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.
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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REP: a new piston engine for X‑Plane 10

A piston engine is a very complex machine and no engine is equal to another one.
While having a talk with a mechanic, he told me that a Turbo Commander based at the local airport (powered with a carburated turbocharged engine) is so difficult to start up that if you use the checklist ad do exactly what they report you will end up flooding the engine. He also said that, after some experience, the pilot ended up with his custom startup checklist.

A photo of the Continental IO-520 simulated in REP taken from Wikipedia

The TSIO-520-R of the Cessna TC210M is not that difficult to manage but it has its own character, fully simulated by REP.
For example, we learned that it always require a little bit of priming, even when it’s warm. Of course, the priming should be more aggressive when it’s cold.
If you prime the engine correctly it will fire up in 2 or 3 prop revolutions.

Another thing that we learned about is the behavior induced by the position of the fuel pipelines above the cylinder heads.
As the pipelines are just above the cylinders, when you turn off the engine the cylinders’ heat warms up the fuel pipelines and transforms the fuel to vapour. This is called vapour lock and causes a lot of headaches to the pilot who wants to startup the engine after 10-15 minutes from the last shut down.
In that case the engine would fire up normally and then die because of the fuel vapour that suffocate the combustion process.
There are many different ways to solve the vapour lock problem, all involving the use of the electrical fuel pump to clear the fuel pipelines from any trace of vapour.
As an example, before starting the engine you may want to close the mixture and turn on the fuel pump for 30-40 secs. This will recirculate fresh air into the fuel pipelines, removing the vapour lock.
Another way is to inject a little bit of fuel in the cylinders using the fuel pump, then start the engine and turn on the pump for few seconds when the engine is firing. This will clear the fuel pipelines but, hey, you have to be very quick to turn on and then off the pump as soon as possible or you will flood the engine!

Speaking of electrical fuel pump, like many other Cessnas, when flying the C210 you should use it only for priming before startup. During the other phases of flight you are supposed not to use it.
If you turn on the pump when the engine is running at low RPMs, you will flood it. You hear it sputting and then the combustion starts to be non-optimal until the moment it dies.

The cylinders combustion process is simulated through their compression too. Specifically, since the TSIO-520-R is a turbosupercharged engine, its compression is 7.5:1, lower than its normally aspirated counterpart.
The cylinder compression causes the propeller to rotate around specific “detention points” in which the cylinder compression is in a stable position. In this video you can see an example of that.

Simulating an engine means simulating the proper thrust too. This is where REP provide the most to X-Plane. X-Plane, in fact, does not provide the correct power output in many cases.

Those of you that currently own the Carenado C210 may do a simple test:

  1. Load the plane
  2. Go to “Settings”, “Data input & output” and select “Engine power”, this will show a small box with the current engine power expressed in HP.
  3. Start the engine.
  4. Read the engine power at many different RPM and MAP settings.
  5. Check the power values against the performance tables provided with the aircraft.

The result of this test is that the default engine power is much overrated or underrated in all of those settings except the full throttle/full rpm setting, at which the engine erogates 310HP.
REP corrects this behavior and make sure that the engine always provides the correct output.

An engine simulated at this level of precision provides another very important feature: a correct fuel burning ratio.
I’ve personally tested that with REP the engine burns the correct amount of avgas at any altitude at any power setting!

A Turbocharger like the one simulated in REP

Now there is only one thing that I did not mention: the turbocharger.
It consists in a small turbine powered by the engine’s exhaust gas. The gas spins the turbine that sucks in fresh air from the other side and compress it, pushing it inside the engine.
This allow the engine to maintain its power at high altitude. The Continental TSIO-520-R can provide 310HP up to 20.000 feet.

A turbocharger has, anyway, its downsides. For example, if not driven by a wastegate it may blow up your engine if you go over its MAP limit (in this case 36.5 inHg).

The TSIO-520-R features an automatic waste gate that dumps the excess of compression to avoid an engine overboost.
The automatic wastegate also keeps your MAP constant! This is a very nice feature during climbs and descents.
You just set your climb power after takeoff and then the automatic wastegate does the rest keeping your settings.

