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Hybrid Jet Engines  
User currently offlineC5LOAD From United States of America, joined Sep 2008, 917 posts, RR: 0
Posted (5 years 6 months 2 weeks 4 days 5 hours ago) and read 5228 times:

Okay, so here is a thought to ponder. I'm not very aircraft engine smart, but would it be possible to make a hybrid gas/electric jet engine. It would operate in the same sense as a hybrid car would, by using gas for power on takeoff, climb, and landing. But at cruise it would use the combo of airflow and electricity to keep speed. Is it possible?


"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
32 replies: All unread, showing first 25:
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 1, posted (5 years 6 months 2 weeks 4 days 4 hours ago) and read 5225 times:

Possible? Yes. You'd have to put an electric engine in the core. I don't know how hard that would be.

The problem is that you run into the usual energy storage issue. Electric propulsion is very efficient but batteries have a relatively low energy density per weight. In other words, they are heavy compared to the equivalent energy stored in jet fuel. Other problems are battery aging and environmental issues.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (5 years 6 months 2 weeks 4 days 2 hours ago) and read 5192 times:



Quoting C5LOAD (Thread starter):
I'm not very aircraft engine smart, but would it be possible to make a hybrid gas/electric jet engine. It would operate in the same sense as a hybrid car would, by using gas for power on takeoff, climb, and landing. But at cruise it would use the combo of airflow and electricity to keep speed. Is it possible?

Starlionblue is right...it's technically possible but not economically viable.

Another major reason not to do it is that you don't get nearly the efficiency gains from a hybrid jet as you do from a hybrid car. The major efficiency problem in cars is that gasoline engines suffer a big efficiency hit when running at small fractions of their full power due to throttling. Car engines almost never run at full power, and they cycle up and down in speed a lot. Electric engines are much better for this so hybrids run electric when they can and then run the gas engine at a relatively constant speed at a high power (high efficiency) when they need to.

A jet engine doesn't really suffer throttling losses and it runs at nearly constant speed for most of it's whole life, so there's a lot less to be gained by going to hybrid.

Tom.


User currently offlineRwessel From United States of America, joined Jan 2007, 2311 posts, RR: 2
Reply 3, posted (5 years 6 months 2 weeks 4 days ago) and read 5170 times:
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Another big win for hybrid cars that most people forget about is regenerative braking. In fact it's probably the single biggest win for hybrids. The hybrid can recapture much of the kinetic energy of the car when it stops - and then use it again when the car starts moving again. It's the major reason why most hybrid get better city mileage than highway mileage (the reverse of conventional vehicles). That starting and stopping is what kills your city mileage in a conventional vehicle.

Of course that completely fails to apply to an aircraft.

That being said, the notion of a hybrid system for aircraft makes a certain superficial amount of sense, in that you want engines that are optimized for cruise for most of the flight, and then lots of extra power for takeoff and climb. The problem is that the engines are already a lot like that because of the effect of altitude. The engine that produces 10000lbs of thrust at full power cruising at 40kft, pretty much inherently can produce five times that at sea level. And for practical airliners, those numbers are both in the ballpark of what you need.


User currently offlineSEPilot From United States of America, joined Dec 2006, 6824 posts, RR: 46
Reply 4, posted (5 years 6 months 2 weeks 3 days 15 hours ago) and read 5099 times:

Rwessel's analysis covers most of the issues. As he says, the primary benefit of hybrids is regenerative braking, which in aircraft is called gliding. So the weight of batteries plus motor/generators would far outweigh any gains, and it really has no benefits at all.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineScipio From Belgium, joined Oct 2007, 838 posts, RR: 9
Reply 5, posted (5 years 6 months 2 weeks 3 days 6 hours ago) and read 5028 times:

If you can make jet engines with an electrical core, than you could theoretically power an aircraft with a small onboard nuclear reactor. Is that correct?

User currently offlineLuv2cattlecall From United States of America, joined Sep 2007, 1650 posts, RR: 2
Reply 6, posted (5 years 6 months 2 weeks 3 days 4 hours ago) and read 4989 times:
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Quoting C5LOAD (Thread starter):
But at cruise it would use the combo of airflow and electricity to keep speed

JW, where would you be getting the airflow from?



When you have to breaststroke to your connecting flight...it's a crash!
User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 7, posted (5 years 6 months 2 weeks 3 days 3 hours ago) and read 4971 times:



Quoting Scipio (Reply 5):
If you can make jet engines with an electrical core, than you could theoretically power an aircraft with a small onboard nuclear reactor. Is that correct?

