Control Lines For all you fly-by-wire fanatics!

Too High

Old 10-18-2015, 07:37 PM
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Hmm.., John. I'm at two inches now, but could go down to one-inch separation easily enough. Nice to have another, simpler option.


PS: What's the PIO abbreviation mean?
Old 10-19-2015, 06:05 AM
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Good morning Davey. No one inch is too big of a jump from two. I would start by simply going down just one quarter inch to one and three quarter inchs at the handle If you do not have a handle that will support that small adjustment just make one they are simple to do. That is a perfectly reasonable handle line spacing when used with the typical sized 1/2A bellcrank.

PIO stands for pilot induced oscillation.

Old 10-19-2015, 10:00 AM
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Thanks John, and will do. I'm glad you mentioned the smaller increment for the spacing as I probably would have overdone it!

You've helped a lot already, but I've another question (perhaps others can chime in here): For a future project, I'm thinking of constructing an all-around control line handle featuring adjustments for line length and spacing. Is the all-around feature (as in 1/2A up to size .40-sized planes) too much to ask of one handle? I've seen some designs on-line, but don't want to embark on a fool's errand!


Old 10-20-2015, 06:11 AM
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Davey, a few things to try:

Check the balance (CG) and make sure the plane is not tail heavy.

Check that the wing and stab incidence are the same (probably 0 ).

Check the control movement. About 20 degrees should be good. Also make sure that the amount of up and down are the same.

Make sure that full up or full down are not transmitting excessive force to the elevator.

If you have too much elevator movement, as mentioned above move the lines closer at the handle.

Good luck!

Old 10-21-2015, 06:46 AM
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Well-written and great advice. Thanks!

Davey Mo...
Old 10-22-2015, 05:40 AM
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Or a further out hole on the control horn.,
Old 10-24-2015, 10:52 AM
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...To John B's explanation of PIO, it is worst where the pilot has tried to correct an unwanted response but gets out of phase.

He corrects too late - the pilot has to notice the deviation, then try a correction. That correction is often too large, and when the model eventually responds - (even a fraction of a second can make it too late to steer out of the deviation smoothly) - the correction overdoes it and goes too far the other way. You're back to the original situation, and it can continue to repeat as you try to catch up. The 'divergences' often get worse the harder you try. PIO isn't new.

Republic Aircraft's XP-56 "Black Bullet' (about 1944?) experimental offering to an ARMY Air Corps (pre-USAF) spec was a tailless, delta wing, pusher-prop design. On the initial takeoff attempt, the pilot got into PIO and crash that nearly killed him. The other two experimentals were the Curtiss(?) Ascender, pusher-prop, swept wing with small stabilator up front. The name is a pun: listen to it. The third was a twin boom pusher-prop of somewhat more conventional looking design.

Some modern jet designs, too, had such problems - early flights of some USAF or USN Fighter /or Attack planes with all-flying tails were shown, in newsreels, landing with the tails whipping up and down frantically, trying to find THE right position.

For us, it's "ONLY" a matter of breaking a model airplane...
(edited - phrasing)

Last edited by Lou Crane; 10-24-2015 at 11:04 AM.

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