Donnerstag, 30. August 2012

Euro Carrier

I. Properties and drawbacks of current aircraft carrier designs.

I've been looking at all those aircraft carrier designs out there and I don't like any of them. What got me started thinking about this, was the poor flight deck design of current carriers. I want to illustrate this by way of example. This is the flight deck of a current Nimitz US aircraft carrier:

I don't think the space on the flight deck is used efficiently. I can see large areas that are basically useless. So I looked at alternative designs.

This design is intended for a smaller carrier than the Nimitz class. The most noticeable differences are: It has 2 Islands, one for the bridge and one for the air traffic control. It has a single runway used for landing and take off. It uses a sky ramp instead of a catapult. But still, lots of space is wasted. It is supposed to be operated with vertically landing aircraft, in particular the F-35S.

1. Efficient use of runway

What got me started, was the very inefficient use of space on the flight deck. Two runways are provided on the Nimitz. One runway is used exclusively for starting aircraft, whereas the other runway is primarily used for landing aircraft. Wouldn't it be far more efficient to use each runway for both starting and landing aircraft, depending on what is needed?

2. Center of gravity

Please also not the asymmetrical placement of the islands on the starboard side of the Queen Elizabeth carrier. The same is true for the island on the Nimitz. The weight of the Island must be balanced by the runway extending on the opposite port side, such that the ship doesn't capsize. Consequently, lots of space on the flight deck is wasted.

3. Catapult vs. sky ramp

Catapults are large, very complex and need several highly trained people for operation. A Sky ramp is simple and reliable. No people are needed for operating the sky ramp. The sky ramp take off is considered to be much safer than a catapult take off. Simplicity, reliability and safety let me prefer the sky ramp over the catapult solution. The disadvantage of the Queen Elizabeth design is that you can only start one aircraft at a time.

So why did the Americans choose the catapult? Some planes don't have the power to launch over a ramp on their own. So this gives you added flexibility. The flexibilty is of little use, if your carrier fleet merely consists of two or three different types of aircraft. The primary reason appears to be speed. With catapults two planes can be started almost at the same time off of a single runway. If an encounter with an enemy carrier takes place, you want to get your aircraft into the air as fast as possible. Whoever gets his planes in the air first, will most probably win the battle. Therefore, this design was chosen by the US.

But, the speed advantage is not so clear cut. You have to make the catapult ready, attach the aircraft to the catapult and communicate with the catapult crew to set it up for the particular plane and its weight and characteristics. A well organized fleet could probably get started from a single runway over a sky jump just as fast as the two catapult solution.

How can aircraft be started and landed in a fast pace from this flight deck? A single elevator is provided adjacent to the take off position. Once an aircraft is landed using arresting wires, the plane is immediately taxied to an elevator adjacent to the landing position and taken away from the flight deck.

So a well organized flight deck with a single landing and take off runway can perform sufficiently fast. This means that I am in favor of sky ramps over catapults.

4. Parking on flight deck.

Dozens of aircraft are parked on the deck of both the Nimitz and the Queen Elizabeth. A single hit by an enemy aircraft or a single crash landing by friendly aircraft can wipe out all of these planes in one blow. Therefore, it is preferable to store most of your aircraft in a protected hangar. The advantage of having a few planes ready on the flight deck is that you can start them very fast. So the time to react to an enemy threat is diminished. But this speed advantage is only true for the first few minutes it would take to get an aircraft to the runway using a lift from the hangar. The bulk of your fleet should be stored in the hangar below.

I've incorporated three aircraft that I find to be particularly useful on a carrier:

1. Navalized Eurofighter Typhoon

This version includes thrust vectoring in order to reduce the minimum landing speed to around 150 km/h. The arresting hook and landing gear are reenforced in order to sustain carrier landing. The additional weight of the aircraft is around 500 kg. The navalized Typhoon is equipped with the newest jet engine EJ 230, which provides 30% additional thrust. The engine will have dry thrust of around 78 kN with a reheated output of around 120 kN. The navalized typhoon is the standard multirole combat aircraft of the Euro Carrier.

2. General Atomics Sea avengers are used for air reconnaissance and stealth attack missions.

There is one thing that should never happen to a carrier. A surprise attack from an enemy air fleet. The American sea avenger automatically monitors the surrounding air and sea and transmits the information in real time to the carrier. The crew permanently monitors the pictures for enemy aircraft and enemy ships. The sea avenger has a very high service ceiling (18288 m) and endurance (20 hours). One of the two UAVs will monitor the skies for 24 hours a day. The Sea Avenger includes a retractable electro-optical/infrared sensor, internal weapons bay, and folding wings. The width of the aircraft is reduced with folded wings; the Sea avenger is schematically depicted with and without folded wings in the following drawings. The aircraft’s structure is designed with the flexibility to accommodate carrier suitable landing gear, tailhook, drag devices, and other provisions for carrier operations.

3. The Eurocopter NH90:

This is a highly versatile helicopter used by many nations around the world on their frigates and carriers. It can be used for hunting down submarines, in rescue operations as well as transporting people and goods. 

So I thought about designing a flight deck that combines the simplicity and reliability of the Queen Elizabeth with the speed and safety of the Nimitz. A minimum number of planes and people operate on the flight deck. The size of the flight deck is as small as possible. this is what I came up with:

I. Design constraints:

1. Single runway: 30*200 m²

A single runway was chosen as a starting point, since more runways just add to the size and weight of the carrier. But this is more or less arbitrary. The size of the runway was chosen for arrested landing, since most naval fighters like the F-18 or Rafale do not land vertically. Vertically landing airplanes like the harrier jump jet tend to be less capable and more expensive than their counterparts. The width of 30 m corresponds to the smallest runways of military airports, so it is already a small runway and landing on a carrier is a lot more difficult than landing on land. The length of 200 m is usually used for stopping the aircraft. 