This autowastegate is oil driven using the same oil that lubrificates the engine. It opens through a spring and closes thanks to the engine’s oil pression.
So, what happens when the oil is cold and not fluid? When you push the throttle the spring opens the waste gate and the MAP goes up very fast but then, when the gate should stop to avoid the engine overboost, the oil is not fluid enough to provide a fast reaction and so you would likely overboost the engine.

A tip to avoid this problem? Warm up your engine before takeoff!

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Introducing the Reality Expansion Pack

It’s been a while since I wrote my last post.
The last time, I told you that at we are working on something huge. So, now I can show you something of it.

What are you talking about?

The project is called Reality Expansion Pack, or REP, and it’s a piece of software made of code, airfoils and sounds.
It’s meant to enhance the X-Plane experience by introducing a more realistic behavior of many parts of the plane (so not only the engine).

Is it Accu-sim for X-Plane?

I want to be clear: even if it’s based on the same principle, this is not a clone of Accu-sim. You will find that something that Accu-sim has is not in REP (for now, at least) and that REP has some features that you won’t find in Accu-sim.

How does it work?

This software is meant to be distributed in specific packages targeted to simulate a specific plane. Each package simulates the correct behavior of the plane and its system under several different conditions.
Those packages, at the beginning, will not be a complete airplane but rather an expansion for planes already on the market.

Carenado (and so Alabeo) already gave us the permission to publish packages targeted to their planes.
We choose Carenado because of the high quality 3D models and sounds and for the variety of its fleet.

As an example, this is the list of some things (many others are still WIP) that the REP package for the Carenado’s Cessna TC210M adds to X-Plane:

  • Continental TSIO-520-R engine, together with its oil driven automatic wastegate turbosuperchager (you may want to read this)
  • Oil system and the oil viscosity
  • Vacuum system
  • Fuel system
  • Braking system
  • Extremely realistic, plugin driven flight dynamics
  • Plugin driven sounds

In the next days I will write a post for each point in the list (and the other features that I did not disclose today) to provide an in-depth explanation.

In the following video you can see a small example of how REP affects the engine and the sounds of the plane.

Ok, so where can I download it?

As I said, this is still a work in progress so the download is not yet available.
There is a big chance that the REP packages will be distributed as payware.

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HeadShake updates to v1.3 and opens to new developers

Few days ago, the guys from asked me to make the plugin more compatible with other addons. I think that’s a good idea beacause a better integration with other plugins (yeah, TrackIr too) is just a simple way to advertise X-Plane in the flight simulation world.

With v1.3, developers will benefit of some public datarefs that provide some useful data about the camera position calculated by HeadShake. All the public datarefs are published in the Dataref Eeditor plugin so you can easily see how they work.

These are the custom datarefs published by HeadShake:

Dataref Type Writable Description
simcoders/headshake/offset_x float no The X offset of the camera
simcoders/headshake/offset_y float no The Y offset of the camera
simcoders/headshake/offset_z float no The Z offset of the camera
simcoders/headshake/offset_yaw float no The camera yaw (0-360°)
simcoders/headshake/offset_pitch float no The camera pitch (0-360°)
simcoders/headshake/offset_roll float no The camera roll (0-360°)
simcoders/headshake/override int yes Set to 1 to pervent HeadShake to command the camera position. The plugin's public datarefs are still updated.

So, if you want to create your own camera plugin and benefit of the effects provided by HeadShake, just set the override dataref to 1, then read the camera offsets and use them in your own code.

That’s it!

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HeadShake 1.2 and some news

HeadShake 1.2

After a long time out of sight, the build of HeadShake 1.2 is ready. This is a bug fix release so do not expect new features in it.

This release is mainly related to solve two bugs reported in the last months by many users:

  1. After an hard landing, the view rotation could not be reset to zero.
  2. The camera position could not be reset at startup on some airplanes.

Thanks to the guys of x737project who were the firsts to report these issues and test the fixes.

What’s next?

As I’ve stated some months ago, I’m working on two big projects. One of them is quite half way from its first release and, I must say, it looks very good. All that I can say is that it’s about fuel metering systems, big bore Continentals engines, spark plugs, engine starters, vacuum pumps and all the other things that “live” on a real plane. ;-)

Did I mention that I’m a real fan of A2A?

See you soon!

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