Comparative methods in Ely, NV
We are making a bit of a study of preheat methods in our shared hangar this year. One RV6 and one RV7A, O-360 and IO-360 respectively. and a Rotax 912-powered LSA too.
For all methods, we put a folded blanket on top of the engine cowl and plug the two forward cowl openings (with bird plugs or folded towels). Temperatures are reported in Farenheit degrees from a thermometer with a remote probe placed on top of cylinder one.
Bulb method: Using a 75 watt bulb in a drop light guard routed in the exhaust exit and placed under the engine oil pan (with the guard facing up in the unlikely instance of a fuel drip onto the bulb): In 12 hours overnight with ambient temps in hangar of 0 to 5 degrees, the engine shows a temperature of 39 to 44 degrees, and oil temps about 50. Allowing 12 additional hours, daytime, with ambient air temps (in our meatlocker of a hangar -- always 15 to 20 degrees colder than outside air) of about 20 F, the above temps rise about 10 degrees, to show 50 or so on the cylinder probe and 60 on the oil. Conclusion: This method works, but takes overnight. Stable temperature is reached within 12 hours; ambient temperatures seem to control after that. Might need to switch to a 100 watt bulb as local temperatures drop into winter.
Heater method: We also evaluated a 1000/1500 watt "bathroom heater" and dryer duct, like that shown in the November issue of Sport Aviation,
http://www.sportaviationonline.org/sportaviation/201111#pg1. The specific heater we used was smaller and cheaper ($18) to buy than the one in the article. A $5 galvanized 5 inch to 4 inch adaptor was split into 4 "legs," which were then flattened in a vice and trimmed to fit the front of the heater, and attached with 2 PK screws to the face of the unit. The heater sits on the hangar floor on airplane centerline, about 3 feet behind the exhaust exit in the cowl. Ducting provided with an all metal FLEXIBLE clothes dryer duct, made oval at the delivery end. (Flexible ducting allows us to use the heater on different planes.) This obtained somewhat better results: In 90 minutes, from an ambient hangar temperature of 20 to 25 degrees and using the low (1500 watt setting), the oil temps are up to 45 or 50, so, call it a 25 degree rise. 25 degrees in 90 minutes is not bad, gets the temps into a good range, and can be done on the morning of the flight instead of overnight. In the other extreme, in an early test, I ran that same heater at 1500 watts for 12 hours overnight when hangar temps were 25 overnight (earlier in the cold season). In the morning, the oil temps were 91 degrees and cylinder probe was 102, roughly a 65 to 70 degree rise. Much more than needed, we thought, since the goal is to get oil temperature and CHT at least above freezing and, ideally, to 40 or so. So, based on these results, our practice is to use 1000 watt setting for the overnight preheat and the 1500 watt setting for the quicker, same day preheating.
Of possible interest to RV-12 flyers, a SkyRanger owner in our hangar, uses the blown air heater on his Rotax 912 with good results too. He has not tried overnight heating yet. Instead, he heavily bundles up his engine cowl on the top and sides, with the heater duct into one large front opening, gets a 30 to 35 degree rise in CHT in only 90 minutes. The oil (separate tank, not a bottom sump, of course) is warmed a similar amount, too.
One other consideration that works for us. The bulb method is super simple, and can be set up and left off at the end of a flight. The pilot, who lives 60 miles away, can call for a "plug in" the day before he intends to fly. Not inconvenient for since the hangar is visited by one of us every day and, with the blankets and bulb fixture in place, its a simple dela to plug in the cord. Setting up the heater and duct would be a bit more of a job.
It's gona be my first winter flying the 6 and I was wondering if you guys have any suggestions as far as preping the aircraft for winter flying?
