S-TEC 60-2 requires re-trim after altitude hold?

[Peter R.]

Speaking of the S-Tec 60-2, I am transitioning to a Bonanza V35B that is
equipped with this AP. The previous owner demonstrated an idiosyncrasy
with the AP that I would like to correct, if possible.

Using the AP to hold VSI, the aircraft is in a climb. Upon reaching the
assigned altitude, I push the ALT button on the AP. The aircraft, since it
overshot the altitude by 100 feet or so, descends and levels off at the
altitude where I engaged the ALT hold, then begins a speed increase to
cruise speed.

Now for the idiosyncrasy: The AP is engaged and the aircraft is holding
perfectly at the desired altitude. However, if I disengage the AP, the
aircraft immediately begins a climb, suggesting that there is a slight
nose-up trim situation that was being held back by the AP.

To overcome this, the previous owner suggested that after level-off,
disengage the AP, manually re-trim, then re-engage the AP.

How can the S-TEC AP be adjusted to hold the altitude after a climb without
the nose-up trim problem? It seems to me that, over time, this problem
could result in premature wear and tear of the AP control servos, no?



--
Peter












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[Ben Jackson]

In article >,
Peter R. > wrote:
>Speaking of the S-Tec 60-2, I am transitioning to a Bonanza V35B that is
>
>Now for the idiosyncrasy: The AP is engaged and the aircraft is holding
>perfectly at the desired altitude. However, if I disengage the AP, the
>aircraft immediately begins a climb, suggesting that there is a slight
>nose-up trim situation that was being held back by the AP.

I have an S-Tec 50. Mine is not connected to the electric trim (not
sure why -- the plane had electric trim as a factory option). The S-Tec
will call for trim if it can't hold the elevator itself (annunciator on
the AP), but it can hold a significant amount of pressure -- enough to
really scare you if you disengage it accidentally or without realizing
the trim situation.

It's not clear from S-Tec's site whether the 60-2 is always installed
in an automatic trim configuration (standard is 'altitude hold with
altitude trim' but optional is 'automatic electric pitch trim'). You
may be seeing normal behavior.

--
Ben Jackson
>
http://www.ben.com/

[Stu Gotts]

Call Autopilots Central in Tulsa and make an appointment to get it
fixed correctly.

On Mon, 1 Mar 2004 10:07:19 -0500, Peter R.
> wrote:

>Speaking of the S-Tec 60-2, I am transitioning to a Bonanza V35B that is
>equipped with this AP. The previous owner demonstrated an idiosyncrasy
>with the AP that I would like to correct, if possible.
>
>Using the AP to hold VSI, the aircraft is in a climb. Upon reaching the
>assigned altitude, I push the ALT button on the AP. The aircraft, since it
>overshot the altitude by 100 feet or so, descends and levels off at the
>altitude where I engaged the ALT hold, then begins a speed increase to
>cruise speed.
>
>Now for the idiosyncrasy: The AP is engaged and the aircraft is holding
>perfectly at the desired altitude. However, if I disengage the AP, the
>aircraft immediately begins a climb, suggesting that there is a slight
>nose-up trim situation that was being held back by the AP.
>
>To overcome this, the previous owner suggested that after level-off,
>disengage the AP, manually re-trim, then re-engage the AP.
>
>How can the S-TEC AP be adjusted to hold the altitude after a climb without
>the nose-up trim problem? It seems to me that, over time, this problem
>could result in premature wear and tear of the AP control servos, no?

[Roger Halstead]

On Mon, 1 Mar 2004 10:07:19 -0500, Peter R.
> wrote:

>Speaking of the S-Tec 60-2, I am transitioning to a Bonanza V35B that is
>equipped with this AP. The previous owner demonstrated an idiosyncrasy
>with the AP that I would like to correct, if possible.

I don't think you are going to find any thing wrong with the AP.
OTOH my experience is limited to only a couple of planes and mine has
an S-Tec 50 with altitude hold.
>
>Using the AP to hold VSI, the aircraft is in a climb. Upon reaching the
>assigned altitude, I push the ALT button on the AP. The aircraft, since it
>overshot the altitude by 100 feet or so, descends and levels off at the
>altitude where I engaged the ALT hold, then begins a speed increase to
>cruise speed.

Is the speed exactly the same as it was prior to the climb, or is the
power setting the same?

If you have climbed and the bo is going faster it will require the
trim be reset.

