Friday 2010-12-17 Dev. update and Discussion

[alexei1789]

it was not a request, but a simple question...

for realism, i would never have thought by myself about the exhaust flammes for a flight sim !

Merry Christmas Oleg, develommental team and the forum

[T}{OR]

A quick summary after watching all the videos posted here, and following the discussion.

Lets not get too carried away...

Precisely that. Like someone already stated that these flames are deliberately overdone.

There are few factors we should consider when talking about (visible) engine exhaust flames:

1. All videos show planes standing or taxiing on the ground.
2. Although visible on many videos, most of us will agree that they are barely visible - or invisible during daylight.

Thus I will point out to three videos which IMHO more accurately represent what should (can) be seen in real life and thus in the game.

"Seafire night ground run" - watch how high RPM affects engine exhaust:

http://www.youtube.com/watch?v=Xs_qt4GCj4A

The thing everyone forgot to mention is a very fast stream of air which is blowing over the exhaust stacks (with higher RPM) - undoubtedly much faster and colder once the plane is airborne => further reducing the exhaust flames length because of the fast air stream and also a small portion due to forced convection (cold air cooling the exhaust pipes).

Just like Oleg said:

Please read with atention: The color of exhaust from the direct pipe and from the extended are different. The temperatue of the flame decreasing with the longer leght of pipe. More lower temperature...

"Spitfire MH 434 - Part 3/5" - this, I believe is how the flames should be represented in the game, starting from 5:30 (fast forward) first the engine start is shown and then camera shows directly into the exhaust stacks:

http://www.youtube.com/watch?v=UDZmq2VrcNQ

After slightly over primed start the only visible flames are during engine start (due to some fuel left from previous unsuccessful attempts). Once the engine has been started watch how there are no flames exiting the exhaust pipes, even when RPM is increased - although they are visible under the right angle (when looking directly into the exhaust pipes like shown in the video).


And last, the most important video IMO... "Bf 109 Stack Flaming" - posted by Richie, which although doesn't feature exhaust flames, it shows exhaust smoke when changing throttle:

http://www.youtube.com/watch?v=48uziQoniI0

If I would have to choose between the right colored exhaust flames and correctly represented puffs of smoke when changing throttle => I would without a doubt choose the latter because it impacts gameplay and is overall more important feature.

[Richie]

A picture of a 109 G-4 low on a darker day with no flames.

[SlipBall]

(quote)T}{OR
If I would have to choose between the right colored exhaust flames and correctly represented puffs of smoke when changing throttle => I would without a doubt choose the latter because it impacts gameplay and is overall more important feature.


I agree, there's something about turbo's that causes a dark smoke after a quick throttle increase...even in todays world with on road vehicles and their modern engines. So I like the idea of the 109 having that behavior

[T}{OR]

Originally Posted by SlipBall

I agree, there's something about turbo's that causes a dark smoke after a quick throttle increase...even in todays world with on road vehicles and their modern engines. So I like the idea of the 109 having that behavior

Pressure-charging might indeed have a bit increased effect on the smoke puffs during throttle changes. Unless I am mistaken, WW2 planes had only superchargers, not turbochargers.

Combustion during constant RPM is totally different than one during variable RPM. The reason for this is rapidly changing and unequal ratio of fuel and air in the cylinder (variable mixture) - accompanied with black puffs of smoke coming out of the exhaust manifold. Once you set on an desired RPM it takes the engine few seconds to 'stabilize'. Fuel consumption is also much higher during these frequent throttle changes, when compared to running at constant RPM (i.e. just like city / highway driving).

Just like you said - the best example are trucks, when the driver adds power it is always accompanied with thick black smoke coming out of the exhaust. Once it is driving with a constant speed, there is barely any smoke coming out of the exhaust. As far as turbos and truck engines... sometimes it takes up to 2-3 minutes for the exhaust gases to 'stabilize' and spin the turbo for it to have a desired effect.

[SlipBall]

(quote)
WW2 planes had only superchargers, not turbochargers.



They are the same, the difference being the power source

[T}{OR]

Originally Posted by SlipBall

They are the same, the difference being the power source

In basic terms, yes.

For a supercharger to work you have to use some of the energy produced on the crankshaft, while turbo uses energy off the exhaust gases which is "free".

The downside is that turbo works best on higher RPM ("turbo lag"), while superchargers can follow and adjust to engine RPM much more rapidly.


IIRC the development of turbochargers and the reason why they are so available todays happened after WW2. => See post 141.


EDIT: As a result, the latest developments led to a process called 'downsizing' where in todays engines you now have a supercharger for low RPM which disengages (usually via magnetic clutch) around 2500 RPM and then turbo takes over.

[SlipBall]

Originally Posted by T}{OR

In basic terms, yes.

For a supercharger to work you have to use some of the energy produced on the crankshaft, while turbo uses energy off the exhaust gases which is "free".

The downside is that turbo works best on higher RPM ("turbo lag"), while superchargers can follow and adjust to engine RPM much more rapidly.


IIRC the development of turbochargers and the reason why they are so available todays happened after WW2.

Yes, you are correct

[Sutts]

Originally Posted by T}{OR

Unless I am mistaken, WW2 planes had only superchargers, not turbochargers.

In basic terms, yes.

For a supercharger to work you have to use some of the energy produced on the crankshaft, while turbo uses energy off the exhaust gases which is "free".

The downside is that turbo works best on higher RPM ("turbo lag"), while superchargers can follow and adjust to engine RPM much more rapidly.


IIRC the development of turbochargers and the reason why they are so available todays happened after WW2.


EDIT: As a result, the latest developments led to a process called 'downsizing' where in todays engines you now have a supercharger for low RPM which disengages (usually via magnetic clutch) around 2500 RPM and then turbo takes over.

Not sure if I understand you correctly. Turbochargers were most definitely used during WWII but on aircraft such as the P-47 and P-38 and bombers such as B-17 and B-24. I don't think any BoB aircraft used them.

[T}{OR]

Originally Posted by Sutts

Not sure if I understand you correctly. Turbochargers were most definitely used during WWII but on aircraft such as the P-47 and P-38 and bombers such as B-17 and B-24. I don't think any BoB aircraft used them.

The function of both is the same - i.e. to compress the air before it enters a cylinder. Either to produce the same atmosphere as if you were flying on sea level or to increase engine power. The difference is how they are driven. Supercharger is linked to the crankshaft usually with a belt pulley or set of gears. Turbocharger is driven by exhaust gases and thus for it to operate efficiently requires certain speed out of those gases - i.e. works best when on mid or high RPM. Early turbochargers were massive in comparison what we have today.

Although they were available before WW2, rapid development of turbochargers started after WW2, IIRC when F1 started using them (they were banned in F1 shortly afterwards due to excessive power these engines produced).



EDIT: You are correct:

Aircraft such as the Fw 190D, B-17 Flying Fortress, and P-47 Thunderbolt all used turbochargers to increase high altitude engine power.

So says Wikipedia.

I presume that you could only mount them in larger (e.g. radial engines), because even in 70's they were massive compared to today. And it makes sense - especially with P-38 which has those long pylons behind engines.