Monday, January 26, 2009

Slow Start

My most recent work rotation took me to Montréal, Québec, just in time for the first deep cold snap of the winter. The airplane was parked outside, with electric heaters in the engines and cabin and extension cords snaking across the ramp and through the snowbanks to the electrical outlets. My handover briefing from the pilot I relived included instructions to use only the outlets along the back fence--the ones to the side would blow fuses--and that I should come out and check the cords on non-flying days, as the FBO had more than once managed to unplug them. We were staying not at the city's major airport, the one named after a former Prime Minister, and not at the secondary airport, which once competed for passenger traffic but now has subsided into its role as a cargo hub, but at a smaller airport across the river. Canada doesn't have airports specializing in private jets the way the US does, so most of the airplanes on the ramp were flying school airplanes, giving us 'big airplane' status.

The first morning that I came out to fly was dark and cold and clear. Not that dark, because although midwinter dawn was hours off, we were in the environs of the second largest metropolitan area in the country, and there was a thin layer of snow over higher elevations, reflecting the city lights further than in the summer. As I left the hotel for the airport, the temperature on the most recent METAR was -20C. The cords were all still plugged in and the airplane warm inside. I put my gear in the warm cabin, complete my cockpit checks and then go back outside. I should have brought warmer gloves.

The airplane appeared to be in good condition, with no ice. One advantage of those temperatures is that the air is too dry to hold much water vapour, thus none deposits on the airframe. The tires were firm enough and not frozen to the ground. When I put my hand inside the engine cowling it feels warmer than outside. It would feel warmer anyway, because it's out of the wind, and it doesn't feel that warm, because there's only so much the heater can do against cold and wind, but it's the only way I have to measure that the block heaters have been working. I leave the engine tents wrapped around the cowlings until we're completely ready to go, then pull and stow them and hop aboard. First priority is to start the engines, then with the brakes set I can set up my cockpit the way I like it and fuss about with flight following and the like while the engines warm up.

I start with the right engine. Cowls are open. I set the engine controls, check that the propeller is clear, and press the starter. I wrote "key the starter" but that could confuse you, as there is no key, just a spring-loaded rocker switch. When I hold it down, it energizes a solenoid that closes the circuit connecting the aircraft battery to the right starter motor. I can hear the clunk of the solenoid engaging from the cockpit. The starter motor turns a little toothed Bendix cog, which engages with a flywheel and turns over the engine. I see the propeller go around once slowly, protesting the bitter cold, and the engine does not catch. Everything conspires against my starting an engine in the cold. The metal parts have contracted ever so slightly, so don't move against each other as well as they should. The oil that should facilitate that movement is a viscous sludge in the bottom of the crankcase. The motor that drives the rotation is powered by a battery which itself is less potent and has less endurance in the cold. And in Canada cold equals dark, which means the same battery is powering lights. I only have the legally required ones on now. I'll put the others on after the battery is charging.

I prime some more: the fuel won't evaporate as easily in this temperature, and the air is denser, so I need more liquid fuel to get the same combustible mixture in the cylinders. As the engine turns it should compress that mixture and energize the magnetoes which in turn are supposed to fire the spark plugs, igniting the compressed fuel and allowing the engine to run on its own, without the impetus of the wheezing starter. I key the starter again. Half a rotation and it stops. Rats.

When all else fails, start the other engine. A running engine drives an alternator to generate electricity and charge the battery. Both my starters share the same battery, so if I can get one engine going I can bootstrap the other. The left engine starts. I bite my lip and mentally whisper useless apologies to it as it clunks and misfires for several seconds, trying to find its rhythm. I wait for the oil pressure to come up, and slowly it does. The battery indicator shows charging. I wait a moment or three and double check all the switches for the right engine, then try it again. No joy. Sigh.

I run the left engine until the oil and cylinder head temperatures are in the green and the battery charge rate is zero. That way I'll have at least one engine I know I can start, then I shut everything down and wrap the left engine in the engine tent. I put the engine tent back on the misbehaving right engine too, for all the good it is going to do. There's no heat left in it. I can't find anything wrong visually. The propeller does turn through manually with resistance, but not so much resistance that it couldn't be explained by heavy pistons moving in cold sludgy cylinders. Or maybe not. I go into the FBO for help.

