Bulent Aliev wrote:

[The Canard Aviators's Mailing list]

Hi, Allen,

I like to exchange on this interesting subjects.

First, CS prop :
About 15 years ago, a nice guy here in France developed a very nice looking
airplane called the Orion. It was shown all over the world, and offered as a
complete Kit, and looking just like you would dream, a four-seater, piston
engine, pusher LearJet.

But the guy was a stylist, all but an engineer, and the plane was a trap,
too heavy, poor structure, poor mechanical design, etc... It was even worse
than the Prescott Pusher...

Just before bankrupcy, the guy killed himself (and an innocent)  in a flat
spin, originated when the MT CS propeller failed. Investigation proved that
one blade pitch horn failed in fatigue, due to high cyclic torsional load on
pitch axis, due to poor wake in this pusher (I've seen the report). The
flight time was very low, as fatigue is at 80 to 90 cycles per
sec.(2-per-rev).

 The wake was presumably better than in an EZ, the wing being much more
forward, and the engine hidden in the tail cone.

The MT propeller was well-known, and has since been used by most aerobatic
champions in the world, but I don't know of their technical evolution. They
are serious german people.

Eight to ten years ago, I saw a swiss VEZ and LEZ with an MT in an airshow,
together with MT engineer, and asked them a question about their confidence
in pitch fatigue, citing the Orion accident. They answered that they had
made measurements, with strain gauges and a slip-ring, to clear this
installation. My personal comment, based on professional helicopter AND
homebuilder experience, is that these measurements are extremely difficult,
and seldom reliable, unlike with VERY  expensive equipment.

I strongly recommend that nobody install a variable-pitch on a pusher
airplane without doing such measurement, or better, asking it to the prop
maker. It rules out most homebuilders, and all but certificated-prop
manufacturer. I suppose that MT could give valuable data and experience.

Second, noise :
There is no doubt for me, after reading many things by specialists, watching
the Starship, the Avanti and other sagas, that the biggest disadvantage of
pushers is external noise. I live on a GA airfield, and I have known, due to
high noise, each time an Avanti or a Starship visited here (not enough for
my pleasure, however). They have (had...) advanced, 5-bladed props, but it
isn't sufficient. Cozys and Longs are also the loudest planes here in their
category.

I'm sure that specialist canardians on the Forum can tell a lot on that.

They are still the one I prefer. Enjoy yours!

Bruno Guimbal  (French VEZ)

The guy obviously  has never heard a North American AT6 :-)

That is interesting about the MT props. My pitch change mechanism
is bullet proof and way over designed. That is probably the last
thing that would break. Unlike the MT our hub is made from 4130
heat treated steel which has a fatigue limit four times higher
than any aluminum. Some say aluminum has no fatigue limit and
it will eventually break no matter what.

BTW the fatigue limit is defined as that stress level below which 
an infinite number of stress cycles can occur without failure.

I guess we could mount a four by four close (1/4 inch) to the prop on the
test stand which would disturb the air flow twice per rev to simulate
a pusher installation. That ought to perturb the heck out of it :-)

Paul Lamar
 
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