REP development: from devs to sim pilots

I want to explain a little bit how REP is developed and what we plan for the next months.
We are at something like the 50-60% of the REP development and we have written more than 12.000 lines of code.
It’s a lot of time that we started this project and so I think you should know why you have to wait so much for it to be ready.

The REP development

As I said in my other posts, REP is not only a plugin but a set of flight dynamics, sounds and, of course, C++ code.
In the past months we created a robust codebase that, if correctly configured, can simulate almost any mechanical part of any aircraft.
Basing on our personal experience as developers and real life pilots, our efforts were spent to provide a deeply modular code structure made of something like LEGO® bricks. We can now add, remove and modify parts of the system on the fly.
Also, a modular system allows us to easily test every component outside X-Plane, using a bunch of automated tests that ensure that everything is working as expected.
Our plan is to have a first version of the software that can be upgraded fast, adding more bricks in order to provide more features.

No aircraft is like another

There’s no way to get an accurate simulation of every airplane with just one software without a very precise configuration.
Let’s be clear: REP will work with one plane at a time. It means that we will release REP for, let’s say, the Cessna 172, then we will release (after few months) the PA28 and so on.
This means that REP will not automatically work with every airplane that you load in the sim because the sim itself does not provide enough information about the airplane you are using.
For example, if the airplane is powered with a turbocharged engine, wich kind of turbocharger it is? How does its wastegate work? Simply we don’t get this information in the sim so we need to configure the systems for each plane we want to fly with REP.
The need for a very deep system configuration requires a lot of attention to details thus it take a lot of time.


  • We’re working very hard
  • Releasing the first aircraft will take much time
  • Releasing the other aircrafts will take much less time

    See you soon!

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    REP: Engine temperature management

    While talking to a friend about REP, he asked me about how the engine temperature and cooling would be modelled. I replied that the engine management will track the engine temperatures and simulate their impact on the engine behavior (and failures). This will make the pilot motivated to take care of his engine.
    Eventually, his point was about how the shock cooling is simulated in REP.

    There are two theories about engine cooling. Someone says that the shock cooling actually does not exists. Someone else says that it’s an important factor to keep in mind when it comes down to correct engine management.

    Let’s start with a number: 30.
    30°F/min is more or less the temperature difference at wich, in theory, a cylinder should start cracking. So, if you follow the first theory, you must be very careful when flying because that temperature ratio is not that hard to reach sometimes. But what about the engine shut down?
    When you shut down the engine at the end of each flight, for few seconds you get a much higher ratio than that but no cylinder cracks.
    So which theory is right? You can find a very interesting article about this topic on AVweb.

    In a Cessna 210 the engine temperature is a key factor

    That said, REP will work in between the two theories as I think it better fits my own real flight experience.
    You will mainly have to follow the rule that says to keep the needles in the green arc. So, for example, after starting up your engine, do not boost up your RPM if the Oil Temperature, the Oil Pressure or the CHT are under the green arc.
    With a modern Continental or Lycoming engine, if you fly with this rule in mind you will hardly encounter a problem when flying.
    If you won’t follow this rule, your flight would end up before takeoff as a failure would be very likely to occur.

    The engine temperature affects the startup behavior too. For example, a cool engine will require some priming before startup while a warm engine will be more prone to be flooded by fuel.

    That’s it! The main mission of REP, apart having fun, is learning more about our planes, right?

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    REP: Landing gear and brakes

    The Reality Expansion Pack is going to provide many features to X-Plane 10. In the other posts I’ve told you about the engine. Since REP goes a long way over the “simple” and “uncomplex” engine simulation, now I want to tell you more about some of the other systems.

    The landing gear

    The landing gear is simulated not only through its physics but also through a variety of sounds.
    When you touch down you hear wich tire touches first thanks to the provided stereo sounds.
    Also, a landing gear may affects the wind sounds. On the C210 you will hear the difference between fliying with the gear up rather than the gear down.

    A Cessna 210M retracting the landing gear

    A Cessna 210M retracting the landing gear

    Also remember that, on some planes, actuating the landing gear may affect the drag. On the C210M, for example, the gear valves open while operating the landing gear. Also, the landing gear rotates while being retracted or extended. This creates a lot of drag while the landing gear is going up or down so you have to keep a little bit of speed after takeoff before retracting the landing gear.
    The drag feeling is even more strong on a plane like the C172RG where you don’t have a powerful engine.

    The braking system

    Speaking of the landing gear, there’s also something else to say about it: usually it’s provided with a braking system.
    The brakes are modelled so the warmer they are, the less they brake. Also, you can hear them squeaking when at low speeds.
    The best way to brake on a General Aviation airplane is to press the brakes for few seconds then release them. After few seconds repeat this operation. This will allow the brakes to cool down.
    Sometimes, if you have enough runway available, you may also let the plane roll and speed down by itself.

    The latest releases of X-Plane 10 now support the spring loaded nosewheel steering. This really enhances the realism of the ground behavior of many Cessnas, such the C210, requiring to use the differential brakes to steer the plane while on ground.

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    HeadShake v1.4 available for download

    A new version of HeadShake is out. This is a bug fix version.


    • If you banked the plane 90° and then shacked the stick to pull Gs in both up and down direction, the look may lock down to the wrong position.
    • The Mac users may have experienced some issues while saving their settings as the preferences file was not saved in the correct folder.

    Mac users please note that, since the preferences were saved in the wrong folder, with the version 1.4 you will experience a preferences reset at the first X-Plane run. Your preferences will then be saved as usual.

    You can find the download page here: HeadShake Features and Download

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    REP: Every startup is different

    I was about to write a post about the oil system but then I stopped and decided to show you something more about the startup procedure simulated in REP.
    In the last days we worked on the startup and shutdown dynamics once more to improve their physics.

    The priming in REP

    I’ve already wrote something about priming in my last post.
    In the video at the bottom of the post you can see (and hear) how the new physics of REP affects X-Plane 10 during the startup and shutdown of the engine.
    Please notice that the first priming is longer than the next ones. Since the fuel lines are empty at first, the first priming needs to be longer than the others to fill them. Then, if you shut down the engine when it’s still cold, you will need to prime it again but less than the first time since the fuel lines are already filled with fuel.
    If the engine is warm you will need a very little priming before cranking the engine.

    The fuselage vibrations

    When the engine is vibrating at startup and shutdown, it can reach the resonance frequency of the fuselage. It means that it is shaking at a specific frequency that propagates and amplifies through the fuselage. This same behavior is simulated in REP. In the video you can hear the shaking sounds more clearly at shutdown.
    Also, if you are using HeadShake you will hit the maximum realism as the fuselage is really shaken up. ;-)

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