The Murphy Builders Site

Thanks for the update Charlie ! Glad you survived - very lucky that
it was full UP, and the flaps could offset it. Really reinforces the
idea of thinking through everything that might happen, and planning
what you will do. I was reaching for the breaker at half trim deflection
when I saw the camera - probably would have had quite a fight to
hold it against the trim too !

From my testing, full DOWN would not be sustainable - just too much
force ! I think Brian, and Robin, would agree ....

If you are going to try it, be PLEASE BE VERY careful, and have a
big, muscular guy in the right seat to help, because you'll need it !
Be extra careful, because that will put a LOT of load on the cables
and the whole system ! Some have suggested flying the trim to the
max. position you would ever need, and putting a stop in there -
certainly for down trim !

I'm not a big fan of trim buttons on the stick - certainly NOT needed
for Rebels or Elites. Although it is nice on the SR/Moose, I've had a
couple of scares - it's just too easy to hit the trim accidentally,
either trying for the mike button, (no fun on short final !), or just
having a passenger's camera press it ! For those who are thinking about
it - be sure it's a completely separate button, somewhere where it's
a bit protected (maybe on the front, or with a flip-up cover ???)

......bobp

-------------------------------orig.-------------------------
On Sunday 19 March 2006 06:59 pm, Charlie Starr wrote:

Had an incident that I thought might be of interest to some. While doing
some airspeed calibrations this past week on my SR-2500 - 60% cruise
power at 3,500 feet, 122 k indicated - the nose suddenly went up into a
pretty steep climb. I was able to overcome this with a very strong
forward push. I found that the elevator trim had run to the full nose-up
position (uncommanded). While I have emergency trim cut-off switches to
remove all power from a trim system in just such a case, I was too slow
witted to realize what had happened and to disable the elevator trim
system before it had run to the full up position - and was not movable by
any of the three trim switches. In my configuration, I have trim
switches on both sticks as well as the rocker switch in the panel.

With a lot of arm force I found that I had sufficient elevator authority
to overpower the trim, though I wouldn't want to hold it for any great
length of time. Reducing power and speed greatly reduced the push needed
to overcome the trim, and in fact - in the lading configuration (A/S
about 70 k and flaps) the trim was about right for a hands off approach.
A go-around might have been interesting, though.

The problem was found to be in the Ray Allen grip switch (a five button
grip - up, down, left ,right & PPT). Evidently the up button either
shorted or was stuck. I didn't like this grip anyway, as it was difficult
to reach all buttons with my thumb or fingers. I have a single
hat-switch type grip on the right side with PPT and like it much better
and will replace the defective one with this type.

It was a bit of an alarming situation, but glad to report that the
airplane was fully controllable even with a fully mis-trimmed condition.
I'll try testing with a full down to see if that is also controlable.

Charlie Starr SR-2500 #065



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This is one reason why I have trim buttons on the pilot grip only. The
passenger gets to use the panel mounted buttons if they want to fly. All
they have on the grip is a mic button. Not happy to hear that the very same
pilot grip that I have installed has already one failure story on the books.
Maybe I'll look for a different grip.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Bob
Patterson
Sent: Sunday, March 19, 2006 3:39 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] SR - Incident during testing


Thanks for the update Charlie ! Glad you survived - very lucky that
it was full UP, and the flaps could offset it. Really reinforces the
idea of thinking through everything that might happen, and planning
what you will do. I was reaching for the breaker at half trim deflection
when I saw the camera - probably would have had quite a fight to
hold it against the trim too !

From my testing, full DOWN would not be sustainable - just too much
force ! I think Brian, and Robin, would agree ....

If you are going to try it, be PLEASE BE VERY careful, and have a
big, muscular guy in the right seat to help, because you'll need it !
Be extra careful, because that will put a LOT of load on the cables
and the whole system ! Some have suggested flying the trim to the
max. position you would ever need, and putting a stop in there -
certainly for down trim !

I'm not a big fan of trim buttons on the stick - certainly NOT needed
for Rebels or Elites. Although it is nice on the SR/Moose, I've had a
couple of scares - it's just too easy to hit the trim accidentally,
either trying for the mike button, (no fun on short final !), or just
having a passenger's camera press it ! For those who are thinking about
it - be sure it's a completely separate button, somewhere where it's
a bit protected (maybe on the front, or with a flip-up cover ???)

......bobp

-------------------------------orig.-------------------------
On Sunday 19 March 2006 06:59 pm, Charlie Starr wrote:

Had an incident that I thought might be of interest to some. While doing
some airspeed calibrations this past week on my SR-2500 - 60% cruise
power at 3,500 feet, 122 k indicated - the nose suddenly went up into a
pretty steep climb. I was able to overcome this with a very strong
forward push. I found that the elevator trim had run to the full nose-up
position (uncommanded). While I have emergency trim cut-off switches to
remove all power from a trim system in just such a case, I was too slow
witted to realize what had happened and to disable the elevator trim
system before it had run to the full up position - and was not movable by
any of the three trim switches. In my configuration, I have trim
switches on both sticks as well as the rocker switch in the panel.

