Engine restart problems!

[MaverickF22]

As far as I can make out the Ka-50 is supposed to fly with crossfeed off unless you have a significant imbalance or a low fuel situation. F-16 was similar in Open Falcon.

 

Logic being, I think, that a separated fuel system is less problematic under battle damage and plain less likely to have something weird happen like dissimilar tank usage, cross feed imbalancing, pressure differentials, and just plain bad mojo. Better to lose half your fuel than all of it if something goes wrong.

 

A16, the switch-art for the crossfeed switch is modeled wrong (compare: reality)?

Glad to hear there's someone else who played Open Falcon!;)

 

The explanation about the N1 or N2 showing 0% RPM when you want to start the engine comes if you have initially started your engine and didn't let it stay at idle for more than one minute, no matter how long after, but at least one minute(60 seconds), after which if you turn it off, the engine will start like never before, LOL!

 

You can also check the vids that i've provided for this aspect on youtube:

 

 

[MaverickF22]

Engine restart problems discousable!

 

So these would be the 2 videos that i've uploaded on youtube, where you can see what i was meaning about...!;):thumbup:

 

http://www.youtube.com/watch?v=4YYVTNF8jTE:joystick:

 

http://www.youtube.com/watch?v=GnsreWnkz-0:joystick:

[zangler]

late coming back to the thread and corrected my response to 'crank' rather than 'false start'

[Frederf]

late coming back to the thread and corrected my response to 'crank' rather than 'false start'

 

God yes I get those confused all the time. A crank is for cleaning out the fuel, a false replicates a failed start. Some day I'll get those straight. Also it's interesting that supposedly you're supposed to manual cancel these processes after 15 seconds when doing it with the APU.

 

The rotor/gearbox has it's own tachometer-generator. It's attached to the main gearbox and it sends its signal to the rotor rpm gauge.

 

There is no gauge for the free turbines on the engines, but they do have overspeed protection (FT/PT 1 and 2). If your free turbine overspeeds to 118%, it will shut the engine down, assuming your governors are on.

 

EDIT: For some reason I was unable to remember both RPM gauges at the same time. The one on the left side of the cockpit is Rotor/Gearbox and the right side is the compressor turbine speeds for each engine, yes?

Edited April 28, 2010 by Frederf

[Bucic]

EDIT: For some reason I was unable to remember both RPM gauges at the same time. The one on the left side of the cockpit is Rotor/Gearbox and the right side is the compressor turbine speeds for each engine, yes?

Even though my major is not engines and I don't know much about the eastern designs specifically my best guess would be exactly that. The reason is that free turbine RPM indication wouldn't be exactly the best indication of engine's operation.

 

I believe that being able to estimate various scenarios is a very important skill. In case of a helicopter rotor - free turbine - gas generator RPM you can use the following hints:

• typical gas generator RPM=~30000
  
• typical rotor RPM=~500
  

The only thing you need to calculate the free turbine RPM is some typical ratio of a high ratio gear train. Which I can't help you with :blush:

Edited April 28, 2010 by Bucic

[Frederf]

So these would be the 2 videos that i've uploaded on youtube, where you can see what i was meaning about...!;):thumbup:

 

http://www.youtube.com/watch?v=4YYVTNF8jTE:joystick:

 

http://www.youtube.com/watch?v=GnsreWnkz-0:joystick:

 

Ack, I'm telling Kamov on you! No way are they going to honor your factory warranty after that. :megalol:

 

I understand why starting the engine before it spools down <7-10% N1 (aka compressor aka GG, this is just me trying to bash the facts into my own head here) might cause a shaft to snap. Starter engages into spinning parts whose latent power overwhelms the starter shaft.

 

However this start the engine and not let it idle for a minute before shutting it down... how is that breaking anything? What's going on there?

[AlphaOneSix]

I believe that being able to estimate various scenarios is a very important skill. In case of a helicopter rotor - free turbine - gas generator RPM you can use the following hints:

• typical gas generator RPM=~30000
  
• typical rotor RPM=~500
  

The only thing you need to calculate the free turbine RPM is some typical ratio of a high ratio gear train. Which I can't help you with :blush:

 

For this particular engine, your gas generator turbine rpm is going to be just shy of 20,000 during normal flight, and your free turbine rpm will be around 15,000. I think the rotor speed of the Ka-50 is just shy of 300.

