To Resist or not to Resist

[Hugh Sistrunk]

Looking for Comments:  

What are the thoughts for using or NOT using resistor type Spark Plugs and Plug Wires - Pros - Cons? 

If Resistor wires and/or plugs are not to be used how is the radio interference dealt with?

NightEagle

[Steve]

Looking for Comments:  

What are the thoughts for using or NOT using resistor type Spark Plugs and Plug Wires - Pros - Cons?  

If Resistor wires and/or plugs are not to be used how is the radio interference dealt with?

NightEagle

I used MC solid plug wires on the high energy Leburg EI and an Icom handheld with a rubber ducky provided antenna - it squelched Ok...

What ever wires used I advocate they have the right angle socket at the plug end secure-tied in place on the plug...

The resistor setup is a (NO-GO) on a Magneto based system but you engine photos show a distributor...

If your heads will take a modern plug then the proper heat range should be available in a resistor plug (Note: I saw a  1/2 with trial heat range plugs in it detonate on the ramp and die - better than in the air)...

With an external antenna on your radio I think you will be able to squelch either type of plug wire & plugs...

The best location for a simple aviation right angle stainless antenna is mounted to the center of the angle cross-tube in the bottom of the footwell...

Les Homan has great results from the 1/4 wave antenna (Handheld has 80 mile range) mounted mid-way back on the Fus truss... The plans for the antenna are in the Group Files and there is a relevant posting in the Forum... Les broadcast loud & clear in the pattern at Rio Vista... He is running a Magneto based ignition...

[Tom H]

Hugh, I spent a lot of time and effort on decreasing static heard in the radio on Stubby, our DE.  It could be squelched out, but when receiving a transmission, the ignition noise overwhelmed all but the strongest/closest transmissions.  Other aircraft or ground stations could hear Stubby loud and clear, but we could not hear them well.  By the way, the aircraft radio is a MicroAir panel mount.  I've heard that some models of radio remove noise better than others, but have not tried that change-out.  The antenna on the airplane is called an inverted V, which further reduced noise when receiving, possibly due to its being further away from the engine.  It is mounted at the rear of the wing, above the fuselage.  The earlier antenna was a simple whip mounted on top of the wing, just behind the spar.

We ended up putting resistor type wires and using resistor plugs on the magneto, as well as the distributor ignition.  Both work fine.

Below is a copy of a long post (message 24432) I made to the old Yahoo Eaglers Nest, summarizing my attempts to quiet our radio reception noise:

Sent: Friday, October 19, 2012 7:08 AM
Subject: Re: Are you running this setup on your mag?...(GP Plug Shields)

Steve and Eaglers, I have some experience with those, and can say a few words:
 
Our 2180 GP engine on DE Stubby was originally set up with one ignition system being a mag with the shielded spark plug wires, using the GP adapters to connect to automotive plugs, straight out of the box as sent to us by GP, and the second ignition system a points distributor/coil with metal wire core plug wires with rubber plug boots.
 
As some of you faithful readers may remember, Stubby's radio was producing noise in the headset when receiving, which originated from the mag system.  (the distributor system was modified from original by fitting metal shield cans over the distributor and coil, and replacing the metal wire core plug wires with resistance type automotive suppression spark plug wires.  This was very successful, and now barely generates noise in the radio.  We may eventually remove the shield cans from the distributor and coil to see if we really need them).
 
To reduce the mag noise, we tried all the usual suggested fixes, which may have helped, but did not cure the problem.  ( these fixes included more/better grounds, fewer redundant grounds, P lead with and without grounded shield, grounded only at mag, only at panel, neither, both, and no P lead at all.  Also tried ferrite cores on P lead, radio antenna lead, radio power leads, headset leads, etc. etc.  We even put in a separate battery to power the radio, no improvement.  I also made an inverted V antenna, which worked as an antenna better than the simple whip, but did not significantly reduce the ignition noise being heard in the radio)  So, we ventured off into some of our own attempts to fix the problem, i.e., shield or suppress the RF noise being generated from the magneto system.
 
