I am sure all readers here have experienced first-hand a secondary stall once or more during their flight training. In fact, for the CFIs in the group, you have probably observed them hundreds of times: An inexperienced pilot gets a little too aggressive in recovering from a first stall, pulls the stick or wheel back too forcefully and increases the angle-of-attack (AOA) enough that he or she encounters another stall, the secondary stall. Here’s a little secret for your memory bank: The T-Tailed King Airs – F90- 200- and 300-series – may be the most likely mass-produced airplane ever built to coax into a secondary stall. Allow me to explain.
Moving the horizontal stabilizer and elevators to the top of the tail means they usually reside in the relatively undisturbed air. As the wing approaches the stall angle-of-attack and air starts to burble over it, little of that disturbed air hits the horizontal portion of the T-tail. Consequently, there is very little pre-stall buffet felt in these planes. Were it not for the stall warning horn installed, it is difficult for the pilot to sense that a stall is being approached.
After the stall is recognized and recovery is begun, the elevators are still very effective, not being blanked by the disturbed airflow off of the wing as happens in a conventional-tailed airplane. It takes little force and control wheel motion in the cockpit to move the elevators enough that the angle-of-attack can quickly be increased to a critical degree…leading into the secondary burble or actual stall.
I will never forget – and I have demonstrated this phenomenon to many other King Air pilots whom I have trained over the years – when Bud Francis, the 200’s Chief Test Pilot, showed me the effectiveness of the elevators and how little force is required to reach stall AOA. In BB-1, the first prototype test airplane, he did a very gentle approach to a clean stall, with airspeed reducing at the rate of about one knot per second, while trimmed for about 130 knots…about 1.3Vs. The stall occurred with a slight buffet and the nose falling, at about 100 KIAS. Bud then kept power at Idle, allowed the nose to drop to increase speed to 120, then pulled back on the control wheel again. However, to emphasize how little force was required, instead of having his whole hand on the wheel he just hooked the little fingers of his two hands on the wheel as he pulled. Very rapidly, a stall buffet was felt as G-forces loaded the wing. Once again the nose was allowed to fall, airspeed was increased another 20 knots – now going to 140 – and the whole process was repeated. Bud kept this up all the way to 160 KIAS, where it was still easy to induce stall buffet using little finger pressure alone. He then had me take the controls and repeat the demonstration from 100 to 160. It was indeed eye-opening to experience the relatively low pull forces that were needed to make the wing experience an accelerated stall even at 160 knots.
Since the T-Tail was a new design on the King Air family with the introduction of the 200 model, Beech was unsure whether the plane would exhibit sufficient stall warning and elevator effectiveness to recover properly, so BB-1 was originally fitted with both a stick shaker and stick pusher. Happily, it was found that neither was necessary so they were not included on production airplanes. What is included, however, is something few pilots have noticed.
So what is this hidden secret? It is a note presented on the “Stall Speeds – Idle Power” graph in the Performance section of the POH. The note states, “A normal stall recovery technique may be used. The best procedure is a brisk forward wheel movement to a nose down attitude. Level the airplane after airspeed has increased approximately 25 knots above stall.”
I wonder how many FAA pilot examiners would not be aghast if they observed a pilot delaying aggressive stall recovery until airspeed had increased 25 knots?! Aren’t we all basically taught to reduce the angle of attack just enough to break the stall, add power (if available), and fly out of the stall? Sure we are, as it should be. In a T-Tailed King Air, that same procedure works perfectly 99% of the time and it’s what we do. But…keep in mind how powerful the elevators on this T-Tail are and be gentle as you add back pressure to initiate the climb back to your assigned altitude. Avoid that easily-induced secondary stall!
Author: Tom Clements, King Air Academy