2. Airframe size


Wing span: 11 m (extended) and 8 m (folded wings)
Length: 16 m 

Sea Avenger:

Wing Span: 20 m (extended) and 16 m (folded wings)
Length: 12.5 m


Length: 19.5 m
Width: 15.5 m

3. Hangar Size

The size of the flight deck determines the maximum size of the hangar below the flight deck. Since you want to be able to move airplanes through the hangar quickly, you need an aisle. 

Centre Aisle: 15*200 m²

At some point the runway becomes too small for moving the airplane through the hangar, since you must also turn it around.

Parking lot: 10*20 m²

This give you some space around the typhoon and Sea Avenger that lets the crew do its work in a reasonable manner.

II. Design Priorities:

1. Maximum number of airplanes
2. Maximum number of airplanes on the smallest carrier area.
3. Maximum number of airplanes in hangar not on the flight deck.
4. Maximum convenience for moving around planes.

Ad 1: The larger your fleet of aircraft, the more powerful your aircraft carrier will be. So maxing out on the number of planes is reasonable. It becomes unreasonable at some point. But that is addressed in the other priorities.

Ad 2: The size of the flight deck basically determines the overall size of the carrier. You want to minimize the size of the flight deck because otherwise your carrier becomes inaffordable. So the Flight deck size per aircraft should be minimized for cost efficiency reasons.

Minimize: Flight deck size/number of aircraft.

Ad 3: Although you want to have many planes, you don't want all of them to be parked on the flight deck for safety reasons. A single hit or crash landing could destroy your whole fleet. So you wish to minimize the number of airplanes parked on the flight deck.

Minimize = Aircraft parked on Flight Deck / Aircraft parked in Hangar.

Ad 4: Flexibility in moving around the airplane in the  hangar and bringing them to the flight deck is paramount. A huge number of planes is useless, if you can't pick out the appropriate plane for the particular job easily. This is achieved by giving each plane direct access to an aisle connecting the plane from the hangar to the lift to the flight deck.

So how do the design constraints interact with the design priorities?

Since you are going to place the hangar below the flight deck and you want to max out the number of planes, then the minimum size of the hangar is 30*200 m² (size of the runway). The central aisle of the hangar takes up 15 *200 m². This leaves you 15*200 m² for parking aircraft below the runway. You are going to need space to the left and right of the runway for the bridge and the air traffic control. For reasons of balance, these two must be spaced apart like in the Queen Elizabeth. The ATC near the landing area and the bridge near the take off area. If you are going to add to the width, then you should add at least 5 m, because this would let you add 10 more planes into the hangar below. Each parking lot needs 10*20 m². The total size is now 20*200 m². So the number of parked aircraft would equal 20*200/10*20 = 20 aircraft. The center aisle - 15 meters wide - would be accompanied by one aisle 10 m wide to the left and right.  The aircraft would be parked in parallel to the center aisle.

We know from every parking garage that it is most efficient to park the cars perpendicular to the aisle in order to max out the number of cars that fit into a large garage. This principle would dictate the we add 10 m to each side of the center aisle. Then the  parking lot (10*20 m²) for each plane could be placed perpendicular to the aisle. The result would be a center aisle 15 meters wide accompanied by two parking aisles, each being 20 meters wide. So the hangar would have a width of 20+15+20 = 55 meters. The total number of fighter aircraft that could be parked in this hangar is equal to 40. The runway on the flight deck has a width of 30 m. This leaves us 25 meters of additional space on each side of the runway. A symmetrical approach should be chosen, such that the center of gravity remains in the middle of the ship. This leaves us 12.5 m of place to the left and right of the runway. We would not try to increase this space to 20 m as in the hangar because we want to minimize the number of planes on the runway in relation to the planes in the hangar. Please note that we need do place the ATC and the bridge next to the runway. We need an elevator at the beginning and end of the runway in order to bring the planes fast to the runway and clearing of planes fast from the runway. Furthermore, we need special parking lots for the helicopters and UAVs on the runway because they do not fit into a single parking lot in each hangar.

So the design constraints and priorities lead to this configuration of the flight deck:

I tried to use the additional space left and right of the runway the best way I could.  Therefore, both the ATC tower and the bridge were placed in this area. The ATC is close to the take off and landing area of the aircraft, because this is what they have to control. They were placed on opposite sides of the runway in order to get the center of gravity of the carrier into the middle. Opposite to the ATC and Bridges are the elevators. Their size has been chosen to be 20*20 m  such that each lift can carry two typhoons simultaneously. Additionally, the lifts may be used to transport people and weapons through the carrier. The elevators also provide a weight balance to the bridge and ATC due to their placement. Additional space was added to the left and right of the carrier in order to provide landing and parking space for the helicopter and UAVs. They were placed somewhat in the middle. The residual space was used for parking a maximum number of Typhoons. They are parked in an angular fashion in order to max out the size of 12.5 meters next to the runway.  So what does the Hangar look like?

The width of the hangar is 55m and its length is equal to 200m. The center aisle is 15 m wide.

The plane elevator measures 20*20 m². The circular ring on the plane elevator is supposed to indicate that the plane can be turned here by 180°. So if the plane enters into the lift in a straight line on the bottom side, it then gets turns around by 180° and points to the ship and is positioned on the opposite side of the lift. Then the next plane enters in a straight line. So you can easily load the lift with two Typhoons. Offloading the lift on the flight deck works just the same way.

The stairway was added for safety reasons, if the plane lift fails. This stairway basically resembles a large fire escape, but you escape to the flight deck not into the sea ;-). So it's an extremely stable and light weight construction; The size is 5*5 m².

In case of a sea battle, people must use the stairway for accessing different levels of the carrier. The lifts are reserved for airplanes, arms, and the wounded as well as a few authorized people such as medics and weapons supply officers. More light weight stairways of the same kind are added to the port and starboard of the carrier.