The GP auto plug adapter shields have an insulator liner made from a plastic material, Delrin, I think.  The plug wire "cigarette" ends, I think they are called, are supposed to slip into the plastic insulators.  First problem, the cig ends would not slip in; either the ends ODs were too large, or the ID of the insulators too small.  So, I had to slightly enlarge the IDs of the insulators on the lathe to allow the cig ends to slip in.  This, of course, reduces the wall thickness of the insulator liner.  Eventually, two of these were punched through by the high voltage, causing missfire.  I have attached a pic (GP plug shield) showing the damaged cig end and insulator liner.  GP sent me replacement liners, but, even before the damage, the noise was there, and the sleeves were a bit of a pain to install on our engine set-up, so we went to the next step.
 
The next step was to replace the cig ends with regular automotive 90 degree plug boots, and attempted to shield the rubber plug boots with woven metal shielding sleeve material soldered to the plug wire shielding, using heat shrink to keep it all in place.  The engine ran fine, but this did not reduce radio noise much at all.
 
Next, we replaced the 90 degree plug boots with straight rubber automotive boots.  I made special aluminum shields which clamped around the plug wire braided shield, making good contact.  The shields fit around the rubber boots, and covered the plugs all the way to the surface where the plug screws into the head.  Also, I made a tab on each shield and connected a ground wire from each shield to the head, and we tried these shields with and without the ground wires.  I have attached a picture of this shield, with the parts pulled apart (fab plug shield).  When assembled, the plug boot is completely inside the alum tube, and the bare shield of the wire is clamped tight between the machined end piece halves, one of which was welded to the alum tubes.  The other half is held on tight with a hose clamp.  It all went together real well.  Bottom line, it was a nice exercise in design, fabrication, machining, but did not substantially reduce radio noise.
 
The next attempt was to replace the shielded mag wires with automotive suppression wires, as I described on a previous note to the EaglersNest:
 
I found a new magneto cap on ebay.  It is the cap that the spark plug wires attach to - that way, I did not have to destroy our existing braid shielded mag cap and wires.
 
I bought a set of Accel Super Stock Spiral Wire, #5040R, from AutoZone.  The wires are 8mm, and feature a "heavy gauge stainless steel alloy conductor", which is spiralled around a "carbon graphite semi-reactive element", resulting in 500 ohms/ft.  This set is red, has pre-assembled straight plug boots and a bunch of HEI and points cap connectors and boots which can be attached after wires are cut to length.  There is even a set of crimper plates that are intended to be used in a vise, I think.  This is a universal set for an eight cylinder engine, so I have four extra wires if I want to upgrade the distributor wires, which are the cheaper resistor type wire right now.
 
I installed four of these new wires to the mag cap, using as a guide the Generation 3 Ignition Company's booklet "Slick Ignition Lead Conversion".
 
We tested this set-up.  What a drastic improvement.  There is still some light background ignition noise, but our useable radio range to/from our base station handheld w/ roof antenna improved from about 8 miles to 30 miles or more, since we can now hear what is being transmitted to us instead of hearing ignition noise.  By the way, our transmissions from the airplane were always strong and clear, even with the original noisy mag wires.  The ground station never had a problem hearing the airplane from a long ways out.
 
Now, testing each ignition by itself, there is no appreciable difference in the ignition noise heard, and not much difference with both on.  This setup works great.
 
Tom Hubbuch
LEU, DE Stubby

[Hugh Sistrunk]

Very Good Info Tom H.  Will save a lot of time and effort duplicating ideas you have already explored - Thanks for the info... I am running a 009 Distrib, so will look at some of this stuff for my setup.

Hugh

[Steve]

We ended up putting resistor type wires and using resistor plugs on the magneto, as well as the distributor ignition.  Both work fine.

