Some of you may have read the Aftermath article in the current Flying Magazine. Here is my letter to the editor.

I’m writing to correct several inaccuracies in the Aftermath article in the most recent (October 2012) edition of Flying magazine. First, the title of Mr. Garrison’s article associates this (N45YV) accident with Deep Stall, which has not been established by the NTSBVelocity Inc., or any other competent body.

At best deep stall would secondary to the actual cause, correctly identified by the NTSB, in-flight separation of one blade of the three-bladed Vesta constant speed propeller. It’s interesting that Velocity was mentioned in the article, but not Vesta, but that is a side issue. Second, the discussion of “three” deep stall Velocity accidents is disingenuous at best. One of these was by factory test Pilot Carl Pascarell (former test pilot for Swearingen, Continental Airlines Captain, USN jet pilot, and aerobatic show pilot, Note 1) while investigating how this situation (Note 2) might be created. He elected to stay with the airplane (though he was wearing a parachute), which was repaired and flying again within the three weeks (Note 3). In the case of N141NH, the accident was caused by flight into the vortex of a Boeing 727 (Note 4). The third was caused by modifications by the builder to decrease canard effectiveness (Note 5) None of these can be fairly construed to reflect on aircraft’s design as they were placed into situations that no airplane should (flight outside of the W&B envelope, into the wake vortex of a jumbo jet, and intentional reduction in canard incidence angle in relation to the main wing).

Further, he states that the lack of injuries was “likely … because their airplanes fell into water, and the rounded undersides of the fuselages provided some shock absorption.” This is completely unsupported by fact. To the contrary, in the aforementioned Sport Aviation article (Note 2), Mr. Pascarell reported “the descent rate appeared to be very low, and there was no discernible forward motion“, which is why he elected not to bail out. He instead rode the aircraft to the water and escaped uninjured, reporting in Kitplanes (Note 6) that he was descending at less than 1,200 fpm. This calls into question, also, Mr. Garrison’s assertion that the Houston crash aircraft’s on-board Garmin’s reported “7,000 fpm” descent which, if true, would then argue against this being an instance of Deep Stall at all. Then Mr. Garrison implies with his “At the time, it was widely believed that the stable stall produced a very low rate of descent. This implied an unexpectedly high, in fact unprecedented, drag coefficient, and novel, semimagical vortices were posited to explain the new phenomenon; but ground tests, conducted by Rutan with an airplane set up vertically on the back of a truck, failed to produce them.” that this low descent rate has never been proved. But an experienced test pilot with a functioning vertical speed indicator and packed parachute is enough for me, particularly since Mr. Garrison does not provide any reference to the testing that supposedly demystified this, apparently irrational yet experiential, belief of Mr. Pascarell’s.

Furthermore, Mr. Garrison fails to mention that he previously wrote an article on deep stall in the Velocity and other canard designs (Note 9). In that article he admits to being acquainted with the facts I’ve outlined above, which seems to show a prejudice against the design or the testing subsequently performed for some reason.

Next Garrison asserts that Burt Rutan did aerodynamic testing “with an airplane setup vertically on the back of a truck“. Maybe, but the only reference to this I can find is from Kitplanes (Note 7), where it states Rutan did this with “a small scale model of the test aircraft” and a car, but then goes on to show Danny Maher’s full scale truck-based test bed, designed in cooperation with Jim Paxton, Chief of Flight Operations at NASA Langley (Note 3). It does not mention any flat-plate testing that Danny may have done with this test bed, but it would’ve been ideally suited to it.

Finally, Mr. Garrison asserts that the vibration of propeller blade loss might have been confused with flutter. However, since this Velocity was outside it’s mandated 40 hour test period, and Mr. Garrison himself indicates the accident pilot had flown it for “250 hours with a two-blade fixed-pitch propeller“, the accident pilot could hardly be expected to suspect flutter at such a low airspeed. The Velocity’s Vne is 200 kias, and is as such extremely docile and stable at a mere 128 kts. If we’re to speculate, it seems rather more reasonable to me that the loss of the blade fractured the engine mount, and the weight of the engine unbalanced the airplane in a completely unique and catastrophic way. In any event, it seems that Mr. Garrison chose to engage in wild speculation and disparage the canard design for a with a flaw that has not been in evidence in nearly 2 decades.

1) Carl Pascarell
2) Sport Aviation, July 1991, Velocity… Solving a Deep Stall Riddle, page 54
3) N81VA, probable cause MIA89LA117
4) N141NH, probable cause MIA93LA011
5) Sport Aviation November 1997, page 112, Canadian Council News, Deep Stall
6) Kitplanes, November 1991, Testing on the Ground, page 75
7) Kitplanes, November 1991, Testing on the Ground,page 72
8) Sport Aviation, September 1991, Deep Stall Cont…, page 55
9) Flying, January 1992, Deep, Deep, Stall, page 102, Google Books

Posted By: Brett Ferrell
Wednesday October 10th, 2012 at 8:52 PM

Categories: Blog
Tags: log

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