Realisticaly starting Jet or Turboprop Engines

[PB4]

Hi all,

I got a setup with hardware switches and a VB application managing these and connecting to FSUIPC.

I built my setup around the KingAir (B200) and have a bit of trouble figuring out which offsets/values should I use.

Normal start :

- I would switch on my ignition switch => this would place the offset 0892 (Eng1 start) in the start position

- After reaching 12% I turn the fuel on from my throttle set

- I release the start switch => what should I write in 0892 since I use the 3B78 offset : Engine 1 generator, driven by another switch ? I assume if I place it in the "Gen" position it would turn on the Engine 1 Generator but I can't turn it off either ??

Now consider I have an hot start, I would place my three position switch in the "Starter Only" position, how would I reflect that ? (one idea is I can place the start offset in the "Start" position and write 0 in the engine fuel offset, but my throttles would certainly interfere with this..)

As a side question how often would I need writing a 1 in the Engine start offset to keep it in this position (my switches are refreshed every second but can be made refreshed 100ms).

Thanks for you help, have a look at my sim : http://fsbeech.free.fr

PB4

[Pete Dowson]

- I release the start switch => what should I write in 0892 since I use the 3B78 offset : Engine 1 generator, driven by another switch ? I assume if I place it in the "Gen" position it would turn on the Engine 1 Generator but I can't turn it off either ??

That jet/turbo switch action derives from the (unrealistic) FS implementation of the starter switch with "Start", "Gen" and "Off" positions, that's all. To switch your generators separately all you need on the starter are the "start" and "off" positions.

Now consider I have an hot start, I would place my three position switch in the "Starter Only" position, how would I reflect that ?

FS only has starter on or off, so you'd have to set starter on again. For jets which typically have "GND-OFF-CONT-FLT" positions I have to use something like this:

GND -> Start

OFF -> Off

CONT -> Off (CONT is only continuous ignition, ignition isn't simulated in FS)

FLT -> Start

This is obviously a compromise. You have to work out how to map "reality" onto FS's simplified systems.

As a side question how often would I need writing a 1 in the Engine start offset to keep it in this position (my switches are refreshed every second but can be made refreshed 100ms).

There's no need. After you write 1 to 0892 FSUIPC does the refreshing of the start for you, it keeps doing it till you write something else there.

Regards,

Pete

[PB4]

Sorry I am not getting that part, what do GND, OFF, CONT,FLT represent ?

Sorry. They are the labels on the four positions on the Starter switch on Boeing aircraft, or at least on the 737NG. I would have thought them to be more widespread, but perhaps not:

GND = Ground (Ground starting) - spring biassed back to Off but magnetically latched till combustion or a time limit.

OFF = Off (Normal)

CONT = Continuous ignition (used in critical periods like takeoff and landing, to prevent any chance of flameout I assume)

FLT = Flight (restarting in flight).

Regards,

Pete

OOPS! I seem to have edited YOUR message to me, instead of adding a reply. Apologies -- that's a first for me! I must have pressed the wrong button!

[Pete Dowson]

I am re-posting my reply to the message of yours which I so rudely, but unintentionally, destroyed above. I am doing this to make it clearer who is saying what!

Sorry I am not getting that part, what do GND, OFF, CONT,FLT represent ?

Sorry. They are the labels on the four positions on the Starter switch on Boeing aircraft, or at least on the 737NG. I would have thought them to be more widespread, but perhaps not:

GND = Ground (Ground starting) - spring biassed back to Off but magnetically latched till combustion or a time limit.

OFF = Off (Normal)

CONT = Continuous ignition (used in critical periods like takeoff and landing, to prevent any chance of flameout I assume)

FLT = Flight (restarting in flight).

Regards,

Pete

[PB4]

thanks Pete no worries for editing the message

It's been a long time I flew (realisticaly) 73's or even Jets, I have foccused on light twins and turboprop. But now that makes sense.

So there is no way to spin the N1 and having ignition off..

I'll try to make it like a "start but with no fuel", any ideas how I can cut fuel other than writing 0 to the fuel lever ? (which would conflict with the actual lever..)

thanks a lot for you prompt replies, will you be at the Interstate 2005 in Paris ? http://planete-cockpit.com/rubrique.php3?id_rubrique=1

We have a team arround my cockpit and will be glad to have a chat with you

ciao,

Ben

[Pete Dowson]

So there is no way to spin the N1 and having ignition off.

