fobjob said:
Didn't the old timers turn their mags off, then on again to blow out the ice with a backfire??
seaplanepilot said:
fobjob
Back when I was learning to fly, the prewar Military Pilots Training Handbook said exactly that. As a last resort leaning the mixture may cause a backfore that may blow the ice out of the carburetor. Never did figure that one out.
I suppose you could try flipping your mags on and off, if you needed something to keep you entertained. Wouldn't do much for carb ice though as it doesn't produce a backfire at all. The bang you get when you turn your mags on and off isn't a backfire (although it's often erroneously called that) it's properly called an
afterfire, it's an explosion that happens
after or downstream of the combustion chamber. Makes a big bang, and it might even blow the stacks off your engine, but it won't do a thing to your intake system, ice or not. A true
backfire is air/fuel mixture igniting in your in your
induction system, ie: fire shoots out your intake. It results from letting the mixture lean out too much on starting (or sticking intake valves). It's the primary cause of DC-6 FEs buying beer for the captain and FO. And yes, it will blow a
big ball of fire out the intake scoop under the right conditions.
I think that this "cure carb ice by making it backfire" probably can be traced back to a chapter in Ernest Gann's "Fate is the Hunter" in which he was in severe icing in a DC-2 and losing power because the air scoops were icing shut. His captain blew the ice off the scoops by leaning the mixture until the engines backfired. Did it actually happen? I don't know, maybe. But maybe Gann took some poetic license and turned some crew-room speculation into a good story.
Will it cure Carb ice to lean an engine out and make it backfire ? I don't know, perhaps, but in Gann's story, apocryphal or not, it was
induction icing that was the problem, not carb icing. I think you'd have a pretty tough time producing a backfire of any strength in a GA engine. I've leaned GA engines out a little too far probably dozens of times and they've just quitetly lost power. You get a much better backfire in a big radial bacause there a much larger volume of fuel/air mixture contained in the Carb throat, blower tnat intake tubes. For sure, turning your mags on and off won't do anything but perhaps damage your exhaust system.