersonic performance your choice is dangerous liquid fuel rocket with a throttle like Kh-22M or Kh-32, or a ramjet/scramjet arrangement. The one high speed solid fuelled rocket anti ship missile is the Kalibre and only uses the solid rocket for the last phase of the engagement over a relatively short distance. This is possible because ships don't move very far very fast... a carrier operating at 45 knots can't turn on the spot and would be detectable from very long ranges so a long flight time is not a problem... unless it is hours...

There is still oxygen at high altitude for combustion, the problem for humans breathing is largely of the inefficiency of the human lung.

A Ramjet powered missile zipping along at mach 6 will be scooping up several kilometres of air per second... combustion shouldn't really be an issue... certainly to 30km altitude or more.

Oxygen concentrations would only become a problem at perhaps 50km or higher.

Of course with any jet engine there are problems with sharp turns where flameouts and stalls might become a problem.

The key advantage of Ramjets is the throttle where a high throttle setting will allow the weapon to climb and accelerate but once it gets to altitude the throttle setting can be reduced to extend range, while closer to the target area the throttle can be opened up again to increase terminal manouver capability.

The ability to chance the throttle setting on older missiles was less important but a modern missile with a digital navigation system with a range of flight profile options and fairly smart attack capabilities could utilise the flexibility of the ramjet propulsion and increase speed and flight range.


With a superior scramjet motor of course performance increases further so new speeds can be achieved... in fact a smart flight management system will become necessary to potentially prevent the missile accelerating during flight as it uses up fuel and gets lighter and faster to prevent it accelerating to too high a speed and being damaged from the heat of friction....

The speed the missile travels at it would need to be scramjet propulsion, and unfortunately such a design requires a large internal volume for air flow and combustion.

I rather suspect the scramjet technology group they have put together will have opened all the old projects based on ramjet technology to see if improvements in technology and materials and of course the step to scramjet might make a few previously far fetched ideas more viable.

HVAPFSDS MBT rounds for use at long range targets would be one example... normally with APFSDS rounds they lose velocity in flight so the closer the target the better the penetration... within 2km they are at their most effective. With ramjet technology the promise was that that high velocity close in could be maintained to extend the effective range of the round to 4-5km, but with scramjet propulsion there is the promise that the rounds could actually be accelerated to higher than muzzle velocity and be effective as a very long range round that has better performance at 10km than at 1.5km.

Obviously potential work on ATGMs and anti ship missiles and a range of other weapon types including anti satellite.

The BRDM-2 was a popular vehicle... its armour wasn't amazing, but it was full amphibious and seemed to have pretty good mobility.

I do remember reading that the extra wheels under the belly that were chain driven were not often used, as a post apocalyptic vehicle it would be a reasonable basis to start from. Not super roomy inside, but then rather more mechanically simpler than the BTR-60 as it only has the one engine.

The other problems include manufacturing and also designation systems.

For instance some countries measure calibre from the depths of the grooves in the barrel while other countries measure calibre from the tops of the grooves (called the lands).

Another issue is tradition and habit... the Russian 7.62mm calibres... ie the 7.62 x 54mm, 7.62 x 39mm, and 7.62 x 25mm calibres are all actually .311 calibre... the same as the .303  

This means you can take an old 303 rifle and rechamber it to 7.62 x 54mm, 7.62 x 39mm, or 7.62 x 25mm.

Here in New Zealand there is still an abundance of old 303 rifles but 303 ammo is getting rather expensive, so a cheap solution is to get them re-barreled in the 7.62 x 39mm calibre of the AK as a short useful hunting round for use against light and medium game like Goats and Pigs.

The advantage is that with a chamber bore adapter you can fire 7.62 x 25mm rounds without any modification of the original 303 rifling..

Would be interesting to see how a rifle can handle such a range of projectiles with the Nagant 7.62mm having projectiles in the 150-203 grain range, the AK 7.62 having rounds in the 122-154 grain range and the Tokarev pistol 7.62mm calibre having 90 grain projectiles.

I imagine a 90 grain projectile in a 7.62 x 54mm case would be a very zippy light recoiling round for use against small goats... would be fun experimenting...

BTW what sort of variety do you have with your ammo collection?