>
>Now for the idiosyncrasy: The AP is engaged and the aircraft is holding
>perfectly at the desired altitude. However, if I disengage the AP, the
>aircraft immediately begins a climb, suggesting that there is a slight
>nose-up trim situation that was being held back by the AP.
>
>To overcome this, the previous owner suggested that after level-off,
>disengage the AP, manually re-trim, then re-engage the AP.

The Bo is very sensitive to trim and speed. slight differences are
going to require retrimming. The AP will correct the situation, but
when disconnected the trim will go back to its manual setting
resulting in a climb or descent. If very far out of trim the change
can be rather abrupt.

>
>How can the S-TEC AP be adjusted to hold the altitude after a climb without
>the nose-up trim problem? It seems to me that, over time, this problem
>could result in premature wear and tear of the AP control servos, no?

As the AP is continually adjusting the trim, it's unlikely it would
add any wear due to the out-of-trim situation.
Get into some turbulence and that sucker can change so fast it'll do a
better job of holding altitude that I can. OTOH that's when I turn it
off to reduce stresses.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

[Julian Scarfe]

"Ben Jackson" > wrote in message
news:5tM0c.156461$jk2.597098@attbi_s53...

> It's not clear from S-Tec's site whether the 60-2 is always installed
> in an automatic trim configuration (standard is 'altitude hold with
> altitude trim' but optional is 'automatic electric pitch trim'). You
> may be seeing normal behavior.

It certainly isn't always -- ours isn't connected to the trim. Sounds like
the AP isn't talking to the trim system in Peter's case, though that may be
because of a problem rather than by choice.

Julian

[CriticalMass]

Peter R. wrote:

>Speaking of the S-Tec 60-2, I am transitioning to a Bonanza V35B that is
>equipped with this AP. The previous owner demonstrated an idiosyncrasy
>with the AP that I would like to correct, if possible.
>
>Using the AP to hold VSI, the aircraft is in a climb. Upon reaching the
>assigned altitude, I push the ALT button on the AP. The aircraft, since it
>overshot the altitude by 100 feet or so, descends and levels off at the
>altitude where I engaged the ALT hold, then begins a speed increase to
>cruise speed.
>
>Now for the idiosyncrasy: The AP is engaged and the aircraft is holding
>perfectly at the desired altitude. However, if I disengage the AP, the
>aircraft immediately begins a climb, suggesting that there is a slight
>nose-up trim situation that was being held back by the AP.
>
>To overcome this, the previous owner suggested that after level-off,
>disengage the AP, manually re-trim, then re-engage the AP.
>
>How can the S-TEC AP be adjusted to hold the altitude after a climb without
>the nose-up trim problem? It seems to me that, over time, this problem
>could result in premature wear and tear of the AP control servos, no?
>

You don't mention whether your a/p installation includes the *optional*
"automatic electric pitch trim" as specified on the STEC web site
<http://www.s-tec.com/products/ap2rpff.html>

The behavior you describe is exactly what I see routinely with the
System 55 a/p in my plane, and is normal without the automatic electric
option, which I plan to have installed soon.

Trim setting for climb power and airspeed is not usually where trim
will be once you level and set cruise power, and that variance is what's
causing the phenomenon you're seeing.

The a/p is capable of holding altitude even with some relatively high
pitch forces, but I agree with you - what's the sense in asking the
pitch servo to work against those pressures? I always disconnect and
retrim when I level out for cruise.

[Peter R.]

CriticalMass ) wrote:

> You don't mention whether your a/p installation includes the *optional*
> "automatic electric pitch trim" as specified on the STEC web site
> <http://www.s-tec.com/products/ap2rpff.html>

I don't know if this AP includes this option. I am still learning a lot
about the aircraft and its systems, but I will look into this.

--
Peter












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[Peter R.]

Roger Halstead ) wrote:

> Is the speed exactly the same as it was prior to the climb, or is the
> power setting the same?

No, the speed is definitely not the same. The aircraft climbs at 110 kts
indicated, then cruises at the top of the green arc with wide open throttle
(this is a turbonormalized engine), which is about 170 kts indicated.

> If you have climbed and the bo is going faster it will require the
> trim be reset.

I was spoiled by the Bendix/King KAP140, which had an altitude select and
capture that used the electric trim to maintain level flight, no matter if
the aircraft were accelerating or decelerating.

If I disconnected the AP (resulting in a loud disconnect tone), the
aircraft was in perfect elevator trim for the attitude and speed.

Of course, the B/K AP did not have GPS steer, which is a nice feature of
the 60-2.


--
Peter












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