What is the electrical power output of a turbofan engine?

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Discussion Overview

The discussion revolves around the electrical power output of turbofan engines, specifically in the context of the Airbus A380. Participants explore the potential for additional electrical power generation within these engines and its implications for powering auxiliary systems, such as small rotors for vertical takeoff and landing (VTOL) capabilities.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant inquires about the typical electrical power output of turbofan engines like the Rolls-Royce Trent 900 and Engine Alliance GP7000.
  • Another suggests looking at the electrical power needs of the aircraft as a starting point for understanding the power output.
  • A link is provided that states Airbus plans to use four generators, each outputting 150 kVAs, with a total requirement of 380 kVAs in cruise.
  • One participant expresses interest in how much electrical power remains after internal systems are powered, questioning if it could be used for additional rotors.
  • There is a humorous exchange about the potential use of electrical rotors for non-critical applications, such as making smoothies.
  • Concerns are raised about the feasibility of using excess power for VTOL, with one participant arguing that VTOL requires dedicated design rather than relying on extra generator power.
  • Another participant notes that using excess electrical energy could reduce engine thrust or increase fuel consumption, emphasizing that there is no free energy available.
  • Discussion includes the idea that rotors would only need power during takeoff and landing, with existing engine power being sufficient for cruising.
  • Participants discuss existing VTOL aircraft designs, such as the Harrier and Osprey, and the reasons for their design choices regarding propulsion systems.
  • One participant suggests that the power output and thrust of the engine should be considered in relation to the mass of the aircraft for VTOL applications.
  • Concerns are raised about the risks associated with VTOL and its regulatory approval for commercial use.

Areas of Agreement / Disagreement

Participants express a range of views on the feasibility of using electrical power from turbofan engines for VTOL applications. While some acknowledge the potential for extra power in multi-engine aircraft, others argue that VTOL requires dedicated designs and that using excess power could have negative implications. The discussion remains unresolved with multiple competing views.

Contextual Notes

Participants highlight limitations regarding the assumptions about power availability, the need for dedicated designs for VTOL, and the implications of using additional electrical loads on engine performance.

royp
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TL;DR
A typical, modern turbofan engine system of an aircraft also works as a generator to produce the electricity. What is the power output we normally have?
Hello All,
Happy New Year!

A typical modern turbofan engine system creates lift as well as propulsion for the aircraft. Somewhere inside the system, the fast rotating device also works as a generator (alternator) to produce the electricity powering electrical/electronics equipments. What is the quantity of power (Kw/Mw) typically produced? For instance, for a Rolls-Royce Trent 900 or Engine Alliance GP7000 (A380-861) turbofan used for Airbus A380 - what is the power output? My personal search on the engine performance did not exactly pick up the specific electrical power.

Can anybody help me with the parameter please?

Many thanks in advance
 
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A good first guess would be the electrical power needs of the aircraft. Have you tried searching for the answer that way?

And is this for schoolwork? I can move the thread to the schoolwork forums if it is. Thanks.
 
Thanks anorlunda, for the link.

No, berkeman: This is not schoolwork. I am trying to figure out how much extra electrical power are left after feeding the internal systems. Whether enough is left to run an additional array of small, electrical rotors.
 
royp said:
Whether enough is left to run an additional array of small, electrical rotors.
Like blenders? For smoothies? :wink:
 
Also, keep in mind that if your smoothie-making (or whatever) electrical rotors are not mission-critical (and can be shut off in an emergency), there should be lots of extra power available on multi-engine aircraft.

Quiz Question -- Why? :smile:
 
berkeman said:
Also, keep in mind that if your smoothie-making (or whatever) electrical rotors are not mission-critical (and can be shut off in an emergency), there should be lots of extra power available on multi-engine aircraft.

