correct as is Cold start without APU: Ground air supply should not be possible to start the engine!

[GNCRamBo]

Hello everyone,

Yesterday I tried the cold start without APU.

First I got an external ground power supply and the starter did not work.

Then I got external ground air supply, and the starter worked and powered the generator in the engine.

But ChatGPT told me that the starter of the AH-64D only works with electric power and not with compressed air. And that the engine cannot be started with compressed air either, but only with the electrically powered starter.

Is ChatGPT wrong?

[Tholozor]

ChatGPT is incorrect. The engines use Air Turbine Starters (ATS) that run on pressurized air either from APU bleed air, engine bleed air (if one is already running), or external ground air.

Edited October 13, 2024 by Tholozor

[Raptor9]

@GNCRamBo, as Tholozor stated, the engine starters are pneumatically powered and can indeed be powered by external air supply.

ChatGPT or similar AI aggregation programs should not be considered a reliable source for anything, as they are unable to ascertain what sources and information on the internet are accurate or not, and are prone to simply repeat rumors, misinformation, misconceptions, or folklore.

[GNCRamBo]

Just not to misunderstand:

The starter (PTO = Power TakeOff drive assembly!?) is powered by external or internal (APU) compressed air.

The PTO then drives a drive shaft that leads directly into the engine and turns the generator part (NG part)of the engine.

The engine is therefore not started directly with compressed air, but indirectly via the PTO.

Is this correct?

[Raptor9]

@GNCRamBo, the engine core (compressor and gas generator rotors aft of the combustor) mechanically drives the accessory section of the engine, which has all of the various other engine-driven components mounted to it such as the alternator, hydromechanical unit (the fuel control), IPS blower, fuel pump, oil pump, lubrication filters, etc. The PTO shaft is what mechanically transfers the engine power to the accessory section so all of the accessory components can function. The rotational speed of the engine, referred to as NG, is measured by the alternator itself, and the alternator provides backup power to the engine electronics so that the engine can still operate in case of a power failure of the aircraft electrical system.

During the start sequence, the engine starter device known as the Air Turbine Starter (ATS) drives the accessory section which back-drives the engine core to spool the compressor during the engine start sequence. The ATS is powered by expelling high-pressure air across an impeller within the ATS itself, and this pneumatic pressure is normally provided by bleed air from the APU; but it can also be provided by bleed air from the opposite engine or from an external pneumatic power source.

The engine is started by pneumatic air from the APU, the opposite engine, or an external air supply. It is not started by the PTO because the PTO is just an internal component of the engine that links one section of the engine to the other, much like how the central engine shaft links the compressor and the gas generator stages. If you do not have pneumatic air to spin the engine, the engine will not start.

[GNCRamBo]

Ok, thanks for this very detailed explanation. I think I've finally understood it

[Kutscha]

Hello

 

if I connect the grpund crew with ground power I would suggest (from my pilots experience) that I ca start the engines witout using the onboard APU. Is this correct?

Butthis does not work power supply top the systems will brake down on idle without APU but Ground power supplied. It only keeps the systems working in throttles to flight.

An is there no indication in the cockpit about a plugged in external power supply like the GPU?

 

THX

[LorenLuke]

2 hours ago, Kutscha said:

Hello

 

if I connect the grpund crew with ground power I would suggest (from my pilots experience) that I ca start the engines witout using the onboard APU. Is this correct?

Butthis does not work power supply top the systems will brake down on idle without APU but Ground power supplied. It only keeps the systems working in throttles to flight.

An is there no indication in the cockpit about a plugged in external power supply like the GPU?

 

THX

Did you connect to the ground air supply as well?

Engines are started via bleed air from the APU, not by electric power it generates.