Dynon EFIS 10A

Glass Cockpits, EFIS Description

Flight and engine instruments used to be the old school style type round gauges we all (well most of us) learned to fly with. These are familiar to everyone. The latest trend in general aviation is electronic displays in cockpits and aircraft are then usually called 'New Generation' by their manufacturers.

You will see addon EFIS like the Dynon Avionics series to integrated systems with 8", 10" and even 15" color LCD screens (daylight visibile!) from Garmin, where even the radio's (COM and NAV), transponders and engine instruments are fully integrated.

These can be coupled to an autopilot (integrated too) and programmed to fly the entire route and instrument approach. You still would have to do the landing yourself.

Installing an EFIS system saves weight and cleans up your panel. It also means that you could do without a vacuum system and remove the hoses, pump and hardware (more weight savings). All of this could mean a single point of failure in the cockpit.

But even with the sixpack we normally used to have, would you go flying if your altimeter did not work?

EFIS Components, I

The EFIS system uses a number of separate components to display all of its possibilities. Some manufacturers sell these sometimes integrated inside the display unit as to reduce the wiring in the aircraft. In case of the magneto meter (flux valve) it might not be a good thing as the engine (large part of metal) can be too close in some aircraft and influence readings.

LCD Screens

The screens are made of Liquid Crystal Displays, LCD. A LCD monitor has number of layers: a backlight (which can be LEDs) on top of that a sheet of polarized glass, a layer of colored pixels as a mask, a another layer of liquid crystal solution which reacts to a grid of X, Y coordinates and a second polarized sheet of glass to close the unit.

The crystals are manipulated by varying electrical charges so that they open and close allowing light of different colors to pass through and creating an image on the screen.

LCD technology is constantly evolving and so different techniques for producing color have been developed. Two of the most common are: Active-matrix or TFT (thin film transistor) technology produces color and images as sharp as any Cathode Ray Tube (CRT, as in the old TV screens) and is superior to the previous passive-matrix LCD technologies.

NITS

LCD brightness is indicated in NITS, candela per square meter (cd/m²) and officially called: luminance. For comparison and to have an idea what it is: a common candle emits about 1 cd and your ordinary 100 W bulb some 120 candela.

AHRS

Attitude and Heading Reference System, can be build with mechanical gyro's, MEMS rate gyro's or Ring Laser Gyro's.

MEMS Gyro Schematic Model

Micro Electro Mechanical System or MEMS vibrating gyro's can be compared to a tuning fork where its resonating frequency changes when a force (or acceleration) is applied. This change in frequency can then be used so that the MEMS rate gyro can sense the rate of turn and in combination with an accelerometer the system senses in which of the three axis (x,y,z or pitch, roll and yaw) the aircraft is moving.

MEMS gyro's are very accurate over short time periods but need external reference for the longer term. GPS heading data is frequently used for this.

Ring Laser Gyro's (RLG) are expensive and their accuracy is very high, with an error of lower than 0.01°/hour, and a MTBF (mean time between failure) of more than 60,000 hours. These are used in larger aircraft and EFIS systems and are a bit too expensive for experimental aircraft.

EICAS Engine Information and Crew Alerting System, EICAS. Most EFIS systems are capable of showing and monitoring engine parameters as RPM, CHT, EGT, Fuel Flow and Pressures and alerting the crew in case that any one goes out of the preset range.

Written by EAI.