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hgmckay
Joined: 23 May 2006
Posts: 397
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 Posted: Mon Aug 28, 2006 5:32 pm Post subject: Elevator Trim Tab Setting |
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Gentlemen:
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I believe I understand how to set the trim tab on my Allegro 2000, but would like to have some independent confirmation or correction. Here is my understanding.
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With the trim tab lever in the cockpit set in the vertical down position, the trim tab should be set in the neutral position relative to the elevator. In this neutral position the wire cable is clamped to hold the tab in this position. When the lever is moved forward (nose down) the tab would be pulled up (by the spring on top of the elevator) relative to the elevator itself. When the lever is pulled back, the tab is pulled down (by the wire cable) relative to the elevator itself. What I don’t understand is the stop screw on top of the tab that limits the max up position that the spring pulls the tab to. How is this stop screw set? What is the limit of the up-deflection of the tab, and how is it measured? Any help would be deeply appreciated.
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Hugh McKay
[quote][b]
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Tue Aug 29, 2006 3:38 am Post subject: Elevator Trim Tab Setting |
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Hugh,
Our brake actuator lever does not hit the console. On my next trip to
the hangar (Wednesday) I'll try to measure the stop bolt lengths as
adjusted on ours and take a couple photos of this area and post them.
Note that in flight, our elevator trim is set so that with max. nose up
trim (handle at 9 o'clock position) this gives an straight and level
angle of attach equivalent to about 70 mph airspeed. I don not know if
the adjustment described in the assembly manual gives this same setting
since we did not build ours. Most GA airplanes I've flown will allow
more nose up trim, to the point of near stall AOA, or at least to touch
down speed, and I was concerned about this at first. However, after
flying the Allegro for a year I think I prefer the trim set this way
because the only way you can get into a stall AOA is by pulling the
stick back past the max. nose up trim neutral position. 9 o'clock is
the trim setting for both take-off and landing with no guess work. The
forces on all controls are very light so you don't need to trim for
final approach speed like on heavier aircraft.
Thom in Buffalo
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Tue Aug 29, 2006 3:43 am Post subject: Elevator Trim Tab Setting |
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Hugh,
I will measure the stop bolt on the trim tab spring too and also take a
photo of this area and post them.
Thom in Buffalo
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_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Tue Aug 29, 2006 5:58 am Post subject: Elevator Trim Tab Setting |
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Thom:
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Why would one set the max nose up trim setting (9:00 Oclock) for level flight? I don’t quite understand this? Would you not want to have some ability to trim the nose up or down? Maybe I’m missing something here! Also why is there an adjustment on the trim tab stop screw ?
<![if !supportEmptyParas]> <![endif]>
Hugh
[quote][b]
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Wed Aug 30, 2006 3:48 am Post subject: Elevator Trim Tab Setting |
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Hugh,
Perhaps we are misunderstanding each other. By 9 o'clock, I mean that
the trim control handle, when looking at it from the center of the
cockpit, is in the 9 o'clock position, i.e., handle extending aft. I'm
not certain if that is the result of the factory instructions or a
previous owner's adjustments. The result, in our case, is that this is
full nose up trim and yields about 70 mph with power set for straight
and level flight. The only disadvantage I see in this is that you can't
trim it to slower flight for final approach, but as I said before, the
control forces are so light that you don't notice the need for slight
back pressure to slow it down to flare and touch down speed. The
advantage is that you can't trim it to stall speed with a load factor
of 1. In an emergency situation, if the trim is set in this position,
then relaxing the elevator will give you a safe AOA which is very
close to Vy.
On the other end of the speed range, 75% cruise power in our 80 hp
Allegro, the trim control handle is set to about 5-5:30 o'clock. There
is plenty of trim control range and it easy to set precisely the
trimmed AOA for any speed above 70 mph. If you want the full nose up
trim to be slower, that is your choice, of course.
Thom in Buffalo
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_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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