Re: Rear engined aircraft. (727 DC9 MD80)

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         07 Dec 94 01:15:45 
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>Jettisoning an engine would SIGNIFICANTLY alter the CG of an aircraft,

Looking just at pitch, since you mention a nose-down attitude below,
the CG would change most dramatically on an aircraft with aft-mounted
engines.  A typical 727-200 Advanced, for example, has an empty weight
just shy of 100,000 lbs, and a MGTOW of around 180,000 lbs.  Each
JT8D-15A engine weighs just a bit shy of 3,500 lbs, plus a few hundred
for accessories and nacelle.  That's two or three percent of a typical
flying weight, and probably not much more than the effect of a few pax
and flight attendents, the latter with meal carts, moving around.

>probably inducing a nose-down attitude that the control surfaces would
>lack sufficient authority to overcome.

Several actual incidents disprove this.  The #3 engine departed an
American 727 operating DFW-SAN near the New Mexico / Arizona border in
the 1980s.  The flight crew, believing the engine had merely shut down,
continued the flight to San Diego uneventfully.  Any change in flight
control forces was small enough that they didn't notice the difference.

More recently, a Northwest 727 lost an engine over northern Florida.
In that case, the crew realized that an engine had detached, but they
still had no significant control problems and returned safely to a
nearby airport.

--
Karl Swartz	|INet	kls@ohare.chicago.com
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