Stuck In The Spin Cycle

November 1, 2001 by Legion Magazine

by Graham Chandler

 

Cut throttle to idle. Ease back on the stick to maintain altitude, reducing airspeed by one knot per second. At five knots above stall speed, gradually feed in rudder so full input is achieved at the stall. Voila! We are in a standard spin.

Now apply full opposite rudder and full forward stick to recover. Whoa! What we have here is a decidedly non-standard spin. Seven turns later our Musketeer trainer continued winding up in ever tighter turns. I heard a terrified: “What the f – – k?” from the pilot on my left as we drilled through 3,000 feet above the twirling northern prairie. In that same instant, my mind frantically reviewed the emergency egress routine we had rehearsed in the hangar: Jettison door, disconnect harness, dive for outside wing, count to five and then pull the ripcord.

Ya gotta be kidding! I had never heard of anyone bailing out of a spinning Musketeer. There must be alternatives to jumping. And so after summoning all my engineering training, I screamed: “Try aileron into the spin!” After an eternity, that move seemed to work, and we bent the poor airplane pulling almost seven Gs to avoid becoming a smoking hole in a wheat field.

It was the early 1970s and I was a Canadian flight test engineer at the Aerospace Engineering and Test Establishment, AETE, at Canadian Forces Base Cold Lake in Northern Alberta.

I was also a recent graduate of the United States Naval Test Pilot School, USNTPS, in Patuxent River, Maryland. Three hours of spinning T-28s over Chesapeake Bay should have prepared me for this.

The Beechcraft Musketeer was an aerobatic version of a general aviation light air plane that had been bought for the Canadian Armed Forces to replace the aged Chipmunk aircraft for primary pilot training. The Forces’ installation of standard military safety equipment, which included survival kits and fire extinguishers, had moved the aircraft’s centre of gravity forward of the range the manufacturer considered safe for aerobatic flying.

Our project was to conduct stress analyses and test flights, including spins, to determine if this range could safely be expanded. Doing manoeuvres in which an airplane is stalled and in an essentially out-of-control, nose-down corkscrew spiral, are an important element of a military pilot’s training. Such manoeuvre allows the pilot to gain confidence in unusual flight attitudes. So, I had to write lots of fully developed spins into the test plan, lest an overzealous or panicky student pilot ever let things get out of hand.

By the time the project was finished, we had racked up approximately 39 hours of pure spinning and discovered a previously unknown spin mode in the Musketeer.

A sub-specialty of the Aerospace Engineering, AERE, officer classification, our job as flight test engineers was to evaluate the effects on aircraft performance and handling of various additions and modifications to Canadian Forces aircraft, as deemed by the policy wonks at National Defence Headquarters in Ottawa.

After being assigned a project directive, we delved into the theory and studied the equations to see what kind of a flight test plan would be needed for any particular aircraft. What airspeeds, altitudes, manoeuvres, instrumentation, etc. all in order to make sure the aircraft could be flown safely at the edges of its design envelope. Once we were comfortable with that, we sat down and wrote up a flight test plan. The next step was convincing all 12 or so signing authorities–all the way up the AETE hierarchy to the senior test pilot and senior test engineer–that we knew what we were talking about.

With the dozen signatures, we could then go ahead and schedule the test flights. We briefed the test pilots for each flight plan and usually flew with them to record data and get a hands-on-stick feel for the aircraft’s flight characteristics under the whole gamut of manoeuvres we designed. We’d then crunch the numbers, do the analyses and write up the results–recommending acceptance or not.

There were only a handful of us and we were considered–at least by ourselves–to be the cream of our trade. We got to attend elite foreign test pilot schools, wear flying suits with our names on them and fly with the test pilots while the majority of our classification were stuck to desks, managing aircraft maintenance organizations and dealing with such mundane matters as scheduling and signing off aircraft inspections and writing up personnel evaluation reports.

For us flight test engineers it was more of the right stuff: Most of the pilots with whom I flew at the test pilot school were fresh from flying A-6s, F-8s and Phantoms off carriers in the Gulf of Tonkin in the South China Sea. At USNTPS we flew in a dozen different types from T-28s and A-4s to variable stability B-26s and thrilled to non-approved dogfighting against the new F-14As which were then under evaluation by the Americans.

Much of the flight test engineer’s work at Cold Lake was routine, but we were–out of necessity–flying at the edges of the envelope most of the time and so surprises were not uncommon. Indeed, during my time at USNTPS and AETE from 1971 to 1976 three close friends and another four acquaintances died in crashes attributed to the risks of test flying.

In 1971, the minister of national defence signed my scroll in commissioning me as a lieutenant in the newly unified Canadian Forces. I was soon posted to 448 Test Squadron at Cold Lake. The following year I was fortunate to be chosen as the only Canadian to attend USNTPS Class 64. Those were the Trudeau years when military cutbacks and shake-ups were daily news. When I got back to Cold Lake in the summer of 1973, 448 Test Sqdn. had been disbanded and absorbed into AETE and the Canadian government was abandoning its traditional NATO air role, converting the CF-104 Starfighter interceptors to a ground attack role.

My first assignment as a neophyte flight test engineer was to come up with new range and endurance figures for the CF-104, an aircraft designed as a sleek and clean fast-climbing high-altitude interceptor. New numbers were critical for Canada’s NATO role, military planners needed to know how far and how fast a 104 could go with air-to-ground rocket launchers and BL755 cluster bombs hanging all over it. Before the project was over, I was amused to discover that, fully loaded, it could barely have made a one-way trip from Cold Lake to Edmonton, less than 200 kilometres away.

