Timeline for What are the pros and cons of adding a gearbox to larger jet engines?
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Sep 26, 2018 at 2:01 | comment | added | Robert DiGiovanni | Turboprop design is what I had in mind, essentially running the "fan" off the turboshaft the same way (ducted fan) using a reduction gear. The design of the compressor/turbine would be up to you. Lots of possibilities here, indeed, including reducing number of blades on the fan, no? | |
| Sep 25, 2018 at 22:41 | comment | added | XRF | @RobertDiGiovanni You state that the fan speed is variable, that is not the case, it is limited to a fairly small range. It is the compressor speed that is being changed by adding a gearbox, not the fan, or rather in this case, the compressor is able to be built to a smaller size relative to the fan that would normally not be possible by allowing the compressor to spin faster. | |
| Sep 25, 2018 at 22:37 | comment | added | XRF | @Penguin The compressor and turbine are already connected and their common diameter means their speed requirements are similar. The turbine design requirements are a lot easier on aerodynamics than the compressor and if it is any part of the turbine you want to run fast, it is high pressure turbine not the low pressure turbine, and that is because of weight savings not basic efficiency. | |
| Sep 25, 2018 at 11:48 | comment | added | Penguin | @XRF. Not quite. The turbine needs to spin fast to be efficient, the fan needs to spin slowly. Adding a gearbox enables both to be optimised, rather than both (partly) comprised. So, it’s about the fan/turbine speed ratio, not the fan/compressor speed ratio. | |
| Sep 25, 2018 at 8:59 | comment | added | Robert DiGiovanni | BTW the British engine was developed from a chinook (helicopter) turboshaft! | |
| Sep 25, 2018 at 8:49 | comment | added | Robert DiGiovanni | You are are saying the same thing I am, the gearbox allows for slower fan speed. Slower bigger "wings" are more efficient. Geared turbofans were developed by the British for noise abatement as well. | |
| Sep 25, 2018 at 7:55 | comment | added | XRF | The goal is actually the opposite. A turbofan engine is unlikely to be designed with supersonic fan tip speeds because of the losses (the odd experimental usage aside). Rather, since the fan tip speed is limited to below the speed of sound, adding a gearbox allows the compressor speed to be increased instead, or maintained as the ratio of fan to compressor diameter increases. | |
| Sep 24, 2018 at 22:40 | history | answered | Robert DiGiovanni | CC BY-SA 4.0 |