Thermodynamics – Engine, Weather and more

A big field of expertise, regarding the effects of heat and thermal transportation. These affect not only engines but also create our daily weather and determine the viscosity of fluids.
For War Thunder, two aspects are essential: Environment ambience and fossil heat emission.

In Arcade engine temperature does not matter.

Aircraft

Atmosphere

Altitude

Thermodynamics also determines air density. For a quick example. Rowing in a boat on the water is easy, each push with the paddle will also push the boat forward. The very same in air though will work too if one is fast enough. Although it is easier to do in the air than in water, the latter requires more strength.

Now aircraft do not use paddles; they utilise propellers which rely on the lift effect (also known as `dynamic buoyancy´) known from wings. None the less a propeller's blade working in a more viscous medium such as water will produce the same force at a lower RPM. For an aircraft using a propeller, this presents problems as with increased altitude the air pressure and henceforth air density drops. On 10 km (6 miles) the plane is confronted with about half of the air density compare to sea level.

Lowered air density affects the vehicle in three different manners.

1. Less air for the combustion or turbo-jet engine. Reducing the available power.
2. Reduced effectiveness of thrust. Aforementioned peddle example for propellers and a reduced thrust for jet engines, as mentioned in point 1.
3. Less drag. Resulting in improved thrust-to-drag ratio and theoretic better top-speed. Though this depends on the high altitude performance of each engine, see point 1.

Engine mechanics

Basic physics that relate to the thermodynamics of aircraft engines. Through the use of these physics, heat emission and the time limit before mechanical failure of the powerplant become far more detailed, while engine management becomes more flexible and adaptable to the conditions it is under (weather conditions, atmospheric conditions, operating conditions and others).

Pre 1.57 vs Post 1.5X

The main differences in the current physics implementation are as follows:

Engine heat emission

In the new thermodynamics model, heat emission is more dependent on the engine settings – the current engine power, supercharger setting, RPM and other factors.

The current implementation did not take most of these factors into account, so temperatures were not very affected by engine settings: for example, with the fall in manifold pressure and power upon ascent over critical altitude, the temperatures continued to rise. The new heat emission model will now take all these factors into account so that during flights higher than the crucial elevation for the engine, the reduced equilibrium temperatures allow for longer flight duration at higher altitudes than at lower ones.

Temperature

"Equilibrium temperature" is now determined by the balance between the radiated heat (the heat is radiated by radiators, the engine itself and the cowl, etc.) and the heat generated by an operating engine.

Depending on the position of the oil or air radiators, the radiator flaps, the amount of heat radiated will change. The modelling of the effectiveness of the radiators is more realistically – the main working area of the radiator flaps is set between 10% to 40% opening, so that any further opening of the radiator flaps only results in an insignificant "Equilibrium Temperature" reduction, but still provides a few more minutes of safe engine operation. It is generally enough to open the radiator flaps to 20-30%, as this will not cause a significant decrease in flight characteristics but will allow the use of the engine within a reasonable temperature setting.

The effectiveness of heat radiation depends on the weather conditions during the mission. Heat transfer with the environment is more effective in cold weather, so the radiator only is slightly opened. However, in a hot climate, the reverse is true so the radiator flaps should are opened more extensive than usual.

The speed of temperature change now depends on the difference between the current temperature and the “Equilibrium Temperature” under current engine settings: the greater the difference between temperatures, the more intensive the heat transfer is and the higher the speed that the temperature changes. Heat transfer characteristics of this is an advantage in aircraft engines – due to the difference in temperatures being higher when the engine settings are changed, the heat transfer is more intensive so that temperatures vary faster and these engines cool down and warm up quicker.

Preliminary warm-up

Preliminary engine warm-up when starting to play has been introduced to prevent having to wait for the engine to reach a safe takeoff temperature (the aircraft appears on the runway with engines that are already warmed up).

Time limits

The time limit for safe engine operation now depends on the current temperature setting.

What this means is that the temperature readings and indicators in every engine setting need to be monitored and the acceptable operational time should not be exceeded. The maximum setting may be used for fifteen to thirty minutes in the majority of aircraft, while the avaliable War Emergency Power setting can last between 5 to 15 minutes or less. If temperature limitations are ignored and the engine is significantly overheated, the operational time is reduced to a minimum, going down to as little as under 100 seconds.

Time is also a limiting factor at other settings too – the lower the power and heat emission of the engine the more prolonged the engine is usable under that setting. It is also possible to achieve longer operational times by setting up the engine by current conditions, by doing things such as fully opening the radiator flaps, it is possible to get another few minutes of operation under the War Emergency Power setting. The more the “Equilibrium Temperatures” are lowered, the more safe engine operation time is available.

Because of this, it is possible for the engine to operate safely in cold weather for a very long time even if the radiator flaps are only slightly open, wherein hot climates the flaps should be opened wider Under normal temperatures, it is possible to exchange drag created by fully opened radiator flaps for a longer time of operation

New display system

The new display system has changed the logic of the way that information about the current state of the engine is displayed. Because the operational time of the engine is now affected by heat balance and the current temperature, it was decided that the timer should no longer be used.

Now the remaining time of operation is shown by the colour of the temperature indicator: white indicates that the engine is operating normally, yellow signifies 5 to 10 minutes, orange 2 to 5 minutes, red – less than 2 minutes and flashing red is a warning that there is less than 1 minute remaining.

Recovery after an extended operating time

After the engine has been operating for an extended period, it requires time to restore the time limit fully.

Prolonged usage at high speeds means that the engine needs to be cooled and lower power settings should be used for a short while so that the engine can "rest". Generally, approximately half of the time limit of the required parameter is needed for full engine recovery (for example, when using WEP under automatic engine control for 5 minutes, it means that after reaching this limit, the aircraft should fly at 100% for around 2.5 minutes to recover all 5 minutes of the WEP limit).

Automatic radiator management

Automatic radiator management now monitors the engine setting and automatically selects a radiator flap position that ensures the optimal combination of cooling and minimal effect on flight characteristics.

The automatic management connected to engine control devices work alongside the engine controls – when the pilot sets the engine setting (by lowering or increasing the throttle), they also set the desired temperature, which is maintained by the automatic radiator management thermostats. In this way, the optimum flap position is maintained during level flight with constant power settings and speed. When the setting is changed to a more powerful one, the radiator flaps are fully closed while heating up to the new automatically set temperature, which serves to both speeds up warm-up time and decreases the drag of the plane, allowing for more snap acceleration. On the other hand, when the engine setting is changed to a less powerful one, the radiator flaps will open fully until the engine cools to a new "Equilibrium Temperature".

Engine damage from overheating

When the time limits are exceeded, the engine begins to lose power, the operation becomes unstable, revolutions fluctuate, and other issues can occur. However, even a damaged engine is savable if you react in time and change the setting to one that is less demanding. For example, such as setting the engine for minimum revolutions, 50% throttle and fully open radiators to cool the engine to a suitably low temperature (so that the temperature indicator shows that the minimum time limit has been restored where it stops blinking). These actions will prevent further damage to the engine and maintain partial engine performance which is enough to return to the airfield and even to be able to participate in aerial combat.

The possibility of saving the engine and its remaining power as well as the speed at which the engine accumulates damage depends on the degree of overheating. For instance, if the engine is heated to the boiling point of the coolant liquid, it will guarantee that the liquid form continues to be lost and vapour will be formed, leading to the inevitable death of the engine after the coolant liquid runs out. However, the damage that occurs as a result of exceeding time limits at a setting which uses a normal temperature will happen slowly and will provide enough time to cool and preserve the engine. The higher the temperatures at which exceeds the time limit, the faster the engine will become damaged and lose power.

Further adjustment of aircraft with new thermodynamics

The majority of aircraft currently use a general thermodynamic setting which is a conversion of temperature settings from the old (current) model, i.e. the temperatures and settings of the old implementation of thermodynamics are modified using general rules and templates that are appropriate for aircraft while retaining features of the old model.

For example, if the plane has not overheated under any of the settings, then the converted thermodynamics will also have relatively soft temperature settings and time limits, and if the aircraft had problems with overheating under the old model, then the temperature settings under the new model will also be more punishing.

In future, when implemented with the flight models, the temperature model will be applied by real-life data. Soon, it is planned to add separate controls for cooling systems (oil radiator and engine/water radiator). At the moment, both methods work together.

Ground vehicles

Thermodynamics as of Update 1.55 is not modelled for ground surfaces vehicles. Related modules such as radiators and ambience temperature have got no effect.