reported shut down differences Endless backfiring on shutdown

[Nealius]

According to reflected proper shutdown procedure (minus clearing the plugs) is:

1. Idle 1200 rpm

2. Pull cutouts (fuel cutoff)

3. Mags off when props stop

However following this procedure causes endless backfire popping noises, and massive flames from the exhaust, neither of which will stop until the mags are shut off. It seems the only way to prevent this is to shut off mags before pulling the cutouts, which is the opposite of correct procedure.

[Art-J]

Do they really never stop for you, or just take w while to do so?

Ever since getting the module when it was released I've always used correct order (cutouts first, mags last) and the engines always stop eventually after the same scripted (probably) number of pops and bangs. At least it seems to be the same. I admit I probably use different RPMs when pulling the cutouts, though.

Is there something fishy going on exactly at 1200 rpm? Will have to test later.

[grafspee]

This issue was brought long time ago on this forum.

This backfire script is present in spitfire p-51 and mosquito because all of them uses same code, could be in P-47 as well but i can't remember.

Shutting via cutouts not by magnetos off is that engine burns out all remaining fuel from carbs it prevents fuel leaking in to inlet or outside of the plane.

This is how this should work.

1 Run up engine to 1200-1500 rpm P-51 manual states it should be 1500rpm

2 Move cutoff lever or mixture lever to cutoff position

3. After lever is moved engine still runs because remaining fuel in fuel system is still distributed to inlet

4. After short period of time engine dies and prop quickly stops rotating if cut out is set in wrong way you may be not able to shut down engine or prop will come to stop after longer time, but if cut out allow to some fuel be distributed to engine it will not magickly stop firing and re-ignite at 100rpm, it will splutter through whole range of rpm.

I had opportunity to visit Duxford air museum this year and in proces of exploring it, at least 3 or 4 spitfires started to take off, do fly by and some aerobatics like loops, so i ended up watching those Spitfires for at least 3-4 hours. I've seen couple start ups and shut downs as well as run ups.

And i say that non of them act like DCS one.

In DCS when you move this cut out lever engine shuts down immediately and when engine is about to stop it splatter again over and over you can see it on tachometer needle bouncing like a ball bouncing of the floor.

My conclusion is that nether start up and shut down works correctly in DCS.

Start ups are way to clean, throttle response with cold engine is way off, engine run immediately smooth as butter which for person who saw at least on start up knows that this is not true.

Have you encounter any unsuccessful start up beside those in which you forget to turn on fuel or mags on ?

And shut downs are off to, mainly because engines react instantly at cutoff lever movement  and whole range from 1500 to 100 rpm doesn't splatter even once and when it is about to stop suddenly fuel is introduced to engine inlet sparking sporadic combustion. At 100rpm engine barely catch up when primer is used so why it should catch up when spark from magnetos are almost non existent due to that coil booster is off and some fumes of fuel magically ignites at 100rpm. This is ridiculous.

 

This recording is the most interesting, we can hear idling spitfire up close and second spitfire is taking off, how i could hear that was exactly same way as on this recording, as soon far spitfire firewall throttle sound of the engine/prop overwhelmed everything else.

If someone ask, yes spitfire  sounds exactly like as on this recording from smartphone difference is only in how loud is that. Smartphone's software lowers microphone sensitivity  when louder sound comes in, so idling and taking off spitfire loudness looks the same but it isn't, taking off spitfire is much much louder, this is why in DCS idling warbirds sounds so quiet. 

Edited November 30, 2023 by grafspee

[Slippa]

I have to admit, I rarely pull the cutouts in the Mossie. I haven’t had any continuous chugging though.

You should get to Duxford in September Grafspee, the Battle of Britain airshow would send your brain into overdrive, check out their ‘fighter balbo’ there’s probably something on YouTube. 

[grafspee]

Just for sake of realism i just shut fuel, engines are running much longer after shut off but they won't enter this splatter loop at low rpm where engine is about to stop.

@Slippa I would love to but i live in Poland,  reason why i've been in UK was different then visiting museum. Maybe some day it will happen  If i would live in UK i would not miss a single air show unless 2 or more would happen at the same time

 

[Slippa]

1 hour ago, grafspee said:

Maybe some day it will happen  If i would live in UK i would not miss a single air show unless 2 or more would happen at the same time

That could be a bit pricey . Maybe some day, I wish you luck, I’m sure you’d enjoy it.

