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Electric Stunt => New electronic technology => Topic started by: fielding mellish on May 04, 2015, 06:20:29 AM
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Guys,
I'm curious about a variation on the electronic bellcrank concept. Instead of handle movement commanding a certain elevator position, what if handle movement commanded (proportionately) a certain pitch RATE? When the handle is neutralized, the model would maintain its current pitch attitude until another correction is received. Would this be possible or practical, and would it make for smoother flying?
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I've put some thought into this myself because with a little bit of custom software you could do this with a TUT board. So, yes it's possible, probably even practical in the sense that you could make the model do what you specify, at least at speed.
As to whether it'd be practical for stunt -- maybe not. Think how fast the airplane rotates in response to elevator with the airplane stopped. That's because the sensitivity of the airplane's rate vs. elevator displacement is zero at zero speed, low at low speeds, and high at high speeds. So you'd need some sort of a speed-sensitive gain from handle to rotation. Also, stunt planes are generally designed to be quite stable, with way-far-forward centers of gravity compared to any other form of aviation. This should translate into a marked tendency for the tail to weather-vane into the direction of the airflow, which you cannot do with a TUT or anything else unless you add vertical flow sensors to the mix (which you could do with a TUT, if you wanted to go there).
I think that if you did it you'd want to have a linear relationship between flap and handle, and a nonlinear relationship between handle and pitch, to give you very little rotation for the amount of up and down you get during level flight and straight segments, yet still get lots of rotation in corners. This is more or less the "Igor flap" concept, just tunable in electronics.
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Wow, it's more complex than I thought. Thanks for your quick reply.
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I'm not trying to drive you off of the idea -- I think it's a worthwhile thing to try, particularly because it would allow you to move the CG back until the airframe's pitch stability is zero or even negative.
It's just not something you want to slap together.
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It's something a controls engineer could do, but I would hope it's outlawed for stunt contests and that anybody who tries it is banished to RC. I presume that fielding is not using his real name out of shame.
If you have a good stunt plane and know how to trim it better than I do, you can do this aerodynamically with traditional control linkage. I flew an Impact once (not mine) that looked like a poor simulation of a stunt plane. The engine made the same sound everywhere, the airplane went the same speed everywhere, and I saw only the profile of the plane: never any wing, never any oscillation. A handle input resulted in a pitch rate proportional to input. It was weird.
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Tim, I didn't see your comments as negative. I was just considering the idea as a thought experiment. The fly-by-wire concept is intriguing, but I doubt I'll ever try it.
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It's something a controls engineer could do, but I would hope it's outlawed for stunt contests and that anybody who tries it is banished to RC.
Aw c'mon Howard. What if you wanted to do a semi-scale stunt version of an X-29? How could you possibly build it with the CG in front of the neutral point?
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Guys,
I'm curious about a variation on the electronic bellcrank concept. Instead of handle movement commanding a certain elevator position, what if handle movement commanded (proportionately) a certain pitch RATE? When the handle is neutralized, the model would maintain its current pitch attitude until another correction is received. Would this be possible or practical, and would it make for smoother flying?
Not sure but isn't this the same as Kim's fly by wire setup a few post's down?
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Not sure but isn't this the same as Kim's fly by wire setup a few post's down?
If I'm not mistaken about Kim's system, it basically has the elevator and flaps following the bellcrank, possibly with something like exponential rate tossed into one or the other surface -- but it always presents a 1:1 mapping of bellcrank position to elevator and flap position.
What Fielding is talking about (if I'm not mistaken), is a system that servos the rate of rotation of the plane to the bellcrank position -- meaning that there would have to be a controller in there that senses the rotation rate and moves the elevator until the plane is moving as fast as it is commanded. It would be a very different system (and probably impossible to fly at slow speeds if you did it exactly as stated).
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If you have a good stunt plane and know how to trim it better than I do, you can do this aerodynamically with traditional control linkage. I flew an Impact once (not mine) that looked like a poor simulation of a stunt plane. The engine made the same sound everywhere, the airplane went the same speed everywhere, and I saw only the profile of the plane: never any wing, never any oscillation. A handle input resulted in a pitch rate proportional to input. It was weird.
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I believe there is only one person (other than Howard) who knows what you are describing.
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I believe there is only one person who knows what you are describing.
That being Howard? He's making a comment about flying -- I presume -- you plane, in his usual -- erm -- straightforward way.