5

Test pilot Carl Pascarell got himself into an interesting situation while testing the Velocity prototype. With an aft-CG, he got himself into such a deep stall that flight was unrecoverable. Amazingly, when he prepared to bail out he noticed that his decent rate with the plane was the same as it was with a parachute, so he decided to ride it out.

Along the way down, he tried several strategies to coax the plane into flying again. The one I find the most interesting is when he achieved a nose-down attitude, but was still unable to recover from the stall:

Oscillating the aircraft with coordinated rudder and aileron, he was able to achieve a 30- to 45-degree bank and a 20- to 30-degree nose-low attitude. Progress? The airspeed indicator showed 20 to 30 knots, and the descent rate increased to 2,500 fpm; but several coordinated 360-degree turns later it was clear that the new method was useless.

What was going on aerodynamically? What was going on to allow for coordinated turns but not for pitch control?

Source article: https://www.aopa.org/news-and-media/all-news/1996/june/pilot/pilots-(6)

(Another explanation worth considering: the article is a little loose on details.)

Kenn Sebesta
  • 5,102
  • 22
  • 49
  • @Pilothead I have no idea how I neglected to include the article link, esp. since I copy-pasta'ed from it for the quote. Thanks! – Kenn Sebesta Sep 25 '22 at 21:11
  • So a pilot was in a plane with no power, falling, and could have escaped, and chose not to?! – Someone Sep 26 '22 at 02:17
  • 2
    @Someone. Yes. He determined that he was safer in the plane than outside of it. Events proved him right. – Kenn Sebesta Sep 26 '22 at 02:29
  • @Someone, he had a parachute, but it would be an emergency parachute that is relatively small so the landing would still be pretty rough. – Jan Hudec Sep 26 '22 at 09:52

2 Answers2

11

The deep stall at aft CG in a Velocity was discovered by the first customer, Neil Hunter, who was not seriously injured in his episode. The stall was duplicated by Pascarell as you mention in the company aircraft at the request of the designer, Danny Maher, showing that there was indeed a design flaw.

enter image description here

To discover the cause the aircraft was mounted at its aerodynamic center on a trailer with a 210lb internal weight which could be shifted forward and aft through the entire cabin. The mount allowed the aircraft to pitch up to near vertical. As the descent speed in deep stall was only 15-20mph the trailer did not need to be pulled very fast.

enter image description here

With the aircraft tufted and cameras mounted, a series of tests showed that the main wing stalled at 18deg, the canard stalled at 20deg and the strakes (which were ahead of an aft CG) stalled at 26deg, leading to pitch up. In a canard the main wing needs to stall last to avoid unrecoverable deep stall and in the original configuration it was stalling first. This contains a description of the tests.

enter image description here

The solution for kits already being built was the installation of a main wing cuff similar to this test article. The wing design was changed for future kits which included an extended trailing edge and modified camber on the aft strake such that no deep stall could be entered, thus not requiring the use of the cuff.

Update: There is at least one discrepancy in the article which states that the "rudder and elevator were useless" when in the stall and also states that the pilot oscillated the aircraft with "coordinated rudder and ailerons". It seems likely that since the aircraft was longitudinally and directionally highly stable in the stall, the turns were initiated by banking with ailerons and airframe stability coordinated the turns. The banked turn increased g loading resulting in a higher rate of descent in an accelerated stall.

Pilothead
  • 20,096
  • 3
  • 54
  • 98
1

Alas, 2500 fpm is also around 30 knots, so the descent angle was around 45 degrees. The pilot may have been close to breaking the stall, but not quite.

The "coordinated turning" was probably a combination of yawing from drag difference of the stalled wings, the lift differential from one being more stalled than the other, and rudder inputs.

Attempting spin manuvers with aft CG is dangerous, but we have to applaud the pilot for staying with it because the rate of descent was similar to bailing out with a parachute.

Robert DiGiovanni
  • 20,216
  • 2
  • 24
  • 73
  • 1
    I often wonder about the judgment of staying with the airplane. Granted, survival chutes may be smaller but as someone who’s been a pilot, paratrooper, and skydiver, no one’s descending under a canopy at around 30 knots. Typical descent rates are in the 17-19 mph or 14-16 Kt range. 30 kts is the equivalent to jumping off a 4-story building and landing on your feet, and would rarely be survivable. I’m assuming that he took the energy absorption of the aircraft into account, but a 30 Kt impact is still a dangerous situation. – Max R Sep 24 '22 at 16:50
  • The 2500 ft/min decent was while he was trying to maneuver the airplane out of the stall. His decent rate while wings level was considerably less. He was also over the ocean. – jvcthd1098 Feb 22 '23 at 16:42