From: bloom@inland.com
Newsgroups: rec.models.rc
Subject: Re: FAQ? (questions about engines)
Date: 31 Aug 92 11:15:33 CST
Organization: Inland Steel Company; East Chicago, IN

In article <1992Aug28.220048.9625@c3177208.ssr.hp.com>, bill@c3177208.ssr.hp.com (Bill Chidester) writes:
> : 
> : Assuming that your needle valves are properly set:
> : There are really only 3 possible things that can cause an engine to 
> : stop or lose a lot of rpm when you pull off the glow battery.
> : 1. Too cold a glow plug.
> 
>    Wrong direction -- a "hot" glowplug refers to peak temperature, it uses
>    a smaller diameter wire element.  It's peak temperature is hotter than a
>    "cold" plug (which has a larger diameter element), but a hot plug retains
>    less heat.  It will cool faster and be more susceptible to quenching due 
>    to a rich idle or rich run.  I have found that a cold plug will loose less
>    RPM than a hot plug when you remove the battery.  The larger diameter wire 
>    provides more surface area for the platinum plating needed to sustain the
>    catalytic reaction, so they just "work better" than a hot plug. They idle
>    better, have a more even speed range and higher top end than a hot idle-bar.
> 
>    Most sport fliers think "hot" means fast and good; "cold" means slow and 
>    bad.  Cold plugs are much more rugged and last longer.  One of our club's
>    best engine guys suggested going against conventional wisdom while I was
>    trying to get a COX .074 running.  Everybody knows a small engine must have
>    a hot plug!  He made me put in a dead-cold Enya, and the engine now runs
>    flawlessly.
> 


Hot and cold mean the same thing in model engines as in car engines.  A 
hotter plug means exactly that: the plug element stays hotter period.  
There is more to heat range than the diameter of the coil.  The gap between 
the coil and the body of the plug also determines the heat range.  Bigger 
gap means slower heat transfer which means a hotter element, everything 
else the same.  A thicker element also means a hotter plug, more mass 
at high temperature takes longer to cool between power strokes.



> : 2. Too cold a fuel or bad fuel contaminated with water.  Cold fuel 
> : is equivalent to low or no nitromethane.
> 
>     Actually, adding nitromethane to fuel will make an engine run cooler, not
>     hotter (allowing lower temperature for a given RPM, or higher RPM for a
>     given temperature).  From the engine's point of view, "cold" = "good", so
>     it will run faster and more efficiently.  I agree with the water contami-
>     nation, especially if you leave fuel sitting in an unsealed container in
>     your flight box.

I don't think the laws of thermodynamics can be violated!  Nitro gives you 
more power thru more heat per power stroke.  Have you measured the 
head temperature of an engine running more nitro???  I'd bet a big dinner 
on this one.



> 
> : 3. Low compression in the engine.
> : 
> : I would do the following to solve your problem.  First, change to a 
> : new fresh fuel of at least 10% nitro of a reputable brand or one that 
> : runs well in one of your friend's engines.  If that doesn't fix it, 
> : then change to a hotter plug, e.g. a Fox R/C long idle bar plug or a 
> 
>      I really have to take exception to this advice.  Fox idle-bars are
>      currently one of the worst plugs on the market.  Stu Richmond tells me
>      that Duke Fox refused to use them in his own engines. Take a look at the
>      elements of several samples -- some will look like overstretched springs.
>      I don't like idle bar plugs in particular, and have taken to using Rossi
>      or Enya cold plugs.  Bob Fiorenze and Don Muddiman both use the cold
>      Rossi's in their jets and recommend them for their ruggedness.  They cost

Of course you should use a cold plug in a ducted fan, because a hot plug 
would cause detonation and the element won't last at high temperatures and 
high pressures.  If you run a hot plug in a fan, you will quickly collapse 
the element against the plug body and the engine will start to misfire.





>      about $5.00 (as opposed to $9.00 for Enyas) and deliver good idle and 
>      speed range (Something I never get with an idle bar).  There's another
>      posting about "Crummy Glow Plugs" telling how they're made that is right
>      on target.  We've found bad batches of Rossi's as well, so nobody's
>      immune!  Try one of the cold Rossi's first, along with a fresh bottle of
>      fuel.  Use your old fuel to clean your engines.

Yes, it's true that the Rossi and Enya plugs are better quality than a Fox 
plug.  For most sport flyers though, they usually don't need to spend the 
extra money.  Most of these engines run fine on Fox plugs.


> 
>      My opinion is, for sport flying, the lubricant is much more important
>      than the nitro content.  I use Morgan Mach 7, 5%, full synthetic.  I
>      would rather ruin an engine and buy a new one than scrape caster residue,
>      so I use synthetic.  Still, I've never lost an engine or a ring while
>      using the Mach 7, but I'm very quick to richen a lean running engine.
>      Mach 7 will form a scum inside the needle valve assembly every few 
>      months.  Closing and loosening the needle valve several times prior
>      to starting the engine will bring back an even engine run.  Every once
>      in a while, the carb will need an actual cleaning.  The jet jockies use
>      Byron's Synthetic/Castor blend.
> 
> :                    If that doesn't fix it, check to see if your 
> : compression is good.  Maybe you need a new ring or piston and liner 
> : if they are worn out or maybe you have a leaking head gasket.
> : 
>      Good advice, especially if you have leaned out a ringed engine.  A bad
>      ring is hard to detect -- most of them will take a heat temper (or is
>      is "de-temper?) and loose their spring.  An ABC engine is much more
>      tolerant of a lean run, but easier to destroy with sand or metal 
>      ingestion.  If you prang a plane, always, always, always, tear the engine
>      down and clean it!  My advice is to use a cold, expensive, non idle-bar 
>      plug, change to a high quality fuel and stick with the combination that
>      finally works for you.  
> 
>      There are a lot of flyers doing very well with $40 engines running 
>      $1.50 glow plugs -- all in all the value you get at the low end of the
>      scale is quite good.  However, I go to the field to fly, not screw
>      around with balky engines:  I think it's worth the extra money to save
>      precious flying time.
> 
> ----------------------------------
> Bill Chidester
> bill@c3177208.ssr.hp.com