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Counter-Rotating Jet-Engine

Rotate the compressor and turbine in the opposite direction from one another.
  (+1, -2)
(+1, -2)
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The exhaust from a normal jet engine spirals out of the nozzle (and also in the combustion chamber), which I think makes them have less efficient thrust.

I think that a counter-rotating jet-engine would correct this problem and greatly improve thrust efficiency (although, I also think that changing the direction of the shafts would also make the engine slightly less efficient, but the increased thrust efficiency should be more beneficial to the engine overall).

In the center of the engine (In the middle of the combustion chamber) there would be a bevel gear attached to the compressor shaft, and one connected to the turbine shaft. Both gears would be contacting at least one other bevel gear, which the change the rotation of second shaft. The angle (or direction) of either the compressor blades, or the turbine blades would of course have to be changed in order for this engine to work.

Also, if this where to be used a turboshaft engine, a drive shaft could come out of the side of the engine at a 90 degree angle, by connecting it to the idler gear in the center of the engine.

(I know this idea could have possibly already been invented, since it seems to me like a fairly obvious alteration. Or else it just won't work for some reason...)

BJS, Sep 11 2006

Jet engine airflow simulation. http://upload.wikim...gine_simulation.jpg
shows the spiraling airflow of a normal jet engine. [BJS, Sep 11 2006]

GE90 cross-section http://ctr-sgi1.sta...edu/CITS/ge90r.jpeg
Notice the vanes downstream of the fan (tagged as "14"). These are structural, supporting the engine within the nacelle, as well as aerodynamic, converting tangential velocity (swirl) to static pressure (thrust). Similarly, see the vanes listed as "5", downstream of the turbine. [Freefall, Sep 12 2006]


       That simulation is drastically oversimplified. The stator blades of the compressor kill most of the spiral, and the same for the turbine and its stators. I read somewhere that the spiral is a very small area of loss for the exhaust, but can be eliminated easily.   

       Throwing in another gear assembly, particularly on the most heavily-loaded shaft, sounds like real trouble. If you are going to do it your way, you will need as many gears as possible where you say //at least one//.   

       There are engine design concepts with counter-rotating compressor stages instead of stators, which kills the spiraling airflow, but I don't know if they have been built.
baconbrain, Sep 11 2006

       Please annotate, people.
BJS, Sep 12 2006

       OK, if you insist.   

       As previously stated, that illustration is drastically simplified. Actual jet engines (large ones, anyway) use stator vanes (AKA "Outlet Guide Vanes", hereinafter referred to as OGVs) downstream of the fan and final-stage turbine. These OGVs are designed to remove the swirl from the flow when the engine is operating at design cruise condition.   

       See the GE90 cross section link for an illustration.
Freefall, Sep 12 2006

       Do you think with the reliance on extra mechanical parts, it could be as robust as the traditional jet engine?
undata, Sep 13 2006

BJS, Sep 13 2006

       How does counter-rotation eliminate swirl? Wouln't it just swirl one way, then the other?   

       There would be violent eddies in the transition zone.
Texticle, Sep 13 2006

       I recommend reading Bill Gunston's books about aircraft engines.
baconbrain, Sep 13 2006

       Do you recomend I delete this idea...?
BJS, Sep 13 2006

       Not really, but I don't see it as a loss if you do.
baconbrain, Sep 13 2006


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