essentially it is a turboprop of more blades and higher RPM.
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Chinese Engine Development
- Thread starter jackbh
- Start date
And having a core exhaust stream that produces thrust.
Turboprops and even turboshafts still produce a non negligible amount of thrusts via core...
Turboprop too (about 10% thrust from core), the smaller diameter of the propeller the higher thrust from core. It is only a quantitive difference.
And directly connected to the main turbine shaft rather than a separate shaft.
Some if not all designs have gear reductions meaning separate shafts, I think. With increased diameter and number of blades, I can't imagine it rotate at the same speed of the turbine shaft. The tip will certainly go supersonic. Without gearbox the diameter has to reduce which cancels out the purpose of open roter making it a high bypass turbofan but noisier.
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Except for GE36 most other "true" propfans like D-27, NK-93 and Allison 578 had a reduction gearbox.
This brings back memories of me a few years ago trying to pin down exactly what defines a propfan, and then just giving up. One can't say even that all propfans are unducted, because the NK-93 *does* have a duct. Perhaps one definite statement one can make about the distinction between turboprops and propfans is this: So far, for all engines called "turboprops," the axis of rotation of the propeller is offset from the axis of rotation of the compressors/turbines of the gas generator, while for all engines called "propfans," the axis of rotation of the propeller/fan is the same as the axis of rotation of the compressors/turbines.
As for any clear distinction between propfans and turbofans, well.... For example, I've seen online statements that the NK-93 geared "propfan" has a bypass ratio in the range of 16-17, while the under-development Rolls-Royce UltraFan geared "turbofan" has a bypass ratio of 14-15, which to me isn't that far off. Plus, the UltraFan apparently has variable-pitch fan blades! So it seems to me there's a plausible case that the UltraFan is crossing over into "ducted propfan" territory.
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Not really true as from the top of my head, NK-12 and AI-20/WJ-6 has a coaxial propeller
Me: "This brings back memories of me a few years ago trying to pin down exactly what defines a propfan, and then just giving up. .... Perhaps one definite statement one can make about the distinction between turboprops and propfans is this: So far, for all engines called 'turboprops,' the axis of rotation of the propeller is offset from the axis of rotation of the compressors/turbines of the gas generator, while for all engines called 'propfans,' the axis of rotation of the propeller/fan is the same as the axis of rotation of the compressors/turbines."
Tomboy: "Not really true as from the top of my head, NK-12 and AI-20/WJ-6 has a coaxial propeller"
Now you can see why I previously gave up!
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