I've seen documentaries of Nimitz carriers that show how planes are being refueled and rearmed on the flight deck. That is far too dangerous. Refueling and rearming of the aircraft must be performed in a safe location, not on the flight deck. People working on the flight deck are merely to be occupied with starting and landing aircraft. Therefore, the arming and refueling must be performed in the hangar only! 

The above layout results in the following design parameters:

2. Total number of aircraft:

51 Typhoon + 2 Sea Avenger + 2 Helicopter.

2. aircraft on flight deck vs. aircraft on hangar

19/36 = 0.53

III. Flight Deck Size per aircraft:

flight deck Size =  11955 m²
number of aircraft = 55
Size per Aircraft  =  217 m²

Every plane has direct access to the aisle or runway.

A more flexible approach for the flight deck would add flexibility in terms of the use of helicopters and UAVs. You wouldn't want to max out the number of planes on the flight deck. The extension in width equal to both sides equal to 7.5 meters. This design alternative would look like this:

1. Total number of aircraft:

63 Typhoon + 2 NH90 + 2 Sea Avenger.

2. aircraft on flight deck vs. aircraft in hangar:

27/36 = 0.75

3.. Flight Deck Size per aircraft:

14000 m² / 67 aircraft = 209 m²

Protection must be offered to the parked aircraft in case of a crash landing. The hangar below the flight deck is 7.5 m meters high. Immersible thin wall - 3 meters high - could be uses as a protection against a crash landing plane sliding into the parked aircraft.

In case of an enemy attack, the aircraft on deck must scramble as soon as possible in order to both fight the enemy and for safety reasons. So the airplanes on the flight deck are fully fueled and equipped with air-to-air missiles.

III. Arrested Landing:

The arresting wires do wear and tear. They have to be replaceable easily. The arresting break itself should be very reliable and need extremely low maintenance. Therefore, I would recommend using a linear eddy current break. The breaking power is based on the principle of transferring linear movement into an electrical current via induction. So breaking is performed without mechanical friction. The principle is widely used, in particular in drop towers for amusement parks:

Please note that reliability and safety are of utmost importance when designing the breaking system of these towers used in amusement parks. The safety of the passenger must be maintained at any cost. The same can be said about the safety of the pilot. We can conclude that this technology is reliable and safe. There is no need for reinventing the wheel. A company specialized in designing these electro-mechanical breaks should be employed for designing the arresting gear.

Please note that such a system may also be used for accelerating the aircraft using a catapult. The overall thrust of this system may not be equal to that of a steam catapult, however less catapult thrust is needed due to the presence of a sky ramp.

This is what the design should look like:

Arresting function:

As the translator moves along the stator eddy currents are generated within the stator. These currents in turn generate a magnetic field, which decelerates the connector. The size of the breaking force depends on the magnetic field generated by the translator coil as well as the magnetic fields generated by the currents in the stator coil and the eddy currents in the ferromagnetic iron alloy. Since breaking is the primary function of this device, the stator iron core is made to generate the largest amount of eddy currents. This means that a single block of iron should be used. The magnetic field of the eddy currents magnetizes the ferromagnetic core in such a way, that the breaking power is increased.

This would be the standard operation of this arresting gear. However, the breaking power could be increased by increasing the magnetic fields generated by the eddy currents. This could be done by generating an additional current through the stator coil. Please note that the magnetic fields in front of and behind the translator are opposed to each other. Consequently, the currents before and after the translator must flow in opposite directions. This can be achieved by providing several independent stator coils along the stator. As soon as the translator passes one of these stator coils, the applied current is made to flow in the opposite direction. The position of the translator may be measured using simple photo sensors, which detect the position of the translator along the stator and operate the respective switch of the associated stator coil.

Acceleration function:

The eddy currents, which are useful for stopping the translator, are counterproductive, when trying to accelerate it. Since the primary function of the eddy break is deceleration and the required speeds for take-off are reduced due to the use of the sky ramp, this is a drawback that does not hurt much. As a rule, the eddy currents generated when accelerating the translator slow down the translator; they generate a magnetic field opposed to acceleration. Consequently, the opposite magnetic field accelerates the translator. Prior to launching the catapult, a current is fed through each of the coils along the stator, which generates an attractive magnetic force to the connector. A current source is connected to each stator coil. A feedback loop stabilizes the current in the presence of eddy currents. As soon as the stator passes one of the coils, a switch is operated, which changes the direction of the current. Consequently, the translator is accelerated along the stator. The need to compensate for the large eddy currents limits the maximum acceleration, which may be achieved.

The airplane with a relatively large kinetic energy must be stopped within a few seconds. Therefore, large breaking forces must be applied. Therefore, the coils should have a low ohmic resistance and high inductivity. This is achieved by utilizing a coil with a high winding number and thin wire with low resistance.

Armament of fighters:

Another important feature is the arming section. The arming section is located in the hangar not on the flight deck! The airplanes can be armed and refuled in each parking lot or in the section immediately before the lift to the flight deck. The Weapons arrive at the arming section via the elevators directly adjacent to the arming section. The usual armament for a typhoon in the maritime attack role is the following:

1. 4 long range radar guided missiles MBDAMeteor (UK, Germany, France)

2. 4 Short range infrared guided missiles IRIS-T, (Germany, Italy, Sweden)

3. 2  Anti-Ship Missiles Naval Strike missile (Norway):

The typhoon is equipped with 4 MBDA meteor long range missiles, 4 IRIS-T short range missiles and 2 Naval strike missiles.

Aircraft Transport in the Hangar:

 Moving the airplanes through the hangar means that they have be turned around their axis and make tight turns. This is not exactly easy. The problem must be defined precisely before it may be solved.

