Why aren't jet liners hybrid?
Discussion
The Spruce goose said:
Why couldn't a long distance airplane have a hybrid fan engine at the rear, which could be used to generate electricity as well as reduce drag when cruising. I know batteries are heavy but the trade off is less fuel and the batteries are reusable.
how do you generate electricity and reduce drag at the same time? Basic physics says you are looking at a perpetual motor scenario that just wont work.RobDickinson said:
how do you generate electricity and reduce drag at the same time? Basic physics says you are looking at a perpetual motor scenario that just wont work.
not really as my other response advises there is no free energy, and the gains would be small percentage but enough to save money,Edited by The Spruce goose on Thursday 12th October 22:38
The Spruce goose said:
not really as my other response advices there is no free energy, and the gains would be small percentage but enough to save money,
yes really. you cannot reduce drag and suck energy out of the airflow with an overall positive gain.All the energy comes from the driving engines, any fan you put there to recover energy will increase drag.
The Spruce goose said:
Mr E said:
Describe this "hybrid fan engine" in more detail?
3 engines 2 in normal place that can provide thrust or electricity generation on the wings, one at very back, full electric where tail point is. use it for reducing drag as the slow air would hit it.How do the regular engines generate electricity more efficiently than they generate thrust!
The Spruce goose said:
3 engines 2 in normal place that can provide thrust or electricity generation on the wings, one at very back, full electric where tail point is. use it for reducing drag as the slow air would hit it.
This isn’t making a lot of sense. Can you try drawing it to illustrate what you mean?What slow air are you thinking of?
The Spruce goose said:
Why couldn't a long distance airplane have a hybrid fan engine at the rear, which could be used to generate electricity as well as reduce drag when cruising. I know batteries are heavy but the trade off is less fuel and the batteries are reusable.
There is already a small (ram air)fan which drops down from the fuselage when certain failures occur this is an electrical backup and only really powers emergency systems, it’s a bit of a last resort and you’re having a bad day it’s needed. Ram air turbine,
|https://thumbsnap.com/UPlnlFgm[/url]A fan that was large enough to produce any meaningful electricity would actually create lots of drag though.
Even things like the little APU (small jet engine in the tail) inlet door adds 2% of the trip fuel if the APU is used in flight,
APU inlet door.
I imagine a larger fan driven turbine would create too much drag to be economically viable and it’s simply much more efficient to generate electricity from the engine driven generators.
RobDickinson said:
this is the equivalent of putting a fan on the roof of an EV to recharge the batteries... give it up lol
That’s exactly what happens on some aircraft. Sometimes military aircraft have things like ECM pods that run on electricity created by ram air, Like this.
These tend to be for addditions to the aircraft though. The aircraft is still producing the majority of its electrics from engine driven generators.
As I said above electrical fans drop down to run systems when main gererators fail as a backup, I think the OP is asking why not do this on a larger scale and the answer is they create too much drag and not enough electricity.
Edited by anonymous-user on Thursday 12th October 22:39
Super Slo Mo said:
This isn’t making a lot of sense. Can you try drawing it to illustrate what you mean?
What slow air are you thinking of?
the wing engines would be the hybrid engines, running on jet fuel as well as providing electric generation. My initial idea was 2 on the wings and in cruise one engine off thrust the other used as a generator.What slow air are you thinking of?
That was stupid so i thought adding a fully electric engine where it could be utilized the best, with the slow moving air causing drag, it could speed it up providing thrust as well as reducing drag, . The rear engine would be fully electric.
this is the idea.
El stovey said:
That’s exactly what happens on some aircraft. Sometimes military aircraft have things like ECM pods that run on electricity created by ram air,
Sure, as a way of creating localised independent electricity at a known cost to efficiency to the aircraft, lets face it jet fighters are not primarily aimed at efficiency...What the OP is suggesting is breaking physics.
The Spruce goose said:
That was stupid so i thought adding a fully electric engine where it could be utilized the best, with the slow moving air causing drag, it could speed it up providing thrust as well as reducing drag, . The rear engine would be fully electric.
this is the idea.
So the rear engine is powered by electricity not fuel? this is the idea.
RobDickinson said:
What the OP is suggesting is breaking physics.
No physics have been broken it is just improving efficiency, like i said not massive amounts maybe 10% over a non hybrid jetliner
The Spruce goose said:
the electric engine at the back wouldn't need the same amount of air as a the jet engines, so an work at higher power whilst the jet engines could work at lower power + provide the electricity generation. all the engines would be smaller than traditional ones.
No physics have been broken it is just improving efficiency, like i said not massive amounts maybe 10% over a non hybrid jetliner
You are fundamentally breaking physics.No physics have been broken it is just improving efficiency, like i said not massive amounts maybe 10% over a non hybrid jetliner
Whatever power you gain from the fan at the rear you have to supply from the engines at the front, plus a bit more for efficiency, as above fans are about 57% efficient so you would have to generate twice the power gained from the engines at the front.
There is no free lunch here, you cant do this.
El stovey said:
So the rear engine is powered by electricity not fuel?
yes the point is there wouldn't be enough air to power a jet engine for combustion, therefore it is a prime place to put an electric engine whilst reducing drag. That is whole principle behind it. in theory i think it would be more efficient than a 2 jet engined plane, all other factors the same.Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff