My Switches panel works fine however I am looking for instruction in exactly how to use the Off/Start rotary knob? So far basically I just ignore the positions and leave it set on “Both/All” because I cannot find any tutorials that show when and how I would use the other positions? i.e. If I select “R” (right magneto) what do I do then? Do I select R and then turn to Start and once right engine is started do I then select L and again select Start until left engine starts? What do I do then, leave the knob on start or turn it back to Both/All ? Seems that if I do the former, when I select “R” and then click past “L” would that then also activate “L”?? Hope I have been clear (probably clear as mud ) Cheers Dan
The start switch controls the aircrafts magnetos (piston driven planes).
The engine has 2 magnetos that act as electrical generators connected to the spark plugs.
After starting the engine you leave it on both.
Part of your pre take off checklists is to test the magnetos. Bring up the RPM and switch from both to R then watch the RPMs drop. Switch back to both and let it come up. Then switch to Left and watch to drop.
For each aircraft type there is a value it should not drop below and a value between the two it should stay between.
This information can be found in the checklists and POH.
I hope that helps.
And to add a little more to skypilotYTS’s good description, the reason is that magnetos are a mechanical system.
As such, they are much more prone to failure than todays electronics.
The reason for the switch is failure related.
Should one fail in flight (actually a “fairly” common issue), you switch to the good one.
Hence the test (mentioned above) before takeoff, to ensure both magnetos for an engine are working properly.
The L and R do not signify left and right engines but left and right magnetos. In a twin engine aircraft, the start switch will usually start both engines simultaneously which, of course, is not generally done irl.
Here’s what happens when a high time PIC decides to skip mag checks. NTSB Report B-17G Crash 'Nine-O-Nine' Part II -18 Dec 2020 - YouTube
How the dial will function depends on both the aircraft you are flying and the drivers in use
For the Cessna 172, it should work as described above. For other aircraft it will depend, but more often or not, when using the default Logitech driver, it will do nothing in a turboprop or jet.
This is where a third party driver such as SPAD.Next comes into its own as it will allow you to configure what the dial does. For example on the TBM930 I have it set up to operate ignition and starter switches. On the 747, I use it to change the mode of the Navigation Display.
Thanks for all the valuable tips. Think I have it now, Stay safe, Cheers Dan