The aircraft must be moved easily in two directions, horizontically and vertically. Furthermore, the plane must be turned around its axis.

I suggest implementing a simple rail system. Two rails run in parallel through the aisle. Two rails run vertically from left to right. I wouldn't want to have rails sticking out of the ground. Instead, the rails should be grooves stuck into the ground. The groove should be so narrow no aircraft tire can get stuck in them. One or two flatbed trolleys are used for moving the plane along the aisle. The trolleys are suspended into the air using magnetic levitation. so the airplane on the trolley basically hovers about 1cm in the air above the ground. This is a well known principle, which has been used in high tech trains such as these:

But, we would use a low tech implementation of this principle. All we need is levitation. The propulsion of the levitated aircraft would be performed by an electrical winch that would be used to pull the trolley in one direction.. The trolley is not supposed to make any turns, it is just to go back and forth on two rails in a straight line. The levitated flatbed trolleys provide both vertical and horizontal movement of the aircraft through the hangar. Finally, we need to be able to turn the plane. This is accomplished by a mechanical bearing, which lets you rotate the flatbed over ground. The size of the flatbed can be extended in the horizontal direction, such that different types of aircraft can be made to be carried by them. The aircraft is removed from the trolley, but reducing the extensions of the trolley until the tire rolls onto the ground of the hangar.

One very simple implementation would be to use a magnetizable iron rod as the trolley's rail. The iron rod extends into the recess in the ground. A long wire is rapped several times around the iron rod. A direct current is fed through the coil, which magnetizes the iron rod and creates a magnetic field. Conversely, a ground wire is rapped around the recess in the ground. An inductor current is induced in the ground wire, when the direct current of the trolley is turned on. This electrical signal is detected and triggers the application of a direct current through the ground coil. This direct current creates the magnetic force that lifts up the trolley in the recess. Voila!

2. Crew's deck:

I haven't chosen to narrow down the size of the deck as we are going down. This is done for simplicity of design. There is enough space to accomodate a large number of people. Given that 2 beds can be stacked on top of each other, a total number of approximately 2000 people could easily live here. Since good sleep is very important, the sleeping rooms are placed somewhat in the middle and somewhat low into the carrier. Thereby the subjective movement during sleep and sea sickness are minimized. The sleeping quarters are shielded from the aisle and restaurant. So the quarters are very quiet.

3. Supply Deck:

Supplies should be stored in the bottom and center of the ship's hull because you want the center of gravity of the ship to be as low as possible. The Hospital has also been placed here, because it should be placed in a remote location, where few people work. What if the weapons start to explode? If this happens the carrier will sink fast and the sick or injured people will die no matter what. This whole area must be enclosed in armored steel in order to provide as much protection as possible. But is this close to the bottom of the hull? Not really, not yet. This area is actually about 10 meters above sea level. So here comes the solution:

So this is the view of the Euro-Carrier from the front. Please note first of all that this is a SWATH design. SWATH stands for small waterplane area twin hull. The two hulls are the cylindrical black hulls, which are in the water. So this is a particular kind of Catamaran. It may be thought of as a ship hull riding on top of two submarines. The greatest advantage is that this design provides a stable platform and large broad decks. The stability is increased because two underwater hulls stabilize the flight deck in the water. Of course, this is only a schematic representation illustrating the overall design principle.

The main drawback of this design is that it resembles a bridge standing on two pillars. That's the catch. The loads on the decks between the pillars must be carried by the structure. But, please consider that the pillars may stretch across the length of the vessel, which adds to the structural stability. The basic idea how this problem can be solved is known from ancient times and it is called an arch. So the technical problem is comparable to building a bridge spanning a distance of about 55 meters. The bridge is 200 meters broad and must carry a particular load. In case of this carrier, the load should be around  30000 tons. If this turns out not to be possible, then an additional cylindrical hull in the center between the two sub hulls could be added to the design configuration. This would be called a trimaran. In any case, this kind of vessel can be constructed given the appropriate number of sub-hulls. But, I have stuck to this simpler design with only two sub-hulls, because I think this is technically possible.

Another drawback is that the draft of the carrier is every deep. The draft of 16 meters is larger than the draft from the much larger Nimitz aircraft carrier (12.5m). But, you don't really want to bring a carrier through shallow waters? So this is of no primary concern. 

This design has several advantages that are relevant to the aircraft carrier. 

You could think of it as a stealth design. I has very few surfaces and angles pointing up. If the side line were linearly extended, then radar signals coming from the side would be reflected into the water. The same could be done for the front and the back. The flight deck itself is mostly even. The greatest reflectors are the aircraft themselves. But, as we know, preferably only very few aircraft will be parked there. Otherwise the flight deck is pretty much a flat plane, which does not reflect radar back to its source. 

The main advantage is a very stable platform even in rough seas. The bulk of the displacement necessary for keeping the ship afloat is located beneath the waves in the tube like hulls. These hulls are is less affected by wave action. Wave excitation drops exponentially as depth increases (Deeply submerged submarines are normally not affected by wave action at all). The trim of the ship can easily be provided within the two sub-hulls. The technical problem is to automatically stabilize a cylindrical hull at around 13 meters below the sea level. This problem is solved on regular submarines; it is solved by using ballast tanks within each sub-hull. The tanks are placed in the front, back as well as the center of the sub-hull.  Water is introduced into said tanks or pressed out of them, in order to keep the sub-hulls at a particular depth below the sea level. Furthermore, dynamic trimming can be accomplished using foreplanes. As long as the distance between the top and bottom of a wave doesn't exceed 10 meters, the proper ship hull is not even affected by waves. The control of the depth of each sub-hull should be like a soft feather, as long as the wave amplitude and therefore the pressure amplitude below water does not exceed +-5 meters. Adjusting the foreplane rudders should suffice. Any displacement stronger than that should be countered with increased strength. For example, if the additional water level starts to plundge the proper hull of the ship into water, then water should be pumped out of the trim cells at maximum speed. At the same time, the large carrier hull automatically increases the lift dramatically if it is plunged into water. 

Secondly, the flight deck is placed roughly 20 meters above the sea water. This give the plane going over the sky ramp additional time to accelerate to its minimum speed for rising into the air.

Thirdly, the cross section area of the carrier below the sea level is minimized. The cross section is largely defined by the cross section of the cylindrical sub halls. Consequently, the drag of the carrier is reduced. The shape of the sub-hulls is optimized for underwater propulsion. So the design principles known from submarine designs can be incorporated here. A reduced drag reduces the fuel consumption and increases the top speed of the carrier.

Now, let's turn to the sub-hulls:

These two cylindrical tubes have a diameter of 12m and a length of 200m. It can be easily shown that these cylindrical tubes provide a lift well above to 40000 tons of displacement. Maybe 40000 tons is overly optimistic and the fully loaded carrier may weigh a lot more. In this case the radius of the tubes must be increased correspondingly. 

Please also note that the cross section of the tubes is slightly larger than the cross section of an astute class submarine (12 m vs. 11.3m) und much larger than the French barracuda class submarine (8m). The tube is approximately twice as long as an astute class submarine (200 m vs. 97 m) or French barracude (99.4 m) . The cylindrical tube is an extremely simple and very stable design. The end of the tube should be fitted with a spherical nose in order to lower the drag; it could be made to be thicker in the middle and gradually become narrower to its ends. This would facilitate implementing a 5*5 m² elevator platform for transporting people and weapons in and out of the tubular hull. This is what it could basically look like:

Of course this is only to illustrate the shape of the underwater tubes. The top of the ship should be a flight deck as illustrated above. 
The tube does not represent a full blown sub and costs much less. For example, no special air control system must be provided. A single "snorkel" at the front leads into the proper ship hull all the way up to the flight deck. The end of the tube is directed into the direction of travel of the ship. An "escape tube" is located at the back of the tube and leads to the flight deck and points to the back of the ship. Simple electrical ventilators blow air into the escape tube and out of the intake tube, thereby providing fresh air circulation within each tube. 

The propulsion gear within the tube is supposed to "just work". Major maintenance requires taking the tube off of the ship in a ship dock. Special crew member may enter the sub-hull in case of malfunctions. The crew is not expected to repair anything but to merely switch off malfunctioning machines and switch on safety replacements. 

The tubes house the propulsion system of the carrier. It is extremely difficult to repair or service the propulsion system, while on duty. Therefore, the most important aspect of the design is reliability, redundancy and very long service intervals. Attempts to increase the performance of the propulsion system at the cost of reliability should be rejected. The propulsion system should just work. That is more important than anything else.
Both sub-hulls are connected to one propeller or pump jet, which drives the aircraft carrier. The carrier goes into a left turn by increasing the speed of the right propeller compared to the left propeller. The right turn is accomplished in the same manner by juxtaposing left and right. This is a very simple and straight forward approach. It has the additional advantage that the drag is not increased by turning a rudder in the water. However, the maneuverability is not very high. This is no real drawback for an aircraft carrier. 

A standard synchronous electrical motor should be used for driving each propeller. These motors are widely used in commercial as well as naval shipping. Consequently, they are very reliable and ready off the shelf. They have several additional advantages: They provide a high torque at low revolution speeds. Consequently, large propellers can be used that turn slow. This reduces the noise signature of the propellers. Finally, the electrical motors themselves are very quiet. 

The permasyn motors provided by Siemens are a good example for suitable electrical motors:

One electrical motor is provided in each tube. If one motor malfunctions then a gear box directly connects the propeller with a gas turbine or diesel engine.

The permasyn motor must be provided with electrical energy. There are three possible solutions. The cheapest solution would be to run several diesel engines within the tube. The only technical problem would be to provide sufficient fresh air to the engines. However, this means that large amounts of Diesel fuel must be carried, which would limit the operational range of the ship or would require refueling very often. 

Preferably, the electrical energy could be provided by a nuclear reactor. Nuclear reactors are designed to run for a very long life time. Reliability is of utmost concern in the design of such a reactor. Therefore, a nuclear reactor is a good choice for a carrier. Additionally, a huge amount of electrical energy can be generated with a very small amount of fuel. The operating range is not limited due to the limited amount of fuel, since the reactor can run for years. However, the huge price and danger of radioactive poisoning of the crew is the main drawback of the nuclear reactor.

Since the sub hulls are separated from the proper ship hull, the problems of protecting the crew against radioactivity is greatly diminished. Nevertheless, the reactor proper is placed into a containment structure. The nuclear reactor is cooled using the sea water as cooling agent for the secondary water cycle. The reactor is set up to provide a constant output of electrical energy. If too much electrical energy is created, then it may simply dissipate. Fuel efficiency is not important in a nuclear reactor, which may run for years non-stop without replacing the nuclear fuel. Consequently, the control system of the reactor can be simplified, thereby increasing its reliability and stability of the reactor. If the pressure within the reactor exceeds a predefined threshold or some other critical state occurs, the nuclear chain reaction is automatically stopped. The residual heat due to the residual radioactivity of the nuclear fuel is still used for generating electricity and driving the cooling pumps for cooling the water. In this way, the heat and pressure within the containment structure can be reduced in a controlled fashion. A Fukushima type event is highly unlikely, because cooling water is readily available. The carrier must return into a dock for repair after such an event. The crew is not expected to service or repair the nuclear reactor. 

I would like to put the salt water used for cooling the secondary water cycle to a different use. Usually, heat energy just dissipates, the warm water is simply let out into the ocean. I would like to use this cooling cycle in order to generate desalinated water from sea water. The desalination should be achieved by evaporating the sea water and collecting the condensate from the steam. The design should be extremely reliable and simple. The desalination process would merely get the preheated salt water output from the tertiary cooling system of the nuclear reactor. A very simple and very reliable electrically driven boiler would evaporate the salt water and a cooled condensation system - cooled with salt water from the exterior - would collect the distilled water. This distilled water can be used for almost everything on board, like washing, showering and cooking. The required mineral supply for the body - lacking in the distilled water - can be supplied by the food. Please note that there is no chance of radioactive poisoning of the water. The cooling salt water cools the water from the secondary cooling system of the reactor. The secondary cooling system is already chemically insulated from the primary cooling system of the reactor.

Since two nuclear reactors are provided, one in each sub-hull, the ship can keep on running on one nuclear reactor. In this case, the electrical energy from the nuclear reactor of one tube is used to run the electrical motors in both tubes. Furthermore, all appliances on the ship are run using electrical energy - except for the airplanes, that use jet fuel. 

The French Charles de Gaulles carrier and French nuclear submarines run on the Nuclear reactor K15, providing 150 MW of electrical power. The electrical power is equal to 150 MW. One such reactor would be more than enough for running the carrier. So the carrier can keep on operating, when running on a single K15 nuclear reactor.

So let us compare the present design with the French, British and American carriers:

The flight deck of the proposed large solution is rectangular and has a size of 70* 200 = 1400 m². This is almost exactly twice as large as the HMS Invincible.  The French Charles de Gaulle carrier is less wide 64 m but somewhat longer 261.5 m. The large width is mostly due to only a small section on the angled flight deck. The overall size of the flight deck of the Charles de Gaulle is approximately 14 000 m²; the flight deck of the HMS Queen Elizabeth is equal to approximately 20000 m², whereas the HMS Invincible's flight deck has a size of roughly  7200 m². The weight of each carrier roughly scales with the size of the flight deck. Queen Elizabeth: 65000/20000 = 3.25 t/m²; Charles de Gaulle 40500/14000 = 2.9 t/m². HMS Invincible 22000/7200 = 3.1 t/m². So a factor of 3 t/m² is realistic for the relationship between weight and size of the flight deck of an aircraft carrier. Interestingly, the Charles de Gaulle appears to be an especially light design, but maybe it is just not supposed to carry as much supplies, in particular jet fuel as the rival British designs.

Consequently, the assumption that this design will weigh in the order of 45000 tons is very realistic. How large are is the displacement going to have to be? 1 ton of water has a displacement of roughly 1 m³. So the tubular hulls must displace at least 22500 tons of water each such that the ship won't sink. The volume of a cylinder is pi*r²*l. r is the radius of the cylinder l is the length of the cylinder and pi is a number roughly equal to 3.14. We assumed the length = 200 m and r =6 m. Consequently, each cylinder has a displacement of  22600 tons. So the overall displacement is equal to 45200 t of water. We haven't even factored in the water displacement of the piers holding the rest of the hull 10 meters above water. If more water is displaced by the tubular hulls than the weight of the ship, then lift is created.

This rough calculation shows that the overall design parameters are realistic. Furthermore, the size of the sub-hulls gives you a lot of room for providing the necessary lift depending on the particular solution you arrive at. The present design most closely resembles the Charles de Gaulles in terms of size and weight. However, it can carry up to 67 aircraft. The Charles de Gaulles carries no more than 40 aircraft, mostly Rafale. The HMS queen Elizabeth also maxes out at about 40 aircraft. Unfortunately the British want to employ US stealth-trash fighters called F-35B. I would take the Charles de Gaulles any time over the HMS queen Elizabeth.

The only aircraft carrier with a greater number of aircraft is the Nimitz-Class, namely 85 compared to 67 of this design. However, this comes at a huge price. The Nimitz-Class is more than twice as heavy as this design, namely 102000 Tons compared to around  45000 Tons.

The French choice of relatively light weight but nevertheless extremely powerful nuclear reactors is very tempting. Since these reactors - 2 × K15 pressurised water reactors (PWR), 150 MW each - are fitted into submarines with less than half of the submerged displacement of the present carrier tubes, it may be safely assumed that far less than 50% of the carrier tubes are going to be used for housing the propulsion system. Therefore, half of the displacement offered by the carrier tubes can be used for carrying something else. Preferably, this empty space should be used for carrying jet fuel. The explosive liquid fuel can easily be pumped into the proper ship hull. Storing the fuel in the tube does not diminish its availability to the aircraft. The explosive fuel is stored in a large distance from the crew such that the crews safety is increased. Except for the explosive missiles and arms, hardly any explosive ordinance is stored in the proper ship hull, i.e. hull excluding the tubes. Since jet fuel is very heavy, 0.8 Kg/l compared to 1 Kg/l for water, the center of gravity is lowered, which in turn stabilizes the carrier in the water and reduced the chance of capsizing. 

The amount of jet fuel that can be loaded into the tubes is not limited by the available space, but it is limited by maximum lift that the tubes can provide for the aircraft carrier. Consequently, much space remains available within each tube. This additional space should be used for storing missiles and bombs for the aircraft. Again, the advantage is that dangerous and heavy ordnance is stored in one location, which is separated from the crew. In order to have access to the weapons, armament crew members step into the arms elevator connecting the supply deck with the respective tube.

The tubes are also used for trimming the carrier and for providing a stable platform for the aircraft. The trimming should be performed completely automatically. No crew member should be required to take care of the trimming of the carrier. For sure, the crew should try to distribute heavy weights evenly across the carrier. But due to the automatic trimming system, this is no longer a prime concern. Again, the primary tools for achieving this are known from conventional submarines and there are automated solutions available. Additionally, the heaviest equipment is already stored in the tubes, in particular the jet fuel and the armament. The jet fuel itself must be used for trimming the carrier.

