Conference vmszoo::rc

    I'm not an expert either but I'll give my two cents worth.
    
    One of the basic rules is never go up in Nitro. If you've been
    using 5% don't later go to 20%. This is especially true of ABC
    engines. The higher nitro runs hotter. As the engine is breaking
    in at a givin temp it will wear to that temp. Run it hotter the
    sleve will expand more resulting in a little blow by that makes
    it run hotter and more blow by and hotter etc. It will eventually
    sag off. Slow down. Check the sleve. If it is purple at all it has
    lost it's temper and is shot.
    
    Never heard of using the glow to tell if the nitro is high enough.
    I would think it would depend on the glow plug and how rich you
    set the engine. Like to hear more. Maybe I'v been missing something.
    I do know that on my Rossi's i have to leave the glow start connected
    for a while so the engine will warm up or it sags off.
    
    I didn't think anything attracted water like Methenal. Never heard
    that Nitro is worse.
    
    I like lots of Nitro but the higher the Nitro the more difficult
    to set the needle and the higher the risk you will damage your engine.
    
    bob
    

    look in 156.nn fro more discussion on fuels & nitro
    
    md

    Just a quick observation - it sounds like your engine is leaning
    out, possibly because the fuel level gets lower and the center
    of the tank might be below the carb???
    
    I'd try richening it a couple more notches, and adjust your idle
    mixture to get good idle.  The sagging condition after it runs for
    a while usually points to lean mixture.
    
    Bill

    
    Also, while on the ground, do you run it full throttle and hold
    the plane in different orientaions like straight up, pointed down,
    etc??  Keep richening the mixture until you get an engine run that
    doesn't lean out at any orientation.
    
    Bill

    What i've always thought/heard is that one of the combustion products
    of nitromethane is nitric acid and that it's the acid that corrodes the
    bearings.

                     !
                   --+--
G. Schrader     o___<0>___o
                  *  *  *

Chris,

I will go through your note with a few comments but basically you are correct.
    
>    1) Nitro affects the engine performance in two ways:
    
>    a) it improves the idle characteristics

Up about 10% Nitro that is correct, above 10% other factors effect the idle 
which complicate the use of nitro.

>    b) it generally increases the power output

Minimal increase in performance is noticed below 10% nitro, above 10% most 
definitely provided the compression is adjusted to optimize the performance.
    
>    2) Nitro is bad for an engine because it promotes rust due to the
>    absorption of water.

Nitro causes engine corrosion because of the acid PH level. I have described
how nitro is made in this notes file but basically it is a blending on nitric
acid and methane gas under pressure. 
    
>    I was told that you can tell if an engine has enough Nitro content
>    by:
    
>    1) While on the ground with Glow clip attached, fully open throttle.
>    2) remove glow clip, if engine rpm decreases then more nitro needed.

What you are actually checking is the plug temperature. If the engine slows
when the clip is removed from the plug the plug is too cold. Sure if you add
nitro it will rectify the condition, however the same result is achieved by
using a hotter plug (ie: change from OS5 to OS8 etc.). 

>    My question is how much is too much?
    
The erratic and over temperature running you describe I suspect is caused by
over compression reducing needle margin and causing the engine to run lean
towards the end of the tank. An extra washer under the head or even under the
glow plug or a colder plug could rectify the problem. 

My recommendation is for general sport flying without getting into engine mods
10% nitro is enough, increase the nitro content and other factors affect the
performance. For sport use if you need a little more power try fitting a Magic
Muffler from Condor Hobbies. They will fit any engine and give a noticeable
increase in performance. It is bolt-on-power as opposed to pour-in-power. The 
Magic Muffler is easy to use without the problems of the full length pipe.

Take time to read note 289 it may help you understand.

John.

    re .-3  Mr??? What did I say to warrant this ?
    
    md

    Thanks for the Help guys,
    
    I was happy with 10%, just could'nt find a bottle under 15% so I
    chose to buy it rather than not fly.  I'll check this weekend for
    5 or 10 percent and get back on track rather than re-adjust the
    engine for one bottle of fuel.
    
    re. 4,5  Yep, Tryed it in every attitude on the ground, worked great
    until it was flown for 8-9 minutes wideopen (happened every time)
    
    Re -.1   Thanks, that sheds a lot of light on the subject.  That
    was the kind of answer I was looking for. 
    
    
    Chris

    re .8
    
    Remember when I (among others) spelled your last wrong?  I was just
    saying thanks and showing that I can spell.  Notice the :-) behind
    it.
    
    Hope I did'nt ruffle your feathers,
    
    Chris
    

    re .-1.. Ooops.. I missed the :-).. Wasn't awake yet..
    
    md

    Late better than never.
    
    Ah,nitro. The more the better.
    
    Everything I heard about water, corrosion, etc, never cuts any cheese
    with them lunatics driving their 1/8 scale cars. They run those
    little .21 engines at 25,000 rpm on 8 % oil and 30 to 40 % nitro.
    The engines develop as much power as an airplane .60, if you can
    believe it, have no propeller to help cooling (mind you the darn
    things are going so fast that they don't need a prop.) and last
    just about enough.
    
    Personally, I have a Magnum .45 for which I have a lot of respect.
    I run it at 25 % nitro and 12 % oil, all synthetic. So it is a little
    hot when I land after 14 - 15 minutes... IT GOES LIKE STINK ! 
    
    I think we blow the need for engine longevity way out of proportion.
    You got to get the most performance out of your engine. There is
    no point in over economizing in engine and, at the
    same time, burn ten dollars
    in fuel every time you go to the field. To say nothing of planes
    that we drive (or fly)  into the ground and always blame on something
    or somebody else (we know very well it was our fault, every time).
    So what I did was to decide that the engines were going to give
    me as much power as they could while they lasted. Know what? They
    last just as long! I have a Fox .35 stunt with more than 150 hours.
    I have a Magnum .45, an OS 40 and an OS .46 long stroke, all burning
    25% nitro. They all have perfect compression, start and run like
    silk. No dead stiks (thank goodness) and I tell you, they all go
    like stink.
    
    However, what works for me doesn't necessarily work for anybody
    else. 
    
    Fern
    
    PS: I love this RC stuff !

    RE -.1
    
    Thanks Fern,
    
    I have gone back to 10% and it seems to be fine.  I am looking for
    some colder glow plugs though, which I think will help.
    
    Chris