Spinning a Jet

 
 

A few weeks back, Scott Glaser of Flight Research, Inc. proposed an interesting project: he wanted to collect spin data on one of FRI's MB-326M Impalas. Read: he wanted to spin a jet.

"Of course," I said, poorly disguising my childish excitement with a level of anticipation akin to a dog with a treat on his nose waiting to be told "go."

I wrote a card, packed up the BoxDAQ, a GoPro, and a flightsuit, and headed for Mojave. I found the jet and installed the BoxDAQ on an existing camera mount. FRI's fantastic life support crew put me through ejection seat training and fitted me with a helmet and mask.

 
 

We briefed 3 spins, all to the left. The first would be a nominal upright spin, 3 turns. The second was upright, 3 turns, with outside aileron during turn 2 and inside aileron in turn 3 to explore aggravated spin. The third was a 2-turn inverted spin entered from a tailslide. This let us explore an entry with minimal forward energy to get us on the vertical axis more quickly.

The flight was piggybacking an FCF. We wrapped up FRI's FCF card at FL250 which was a great place to kick off a spin. The Impala is a well behaved airplane, with a very well-tuned buffet occurring a few knots before the stall break, and plenty of advance notice before tucking into a traditional inverted incipient. It was challenging to use the SARO modifiers in a 3-turn spin - since the Impala has much more kinetic energy than what I'm used to, and stalls at much higher airspeeds, it takes much longer to get established on the vertical axis. This means that our spins appeared highly oscillatory, punctuated by 60+ degree pitch rocks every turn.

From a cockpit feel standpoint, outside aileron appeared to bring the nose up and slow the rotation rate, while inside aileron caused an apparent tuck and increased rotation rate. What's interesting is that the data shows a minimal change in spin characteristic, suggesting that cockpit feel might be a little over-sensitized due to the forward seating location of the pilots.

The spin entry from a tailslide was surprisingly gentle, with slow negative G onset and none of the harshness I'm accustomed to from inverted entries in Extras and other lightly loaded aircraft. Without forward kinetic energy, the aircraft quickly settled into a 70-degree-nose-down attitude with minimal oscillation.

 
 

The X-Plane simulations give away a lot of the magic on this one. They show a very horizontal flight path for the upright entries, barely transitioning to dominantly vertical by the time recovery is affected. The tailslide entry shows off my less-than-great skills as a jet pilot.

 
 

For me, the big points were mostly related to what the airplane felt like. Being placed so far from the center of gravity has a big impact on the "feel" of the spin. While it isn't harsh, you feel like you're being swung around a lot. The feel of the rotation rate was moderate, but the data suggests that it's about half as fast as an Extra, and a third as fast as my Jungster.

The altitude lost during recovery is dramatic. I'm used to the recovery being about one turn's worth of altitude, perhaps a little more - usually less than a thousand feet. While the rotation always stopped in less than one turn, the Impala will dump a couple thousand feet in a hurry as it builds speed. In the first spin, I had a very noticeable tendency to recover into the buffet - this is startling, but Scott told me it was perfectly acceptable as long as you listen to the airplane and don't try to ask any more from it.

It was an incredible experience to take the feel of the airplane and put it next to the data. I can't wait to see how this data is used to enhance FRI's upset recovery training program. I've worked for a long time to focus on learning as much as I can about spins, and I hope this data helps other do the same. 

I owe a big thinks to Flight Research for making this happen. They're a very professional operation doing some cool things in the realm of upset recovery training - check out what they're up to here: http://www.flightresearch.com/.

Go spin something!

 

 
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