In article ,
"Morgans" wrote:

"Steve Hix" wrote
Like Mignet and his Pou-du-Ciel (Flying Flea).

Everything going swimmingly, unless you manage to somehow get it
inverted.

At which point it becomes so stable that it would stooge about until it
ran out of fuel, no way to bring it upright again.

How about half of an outside loop?

That was *if* you were lucky, having enough altitude to complete the
half outside loop before hitting the ground.

It was a problem involving interference between the two tandem wings of
the Flea. (The only controls available in the original Fleas were pitch,
controlled by tipping the front wing up or down, and rudder, which
controlled roll through a lot of dihedral inducing yaw-roll couple. They
were not very good at handling any crosswind component on landing, but
most were flown off large open fields, letting the pilot operate
directly into the wind.)

Suppose the pilot pushed the stick forward to gain speed. As the speed
built, up the rear wing, operating at a greater effective angle of
attack (being fed air from the front wing) would gain lift and pitch the
aircraft's nose further down.

The pilot's normal reaction would be to pull back on the stick, which
increased the front wing's angle of attack by lowering the trailing edge
of the wing.

Because the trailing edge of the front wing was close to the leading
edge of the rear wing, the front wing's downwash accelerated the air
over the rear wing increasing its lift and thus increasing pitch-down,
resulting in flight directly into the ground if you had insufficient
altitude.

If you had enough altitude, it would fly a half outside loop, and at
that point become so stable that there was no recovery from the inverted
flight.

Eventually, the design was tweaked to get around the problem, but not
all examples of the Flying Flea were updated.