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T5 temp too hot for no reason?


Ghroznak

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I went to Papau New Guinea to fly my Twin Otter (300-wheeled) around all those nifty little grass runways.

While doing so I noticed my T5 temperatures were really high (much higher than I was expecting).

Background info:

Ground temperature was 25°C, while the outside temperature (as shown both on the overhead thermostat and my active sky) at 11.000ft were at 10°C-12°C. I had no deice turned on except for the Pitot heating.

However, even with the Torque setting at 25 the T5 temperature was pushing the orange band and creeping towards red. I checked the Shift+2 checklist and the blue markers / indicators for continuous torque at ambient temperature showed that I could have engines at 42 on the Torque... but if I pushed the Torque even close to 30 the T5 temperature was deep into orange and almost pushing the red line.

I tried resetting the Twin Otter... then tried to switch to a different Twin Otter than the wheeled variant to a Tundra variant but still had the same temperature levels on my T5 despite low Torque.

Is this normal?

When I was flying in Alaska (with temperatures around +5°C to -5°C) the T5 seemed to be holding fine even with the Torque running continuously at 35-40.

I've added a screenshot of the instrument levels. What I noticed also was that T5 was high even at low Torque, but also the oil temperature seems quite low too? At least considering the temperature of the turbine?

**edit** Added a screenshot at bottom showing the blue line, but even at Torque setting to 30 my T5 is in orange (as seen by orange indicator on the T5 in center of those dials), despite it showing me I should be able to do over 40.

Hot_Otter.jpg

Hot_Otter_2.jpg

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I think it's normal. At higher altitude the engine efficiency is less due to the thinner air; the mixture is leaner so it runs hotter and hence you won't necessarily make the maximum calculated torque without exceeding temp limits. I tried this out and it behaves the same for me. As far as I can tell the blue line shows the torque setting where the T5 will go in to the red - in other words you need to be in the orange T5 zone to approach the blue line.

(P.S. Why do you have your standby boost pumps switched on?)

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I could not go near the blue line at all. When my Torque setting reached 30 the T5 dial was literally 1 pixel away from moving into red zone. Pushing it to 40+ would be a guaranteed engine fire.

Why wouldn't I have my standby boost pumps on? Isn't half the purpose to be on standby? :P Thats my deduction anyways. Not sure why they aren't mentioned in any of the checklists though.

That said, I did turn them off for a period to see if anything changed with regards to T5 (shouldn't matter, and it didn't matter).

Surprising to see such hot temperature though even at 11.000ft with 10°C OAT. Guess this means I need to be extra aware of the T5 gauge whenever I fly around in the south Pacific.

 

 

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I could not go near the blue line at all. When my Torque setting reached 30 the T5 dial was literally 1 pixel away from moving into red zone.

Well these are only my speculations, so don't take anything as too dogmatic. But I guess the blue lines are calculated by an algorithm, whereas in the real world you would calculate the torque limits manually using charts (or the DHC6 torque slide rule). You will notice that the blue lines move around according to external factors like altitude and OAT.

Your standby boost pump switches are for emergency use only. On each side the standby pump activates automatically in the event that the main pump fails (although it never does in the sim). You only need the manual swicth if the auto-changeover fails and you get a warning light (also never).

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It´s Ok to be in the orange range.

Depending on many factors, the higher You fly, the more You ar restricted by T5 temps rather than torque.

Normally You will become T5 restriced above 16.500 ft flying altitude, and at a lower altitude if the OAT is higher compared to ISA conditions.

So what You experience looks quite normal, cause what I see is also that You fly with max prop RPM.

Lower prop RPM and You will see a higher torque reading while the T5 should become lower.

 

Finn

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