Montréal is a French-speaking city, but the aviation language is English and everyone at the FBO speaks it well or at least passably. I ask them for a ground power unit, which they can provide, and they also offer a Herman-Nelson machine, basically a giant blow dryer to heat up the engine. I drink tea inside while they run the forced air heater, then come out and pull the tents again to try a new start, With the engine warm and the battery bypassed to run the starter off a generator, the engine should start now.

With the starter engaged the propeller turns as slowly as before, and only one revolution. I happen to know that one ramp worker here is an apprentice aircraft mechanic, and he is working today. We communicate by handsignals and I shut everything down so he can turn the propeller and inspect. A few more tries, but no start. There's something wrong beside the cold.

There's a maintenance organization on the field that we have used before. I call and they have time to look at it, but not a lot of time. As luck would have it, there's another company airplane sitting idle here, with a bigger problem, so we have them pull the starter out of that one and put it in this one. That takes a few hours, everything does, so there's lunch and more waiting, and paperwork but we finally get out for a flight, one which takes me to the very last minute of my duty day, including an extra hour that my company op spec allows, provided I get extra rest the next day.

9 comments:

Dispatcher said...

Cool story, literally! I don't envy you at all fumbling around in -20. I've had similar problems with ground equipment but rarely in anything cooler than -5, with a bit of wind. Murphy's Law ensures that on these cold days things go wrong more often.

Ovesse said...

brrrrrr..... where are me MITTS! TOUQUE! HOT RUM!!!

Great writing - thanks.

Paul said...

I don't know how you folks carry on at -20C. I've said that before. The cold eats starters, batteries, and engines.

Yesterday, it was -7C, but with a -14C wind chill, in upstate NY when I needed a preheat. I have a portable combustion pre-heater that I use, but yesterday I was counting on the FBO for a pre-heat.

They have one of the trailer-mounted Herman-Nelson heaters you talked about. Scary beast it is. Makes some terrible noises when it starts up.

That's if it starts. Theirs is powered by a Diesel engine, go figure. Anybody who's tried to start a cold-soaked Diesel knows how hard it is. Anyhow, after 15 minutes of cranking and spraying starting fluid into the air intake, they got it started. I think the comment was that it ran fine a couple of weeks ago... Mostly they service jets. I'll bet the GPU starts ok. *sigh*

--paul

Mark said...

Thanks for the excellent description of why engines don't like the cold. I have often wondered why aviation engines don't use synthetic fuel that does not loose any viscosity when the temperature drop.

Mark

Aviatrix said...

Mark, I'm sure you meant synthetic oil. I don't know, and perhaps some newer engines can take advantage of the greater temperature range of synthetic oils. I've never had an aviation mehanic use or recommend a synthetic grade so there must be some technical aspect of the older engines that doesn't accommodate them.

dpierce said...

A Valvoline rep once told me that synthetic oil interacts poorly with leaded gasoline, and will cause the lead to pool, clump, and form deposits. (Take that for what it's worth.)

nec Timide said...

I use (and have for several years) AeroShell 15W50 which is a synthetic blend multi-weight oil, unless we are breaking in parts (cylinders and rings) when we use AeroShell 100 which is single weight (SAE 50) and not synthetic. The multi-weight oil does ease winter starts a bit but a recommended oil for automobile engines for a Canadian winter would be 5W30. So, even though cold 15W50 would flow better than straight SAE 50 oil, it won't be anything like as easy to pump around as the oil in a car at the same temperature. Conventional wisdom is that synthetic oil is too slippery to give a good break in. I don't know about that, but when the parts supplier and mechanic (both of whom I'm paying many dollars to) agree, I figure I should take their advice.

The nnW is the winter, or cold weather SAE rating of the oil and (from what I've read) indicates the viscosity of the oil at 0F. If you are always going to keep your engine and oil warm, then the advantage of multi-weight oil goes away.

BTW I use AeroShell only cause there is a bulk dealer near me that will sell me oil by the case at a significant saving.

A Squared said...

Maybe Canada's different, but there's a great many piston engines run on Multi-viscosity oil in the US. When I was flying hte DC-6 we used A multi-vis oil, Phillips IIRC

nec Timide said...

@A Squared: I guess I should have said I'm in Canada, so there is at least one :)

Most of my neighbors on the field also seem to use multi-viscosity oil. Phillips being a popular brand as well.

But there is nearly a $2CAD/qt premium on the multi-vis. So, I can see if you have many planes, with two engines, flying a lot and doing oil changes, and you're paying pilots who can babysit the plane and keep it warm, it can add up pretty quickly.