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Flap actuator rod end bearings

 
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gerf(at)gerf.com
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PostPosted: Fri Jan 05, 2007 1:32 pm    Post subject: Flap actuator rod end bearings Reply with quote

N696WG(RV-9, Aerosport IO-320) got its Special Airworthyness Certificate thismorning. One thing that came up was that the DAR didn't like the typeof rod-end bearing that attaches the flap pushrod to the inboard rib ofthe flap. He complained that this type of rod end doesn't have a boltand wide area washer to retain the bearing in place in the event of afailure (from the plans this is a CM-4MS rod end bearing). If thebearing fails it can slip off the end and loose your flap into thewind. Obvious potential for an immediate role and catastrophe.

Have folks changed out these rod end bearings for alternates ? And if so what have you changed them for ?

g


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kboatright1(at)comcast.ne
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PostPosted: Fri Jan 05, 2007 1:57 pm    Post subject: Flap actuator rod end bearings Reply with quote

Check the archives. Several posts address this issue.

Here's one quote from Gary Vanremortel:

Quote:
I did replace the aluminum links per plans with 4130 steel tubing based on
a
comment made by Tom Green. I also used a normal (non-studded) rod end
bearing (same as the top one) on the lower end of the link, a real AN4 bolt
and a steel spacer (was a 1/4" ID drill bushing) in lieu of the studded
bearing which the manufacturer does not load rate. I also used a large OD
capture washer on the inboard side of the bearing in case the race breaks
formation with the rest of the bird. This to avoid the dreaded split flap
condition.

Quote:
-Gary VanRemortel
vanremog(at)aol.com

KB
---


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recapen(at)earthlink.net
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PostPosted: Fri Jan 05, 2007 1:57 pm    Post subject: Flap actuator rod end bearings Reply with quote

I'm interested in this myself for the same reason your DAR was....

These are standard with all of Vans kits that I know of. I haven't heard of anyone swapping them out and your DAR is the first I've heard of that didn't like them - although now hearing his story, I'm inclined to be concerned myself.

I have heard of one of the links that this bearing is attached to failing, the associated landing was uneventful - I don't know when in the sequence it failed.

I would think if it failed in flight with the flaps retracted, aerodynamic pressure would keep the failed one up and you would get asymetric (sp) deployment when you attempt to lower the flaps which you should recognize easily. I would also think that there would be too much pressure on it to fail in this manner if the flaps were already deployed.

My (probably not even) .02 worth
Ralph Capen

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Bob Collins



Joined: 11 Mar 2006
Posts: 470
Location: St. Paul, Minnesota

PostPosted: Fri Jan 05, 2007 2:47 pm    Post subject: Flap actuator rod end bearings Reply with quote

I think your DAR is very wise. There are several areas on my plane where I've added washers around the rod-end bearing to prevent failure. One of the ones I see people going "unwashered" quite often is the TruTrak servo arm. I really think large washers should be added on either side of those as well.
-------------- Original message ----------------------
From: "Ralph E. Capen" <recapen(at)earthlink.net>
Quote:

> >N696WG(RV-9, Aerosport IO-320) got its Special Airworthyness Certificate
thismorning. One thing that came up was that the DAR didn't like the typeof
rod-end bearing that attaches the flap pushrod to the inboard rib ofthe flap. He
complained that this type of rod end doesn't have a boltand wide area washer to
retain the bearing in place in the event of afailure (from the plans this is a
CM-4MS rod end bearing). If thebearing fails it can slip off the end and loose
your flap into thewind. Obvious potential for an immediate role and catastrophe.


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phil(at)petrasoft.net
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PostPosted: Fri Jan 05, 2007 3:04 pm    Post subject: Flap actuator rod end bearings Reply with quote

I seem to remember reading once that Van did some testing on one of
the designs many moons ago, where they deployed one flap on purpose
and they found that the ailerons were more than adequate to handle
the roll moment. I wish I could remember where I read that.