Quiz Question -- Why? :smile:

That is very vital information ("... lots of extra power available on multi-engine aircraft"), berkeman. Thanks. Actually I was toying with the idea/design of having an array (say 4 x 50) of tiny rotors at the bottom and along the length of the aircraft. (Just to clarify: these rotors will be shielded properly to avoid damage and air will be sucked in). The objective is to get necessary lifts by these rotors for the aircraft in an attempt to achieve VTOL (not for A380 but more modest-sized aircrafts)? I was wondering how to power these rotors.
 
royp said:
That is very vital information ("... lots of extra power available on multi-engine aircraft"), berkeman. Thanks. Actually I was toying with the idea/design of having an array (say 4 x 50) of tiny rotors at the bottom and along the length of the aircraft. (Just to clarify: these rotors will be shielded properly to avoid damage and air will be sucked in). The objective is to get necessary lifts by these rotors for the aircraft in an attempt to achieve VTOL (not for A380 but more modest-sized aircrafts)? I was wondering how to power these rotors.
There's nowhere enough excess power available for VTOL. VTOL takes a purpose-built aircraft design, not using a few extra kW of generator power. And I would also point out that VTOL power is mission-critical, so that shoots that other whole line of Quiz Question that I was asking...
 
Of course using "excess" electrical energy will reduce the engine's thrust or increase fuel consumption. Additional load on the gas turbine will decrease it's life too. There is no free energy available.
 
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  • #10
I totally agree that it has to be a dedicated design (not the proverbial pig with wings...). But I assume that the rotors will need power during take-off/landing only? For gaining height and cruising of the aircraft, the existing engine power (assuming the engines are sufficiently powerful) will suffice?
 
  • #11
royp said:
I totally agree that it has to be a dedicated design (not the proverbial pig with wings...). But I assume that the rotors will need power during take-off/landing only? For gaining height and cruising of the aircraft, the existing engine power (assuming the engines are sufficiently powerful) will suffice?
What detailed reading have you done so far about current VTOL aircraft?
 
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  • #12
I assume that you already know about Harriers and Ospreys (aircraft, not birds). Why do you suppose each of these aircraft designers chose not to mix jets and propellers?
 
  • #13
Please allow me to reply tomorrow...
 
  • #14
DaveE said:
I assume that you already know about Harriers and Ospreys (aircraft, not birds). Why do you suppose each of these aircraft designers chose not to mix jets and propellers?
The F-35B does have both a jet engine for thrust and a driven lift propeller. It actually gives the F-35B an advantage over the Harrier design because the propeller does not generate the hot exhaust that can cause problems at the jet inlet.
 
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  • #15
royp said:
That is very vital information ("... lots of extra power available on multi-engine aircraft"), berkeman. Thanks. Actually I was toying with the idea/design of having an array (say 4 x 50) of tiny rotors at the bottom and along the length of the aircraft. (Just to clarify: these rotors will be shielded properly to avoid damage and air will be sucked in). The objective is to get necessary lifts by these rotors for the aircraft in an attempt to achieve VTOL (not for A380 but more modest-sized aircrafts)? I was wondering how to power these rotors.
You should look at the power output (not by a generator, but the actual output of the engine) and thrust vs the mass of the airplane. I think you will find that the takeoff roll is what it is, and there is little opportunity for reducing it with larger fans.
 
  • #16
You are not the first who is thinking about VTOL by electric fans, but I think a direct approach would be more ... direct.

Te problem is the size. It works for an aircraft with limited range/size, but not for anything big. The linked engines can produce thrust of ~ 350kN: that would be able to make 35t mass hover. A380 is four engine, so you can have raw capacity to lift 140t against the 500+t MTOW when it's done the classical way.
And that's just hovering alone.

Also, VTOL is a risky business: I'm not sure it would gain approval for commercial/passenger usage.
 
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  • #17
FactChecker said:
The F-35B does have both a jet engine for thrust and a driven lift propeller. It actually gives the F-35B an advantage over the Harrier design because the propeller does not generate the hot exhaust that can cause problems at the jet inlet.
Thank all of you very much for your rich and very knowledgeable contribution. I got some very valuable insight!
 
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