Finally, acoustic sensors should be provided at the bottom of the cylindrical tubes in order to assess the depth of the ocean. But, the sensors may also be used if possible as pressure sensors. The measured pressure under the vessel is a gauge for the depth below the sea level. The precise position of the carrier is known using GPS. Conventional sea maps provide the information about the sea depths. But, if one of these systems fails or the carrier is moving across "unchartered area", then these simple sonars could become very helpful. 

What is the greatest threat for such a carrier design? Well, let me say, that unless the sub-hulls - placed 10 m below the sea level are hit, the carrier is not going to sink. The sub-hulls have to be hit in order to truly sink the carrier. So no rocket and no bomb can sink the carrier that doesn't hit the submerged cylindrical hulls. Bombs may devastate the flight deck and kill hundreds of people, but unless the carrier hull proper is separated from the sub-hulls, the carrier wont sink. The bridge carrying the carrier proper is 200 m long, You can shoot holes into this bridge structure, but that won't flood the carrier with water and it wont kill a single crew member. If the bridge breaks, then the carrier hull proper will drop onto the sea. Even if it didn't sink, the carrier would be a sitting duck, waiting for the final kill. But, you would probably need several rocket hits on the 200 m long bridge in order to completely break the bridge.

The greatest threat for the carrier are torpedoes that hit one of the sub-hulls, in particular close to the screw. But being hit below water near the screw is also the greatest threat to a regular carrier or any kind of ship. Even, if the carrier wouldn't sink, it would be left unmaneuverable. So a good towed sonar should be implemented that monitors the waters behind the carrier. Due to the relatively loud screw, the ship is practically deaf in this direction, unless it uses a towed sonar. A state of the art decoy system - towed decoys or active acoustic decoys resembling small torpedoes - should protect the carrier against torpedo hits. Helicopters should be used to hunt down the enemy submarine launching torpedoes. The carrier must be accompanied by Frigates, which are specialized in hunting down submarines using helicopters.

Since enemy destroyers will most likely not be able to come close to the carrier, they can launch torpedoes or long range guided missiles against the carrier. The defense against torpedoes has already been described. So the second biggest threat are long range missiles, usually radar guided naval cruise missiles. They can inflict considerable damage, destroy the flight deck or destroy the bridge or flight control tower. This would render the carrier useless. It could no longer maneuver (destroyed bridge) or launch or land aircraft (destroyed flight control tower and runway) The proper defense against long range radar guided cruise missiles are short range, highly maneuverable infrared guided missiles. Additionally, the carriers radar system could be used to jam the active radar of the approaching cruise missile. But a semi-smart missile using GPS-guidance or home-on-jam technology won't be completely fooled. So, the short range rocket defense is the best bet. 

The Euro carrier's SAM air defense system is the (American/German) RIM-116 Rolling Airframe Missile (RAM):

Several batteries are placed around the flight deck. This defense system is operated from the bridge of the carrier. The range of these missiles is around 5–8 km. Future missile launchers may utilize the new LFK NG:

The first line of defense against surface enemy threats on a carrier are supreme surveillance and a quick reaction force of aircraft, which attacks enemy ships before the come into the range of the carrier. Furthermore, the carrier is protected by a fleet of at least 4 warships, which protect it from direct attacks. A submarine can also be used for protection against enemy submarines. But, if the sonar suite in the sub-hulls of the carrier is sufficient enough, an attack submarine may not be necessary for protection. 

What about stealth? This is the buzz word that has been used for generating lot's of revenue for Lockheed Martin who are trying to sell their crap-stealth designs such as the F-35 using lots of buzz words. But, don't waste your money on stealth when designing an aircraft carrier. A carrier is a big bazooka and any semi-smart enemy is going to be able to detect it. If you can incorporate stealth measures without adding to the complexity, cost and reliability, then do it. An example is the use of the heated sea water for generating drinking water. It is energy efficient, because it uses the dissipated heat from the reactor. It is also stealthy because it reduces the under water heat signature, because less hot water is dissipated into the ocean. That's nice, but it's not very important. The two nuclear reactors provide more than enough energy. Using the preheated energy means that only a single water intake and outtake have to be designed in the sub. So this is more about reducing complexity. The reduced heat signature is irrelevant, because you can use radar or sonar to easily detect the carrier from a long distance.

The basic design principles for all the equipment in the sub-hulls of the carrier are reliability and long service intervals. So reliability and simplicity should always be chosen above complexity and efficiency. The crew is not expected to repair gear in the sub hulls. Noone is expected to work there on a regular basis. If something malfunctions, then someone may enter the hull, turn off the malfunctioning machinery and turn on the safety replacement.

Since a carrier is only the main part of a battle fleet, I would like to say a thing or two about the submarine that protects the carrier against enemy submarines. Now a submarine is a stealth weapon and its effectivity and survivability depend almost exclusively on stealth. So don't compromise stealth when designing a sub. Stealth means that the sub must be small and extremely quiet.

The best possible protection would probably consist of designing unmanned submerged vehicles. They should run on electrical motors alone. Their batteries can be recharged using the electricity from the carrier. They should be connected to the carrier via a very long optical cable. So they can loiter for a long time submerged and detect enemy submarines. Last but not least, unmanned submarines that are wire guided are much cheaper than regular submarines used for the task. So these unmanned submarines are basically torpedoes designed for endurance - not speed - and with a top notch passive sonar. If the unmanned vehicle detects an enemy submarine, then a torpedo is launched from the carrier. The torpedo gets its target coordinates from the unmanned submarine. This solution would be cheaper and a lot stealthier and more efficient than the use of full blown submarines for protecting the carrier.

