Hello, all. I’m writing this topic to note two issues related to each other in this situation: an incorrect economical speed and an overspeed restriction limiting my airplane’s efficiency. For reference, I used the Embraer E175. Take a look at these two images:
I’ve circled important parameters I want you to focus on: ground speed and fuel remaining (endurance time). I could include altitude since there’s a change, but that’s not what I want to focus on.
If you take the ground speeds and multiply then by their respective fuel times, you’ll notice being at Mach.83 is more economical, maximizing my range. However, you see that big warning about overpseed? Well, that’s limiting my efficiency. Anyone who knows the economical cruise speed of an E175 knows that the speed I’ve shown is nowhere near the speed for a real life one.
I know Infinite Flight is striving for “realism,” but an issue like this isn’t really helping. I don’t want to get a violation on the Expert Server just because the point of efficiency lies beyond the real world speed limit. You could say fly on the casual server, but that’s not a productive solution at all because nothing gets done if you just deflect from the real problem here. Please address this. I’ve also noticed this on the 737 NGs, which upsets me becuase they’re the most “realistic” planes in IF (physics-wise with the least bugs) and their efficiency is just being limited on the basis of “realism” when that restriction holds no value considering the actual efficiency achievable in IF.
If you’ve made it to the end of this, congratulations! I don’t know of any appropriate solutions considering what the community prioritizes and what the devs prioritize. I’m looking for a unique answer as to what to do with a flight model issue such as this one. I keep hearing IF uses real world data in their aircraft and releases tutorials using real world data, but then testing on my own, I discover divergence, making me question implementation of data and whether the tutorials are following the simulator aircraft or the real one. It can’t be both. One becomes a danger to the other.
Also, what I don’t think is helping, is you are at 37000ft, at 100% load. This is too high for pretty much any commercial aircraft at MTOW, and typically the heavier you are, the higher the most efficient cruise speed is, so its not entirely surprising that the aircraft needs to go beyond its MMo at an altitude/weight combination that is beyond its operating window.
I did a simulation in Simbrief (with custom E175 (and the E190 for good measure) airframes using IF’s figures) with takeoff weight being at MTOW - and it gave FL320/FL330 for initial cruise on both aircraft.
Edit: 2nd simulation gave FL340/FL350 given different wind conditions. But FL370 is definitely too high.
Schyllberg, this isn’t helping. Let me ask the purpose of the overspeed (MMO inc this case). Disregard the sim for a moment. Why is that a limitation? Why do planes never fly above this speed? Now include the sim in this scenario. What is the purpose of the overspeed? It’s not do anything and the aircraft is flying above the overspeed efficiently. That’s a problem.
There’s also thermal and aerodynamic limits, as well as the balance between engine thrust and aerodynamic drag. It gets very technical so that’s just a very simplified explanation.
It’s not. In IF, that’s the most efficient altitude at MTOW believe it or not. Have you looked at the fuel burn? You can start at MTOW from 35,000 - 37,000 feet. 37,000 feet burns slight more fuel, but the speed gained makes up for it. A big note is that this is for IF purposes, not the real world or what SimBrief is telling you. This is a big distinction.
I think there’s a bit of a mix-up here between theoretical efficiency and certified operational limits.
Even if the raw fuel flow calculations in IF suggest that flying slightly above MMO gives better range in certain conditions, that doesn’t automatically mean the overspeed limit is wrong. MMO isn’t set based on what’s most fuel-efficient — it’s a structural and aerodynamic limit defined by the manufacturer.
In real life, airlines don’t operate aircraft beyond MMO just because a performance curve might look better there. The aircraft simply isn’t certified to fly in that regime. So even if the simulator’s math shows marginally better efficiency above the limit, it wouldn’t be realistic to allow it operationally.
If anything, the discussion might be more about whether the drag/thrust modeling near MMO is perfectly tuned — but removing or raising the overspeed protection wouldn’t really be the correct solution.
Except the limitation in IF is higher than real life. The overspeed warning that occurs in IF is the equivalency of being written on paper and has no real meaning, since it’s not the actual limt. Another thing is that your wings are approaching transonic to supersonic speeds because the airflow above the wing is going faster than underneath. This starts the formation of shockwaves and vibrations, which creates a lot of drag (wave drag) and instability. Now is there any noticeable drag here in my initial post? The answer’s no. The n1 increase is nothing more than me climbing to a higher, thinner altitude. A 2% n1 increase doesn’t indicate in any way of approaching a limit or any struggle if you will. That’s about as much as what was simulated on the MAX using spoilers in flight. Now compare that to the A380 and B77W as you approach MMO.
It’s in my first post. Mach.83 (sim) is not equal to Mach.82 (real life). In fact, the speed in IF might be higher than Mach.83 and probably Mach.84 to Mach.85. The speed I’m flying at is my Vmd benchmark at sea level ISA with OEI Vmd testing, and that gets even higher as you go to higher altitudes. It still doesn’t affect anything because I verified that 37,000 feet gave me a better economical cruise speed and that ended up at Mach.83. Even if it was Mach.82, it would still be wrong because flying at MMO in the real world is not the economical speed. IF is different tho.
I would say that you’re overcomplicating and overthinking it.
MMO isn’t an arbitrary limiter that reduces efficiency. It’s a certified boundary tied to real aerodynamic/structural limits. In real life you don’t expect “best economy” to be beyond MMO, because physics starts getting uglier as you approach it.
However, we’re most likely not simulating those aspects since there wouldn’t be any real purpose of doing it.
I’m now at 259 KIAS with 488 knots GS (no winds) at Mach.85. Endurance is now averaging about 5:56. That’s just Vmd alone. Economical cruise speed is still higher since it’s for the best range. I forsee Mach 0.86 to 0.88, which is insane for a short-haul narrowbody.
I don’t think I am overcomplicating it. I basically explained the full picture, not just some structural limitation. I even explained the aerodynamic limitations being wave drag, shockwaves, and vibrations, symptoms of what you just explained MMO is (aerodynamic/structural). However, to say there’s no purpose simulating it is exactly why the plane is flying as it is right now. So given the context, I’m going to say the speed restriction is effectively useless because you’re not simulating anything. It’s just there for the sake of being there because the real aircraft is limited there, not because the IF aircraft is limited there. Am I making sense?
