Avionics Planning: Start Early in the Build

One of the most common regrets among first-time builders is not planning the avionics suite early enough. Wiring harnesses, display mounting provisions, and antenna placements need to be considered before the fuselage skins go on — not after. Before you buy a single avionics box, think through your intended use: local VFR flying, cross-country IFR-adjacent operations, or something in between.

Since the Rans S-21 operates as an experimental aircraft, you have significant freedom in avionics selection — you're not constrained to TSO'd equipment the way certified aircraft are. This opens up a broad and often more affordable range of options.

Primary Flight Display (PFD) / EFIS Options

The glass cockpit has become the default choice for new S-21 builds. The most popular options in the experimental LSA space include:

Garmin G3X Touch

The G3X Touch is arguably the most popular EFIS system in the experimental homebuilt market, and for good reason. It offers an integrated PFD/MFD, GPS navigation, engine monitoring, and optional autopilot integration in a polished, intuitive interface. The ecosystem integration with other Garmin products is seamless. It's not the cheapest option, but the support network and feature set are hard to match.

Dynon SkyView HDX

Dynon's SkyView HDX is the perennial competitor to the G3X. It's a mature, capable system with strong community support, a well-established track record in experimental aircraft, and competitive pricing. Many builders choose Dynon specifically for its reputation for responsive customer support and regular firmware updates. The interface is clean and readable in bright sunlight conditions.

MGL Avionics

For builders working with a tighter budget, MGL Avionics offers capable EFIS solutions at a lower price point. The feature set is comprehensive for VFR operations, and the South African manufacturer has a solid following in the experimental community. The interface is less polished than Garmin or Dynon, but the core functionality is reliable.

Comparison at a Glance

System Best For Relative Cost Autopilot Integration
Garmin G3X Touch Full-featured, polished builds Higher Excellent (GFC 500)
Dynon SkyView HDX Balance of features and value Moderate Excellent (Dynon AP)
MGL Avionics Budget-conscious VFR builds Lower Available (limited)

Engine Monitoring

For Rotax 912-powered S-21s, engine monitoring is important for both safety and engine longevity. Many EFIS systems include integrated EMS (Engine Monitoring Systems). If buying a standalone unit, the Rotax MFD (Multi-Function Display) is an OEM option, while third-party solutions from companies like Electronics International offer comprehensive monitoring at competitive prices.

Key parameters to monitor on the Rotax 912 series: CHT (cylinder head temps), EGT (exhaust gas temps), oil temperature, oil pressure, fuel flow, and RPM.

Radios and Transponders

For communication and transponder needs:

  • Garmin GTR 20/200 — compact, popular VHF comm options for experimental aircraft
  • Icom A210 — a reliable, affordable panel-mount comm radio with a good reputation
  • uAvionix echoUAT / SkyBeacon — ADS-B Out solutions that satisfy the ADS-B mandate; the echoUAT also provides ADS-B In
  • Garmin GTX 35R — a remote-mount Mode S transponder with ADS-B Out

Final Advice: Build a System, Not a Collection of Boxes

The biggest mistake in avionics selection is choosing individual components without considering how they integrate. Pick a primary ecosystem — Garmin or Dynon — and build around it. Cross-brand integration is possible but adds complexity. A coherent, integrated panel is easier to fly, easier to maintain, and generally easier to sell when the time comes.