QUESTION: I’m fortunate in that, in addition to giving glider rides, I’m able to fly the tow planes for a couple of glider operations. The tow planes are CallAir A-9s and Pawnees. All are equipped with O-540s. One of the organizations requires that the tow plane be shut down if the wait for the next hook-up is longer than three or four minutes. The thought is there is less wear and tear on the engine restarting it vs. letting it idle for five or so mintues.
Is this practice beneficial or does the extra wear and tear on the starter, solenoid, battery, etc., make it impractical?
Lake Elsinore, Calif.
Boy, it’s been a long time since I’ve been around a CallAir A-9. There is no doubt that those, along with the Pawnee, make great tow planes and many of them are now living a second life in that capacity.
From my perspective regarding the shutdown vs. running between tows, I’d rather keep the engines running. There are always circumstances where this may not be practical, but for my money, I’d let them run.
There are things that you must be aware of if this is done. You must make certain that the engine baffles are in good condition and doing their job of directing the cooling air properly. You may also experience some spark plug fouling if the mixture is on the rich side.
Close inspection of the spark plugs would give you the story here. It’s not unusual in a tow plane environment that plug fouling can be caused by rapid descents, too, and these should be avoided. By keeping the power up on descents, you can minimize possible fouling.
If plug fouling does cause you problems, I’d suggest you consider going to a hotter plug, if you can. A quick check of the latest revision of Lycoming Service Instruction 1042 will give you the information you need here.
My recommendation is to keep the engines running and save the wear and tear on the electrical system, starter, etc., if you have to restart them in a short period of time. Just keep your eye on the CHT temperatures and watch out for the lead fouling.
Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.