I'm sure someone has tried this but was just curious to the results. Use an RC carb with a swing weight. Nose up throttle open nose down throttle closed and some kind of detent for level flight. I can see already there would be a problem for inverted flight. Has anyone tried this?


MM

I'm sure someone has tried this but was just curious to the results. Use an RC carb with a swing weight. Nose up throttle open nose down throttle closed and some kind of detent for level flight. I can see already there would be a problem for inverted flight. Has anyone tried this?

   If you are imagining a pendulum that seeks vertical, it won't work at all. It will follow the local acceleration, not just gravity, so it will swing forwards and backwards with maneuvering. You can use that effect (Igor's accelerometers sense the fore/aft acceleration) but a mechanical pendulum will not stay vertical or sense vertical in any way.

     But in general, yes, pendula that sense centrifugal force have been used extensively, effectively, it senses the speed of the airplane. Look up "swing weight carburetor".

    Brett

Wow.  Brett responded, and yet didn't respond.  Hopefully it was just a brain fart and not an ischemic* event.

At any rate (and I'm purely channeling Brett here, I wish I could easily dredge up some of his historical comments on the subject), various mechanical arrangements involving pendula, weights and springs, and/or linkages from the bellcrank have all been tried, and you can measure it's success by how many people have won the nationals with it -- which is, zero.  The consensus is that a properly done tuned pipe setup works Just Fine -- and since the winners circle at the Nats and the World's seems to be populated by tuned pipes and electrics, the consensus may well be right.

* It has nothing to do with fish -- that would be an ichthemic event.  Ischemia is a blood stoppage** somewhere important.   On a side note, however, eating fish supposedly reduces your chances of experiencing one.

** Like a stroke or heart attack***

*** Yes, I'm enjoying this, in an evil nerd sort of way.

    Sorry I am not working fast enough for you, geez. And I don't think anybody is likely to find stroke jokes funny this week.
     Brett

Is anyone pursuing modern electronica for throttle control?


MM

Is anyone pursuing modern electronica for throttle control?

I'm sorta on record as experimenting with it for the last few years, but it's mostly been sitting on top of my oscilloscope, taunting me while I do paying work.  Brett's comments discouraged me, because I give him about a 70% chance of being correct, and within the remaining 30% I give it about a 50% chance that you need to have as much arcane knowledge, and maybe even rework capability* of 2-stroke engines as you do to make tuned pipes work correctly.

* I base this on what I know about the difference between (4-stroke) drag race engines vs. short-track race engines.  For a drag racer, you build the engine so that all of the intake and exhaust passages are BIG, for maximal power output.  As a consequence, at part throttle the air doesn't move very quickly inside the engine, and as a consequence of that, throttle response sucks.  A short-track engine, OTOH, uses much smaller intake and exhaust passages, a much smaller carburetor, etc..  It has significantly less power at the top end, but when you blip the throttle you get power right now.  I assume the same holds true for 2-stroke engines; I suspect that an engine built for good throttle response at 9000 RPM will have a smaller carb than one built for max power at 20,000RPM, and probably a smaller intake port, transfer passages, and exhaust port to boot.  Brett suspects that an exhaust throttle would fix all of this; he may be correct, but I suspect that an engine designed for maximum torque at 9000RPM would do better even with the exhaust throttle.

I'm sorta on record as experimenting with it for the last few years, but it's mostly been sitting on top of my oscilloscope, taunting me while I do paying work.  Brett's comments discouraged me, because I give him about a 70% chance of being correct, and within the remaining 30% I give it about a 50% chance that you need to have as much arcane knowledge, and maybe even rework capability* of 2-stroke engines as you do to make tuned pipes work correctly.

* I base this on what I know about the difference between (4-stroke) drag race engines vs. short-track race engines.  For a drag racer, you build the engine so that all of the intake and exhaust passages are BIG, for maximal power output.  As a consequence, at part throttle the air doesn't move very quickly inside the engine, and as a consequence of that, throttle response sucks.  A short-track engine, OTOH, uses much smaller intake and exhaust passages, a much smaller carburetor, etc..  It has significantly less power at the top end, but when you blip the throttle you get power right now.  I assume the same holds true for 2-stroke engines; I suspect that an engine built for good throttle response at 9000 RPM will have a smaller carb than one built for max power at 20,000RPM, and probably a smaller intake port, transfer passages, and exhaust port to boot.  Brett suspects that an exhaust throttle would fix all of this; he may be correct, but I suspect that an engine designed for maximum torque at 9000RPM would do better even with the exhaust throttle.

   I don't think there is much if any arcane knowledge required to make a tuned pipe engine work. Nothing has ever been better documented in more detail, and the engines themselves are so repeatable from copy to copy that you need to know nearly nothing aside from how to read.

  I give myself about a 90% chance of being right about the conventional throttle but about 50% on being right about the exhaust throttle. I base that observation on Scott Bair's experiments with both in the early 80s, and as far as I can tell, nothing of consequence has changed about it since then. Except that we have a far better potential solution already (see above). His system, with NO feedforward (which is what his did), worked better than it did with it - after he more-or-less built his own .8ish cu in engine with so much compression you couldn't start the airplane with the glow plug seated (because the torque required to turn it over TDC was more than enough to tear the front of the airplane off).

   Of course it is possible that you could come up with a fuel injection system that dealt with the lag inherent in the abrupt flow rate changes that conventional systems don't handle very well. Igor and I had brief speculation back on the FAI Rules Forum about how you might implement feedback control.

   At this point, with piped engines that do more-or-less what you would want as a response, a readily available feedback electric system, and an excellent 4-2 break system from the good people of the Ukraine, what improvement you would make using a lesser 4-2 break engine and a throttle. Aside from an academic exercise, which might be worth it for knowledge alone.

    Brett

I'm sure someone has tried this but was just curious to the results. Use an RC carb with a swing weight. Nose up throttle open nose down throttle closed and some kind of detent for level flight. I can see already there would be a problem for inverted flight. Has anyone tried this?


MM

I saw a trick in Hint's 'n Tips or some such in one of the magazines.  The guy used a 4 armed bellcrank.  Two longer arms for the lines.  The two shorter arms bumped a spring-loaded pushrod that would push the throttle slightly open when either up or down control was given.  It would probably have to be trimmed very carefully, but would give extra power when needed.  With modern hardware and ball links it could be made very sturdy.

You can set up a speed governor based on a J Roberts 3-line bellcrank.  Have it spring-loaded to go high with slack lines and reduce power as line pull increases. 

The engine would be screaming at takeoff and reduce power as line pull increases. 
It would be a simple matter to calibrate after a test flight.