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Engine surge and flameout


Accipiter
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After flying this aircraft for a first few test flights, I must say what a superb simulation this is! So impressed was I, I splashed out and bought the Mig 21 as well in the sale:thumbup:

 

The only question (so far) is that I am experiencing a lot of engine surges and subsequent flame outs?

 

I follow the procedures, fly carefully, fuel to manual, to no avail, I can not re light the engine. The re start switch does not appear to work.

 

I know it's probably my high alpha habit I have got into after flying the Hog for ages, but were these Viggens prone to such failures at slow speed/high alpha? If yes, then can the relight be tweaked to work better please?

 

My crew chief says he's running out of parachutes, not to mention aircraft!:cry:

 

Cheers.

[sIGPIC][/sIGPIC]i7 Haswell @ 4.6Ghz, Z97p, GTX1080, 32GB DDR3, x3SSD, Win7/64, professional. 32" BenQ, TIR 5, Saitek x55 HOTAS.

Search User Files for "herky" for my uploaded missions. My flight sim videos on You Tube. https://www.youtube.com/user/David Herky

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Yeah, the RM8B of the JA had an extra compression stage that took care of that problem. Remember, the AJS is not a fighter. It did many things well, but not dogfighting.

Win10 x64 | SSDs | i5 2500K @ 4.4 GHz | 16 GB RAM | GTX 970 | TM Warthog HOTAS | Saitek pedals | TIR5

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I used to have a lot of compressor stalls (much more so than surges), but things have really settled down since I started paying attention to the AOA warning tones. With the high induced drag of the Viggen's delta configuration, it rarely benefits the situation or performance to operate above 15-16 units of AOA IMHO.

 

I've only had a few surges lead to a flameout, but if you have enough stalls (thumps) followed by a surge, the engine may not relight due to damage that is modeled. Reducing AOA promptly after the onset of stall improves the odds of keeping the engine operational. If the engine "hangs", retarding the throttle to idle and smoothly advancing the throttles once RPM has idled will usually work as well.

 

Lastly, it is critical to that you lower the AOA below 15 (and even lower if possible) or none of the recovery maneuvers will work (just in case you are holding the AOA while attempting to clear the stall). I also find myself using the standard engine start switch after a real compressor surge, since the RPMs have typically decayed quite a bit once I realize that its a real surge. I think the airstart switch activates the ignition system into a continuous mode, but won't work if RPM declines past a certain point (though I don't know what the number is).

 

For me, prevention has been the best approach. :)

 

-Nick

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I used to have a lot of compressor stalls (much more so than surges), but things have really settled down since I started paying attention to the AOA warning tones. With the high induced drag of the Viggen's delta configuration, it rarely benefits the situation or performance to operate above 15-16 units of AOA IMHO.

 

I've only had a few surges lead to a flameout, but if you have enough stalls (thumps) followed by a surge, the engine may not relight due to damage that is modeled. Reducing AOA promptly after the onset of stall improves the odds of keeping the engine operational. If the engine "hangs", retarding the throttle to idle and smoothly advancing the throttles once RPM has idled will usually work as well.

 

Lastly, it is critical to that you lower the AOA below 15 (and even lower if possible) or none of the recovery maneuvers will work (just in case you are holding the AOA while attempting to clear the stall). I also find myself using the standard engine start switch after a real compressor surge, since the RPMs have typically decayed quite a bit once I realize that its a real surge. I think the airstart switch activates the ignition system into a continuous mode, but won't work if RPM declines past a certain point (though I don't know what the number is).

 

For me, prevention has been the best approach. :)

 

-Nick

 

Thanks chaps.

 

Copy that Nick, both the AOA and the Airstart being a continuous ignition would make sense and explain why I can't relight properly... My "thumps" (great modelling by the way!....swear my chair vibrates as well!!), are happening at low level, so I don't have much room to lower the nose. This is a serious simulation for sure!

 

I havn't dropped a single bomb yet, just flying and navigating with INS is a real challenge to master.:)

 

 

I will practise some more.

 

Regards

 

David


Edited by Accipiter
incomplete sentence

[sIGPIC][/sIGPIC]i7 Haswell @ 4.6Ghz, Z97p, GTX1080, 32GB DDR3, x3SSD, Win7/64, professional. 32" BenQ, TIR 5, Saitek x55 HOTAS.