[Nealius]

I may have to adjust my shutdown by starting with fuel as well. Last night I had this experience:

-Idle 1200rpm

-Run engine up to 2000rpm for a count of 4

-pull cutouts, rpm drop to 1000 advance throttles max to clear plugs (Reflected tutorial)

-when rpm hit near zero the engines started endlessly sputtering

-reduced throttle to idle, shut off both tanks, shut off fuel pressure cock, engines still spinning and stuttering with massive flames

-turned off mags, sputter and flames immediately stopped

 

I sometimes get a similar issue when feathering one of the engines if I don't turn off the mags nearly immediately.

[Art-J]

Nah, repeated the procedure above and with hot mags they do stop after a few sputters eventually, so it's just extra few seconds. The old Fw-190 A8 bug when the engine used to sputter between 30 and 60 seconds - now THAT was "endless". Current Mossie cannot compare  . So i don't think that "by the book" procedure needs altering, unless someone's in hurry.

What's more puzzling and worrying, however, is difference between hot-start and cold-start missions:

a) hot-started ones always yield fast and sputter-free engine shutdown (even with hot mags and after spark plug clearing at 2000 rpm);

b) cold started ones always yield sputtery shutdown, no matter if engine runs at higher rpm or idles.

Attached tracks show the difference, even though conditions and engine temps were comparable in both cases (engines restarted shortly after shutdown) and thus, from principles of piston engine operation point of view, there should be no difference in how they stop. Cut-off is cut-off. Or is it?

I wonder if simulation code responsible for priming during cold starts doesn't "carry through" the mission for some silly reason, all the way to subsequent engine shutdown procedure? Priming by the player is, in theory, the only difference between cold-started and hot-started missions.

2.9_cutoff_test 2 idle.trk 2.9_cutoff_test 1 high rpm.trk

Edited November 27, 2023 by Art-J

[grafspee]

@Art-J I agree, this splatter sounds and acts like this during start up with primer. 

[Art-J]

I suspect there also might be other iffy things going on in DCS Mossie engine simulation in cold-start vs hot-start scenarios.

For example, when the plane was released and I only used one Warthog throttle, I had to assign that single grey slider to both engine RPMs combined, while using physical throttles as separate virtual throttles as well. Because of that, I quickly noticed back then that in all hot-started missions both engines were always perfectly in-sync, but in cold started ones, they were always a little bit out-of-sync, even when oil and coolant temps evened out between both, at various power settings. They shouldn't be, because virtual RPM levers were assigned to the same physical slider. But they were. Never made a difference if I started port or starboard engine first at the beginning of a mission.

Wanted to make a bug report about it, but shortly after, I just purchased another throttle quadrant to have more axes available. And so nowadays I don't pay attention to this strange issue  anymore and just adjust RPMs accordingly to synchronize them. I wonder if it's still present in 2.9, though.

Edited November 27, 2023 by Art-J

[SUNTSAG]

Just for information and to enlighten folks as the correct documented procedure for engine shutdown, as laid out in A.P (Air Publication)2019E updated to AL5 (Amendment List 5) in 1944. (Image provided). There are many versions of the pilot notes on the internet, often dated from the 1950s but the January 1944, reprinted April 1944, reprinted August 1945 are the versions upon which the DCS mosquito is modelled.

I am not saying this will improve your experience but it will give you the correct basic procedure to follow. I hope it helps. Cheers.

[hazzer]

This is one of the many engine issues I have tried to raise in the past which seem to be ignore. 

As stated above this issue spans into almost all of the warbirds (mainly the merlin engined ones). When you shut the engine down you should cut the fuel off, in the aircraft it is usually mixture cut off or similar. In DCS it is as if there is still fuel getting into the engine making them splutter and backfire. Completly unrealistic. 

 

The only way to make it cut off correctly is by turning the maggs off which is not realistic. 

[Nealius]

@SUNTSAG Clarification questions since some of the terminology seems different in that doc:

1. After engines stop the cutouts should be pushed back in even if fuel tanks are still selected, correct?

2. Ignition = magnetos?

@Art-J Interesting you should mention the priming, I've been thinking there's issues with that as well. More specifically, after requesting priming the priming action does not stop until you hit the booster/starter buttons, leading to the second engine you start being over-primed every time.

