Offical status of engine thrust issues?

[Pocket Sized]

The Viggen still suffers from a bug that makes the engine have far too much afterburning thrust at altitude, leading to absolutely absurd acceleration (and top speed until overspeed damage was added). It also appears to have too little thrust at full mil unless manual fuel regulation is turned on, especially at high altitude.

 

What sort of progress has been made on these issues? They're the only "holes" I can find in the otherwise fantastic flight model.

[RagnarDa]

Thank you!

 

Unfortunately I haven't looked into this issue just yet. Me and Swither has focused our efforts on integrating a CI/CD-chain that will hopefully catch bugs like these earlier and also speed up development for this and future modules. This is the reason you might not have seen as much bug fixes the last couple of weeks. I hope you can wait a little longer.

[Pocket Sized]

I most certainly can wait, you guys take all the time you need.

[Pocket Sized]

Just to make things easier for everyone, I'll try to compile as much info as I can here.

 

https://forums.eagle.ru/showpost.php?p=3033748&postcount=29

 

Equilibrium airspeed with a clean aircraft is around Mach 0.92 or something like that at 10km. Any external loadout at all (including the drop tank) and you can't maintain level flight at 10km on dry thrust at any airspeed, and forget about climbing there dry. However, with low drag loadouts (basically, anything that doesn't involve the anti-ship missiles, bombs or rocket pods - unsure about the bk 90) you should be able to maintain Mach 0.9 or at the very least 0.85 at altitudes between, say, 4 and 8 km, ish.

 

Best distance economy is achieved with Mach 0.9 at around 7-7.5 km with most loadouts except the draggiest ones (again, rocket pods, bombs, anti-ship missiles). With 16 bombs you need to go down to around 6 km. If you're ferrying a clean aircraft with full fuel though, the manual is correct and 10km is the best cruise altitude.

 

This thread has some pretty informative findings and comparisons to the real flight manual, as well as this one.

 

Summary of in game behavior with automatic fuel regulation:

 

1. Too little dry thrust at all altitudes, EPR reaches ~1.8 at sea level and decreases significantly with altitude. (1.6 @ 10km)

2. Afterburner stops working at a lower altitude than it should.

3. Engine will die if ground idle is selected at medium-high altitude, maybe this is realistic?

4. Slightly unstable ground idle when stationary.

 

Manual fuel regulation:

 

1. Dry thrust is (maybe) slightly low at low altitudes, EPR only reaches ~2.1 at sea level. Max EPR increases slightly with altitude. (2.35 @ 10km) If it is manually kept at 2.2, performance appears to be very very accurate. (Successfully replicated 0.92M @ 10km, clean airframe)

 

Additional remarks:

 

The afterburner overperforms at high altitudes in both fuel modes. The only apparent difference between them is the afterburner blowout altitude (much higher in manual mode). While performing a 0.95M Zone 3 climb, the aircraft will begin accelerating at an increasing rate after the initial climb angle is established. My guess is that afterburner thrust is remaining relatively constant while drag decreases with altitude. This has been improved in recent updates, however, and the aircraft won't readily accelerate past M2.1 as it would before.

 

I will probably update this with corrections or additional info in the near future.

Edited April 22, 2017 by Pocket Sized