It hit a "mountain of turbulence" and the tail "dug in"? What universe
did that happen in? Aft CG would exacerbate any tendency to a pitch
overshoot after a tab failure, but I can't see how any amount of
turbulence could produce a 10G pitchup without a coincidental tab
failure, unless the plane was totally unstable and Leeward was crazy to
be flying it. The pitch-up would reduce tab loads, not increase them.
Actually, the tab seems to have had two or three failures: possibly an
actuator first, then a hinge, and then the tab itself, mid-span. Maybe a
hinge was the first to go. NTSB metallurgists should be able to identify
pre-existing fatigue cracking, if there was any.

People are going to have axes to grind here, and blaming the pilot is
always a good strategy. Funny that the Hannah/Voodoo precedent is not
mentioned in this explanation. Another turbulence-mountain?

Peter Garrison

So here is the scoop I got over the weekend. Turns out one of the mechanics
at the airport was on the ground team for one of the unlimited racers and
had the spot in the pits right next to the lost plane. The ground team had a
real time data feed from the airplane.

Looks like the plane had a high speed flutter on the port elevator trim tab.
The pilot reported a vibration.

The trim tab came off in flight which caused the entire tail group to twist.
There are trim tabs on both sides and the asymmetry caused a huge over load.
Also high power settings require a lot of nose down trim to stay level, the
loss of the trim tab could not be overcome by the pilot. The twist in the
tail group made the tendency to nose up even greater and caused damage to
the internal structure in the tail  looking at the pictures you will see the
tail wheel is down and the gear doors are gone  stuff was coming apart in
there.

The twist and the loss of trim caused a near instantaneous 11G pull up  this
probably incapacitated the 73 year old pilot and may even! ; have broken the
mounts on the pilot seat. Note you cannot see him in the cockpit. The 11G
pull also caused a brief loss of engine power from low fuel pressure the
pump could not overcome 11G.

After the 11G pull up the airplane unloaded in steep climb  with the G off
the engine regained power.

Without the pilot to overcome it the airplane torque rolled causing a split
S into the ground.
The data showed that the airplane was pulling 105 inches on manifold
pressure on impact. The "normal" race boost would be 60 to 70. So the
airplane was going just under 500MPH when it hit so no fire just total
disintegration


Mike Ethridge


As I understand it there was only one trim tab. The other had been removed.
Therefor there would be no torque on the elevator tube due to that.
Only due to the stick angle.


Paul Lamar

Right Paul..  Loss/disconnect of the single tab would have actually
unloaded the elevator system.  The single tab would have caused an
asymmetric loading on the connection between one elevator and the
other.  If the tab became disconnected, it would have eliminated this
asymmetrical loading.

As the tab is small, and so close to the rolling center of the
fuselage, it would have caused only a small roll moment.  It might not
have been the source of the rolling behavior..

Engine torque causes a roll and yaw to the left.  That's why you have
to add right rudder to counteract it on a western-built airplane.  The
airplane did not "torque roll."  "Our" airplanes torque roll to the
left.  I believe the pilot might have continued to push right rudder -
his last conscious thought might have been concern about rolling to
the left as a result of turbulence.  A contributing factor might have
been the larger elevator area on the right as compared to the left,
once the tab had become disconnected.

Normally, wake turbulence moves outward and downward from the airplane
that generates it.  There was wind from the southwest - which may have
caused wake turbulence to remain relatively stationary near that
pylon.


Regards,

Matt-