[RvETito]

Nr=90% is 272RPM which corresponds to 100% (15000RPM) free turbine RPM.

 

As for the letting the engine running longer than a minute - you normally do that before shutting it down for cooling but it shouldn't affect the start process at all.

[MaverickF22]

I can only hope that all of you guys had time to watch this 2 parts/20 minutes vid of mine, so you can get more questions and answers...!

 

I'm glad i could find you people!:D

 

Cheers,

Mav.

[Bucic]

Ack, I'm telling Kamov on you!

I think the engines have separate warranty provided by Klimov :D

 

For this particular engine, your gas generator turbine rpm is going to be just shy of 20,000 during normal flight, and your free turbine rpm will be around 15,000. I think the rotor speed of the Ka-50 is just shy of 300.

 

Nr=90% is 272RPM which corresponds to 100% (15000RPM) free turbine RPM.

 

As for the letting the engine running longer than a minute - you normally do that before shutting it down for cooling but it shouldn't affect the start process at all.

 

Thank you both.

[Frederf]

As for the letting the engine running longer than a minute - you normally do that before shutting it down for cooling but it shouldn't affect the start process at all.

 

In the YouTube video posted above the player starts the engine and then shuts it down before a minute has elapsed. This is what breaks the ability to restart the engine... is this normal?

[mvsgas]

In the YouTube video posted above the player starts the engine and then shuts it down before a minute has elapsed. This is what breaks the ability to restart the engine... is this normal?

I think he already answer, not sure

It seems like it's longer than 1 minute. I'm now investigating it deeper but it seems to me that we have a spool down time bug. This is exactly starter driveshaft shear but it shouldn't be happening when the compressor RPM reads zero.

 

I'll bring that to the devs. Thanks for the finding, good catch.

 

http://forums.eagle.ru/showpost.php?p=888352&postcount=45

[Frederf]

Those are two separate issues. The video shows 2 ways to break your starting ability.

 

#1 is to engage the starter when the compressor RPM is higher than some certain value

 

#2 is to shut down an engine after it has idled for less than approx. 1 minute

 

Your AirTito quote is regarding #2 (I think).

[mvsgas]

Sorry, I must have misunderstood you, Frederf. To me it made since, but I don't work on hellos so I don't know any better :joystick:

- RPM above 0% while on the ground=starting system damaged if a start is attempted

As to what the user's problem is - we can only guess until he provides a track. One possible reason is when you hit the Start button while the compressor is still spooling down - especially on the ground, in flight you'are allowed to start at up to 7% compressor RPM at windmilling. That will cause the starter's driveshaft to shear and it's modeled in BS.

 

- Engine shutdown before "X" amount of time will induce a starting failure and it shouldn't.

It seems like it's longer than 1 minute. I'm now investigating it deeper but it seems to me that we have a spool down time bug. This is exactly starter driveshaft shear but it shouldn't be happening when the compressor RPM reads zero.

 

I'll bring that to the devs. Thanks for the finding, good catch.

 

I guess We will have to wait until AlphaOneSix or AirTito get a chance to be back.

One thing I'm very curious about.

The videos posted by MaverickF22

http://forums.eagle.ru/showpost.php?p=890310&postcount=51

 

I must admit, I just watch them today, is that the way you are suppose to start the KA-50?

I know this is just a game it it may not matter, I'm just curious. I really thought the engine where ether going to caught on fire or blow up when I saw him start APU with engine fuel cutoff valve open and the throttle set to "Auto"

 

I'm way more conservative when starting engine. I even wait for the APU EGT/FTIT to stabilize before attempting a start (I guess I'm a bigger geek that I thought possible :D )

Edited April 29, 2010 by mvsgas

[Frederf]

Yeah, the failure on shutdown was the confusing one. You know it just occured to me that I can't really separate the #1 and #2 cases logically. I can't really say that #2 is a separate problem since I don't really know that the starter is breaking on an early shutdown, just that after an early shutdown it doesn't work on the next start up.

 

Maybe an early shutdown leads to a bug where the RPM doesn't spin down like it should and thus on the next start up the RPM is too high and breaks it on the 2nd start and not on the 1st shutdown. That would mean that #1 and #2 are basically the same behavior.

