Friday, May 30, 2008

Cold Morning Starts

We all know someone, particularly Jab drivers, who complain about their cold morning start problems. Well after coming across a book by F. Potts " A Guide to Bush Flying" he has a chapter about cold starts in Alaska.

We really have it so, so easy. In fact we have it so easy, we don't even have a problem.

Extracts from "A Guide to Bush Flying"

Section I: Equipment and Environment

Part IV, Chapter 12: Preheating Equipment and Methods

Engine Compartment

“Aviation fuel is distilled with a much lower vapor pressure than automobile fuel so that during the climb to altitude engine failure will not be experienced due to vapor lock. What this means from an operational point of view is that once temperatures get down to -9 degrees C, the engine will require preheating so the fuel can properly vaporize for ignition.” (Aircraft using mogas will experience vapor lock at a much higher temperature) Take note here guys. JM

Compounding the problem, at about -21 degrees C most oils (the exceptions being synthetics like the discontinued Mobil AV-1) become too thick to lubricate the cylinders and bearings properly, and if you could manage to start your engine at this temperature (by heavy priming, or a bit of mild preheating), the wear that would take place until the oil began to flow would probably be equivalent to more than 50 hours of normal operation.

(Mike Busch, the Cessna Pilots Association's engine specialist, claims that one cold start at the lower temperature extremes can cause as much wear as 500 hours of normal cruise operation)

There are no convenient ways around these problems, and, like the FAA and taxes, they are a fact of aviation life

The best bush preheating rig is one that uses a simple old-fashioned gasoline blowtorch that can be operated on avgas taken directly from the airplane's fuel sumps

Blowtorch and stovepipe method. The equipment list for this system consists of a small fire extinguisher, one or two gasoline blowtorches, three lengths of 3" stovepipe, an insulated engine cover, and a two- or five-gallon metal gasoline can. Here is how the system works:

1. After the last flight of the day, the oil is drained from the engine into the gasoline can. Quick-drains should be installed on all airplanes in the fleet to facilitate this daily chore.

2. The can of oil is taken inside your office or home, where it is placed near the stove so it can be kept warm until needed again.

3. When the airplane is to be called into service, the can of oil, with the lid removed, is placed on top of the stove and heated to about 122 degrees F/50 degrees C.

4. While the oil is warming, take the three lengths of 3" stovepipe and fasten them together. Place one end inside the engine compartment and temporarily rest the other end on the ground. The best place for the pipe to go into the Super Cub's engine compartment is on the right side by the brace to the exhaust stack. With the Cessna 180/185, it is best to drop the right cowl-flap and place the pipe there (see illustrations 28 and 31).

5. Carefully light the blowtorch away from the airplane, and when it is operating properly place the nozzle into the lower end of the stovepipe.

With the Cessna 180/185 and 206 you should use two blowtorches, and these must be placed in the same pipe (see illustration 31). Never use two pipes, one going to the right side cowl-flap and the other going to the left side cowl-flap, because of the danger that one of the blowtorches might go out, while still spraying fuel into the stovepipe. The second torch could then ignite the fuel inside the engine compartment. With both torches in the same stovepipe this danger is averted.

6. Adjust the insulated engine cover over the top and sides of the engine compartment so the right cooling air-inlet, behind the prop, is covered and the left air-inlet is open (see illustration 28). This is done to allow the heated air to pass over the engine and out the far side, taking the cold with it. Remember, heat-circulation is the name of the game. When using combustion heaters, if both air-inlets are blocked, it will take longer for the engine to reach starting temperatures.

7. When the engine is warm enough that the prop moves freely and the carburetor or fuel-injector is able to vaporize fuel correctly (about 45 minutes at -4 degrees F/-20 degrees C; 1+20 at -40 degrees F/-40 degrees C), the blowtorch(es) can be turned off and set aside to cool. At this point the hot oil is poured into the engine, three or four shots of priming are given, and the engine is turned over four to six times by hand. It is now ready to go, and should start on the first turn of the prop.


Cold also affects the battery; at seriously low temperatures it will not have enough power to start the engine. In the bush you must either remove the battery and take it inside for the night so it can be kept warm, or you must handprop the airplane for the first flight of the following day."

And we think we have it bad on cold mornings.