N941WR
Legacy Member
Over the years I have been asked how to hand prop a P-mag equipped engine with a dead battery.
It is a rather simple thing to connect a 9 volt battery to the P-mags and hand prop it. However, hand propping an airplane has some serious safety issues associated with it and if you have not been trained on how to hand prop an airplane, DO NOT try it until you receive the proper training.
Engines with wood or composite props are more difficult to hand prop due to the light weight of the propeller.
Tricycle geared airplanes and airplanes with high compression pistons both present unique challenges which I will not go into here.
Below is a simple diagram that shows how someone may opt to permanently wire a 9 volt battery connector to there ignition system. When NOT in use, remove the 9 volt battery and cover the terminals to keep them from shorting out.
I recommend you install the 9 volt battery terminals in the cockpit, in a place where it can be reached while sitting in the pilot's seat.
A simple option is to use a battery holder such as these:
Wiring diagram:
To hand prop your plane with this set up, put a competent pilot in the "pilot's seat", turn EVERYTHING off, prime the engine, set the throttle full aft for minimum power setting, pull the prop through a couple of times until it stops at the top of a compression stroke. Set the brakes, isolate the P-mag to be powered by the 9 volt battery by pulling its breaker, un-ground the P-mag, leave the master off, plug in the battery, carefully hand prop the plane. Remember, you have bypassed the mag switch, if the engine doesn't start, remove the battery before repositioning the prop or it WILL fire.
Once the airplane is running, return to the pilot's seat, increase RPM's to around 1,000 (something above the P-mag's self powering cutoff point), remove the 9 volt battery, turn on the other mag, turn on the master and let the airplane charge the battery.
This method is to be used in an emergency and should not be a normal operating procedure. It is much more desirable and safer to charge the aircraft battery than attempting to hand prop this or any airplane.
Thoughts, comments, etc.?
It is a rather simple thing to connect a 9 volt battery to the P-mags and hand prop it. However, hand propping an airplane has some serious safety issues associated with it and if you have not been trained on how to hand prop an airplane, DO NOT try it until you receive the proper training.
Engines with wood or composite props are more difficult to hand prop due to the light weight of the propeller.
Tricycle geared airplanes and airplanes with high compression pistons both present unique challenges which I will not go into here.
Below is a simple diagram that shows how someone may opt to permanently wire a 9 volt battery connector to there ignition system. When NOT in use, remove the 9 volt battery and cover the terminals to keep them from shorting out.
I recommend you install the 9 volt battery terminals in the cockpit, in a place where it can be reached while sitting in the pilot's seat.
A simple option is to use a battery holder such as these:
Wiring diagram:
To hand prop your plane with this set up, put a competent pilot in the "pilot's seat", turn EVERYTHING off, prime the engine, set the throttle full aft for minimum power setting, pull the prop through a couple of times until it stops at the top of a compression stroke. Set the brakes, isolate the P-mag to be powered by the 9 volt battery by pulling its breaker, un-ground the P-mag, leave the master off, plug in the battery, carefully hand prop the plane. Remember, you have bypassed the mag switch, if the engine doesn't start, remove the battery before repositioning the prop or it WILL fire.
Once the airplane is running, return to the pilot's seat, increase RPM's to around 1,000 (something above the P-mag's self powering cutoff point), remove the 9 volt battery, turn on the other mag, turn on the master and let the airplane charge the battery.
This method is to be used in an emergency and should not be a normal operating procedure. It is much more desirable and safer to charge the aircraft battery than attempting to hand prop this or any airplane.
Thoughts, comments, etc.?
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