Radiation.........shielding for the reactor.........weight of the reactor.........radiation contamination in the event of an accident, any one of those make it a bad idea.

Jet engines burn fuel to accelerate the air flowing through them, and extract that energy with the turbines. How much electrical energy would it take to create that much instantanious heat (3,000 + degrese F) as you have in the combustion chamber of a typical jet engine?

The military experimented with a neuclear engine in the 50s, radiation was the big problem. The exhaust was radioactive, and the engine was also even after shutdown. They tested it, it worked, and then they scraped it after the tests. I think I saw the special on the Discovery chanel.



"Saddest thing I ever witnessed....an airplane being scrapped"
User currently offlineDFWramper From United States of America, joined Nov 2008, 57 posts, RR: 0
Reply 8, posted (5 years 6 months 2 weeks 3 days 3 hours ago) and read 4969 times:



Quoting Rwessel (Reply 3):
The hybrid can recapture much of the kinetic energy of the car when it stops



Quoting Rwessel (Reply 3):
Of course that completely fails to apply to an aircraft.

Regenerative braking doesn't apply....but altitude and speed sure have a bunch of POTENTIAL energy that's just ripe for the picking.....how to harness it and recapture it as a plane descends for landing?


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (5 years 6 months 2 weeks 3 days 1 hour ago) and read 4942 times:



Quoting Scipio (Reply 5):
If you can make jet engines with an electrical core, than you could theoretically power an aircraft with a small onboard nuclear reactor. Is that correct?

As Ex52tech notes, it's been done. However, having a nuclear generator produce electricity to power an electric motor to power a fan would be a horrible way to do it. Much easier to just directly heat the air with the nuclear reactor and call it good.

Tom.


User currently offlineJA From United States of America, joined Dec 2004, 563 posts, RR: 1
Reply 10, posted (5 years 6 months 2 weeks 3 days ago) and read 4935 times:

Most hybrid vehicles are set up the wrong way.

Today's hybrid vehicles are set up so that the engine "kicks in when needed". Electric motors provide gobs and gobs of torque and power, but the issue of energy storage is an issue. The solution is to provide the electric motor with electricity using a generator powered by a fossil or alcohol fuel. The plane keeps its normal fuel tank and feeds a steady state generator (think small gas turbine) that sends electricity to the motor. The motor turns the fan and then helps create the compression to push the airplane. I am oversimplifying, but it might be able to work.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 11, posted (5 years 6 months 2 weeks 2 days 23 hours ago) and read 4929 times:



Quoting JA (Reply 10):
The solution is to provide the electric motor with electricity using a generator powered by a fossil or alcohol fuel. The plane keeps its normal fuel tank and feeds a steady state generator (think small gas turbine) that sends electricity to the motor. The motor turns the fan and then helps create the compression to push the airplane. I am oversimplifying, but it might be able to work.

Except it violates conservation of energy. Current jet engines are very efficient at converting fuel energy to thrust. As long as you're using a given fan, the energy demand is basically fixed by the thrust. So your "small" gas turbine has to put out that much energy + enough to overcome the generator, transmission, and motor losses. Since that energy output is necessarily larger than the energy that your current jet engine puts out, the "small" gas turbine is, in fact, a large gas turbine...bigger than the jet engine you replaced.

Tom.


User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 12, posted (5 years 6 months 2 weeks 2 days 21 hours ago) and read 4910 times:

I think it would only makes sense when taxing, if the weightpenalty isn´t too grand.

User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 13, posted (5 years 6 months 2 weeks 2 days 15 hours ago) and read 4872 times:



Quoting JA (Reply 10):
The solution is to provide the electric motor with electricity using a generator powered by a fossil or alcohol fuel. The plane keeps its normal fuel tank and feeds a steady state generator (think small gas turbine) that sends electricity to the motor. The motor turns the fan and then helps create the compression to push the airplane. I am oversimplifying, but it might be able to work.

The K.I.S.S. method of engineering seems to me to apply here. How about we just burn fuel in regular jet engines like we do now, and call it good.

Re-inventing the wheel is not always the way to go.
The manufacturers and the airlines need to keep costs down, espically right now, not embark on something that will change everything from manufacturing to operations to maintenance. The bottom line here is to jam as much freight and passengers as you can into an airplane, not take up all that useable space with reactors, storage batteries, or some knetic energy recovery system.  duck 

We would be better off moving on to dylithium crystals and impulse or warp drive engines..............Scottie!  mischievous 



"Saddest thing I ever witnessed....an airplane being scrapped"
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 14, posted (5 years 6 months 2 weeks 2 days 12 hours ago) and read 4841 times:



Quoting Alessandro (Reply 12):
I think it would only makes sense when taxing, if the weightpenalty isn´t too grand.

