Aftermath: Three Blades, Minus One
The only witness to the accident was a nonhuman one: a Garmin GPS, which recorded the groundspeed and altitude of the Velocity at intervals of approximately one second. The story it told was bizarre. It appeared that within three or four seconds of the failure — to judge from the location of the separated prop blade relative to the wreckage — the airplane, without climbing, decelerated very rapidly. Within 10 seconds, its groundspeed fell to zero, a 0.75-G deceleration that an airbrake would be hard put to match. Almost immediately after beginning to slow down, it settled into a steady descent at nearly 7,000 fpm and maintained that rate to the ground.
The “probable cause” of the accident, the NTSB decided, was “the pilot’s loss of control following an in-flight failure of the propeller.” A detailed examination of the errant propeller blade revealed that it had failed as a result of improper surface preparation where metal parts were bonded to composite ones. The manufacturer of the uncertified propeller, the NTSB observed, “states that the propeller is not deemed airworthy and that it is the pilot’s responsibility to ensure that the propeller is properly tested prior to flight.”
The airplane was found the next day, two miles from the runway, at the edge of a small wooded area. It was lying upside-down. The wings had broken at midspan in the negative-lift direction, evidently from the impact upon the upturned tips, but they had remained attached to the fuselage, and the fuselage itself was in one piece and looked practically repairable. One would have thought the airplane had fallen inverted, except that the right landing gear leg, a spring of glass fibers and epoxy as big as your arm, was broken where it entered the fuselage, suggesting a violent impact. Possibly the airplane descended upright, bounced and then came to rest inverted. A striking feature of the wreckage, however, was the absence of longitudinal crushing. The airplane was evidently in a more or less level attitude when it struck the ground.
The NTSB’s accident report (CEN09LA288) did not comment on the surprising fact of a fast-moving airplane practically halting in midair and coming more or less straight down at an unvarying vertical speed of 67 knots. Nor did it detail the pilot’s injuries — beyond the coroner’s standard formula of “blunt force trauma” — in a way that might have hinted at the airplane’s attitude on impact.
When a conventional airplane descends vertically, it is either in an inverted dive — in which case it crashes at a very high speed and is completely demolished — or in a spin, in which case the nose is usually down and at least some longitudinal crushing occurs on impact. Only after a flat spin, in which the nose is close to the horizon, would the wreckage exhibit no longitudinal crushing. A flat spin has occurred (during experiments by a professional test pilot) in a modified Long-EZ; it took 15 turns, an altitude loss of 4,000 feet and extreme persistence and self-possession on the pilot’s part to find the means to recover. Canard airplanes are said to be spin-proof, but “practically spin-proof” might be a more accurate description.
The constant rate of descent is noteworthy. It is near the stalling speed of the airplane, and, since the drag coefficient of the airframe in a level, vertical descent is similar to its lift coefficient in a normal landing, it encourages the hypothesis of a stable, “locked-in” stall.
But if such a stall occurred, how did it happen? And what did the failure of the propeller have to do with it?
The usual precursors of wing stall in a canard airplane are low speed and an aft CG. The heavier propeller would have moved the CG aft somewhat, and with only the pilot in the airplane the CG would have been in the aft part of its range. But the Velocity’s indicated airspeed at the time of the prop failure
was quite high — probably around 128 knots.
One plausible theory is that the pilot, startled by the violent vibration of the unbalanced propeller (and possibly even thinking that he had encountered flutter), abruptly applied full aft stick in order to slow down or gain altitude, or both. This could have resulted in a 4-G pull-up — not enough to break anything, but enough to pitch the airplane sufficiently rapidly that its rotational momentum might have allowed the wing to stall.
It’s just a theory — but it goes further than mere “loss of control” to account for the strange tale told by the GPS.
This article is based on the NTSB’s report of the accident and is intended to bring the issues raised to our readers’ attention. It is not intended to judge or to reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory.