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michael-t

T.O./LAND vs. Normal Flight Condition levers

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When shifting the condition levers from "Normal Flight" to "T.O./LAND", the engine temperature goes slightly up into the yellow range. On the other side, I have learned that the same engines in the PMDG JS41 get cooler when the condition levers are advanced. Per the JS41 manual, this is due to a cooling effect on the engine core of the surplus fuel. Could someone please explain why the Bronco seems to behave different?

Michael

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I think that's because the propeller setting changes with the condition levers (RPM up, prop flatter, torque down. There is no reason more fuel is injected though as the difference between the settings only changes the lowest RPM (from 70% to 96% in flight). This allows the engine to respond faster.

But Finn (who is at the Christmas diner now) will know more.

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When shifting the condition levers from "Normal Flight" to "T.O./LAND", the engine temperature goes slightly up into the yellow range. On the other side, I have learned that the same engines in the PMDG JS41 get cooler when the condition levers are advanced. Per the JS41 manual, this is due to a cooling effect on the engine core of the surplus fuel. Could someone please explain why the Bronco seems to behave different?

Michael

The Jetstream engines have nothing in common with the Bronco motors other than a common core and about three times the power. Not sure if there is ANY commonality in the fuelling system? Anything other than the most sweeping of generalisations is likely fraught with potential blunder.

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When shifting the condition levers from "Normal Flight" to "T.O./LAND", the engine temperature goes slightly up into the yellow range. On the other side, I have learned that the same engines in the PMDG JS41 get cooler when the condition levers are advanced. Per the JS41 manual, this is due to a cooling effect on the engine core of the surplus fuel. Could someone please explain why the Bronco seems to behave different?

Michael

As far as I know, in the Jetstream, the condition levers do not control fuel flow except when in Beta mode (through means of a fuel governor). The reduction in temperature is more likely caused by the increase in mass air flow through the turbine due to the increase in RPM. Could you tell me which section/page of the J41 document describes it as being a result of surplus fuel, perhaps I'm mistaken?

As for the Bronco, I'm not getting much out of the manual. It is unclear to me which levers control which functions. It mentions;

- The power levers control thrust output (how, do they alter fuel flow, do they alter the propellor pitch directly, or can they do both, like the Jetstream does with PG Mode and Beta Mode?)

- The condition levers control fuel flow and set minimum RPM (do they tell an underspeed governor you want a minimum RPM of X and open some fuel valves or do they actually control fuel flow rates and propellor pitch?)

Without knowing those factors it might be tricky to explain exactly why the TiT in the Bronco increases. It could be adding fuel, combined with the increased airflow, causing more combustion in the turbine. Or it could just be the SRL computer intentionally indicating a higher TiT to add extra protection against engine overheating.

I like to know this kind of stuff. It's one thing to see what effect pulling this or that lever has, it's another to know how the effect is achieved. Is there a possibility for more info on those items?

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Propane,

thank you for your comments. I read up the PMDG JS41 docs and "surplus fuel" was my misunderstanding. As you already mentionend, PMDG writes of "reducing RPM is going to reduce the mass-flow".

I also would like to see more precise technical documentation about the Bronco. I admired this plane from the days when I was a little boy. Together with my father, we every year visited the Royal Air Force Wildenrath air shows. The Broncos, Vulcans, Lightnings, Canberras, Belfasts and so on deeply impressed me.

Michael

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