Startup procedures
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I have a question regarding engine starting procedures. If I'm reading the checklists correctly, for a battery-powered start, the prop levers should be full forward. However, for an external power start, the procedure calls for the props to be in feather. The first scenario makes sense to me - it reduces the load on the starter - but what's the rationale for feathering the props when using external power?
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OK, so given the apparent benefits of prop feathering (lower noise, prop wash), perhaps the full-forward position implying faster spool-up of the free turbine during a battery start helps reduce max ITT (by more efficient exhaust flow), especially when N1 acceleration is slower due to limited starter power?
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OK, so given the apparent benefits of prop feathering (lower noise, prop wash), perhaps the full-forward position implying faster spool-up of the free turbine during a battery start helps reduce max ITT (by more efficient exhaust flow), especially when N1 acceleration is slower due to limited starter power?
@piosto said in Startup procedures:
OK, so given the apparent benefits of prop feathering (lower noise, prop wash), perhaps the full-forward position implying faster spool-up of the free turbine during a battery start helps reduce max ITT (by more efficient exhaust flow), especially when N1 acceleration is slower due to limited starter power?
ITT isnt really affected by how fast the Np turbine spins. Some aircraft like the ATR lock the right hand Np with a brake and run the engine like an APU. On the twin otter, the prop stap doesnt block the intake but attaches to the cowling and there have been instances of starting the engine with the prop strap installed and not damage is done
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OK, so given the apparent benefits of prop feathering (lower noise, prop wash), perhaps the full-forward position implying faster spool-up of the free turbine during a battery start helps reduce max ITT (by more efficient exhaust flow), especially when N1 acceleration is slower due to limited starter power?
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@piosto said in Startup procedures:
OK, so given the apparent benefits of prop feathering (lower noise, prop wash), perhaps the full-forward position implying faster spool-up of the free turbine during a battery start helps reduce max ITT (by more efficient exhaust flow), especially when N1 acceleration is slower due to limited starter power?
ITT isnt really affected by how fast the Np turbine spins. Some aircraft like the ATR lock the right hand Np with a brake and run the engine like an APU. On the twin otter, the prop stap doesnt block the intake but attaches to the cowling and there have been instances of starting the engine with the prop strap installed and not damage is done
@ProfCrash Because there is no mechanical connection.
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Thanks for your inputs, but I'm still a bit confused. While I understand there's no mechanical connection between the gas generator and the propeller section, subtle factors—like the inertial separator position or even wind direction—can still influence ITT during start. That's why I'd assume that if N2 spools up faster (as might happen with props full forward), it could improve airflow through the engine and reduce ITT at least slightly.
If that's not the case, then my original question still stands: what’s the rationale behind using full-forward props for a battery start, but feathered props for an external power start?
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Thanks for your inputs, but I'm still a bit confused. While I understand there's no mechanical connection between the gas generator and the propeller section, subtle factors—like the inertial separator position or even wind direction—can still influence ITT during start. That's why I'd assume that if N2 spools up faster (as might happen with props full forward), it could improve airflow through the engine and reduce ITT at least slightly.
If that's not the case, then my original question still stands: what’s the rationale behind using full-forward props for a battery start, but feathered props for an external power start?It doesn't make any significant difference in ITT if starting feathered vs. full forward. On the actual aircraft, the peak ITT is usually achieved well before the propeller RPM has reached a hundred or so. Battery and hot section condition are the primary determinants in the health of your starts.
The only reason you maybe keep things feathered with an external power start, is simply for noise and comfort of the ground crew. They have to remove the GPU plug from the L/H wing. Less air being drawn and sucked across the wing. Reduces risk of a hat or something being drawn into the spinning propeller.
It's less an issue though with Starship's "backward" PT6 installation.
Patrick