Ken Szalai, then the director of Dryden Research Flight Center, served as NASA’s senior aeronautics representative at the Paris Air Show.33 Years later, he recalled that when the show announcer broadcast that the X-31 was next to fly, people began streaming out of the various chalets bordering the flight line to watch its debut.34
Four basic X-31 signature maneuvers comprised the X-31’s Paris show rou-tine: the post-stall loop with a 150° heading reversal, the Mongoose turn, the Herbst turn, and a post-stall loop with a 180° and then 90° heading reversal.
Planners also designed a “low” show routine (in the event of a low cloud ceil-ing) consisting of two Mongoose turns and one Herbst turn. Thus, in the final
Into the air: the first X-series airplane in foreign skies. (Rockwell)
Desert Disaster, Triumph in Paris, and a New VECTOR
approved airshow routine, the aileron roll (which had received much pilot criticism), Sukhoi-like “cobra” maneuvers, and post-stall split-S maneuver were eliminated.
The first maneuver in the full “high” show was the post-stall loop with 150°
heading reversal. The pilot pulled 2.0 g’s and then maintained 20° angle of attack until the velocity vector passed the horizon inverted. At this point, the pilot would pull to 70° angle of attack and, upon reaching it, execute a 150°
left post-stall velocity vector roll. Upon completion of the velocity vector roll, he would reduce the angle of attack to less than 30°.
The second maneuver was the Mongoose turn. The pilot would fly at 180 to 200 knots indicated airspeed, roll to 70° to 90° left bank and pull to 70°
angle of attack, and continue the turn to the opposite heading before—while maintaining 70° to 90° left bank—executing a nose-up nose slice via a right velocity vector roll to a vertical nose position. The angle of attack was then reduced to 50° and the aircraft was flown straight out and accelerated.
The third maneuver was the now-familiar Herbst turn. For this maneuver, the pilot would stabilize at 30° angle of attack in level flight, then pull to 70°
angle of attack. He would then reduce the angle of attack to 50° before com-mencing a left climbing turn, making a 150° heading change with a velocity vector roll, then returning to level flight and accelerating. (Compared to previ-ous experience, this maneuver had been modified somewhat so that the plane maintained a profile closer to a “climbing turn” instead of the velocity vector roll typical of the end of a Herbst turn pull.)
The fourth and final maneuver was another post-stall loop, this time with 180° and then 90° or 180° heading reversals. The pilot would pull to 3.0 g’s and maintain a 15° to 17° angle of attack
until the velocity vector passed through the horizon inverted. The aircraft would then be pulled to 70°
angle of attack and the pilot would execute a 180° left post-stall veloc-ity vector roll, stop, and make a 90°
or 180° velocity vector roll to the right. Upon completion of this roll, angle of attack would be reduced to below 30°.35
It is important to note that unlike most airshow routines, in which each maneuver flows into another maneuver (and, since the
subse-quent maneuver is dependent upon The X-31 at high AOA in Paris; note the position of the canards. (Rockwell)
Flying Beyond the Stall
the previous one, energy management is very critical), in the X-31 routine each maneuver was performed separately. Thus, an emphasis on maneuver safety and quality could be more tightly focused. Each separate maneuver could be easily simulated and the failure matrix for each maneuver could be well defined.
The whole objective of appearing at the Paris Air Show was to showcase X-31 thrust-vectoring technology, so the use of separate distinct maneuvers was not only the safest approach to the demonstration routine; it was also the most effective, from an observer’s standpoint, in presenting what the technology could accomplish in flightpath modulation.36
John T. Bosworth, Dryden chief engineer at the time of the Paris Air Show, enumerated various lessons learned from the X-31’s Paris experience:
1. Seeing is believing! I, as an engineer, tend to underestimate the impact of advertising. I liked to believe that an idea like thrust vectoring would sell itself on its technical merits through tech-nical reports. Two events illustrate the impact of a big air show:
• The sale of several F-15 aircraft to Egypt was made con-tingent upon the ability to upgrade to thrust-vectored engines in the near future.37
A science reporter who had been reporting on the X-31 over the last four years made the comment that “she never really understood the capability until she saw it.”
•
2. The Aerospace Industry is truly a world market and Dryden is not necessarily at the center of it. We tend to overestimate the exposure the work we do at Dryden gets. It is in all the publi-cations that we read, however, the average Joe “off-the-street”
doesn’t read Aviation Week.
3. Part of NASA’s charter is to promote aeronautics and inspire today’s youth to a career in a scientific field. Air shows provide an opportunity for this (although we may have inspired more French youth than American).
4. An air show is a public affairs expedition. Pictures, brochures, decals, patches, hats, t-shirts, etc. are as important as the technology demonstration itself. Bring lots of these along to give out.38
Desert Disaster, Triumph in Paris, and a New VECTOR
The X-31 proved to be an airshow crowd-pleaser. (NASA DFRC)
The comment about memorabilia is evidence of the crowd’s intense inter-est in the airplane. Everyone wanted some remembrance of the show. An additional eyewitness review of the X-31’s performance is provided by Rogers Smith, who, though not able to fly in the show, was on hand to provide sup-port. According to Smith,
[The X-31 put on a] fantastic air show, absolutely the most spec-tacular I’ve ever seen. I saw every one of them—I stood with the crowd on some of them and I was in the control tower on others and I was right underneath it at other times. But to deal with the crowd and watch even hardened veterans—military—who had no concept of what it could really do and [then] seeing it, was jaw dropping for the crowd. It was spectacular!39
A couple of anecdotes related to the author by Mike Robinson further serve to illustrate the impact of the X-31 demonstration:
While in the Rockwell Chalet (we had a prime show viewing loca-tion) I was approached by a gent in a flight suit with a huge video camera who introduced himself as part of the Russian delegation at the show. He asked if he could be allowed to film the X-31’s flight from our porch. We accommodated him and little more need be said about the impression it made on the Russians.… Then there was the famous Av Week [Aviation Week & Space Technology
Flying Beyond the Stall
magazine] quote which went to the effect, “The X-31 was the hit of the show, every time it approached show center and initiated a maneuver everyone was amazed…but even more amazing was that immediately thereafter we didn’t see the pilot in a chute.”40
Four practice flights and eight airshow flights were flown at Paris. Luckily, the weather cooperated, and the first airshow performance on President’s Day was a high show. The weather mandated only one low show performance, on June 13, 1995, and only one flight was canceled, due to a flight control computer power supply failure on power-up. June 18 was the last day of the airshow; the next day, the airplane was flown back to Manching, with a stop in Köln-Bohn. Over the next 5 days, technicians defueled the X-31, removed its thrust-vectoring vanes, Kiel probe, and right wing, and then loaded it onto a pallet. The X-31 was rolled aboard a USAF C-5 on June 24 and flown from Manching to Edwards the next day. There, the team had to wait for a fix to the C-5 before unloading because the C-5 would not “squat” to the unloading position. The X-31 was unloaded on June 27 and the wing was reattached on June 28. The airplane was placed in storage in Building 4826 at Dryden. By Friday, July 7, its engine had been removed and the X-31 team had been reassigned. It seemed that the X-31 had flown its last flight.