Re: Those swinging engine pods!

From: (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         20 Mar 94 22:29:51 PST
References:   1
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In article <>,
Robert Jacobson <> wrote:
>While I've now flown enough miles not to get alarmed, I'm still surprised
>to look out the window of the 747 in which I'm traveling and see the
>engines swaying in turbulence.  How much do the engines actually travel,
>how does this affect their efficiency, and what type of construction is
>used that permits such wild movement without the engines tearing off and
>leaving us without power?  Thanks for your answers.

Well, not to alarm anyone anymore than they are ordinarily, but those
engines will move about even in still air.  This is a result of the speed
the airplane flies, and how it damps out flutter.  The engines are out of
phase with the wing.  The engine struts incorporate a "spring beam" to
change the natural frequency of the engine & strut with respect to the

I didn't know this until recently, but a four-engine airplane can cruise
faster than a twin (given the same wing construction) because it has those
ouboard engines to damp the flutter.  Not being all that familiar with the
A330/A340, I was wondering if this effect showed up with them?  Granted the
A340 doesn't fly very fast to begin with (M 0.82 nominal), but does the
A330 fly any slower?  Say, Mach 0.80?  Kurt?

"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."