 

No, you're not supposed to start the Ka-50 that way. It's very rough and mean and it makes me feel pain just to watch. However it does work in a very mechanically unsympathetic way. Video is designed to show the limits of what causes damage and what doesn't.

[RvETito]

In the YouTube video posted above the player starts the engine and then shuts it down before a minute has elapsed. This is what breaks the ability to restart the engine... is this normal?

 

No.

 

What MaverickF22 does (starting an engine with throttle at Auto) is completely possible IRL and I've seen it myself on the very same TV3-117VMA engine - the fuel control unit had an Idle mode failure (the governor cam was stuck) and the engine has no problem doing that but that leads to excessive wear because it increases engine power while it's still "cold". You need the oil to warm up to a certain temperature in order to increase engine's power above Idle. Though this wear is not modeled in BS but FYI doing it will be penalized IRL ;)

[Frederf]

I wasn't asking if the start-at-high-throttle was normal, but rather the following behavior:

 

 

• Start engine normally
  
• Shut down engine immediately (time < one minute)
  
• N1 and NR RPMs are shown to be 0
  
• Subsequent start is impossible
  

Is the fact that this happens correct? What's the cause of this behavior?

[MaverickF22]

Video is designed to show the limits of what causes damage and what doesn't.

 

You've got that right..., i know what the manual says about a normal startup, the gearbox oil pressure should be at x and the oil temp at y before moving the throttle to idle, the fuel cutoff valves opening moment and all that it says..., though i wanted to show the available engine management and it's limits that are more or less realistically modeled in the game...!;)

 

Let's make it better, every day this unbeatable simulator should know more and more, as much as we do...!;)

[AlphaOneSix]

I wasn't asking if the start-at-high-throttle was normal, but rather the following behavior:

 

 

• Start engine normally
  
• Shut down engine immediately (time < one minute)
  
• N1 and NR RPMs are shown to be 0
  
• Subsequent start is impossible
  

Is the fact that this happens correct? What's the cause of this behavior?

 

That is what happens in the game right now, yes.

The cause is an apparent bug.

[RvETito]

It is indeed a bug but it has a logical explanation. After discussing the subject with Yo-Yo (ED's physical models lead programmer) I got the idea what's behind it. The reason this to happen is the spool down time of the starter itself. Remember it's actually an air turbine driving a spool engaged to the accessory gearbox of the engine. At approximately 60% compressor RPM the starter disengages (START VLV light goes off) but it's turbine keeps turning and fully spools down for approx. 100 seconds. We think that this is too long but there is nothing given in the manuals of the TV3-117 for that. Trying to adjust that time has led to some problems AFAIK so for the moment it stays as is. So what you experience now with the engine unable to start is that you initiate a start with compressor RPM zero while the starter is still spooling down- it's driveshaft gets overtorqued and it shears. So I suggest 3 min 20 seconds (200 sec) pause after START VLV light extinguishes before initiating a start of the same engine, assuming compressor RPM is zero.

 

Hope it's clear now.

[mvsgas]

Awesome thanks

[sobek]

In this case, this bug is welcome and perfectly acceptable, IMHO. Good find. I think i stumbled upon this in my first days of fiddling with the engines but quickly forgot about it, since when handling them normally you do not encounter this problem. Awesome to finally have an explanation.

[Frederf]

Well, that's even less of a bug than I first thought. I thought it was the GG RPM (despite showing 0%) that was causing the shear. Turns out it's the starter spool (which doesn't have a cockpit gauge) that is supposed to have an extended spool down time, the bug being that the time is at least twice as long as its supposed to be. Still, it sounds like "working as designed" in that starting the engine again before the starter has slowed down (independent of N-GG) causes shear. Slow down time is just off.

 

On an engineering (not programming) related question: Why would the starter take so long to slow down compared to the compressor? The N-GG gauge is pretty quick to hit 0% after engine shutdown. I haven't timed it but isn't it <30 seconds? Curious.

[sobek]

Why would the starter take so long to slow down compared to the compressor?

 

Because it has no fan attached to it that draws additional energy? Just a guess.

 

Also (although maybe that is just a misunderstanding of your post on my part) did you notice that they wanted to turn the time down, but could not for programming reasons?

[RvETito]

The 'bug' is that the starter should spool down faster than the compressor but currently it is not worth to adjust it. I think we can live with that, some technical self discipline won't hurt ;)