It seems to me that this is a very simple, lightweight design. The
failure mode is 'fairly' benign and those bearings are easy to check
during pre-flight (I give mine a pretty mean tug before every
flight). So, why add weight or complexity on a design that is flying
in thousands of airplanes without a real good reason.

Phil
On Jan 5, 2007, at 3:56 PM, Ralph E. Capen wrote:

[quote]
<recapen(at)earthlink.net>

I'm interested in this myself for the same reason your DAR was....

These are standard with all of Vans kits that I know of. I haven't
heard of anyone swapping them out and your DAR is the first I've
heard of that didn't like them - although now hearing his story,
I'm inclined to be concerned myself.

I have heard of one of the links that this bearing is attached to
failing, the associated landing was uneventful - I don't know when
in the sequence it failed.

I would think if it failed in flight with the flaps retracted,
aerodynamic pressure would keep the failed one up and you would get
asymetric (sp) deployment when you attempt to lower the flaps which
you should recognize easily. I would also think that there would
be too much pressure on it to fail in this manner if the flaps were
already deployed.

My (probably not even) .02 worth
Ralph Capen

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khorton01(at)rogers.com
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PostPosted: Fri Jan 05, 2007 4:06 pm    Post subject: Flap actuator rod end bearings Reply with quote

It would be possible for a builder to do a flight test to check what
would happen if this failure occurred. If I were doing the flight
test, I would do it as follows:

Remove one flap rod, and use some duct tape at the inboard trailing
edge of the flap to hold it up against the fuselage. This is to
ensure that it remains retracted on the ground and during take off.

Review bail out procedures, and select a test area in an uninhabited
area. Don a parachute and helmet.

Do a take off and climb to a safe altitude.

Slow to normal approach speed, and set up in a simulated stabilized
approach using whatever power you normally use.

Select flaps down, using aileron to hold wings level. If you run out
of aileron, note how much flap is deployed, then retract the flaps.

If you reach full flap and still have some aileron left, release the
stick to allow it to go to neutral. Wait one second, then grab the
stick and recover control. This is a rough simulation of what would
happen if the flaps were fully deployed, then one flap bearing (or
flap rod) failed, and that flap suddenly retracted. If the response
with a one second delay wasn't too frightening, repeat with a longer
delay before resuming control.

Retract the flaps and repeat at approach speed with idle power.

Retract the flaps, then try the whole thing again at approach speed,
but in a full power climb. This simulates what would happen if the
failure occurred when you aborted a landing, and had not yet
retracted the flaps.

Repeat at max speed for flap deployment, using various power settings.

Finish the flight with an approach and landing with the flaps retracted.

Repeat the whole exercise for the other flap, as it isn't obvious
which side would be the worse failure.

If the results from all the above tests show that this is a
survivable failure, then everything is OK as is. If the results show
there is a problem, then modify the design to address the DAR's
concern. You would also need to figure out how to ensure a flap rod
never fails, as the results of that failure would be the same as a
failure of the bearing. Maybe some sort of repetitive inspection
would be in order.

Kevin Horton

On 5 Jan 2007, at 18:03, Phil Birkelbach wrote:

[quote]

I seem to remember reading once that Van did some testing on one of
the designs many moons ago, where they deployed one flap on purpose
and they found that the ailerons were more than adequate to handle
the roll moment. I wish I could remember where I read that.

It seems to me that this is a very simple, lightweight design. The
failure mode is 'fairly' benign and those bearings are easy to
check during pre-flight (I give mine a pretty mean tug before every
flight). So, why add weight or complexity on a design that is
flying in thousands of airplanes without a real good reason.

