The aft edge of a delta wing is further aft than ailerons would be on a
conventional aircraft. The elevons on the trailing edge both work in the
same direction for elevator action and in opposite directions for roll. The
two inputs are combined when executing a bank entry with a pitch change at
the same time. All successful delta winged aircraft are basically stable
if handled with care. Many have pitch dampers to assist in stability. The
B-58 delta I flew had roll, pitch, and triple-redundant yaw dampers. When
things went right it was an extremely stable platform. In flight refueling
was a piece of cake. But when things went wrong it could eat your lunch.

One issue that might confirm your suspicions that a delta is not always
stable is "elevon coupling" during a landing attempt. If you're sinking
towards the runway too fast and try to correct too quickly you find one area
of instability. To raise your nose quickly you must move the stick back
quite a bit. That raises both elevons. Elevons are part of the delta wing.
Raising them temporarily loses lift. So, by moving the stick aft quickly
the aircraft descends due to loss of lift until the nose raises enough to
stop the increased descent. When you have the desired pitch attitude and
move the stick back towards neutral the elevons come down to a relatively
streamlined position further increasing lift. Whoops, ballooning above the
runway. Try to correct by pushing the stick forward to lower the nose
causes the elevons to come down (like adding flaps). So while your nose is
coming down the elevons have increased the lift adding to the balloon.

I've seen guys going down the runway like a jackrabbit due to elevon
coupling. I had it happen to me on the checkout ride in a TB-58 and thought
I wouldn't be cleared to go "solo" (pilot) in the B model which doesn't have
an instructor pilot position. But my following landings were OK and the
instructor (in debriefing) asked me if I had previously thought "elevon
coupling" was an old wives tale. I had to admit he was right. He asked
what I'd learned. I said I learned if I can't control the flare without
making rapid large pitch inputs it's time to go around. He said "Go forth
and fly, Grasshopper, because you have learned a valuable lesson". (a
little poetic input)

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"xerj" wrote in message
...
I remember coming across the answer somewhere, but I've lost it.

Anyone know?

TIA