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.

Fixes

  • 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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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 SimCoders.com 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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