letters from Ted

Hey Everbody, the post on 'compression' and glowplugs made me think of this email exchange from Ted Fancher (Stuka Stunt 2003) and thought it was worth passing on:


RE: hot plug vs cold
From: Ted Fancher
Date: May 29th 2003
>Mark,

I'm very reluctant to make specific recommendations on engines I've never personally run. Please take this response with that in mind.

My feeling is that most any engine that is generally intended for RC use is going to be timed to run at higher revs than are appropriate for stunt use with the "traditional" six pitch props. I would expect to try and run the LA in a constant speed mode, preferably a steady four stroke. I would expect to run a four pitch prop around 10-11K, most likely either an 11 or perhaps a 12 inch diameter...start with elevens. I use 10% nitro fuel as the standard from which I make any changes depending on the given engine and conditions.

The engine should be able to spin an 11 X 4 prop at a steady four cycle at the desired revs to fly the plane at a speed with which you are comfortable (don't get sucked in to assuming max length lines are necessary. Line length is another good trimming mechanism. Don't be afraid to shorten lines to regain desired tension if the engine is happy at a speed which doesn't suit the longer lines). If the engine breaks into a two cycle during maneuvers but doesn't run away you can live with it. If it breaks and the plane surges forward too much for comfort either increase the nitro (thus requiring a richer mixture) or consider adding one additional head shim at a time...the nitro will provide more torque at the same RPM and run richer, the head shim will reduce torque and power a tiny amount but will also run richer. Both options will get you closer to the steady four stroke if that is your desire. Someplace in between will result in a break at different load levels...which is what you were originally asking about. Hope this helps.

Ted >
>
>
>Thanks! it points me out of the woods, but one last
>question: your guess: LA46 2-4-2 or hot plug, mostly 4
>cycle? For better line tension
>Thanks! You'e been a big help, I used to read your Twister
>article over and over.
>
>Mark Boesen

>Hi Ted,
>>>
>>>So would a earlier break say 10:00 area on a loop, be better
>>>than a constant four cycle with a hotter plug? Better as in
>>>more power, more line tension?
>>>
>>>Thanks, Mark
>>
>>Hi Mark,
>>
>>Well, as always in this game, it's never quite that simple.
>>It depends on the engine (low timed Fox .35 versus the
>>modern schnerle ported engines we try to tame for stunt),
>>the airplane and the way the pilot likes to fly.
>>
>>With a stock Fox you're probably better off doing the
>>classic 4-2-4 thing. The modern engines are ported to
>>deliver their power at much higher revs and allowing them to
>>break makes way too much power compared to the four cycle
>>mode. As a result we find we need to run them in a constant
>>RPM mode with props pitched appropriate to the revs.
>>
>>One of the reasons for the current love affair with four
>>strokes is the consistency of power delivered by an engine
>>which "can't" break. With enough power to weight the things
>>fly just like they've got an electric engine on
>>them...constant torque and RPM...thus, constant speed. Very
>>few drawbacks once the right mixture is found.
>>
>>My personal preference for tuning a two stroke run is to use
>>nitro content or head shims to adjust the break (if any). I
>>think you can safely run any hot range plug and the stock
>>engine won't suffer any RPM loss when you disconnect the
>>battery. This test gets you in the "workable" range of the
>>engine. You can then adjust the break by playing the head
>>shim/nitro game. More nitro or less compression ratio (more
>>shims) will result in a later break when launched at the
>>desired lap time RPM, and vice versa.
>>
>>Hope this answers your question.
>>
>>Ted Fancher
>Mark,

I'm very reluctant to make specific recommendations on engines I've never personally run. Please take this response with that in mind.

My feeling is that most any engine that is generally intended for RC use is going to be timed to run at higher revs than are appropriate for stunt use with the "traditional" six pitch props. I would expect to try and run the LA in a constant speed mode, preferably a steady four stroke. I would expect to run a four pitch prop around 10-11K, most likely either an 11 or perhaps a 12 inch diameter...start with elevens. I use 10% nitro fuel as the standard from which I make any changes depending on the given engine and conditions.

The engine should be able to spin an 11 X 4 prop at a steady four cycle at the desired revs to fly the plane at a speed with which you are comfortable (don't get sucked in to assuming max length lines are necessary. Line length is another good trimming mechanism. Don't be afraid to shorten lines to regain desired tension if the engine is happy at a speed which doesn't suit the longer lines). If the engine breaks into a two cycle during maneuvers but doesn't run away you can live with it. If it breaks and the plane surges forward too much for comfort either increase the nitro (thus requiring a richer mixture) or consider adding one additional head shim at a time...the nitro will provide more torque at the same RPM and run richer, the head shim will reduce torque and power a tiny amount but will also run richer. Both options will get you closer to the steady four stroke if that is your desire. Someplace in between will result in a break at different load levels...which is what you were originally asking about. Hope this helps.

Ted