Edited November 28, 2023 by Nealius

[average_pilot]

8 hours ago, hazzer said:

This is one of the many engine issues I have tried to raise in the past which seem to be ignore. 

As stated above this issue spans into almost all of the warbirds (mainly the merlin engined ones). When you shut the engine down you should cut the fuel off, in the aircraft it is usually mixture cut off or similar. In DCS it is as if there is still fuel getting into the engine making them splutter and backfire. Completly unrealistic. 

 

The only way to make it cut off correctly is by turning the maggs off which is not realistic. 

I agree. The point of the thread is that in DCS the engines are capable of violating the most essential physics and keep turning endlessly without receiving any fuel, which is something worth to look at and fix for the sake of physical coherence of the simulation.

Edit: To further clarify my point, you may damage an engine IRL not following the correct stop procedure but it will surely stop moving no matter what if the fuel is cut off.

Edited November 28, 2023 by average_pilot

[Art-J]

I remember Yo-Yo's post in one of the wishlist threads (for less regular startup and shutdown sequences) where he said coding all idiosyncrasies of fuel, ignition and exhaust during these transitional phases would be a waste of time in combat sim where most of folks just want to take off and blow s..t up. I kind of understand that, because no matter how cool the nerdy-feature is, once the novelty wears off majority won't care about it anymore. So, simplified sequences are here to stay and I can deal with it, even though I use DCS primarily for non-combat flying.

There are, however, some noticeable issues even with these simplified procedures.

To sum it up, there seem to be two scripted shutdown sequences in all Merlin-powered DCS planes, one quick and "clean" without excessive backfire (maybe just a few muted pops) and one longer, "dirty" with excessive and loud backfire. In Spit and Mustang you'll get one or the other depending on engine RPM when mixture cutoff is activated and on moving the throttle lever forward or keeping it aft.

In Mossie, though, looks like you get clean sequence in all hot-started mission no matter what, and dirty sequence in all cold started missions, no matter what. That doesn't make much sense.

[hazzer]

1 hour ago, average_pilot said:

I agree. The point of the thread is that in DCS the engines are capable of violating the most essential physics and keep turning endlessly without receiving any fuel, which is something worth to look at and fix for the sake of physical coherence of the simulation.

Edit: To further clarify my point, you may damage an engine IRL not following the correct stop procedure but it will surely stop moving no matter what if the fuel is cut off.

 

Yeah agreed. In other situations with the carbed engines, I have had to shutdown an aircraft by going to full throttle with the mixture in cut off (as it kept running). Which killed the engine as it got too much air. My point being is that it it seems the dcs engine simulation is actually a lot simpler than I initially thought. What is impostant though as stated here, the current shutdown script is wrong. 

6 minutes ago, Art-J said:

I remember Yo-Yo's post in one of the wishlist threads (for less regular startup and shutdown sequences) where he said coding all idiosyncrasies of fuel, ignition and exhaust during these transitional phases would be a waste of time in combat sim where most of folks just want to take off and blow s..t up. I kind of understand that, because no matter how cool the nerdy-feature is, once the novelty wears off majority won't care about it anymore. So, simplified sequences are here to stay and I can deal with it, even though I use DCS primarily for non-combat flying.

There are, however, some noticeable issues even with these simplified procedures.

To sum it up, there seem to be two scripted shutdown sequences in all Merlin-powered DCS planes, one quick and "clean" without excessive backfire (maybe just a few muted pops) and one longer, "dirty" with excessive and loud backfire. In Spit and Mustang you'll get one or the other depending on engine RPM when mixture cutoff is activated and on moving the throttle lever forward or keeping it aft.

In Mossie, though, looks like you get clean sequence in all hot-started mission no matter what, and dirty sequence in all cold started missions, no matter what. That doesn't make much sense.

Its a shame that this is the case, as like you I rarely actually fly combat and just enjoy the flight model and messing around in VR. I wish the engine simulation was far more realistic in many many ways, this startup issue along with the abnormally high oil pressure in startup playing a big part in my irritation with the sim. 

 

I hold out hope that one day these things will actually be fixed. 

