When designing a GA aircraft, I have sized a powerplant (in kW) needed to run the plane on its mission. However, this does not consider the power needed for avionics, de-icing, etc. How do I approach finding the numbers for these systems? Are they significant?

For de-icing, this study from Hamburg University shows some example power consumptions from 23 KW/m^2 to 44 KW/m^2. For sizing an engine, should I just assume the thrust will have to be decreased in order to accommodate de-icing?

  • $\begingroup$ De-Ice is a pretty big topic and with the additions you have made it may warrant its own question all together (One id be happy to work on an answer for). You may want to give some more details on the airframe specs as De-Ice systems vary based on many factors. $\endgroup$
    – Dave
    Commented Nov 16, 2017 at 18:58

1 Answer 1


This depends heavily on how the plane is set up especially these days with the prevalence of glass in the cockpit even in GA planes. For a point of reference most small GA planes like the Piper Cherokee run 60-100 amp alternators which usually have a bit of headroom in them but power everything and charge the battery just fine. If you want to fly in most airspace you are going to need to power at least a transponder and a radio (more than likely two radios).

The Garmin GTX330 is a 250 Watt transponder and is fairly common in the Archers I fly.

Your run of the mill Garmin GTR 225 radio comes in 10 and 16 watt versions.

To get the total requirement just add up all of your components draw. Most manufacturers list power requirements (or voltage and current draw requirements) for any given piece of equipment and you will have your required power.

As for De-Ice requirements this depends on the type of system you implement. A weeping wing will only require power to drive the fluid pump and the windshield heater where as a boot style system will require enough power to drive the compressor that inflates the boots. Although its becoming increasingly more common to see FIKI on GA planes the majority of the small aircraft fleet still lacks FIKI capability.

  • 3
    $\begingroup$ The GTX330 has a 250 W RF output power, but it transmits a very small fraction of the time. Consequently, its power draw is 27 watts. Conversely, voice radios are used with long transmit periods, and are never 100% efficient, so their design power draw may be several times RF output. $\endgroup$
    – user71659
    Commented Nov 16, 2017 at 19:21
  • 1
    $\begingroup$ To follow on from @user71659 - the GTR225 (10W RF) is specified for 8.3W (0.59A @ 14V) of supply power draw (typical) with a maximum operating draw of 60W (4.2A @ 14V), so in terms of the electrical system design you have to build to the maximum expected draw. There's no getting around the need to crack open the manual for every single instrument or system being installed. $\endgroup$
    – J...
    Commented Nov 16, 2017 at 19:44

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