Say Dean...    One of our flying buddies wears a pacemaker.  So if he launches an E stunt machine at nominal 20 volts, 50 amp, 13khz pulse rate, and around 6-700 watts, is there any danger of EM interference causing the pacemaker to miss?

     A little searching turns up a 10 gauss limit on magnetic fields, with 1-4 kv/m for electric fields.  See http://www.wiganleigh.nhs.uk/Internet/Specialties/Cardiology/pacemaker_faq.asp for some practical tips for pacemaker wearers.  It turns out that nearly all household appliances are OK.  Industrial hygiene guys limit access to electric machinery emitting more than 5 gauss.  Chainsaws and trimmers held close to the chest are prohibited.  Snow blowers and lawn mowers are Ok as long as the user doesn't get near the ignition system of a running engine.  All current pacemakers are now shielded from new.

     An RC groups search turns up nothing.   My SWA guess is that the fields from our systems are too small to be of much risk.  Are we safe to allow pacemaker patients to use/launch electric airplanes?

     

Ya, I have a freind that has a pacemaker so I asked him how long the battery lasted on that unit and he said ten to twelve years so I told him if they would put solar cells on that bald spot of his the battery might last longer. He really got5 charged up on that one!

Hey Dean - It looks like proximity is the risk trigger.  As long as the helper stays aft of the wing and SC, it's probably safe enough.  HOWEVER, I did email Castle about it and got no response at all.  If you talk things over with the powers that be, it might be a good idea to apply a gentle nudge in the direction of safety.  Best, Tom

The magnetic field strength is strongest inside the motor.  The magnetic path is almost completely closed so that little, if any, magnetic force (lines) exist away from a running motor.  Wiring carrying heavy currents also have a magnetic field encircling the wire.  But a wire represents only one turn of an electromagnet, so the inductive field is again slight.

Magnetic field strength is attenuated by the square of distance.  Even if strong adjacent to the source, the field strength becomes insignificant more than a few inches away.

F.C.

Found them.