Bill Crawford’s Flightlab Blog

I just finished updating the ground school texts available on my website, www.flightlab.net. Click on “Download Course Notes & Documentation.” Please take a look. Here’s the background.

In 1997, about when I began teaching aerobatics, I took a course at the National Test Pilot School, in Mojave, California, called “Introduction to Performance and Flying Qualities Flight Testing.” This was an abbreviated version of their professional test-pilot course. It happened to occur during the fiftieth anniversary, on October 14 of that year, of Chuck Yeager’s assault on the sound barrier in the X-1 rocket plane. Edwards Air Force Base, the former Muroc Army Air Field of sound-busting days, is just south of Mojave. The plan was for Yeager to depart Edwards in an F-15 to break again what was really no longer a barrier, fifty years to the minute. At NTPS, they shuttled us out of a class on supersonic aerodynamics and pointed to the sky. We admired the contrails and heard the boom, then they shuttled us back in for more academics. It was absolutely the best lecture demonstration I’ve ever seen.

A year ago, I attended the NTPS “Technical Pilot Course.” No sonic booms, but now at least a good restaurant on the field. Unfortunately, despite the presence of Burt Rutan’s Scaled Composites and other outfits full of bright people tinkering with weird machines, Mojave has zero appeal once the sun goes down. It’s a truck stop on a long drive to someplace you’d prefer to be.

NTPS runs an efficient classroom. The information comes quickly and from multiple directions—one hour you’re trying to understand stick-free maneuver points, the next hour FAA Part 23 certification requirements. Then they hustle you into an aircraft to record data for drag polars. It’s terrifically stimulating, but it’s impossible to digest everything in real time. I often found myself nodding politely, pretending that my brain was actually operating. The value of the abbreviated courses is that the subject is laid out in organized but general terms. You get to see the main areas of concern, and how they link up. Afterwards, you can select the relevant subsets and hit the books to build on what NTPS gives you. It’s not for the passive.

Relevant to me is the ability to demonstrate and explain the varieties of aircraft response, especially during aerobatics and unusual-attitude training; but throughout the normal modes of flight as well. The texts on the Flightlab website are my self-assigned homework toward this end, dating back to the first trip to NTPS. I encourage my students to use them as a starting point for their own homework, at whatever study pace feels best.

On that first trip to NTPS I especially wanted to learn more about the relationship between big and little. I was often flying little aerobatic airplanes with pilots whose regular aircraft were big transports. The question was this: how should the lessons learned in a small aircraft be transferred to a big one, given the differences in control forces, wing planform, operating speeds, inertial characteristics, structural limitations, and especially the differences in the actual validated flight-test envelopes? The validated envelope is important because aircraft are flight tested within the envelope of intended use, with some additional level of abuse thrown in. You determine the spin departure and recovery characteristics of a Zlin, for example, by doing spins. Spins are part of the flight envelope. But you don’t explore the spin departure, let alone the recovery characteristics, of a 737—that’s way out of the intended envelope for aircraft type. Despite Boeing test pilot Tex Johnson’s high jinks with the 707, you don’t roll one either. So the relationship between big and little airplanes is sometimes a connection made through aerodynamic principles and engineering formulas rather than demonstrated facts. When you’re teaching a pilot to recover from unusual attitudes in an aircraft that will be significantly different from the trainer, it’s important to know what it is you don’t truly know.

The people you’d expect to know what they don’t know sometimes don’t know at all (huh?). When American Airlines developed its Advanced Maneuver Program for upset training, it faced criticism from the airframe manufacturers for recommending more aggressive rudder use than the manufacturers believed appropriate for swept-wing transports at high angles of attack. The aggressive rudder was meant to accelerate roll rate when the ailerons began to lose effectiveness. The manufacturers pointed out that the technique was more applicable to a certain generation of swept-wing jet fighters than to swept-wing transports. The head of the American program was a former fighter pilot.

While some pilots like learning about aerodynamics, others seem to freak. I enjoy it when I can nudge those in the latter category into the former. Very often this involves a kind of eureka moment when the student, having been bewildered in the past, suddenly understands why aircraft act as they do in a particular area of flight. Then they get greedy for knowledge. The times when understanding comes together with experience are what make learning, and teaching, so much fun. It’s too bad Yeager isn’t always available for a demo.

When I teach aerobatics or unusual-attitude recovery, I always start with a set of stability-and-control flight-test maneuvers, originally learned at NTPS. They’re the same as those used during FAA certification, but sloppier because we can have a good time and don’t have to take data. The test maneuvers help break aircraft behaviors into their aerodynamic constituents—the building blocks of force and moment that generate aircraft response. Once you get a sense of how the individual building blocks work in simple cases, you can start to understand how they combine to generate the complicated stuff—for instance, the stuff that goes on when an airplane departs into a spin.

Concerning spins, here’s a project. I want to take a look at the actual susceptibility of various aircraft to skidding-turn-to-final stall/spin departures. I’m referring to the classic situation where a pilot is low on base and uses the rudder to turn onto final, while holding opposite aileron to keep the wings more or less level, and back stick to keep the nose up. This “cross-controlled” entry scenario is often invoked in the pilot magazines as the cause of many fatal accidents, or as the reason why something bad will happen unless you, the magazine-reading pilot, stay sharp, current, vigilant, renew your subscription, etc. My experience playing with this scenario—at altitude, of course—is that it might not be so easy to get an aircraft to depart as claimed. In my Zlin and Airwolf, the rudder and stick forces become quite high before the aircraft starts to drop a wing. You’ve got to be pretty dense not to figure out that you’re doing something silly. In a 7GCAA Citabria (like my old skywriting ship or the one I occasionally get to borrow), full rudder, full up elevator, and full opposite aileron won’t provoke the dreaded response at all. The thing just flies crooked.

I hope to put together some aircraft-specific data on this—thus a call for volunteers. Bring your plane down to Plymouth. It’s a flyer’s paradise. We’ll tuft your wing and then video it in normal straight-ahead stalls and in crossover entries. We’ll hold the crossover inputs just until we get the wing to begin to drop, then we’ll recover—nothing scary, no heroics, everything legal. Then I’ll buy you lunch at Jane’s, and eventually put the video on the web and maybe write about what a hot stick you are. If you have a high-wing aircraft we’ll skip the wing tufts, but you’ll still get lunch and the unspoken thanks of vigilant pilots everywhere. Could make it a BFR. I’m interested in older as well as newer designs.