As mentioned in the last post, Thursday’s test flight after working on the carburetors was kept short … but it also served the purpose of warming up the engine. Only two warm days remain before a forecasted instant 50 degree drop in temperature grips northeast Ohio, so decided after Thursday afternoon’s test flight was completed, the time had come to begin installing the Rieff preheating system for the Rotax 912 engine while the engine was warm and air temperatures at the hangar were still in a range that the epoxy could be kept warm enough to cure. The main reason about being concerned about the temperature stems from the slow cure epoxy used to install a couple of components in the Rieff preheating system onto the Rotax engine. The epoxy used requires near 70 degree temperatures to cure correctly and even at that, the cure time is 24 to 48 hours … that will be hard to accomplish in an unheated hangar when nighttime lows are 20 degrees and highs for the day around the mid 30’s. So I needed to sacrifice two wonderful 70 degree flying days to let the epoxy cure.
Rieff offers three preheating system kits specifically designed for the Rotax 912 engine. They are available in different wattages … 150, 250 and 350 watts. Because the winters in northeast Ohio are not as severe as some locations in the US, the DOG Aviation procurement department chose the 150 watt version based on the info from Rieff about the heating capabilities of the 150 watt system. The Rieff WEB site states “PERFORMANCE (standard 150 watt system) - RV-12 aircraft in a hangar with two tennis balls plugging the air inlets, towel stuffed in oil cooler inlet, and blanket over the cowl Ambient temp 20-23F …. After 12 hours of heating time oil temp was 96F (temp rise of about 75F above ambient) Temp measured by Dynon engine monitor”. Based on that information, I feel the 150 watt system should work nicely here in northeastern Ohio. If it is much colder than 20 degrees, I think I would likely prefer staying at the house reading a good book.
The 150 watt Reiff preheating system for the Rotax 912 engine chosen for the DOG Aviation RV-12 consists of two heating elements, a thermostat, a pack of epoxy, wire ties and wires with premade connectors. One of the heating elements is for the oil tank and the other heating element is for the engine case. The heating element for the oil tank is a long 50 watt “HotBand” stainless band clamp which has an orange colored heating element affixed onto the band. The second heating element is a 100 watt "HotStrip" and attaches onto the bottom of the engine casing with the epoxy. The thermostat is attached onto the oil tank and it too requires being affixed using epoxy.
Instillation is fairly straight forward, the “HotBand” clamp is installed around the oil tank and snugged down, but not over tightened … over tightening will damage the heating element. The areas on the engine and oil tank that will have epoxy applied are to be scuffed with a ScotchBrite pad and cleaned with solvent to remove oils. The smooth side of the “HotStrip” also receives a scuffing with a ScotchBrite pad and cleaning with solvent.
Next, a socket is used to roll over the plastic epoxy package to mix the two part epoxy components together. The epoxy is then slathered onto the bottom of the 100 watt “HotStrip” and it is affixed onto the bottom of the engine casing on the right side adjacent to the #1 cylinder. I used a piece of wood wedged between the oil cooler and the “HotStrip” to keep the strip seated firmly onto the engine casing. I later discovered this area presented more of a challenge than I thought it would in that, the engine casing is at an angle and much to my surprise the “HotStrip” slid away from where I had originally placed it. It is OK but now it looks much messier because there are smears of epoxy all over the bottom of the engine. If I had it to do over, I think I would have used a piece of duct tape to prevent movement in addition to the wood or a foam block to keep upward pressure on the “HotStrip” while the epoxy cures.
While the epoxy cures on the engine, the remaining epoxy in the package is to be placed in a freezer overnight because it will be used again the next day. The following day, the remaining epoxy is used to overlap the edges of the “HotStrip” this will prevent it from falling away from the surface of the engine should it loosen up from the epoxy on the bottom of it.
To offset the cooler night time temperatures, a piece of plastic covered with a moving blanket was placed over the engine. Two halogen shop lights were used to create heat … one placed under the oil tank area and the other placed under the engine near where the epoxy was applied to the “HotStrip”. The halogen lamps generate quite a bit of heat so, until the temperatures make the big plummet forecasted, the two lamps should allow the epoxy to stay warm enough during the evening hours so it cures nicely. Only have 36 hours for this to pan out after that ... winter will arrive in northeastern Ohio in one big blast.
The day after the above photo was taken, a quick trip was made to the hangar to check on the progress … the epoxy appeared to be curing nicely so the remaining epoxy was applied to the edges of the "HotStrip" per the instructions and left to cure. Have not completed the wiring because decided to stay hunkered down at the house. We were in the 70’s on Friday and on Saturday plummeted to lows in the 20’s with daytime highs in the 30’s with snow. After 35 years out in California the first winter cold and snow usually keeps me in the house until I get acclimated to the cold ... (which truthfully never happens). I still need to finish up on the Rieff preheating system ... the wiring connectors still need to be installed and dressed out with wire ties. Sounds like a good project when we get back into the 40’s.
