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Could another explanation exist for the loss of a
highly skilled pilot? I knew David from the High
Performance training sessions he and Pete Zaccagnino ran at Lakeland and I
extend to Kathy my deep condolences.
If one discounts the theory that he tried to turn
back, perhaps there is an explanation to be found in the deep stall
characteristics of that particular aircraft.
Observers in the crash report said "the airplane
pitched nose-up about 20 to 30 degrees". "Black smoke trailed from
the engine exhaust system, the engine sputtered and then stopped producing
power". "The climb and the turn after the loss of engine power were
performed at a very high deck angle". "The aircraft entered a smooth
roll to the left, yawed left then plunged to the ground, near
vertically".
Diverging for a moment to a report by Dave Allen
(LML 05.15.04) who was flight testing an ES for an owner. "I was
doing a stall series, and near the end was taking the deep stall to the point of
wing drop. When I brought the stick forward and applied full opposite
rudder, the Lancair not only did not recover, but fell into a fully developed 3
turn spin".
When one peruses the Summary of Lancair Accidents
in the NTSB database, there is an over-representation of stall/spin incidents
involving IV/IVP's. Some of these accidents involved the loss of highly
experienced pilots.
Kissimee FL 7/11/01
Bozeman MT 11/05/02
Geelong (Aust)
12/20/02
Mesa AZ 2/17/04
Novalato (Mexico) 4/7/04
Grand Canyon AZ
5/18/04
Vermontville MI
5/31/04
A discussion on the stall characteristics of the
Lancair wing led to a posting from Martin Hollmann (LML 01/26/05) referring to
the airfoil used at the ROOT of the Lancair wing. "The wing is designed
with the RXM5-217 airfoil - a very gentle stalling airfoil" This benign
characteristic is further discussed in his book 'Modern Aircraft
Design' (page 40) and further represented by a lift curve (p 225)
showing a smooth stall with a gradual loss of lift.
The same posting from Martin Hollmann (LML
01/26/05) states of the airfoil at the TIP of the Lancair wing "Yes, the
NACA64212 airfoil has a sharp stall. However the wing is designed with the
RXM5-217airfoil, a very gentle stalling airfoil, at the root and the NACA64212
at the tip. The wing is washed out so that the root stalls first.
The wing tip is not designed to stall and as such the question of how it stalls
is not relevant. The NACA64212 airfoil was chosen for the tip because it
has a high lift coefficient and it is very effective with an
aileron". These comments are outlined also in 'Modern Aircraft
Design' (p 40) and represented by a lift curve (p223) showing a sharp stall and
complicated lift tendencies.
In a normal stall, the airflow detaches from the
lift surface starting at the rear of the wing surface and progressively moving
forward as the angle of attack increases. Then by lessening the angle of
attack the air progressively reattaches to the surface. However the graph
(p223) suggests this wing foil does not show this progression. The air
does not progressively reattach, but pauses, then suddenly reattaches over a
very short variation in angle of attack, producing a sudden maximum
lift.
Returning to the Dave Allen posting (LML 05.15.04)
he stated "when I brought the stick forward, the Lancair not only did not
recover, but fell into a fully developed 3 turn spin" He was a test pilot
and experienced a totally unexpected response - an uncommanded
response.
This anomoly may have little consequence in an
aircraft with perfectly symmetrical wings, but these are home-built wings and
any lack of symmetry at the tip provides the basis for assymetric
lift. Even if the assymetric lift is only momentary, the
aircraft is at or past stall and at its most vulnerable.
Could this phenomenon explain the
over-representation of stall/spin accidents in the statistics?
Could this explain the demise of some highly
experienced pilots, facing, like Dave Allen, a totally unexpected
occurrence?
Could this explain the David Hickman
experience? He was in a nose high attitude, losing or having lost power,
the wings were stalling and he was experiencing an uncommanded roll to the
left.
It appears to me as a non-aerodynamist, a
non-engineer, but a keenly interested follower of the tragedies that are
befalling our community, that this aircraft cannot be flown slow, cannot be
inadvertently flown close to its stall and must be built with great care and an
even higher level of precision.
Ref: Dave Allen 23831
Robert
Overmars 27776
Martin Hollmann
27896
Modern
Aircraft Design 6th Edition 2002
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