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I'm designing an electric fan propulsion system for a hybrid-electric business jet. The hybrid business jet uses a series hybrid configuration and distributed electric propulsion. The electric fan propulsion system is for the distributed electric propulsion part of the engine and consists of the fan, intake duct and propulsive nozzle. So far, I've designed it so that the efficiencies of each component is as close to 1 and optimising the fan pressure ratio so the mass flow rate is large and the exit velocity is small (to improve propulsive efficiency). I'm currently unsure whether there are any other parameters I'm failing to consider and would like some more insight.

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  • $\begingroup$ As has been pointed out fairly recently in another comment elsewhere (can't remember where), this sort of question should not be viewed as being about resource allocation. $\endgroup$ – quiet flyer May 8 at 23:39
  • $\begingroup$ @quietflyer I'm really sorry maybe it's because I'm new to the site, but I really am not sure what you mean by resource allocation. I've received this comment about off-topic resource location in another of my questions that got closed and was voted by the same account I think but I don't understand why or what this means. $\endgroup$ – StrugglingEngineeringStudent May 8 at 23:42
  • $\begingroup$ My comment was meant to be in support of your question as a legitimate question. If you find the help pages for the site, you'll find a note about questions about resource allocation being not allowed-- I interpret this to mean "where can I buy product x", or maybe "where can I find a book addressing topic y". Most likely including "where can I find the data sheet on component z". Anyway welcome to ASE. I suspect most of the "close" votes may have related to a possible perception that the question was a broad engineering question possibly not really focussed on aviation. $\endgroup$ – quiet flyer May 8 at 23:50
  • $\begingroup$ @quietflyer I agree but the OPs comment on the answer below makes it clear that resource location was the main motivation of the question. However since the edit it's much better. $\endgroup$ – Sanchises May 9 at 5:11
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Well, if all you care about is the fan performance by itself, then you've pretty much got it. Maximize the component cycle efficiency and maximize the propulsive efficiency and that's it. But if you want to start getting more real-world, then things to think about:

  • Off design conditions. You can perfectly optimize efficiency at one condition (i.e. for a large commercial airliner this would be cruise: Mach 0.8 @ 40,000 ft), but the thing still has to have acceptable performance at other conditions (e.g. takeoff, Mach 0 @ 0 ft). You may have to compromise on cruise efficiency to get acceptable takeoff performance.

  • Since this is an electric fan, it will be driven by some kind of a motor. That motor will have some speed where it is most efficient. That may not be the speed at which your fan is most efficient. You'll need to match the two of them to maximize overall aircraft efficiency.

  • If you want to go even one step further, that electric motor has to get power from somewhere. Presumably a battery. To get peak efficiency from the motor might demand X current at Y voltage, but your battery might be optimized for less than X current. Again, you may need to match the power source to the motor.

  • If you want to go even further, there are a number of real-world turbomachinery considerations to deal with including: Operability / stall margin, Inlet distortion tolerance (i.e. crosswind), Fan blade aeromechanics (i.e. flutter)

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  • $\begingroup$ No I don't know of any books sorry $\endgroup$ – Daniel K May 8 at 23:25

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