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d-m-hague(at)comcast.net
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 Posted: Sat Oct 06, 2007 6:27 pm Post subject: trim tab attachment |
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OK, after the 5th flight in my US I've decided I need to add an elevator
trim tab. It takes constant back pressure to hold it level at any power
setting, not much force but let go and it dives at an alarming rate. I
thought of using a bungee but I like the idea of a tab better as it's fail
safe if anything fails in the elevator linkage. Or I may set the trim tab
to a survivable glide speed and also add a bungee trim for fine adjustment.
Anyway, what is the best way to mount it? I assume riveting it on, to the
lower surface of the elevator, but I don't want to weaken anything. Do I
rivet it to the trailing edge tube, or the ribs, or both?
-Dana
--
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"I'm a lawyer." "Honest?" "No, the usual kind."
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sat Oct 06, 2007 6:45 pm Post subject: trim tab attachment |
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> Anyway, what is the best way to mount it? I assume riveting it on, to
the
| Quote: | lower surface of the elevator, but I don't want to weaken anything. Do I
rivet it to the trailing edge tube, or the ribs, or both?
-Dana
|
Dana:
If it was my problem, first I would insure those big ole barn door ailerons
are rigged correctly in flight, not necessarily sitting still on the ground.
If they are drooped a tad, the aircraft will want to pitch down.
The US low thrust line in pusher configuration should encourage the US to
climb under power.
john h
mkIII
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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d-m-hague(at)comcast.net
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| Posted: Sat Oct 06, 2007 6:59 pm Post subject: trim tab attachment |
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At 10:45 PM 10/6/2007, John Hauck wrote:
| Quote: |
If it was my problem, first I would insure those big ole barn door
ailerons are rigged correctly in flight, not necessarily sitting still on
the ground.
If they are drooped a tad, the aircraft will want to pitch down.
|
Thanks John, that was one of the things I checked today. On the ground,
they're dead even with the wing (wing lower surface to aileron lower
surface). In flight, if anything they ride a bit higher. I considered
reflexing them a bit and I still might try that, but I don't want to raise
the stall speed.
I also considered that the plane might be nose heavy, but I have plenty of
elevator authority through stall and/or flare, and as near as I can tell
the elevators are even with the stabilizer when I'm holding the back
pressure required for level flight.
-Dana
-Dana
--
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"I'm a lawyer." "Honest?" "No, the usual kind."
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sat Oct 06, 2007 7:12 pm Post subject: trim tab attachment |
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> I also considered that the plane might be nose heavy, but I have plenty
of
| Quote: | elevator authority through stall and/or flare, and as near as I can tell
the elevators are even with the stabilizer when I'm holding the back
pressure required for level flight.
-Dana
|
Wing incidence may not be correct. Too much or too little, I do not know
how that would affect pitch attitude.
On my US, I rigged it according to the construction manual. It still needed
rudder, aileron, and elevator trim tabs to zero out any adverse pressure on
the stick. I made all the tabs out of .016" alum. They were easy to bend
for adjustment. I also believe they were relieved of some of their angle of
attack as airspeed increased. My FS was rigged identically. Trimmed out
perfect with the same three trim tabs.
john h
mkIII
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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d-m-hague(at)comcast.net
Guest
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| Posted: Sun Oct 07, 2007 4:43 am Post subject: trim tab attachment |
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At 11:11 PM 10/6/2007, John Hauck wrote:
| Quote: | Wing incidence may not be correct. Too much or too little, I do not know
how that would affect pitch attitude.
|
Insufficient wing incidence (or more correctly, insufficient declage, which
is the relative angle between wing and stabilizer) would cause a nose down
tendency. I don't think that's the case, though.
| Quote: | On my US, I rigged it according to the construction manual. It still
needed rudder, aileron, and elevator trim tabs to zero out any adverse
pressure on the stick. I made all the tabs out of .016" alum. They were
easy to bend...
|
How did you attach them? Rivets I assume, but into what? The trailing
edge or ribs or both?
-Dana
--
--
"I'm a lawyer." "Honest?" "No, the usual kind."
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sun Oct 07, 2007 5:26 am Post subject: trim tab attachment |
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> How did you attach them? Rivets I assume, but into what? The trailing
| Quote: | edge or ribs or both?
-Dana
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Back then, I attached to trailing edge with 1/8" fabric rivets, about 1"
spacing.
If you put enough hours on the aircraft you will probably have to replace a
trim tab or a rivet or two.
On the mkIII I attach the only trim tab to the rudder using two ribs and no
rivets in the trailing edge.
john h
mkIII
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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