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What Went Wrong With The Unducted Fan Engine?

Tue Jan 17, 2006 6:24 am

With the cancellation of the 7J7, why did airlines dislike the unducted fan engines?

Does it have to do with the image of propellors being obsolete technology? I have heard of some people who are afraid to fly on turbroprops.
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RE: What Went Wrong With The Unducted Fan Engine?

Tue Jan 17, 2006 6:31 am

I think there was three things that went wrong..

One Was the Vibration that the Fanprops caused and they were quite loud..

Two was that Fuel prices went down..

and Three was safety concerns of the High speed props breaking off and damaging the Airframe..

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RE: What Went Wrong With The Unducted Fan Engine?

Tue Jan 17, 2006 6:48 am

The single really prohibitive reason was noise.

The unducted fan engine is like the name says a fan engine with no duct. Nowadays the duct is an extremely important thing for noise reduction.

That doesn't mean that the duct is the only thing which infuences noise. Shape of the fan blade is also an important issue.

But I think that it proved impossible to create a high speed unducted fan engine which could meet present day noise criteria.

An ordinary turboprop engine is of course also sort of unducted fan. But it isn't feasible for speeds near the Mach 0.8 region. It keeps noise down by having a massive "fan" diameter and consequently a lower, subsonic fan tip speed.

The problem is really the constant supersonic boom of the fan tips.
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