If the work on a new plane is going on (you’ll discover more about this in the next weeks), it does not mean we cannot improve what we already have.
REP 4.2.0 hits stable release with an interesting set of features.
Fine-grained Fuel Metering System
The fuel metering system has been totally rewritten. There were few things I didn’t like and a simple update wouldn’t fit the needs. So I decided to redo it from scratch. This does not happen often in REP but when you have to, you have to.
The main reason for this was to have a perfect relation between fuel flow and power output. But this means we have opened a new path for features!
In fact, all the engines have now a perfect representation of their own fuel metering system.
TCM System
The Baron and the Bonanza use this system.
This fuel injection system is as simple as it can be. That is, the throttle position controls the amount of fuel that goes into the engine. It does not compensate for altitude or density changes, nor does it correct for MAP.
It’s then really important to properly lean the mixture, especially at altitude.
TCM Turbocharged System
The Centurion uses this system.
This fuel injection system is almost as simple as it can be, like the one described in the paragraph above. That is, the throttle position controls the amount of fuel that goes into the engine. It does not compensate for altitude but it does compensate for MAP.
Since the engine is turbocharged, only minor mixture corrections are required during flight:
- Mixture full rich for takeoff
- Lean to 120pph during the climb
- Lean to the required cruise power
- Mixture full rich for landing
Bendix RSA System
The Cessna 172 and the Super Cub use this system.
This fuel injection system is provided with a Venturi that senses the amount of air that goes to the engine and so regulates the fuel flow accordingly.
With altitude, the air density reduces more than the fuel density. So this metering system still requires the pilot to lean the mixture at high-density altitude.
Lycoming Carburetor
The SF.260 use this system.
The carburetor was already well modeled. But it has been improved further with this update.
The Carburetor has a Venturi that senses the amount of air that goes to the engine and so regulates the fuel flow accordingly. As stated for the Bendix RSA System, with altitude the air density reduces more than the fuel density. So this metering system still requires the pilot to lean the mixture at high-density altitude.
Tuned Fuel Injectors
The cylinders and air induction positions lead to a different amount of air being sucked in each cylinder for a given throttle position.
That is, more air goes into the #1 and #2 cylinders than in #3 and #4. In a 6 cylinders engine, the spread between #1 and #6 is quite wide.
Factory fuel injectors deliver the same amount of fuel to each cylinder. That is, cylinder #1 runs leaner than #2. The richer cylinder is usually #5 or #6.
This spread affects the engine performance, especially when running lean of peak with only one EGT probe. Usually, leaning LOP for the hottest cylinder (#5 or #6 in a 6 cylinders, #3 or #4 in a 4 cylinders) means being widely LOP for the #1 cylinder, thus experiencing a loss of power together with a rough running engine.
In the Maintenance Report, it is possible to replace the factory injectors with tuned ones, made to properly release the correct amount of fuel based on the cylinder number. Tuned injectors allow for:
- Smoother LOP operations
- Fewer vibrations
- Lower fuel burn of about 1 GPH
Pimp up your plane even more!
You can now replace your exhaust system with a tuned one.
The main goal of the Exhaust System is to emptying each cylinder of spent exhaust gases.
Factory exhausts usually aren’t length-tuned. That is, the length from the cylinder’s outlet valve to the end of the exhaust is not the same for each exhaust tube. This causes the formation of shock waves when the exhaust gases from one cylinder hit those from another cylinder. That is, the emptying effect is lower than desired.
Using the Maintenance Report it is possible to replace the factory exhausts with tuned ones. Tuned exhausts allow for:
- ~10% more power
- Fewer vibrations
- Lower fuel burn
- Lower CHTs
Improved Manifold Pressure behavior
There was an imperfection in the MAP behavior. That is, at low power, decreasing the prop RPM did not raise the MAP enough. In some cases, there was no MAP rise at all!
Now, this has been ironed out. Even at low power, like during the engine run-up, decreasing the propeller RPM with the blue lever will cause the MAP to rise properly.
Automatic backup of the status files
All the status files are automatically backed up when they are modified.
You find the backups in the X-Plane output/preferences/REP folder, inside the subfolder of each aircraft.
What’s next?
The first REP turboprop is almost ready. It’s right behind the corner.
And we’re working on REP 4.3.0 as well, that will aim mainly to the Piper Super Cub. Finally, it will get an update, even tho it will be on SimCoders’ side only. More about this in the next weeks.