Search User Files for "herky" for my uploaded missions. My flight sim videos on You Tube. https://www.youtube.com/user/David Herky

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I can add that the Viggen prefers to be flown above 600 km/h, preferably 800 km/h and up.

Those speeds can be kept at dry thrust once you're up there, so she's more economical there too.

Below that she's heavy as a brick, so it doesn't really make sense to crawl around there, except when you're landing. ;)

 

Like BlackLion213 says, really pay attention to the high AoA warning tones.

They come first, then reduction of thrust together with higher drag, then, if you persist, comes the compressor stalls.

Fly her smoothly, and she will stay happy. :)

System specs:

 

Gigabyte Aorus Master, i7 9700K@std, GTX 1080TI OC, 32 GB 3000 MHz RAM, NVMe M.2 SSD, Oculus Quest VR (2x1600x1440)

Warthog HOTAS w/150mm extension, Slaw pedals, Gametrix Jetseat, TrackIR for monitor use

 

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I can add that the Viggen prefers to be flown above 600 km/h, preferably 800 km/h and up.

Those speeds can be kept at dry thrust once you're up there, so she's more economical there too.

Below that she's heavy as a brick, so it doesn't really make sense to crawl around there, except when you're landing. ;)

 

Like BlackLion213 says, really pay attention to the high AoA warning tones.

They come first, then reduction of thrust together with higher drag, then, if you persist, comes the compressor stalls.

Fly her smoothly, and she will stay happy. :)

 

 

Thanks again.

 

I have had a much more productive "type training" session today. No surged compressors. Got the Navigation sorted, wp updates, take off and landing in all weather!

 

So to finish off, I put a simple mission together that would test my maneuvering.....Placed a couple of Helis in an orbit around a few hills and valleys. Slash and run, turn and climb, yo-yo and hey this beauty does it all. Just listen to that AOA warning beep and the sidewinders do the rest! Not bad for a mud mover without an internal cannon.:smilewink:

 

Now for some bomb practise! Best $50 I ever spent!:D

 

Cheers!

 

 

David

[sIGPIC][/sIGPIC]i7 Haswell @ 4.6Ghz, Z97p, GTX1080, 32GB DDR3, x3SSD, Win7/64, professional. 32" BenQ, TIR 5, Saitek x55 HOTAS.

Search User Files for "herky" for my uploaded missions. My flight sim videos on You Tube. https://www.youtube.com/user/David Herky

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I can confirm it may be quite tricky when you get to Viggen from real modern fighter.

 

I am used to fly M2k, which is true dogfighter. They look similar, but what different they are. The engine of Mirage is awesome. I really miss its power and ability to "not need to care about anything" in Viggen. But when you fly few times some older aircrafts (like Fishbed), you will find out it is actually not so bad.

 

There is a high AOA warning sound. But it is ok to exceed the safe AOA limit for a short while. When the "bang" sounds occur however, you really need to get back to comfortable AOA asap. Even at this point, the engine is able to survive without stall. Only the further ignoration of the situation will destroy it.

 

I didn't have the heart to press the plane any further. So I have yet to stall my first engine in Viggen. Lucky for me and my Viggen. General thought - when you are in position you need to use such AOA you are doing something wrong. Either you execute your attack badly or you found yourself in situation the plane is not designed for (f.e. dogfighting).

The Ancient Fox

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General thought - when you are in position you need to use such AOA you are doing something wrong. Either you execute your attack badly or you found yourself in situation the plane is not designed for (f.e. dogfighting).

 

Exactly! However, if you use your energy efficiently, low level "dogfighting" with a slower opponent, is possible. My scenario included some helicopters, at 50 metees, loitering over the primary target. The good old Yo-yo is the way to do it. Burner on, over the arc and cut the turning circle. A flat turn in the Viggen is not on.

 

This is a super simulation. :thumbup:

 

Cheers.

 

David


Edited by Accipiter
typo

[sIGPIC][/sIGPIC]i7 Haswell @ 4.6Ghz, Z97p, GTX1080, 32GB DDR3, x3SSD, Win7/64, professional. 32" BenQ, TIR 5, Saitek x55 HOTAS.

Search User Files for "herky" for my uploaded missions. My flight sim videos on You Tube. https://www.youtube.com/user/David Herky

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