Here's a possibly more feasible idea: Put some sort of electric system to drive the wheels themselves, and have the electricity come from the APU. This system would only be used when takeoff queues would be very long. I'm sure the fuel saved in those situations would justify the added weight.

Wasn't a company working on some sort of system like this with a motor to be attached to the NG?

Quoting Ex52tech (Reply 13):

We would be better off moving on to dylithium crystals and impulse or warp drive engines..............Scottie!

What about conveyor belts running in the same direction as the plane for T/O? Big grin  duck 


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 15, posted (5 years 6 months 2 weeks 2 days 8 hours ago) and read 4812 times:



Quoting FLY2HMO (Reply 14):
Here's a possibly more feasible idea: Put some sort of electric system to drive the wheels themselves, and have the electricity come from the APU. This system would only be used when takeoff queues would be very long. I'm sure the fuel saved in those situations would justify the added weight.

Wasn't a company working on some sort of system like this with a motor to be attached to the NG?

They still are:
http://www.wheeltug.gi/

Tom.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3476 posts, RR: 67
Reply 16, posted (5 years 6 months 2 weeks 2 days 4 hours ago) and read 4779 times:

Quoting Rwessel (Reply 3):
Another big win for hybrid cars that most people forget about is regenerative braking



Quoting DFWramper (Reply 8):
Regenerative braking doesn't apply....but altitude and speed sure have a bunch of POTENTIAL energy that's just ripe for the picking.....how to harness it and recapture it as a plane descends for landing?

Since descents from cruise altitude are made at flight idle, the kinetic and potential energy of cruising flight is already being used. Fuel mileage during descent is better than any other part of the flight profile.

Better ATC procedures and improved FMC capability to minimize holds and delay flap and gear extension can make further gains but they won't be dramatic.

[Edited 2009-01-10 18:35:44]


Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 17, posted (5 years 6 months 2 weeks 2 days 4 hours ago) and read 4771 times:



Quoting Ex52tech (Reply 13):


The K.I.S.S. method of engineering seems to me to apply here. How about we just burn fuel in regular jet engines like we do now, and call it good.

Re-inventing the wheel is not always the way to go.
The manufacturers and the airlines need to keep costs down, espically right now, not embark on something that will change everything from manufacturing to operations to maintenance. The bottom line here is to jam as much freight and passengers as you can into an airplane, not take up all that useable space with reactors, storage batteries, or some knetic energy recovery system.

We would be better off moving on to dylithium crystals and impulse or warp drive engines..............Scottie!

Nag, the bottom line is to fly airplanes as fuelefficent as possible, have a plane that flies for long periods without major technical problems and don´t cost too much.
My idea would be to replace ballast with batteries (I assume the ballast and batteries are about the same density) to recoup the energy during landing and use it during taxi.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3476 posts, RR: 67
Reply 18, posted (5 years 6 months 2 weeks 2 days 3 hours ago) and read 4765 times:



Quoting Alessandro (Reply 17):
My idea would be to replace ballast with batteries

Very few commercial airplanes require ballast.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 19, posted (5 years 6 months 2 weeks 2 days 3 hours ago) and read 4763 times:



Quoting FLY2HMO (Reply 14):
What about conveyor belts running in the same direction as the plane for T/O?

Trying to start that thread again I see.  cheeky 

Quoting Alessandro (Reply 17):
Nag, the bottom line is to fly airplanes as fuelefficent as possible, have a plane that flies for long periods without major technical problems and don´t cost too much.

Sounds like you are making reference to the K.I.S.S. method......... Not sure what the Nag means though.  scratchchin 



"Saddest thing I ever witnessed....an airplane being scrapped"
User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 20, posted (5 years 6 months 2 weeks 2 days 2 hours ago) and read 4750 times:



Quoting OldAeroGuy (Reply 18):
Very few commercial airplanes require ballast.

So it died off with the use of DU as ballast?


User currently onlineMir From United States of America, joined Jan 2004, 21512 posts, RR: 55
Reply 21, posted (5 years 6 months 2 weeks 2 days 2 hours ago) and read 4744 times:



Quoting Rwessel (Reply 3):
Another big win for hybrid cars that most people forget about is regenerative braking. In fact it's probably the single biggest win for hybrids. The hybrid can recapture much of the kinetic energy of the car when it stops - and then use it again when the car starts moving again. It's the major reason why most hybrid get better city mileage than highway mileage (the reverse of conventional vehicles). That starting and stopping is what kills your city mileage in a conventional vehicle.

