Hot Start and Hung Start in PSX

[torrence]

Based on Jon's nice tutorials on Engine Start, I have a few questions.  Although I have occasionally been called a "rocket scientist" I don't know much about the details of modern jet engines (rockets are designed by brilliant engineers, we scientists just get to use the resulting data).  So I'm unclear on what causes the difference between hot starts (EGT running away) and hung starts (EGT going up but hanging there without fully igniting the engine).

Jon's tutorial and PSX are pretty clear on hot starts - cut-off, motor for 30 sec, retry start up to 3 times.  I'm less clear on hung starts - Jon's procedure obviously works for a hung start on PSX (cut-off etc.).  But in PSX for a hung start I've also noticed that in either Manual or Auto Start, if I don't cut-off and just wait, after about a minute the EGT goes down and eventually the engine will start in any case with no obvious problems or warnings. 

Secondary question:  In PS1 days I used to think that I just wasn't fast enough with my fingers to cut-off the fuel flow on a hot start and prevent a 'red box' on that engine.  Jon's tutorial seems to suggest that with a hot start you get a red box anyway (even with Auto Start).  So does maintenance have to clear this before the flight can proceed or is this just an item to get checked afterward?

Cheers,
Torrence

[Magoo]

The one hot start I've had in real life was with autostart on a P&W and yes the box went red, it apparently exceeded the manual start limit but the engineer said it didn't exceed the autostart limit? None of us was aware there was a difference, anyway, the engineer cleared the fault and the engine started again with no problem...

[emerydc8]

Jon's tutorial and PSX are pretty clear on hot starts - cut-off, motor for 30 sec, retry start up to 3 times.  I'm less clear on hung starts - Jon's procedure obviously works for a hung start on PSX (cut-off etc.).  But in PSX for a hung start I've also noticed that in either Manual or Auto Start, if I don't cut-off and just wait, after about a minute the EGT goes down and eventually the engine will start in any case with no obvious problems or warnings. 

According to one of my manuals, a hung start is indicated by a fuel flow of 500 PPH and engine not reaching idle N2. On the CF6 model I used in PSX, it (correctly) never gets to idle N2 and it doesn't overtemp on a programmed hung start. Are you using a CF6 model?

I've never experienced a real hung start on a CF6 (744 or DC-10), but on a JT3D and JT9D, my experience is that a hung start will usually go hot on you if you leave it long enough. Oddly, the mechanics' first attempt to fix a hung start (presuming the engine was still running) was to deploy the reverser. This was on the non-FADEC engine (cable driven), so maybe the reverse had a different fuel schedule for the fuel control unit and it would get it over the hump. I'm sure John H. can explain why.

Jon

[torrence]

According to one of my manuals, a hung start is indicated by a fuel flow of 500 PPH and engine not reaching idle N2. On the CF6 model I used in PSX, it (correctly) never gets to idle N2 and it doesn't overtemp on a programmed hung start. Are you using a CF6 model?

Thanks, Jon

Yes, I'm using a CF6 model so that I can compare things with your videos.  PSX behaves as you say, but I'm still wondering about what happens in PSX if you don't do anything at all when a hung start occurs.  As I noted, on  my system, if I just wait for awhile (couple of minutes - I haven't timed it carefully) without doing anything when hung start occurs EGT starts to drop and N2 increases until it eventually completes start normally (apparently).  Doesn't seem to matter if Autostart is ON or not. 

Cheers,
Torrence

[emerydc8]

Hi Torrence,

I tried the hung start scenario and you're right -- after about a minute of hanging at 25.5% N2, it eventually does continue to start normally (manual start). I never noticed this before because (1) I had programmed in the hung start and was expecting it, and (2) it was evident that the start was not progressing normally when it hung at 25.5%, so I took corrective action prior to the engine fixing itself.

I probably would have never noticed this if you hadn't brought it up, although I think it's just a minor issue and perhaps Hardy intentionally designed it this way. Probably in real life, a hung start might fix itself if you let it continue and kept an eye on the EGT. Good observation.

Jon

[Hardy Heinlin]

Hi,

it's intentionally designed this way. There is some life in the engine model.

Before you guys ask about extended autostart retry programs for each engine model: I'm planning to work on this really soon now.


|-|ardy

[florismulock]

HI all,

i was just wondering what is causing the hot and hung start. is it just the fuel flow?(see below)   and i couldnit find the hot and hung start under failures.  ? a while a go i got a failure file (situ) from the admin (icing situation which wasnit in the failure section aswell)).  How can i make my own failures?

or even better how can i make a hot and hung start without using the failure section of the game? (putting the fuel to early?)


