Push-Pull propeller combinations.

On Sep 3, 12:41*am, Daryl Hunt wrote:
On 9/2/2010 8:08 AM, Eunometic wrote:





Several aircraft have been built with both a pull (or tractor)
propeller and a push (or rear) propeller aligned with each other.

Supposedly the arrangment is inefficient, yet the some of the Dornier
aircraft were record breakers.

Given that some aircraft were ruined or delayed by the problem of
combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
the B-29 with its backup V-3420) * it looks like an attractive
proposition.

What's going on here?

List of such aircraft:

Cessna 337 Skymaster

I built a flying scale model of the Skymaster. *Trust me, it
needed an Engineer rather than an AC Mechanic model builder. *The
initial flight saw a yawing affect. *I lengthened the boom a bit,
increased the horizontal stab and tightened everything up. *It
flew fine after that. *But, danged, was it fast. *The Engines
didn't need to be sinced but it would have definately helped. *I
made the mistake on the first one of putting both the same in
relationship with the body. *Bad mistake. *One needs to be
slightly higher. *The next model had the rear elevated in
relationship to the front motor. *All of a sudden, it turned into
a piece of cake to fly and danged, it got faster. *I used two
different motors. *The gear box idea I doubt if it would have
made much difference between a single prop and a front and rear
prop. *If you have that much motor, use a heavier cutting prop.
If you don't have the power up front, add another motor in the
rear.


Sounds like there are a few 'tricks' in squeezing the best out of this
arrangment.