[Nealius]

1 hour ago, Art-J said:

I remember Yo-Yo's post in one of the wishlist threads (for less regular startup and shutdown sequences) where he said coding all idiosyncrasies of fuel, ignition and exhaust during these transitional phases would be a waste of time in combat sim where most of folks just want to take off and blow s..t up.

I don't really follow the logic in that. For one if we applied that logic to all the modern aircraft we would have much more simplified startup procedures than we do now. Two, if someone just wants to take off and blow stuff up they can fly some other WW2 combat sim. The logic seems selectively--and conveniently--applied.

Edited November 28, 2023 by Nealius

[SUNTSAG]

This is my preferred approach to following the documented procedure….a picture paints a thousand words. Cheers.

[Art-J]

@NealiusOK, but to play devil's advocate, I'd say modern planes might not be the good example. They are heavily automated after all and the only thing pilot needs to do in them is pushing the relevant buttons in correct sequence. One cannot make it either less immersive/realistic (without going full FC3) or more immersive/realistic, as there's nothing "analog" left for player to do. OK, Sabre and MiG-15 can have their engines flooded if we move levers too fast, but other than that, it's always just click click click in correct order.

So In my opinion the logic is already the same for DCS warbirds and modern aircraft currently - just a string of scripted events which make the engine go hot or cold in repeatable manner (aformentioned Mossie shenanigans notwithstanding!). Certainly makes programming auto-start and auto-stop sequences easier for devs and I was quite surprised reading some time ago how many DCS players use these shortcuts even in fully-clickable modules. Simply put, nerds like us who would like to fiddle with primers, magnetos and mixture levers according to variable weather conditions really seem to be minority in DCS.

And since the whole WWII shebang has always been a bit of a side-quest for ED in grand scheme of things, I don't think we will ever see more fidelity implemented in engine modelling (even though I'd absolutely love to face more challenge while starting piston-powered machines).

[Nealius]

I would counter that devil's advocate with the F-16's hung starts if you don't wait for the SEC light to go out before setting throttle to idle.

@SUNTSAG Have you had issues using hotkeys or HOTAS/MFD mapping instead of mouse for the fuel stuff? In VR that fuel panel is hard to use the mouse on, so I have those mapped to various things.

[grafspee]

@Art-J I won't hold my breath for full fidelity start ups and shut downs but ED could at least remove this splattering loop at 100rpm. This is my main issue and main issue of this topic.

[average_pilot]

Yep. The problem isn't complexity but coherence within the current level of complexity of the engine modeling.

[SUNTSAG]

4 hours ago, Nealius said:

I would counter that devil's advocate with the F-16's hung starts if you don't wait for the SEC light to go out before setting throttle to idle.

@SUNTSAG Have you had issues using hotkeys or HOTAS/MFD mapping instead of mouse for the fuel stuff? In VR that fuel panel is hard to use the mouse on, so I have those mapped to various things.

No as I am a cockpit switch junky rather than a key binder...even when flying in VR. Obviously I bind some elements but that is simply a personal preference. Cheers.

[Nealius]

Cheers I'll try the pilot's notes procedures later today. I saw "use mouse" in the pics and wondered since I have my cutouts mapped to Warthog throttle switches and the fuel selector knobs mapped to Cougar MFDs.

[Slippa]

I spent around a year using DCS mainly learning to cold start, fly and hopefully land my prop warbirds. Now and then I’d load up and try some targets. I was chuffed to bits so much is modelled and not knowing any different I was impressed with how well the engine management was done. Sounds are great too.

I’m one of the nutters that flicks those switches in the back of the receiver in the Mossie, even though they do nothing. When I go through startup I slide the screen wiper up every time in the vain hope one day it’ll work. I’ve seen the wipers move, only it was in the model viewer. I don’t hold out much hope I’ll see it working properly, it’s not that big a deal, or it wouldn’t bug me so much if it hadn’t been modelled at all. I like everything to be working, if it’s there, it should be working. It’s a bit gutting to think we’ve got random failures working when we’ve got crazy engine modelling, fuel systems or whatever.

it needs looking at doesn’t it.

Nealus I have my fuel tanks bound to switches on the warthog throttle. Doesn’t fail as such but could do with setting up better, I can swap tanks over mid-flight on either engine but only one way. Bit awkward to explain what I’ve done without looking at it now. In short, I’ve had no trouble with them working.

Glad to have the Mossie pilots notes Suntsag, cheers.