Re: Wing vs. tail-mounted engines?

Date:         19 Apr 2001 16:40:36 
From:         "matt weber" <mattheww@Qwest.net>
References:   1 2 3 4 5
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At 03:37 PM 4/9/01 +0000, you wrote:
>matt weber <mattheww@Qwest.net> wrote:
>--cut--
> >>
> >>(I can't think of any case of failure of the wing box or root structure
> >>causing an accident on a post-war commercial airliner -- can anyone?)
> >That what caused the Two Electra accidents indirectly. The whirl mode
> >failure of the engine mounts caused the wingbox loading to exeed the design
> >limits, and the actual failure was the  wings came off the aircraft.  The
> >fix was to stiffen the wing, and make the engine mounts stronger.
>
>Bit more than that Matt,,,they discovered that the 'whirl mode'
>problem was causing sympathetic vibration of certain stiffeners
>and support structures in the wings and that the fix was to add
>syncronization and syncrophasing of the propellers. This system
>is now used on all twin and four engined a/c using Allison T-56
>type engines. C-130, P-3, and Convair 580's are the types that I
>know about, there's likely others. This system has the added
>benefit of reducing crew fatigue due to less engine induced
>vibration.

Synching up the props is a lot older then the Electra.  The L1049
(Constellation) has it.

However had the wing been adequately stiff in the first place, it would
have damped out the sympathetic vibrations in the first place, and raised
the frequency at which the wing would resonate to a frequency well beyond
what could be generated by precession caused by partial engine mount failure..

Matt Weber