Of course that completely fails to apply to an aircraft.

Not completely - there is the kinetic energy on landing. Probably not enough to make a meaningful difference in flight, but it might be useful for the taxi-in.

Quoting FLY2HMO (Reply 14):
What about conveyor belts running in the same direction as the plane for T/O?

With the brakes on, they would work.  biggrin 

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3476 posts, RR: 67
Reply 22, posted (5 years 6 months 2 weeks 2 days 1 hour ago) and read 4740 times:



Quoting Alessandro (Reply 20):
So it died off with the use of DU as ballast?

DU was replaced with tungsten, it's a lot less hassle.

However, DU and tungsten are used primarily as control surface balance weights to prevent flutter. In terms of volume, there is very liitle material of this type on airplanes today, certainly not enough to provide meaningful battery power. Besides, having batteries in the ailerons or elevators wouldn't be very convenient for running taxi motors.

Ballast is avoided because it's dead weight that doesn't add any structural strength and reduces airplane payload.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 23, posted (5 years 6 months 2 weeks 2 days ago) and read 4730 times:



Quoting OldAeroGuy (Reply 22):

DU was replaced with tungsten, it's a lot less hassle.

That is interesting indeed, and safer I dare say - back to WWII at last!

What would be the total weight of counterbalances in a plane such as a 747 or a 380 and are the amounts decreasing?

When the discussion about ballast started I thought they must be talking about the pax.


User currently offlineRwessel From United States of America, joined Jan 2007, 2311 posts, RR: 2
Reply 24, posted (5 years 6 months 1 week 6 days 23 hours ago) and read 4587 times:
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Quoting Ex52tech (Reply 7):
Jet engines burn fuel to accelerate the air flowing through them, and extract that energy with the turbines. How much electrical energy would it take to create that much instantanious heat (3,000 + degrese F) as you have in the combustion chamber of a typical jet engine?

The energy density of Jet-A is about 43MJ/kg. Assuming equal efficiencies, that gives you a trivial conversion - remember that one Joule is one watt-second. So an airplane burning 1000lbs of Jet-A per hour is using about 5.5MW (continuous). Equivalently, that's about 7400hp. Scale those number up by a factor of about 25 for a 747...

OTOH, an electric motor driving the front fan will be rather more efficient that the turbine in raw terms, (probably about 80-90% of the energy would get sent to the front fan as opposed to 35-45% for the gas turbine). That however excludes storage losses. And any losses getting the electricity to the aircraft as well, but that's a different issue.

The problem is the lack of any storage device that can store electrical energy at the required densities - the very expensive Lithium Ion battery in your laptop stores less than *1* MJ/kg (typically around .5-.75MJ/kg). And we use those expensive Li-Ion batteries because they're particularly good t storing energy (the lead acid batteries in your car, while vastly cheaper, only store about .1MJ/kg).

If you could build a fuel cell, or similar device, that could convert Jet-A to electricity with much higher efficiency, it might be worth it to do that, and then use an electric motor to drive the fan. Unfortunately fuel cells are not available in the sizes required, nor are the ones that can run off non-hydrogen fuel sources nearly as efficient as the hydrogen/oxygen kind. And hydrogen has a huge volumetric energy density problem.

People keep forgetting just how good the medium chain hydrocarbons are as a fuel/energy source.


25 JA : I would think, however, that an optimized generator powered by Jet A would still provide significant savings. For example, instead of 45% efficiency
26 SEPilot : You are still stuck with the inefficiency of the gas turbine driving the generator plus the inefficiency of the electric system, plus the added weigh
27 DocLightning : Until that single turbine fails midway between SYD and SFO. You always need a minimum of two engines on a heavier-than-air craft that is going to be
28 Rwessel : To expand on what SEPilot said: Unfortunately the best gas turbine generation systems (used for stationary power plants), run at closer to 55-60% eff
29 OldAeroGuy : Yeah, the idea of a water replenishment airborne tanker sounds pretty neat to me. Perhaps steam propulsion would be better coupled with a nuclear pow
30 SEPilot : One thing that nobody has considered is the size and weight of electric motors/generators required to provide enough power for a transport category ai
31 Post contains links Rwessel : Well, you would probably be looking at a superconducting design of some sort. And an issue is that no one has really worked the size/weight issues on
32 Wingscrubber : Remember that turbofans produce the majority of their thrust from the fan and not just simply the hot gasses escaping the core causing reaction thrust
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