Balance is one issue. The wing wants to be near the engine (look at pushers
vs. pullers - pushers are rear wing, pullers are front wing). So you can't
just stick another engine on the tail of a standard config plane.

Thrustlines are another issue. If you are flying and you lose the front
engine, do you nose up? Nose down? Ditto for the rear.

Google for the Cessna Skymaster to read up on the pros and cons.

Then go to www.scaled.com and look at some of Burt Rutan's designs like the
Rutan Bommerang for some out-of-the-box thinking on twins.

One might ask - why do you want two engines?
- More power? Get a bigger single engine.
- More reliability? Get a more reliable single engine. There are many
alternatives to continental and lycoming one the scene now. People have
been saying this for years, but it's really true now. Since you are
thinking about a new design (experimental) you don't need to wait for FAA
certification to use an engine. I haven't checked the NTSB database (you
certainly could - www.ntsb.gov/ntsb/query.asp), but from googling other
peoples discussions, it seems the accident rates for singles and twins are
the same.

Enjoy the argument that's about to start, or check the archives of this
newsgroup for basically the same argument, only repeated every few months...

"Shin Gou" wrote in message
om...
Hello all,

I am currently brainstorming/daydreaming of a twin design. I would
choose a pair of Rotax 912 or Jabiru 2200 or 3300. Considering the
place configuration of two engines on a twin, I am just wondering what
are the pros and cons of center-line push-pull design. There're far
less such configuration than side-by-side engine configuration among
twins, so I think there must be a reason.

The biggest (if ther's any other) advantage of push-pull design seems
obvious: the center line configuration eliminates the torque effect
when one engine fails.

So what're the cons? Besides the heating issue of the rear engine, I
can only guess it might be the efficiency issue. The front engine
disturbs the air flowing through the rear engine. If it's true, how
big is this disturbance? Say if the side-by-side two engines'
efficiency is 200, what's the possible number for push-pull
configuration, 180,160,150? If the number is no lower than 150, I
think it's tolerate for my use.

Thank you very much in advance.

Shin