Friday 2010-12-10 Dev. video update and Discussion

[The Kraken]

Originally Posted by Osprey

I would like to hear the argument and evidence as to why it should be red and yellow rather than blue.

It's about the startup effect and not the exhaust glow of running engines. Whether we'll see a blue glow at night, possibly even depending on engine settings as explained in some posts (probably overkill though), is a different issue. Fingers crossed

Anyway, nice details and I'm especially happy to see the subtle reflectivity on the plane skin again, which has been absenst in all screens since months.

[Krt_Bong]

You know on one of the other sim forums they're having a discussion about why an HP 0/400 might still be able to fly with no wings and only 1 engine, I guess we should count ourselves lucky all we got is what colour the exhaust flames should be

[merlin66]

Thanks for the update Oleg!

About the flames, it seems to me there are two main effects:

1. Yellow / red flames from excess fuel exiting the exhaust sometimes during startup. This is so visible it can be seen both at day and night, as shown in pictures in this thread. This is probably so bright it will illuminate the plane at night.

2. Blue flames: at night you can see that the exhaust itself is has a blue glowing color, at least at high power settings (see the Reno video earlier in this thread). This isn't very visible in daytime. Pilots often describe seeing only the blue exhaust flames of the enemy planes at night.

Edit: So my conclusion is:
- The startup flame in your first video looks perfect (and this should illuminate the plane if seen at night)
- The yellow flames in your night video: If this is supposed to be the second effect (engine running smoothly), the flames should probably be more blue and not illuminate the plane that much. But my main reference is the Reno video earlier in this thread, maybe running at lower power settings with shorter exhaust pipes (Spitfire vs. Sea Fury) gives more yellowish flames.

Here is another example of the first kind of flame:

http://www.youtube.com/watch?v=uNXGDi79aPw

[ATAG_Dutch]

Originally Posted by The Kraken

It's about the startup effect and not the exhaust glow of running engines.

Sorry, but the motor in the dark is running, not starting up. The timing between the flashes is too even. Also, if it was starting up, we'd presumably see a similar long flame to the daytime start clip.

Skoshi does have a point in the cylinder scavenging / cam overlap being a possible source of unburnt fuel, but all the video and literary evidence screams 'blue!'

[The Kraken]

Originally Posted by Dutch_851

Sorry, but the motor in the dark is running, not starting up. The timing between the flashes is too even. Also, if it was starting up, we'd presumably see a similar long flame to the daytime start clip.

Hmm good point about the 2nd video. To be honest I'm not sure what exactly it's showing; the engine indeed runs evenly but with very low RPM (or time is slowed down). At any rate I have a hard time imagining the final game will show all planes at night with a strobe light effect around the engine...

[flyingblind]

I don't think an exact colour match could ever be achieved as every monitor shows a slightly different colour anyway. The only comment I would make about the first video compared with the real life videos people have posted is that in real life the yellow flames are produced by a cloud of unignited fuel/air mixture being expelled from the engine and subsequently being lite by the burning exhaust gas once the engine has fired. As such no pressure is involved and the flames are quite 'lazy' in appearance. In Olegs game video the yellow flames are being expelled with considerable force. In the second video it looks like the engine is idling before takeoff rather than running under power so exhaust gases could well look more yellow than blue.

[T}{OR]

Originally Posted by flyingblind

I don't think an exact colour match could ever be achieved as every monitor shows a slightly different colour anyway. The only comment I would make about the first video compared with the real life videos people have posted is that in real life the yellow flames are produced by a cloud of unignited fuel/air mixture being expelled from the engine and subsequently being lite by the burning exhaust gas once the engine has fired. As such no pressure is involved and the flames are quite 'lazy' in appearance. In Olegs game video the yellow flames are being expelled with considerable force. In the second video it looks like the engine is idling before takeoff rather than running under power so exhaust gases could well look more yellow than blue.

+1000

And it also depends on the mixture / priming of the engine in the first place. The biggest remark is just that - on low RPM when starting an engine the flames should be 'lazy', because un-ignited fuel is coming out of the engine cylinders and thud burns outside it - vertically. Only when the engine actually starts the flames get expelled horizontally (axially with the each cylinder exhaust pipe) as in many videos posted here accompanied with a transparent blue flames. Not to mention the vast amount of smoke as well (but this effect is done nicely).

[smink1701]

Oleg,

Flame looks fine...only lasts a few seconds anyway. The visuals we've seen are amazing. I hope you put equal effort in getting the sounds right. IMHO

[FG28_Kodiak]

Have found this table for the Allison V-1710 Models 'E' and 'F' (from Allison Service School Handbook ALD-SSH-5) I know its not a Merlin

[Blackdog_kt]

Originally Posted by FG28_Kodiak

Have found this table for the Allison V-1710 Models 'E' and 'F' (from Allison Service School Handbook ALD-SSH-5) I know its not a Merlin

That's very useful. It also confirms what most people have been saying, that the temperature of the exhaust gas and the subsequent colour is a consequence of a variety of factors that can affect fuel burn. High or low power, mixture settings, etc, all seem to play a role.

The most interesting part in the picture you posted is the possibility to diagnose problems or verify the correct operation of the engine.

For example, leaning the mixture. In today's general aviation piston engined aircraft, leaning is usually done by moving the mixture lever back until you see the EGT (exhaust gas temperature) gauge reach a peak, if you lean any further it will start dropping again. So, for example let's say the peak EGT occurs with the mixture lever at the 75% forward position. If you move it forward/backward from that position the EGT will drop. What the pilots do is start leaning and watch for the reversal in the needle (watching it rise, then drop again from over-leaning), at which point they enrich it a bit to get it back to peak EGT.
Then, they enrich a bit further until the EGT drops a set number of degrees, which is usually specified in the aircraft manual. This is usually stated like this: "lean mixture as follows: for best cruise enrich to 50 degrees below peak EGT, for best economy enrich to 30 degrees below peak EGT". Peak EGT is not a constant but that doesn't bother us. For example, if running 75% power the EGT on the whole (which includes the peak value) will be higher than what we would get if running at 60% power, but all we care about is "catching" the highest temp on the gauge and enriching a set number of degrees from that, not what the highest temp actually is.

So, why do we care? Because i think most aircraft in WWII didn't have an EGT gauge, but the picture you posted showed the same method being possible to use by watching the exhaust stacks.
Lean mixture on the allison gives a blue flame, rich mixture gives a red flame near the stack and a blue flame further away but it says the blue flame moves closer to the stack as the mixture is corrected. Finally, the correct mixture has the blue flame near the stack and the red flame behind the blue one.
So, one could theoretically lean the mixture until he sees too much of a blue flame that signifies the peak EGT (the higher temperature of exhaust gas, which gives off the blue glow). Then, they would have to enrich it a bit as described before, judging when to stop by the appearance of red flame behind the blue one, but not going as far as having the flames reversed (blue after red) because that would signify an overly rich mixture.

Excellent stuff!