According to one of my manuals, a hung start is indicated by a fuel flow of 500 PPH and engine not reaching idle N2. On the CF6 model I used in PSX, it (correctly) never gets to idle N2 and it doesn't overtemp on a programmed hung start. Are you using a CF6 model?

[John H Watson]

According to one of my manuals, a hung start is indicated by a fuel flow of 500 PPH and engine not reaching idle N2.

Hung starts can be caused either by low fuel flow or low duct pressure. If fuel flow is below 205KGH (450PPH), a successful start is not likely. Fuel is pumped to the nozzles in the combustion chamber by mechanically driven fuel pumps which depend on N2 engine rotation (N3 on RB211 engine). However, the pumps are capable of providing a surplus of pressure (which is why the fuel which is delivered to the combustion chamber is metered).

If both manifold bleed pressure and fuel flow are normal during a hung start, there could still be a problem with the EEC, duct leaks or damaged engine internals. I suppose there could be a problem with the start valve. The pilots are only given an indication of "valve open" (just off the fully closed stops), not if the valve is fully open.

Rgds
JHW

[Jeroen Hoppenbrouwers]

Can a hung start be caused by excessive tail wind into the exhaust pipe, or is that more a reason for a hot start?


Hoppie

[florismulock]

The critical part is injecting the fuel. If the fuel is ignited before there is enough air flowing around the chamber, its temperature will increase dramatically and exceed the design limits of the combustion chamber and turbine blades, thus causing a failure. This condition is known as a hot start

how to create this conditions?  hung start and hot start?  perhaps someone could give me a situ file?  or even better show me how to make my own situ files.

[Avi]

You don't need any specific situation file. Just go the Self-induced malfunctions page and select Hot start and/or Hung start for any specific engine or a random one.
That simple.

Cheers,

[Hardy Heinlin]

There's also a description in the Aerowinx manual on page 54.

[Hardy Heinlin]

Extendended autostart programs specific to each engine model are now available in PSX version 10.1.1, along with a new feature that allows the user to set the number of restarts required until a hung or hot start is cleared:

http://aerowinx.com/board/index.php?topic=4020.0

[744]

Ref Hung Start,..... I'm trying to create a scenario where the second Autostart attempt is unsuccessful following a Hung Start which then generates an upper EICAS "ENG 2 AUTOSTART" msg. In other words, I want to fail the Autostart for Engine No 2 but with the Autostart selected ON in the correct sense. I've tried various combinations of circuit breaker pulls, all to no avail. Any help appreciated as I'm sure I'm missing something obvious on this...

Thanks in advance, Steve.

[Avi]

Just out of curiosity, which circuit breaker did you pull out and what did you expect to get?

Anyway, to get what you want you need to go to the Malfunction / Self-induced page, "check" the engine you want for Hung start and to select the "Start attempts required" as you wish.

Note that after each unsuccessful start attempt you need to set the fuel control switch to Cutoff and then back to Run.

Good luck,

[744]

Thanks Avi.

After the first failed Autostart attempt, I pulled CB's, P6-1 "F2" (IGN 1) and P6-3  K20 (IGN 2) thus preventing, trying to prevent Autostart from starting the engine. However I couldn't get the EICAS to display AUTOSTART! I also tried turning OFF the engines EEC.

I've looked as you suggest Situation > Malfunctions > Self-Induced > Hung Start (ENG 2) but I cannot see an option to manage "Start Attempts Required"

I'm trying to generate an AUTOSTART EICAS, thus requiring a "Manual Start"

For info I'm on version 10.0.9h,

Regards, Steve.

[John H Watson]

 

I pulled CB's, P6-1 "F2" (IGN 1) and P6-3  K20 (IGN 2)

And the Standby Ign CB "G20"?

I haven't looked at the circuit recently, but we were always told to pull all 3 CBs during maintenance.

Cheers

[744]

I pulled CB's, P6-1 "F2" (IGN 1) and P6-3  K20 (IGN 2)

And the Standby Ign CB "G20"?

Genius....Thanks, "ENG 2 AUTOSTART" on upper EICAS as required!

Thanks John

[Hardy Heinlin]

To get all engine model specific autostart features you need to install the latest PSX version.

Version 10.0.9h is too old. There have been some massive updates recently:

http://aerowinx.com/board/index.php?board=6.0


|-|ardy

[744]

10.1.2 ...all done, thanks Hardy