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Touring Motor Gliders Association (TMGA)

Extended idling while soaring with the engine running

Eric Greenwell

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There are times when it's convenient or safer to soar "engine on" (idling), than to turn it off. Some Rotax 912 pilots have suggested that might be hard on the engine and/or the gear box, others (including a Rotax authorized mechanic) say "no problem" with idling in flight (but everyone agrees - don't do it for hours on the ground!).

For example, my last flight was great, with four hours soaring along a 55 NM convection/convergence line, with the engine idling the entire time. Idle speed was typically 2100-2200, with the oil temperature kept in the 150-180 F range using the cowl flap (this is in a Phoenix). It ran smoothly the entire time, including a few minutes of 5000 rpm cruise at the end of the flight to test the fuel flow meter.

Does anyone know the answer? Has anyone tried to contact Rotax?

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  • 11 months later...

Many pilots have flown with the Rotax at idle for extended periods without any reported problems.  Rotax wants the engine temperature to be at 190F to properly burn off water and maintain clean spark plugs and reduce lead fouling.  If you run at idle for extended periods, run the engine rpm up to 3000rpm every few minutes to help keep the plugs from fouling.

I prefer to shut down the engine, but I am probably more comfortable and confident with an in-air restart than others may be.  I have only had one problem early on in the Lambada when I assumed the engine was cold at high altitude and used choke initially and flooded the engine.  It took 800 lost feet of altitude at full throttle and no choke, to get it started.  For an in-air restart, use no throttle, and no choke.  If it does not fire immediately, keep cranking and slowly pull out the choke.  When you hit the optimum choke for the temperature and altitude the engine will start right up.  You have to pin the stick with your knees while you do this.

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