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Engine RPM after startup


C-130Hercules
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Hi everyone,

After seeing this video, I have some questions.

I know that the turboprops of the Herc are constant speed ones, meaning the pitch of the blades is adjusted in order to gain speed.

In the video above, a Fat Albert is going through startup procedures. At 0:05 engine No.3 starts up and at 0:43 it seems like the engine is at idle speed. Then at 0:46 the engine increases its RPM which can be heard and seen.

This startup procedure is repeated for the engines No.4, No.2 and No.1.

When the video reaches 2:11, the engines somehow decrease their RPM. And with this RPM, the Fat Albert starts to taxi.

Is there some kind of switch to increase and decrease the RPM of the engines?

And what is the use of this increase and decrease of RPM?

 

I hope to hear from someone soon.

Kind regards,

C-130Hercules

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The engines have 2 speed settings, low speed ground idle and normal. Low

speed is used to start and stabilize the engine, and also to do minimum

torque calibration. Engines are generally held in low speed for taxi as it is

easier to control oil temperature, than in normal. The #3 engine is

sped up to normal to provide extra bleed for a quicker start on the other

engines, and to provide air for the air conditioning packs. The APU

provides +-40psi air pressure (unloaded) while an engine provides 80

to 100psi, although this is regulated to 70psi on some

models

 

Also use of low speed reduces fatigue on turbine assemblies

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