VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #21  
Old 05-25-2019, 12:05 AM
crabandy crabandy is offline
 
Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 2,099
Default

I have the dual SDS ignition and replaced my original iridium NGK plugs after 300+ hours during my condition inspection. No engine running issues at all, the ground electrode had started to taper/wear a smidge. Iíve got over 100 hours and a condition inspection on the new ones, Perhaps in a couple hundred hours Iíll replace the iridium with the standard ES plug and see what happens to save a few bucks.
__________________
RV 7 400 hours and counting
19 donation done
Reply With Quote
  #22  
Old 05-27-2019, 01:32 PM
svyolo svyolo is offline
 
Join Date: Oct 2017
Location: bellingham, wa
Posts: 162
Default

So what is the mechanism that makes a Lycoming eat auto spark plugs. I can understand lead fouling, but why would an 8.5-1 engine "wear out" plugs faster than an 11-1 auto engine?
Reply With Quote
  #23  
Old 05-27-2019, 02:25 PM
rv7charlie rv7charlie is online now
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,871
Default

Running at 60-75% power continuously, while the car is running at ~10-15% power continuously?
Higher heat load due to both higher effective combustion pressures (higher MAP, power), and more difficult to shed heat due to 300-400 degree heads, instead of 180 degree heads?
Reply With Quote
  #24  
Old 05-27-2019, 02:37 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,880
Default

Quote:
Originally Posted by svyolo View Post
So what is the mechanism that makes a Lycoming eat auto spark plugs. I can understand lead fouling, but why would an 8.5-1 engine "wear out" plugs faster than an 11-1 auto engine?
They don't.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #25  
Old 05-27-2019, 02:51 PM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,318
Default

Quote:
Originally Posted by DanH View Post
They don't.
I replace auto plugs on customers aircraft regularly, after a couple hundred hours the gap has grown significantly from wear even on the iridium. I think iridium can go around 200 hrs while the std ones last about 100 hrs before you start seeing wear.

I heard somewhere it is the leaded fuel that does it, makes sense as I grew up working on cars and used to change plugs every 10k mile back when we had leaded auto fuel.
__________________
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154

Last edited by Walt : 05-27-2019 at 09:14 PM.
Reply With Quote
  #26  
Old 05-27-2019, 03:20 PM
svyolo svyolo is offline
 
Join Date: Oct 2017
Location: bellingham, wa
Posts: 162
Default

Back when we had leaded auto fuel, most cars didn't have EI or fuel injection. Usually carbs and distributors.

I know cars operate at lower power (and MP) on average, but I would think the much higher compression ratios would more than make up for that. I would think the combustion pressure and temperature are much higher in the car. The coolant may be 180F, but the combustion Temp is much higher.

But that is just a guess.

I will be running SDS EFI/EI. I think I will use one set of plugs until I notice a change in how it runs when I do the "mag check". The other set I will change at a regular interval. I will also be running at fairly low power settings, and LOP the vast majority of the flight.
Reply With Quote
  #27  
Old 05-28-2019, 09:27 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,880
Default

Quote:
Originally Posted by Walt View Post
I replace auto plugs on customers aircraft regularly, after a couple hundred hours the gap has grown significantly from wear even on the iridium. I think iridium can go around 200 hrs while the std ones last about 100 hrs before you start seeing wear.
Absolutely Walt. I'm just saying the observed wear (loss of material from the electrodes, thus increased gap) is perfectly normal. High energy ignition systems should ionize across very large gaps without difficulty. It does load the plug wire insulation. As the plug gap gets larger, peak voltage goes up.

In fairness, I should note that not all EI's perform the same in this regard, even with the same coil. E-Mag purposely limits dwell or amperage (I'm not sure which, but it's in my notes somewhere) to the coil primary. The result is lower peak voltage and/or duration. Brad's position is enough is just right, and more is just a power sink. The limitation may or may not be related to internal generator output.

As Ross noted previously, his system will fire across a very large gap. Robert Paisley has long posted an energy comparison for a system that was, at that time, an SDS. I imagine the current System 32 also has significant coil output.

Quote:
I heard somewhere it is the leaded fuel that does it, makes sense as I grew up working on cars and used to change plugs every 10k mile back when we had leaded auto fuel.
Lead and carbon are conductive deposits on the ceramic center insulator. The key factor here is voltage rise. Rise time is fastest with CDI, followed by EI, with points triggered bringing up the rear. Fast rise time means not so much leakage across the ceramic. Think of a flood of electrons arriving at the gap, with some leakage down the ceramic. If the flood arrives slowly, the crest never gets very high...in this case, high enough to jump the gap.

In the good ole days we ran points ignitions (slow rise and not much peak) and leaded fuel (more conductive deposits), and cared for plugs a lot.

Let me say that if an owner wants to change plugs at every annual, well, fine. As noted, it does lower insulation loads on the plugs wires, and there is some lead contamination, just like those cars when we were kids. I do not think there is safety related reason to do so, no "insurance" as some have expressed. If anything, it is removing a part that is known to be operational, and replacing it with a part which is unknown.

From the Bosch Automotive Electrics/Electronics Manual ("CDI" = capacitive discharge, "TI" = EI, "CI" = points type):



__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 05-28-2019 at 11:06 AM.
Reply With Quote
  #28  
Old 05-28-2019, 10:50 AM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 4,768
Default

Quote:
Originally Posted by DanH View Post
If anything, it is removing a part that is known to be operational, and replacing it with a part which is unknown.
So you don't replace your tires until you get a flat? Brake pads before you have a failure? How do you determine when your engine oil has become non-operational?

Yes, I know what your point was - but you're painting with a mighty broad brush with that statement.
__________________
Greg Niehues - PPSEL, IFR, Repairman Cert.
Garden City, TX VAF 2019 dues paid
N16GN flying 500 hrs and counting! Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
Reply With Quote
  #29  
Old 05-28-2019, 11:32 AM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,421
Default

Plug life depends on several factors, ignition type and brand being among those. Most of our customers are changing standard plugs at 100-200 hours, depending mostly on hours flown between inspections. Those using Iridium plugs are doing so generally in the 200-300 hr. range.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 436.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm


Reply With Quote
  #30  
Old 05-28-2019, 01:08 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,880
Default

Quote:
Originally Posted by airguy View Post
Yes, I know what your point was - but you're painting with a mighty broad brush with that statement.
Quite true. Humor another stroke.

The "replace at annual" common practice has little to do with actual plug condition. Rather, it's an outgrowth of the annual cleaning ritual we all practiced with massive plugs and magnetos. We feel like we're not doing the "proper" maintenance if we don't unscrew them for a look. At $3 each, it's not worth cleaning them, and replacing them feels good.

It's cultural. And woe to the guy who admits he doesn't do it. Unclean! Unclean!

Seriously, the better survey question might be "How many hours have you gone on a set of auto plugs, with EI, before noting an abnormal drop, or roughness?"
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 05-28-2019 at 01:18 PM.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 08:38 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.