This was posted in the org by ramzzess.

https://forums.x-plane.org/index.php?/forums/topic/326186-flightfactor-777-engine-expansion/#comment-2868707

FlightFactor has always had the policy of produce payware upgrades and free updates. The choice between the former and the latter as well as the cost of the upgrades depends largely on the amount of work we have to put into producing and maintaining the new functionality. For example, adding a BBJ variant to an existing product, say the 777-200ER, would mean some 3d work from our artists and some administrative stuff to produce an update, therefore such a product would come as a free update to some existing packages. On the other hand, say the 777-300ER is much more than 3D. It is different interiors, aerodynamics, performance and engines,  some difference in systems separate packages etc. therefore, such a product will be an upgrade. Our general policy is to make the upgrades much cheaper than the base product and give you guys a large choice so each can pay only for what he needs. 
You are all probably are aware of the fact that FlightFactor has been moving slowly buy steadily away from XPs built in stuff and building more and more system from the ground up. We have long ago moved to using our own aircraft systems, our own sounds, visuals and an input system. A few months ago I have finally been able to produce a working standalone engine model and v28 of the 777 was shipped with a GE engine where the thrust is fully calculated by us. This has allowed for several things: 
•    very precise start and shutdown sequences
•    correct temperature 
•    very precise control over engine speeds 
•    enroute performance within 1% of N1 to the manual (just set the speed, altitude and see N1 will be exactly like in LRC)
•    climb and descent performance without 3% of the manual
In the last 4 weeks I have been personally working on the next stages of this endeavor and have built my own drag model (quite close to Austin's) but which given us even more control and ability to make the airplane fly closer to reality.
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--next section is for those who want more details  
The next stage is more engine types, and here we come to a dilemma, a lot of 777 engines are EPR (engine pressure ratio) controlled instead of N1. Actually,  the engine is controlled by fuel flow, but that is almost the same as controlling N2 and as N2 and N1 are basically linked independent (almost) of environment it is the same as controlling N1 directly. Thus, a leap from an N1-engine to an EPR-engine is much more complicated. EPR was once introduced as a controlling parameter of jet engines because of its high correlation with thrust. The idea was, that EPR is almost the same as thrust. So constant EPR will give constant thrust. While that was "kind off" correct for a 70s pure jet it is not so for more modern high bypass ratio turbofan. The EPR is PW and RR engines used on the 777s over the years is a "mystical" parameter highly non-correlated with anything. This is not only due to the hi bypass ratio of these engines but also due to the fact that different engines measure EPR in different places. Thus, coming up with an EPR model for an engine is no easy task, but it has been done! We now have the ability to produce engines with EPR with 1% of performance charts just like N1. 
You can read more details about the tests we perform in the performance pdfs provided with the model.
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So with all that said, we are really looking forward to producing many of the possible engine variances in the 777 family, hint, historically 18 different engines have been mounted on 777s which makes for 27 fuselage-engine combination. Each one we make, and I am not promising anything, will require in-depth tunning and rigorous testing to get to those precents. 
As currently the only model available is 777-200ER with a GE90-90B the first engines to be added will be PW 4090. We will then continue with other types including RR Trent of course.
As an expansion of our upgrade policy we shall introduce an Engine Expansion - a separate product for the 777 family which will give the user a "key" for all available engine for all available models of the 777, including those that have not been produced yet. This means that once you have the EE pack, you are getting all available engines as soon as we ship them for all 777 extension. So get the EE pack now will only add the PW4090 engine to your 777-200ER, but as soon we ship the RR engine for the 777-200ER you get it for free, and when you buy the, still non-existent, 777-300ER model you shall get all available engine for that model too. Basically its a once in a lifetime purchase for all possible engines.
I can't personally promise you all 27 engines will be made, but we do plan to make quite a few.

 

 

Called Engine Engineering 🙂