There were a few more thrilling projects for me on the Starfighter, including altimeter position error testing. This test gave us one of the few chances available in Canada to go supersonic, skimming the treetops and then entering a 6-G zoom climb, all the while trying to write down the aircraft’s airspeed and altimeter readings on a knee pad in the back seat.

However, the most memorable project of them all was Project Directive 75/26, the lovable Musketeer. For that one I was assigned a project test pilot, a seasoned U.S. Air Force exchange fellow by the name of James Birmingham. After a year of dodging surface-to-air missiles over North Vietnam in an F-4 Phantom, the major was thrilled to be flying the simple little yellow trainer over the northern boreal forest. When it came to test flying, he was the consummate perfectionist. Which was how we discovered that spin from hell.

After pulling out of the dive, we returned to base, closed off the flight plan and repaired to the officer’s mess to discuss our brush with death over a few beers and an energetic game of crud. In a mess dominated by Canada’s largest concentration of fighter jocks, I garnered very little advice other than the following observation: “If you ain’t a fighter pilot, you ain’t shit anyway.”

The incident and my obvious trepidation became the basis for our starring in a tongue-in-cheek squadron-made movie featuring an intrepid silk-scarfed test pilot seen waltzing out to his Musketeer with a blonde on his arm. Subsequent footage shows him kissing the girl goodbye and then strapping his brave self into the cockpit. That’s when the trembling flight test engineer arrives under military police escort and obviously filled with the fear of having to endure more dizzying spins.

The next sequence is taken from inside the spinning Musketeer, and this is followed by footage on the ground showing the girl flinging herself onto her hero while the limp and hapless engineer is hauled out of the cockpit and into a waiting ambulance.

The movie wasn’t far from the truth and making it was a welcome distraction from the seriousness of the incident. However, we still had to get down to business and find out what caused the white-knuckle spin. Ottawa had quickly issued a directive banning spins in the Musketeer until we convinced them it was safe again.

We analysed the data from sophisticated ground camera installations that measure aircraft parameters under test. We also replayed films taken from a chase helicopter and discovered little other than that terrifying spin was much flatter or less nose down than the others. Unusual, we thought, because research had shown that the more forward the centre of gravity, the more nose down the spin, and therefore the more readily it should recover. It is at the more aft centres of gravity that aircraft spin flatter and recovery takes longer.

So it took a bit of head scratching to figure out why we encountered such a scary flat spin at our forward centre of gravity.

Naturally, we were reluctant to try the same spin again before figuring out why it took four instead of the usual one turn to recover. Running out of ideas, we packed our suitcases, strapped on a T-33 aircraft, and flew down to show the film to the National Aeronautics and Space Administration, NASA, in Langley, Virginia, where they had been studying spins for years and boasted the world’s only vertical spin research tunnel. They watched the film and said: “You guys are crazy to spin that thing in the first place.” They then suggested we don’t do it again without a spin chute.

A spin chute mounts on the back of an airplane and is useful for getting out of flat spins by pitching up the tail and pointing the nose at the ground. But the chute wouldn’t have helped us because mounting one near the tail would have moved our centre of gravity too far back, negating the whole idea of the test project.

Offsetting that by adding more ballast up front wouldn’t work either, because that would make us overall too heavy for aerobatics. So, with NASA’s expert help we came up with a gradual buildup program to try and duplicate the spin from hell.

Our discussion with NASA spin doctors hatched a suggestion that our problem had something to do with spin entry technique. So we tried two varieties of entries, the abrupt and the smooth. The abrupt didn’t pay much attention to finesse. The technique was to cut the throttle, haul back on the stick until the airplane almost stalled, and just when the controls got feeling mushy, booting in full rudder all at once. It was meant to be rough–just the way a nervous student pilot might do it.

The smooth entry, on the other hand, was the picture of divine accuracy–played by the book. Birmingham loved this one. He’d revel in holding his airspeed reduction to an impeccable one knot per second and delight at taking precisely five seconds to ease the rudder from neutral to full extension, achieving it all exactly when the stall occurred. The Musketeer responded accordingly by entering the spin slowly, gradually, serenely.

For both entry types, we gave ourselves lots of altitude and started with incipient spins, then a half turn, one turn, two turns, and eventually four. It worked. After just a few dozen spins we began to discern a distinct difference between the two types. And after hundreds of spins of both types, results became nicely predictable. In 80 per cent of the smooth entries when we let it go for two or more turns, it took an additional two and a half turns to recover. Whenever we pretended we were students a little short of accuracy, the Musketeer would spin nose down and snap out of it on command in half a turn.

Spins aren’t well understood even now, but this was a strange phenomenon that left us and the NASA spin engineers flabbergasted. Neither we nor theory ever explained why they differed, but we learned enough to put warnings into the Musketeer aircraft operating instructions to use lots of sky when spinning.

After all that excitement, what could an AERE officer possibly do for an encore? Well, in the military’s way of doing things, it was time for a transfer: Career management, they called it. I soon met the fate of my AERE brethren, banished to Edmonton and chained to a desk with a sign on my door that read: Squadron Aircraft Maintenance Engineering Officer. Meanwhile, the skies over CFB Moose Jaw were full of the sound of happily spinning Musketeers.

Member Benefits Package
Last Post
Subscribe

CONNECT

Classified Ads

Like what you see?

Sign up for Legion Magazine's weekly newsletter.
SIGN UP
close-link