Heat exchange and electrical system

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ricfishner
Posts: 2
Joined: 09 Aug 2018, 16:51

Heat exchange and electrical system

Post by ricfishner » 09 Aug 2018, 17:36

Hello,
first I have to thank you for this amazing add-on! Although in Early Access state I find it bringing up a huge immersion factor and it did force me to "learn flying again", without all the fancy nav aids. There's also a lot of eye candy, but unlike some other (just) good looking add-ons I feel it is all there for a reason ;)

So after falling in love with it I decided to stop all my (virtual) flying duties down in South California and transfer the Vega up north to Alaska.
I did so with several stop overs along the North american west coast.

During the trip I experienced two things that I consider to be somewhat wrong:

(1) Heat Exchange issues
on a longer leg (about 2 hours flying time), all of a sudden I had the oil pressure warning light coming up. As the manual states that the failure module is not implemented yet, I wondered how that happened. I closed the sim and started the next leg; again, after 1 to 2 hours I lost oil pressure. The oil quantity according to my mechanic Jack and the debug tool was just fine (around 29.9 l). I also tried deleting the data.dat file and had it rebuild for new, but the same issue occured. So far I found out that it seems to be linked to extreme temperatures I see in the Heat Exchange section. It seems that the engine back temperature is fine for a while but then starts to raise quickly. This seems to be affecting the temperature of other parts (oil pump, fuel pump etc.), and this again interferres with engine back temperature, so it raises even more quickly (constantly adding up). A downward spiral.. I've encountered temperatures as high as over 2000°C and don't think this is in "normal range".
Even more strange: Right after touchdown, the engine's back temperature drops again (to around 200°C), and after shut down it goes down into minus degrees..

(2) Elecrical section in data.dat
because of the above issue I checked again the data.dat file (no changes made, just looking for something strange) and I found a line "=0" in the electrical section. First I thought it may be my mistake, having deleted something. But after rebuilding the data.dat file the line is still there, just "=0". Also the log.txt seems to catch it, as there a numerous entries saying "electrical system data not located in config file. Resetting battery specs.".

I'm using prepar3d V4.3 with Active Sky, my default flight is the standard one.
For the Vega I only tweaked the sound files (as recommended here in the forum) and added the handheld radio as per instructions in the manual.


Kind regards,

Ric

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Vitus
Posts: 183
Joined: 17 Jul 2017, 15:19
Location: Görlitz, Germany
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Re: Heat exchange and electrical system

Post by Vitus » 09 Aug 2018, 18:35

Hi Ric,

Thank you so much for your kind words, it's wonderful to hear that you're having such a great time with the airplane.

As for the issues you found:
1. The thing about the heat-exchange module is that the calculations are all based on real physics, so the way the heat is being transferred from one component to the other is accurate. The issue is that for each of these calculations the parameters need to be correct as well, and those are very difficult to get right. It'll be a long process to tune all these relationships until they properly represent reality and your report helps me with this.
At 2000 degrees centigrade, steel starts to glow white. So essentially you just melted your engine away, so I think the oil pressure warning light should be the least of your problems :lol:

But just to give you the insight why the light wet on: as the engine heats up, energy in form of heat is transferred to connected components, the surrounding air and the oil that circulates those components. The oil viscosity (a measure of its liquidity) is mostly dependent on it's temperature. So when the oil starts to reach, say 100 degrees, it gets too runny and as a result the pressure in the system starts to drop. At these ridiculous temperatures of 2000 degrees, your pressure must have dropped to something around 1 psi? So that's why the light went on in the first place.

Now for the greater mystery: how could the temperature ever rise to those levels?
It would be awesome if you could provide some more experimental data. What I'd love to know is the conditions you flew in (outside temperature), the oil type you used, how long your flight was aaaaand, most important: your engine settings when this happened. For instance, if you flew the engine with a fully open throttle and a lean mixture, I wouldn't be surprised about a catastrophic result like this ;)

But yes, ultimately this is probably an issue to do with the amount of heat being transported off the rear section of the engine. I'll keep tuning it until it's right.

2. Yes, and there is a reason for this: I programmed all necessary components for a ADF/NDB radio into the electrical system - an additional fuse, the consumers, etc. But since our 5C wasn't usually equipped with one, those sections of the code are disabled. The save/load code for the radio however is still executed, but since it's not initialized with a name (i.e. "ELEC RADIO") it submits an empty string to the data file, resulting in two unnecessary entries. The Direction finder radio will probably be part of the "Winnie Mae" to make those long-haul flights easier. The "Resetting battery specs" message always pops up in the log file after the data file was found empty, so that's normal :)

I hope this sheds some light, and thank you again for your feedback!
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ricfishner
Posts: 2
Joined: 09 Aug 2018, 16:51

Re: Heat exchange and electrical system

Post by ricfishner » 12 Aug 2018, 15:46

Hi Vitus,

thanks a lot for the insights! So, the next flights I had an eye on the parameters you mentioned. I did 4 flights, most of them being part of my ferry flight to Alaska. Unfortunately, again I experienced very high temperatures during three of the flights. Here are some Details:

1 - from Chilko Lake to Smithers, about 230 nm, using real weather (AS for P3D V4). Cruise at ~9000 ft. Outside temparature was around 9°C. Manifold 27,8 inHg (ok, close to the recommended 28 inHg as per checklist). According to the tooltip, my throttle was set to somewhat like 78%. The mixture was about 58% most of the time, which I think was pretty rich (soundwise), but I was trying to avoid a too lean mixture. Cylinder head temps were around 200°C. After about 1 hour the Engine back temp started to raise again and soon oil pressure was all gone. Anyway, I made it to Smithers as a glowing chunk of metal ;)

2 - from Smithers to Takla Lake, around 100 nm, again with real weather. I used pretty much the same power settings as in the 1st flight. This time I had no problems with temperature, but flight was shorter (just below 1 hour).

3 - from Takla Lake to Dease lake, around 200 nm, real weather. This time I reduced power settings, so I was cruising at around 9000ft with 24.4 inHg (throttle at 74%) and mixture to 40% (which "sounded" about right). Outside temperature was a bit cooler now, around -5°C. Cylinder head temps again just slightly above 200°C. Again, after about 1 hour the engine back temperature started raising.

4 - simple test flight over Germany, from Rinteln to Ruegen. This time without AS, just in standard "nice weather". I cruised at 3000ft to 4000ft with 24 inHg and mixture around 69% (again, pretty rich I think). Outside temperature was around -3°C, cylinder head temps just below 200°C. Again, I was fine for about an hour before temperatures raised.

So, I feel it is an issue with the flight time. For the first hour the engine back temperature stayed around 20°C during all my flights. After that it started raising constantly. Once it gets over 40 - 50°C, things go bad pretty fast. :shock:
And it seems to be always the engine back temperature that starts getting out of whack, cylinder heads and other parts, as well as the oil temps and pressure are still fine for a while even if I see the engine back back temperature being over 100°C. They start heating up after that.

I hope this helps to track down the problem! I will keep watching it and let you know if I find out more.


Best regards,

Ric

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Vitus
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Location: Görlitz, Germany
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Re: Heat exchange and electrical system

Post by Vitus » 14 Aug 2018, 10:07

Hey Ric, that's very interesting. Thanks a lot for your detailed analysis. I'll try to recreate some of your experiences and try to adjust the heat model to prevent this in the future. As I mentioned in the release notes of the last update: there's still a lot of tweaking required to get the numbers right.

Thanks again!
Otmar
Image Wing42 | The Simulation Company

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