Conventionally, the US uses nuclear subs in order protect its carrier fleet. Nuclear subs are used because of their long endurance and high speed. They can remain submerged for several months. Nevertheless, people need to eat and catch some fresh air once in a while. Furthermore, they need to get out of the sub for psychological reasons. Therefore, an endurance beyond 3 months has no practical meaning. Conventional Diesel-electric subs have such an endurance. The stealthies submarines are the 212's: 

However, the US has chosen to sacrifice the stealth of its subs in favor of endurance and speed. Why is that so? Well, a nuclear reactor is just way louder than an electrical motor. Therefore, Diesel-electric subs are much stealthier than nuclear subs. They are also a lot cheaper. But what about their limited range? Well this is my proposal:

Throw out the Diesel engine from the diesel-electric sub and turn it into an all electric sub. The Diesel is the loudest part of the sub. So this improves its stealth and reduces its size and complexity. Add some more batteries to the sub in order to increase its range and endurance. If it has an endurance of 1 week running on batteries, then that's fine. If you want a longer endurance, then use fuel cells for generating electricity, like in the U212s. Let the sub surface beneath the hulls of the carrier. In this position the sub is undetectable from above .Recharge the submarine's batteries by lowering an electrical line from the carrier into the sub. Finished. 

Both proposals give you long range submarine protection using cheaper and more stealthy all-electric submarines.

The concept of distributing energy from the nuclear powered carrier to the other vessels of the carrier fleet could be extended to these vessels. Since most modern frigates and destroyers run on Diesel-Electric engines, electric power for stealth, Diesel for endurance. Some of them can run additionally on gas turbines for short term fast speeds. This principle is called: Combined diesel-electric and gas (CODLAG). 

So the bottle neck of a carrier fleet in terms of endurance will always be Diesel, Jet Fuel, water and Food. The carrier fleet must be supplied with these products on a regular basis by support ships. So there is no use in extending the durability of the carrier ad infinitum without increasing the range of the supporting fleet. Since conventional frigates are much smaller than a carrier, they need much less Diesel for an extended range. However, the range could be extended by running all the conventional electrical appliances on the frigates using fuel cells - the same technology used on the U212. Creating Oxygen and Hydrogen could be performed on the carrier using its excessive nuclear energy. The hydrogen and oxygen would have to produced on the carrier using the well known principle of electrolysis. The surrounding ships could also be supplied with distilled water from the carrier. Preferably, the liquid and gas is transferred using appropriate hoses for oxygen, hydrogen and distilled water.  In this way, the massive 2*150 MW nuclear reactors could be put to good use. 

By the way, the CODLAG principle could also be implemented on the carrier. In this case, the gas turbine for directly powering the propellers via a gear box would be the steam turbine of the nuclear power plant. In my opinion, this would be too complex and prone to error in the long run. In my opinion, the solution using electrical engines is simpler and more reliable in the long run. Short term use of a mechanical gear box linking the steam turbine to the propeller for boosting the top speed of the carrier for a relatively short period of time is a smart idea. In case of emergency, the carrier would have enough energy and speed to run away from an enemy or keep the enemy at a safe distance. So the gear box would only be used for short top speed runs or in case the electrical motor is out of order, i.e. as a temporary replacement.

1 Kommentar:

  1. Very interesting stuff.

    Never having worked on or around aircraft carriers I do nevertheless have some friendly criticism:

    1. I'm pretty sure the strange deck layouts developed over the years for the USN super-carriers is primarily intended to maximize sortie rates, not fulfill some other design requirement. They have the most experience in Carrier operations and I really doubt a single runway 2 elevator system can generate higher sortie rates. The angled flight deck was a very important development in carrier operations.

    2. Another important reason the USN uses Catapults is they allow you to launch aircraft that would otherwise be too heavy because they are so loaded with weapons and other payloads. A ski jump limits combat load and endurance.

    3. Your typical Typhoon combat load sounds great but per point 2 it is probably unrealistic. I would have to check if that load-out is possible with on the Typhoon hard-points. Also most combat loads include external fuel tanks, which extend range/endurance at the cost of weapons/non-weapon pods.

    4. I believe having all above flight deck structures on the starboard side is accepted as crucial for flight ops safety.

    5. Arming and fueling aircraft below decks is expressly forbidden in the USN (I assume in other navies as well) because it is exponentially more dangerous in an enclosed space than on the open flight deck.

    6. Your design seems way to cramped, especially in the hangar. Just cause it "fits" doesn't mean it is a sufficient space to work in. For one, there is not enough room to perform significant maintenance on planes in the hangar. Imagine trying to remove an engine or other large component from a plane packed in that parking lot! Then you have to move the removed parts to a space to work on them; you need workshop space. Also, I wouldn't want to try moving the planes around in that hangar, even with cool mag-lev toys. A single track in the aisle would severely limit your flexibility as two trolleys could never move past each other. So they would effectively have to wait for each other in various situations.

    7. In peacetime operations you will need more than two AEW and Helos, not to mention war-time demands. Assuming you can operate two AEW platforms for 12 hours each perpetually is a recipe for disaster. They will have problems and need maintenance, sometimes these problems will develop while one is in the air, it will have to land (if it even survives) and the second platform may not be available for a long time due to it's own maintenance needs. In addition you need to be able to fit both AEW and Helos in the hangar so they can be stored and maintained, the flight deck will not cut it for either.

    8. Making the escorts dependent on the Carrier for their basic needs like power/propulsion and water is very limiting. It means both that they can only operate in close proximity to such a mother ship and if their mother ship is destroyed they are sitting ducks with a limited water supply.

    9. I can't comment on most of the intriguing engineering you have proposed but I think the design suffers from waaay too much abstraction. The scientific principles very well may make it possible to build, but without loads of design input from the operational side you will end up with a vessel that doesn't do it's job well. In my experience this is a major pitfall in the engineering world.