Turbo Electric Propulsion

[Kioki1]

Hello Forum,

Any ideas on this concept. Please refer to the attachment.

Cheers
George

 

[rb1957]

yech !

why have a FF engine to create electricity for an electric drive motor ? Where's the efficiency in that ? You'll still need a gearbox at the propulsor.

another day in paradise, or is paradise one day closer ?

 

[Kioki1]

Thanks for the response. My concept does not require a gear box to drive the propulsor (propellor, ducted fan, whatever).

 

[IRstuff]

Is this supposed to be new? Naval propulsion has been using generators driving electric motors for quite a while now.

However, how do you propose to achieve high sub-sonic velocity regimes?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[rb1957]

your propulsor is spinning at the same speed as the motor that's driving it ?? ok ...

another day in paradise, or is paradise one day closer ?

 

[Kioki1]

Thanks for the response, this forum stuff is new to me. I realize this basic concept is not new, but I believe there is nothing
"new" in the universe, for example diesel-electric locomotives predate marine aps by many decades. There is a tsunami of knowledge/activity emerging regarding "electric"/"hybrid" aircraft."high subsonic velocity regimes" is lofty stuff about which I know nothing. My personal transportation is a Vans RV-8 which cruises 200 MPH on 9 gal/hr.

 

[rb1957]

ok, a Vans RV8 is a small kit plane, with a conventional engine. If you're planning to re-engine, I believe you will need a gearbox but then I don't know enough about electric motors to know if they work efficiently at low rpms (like a propeller would be at). I suggest learning about propellor design, in particular the propellor on the Vans ... what's the power input (from the gearbox) like ? a power vs speed graph. then can you get an electric motor to match this ??

another day in paradise, or is paradise one day closer ?

 

[btrueblood]

My issue is not with the idea itself, but with the added weight. Electric motors are not light, nor are generators (lots of copper and iron in them things).

 

[Kioki1]

Thanks for the response. Your "issue" assumes a weight increase which is subject to further analysis. Note that eliminating both the Main and Accessory gearboxes saves a significant amount of weight and also that driving the Generator at Gas generator speed results in increased power density. I submit that it is possible that further analysis might reflect a net weight saving.

 

[btrueblood]

It's potentially possible, but unlikely. A transmission rated for a few hundred horsepower is much lighter than the equivalent electric motor. But I don't know if anybody is looking at aluminum windings for induction motors, which might change the game.

Your point is valid that the system is proven and works for ground transport, especially locomotives (your example) although those do not use turbines but diesel engines for better fuel efficiency. What locomotives do not mind is extra weight, as it helps them develop traction. For aircraft, weight is a big negative.

 

[Compositepro]

Electric motors and batteries have become the preferred power for drones. As they scale-up, more motors and props are used rather than making larger motors and props. Small props operate at high rpm which allows one to get high power from a small electric motor while motor heat is relatively easy to dissipate. Also, since lift, thrust, and weight get more uniformly distributed, structural weight can be minimized.

The next thing to consider is the weight of batteries versus a gas turbine, generator, and fuel. Use of high voltage helps to keep down the weight of generators and motors, although batteries do not fit well with high voltage. So leave out the batteries and you have turbo-electric propulsion. High voltage also keeps copper weight down.

 

[Kioki1]

The ultimate proof of concept will come if I build something and start testing. What has prompted me to delve into this has been such programs as the XTI Trifan 600 and as wwell as numerous newsy items on the web suggesting that not only small craft but even transport class aircraft could benefit from "turboelectric" propulsion so if it is a crazy idea at least I am not alone. What really intrigues me is such concepts as "rim driven ducted propulsors". Stay tuned y'all.

 

[Compositepro]

There is no proof of concept required here. The concept is well-proven. What is needed is a trade study for a specific application that shows this concept to be superior in that specific application compared to alternative approaches. What you really mean is that you want to tinker on something that interests you, for a while.

"What really intrigues me is such concepts as "rim driven ducted propulsors"". This gives you away as a tinkerer. Nothing wrong with that except that this forum is intended for working engineers to provide tips to other working engineers. Hobby project postings by non-engineers are strongly discouraged.

 

[verymadmac]

I have toyed with a similar concept for a while. The only places where it currently appears to possibly be of value for GA sized aircraft is enable a more exotic airframe configs such as NASA's X57. The decoupling engine mass from prop location allows a great many previously impractical configurations to become somewhat more practical. On the automotive engine conversion side it may also allow the building of "simple" turbo compounded engines.

For firewall forward on an RV, its possibly simpler than if the engine required a custom reduction drive but can't see any other gains unless you are getting a really good deal on an engine.

 

[raiderz]

You are aware rim driven propulsion is already being done...
Most cargo ships have a electric / magnetic rim driven propulsion systems.

 

[VEBill]

An approach might be to plot out the data points to reveal the otherwise hidden scaling laws driving the relationships of the parameters. Then it would become apparent if the overall system advantages get better or worse with increasing scale. For some systems, things get increasing advantageous with incresing scale; others are the complete opposite where the scaling laws impose fairly firm limits.

For example, how does an electric generator or motor power scale with its mass? How does the power requirement of an air vehicle scale with its size. Wing performance versus scale. Etc. Etc. You put all these relationships together (end-to-end, in a spreadsheet if you like) and the feasibility versus scale falls out. It may prove that little drones are easy while large aircraft have the basic physics working against them. Or perhaps it's vice versa.

It's a paperwork exercise that should guide future plans. No need to bend metal until this analysis is completed.

 

[berkshire]

It would appear that Airbus and a few others are looking at this concept. They are setting up a flying testbed using an old HS146

https://newatlas.com/airbus-rolls-royce-siemens-e-fan-x-hybrid-electric-aircraft/52389/

B.E.

You are judged not by what you know, but by what you can do.

 

[rb1957]

yeah, I'd seen that. I take it it is just a technology demonstrator (ie can we have a reliable electric engine ... why not ?).
But they're not thinking of having an electric drive driven by a FF engine ('cause where's the reduction in FF emissions there ?).

But then I can't see a weight efficient battery pack, so maybe they are planning this as a deliverable technology, and are hoping that there are aerodynamic gains by decoupling the fan from the engine ? And maybe there are efficiencies to be found in dropping the turbo-jet combustion ... ie optimise the power generation and the propulsion efficiency separately ?

another day in paradise, or is paradise one day closer ?