Check out the science at this website - what works fine may not be durable: http://www.brightsparkmagnetos.com/faqs/FAQs%20about%20magnetos%20generally/Are%20suppressors%20and%20resistor%20sparking%20plugs%20OK%20to%20use%20with%20magnetos.htm

[Tom H]

Steve, that's an interesting test.  Other parts of the site indicate that some mags have "safety" gaps, set around 7 mm gap, to protect the insulation if there is no other place for the building voltage to go.  That's around 1/4 inch.  It takes a much higher voltage to jump 1/4" as compared to the plug gap of 0.016".  Until the spark occurs, the voltage is building up in the coils, and subjecting the insulation to stress.  I suppose the mag insulation is designed to tolerate voltage build-up to jump 7 mm in air without serious degradation.

The ignition wire we are using is 500 ohms/ft, maybe 2 ft per wire, total 1000 ohms per plug wire.  I don't  know the plug resistance.  Possibly 1500 ohms. 

I don't have any hard data, but I believe our added 2500 ohms in the plug wire and plug does not increase the required voltage to spark the plug to anywhere near a mag insulation damaging voltage, i.e., a voltage higher than required to jump 7 mm.

The resistance does slow down the rate of discharge, resulting in a weaker, longer duration spark, and reduction of ignition noise.  Engine seems to operate just as well.  Radio is useable.

Overall, I understand the point of the article.  We could see reduced longevity of the mag.  Maybe.  Good to be aware of the possibility.

[Steve]

I don't have any hard data, but I believe our added 2500 ohms in the plug wire and plug does not increase the required voltage to spark the plug to anywhere near a mag insulation damaging voltage, i.e., a voltage higher than required to jump 7 mm.

The resistance does slow down the rate of discharge, resulting in a weaker, longer duration spark, and reduction of ignition noise.  Engine seems to operate just as well.  Radio is useable.

Overall, I understand the point of the article.  We could see reduced longevity of the mag.  Maybe.  Good to be aware of the possibility.

I have taken the following dialog from an AVWEB article "Mag Check"

>The Distributor
The high-voltage pulses produced by the secondary winding of the coil must be directed to the spark plug of each cylinder in sequence. The magneto accomplishes this by means of a mechanical distributor. The high-tension lead of the coil is connected to a rotating wiper electrode on a large distributor gear that turns at half crankshaft speed inside the mag's distributor block, passing in close proximity to individual electrodes connected to the four or six or eight spark plug lead wires.
The distributor block is made of insulating (dielectric) material capable of withstanding tens of thousands of volts. It is essential that the inside of the distributor block remain scrupulously clean and dry. The slightest bit of contamination — moisture, oil, or dirt — can impair the dielectric properties of the block and allow internal arc-over between distributor block terminals, causing engine misfire...particularly at high altitudes. Once such arc-over occurs, it tends to leave a carbonized track in its wake, facilitating subsequent arc-over events.
>
The Slick Mags we use have a distributor and in many incidences are New/Old product that is 30 - 50 years old... In the West I see GA fleet mag distributor failure several times a year because of moisture in the low lands and or flying to altitude to get across the high country...

The distributor area is compromised in the cutcase engines with oil vapor and occasionally in the fullcase engines... This is the first place I would expect the higher resistance sparkplug and wires to show stress in the system...

Stubby has the the good secondary ignition... If I were flying stubby and felt a miss-fire I would be inclined to shutdown the mag first as I think it is being asked a lot of with the modern resistance plugwire and plug setup...

Most of the 1/2 engines with mags these days are getting the Slick 2220... Those mags are close to 50 years old / have the distributor function and should be inspected inside the cap before first flight... Read the manuals to get the running clearances for points / plugs plus how to lube the breaker points cam... They are usually being flown as single ignitions on the 2 cyl engines - inspections standards are once every 100 hours and overhaul at 500 hours... I think it prudent to fly this single ignition setup with solid core non resistant wires and spark plugs recommended by Hummel or GPAS... 

BTW: I really like the Leburg dual EI ignition but you could tell that...