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Old 31st October 2012 | 12:27
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R1no
 
Joined: Oct 2012
Posts: 4
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From: Australia
Turbofan/prop/UDF efficiency

Hi everyone,

Nice to meet you all. A couple of questions that I have had reading about aircraft propulsion on mighty Wikipedia have remained unanswered throughout the years. I finally decided that it would probably be a good idea to rock up here and ask for some professional opinion, otherwise I'd go insane thinking about it all day.

1. I understand that props have problems with wave drag at the tips as the tips approach the speed of sound. Why is it that the fan inside a turbofan does not experience the same problem? Is it because it has so many blades?

2. Carrying from the above question, I've also read that adding more blades to a prop makes it harder to balance, such that we don't usually see more than 8 blades on a single prop. Why is it that again, fans are granted some kind of exception from the rule?

3. An unducted fan or propfan looks almost exactly like a turboprop and works on pretty much the same principle. Neither Wikipedia nor Google have come up with a satisfactory answer on how they are different and why UDF/propfans can work at greater speeds (smaller blade diameter/more blades? But can't you just do that to a turboprop?)

Thanks in advance.
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