I think the ignition is powered by the battery, APU generator, or ground power, and the switch on a 737 is "left", "both" or "right", there's no "off".

But if you have all the power sources off I think the only way to get N2 turning is with external air pressure. But I'm not even sure about that. You need to ask a real pilot.

I'll try to make it like a "start but with no fuel", any ideas how I can cut fuel other than writing 0 to the fuel lever ? (which would conflict with the actual lever..)

Why does it matter if it conflicts with the actual lever?

I must admit that I'm a bit puzzled about what you are really trying to accomplish. This is to do with recovering from a "hot start", correct? How are you simulating that in any case -- FS doesn't do it for you, does it?

will you be at the Interstate 2005 in Paris ?

They've moved to France now? The last one I went to (#7?) was at the Aviodome at Schiphol, as part of the "Green" teram -- a collection of enthusiasts who'd never met before except in FSFORUM on CompuServe. I think we came in last! :wink:

Anyway, sorry, no, I won't be there. I don't get around so much these days, at least not alone, because of my very poor eyesight. When I do go to places it's because a friend also wants to go, or it is something my wife is interested in (the latter most certainly doesn't include Aviation! :wink: )

BTW I'm afraid after this my next message will not be till Tuesday night or Wednesday as I am away for a long weekend (with wife and youngest daughter).

Regards,

Pete

[PB4]

hi Pete,

Thanks for your time,

I'm trying to replicate the exact sequences of turboprop hot start :

basically here are the steps as I understand them :

- you try to start the engine normaly by switching on "Ignition and Engine start" on Engine 1, this spins the first stage (compressor) and continuously activate the ignition sparks in the combustion chamber

- Once you reached 12% you move the fuel levers from "cut off" to "Low idle" => this injects fuel in the chamber and as the chamber is full of sparks this supposely detonate and accelerate the air flow in the compressor.

- now if you injected fuel too early the compressor is not spinning fast enough and fuel is accumulating in the combustion chamber, ITT reaches abnormaly and this is where the pilot detects hot start

- Pilot cut fuel off to prevent any more fuel accumulating in the chamber

- Pilot places the start switch in the "start only" position so that the compressor still spins, creating an air flow which cools and evacuates hot gases and also this stops the sparks so that any remaining fuel is not burned.

I am not a real turboprop pilot so this may not be 100% accurate but I think it is close enough. Sorry as well if you already knew all that I just wanted us to be on the same base.

I just wanted to be able to replicate the fact that in the "start only" position the starter is spining the compressor but ignition is not activated.. I think I'm trying to be too accurate here as anyway if we have an hot start fuel will be cut off thus it should not matter if ignition is still on.

As well I though writing 0 to the offset of the lever might conflict with FS reading the position of the physical lever (if it is in "high idle" for example) but actually in hot start fuel lever will be "cut off" anyway...

Regards,

Benoit

[Pete Dowson]

I'm trying to replicate the exact sequences of turboprop hot start

...

I just wanted to be able to replicate the fact that in the "start only" position the starter is spining the compressor but ignition is not activated.

Okay, I don't know there is such a position on an ordinary jet -- there seems no reference to it in any of my manuals, even though the condition certainly still occurs. The rule normally is to abort the start attempt, switch the fuel levers back to cut-of, and not attempt again for a period of time. I assume this is for the fuel to dissipate naturally -- the N2 rotors will still be spinning for a time.

The point as far as FS is concerned is that the "starter" switch starts and the fuel switch operates the fuel. There's no ignition switch in any case, and hot starts aren't actually ever going to occur because it doesn't simulate them.

Now, for your purposes, the controls you have are just that, start and fuel. Whatever you want to simulate above and beyond that will be via your own indicators and gauges and switches, just utlising whatever FS can provide towards that. Of course you can have your own fuel switches on idle but the FS ones on cut-off if that's what you want.

>> As well I though writing 0 to the offset of the lever might conflict with FS reading the position of the physical lever (if it is in "high idle" for example) <<

But there's no physical lever in FS -- you can control the position of your lever in your programming. If by "physical lever" you mean graphics on in some FS cockpit panel then, of course, the value will change that -- but surely for realism you don't use any FS panels?

>> but actually in hot start fuel lever will be "cut off" anyway... <<

Ah, so it is as it is for Jets then.

Regards,

Pete