Roy Bourgeois wrote:

I read all of this stuff with interest since I've spent most of my soaring
career in long wing gliders (18 years in an 20m ASW-17 and 5 in a 24.5m
Nimbus 3). While I respect Stan and his extensive resume - he acknowledges
that he has no experience flying the open class ships. I have not found
that the long wing gliders are any more or less susceptible to spiral
dives, spins or unexpected acceleration as opposed to 15m ships. If
anything, they are more stable tend to telegraph the stall pretty early
and spin pretty slowly. The Nimbus does have a remarkably short span
stabilizer which when stalled can cause pitch down - but this is pretty
rare and easily recovered from. I also confess that I do not understand
the second hand comment about "extreme rudder sensitivity" (all open class
pilots wish it were so!). It should also be noted that most of these
break ups seem to happen in the 2 place ships (or 2 place with engine
versions) where the fuselage is hanging more weight on the same wing that
is fitted
in the single place pure glider model. While single place N3s and 4s have
crashed, I don't think any have come apart in the air. This tells me the
problem is more complex than just wingspan.

What is clear is that opening the dive brakes at high loads and high wing
flexion is the last step before disaster. It suddenly increases the
bending
moment outboard of the brakes and pushes the wing to failure. This was
found in both the Spain and Minden accidents. Stan spends a great deal of
time talking about what happens to aileron loads at high wing flexion. It
would be more interesting to study what happens to the dive brakes when
the wings are flexed at 45 degrees. Do they pop open because of forces on
the
control rods (or forces on the caps caused by the flexion)? I don't think
that there is any real data or experimentation on this issue (and I'm not
volunteering to be the first!). When the factory does their stress load
testing - I do not believe that they actuate the dive brakes and the issue
cannot be studied by merely stressing a wing with a dive brake rod
unconnected to the fuselage. Also, there is no scientific study as to
what pilots do in sailplanes when surprised by high angle dives and high G
pull outs. My my own experience (32 years soaring , 2000 hrs, active
CFI-G) leads me to doubt that the pilot reaches for the dive brake while
plummeting down in a dive. More likely, he over stresses by a too
dramatic pull out during which an un commanded dive brake pop out occurs
that
destroys the wing. Because of the location of the dive brakes on the
Nimbus 2 and 4 (they are quite far inboard) - this creates loads that
would not be found on a 15m ship pulling the same G load.

This is not to be critical of anybody - all of this is good for all of us.
So I thank Stan for his article.

Roy B.


tel: 508 798 8801
fax: 508 754 1943
Wasn't the 4 breakup in the NZ world's a single place?

Frank