I have tried to focus on Soviet and Russian ammo types but I have a few others as well... I am missing the Soviet HMG calibres... ie 12.7 x 108mm and 14.5 x 114mm, but also would be interested in 5.45 x 18mm pistol ammo. I have a Nagant 7.62 revolver round, a 9 x 18mm Makarov, but none of the new suppressed ammo types or exotic rounds.

I also have a western 105mm howitzer shell and three rounds of 25mm cannon shells with links from a LAV... both from my Nephew... (all fired of course)

We have discussed this before but very simply all three can be thought of as long tubes that start out wide... get narrow in the middle and then get wider at the rear.

The Turbojet has a shaft down the centre with fan blades mounted on them all the way along the tube. The ones at the front are large and suck air into the engine. The ones in the middle are smaller but still fill the tube and are geared to the shaft at the front of the engine... so as fuel is added to the middle narrow section and burned it is forced back out the rear of the engine developing thrust.

The narrow bit in the middle of the tube is the high pressure section or hot section and as more fuel is added the air moves faster through the tube... making the blades at the front turn faster accelerating the engine.

There are lots of different engine types... a Turbojet is just that single tube of air flow, a low bypass turbofan has the front fan enlarged and another tube around the outside where air flows through. In a turbojet the air is hot and is flowing fast but by heating it is is lower in density than normal air. A low bypass turbofan directs some cold air around the outside and then blows it out the rear... the cold air being denser and offering more push and because it is still oxygen rich burning fuel in the exhaust in an after burner is more powerful and efficient.

A high bypass turbofan has a small turbojet driving a much larger fan and most of the thrust is from that larger fan blowing subsonic air... commonly used on subsonic transports and civilian airliners.

A ramjet has no blades and no shaft... air comes in the front and is compressed as the tube narrows... fuel is added and burned which heats the air and generates thrust... simple and cheap and very light.

The problem is that most jet engines burn fuel at subsonic speed and choke on supersonic airflows so a mach 2 fighter has ramps on its air intakes that open during takeoff when air is moving slowly so that more air can enter the intake. At high speed the ramp closes and reduces the amount of air entering the intake which reduces its speed to subsonic.

On a scramjet... or supersonic combustion ramjet, you have a tube of a design that allows fuel to burn at supersonic speeds so not complex air intake is needed and the only limit on speed is the heat capacity of the aircraft and the engines... a ramjet just needs forward movement... during WWII Polikarpov tested ramjet engines on an Il-15 biplane that could fly at about 200km/h. The ramjet engines added about 40-50km/h to the top speed but it shows forward speed does not need to be high to start a ramjet engine.

Top speed for a scramjet is orbital speed or higher.

Because of its design you could fit an aircraft with scramjets and close the intakes on takeoff and pump fuel and oxygen into the chambers to accelerate down the runway on rocket propulsion... once moving forward however the O2 could be cut off and the intakes opened to use air for the O2 and liftoff could be achieved using scramjet propulsion right up to space where the intakes could be closed again and rocket mode could be used.

Similarly a Turboscramrocket design could be used where on takeoff it could get airborne via a turbojet engine... once airborne the airflow through the jet engine could be cut off and airflow through the scramjet could accelerate the aircraft to altitude and orbital speed... once in orbit the intake could be closed off and rocket mode could be used to manouver in space till rentry and landing normally using turbojet and or scramjet.

I have a question Garry, it's not related to viruses but with the creation of Zirconium scramjet cruise missile, what's the likeliness that scramjets find their way on to S-400/S-500 SAM missiles? Will it allow the missiles to have increased speed and range but with smaller dimensions, or is this just pure fantasy and not applicable to SAM missile fundamental properties?

It is all about design compromise. Ramjets are like jet engines and are relatively efficient... though for use in aircraft the key is re usability, so a jet aircraft is more efficient than a rocket powered aircraft for day to day flights. when the goal is to get to space however the jet just can't give enough speed so the Space Shuttle and Buran are rocket powered, which is expensive but to get to orbital speeds there really is no current alternative in terms of jet engines.

With designs of missiles low cost becomes critical as these engines will only be used once, so rocket and ramjet and now scramjet are the three competing options. In terms of volume a ramjet requires internal space to burn the fuel, though modern Russian ramjets use that internal space to fit a rocket engine to get the missile up to speed before the ramjet is started which means multi stage rockets are not so critical, though technically it is a multi stage rocket/ramjet.

