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txpilot
Joined: 26 Feb 2007
Posts: 87
Location: Houston, TX
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 Posted: Tue Mar 01, 2011 9:31 pm Post subject: Control Issues in Phase 1 testing |
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I now have 16 hours on my 701 and I've found a few issues that are curious, to say the least.
First, it seems the aircraft cannot be trimmed for level flight with the flaps down. Although the elevator trim is neutral or slightly down in cruise with the flaps up, no amount of up elevator trim will prevent the airplane from nose-diving (HARD) with the flaps down.
Second, I'm following the AC 90-89A guide for test-flying my airplane. I'm conducting the "Lateral-directional Stability Control Tests" described on page 51 of this document. I've found the rudder will not spring back to neutral in flight but will instead maintain its last set position, even at near full deflection! I think it's because there is no vertical stabilizer and there's a lot of rudder surface area ahead of the rudder hinge. I'm concerned a full deflection, especially near maneuvering speed, may cause a control lock in full rudder deflection.
Third, I conducted the "Spiral Stability" check described in the same Advisory Circular. To my surprise, the aircraft maintains neutral stability (i.e. - it will not return from a banked condition to level flight). This is not typical of high wing aircraft. Although this is not a critical safety issue, it does make the airplane a little more difficult to fly.
Has anyone else noticed these issues in their aircraft?
Thanks,
Dan Ginty
N787DG
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klondike(at)megalink.net
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| Posted: Wed Mar 02, 2011 5:13 am Post subject: Control Issues in Phase 1 testing |
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Dan-- Sounds like you still have the bend at the trailing edge of the
elevator. Many moons ago, Chris said to take the bend out.
Fritz
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rockiedog2
Joined: 03 Mar 2010
Posts: 19
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| Posted: Wed Mar 02, 2011 5:24 am Post subject: Control Issues in Phase 1 testing |
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Yes , we've noticed. Those are pretty much "normal" 701 flight characteristics; to varying degrees. Welcome to the 701...
[quote][b]
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cdnch701builder
Joined: 21 Aug 2010
Posts: 21
Location: Canada
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| Posted: Wed Mar 02, 2011 11:04 am Post subject: Control Issues in Phase 1 testing |
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Dan
Sounds like you have the problem with running out of elevator other
builders have! Attached is CH's cure for the problem... they should
re-publish in Zenair news to make everywhere of the problem. They never
the change to the drawings... after they went to the heavier 912 engine!
Ron
:--)
:--) <txpilot(at)consolidated.net>
:--)
:--) I now have 16 hours on my 701 and I've found a few issues that
:--) are curious, to say the least.
:--)
:--) First, it seems the aircraft cannot be trimmed for level flight
:--) with the flaps down. Although the elevator trim is neutral or
:--) slightly down in cruise with the flaps up, no amount of up
:--) elevator trim will prevent the airplane from nose-diving (HARD)
:--) with the flaps down.
:--)
:--) Second, I'm following the AC 90-89A guide for test-flying my
:--) airplane. I'm conducting the "Lateral-directional Stability
:--) Control Tests" described on page 51 of this document. I've
:--) found the rudder will not spring back to neutral in flight but
:--) will instead maintain its last set position, even at near full
:--) deflection! I think it's because there is no vertical
:--) stabilizer and there's a lot of rudder surface area ahead of the
:--) rudder hinge. I'm concerned a full deflection, especially near
:--) maneuvering speed, may cause a control lock in full rudder
:--) deflection.
:--)
:--) Third, I conducted the "Spiral Stability" check described in the
:--) same Advisory Circular. To my surprise, the aircraft maintains
:--) neutral stability (i.e. - it will not return from a banked
:--) condition to level flight). This is not typical of high wing
:--) aircraft. Although this is not a critical safety issue, it does
:--) make the airplane a little more difficult to fly.
:--)
:--) Has anyone else noticed these issues in their aircraft?
:--)
:--) Thanks,
:--)
:--) Dan Ginty
:--) N787DG
:--)
:--)
:--) Read this topic online here:
:--)
:--) http://forums.matronics.com/viewtopic.php?p=332451#332451
:--)
:--)
:--) =
:--) = - MATRONICS WEB FORUMS -
:--) your generous support!
