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To: UNGN
If you spin the prop slower, the plane is going to go slower, which is unacceptable.

One of the reasons why the ATR-42/72 turboprop airliners switched from four-blade propeller units to six-blade propeller units was the very fact this allows for slower fan blade speeds for the same thrust output, which 1) reduces noise quite a bit and 2) reduces fuel burn due to slower speed of the engine during flight. Why do you think Lockheed did the same thing with the C-130J, the current model of the famous Hercules cargo transport?

Hence the reason why the switch from eight-blade to ten-blade propfans. With more blades, this allows for slower blade spin speeds with all the benefits I mentioned above.

35 posted on 06/06/2006 9:45:29 PM PDT by RayChuang88
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To: RayChuang88
Those are 350 mph turboprops. We are talking about 450 mph UDF's. The Tip speeds on the UDF are Mach 1+ by design.

Apples and Oranges.

If you put on more blades and spun the prop slower, you may be quieter, but you also aren't going 450 mph anymore.

37 posted on 06/06/2006 10:26:08 PM PDT by UNGN (I've been here since '98 but had nothing to say until now)
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