ESP, as I've explained, is a stability augmentation feature. It offers protection from overly steep pitch angles, starting at 17.5 degrees nose up or nose down; overly steep bank angles, from 45 to 60 degrees; and high airspeeds, starting at 185 knots indicated.
Flying the SR22 with ESP in normal realms of flight was just like flying an SR22. There was no difference. When ESP became active, because I purposely pushed the margins of the envelope, the system kicked in. In a steep banked turn, the 30-degree reference bars on the attitude indicator became double lines, indicating to me that ESP was active. At 45 degrees, the force came in, and the feel of the airplane was slightly heavier but still very controllable. At 60 degrees, the system went to full force, which felt heavier but still controllable. Lessening the bank to 30 degrees turned ESP off again.
The most dramatic demonstration was the spiral dive that I mentioned in the opening, from which ESP was able to recover with no pilot input. It didn't return me to straight and level, but it did succeed in raising the nose and wing to recover from the spiral dive. After a couple of oscillations with ESP active, the system took control, assuming, rightly, that the pilot was not in meaningful control of the airplane. Once back in control, the pilot could, with the press of a yoke-mounted button, resume his flying duties.
One thing you'll notice missing from this list of ESP functions is underspeed protection. That's because Garmin's system relies on an angle-of-attack sensor to issue stall warning information to the system, something the stall warning device on the standard SR22 cannot do. (The Experimental SR22 I flew had angle of attack, so I was able to fly with that utility.) Underspeed protection will be offered on the King Air G200 — which has an available angle-of-attack sensor — and potentially many other airplane models. The system provides protection by lowering the nose when the stall warning comes on and adds maximum force at 2 degrees positive angle of attack, staying on until 2 degrees nose low, allowing for both easier stall prevention and recovery.
The second system function is auto-pilot protection, of which there are two modes, one for when the phase of flight is altitude critical and the other for when it's not. In altitude noncritical modes, the system slows down to the minimum autopilot commandable speed, which is 80 knots in the SR22. In altitude critical modes, the autopilot will go even slower, down to as slow as 70 knots with full flaps, in an effort to hold off losing altitude when there might not be much altitude to lose.
Finally, the new autopilot adds one very desirable new feature to the mix: automated go-arounds. With the touch of the TOGA button on the throttle, the system will keep the autopilot engaged, command the climb, switch the navigation mode to "nav" and sequence the flight plan to the missed approach segment. All the pilot has to do is add power and switch the autopilot to "nav." It's a great new capability.
Flying Avidyne's DFC90
A few days after my adventures in Kansas, I visited with Avidyne Corp. in Lincoln, Massachusetts, to learn about and try out its DFC90 autopilot with envelope protection.