:--) --> http://www.matronics.com/contribution
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cdnch701builder |
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b.carl@sympatico.ca
Joined: 20 May 2008
Posts: 77
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| Posted: Wed Mar 02, 2011 1:54 pm Post subject: Control Issues in Phase 1 testing |
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Dan
I believe the V blocks on the nose gear bearing are designed to return the
rudder to the neutral position in flight to act as a fin and provide
directional stability. Unfortunately they are not always effective if the
rudder control system has a lot of friction; and the system does have a lot
of friction. You may want to try and reduce friction and check if your
blocks are optimized..
In my case, since the blocks did not seam to help much and had to keep my
feet on the pedals all the time, I installed a nose wheel steering
disconnect to reduce the friction. in flight. This makes the rudder control
lighter and spares the legs on long flights. The rudder pretty much acts as
it did before; when deflected up to two ball width, it stays deflected. and
needs to be returned ,even with the reduced friction in my system. This
shows that the a|c minus rudder has close to 0 stability; that being the
case there is no aerodynamic force to return the rudder to neutral so it
stays aligned with the airflow.
In cruise, I found that once the a|c is in trim and the rudder is in neutral
just using the pedals as foot rest gives a pretty comfortable ride even in
light turbulence. In that situation the rudder becomes a big fin and for a
small, a|c gives good directional stability.
I experimented by adding a ventral fin (about two 2 sqf). It did little for
stability in the air but made the aircraft much more difficult to turn
downwind on the water (I`m on floats).So it came off.and is now a
conversation item on the wall in my hangar.
As to your concern about rudder lock, my testing with floats (they make the
a|c less directionally stable) I find that the rudder becomes harder to
deflect from neutral :
1- the further it is deflected: and
2 -the higher the IAS.
I must emphasise that I have not conducted this test at any where close to
manoeuvring speed but I doubt a rudder lock could happen.
In summary. the testing I have done leads me to believe the rudder is
effective and when used properly control the a|c in all normal manoeuvres.
Since the rudder is also a large part of the fin area, I expect the loss of
same would render the a|c uncontrollable. So I check rudder very closely
before flight.
Carl
ays
---
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klondike(at)megalink.net
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| Posted: Wed Mar 02, 2011 2:49 pm Post subject: Control Issues in Phase 1 testing |
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I elected to do away with my V noch on the 701--- have you folks
looked close on how much the V notch makes the support plate flex?
Much smoother rudder action without the notch.
Fritz
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JohnDRead(at)aol.com
Guest
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| Posted: Wed Mar 02, 2011 8:33 pm Post subject: Control Issues in Phase 1 testing |
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Re: bending the elevator. There was a note from Zenith that described cutting a grove down a piece of 2 x 4 to fit the trailing edge and then to bend the edge up. A call to the factory would verify.
Regards, John
CH701 - Colorado - Jabiru 3300
Cell: 719-494-4567
Home: 303-648-3261
In a message dated 3/2/2011 6:13:49 A.M. Mountain Standard Time, klondike(at)megalink.net writes:
[quote]--> Zenith701801-List message posted by: "fritz" <klondike(at)megalink.net>
Dan-- Sounds like you still have the bend at the trailing edge of the
elevator. Many moons ago, Chris said to take the bend out.
Fritz
---
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ronlee
Joined: 25 Dec 2006
Posts: 141
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| Posted: Thu Mar 03, 2011 3:45 pm Post subject: Re: Control Issues in Phase 1 testing |
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I had the same problem with the trim not holding the nose up with flaps. When I built the plane I even put a larger trim tab then plans called for because I knew this was a 701 problem, still would not hold the nose up. Straightened the trailing edge and that helped some but still not enough, so I put VGs on the underside of the HZ stab and it worked like a charm. I couldn't believe the difference they made. It sure made me a believer in the power of VGs. I still have to hold back just a touch on the stick with full flaps, but almost none.
I never put the aluminum V blocks on while building because I knew of this 701 problem. I replaced them with level (no V grove) nylon sliders. Less friction so the rudder works with much much less rudder peddle pressure then the two other 701s I have flown. Neither of them returned to center because of the
V grove anyway. That steel sliding on aluminum is a sticky situation, not good
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Ron Lee
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rockiedog2
Joined: 03 Mar 2010
Posts: 19
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| Posted: Fri Mar 04, 2011 3:36 am Post subject: Control Issues in Phase 1 testing |
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Hi guys
Over on Zenith builders and Flyers list there is a thread of an aux elevator trim that I posted. It's working good for me.
FYI
Joe
[quote][b]
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