The critical technology however is scramjet engines which in theory have no top speed, yet are fundamentally simple devices with few moving parts and no blades or shafts or "turbine" sections.

The huge advantage of a scramjet is the ability to throttle.

Solid fuel rockets are baked like cakes. to make them lighter they have the centre hollow, so instead of burning from one end to the other like a fuse, they burn from the centre outward, which means the walls of the rocket can be made thinner and lighter because as the rocket burns the pressure pushes out sideways is supported by the remaining fuel left to be burnt. Making the hold up the middle star shaped increases the surface area of the rocket fuel burning. the inner layer that burns first is high energy fast burning fuel generating high thrust to launch the missile and accelerate it rapidly to high speed. the next layer is slower burning that takes much longer to burn and does not accelerate the missile, it just allows it to cruise without losing speed for a few minutes.

A missile has a peak speed where drag overcomes the thrust and so any extra thrust is largely wasted... once the missile gets to that speed then continuing to burn at full thrust is a waste of energy. Simple calculations can be made to determine how long the high energy fuel should burn with the remaining fuel being much slower burning to maintain speed for much much longer and greatly extending flight range.

For S-400 et all the calculations are made easier because they are all ground launched and start from zero speed.

An AAM on the other hand might be launched from a hovering helo, or a high flying MiG-31 at mach 2.6.

Ramjets are efficient high speed jet engines where air is sucked in, fuel is added and burned and is blasted out the back generating thrust. You can throttle up and down depending on where you are and where you want to go.

Ramjets were tested on the I-15 Polikarpov Biplane and don't need to be moving through the air at very high speed to work, though obviously they are most efficient at higher speeds.

Solid fuel technology has improved significantly, so the Solid rocket SA-11 and SA-17 replaced the rocket ramjet SA-6 in service some time ago. For very long range however the turbojet powered Granit has been replaced by the ramjet powered Onyx... the range is shorter, but the missile is about 4 tons lighter too... the Granit is 7 tons and the Onyx is about 2.5 tons in the air launched model.

Scramjets offer even higher speed and efficient use of fuel with the added benefit of a throttle, but the main problems remain volume and of course the need for rocket launch.

Creating a scramjet S-400 likely wouldn't make it smaller or lighter, so I doubt they will bother, but for very long range very high speed missiles scramjet propulsion will probably be the mode of choice.

Scramjets characteristics are still relatively unknown, so Ramjets would be the safer bet. Ramjets also allow for the missile to throttle down to around Mach 1, which could improve range dramatically.

A scramjet is merely a ramjet that is designed so that the fuel can be burned at supersonic speed. The intake ramp on an F-16 was simplified and fixed which is what limits it to mach 2 or less. The intake ramp contracts at high speed and reduces the amount of air coming in the front of the aircraft at high speed. With its simplified fixed ramp the F-16 can't go faster than mach 2 because the air coming in is coming in too fast and would choke its engine. A scramjet on the other hand could take air coming in at any speed and still produce thrust.

the ramjets tested on the I-15 biplane increased flight speed by something like 85km/h and could be operated at speeds as low as 100km/h.

Like any engine aircraft combination certain configurations will be efficient, so you might find that a missile with a ramjet engine might operate best at around mach 2.5 or so, but scramjets would likely operate most efficiently above mach 5-6.

The Russians put a scramjet engine on the nose of an SA-5 SAM which replaced the warhead and guidance section with a small scramjet engine and fuel, so the missile is launched... its solid rocket boosters burn and fall away, the main rockets burn till the missile gets to about 15,000 m altitude and mach 5, when the scramjet engine on the nose of the missile is started. It accelerates the entire missile from mach 5 to mach 6.5 and burns for about 180 seconds... in other words about 3 minutes.

In those three minutes of burn time when the small scramjet operates the missile covers about 350km.

The limit of a turboprop engine is the speed of sound, the limit of a turbojet engine is about mach 3 in conventional mode. The limit of a ramjet engine is mach 5-6 or so. The limit for a scramjet is heat. If you had materials that could take the heat and speed a scramjet can take you to orbital speeds... into space... though in space it would no longer function of course.