Phil
On Jan 5, 2007, at 3:56 PM, Ralph E. Capen wrote:

>
> <recapen(at)earthlink.net>
>
> I'm interested in this myself for the same reason your DAR was....
>
> These are standard with all of Vans kits that I know of. I
> haven't heard of anyone swapping them out and your DAR is the
> first I've heard of that didn't like them - although now hearing
> his story, I'm inclined to be concerned myself.
>
> I have heard of one of the links that this bearing is attached to
> failing, the associated landing was uneventful - I don't know when
> in the sequence it failed.
>
> I would think if it failed in flight with the flaps retracted,
> aerodynamic pressure would keep the failed one up and you would
> get asymetric (sp) deployment when you attempt to lower the flaps
> which you should recognize easily. I would also think that there
> would be too much pressure on it to fail in this manner if the
> flaps were already deployed.
>
> My (probably not even) .02 worth
> Ralph Capen
>
> --


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rocketbob(at)gmail.com
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PostPosted: Fri Jan 05, 2007 6:16 pm    Post subject: Flap actuator rod end bearings Reply with quote

Hmmm. Seems to me that almost 5000 RV's have been flying with these flap rod ends and there's never been a documented failure of them, at least that I am aware of. A good preflight would prevent a problem with the rod ends from causing any sort of flight control problems.

Regards,
Bob Japundza
RV-6 flying F1 under const.

On 1/5/07, Gerry Filby <gerf(at)gerf.com (gerf(at)gerf.com)> wrote: [quote]--> RV-List message posted by: "Gerry Filby" < gerf(at)gerf.com (gerf(at)gerf.com)>

N696WG(RV-9, Aerosport IO-320) got its Special Airworthyness Certificate thismorning. One thing that came up was that the DAR didn't like the typeof rod-end bearing that attaches the flap pushrod to the inboard rib ofthe flap. He complained that this type of rod end doesn't have a boltand wide area washer to retain the bearing in place in the event of afailure (from the plans this is a CM-4MS rod end bearing). If thebearing fails it can slip off the end and loose your flap into thewind. Obvious potential for an immediate role and catastrophe.
[b]


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rv8ch



Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

PostPosted: Fri Jan 05, 2007 10:59 pm    Post subject: Flap actuator rod end bearings Reply with quote

Kevin Horton wrote:
Quote:
It would be possible for a builder to do a flight test to check what
would happen if this failure occurred. If I were doing the flight test,
I would do it as follows:

Remove one flap rod, and use some duct tape at the inboard trailing edge
of the flap to hold it up against the fuselage. This is to ensure that
it remains retracted on the ground and during take off.

Review bail out procedures, and select a test area in an uninhabited
area. Don a parachute and helmet. ...

Wow, Kevin, reading that gave me the chills. I think I'll wait for the
results of your testing! Smile
--
Mickey Coggins
http://www.rv8.ch/
#82007 finishing
do not archive


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khorton01(at)rogers.com
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PostPosted: Sat Jan 06, 2007 7:21 am    Post subject: Flap actuator rod end bearings Reply with quote

On 6 Jan 2007, at 01:57, Mickey Coggins wrote:

Quote:


Kevin Horton wrote:
> It would be possible for a builder to do a flight test to check
> what would happen if this failure occurred. If I were doing the
> flight test, I would do it as follows:
> Remove one flap rod, and use some duct tape at the inboard
> trailing edge of the flap to hold it up against the fuselage.
> This is to ensure that it remains retracted on the ground and
> during take off.
> Review bail out procedures, and select a test area in an
> uninhabited area. Don a parachute and helmet. ...

Wow, Kevin, reading that gave me the chills. I think I'll wait for
the results of your testing! Smile

Maybe it sounds a bit morbid to detail the preparations in that way,
but this is exactly the process that everyone should do before any
flight tests that are probing the edges of the envelope. It is far
better to be over prepared than to be caught by surprise.

I lost a very good friend who chose not to wear a parachute on a
flight test which was exploring the edge of the envelope with a new
flap angle. They lost control, then screwed up the procedure to use
the stall recovery chute, because they had not reviewed the details
of this procedure before the test. They could have bailed out if
they had been wearing parachutes, but they weren't, so three lives
were lost.

Prepare for every test flight like your life may depend upon it.

Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8


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