Mags at engine start / Checklists

[aerobatic sean]

Some reassurance required - just reviewing my checklists for flying the supercub PA18 - is it worth flying anything else ! - for engine start it is an easy flow from right to left ending with starting the engine on LEFT MAG only - immediately after start I switch MAGS TO BOTH.
After start do a DEADCUT check as well.
I think I learnt this at a US flightschool which had 4 supercubs - I think it to check that an engine will fire with only one set of plugs by starting on left only.
Is this a good procedure ?
and then I can use on all aircraft surely.

Re CHECKLISTS - both the written and memory checklists can be improved oneself - does everyone else find that invariably that flightschool/manufacturers checklists can be improved by just sitting in the aircraft and taking every item in correct order a,thinking the flight through and arranging into a sensible flowlist.
thanks

keep blue side down

[DB6]

Not sure about the Supercub - others will know though - but starting a Firefly on one mag has more to do with the fact that the left mag is equipped with a booster coil which emits a 'shower of sparks' to aid starting. The right mag does not have this device. Maybe the same with the PA18.
Checklists: BUMPFICH, FREDA and HASELL pretty much takes care of it all really.

[QDMQDMQDM]

I start my Super Cub on both mags. I do a left to right cockpit check for vital actions prior to take-off. I don't have a right to left check prior to starting, since apart from the master and primer the action is all on the left.

You need to ask this question at www.supercub.org, Sean. You will find the most extraordinarily knowledgeable SC owners there who will answer your most detailed questions about the SC in a flash.

QDM

[Mike Cross]

The use of one mag for starting is usually because that mag has an impulse coupling in it. This holds back the rotor against a spring until it suddenly flicks free, generating a strong spark. It only operates at low speed and also retards the ignition. This makes sure the cylinder is past top dead centre before the engine fires so it doesn't kick back and slice off your fingers (one reason I never hook my fingers over that nice sharp trailing edge). If you had both switched on you would have a risk of kick back from the non-retarded mag, and if it's electric start you stand a good chance of knackering the starter drive if that happens.
Interesting thought came to me the other day. We all switch each mag drop off in turn and are happy if we see a small (say <125) drop in RPM but how many of us would pick up on the dangers of getting no drop? Chances are it means that the mag didn't switch off and is permanently live. Stop the engine on the mixture, turn of the switch and you've still got a live mag.

[stiknruda]

For engines with an impulse coupling on the left mag (the thing that emits the loud click when you pull the prop over by hand) OR has a "shower of sparks" on the left mag:

Then if the a/c has a combined mags on/key start it will almost certainly ground out the right mag when the key is at the START position. Releasing the pressure on the key returns the key position to BOTH and both mags should now be live.

With the same scenario in para 1. IF the a/c is equipped with independent mag switches and an independent start switch, you should only start with the LEFT mag selected on.

If hand swinging the previous paragraph applies, too.

Hope that this helps,

Stik

[DubTrub]

Although having impulse on the left is the norm, some aircraft have two impulse mags, then it can be swung with switches on both (or even Right, if you feel so inclined).

Sean, I assume your Supercub has the push-button start...It would not surprise me if it had two impulse mags.

[machonepointone]

Mike Cross

Not getting a mag drop when switching one of the mags off could also mean that the magneto was not working in the first place. Either way, your course of action in shutting down is correct. However, (and I do not necessarily advocate this), to see what is actually wrong try switching the other mag off. If the engine keeps running but shows a drop in RPM then the first mag was live. If the engine stops then the first mag was not working. I am not a fan of this suggestion as it leaves fuel in the cylinders. However it does aid in the diagnosis.

M1.1

[Rocket2]

Just started mine on both (push button start switch) :ok: