[NSRCA-discussion] YS 160 - 170 Conversion to CDI

[Earl Haury]

Vince

Glow ignition has the advantage of light weight and simplicity, but a disadvantage in that the ignition point can't be precisely controlled. Spark ignition is essentially the opposite. Glow ignition made powered model aviation practical for the masses by its simplicity, and later the lack of RFI for RC. Of course, advancement in SI systems and materials now minimize the RFI & weight penalties which have rendered these systems commonplace for gasoline fueled 2-stroke cycle model engines.

So - what is accomplished by converting a glow engine to SI? The accurate control of ignition can reduce the chance of knock which drives heat input upwards - removing this excess heat is one of the reason for the high oil content of glow fuel - so less oil should be needed in the fuel. (Gasoline fueled SI engines need very little oil for lubrication.) We also tend to run glow engines on the rich side of optimum power A/F to prevent detonation (knock) - so ideal control of ignition should allow leaner operation and better fuel economy. Certainly a better idle is attainable through reliable ignition events at low speed. OTOH - the ignition system is required to convert low voltage to really high voltage (rapidly) and this comes a the price of weight, both for the system (which requires a coil / transformer, RF shielding - even with a capacitor discharge {CDI} that YS appears to be using) and a power source. It's not certain if the benefits of a simple conversion offset the weight penalty at this point.

However - there are additional avenues available with SI. Glow engines have a relatively low compression ratio, both to accommodate various fuel mixtures (% nitro) and minimize knock. Increasing the C/R is an efficient way to increase power - I toyed with this in the YS-AC days (still have the ignition system) but the weight penalty was too great at that time as both the ignition system and NiCads for power were heavy.  Increased C/R requires exact control of ignition - ideally with a feedback system to tailor spark timing to real time operation (most cars have this). Spark timing requirements vary with speed and load (less important for model engines), so some system sophistication is desirable to accommodate these needs. 

Compliments to YS for their development work. As usual - they're innovative in developing a relatively simple system compatible with current engines. I expect future YS use of SI will include both more engine optimization and SI system sophistication. So - I've generally considered a YS DZ akin to a Fuel Dragster engine with a ignition system handicap - looks like the handicap is going away and there'll be a methanol / nitro burning supercharged 4-stoke cycle model engine with accurate spark control (and it'll last a lot longer than the dragster engine). Kudos to YS.

Times are good in pattern with developers and marketers of engines, motors, fuels, and batteries providing us with options to power our airplanes that best suites our needs and desires. Sure beats wound up rubber bands!

Earl 








  ----- Original Message ----- 
  From: vicenterc at comcast.net 
  To: NSRCA NSRCA 
  Sent: Friday, May 16, 2008 6:09 AM
  Subject: [NSRCA-discussion] YS 160 - 170 Conversion to CDI


  Any comments on this conversion.  Sounds very interesting.

  http://www.rcuniverse.com/forum/m_7498725/anchors_7502394/mpage_1/key_/anchor/tm.htm#7502394

  --
  Vicente "Vince" Bortone


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