MolaKule Q&A on Aircraft Structures VII Engines

[MolaKule]

New Engine/Nacelle Question:

On most aircraft, the turbofan engine is "setback" in the nacelle. I.e., from the front of the nacelle to the fan, there is a space.

Owing to the shape of the nacelle, explain why this position is preferred.

 

[barryh]

Could there be air spillage out the front if the fan was not set back in the nacelle.

 

[tbm5690]

New Engine/Nacelle Question:

On most aircraft, the turbofan engine is "setback" in the nacelle. I.e., from the front of the nacelle to the fan, there is a space.

Owing to the shape of the nacelle, explain why this position is preferred.

Obviously the only reason is to allow for cool pictures of pilots sitting/standing in the nacelle.

 

[barryh]

Another reason for the fan being set back in the nacelle might be noise reduction.

 

[MolaKule]

Another reason for the fan being set back in the nacelle might be noise reduction.

It does reduce fan noise to some extent.

Owing to the shape of the nacelle, explain why this position is preferred.

The general shape of the nacelle is one of a converging duct, but there is an additional factor in play. Since the 'area' of the inlet is larger than the fan's area, this represents a "ram" effect in flight, increasing air flow and pressure through both the nacelle and the core.

Remember, It comes down to four distinct parts that can be described with four verbs: suck, squeeze, bang and blow.'

 

[MolaKule]

New Engine Question:

The Boeing 787 has 2 VFSG units per engine.

Define these units and explain their respective functions.

 

[Skippy722]

New Engine Question:

The Boeing 787 has 2 VFSG units per engine.

Define these units and explain their respective functions.

Variable Frequency Starter Generator units. 787 is all electric, no bleed air, so they are capable of starting the engines and then generating power for the aircraft.

 

[MolaKule]

Variable Frequency Starter Generator units. 787 is all electric, no bleed air, so they are capable of starting the engines and then generating power for the aircraft.

Very good.

It also has two more generators in the APU for a total power generating capability of 1.4 Megawatts, enough equivalent power for 84 homes.

 

[Cujet]

Variable Frequency Starter Generator units. 787 is all electric, no bleed air, so they are capable of starting the engines and then generating power for the aircraft.

Neat.

Our business jets use something akin to a hydraulic automatic transmission to keep all 3 of the integrated 3 phase, 40KVA generators in sync. All three stay in phase perfectly. We call it an "Integrated Drive Generator (IDG)" which combines a Constant Speed Drive (CSD) and a generator into a single unit. They are exceptionally reliable and lighter than the wild frequency generators + converters.

The Variable Frequency generators were something we used years ago on the Gulfstream IV (4). The conversion from wild frequency AC to 400HZ was, at the time, very problematic.

Yes, that little device makes 40,000 Watts (or a bit more/less) depending on Power Factor. It uses 2380 engine oil as a working fluid.

 

[MolaKule]

Neat.

Our business jets use something akin to a hydraulic automatic transmission to keep all 3 of the integrated 3 phase, 40KVA generators in sync. All three stay in phase perfectly. We call it an "Integrated Drive Generator (IDG)" which combines a Constant Speed Drive (CSD) and a generator into a single unit. They are exceptionally reliable and lighter than the wild frequency generators + converters.

The Variable Frequency generators were something we used years ago on the Gulfstream IV (4). The conversion from wild frequency AC to 400HZ was, at the time, very problematic.

Yes, that little device makes 40,000 Watts (or a bit more/less) depending on Power Factor. It uses 2380 engine oil as a working fluid.

Do you recall if they used 3-phase Y or Delta configs?