Motoring the engine?

[delta9857 1]

Hello everyone,

 

I have a question about starting up the Jetprop. IRL when the starter is pressed and you begin to hear everything spooling up (before fuel is introduced), shouldn't the prop begin to turn? I know IRL pilots do this to suck air into the engine to lower the ITT before igniting it to avoid a hot start (at least, they do it in the Piper Meridian). Or is this a limitation of FSX?

 

If anyone knows how this could be achieved it would be much appreciated.

[vonmar 122]

"I know IRL pilots do this to suck air into the engine to lower the ITT before igniting it to avoid a hot start"

 

Where did you learn this?

 

Battery power to prop reduction gears drivetraine during turbine spool up?

 

Feathered prop turning (low rpm) to cool jet engine hundreds of degrees?

 

One hand on condition lever ready to shut down fuel if ITT does not drop will avoid engine damage.

[Lifeguard911 9]

This may be what Delta9857 refers to. The prop is seen spinning before the pilot says he will introduce the fuel-

 

This is our new Piper Merdian starting its Pratt & Witney PT6A-42A engine. We had just landed from our maiden flight so the pilot taking the plane back for us runs the starter a little longer to get cold air into the compressor section to lower the temp before adding fuel.

 

[media=]http://www.youtube.com/watch?v=Q8-rm5pNjDA[/media]

[delta9857 1]

Where did you learn this?

 

A friend of mine owns a Piper Meridian and this is what he does.

 

And Lifeguard911, I was actually just about to embed that exact video until I saw your post! That is exactly what I meant. So, does anyone know if this is possible in FSX? It's only a small detail but I think it's important nonetheless.

 

Maybe Carenado will be able to implement it in their upcoming TBM 850?

[CoolP 283]

On the actual engine suck in air action, this isn't a thing happening due to the prop movement. If I'm right, the generator acting as the starter turns the gas generator until the combustion sets in. So, as it turns, it sucks in air, compresses it and delivers it to the combustion chamber where it 'waits' for the fuel being commanded by the condition lever.

 

So the first prop movement happens when compressed air (and later hot gas) enters the power turbine, which then drives the prop. The turning prop therefore acts as a sign of an airflow through all stages of the PT6A. Seems like this airflow and the corresponding gas generator rpm are the target of the folks trying to avoid a hung or hot start.

 

Just guessing, but from experiencing all the other turbine planes of mine, I think we are seeing a combo of FSX limits and dev work here when it comes to the not moving prop and other things. For example, the startup on all my free turbine planes comes in way too fast for me, at least from the gauge indications. The C208 has a nice slow startup phase on the sounds.

[Lifeguard911 9]

I don't know if you could model that or not. When I think about the different turboprops I have in FSX such as the Piper Cheyenne, the props don't start turning until the fuel condition lever has been advanced after the ignition is started.

I agree with you that a prop that began moving when the starter is engaged would be a nice visual effect to have, providing the real aircraft actually does that.

[HawkDsl 50]

TBM850!!

 

Oh man Oh man... now we're talking.

 

Even the king of TubProp's, RealAir Duke, wont spin up until you hit the gas. I'm sure it can be done though... FSX is doing allot of stuff with all these new planes that I'm sure even Microsoft didn't think it could do.

[delta9857 1]

Would it be possible for someone to make a quick mod that just animates the prop spinning when the starter is pressed?

[sheepfu 3]

CoolIP is correct. This turbine engine is not the same as a piston engine. In general props on piston engines are connected to the cranksaft. A turbine engine works differenty. The Compression section and the hot section are seperate. In a jet think N1 and N2. What motoring is doing is driving the cold compression portion of the engine. Thus just like fans on your computer it is drawing air in and through the Hot section of the engine. Since the Hot section also has rotating parts, this air movement causes the Hot section to turn as well and through the transmission, the prop will spin. Check out the diagram below of the PT6.

 

 

FSX really breaks down when it comes to turbo props. It is unable to treat the Hot and Cold halves of the engine seperately. Therefore developers are stuck tweeking the behavior of the engine to try to emulate how it really works. A seperate prop animation would be difficult to produce as it would still be tied to what FSX is assuming the engine rotation visually is.

[deltapilot 0]

You're only going to see slow prop movement on x-plane 10. Not every prop either. I personally saw this on Carenado C208 for XP10.

 

-Tristan