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  • July 15, 2019, 01:04:39 PM

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Author Topic: Drastic trim problem fix  (Read 449 times)

Offline Randy Powell

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Drastic trim problem fix
« on: July 09, 2019, 11:52:33 AM »
So, you know how when you have an issues but you tell yourself, I don't need to fix it, I can just work around it? No, well, that's where I was. I made an error in the assembly of this plane and hoped I could trim around it. I couldn't. So, new control surfaces. Should have it back in the air in another week or so. Lot of stinking work for a stupid mistake.

Sigh....
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 Randy Powell

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Re: Drastic trim problem fix
« Reply #1 on: July 09, 2019, 12:15:08 PM »
What was the mistake?
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Offline Randy Powell

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Re: Drastic trim problem fix
« Reply #2 on: July 09, 2019, 03:57:23 PM »
Didn't leave enough room to allow full deflection. When it turned out that I had to add nose weight, I didn't have enough elevator. I will now
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Offline wwwarbird

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Re: Drastic trim problem fix
« Reply #3 on: July 09, 2019, 08:51:35 PM »

 Looks like a lot of fun...NOT.

 What do you use for hinges and how were you able to remove the original control surfaces?
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Offline Howard Rush

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Re: Drastic trim problem fix
« Reply #4 on: July 09, 2019, 10:49:58 PM »
Randy has a history of flying on one line and snagging things with the slack one.  This time he figured it prudent to do the fix before attempting another flight. 
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Offline TDM

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Re: Drastic trim problem fix
« Reply #5 on: July 10, 2019, 11:49:10 AM »
Randy that much deflection is basically an air brake rather than control impute. I don't think in real practice you apply more than 25 degrees of deflection on any surface and anything more than that is not effective. For such drastic deflections you must have some turbulators in front of the hinge-line to keep the airflow attached to the flying surface.
The question is why go through all this where a little tail weight takes care of the turn.   
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Online Brett Buck

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Re: Drastic trim problem fix
« Reply #6 on: July 10, 2019, 11:59:35 AM »
Randy that much deflection is basically an air brake rather than control impute. I don't think in real practice you apply more than 25 degrees of deflection on any surface and anything more than that is not effective. For such drastic deflections you must have some turbulators in front of the hinge-line to keep the airflow attached to the flying surface.
The question is why go through all this where a little tail weight takes care of the turn.

     I, too, am curious how much it moved *before* it was fixed, because the modified version moves a good 10 degrees further than I have on any of my airplanes, and normal trimming doesn't require anything near that much movement.

     Presumably, the surfaces were removed by removing the continuous hinge pin, and the new surfaces built around the existing hinge positions.

      Brett

Online Ken Culbertson

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Re: Drastic trim problem fix
« Reply #7 on: July 10, 2019, 12:08:49 PM »
Randy that much deflection is basically an air brake rather than control impute. I don't think in real practice you apply more than 25 degrees of deflection on any surface and anything more than that is not effective. For such drastic deflections you must have some tabulators in front of the hinge-line to keep the airflow attached to the flying surface.
The question is why go through all this where a little tail weight takes care of the turn.
IMHO there is such a thing as using too much control but no such thing as having too much control.
Wasn't the original issue having to add nose weight?  I won't let a ship off of my workbench that has less than 40 degrees.  Most have 45.  It is rare that I need to do a one liner but when I do need it I want it there even if it stalls the plane as long as I can get the nose pointed up for the motor to save the day.

Now having said that if you need more that 25 to turn a decent corner then you are in fact nose heavy, so my question would be why would you want to be nose heavy?

"But, that is just me and I could be wrong."

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Online Alan Resinger

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Re: Drastic trim problem fix
« Reply #8 on: July 10, 2019, 02:22:06 PM »
I watched Randy fly at Auburn a few weeks ago and could tell immediately that he had problems.  Both the flaps and elevators were hiindged to closely to the wing and stab and could not deflect more than ten to fifteen degrees before hitting their limit.  It was an accident loking for a place to happen. Paul and I checked the CG anl luckily Randy took our advice and put the model inthe car with suggestions in hand.  Glad to see repair and replacement is progressing.  See you north of the border early August Randy..

Offline Randy Powell

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Re: Drastic trim problem fix
« Reply #9 on: July 10, 2019, 02:37:17 PM »
Yea, at the Auburn contest, Alan and Paul told me what I already knew. The thing was hinged too closely. Has 12 degrees of deflection. Not enough, obviously. Now has about 38 degrees at full tilt. And no, I doubt I'll use more that 20-25 degrees. And the controls are much more free. Should fix the issue.

An no, it's not nose heavy. It was tail heavy and a bit squirrelly. Added nose weight and the touchiness went away but then it wouldn't turn. So, now it will turn. I hope, anyway.
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Offline wwwarbird

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Re: Drastic trim problem fix
« Reply #10 on: Yesterday at 08:46:49 PM »
 Any more progress on the fix?
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Online Ken Culbertson

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Re: Drastic trim problem fix
« Reply #11 on: Today at 06:29:34 AM »
Yea, at the Auburn contest, Alan and Paul told me what I already knew. The thing was hinged too closely. Has 12 degrees of deflection. Not enough, obviously. Now has about 38 degrees at full tilt. And no, I doubt I'll use more that 20-25 degrees. And the controls are much more free. Should fix the issue.

An no, it's not nose heavy. It was tail heavy and a bit squirrelly. Added nose weight and the touchiness went away but then it wouldn't turn. So, now it will turn. I hope, anyway.
Randy, since there are multiple ways to correct this issue I am curious (not critical, just curious) why you elected to build a whole new set instead of modifying the originals.

Ken
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