With a lot of arm force I found that I had sufficient elevator authority
to overpower the trim, though I wouldn't want to hold it for any great
length of time. Reducing power and speed greatly reduced the push needed
to overcome the trim, and in fact - in the lading configuration (A/S
about 70 k and flaps) the trim was about right for a hands off approach.
A go-around might have been interesting, though.

The problem was found to be in the Ray Allen grip switch (a five button
grip - up, down, left ,right & PPT). Evidently the up button either
shorted or was stuck. I didn't like this grip anyway, as it was difficult
to reach all buttons with my thumb or fingers. I have a single
hat-switch type grip on the right side with PPT and like it much better
and will replace the defective one with this type.

It was a bit of an alarming situation, but glad to report that the
airplane was fully controllable even with a fully mis-trimmed condition.
I'll try testing with a full down to see if that is also controlable.

Charlie Starr SR-2500 #065



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Interesting? Why would full down be worse than full up when most
Moose elevators are rigged with much more up throw than down throw?

Sounds like the trim tab is way too large maybe?

Any idea what CG range you were in Bob when you messed with the down trim?

Let us know what you find out Charlie.

Cheers,
Bill

-----------------------------


Thanks for the update Charlie ! Glad you survived - very lucky that
it was full UP, and the flaps could offset it. Really reinforces the
idea of thinking through everything that might happen, and planning
what you will do. I was reaching for the breaker at half trim deflection
when I saw the camera - probably would have had quite a fight to
hold it against the trim too !

From my testing, full DOWN would not be sustainable - just too much
force ! I think Brian, and Robin, would agree ....

If you are going to try it, be PLEASE BE VERY careful, and have a
big, muscular guy in the right seat to help, because you'll need it !
Be extra careful, because that will put a LOT of load on the cables
and the whole system ! Some have suggested flying the trim to the
max. position you would ever need, and putting a stop in there -
certainly for down trim !

I'm not a big fan of trim buttons on the stick - certainly NOT needed
for Rebels or Elites. Although it is nice on the SR/Moose, I've had a
couple of scares - it's just too easy to hit the trim accidentally,
either trying for the mike button, (no fun on short final !), or just
having a passenger's camera press it ! For those who are thinking about
it - be sure it's a completely separate button, somewhere where it's
a bit protected (maybe on the front, or with a flip-up cover ???)

......bobp



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Hi Bill !

The down direction is worse, because there's nothing you can do
to offset it. With up elevator, slowing down and lowering the flaps
both help to balance the effect of trim - one because the c of g being
forward naturally causes a nose down effect when power is reduced,
and two, lowering flaps causes a pitch-down effect because of the
aerodynamics. Both offset the effect of full up trim - in fact, that's
why we HAVE up trim ! :-)

The tab might be a bit too big, but you can use all of it on
approach, as Charlie found - although go-around would be challenging !

I was at a moderately forward C of G - just 2 of us, and maybe a
couple of hundred pounds in the baggage area .... I certainly was
not strong enough to hold that much back stick for long enough to
manage a safe landing !! It would have been possible with both of
us pulling, as long as it was sooooon ...

Think the best solution is to limit the max. down (actually -
up travel) ;-) on the elevator trim tab, to the max. needed -
as determined by flight testing with aft c of g's. This will be
whatever the individual builder is happy/comfortable with. Then,
even if it runs away, it can't get beyond controllability.

.....bobp

-------------------------------orig.-------------------------
On Tuesday 21 March 2006 10:51 am, Bill Smith wrote:

Interesting? Why would full down be worse than full up when most
Moose elevators are rigged with much more up throw than down throw?

Sounds like the trim tab is way too large maybe?

Any idea what CG range you were in Bob when you messed with the down
trim?

Let us know what you find out Charlie.

Cheers,
Bill

-----------------------------


Thanks for the update Charlie ! Glad you survived - very lucky that
it was full UP, and the flaps could offset it. Really reinforces the
idea of thinking through everything that might happen, and planning
what you will do. I was reaching for the breaker at half trim deflection
when I saw the camera - probably would have had quite a fight to
hold it against the trim too !

From my testing, full DOWN would not be sustainable - just too much
force ! I think Brian, and Robin, would agree ....

If you are going to try it, be PLEASE BE VERY careful, and have a
big, muscular guy in the right seat to help, because you'll need it !
Be extra careful, because that will put a LOT of load on the cables
and the whole system ! Some have suggested flying the trim to the
max. position you would ever need, and putting a stop in there -
certainly for down trim !

I'm not a big fan of trim buttons on the stick - certainly NOT needed
for Rebels or Elites. Although it is nice on the SR/Moose, I've had a
couple of scares - it's just too easy to hit the trim accidentally,
either trying for the mike button, (no fun on short final !), or just
having a passenger's camera press it ! For those who are thinking about
it - be sure it's a completely separate button, somewhere where it's
a bit protected (maybe on the front, or with a flip-up cover ???)

......bobp

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