EAA Sport Aviation - October 2011

periods. And that’s where Garmin’s ESP development began.

The key word in ESP is really “ stability,” not “protection.” A properly designed airplane is stable, meaning it tries to fly straight and level and maintain its trimmed airspeed until the pilot makes control inputs or the flight path is disturbed by turbulence. What Garmin’s ESP does is use electronics to add to that natural stability without altering the way we normally fly.

ESP uses the servos that are the core part of Garmin’s autopilot system to add stability—stick force, really—when the human pilot deviates too far from a normal attitude. Just as natural aerodynamic forces demand more stick force to pull the nose further and further up from the trimmed condition, or to roll into a steeper bank, ESP adds stick force to let a pilot know his attitude is moving far from straight and level.

ESP can start to add stick force at any attitude, but in the Cirrus and Beech King Air 200, the first two airplanes certified with ESP, the system comes on at 45 degrees of bank. In the world of transport flying the maximum normal bank angle is 30 degrees, but Garmin’s testing with a variety of pilots found that in GA airplanes pilots will sometimes fly steeper banks briefly, particularly in the VFR traffic pattern. But in any phase of flight 4 5 degrees is a lot of bank and is never really flown unintentionally.

So, at a 45-degree bank angle ESP comes on very smoothly and adds 10 pounds of force to the stick. In other words, the servo is exerting 10 pounds of effort to move the controls to level the wings. If the pilot persists in holding the steep bank, the ESP added stick force builds smoothly to 20 pounds. The added stability force of ESP remains on until the bank angle returns to 30 degrees or less.

Actual stick forces may be higher or lower in other airplanes as ESP is certified in them, but the concept of half the available added stability coming on initially and then gradually building to all available stick force will be the same. ESP does the same thing in pitch, coming on at 17. 5 degrees nose-up and building to max force at 20 degrees.