Out of trim flying hand flying & auto-pilot

[Ibra]

Hi all,

On two topics "pattern speeds" and "configuration warnings", out of trim flying did come up as source of loss of control accident (LOC), these are highly relevant for Go-Around and EFATO accidents where the sudden change of power makes the aircraft sitting on the "wrong trim"

Has anyone tried slow flying on analog APs on alt & pitch hold with 0% to 100% to 0% power? in landing/clean config? where does the trim go? does the AP disconnect?

I don't have alt hold on M20J with an analog AP (other aircraft where I tried alt hold & power had envelope protection that kicks in)

Just curious, not that I am planning to fly before GA & EFATO on AP 

[carusoam]

The more modern Mooneys designed things to match speeds...

Like flap speed and trim speed occur at the same rate... seems like magic... but it’s just Engineering... 

 

On a GA... I can put in all 310hp in under a second... there is no flap speed or trim speed that will match that... no matter what the AP’s skill is...

with my thumb on the trim button... and feels like forever... while controlling the yoke...

It feels like forever... because the thumb is pushing on a very expensive switch... that has no really firm click to know it is engaged...

PP thoughts only, not a mechanic... or CFI...

Best regards,

-a-

[Ibra]

4 hours ago, carusoam said:

On a GA... I can put in all 310hp in under a second... there is no flap speed or trim speed that will match that... no matter what the AP’s skill is...

Yes, AP trim design does not seem to go that fast even compared to a pilot in a hurry, the trim wheel on the AP clicks like slowly a snake 

I am not sure about analog AP design for trim speed, how much angle/seconds? angle vs wheel rotation? or vs trim surface rotation? but I am sue one need lot of trim speed

Also, there are yoke forces with 0% power stick force is almost zero while with 100% power it goes huge, you can't have same AP trim speed for both?

Surely in GA we can still fly any speed/power with any trim position (so not Boeing MCAS or Airbus FBW discussions), but I only few two times without trim,

- A vintage that I fly regularly, Druine Turbulent D31, no trim and stick just floats freely inside the cockpit

- One-off as RHS trim guy while LHS did maintenance ferry (electric trim only and 2 dead alternators )

[carusoam]

I have a KAP150... it’s early digital...

It can level off at the top of a climb with little overshoot or oscillation... in smooth air.

early 90s technology...

It has two motors... one for attitude control and one for trim....

I have never seen the trim motor actually working... never thought to watch it that closely... 

PP thoughts...

Best regards,

-a-

[Yetti]

On 3/4/2020 at 7:23 PM, Ibra said:

Hi all,

On two topics "pattern speeds" and "configuration warnings", out of trim flying did come up as source of loss of control accident (LOC), these are highly relevant for Go-Around and EFATO accidents where the sudden change of power makes the aircraft sitting on the "wrong trim"

Has anyone tried slow flying on analog APs on alt & pitch hold with 0% to 100% to 0% power? in landing/clean config? where does the trim go? does the AP disconnect?

I don't have alt hold on M20J with an analog AP (other aircraft where I tried alt hold & power had envelope protection that kicks in)

Just curious, not that I am planning to fly before GA & EFATO on AP 

It would be fun to try, but I think it will disconnect.  A/P probably have some placard about being disconnected during landing and takeoff with the manufacture thinking why would anyone try this.   Probably want to try it up high

[PT20J]

16 hours ago, carusoam said:

early 90s technology...

Actually, according to the BK Installation manual, it was developed in 1980. Mine flies great for 40 year old technology. 

Skip

[Ibra]

2 hours ago, Yetti said:

A/P probably have some placard about being disconnected during landing and takeoff with the manufacture thinking why would anyone try this

I am sure there are limitations on AP pitch as well as the trim but we don't see much of that as we tend to only use them for cruise

On hedging corrections, I recall one day when I tried an AP in NAV mode with load of crosswinds correction near my home base VOR, it did give me a nasty surprise, funny bit as I was reducing power I noticed it was about to give up and 50ms before I press to disconnect myself and take control it did disconnect itself, I still got surprised how the aircraft was thrown at me at 1200ft agl out of trim in clear sky, I nonetheless pulled so hard and only stopped when stall warmer kicked at 100kts 

 

Edited March 6, 2020 by Ibra

[PT20J]

Today I tried an experiment in my 1994 M20J with a KAP 150 autopilot. I set the autopilot on heading hold and altitude hold in cruise and reduced power. The 40 year old autopilot (KAP/KFC 150 was introduced in 1980 according to the installation manual)  held heading and altitude at 65 KIAS. Roll response was a little sluggish but acceptable if I added enough right rudder to keep the ball centered. The airplane was in trim when I disconnected the autopilot. 

Skip

[carusoam]

Skip,

How does it end if the power is reduced more?

Slow descent, at full aft trim?

Wondering out loud,

-a-

[PT20J]

9 minutes ago, carusoam said:

Skip,

How does it end if the power is reduced more?

Slow descent, at full aft trim?

Wondering out loud,

-a-

I didn’t try it but from the way it was acting, I think it would fly it into a stall. I know that the S-TEC on the early SR-22s would. 

Skip
 

[carusoam]

Lack of O2, or excess CO...

Could result in such an AP controlled / Loss of Control situation....

It would be really cool if APs were to take this into account...  (guess that is what auto-land options are...)

MS has lost two planes this way, yet only one pilot... 

One plane was trimmed for the climb... and harshly landed in a field... (the Dan Bass story)

Another crashed East of Atlantic City, engine out, at full cruise speed... (A long body headed to a MAPA safety conference)

Getting the speed down, while still flying is everything.

PP thoughts only, not an AP programmer...

Best regards,

-a-

[cliffy]

Some APs have auto trim systems and some don't 

Many Brittian systems only have an eyeball that shows the pitch out of trim and which way to turn the big wheel on the floor to get rid of the

O of T condition.     Disconnect out of trim and Whoopee  wild ride. 

Have even had autotrim fail in Boeings. Then the entire pitch channel is MEL'd out of service to negate the issue of a disconnect out of trim. 

Just an item to think about- IF you have an AP with autotrim, don't get complacent, make damn sure you are holding the wheel real tight when ever you disconnect the AP just in case the autotrim had failed and you are for real way out of trim. Have had this happen many times over the years 

Always be ready for an out of trim when ever you disconnect.    

[Ibra]

4 hours ago, cliffy said:

Many Brittian systems only have an eyeball that shows the pitch out of trim and which way to turn the big wheel on the floor to get rid of the O of T condition. 

S-TEC50 in an old Cessnas had two lights UP/DN flashing for you to offset AP Out of Trim condition

Seems like healthy set-up vs an AP auto-trim that rolls the trim wheel at 10 turns/second

[PT20J]

The King autopilots have internal checks on the trim system and will disconnect in cases of uncommanded trim operation. 

Here are the two autopilot scenarios that I’ve seen most often get people in trouble. 

Overriding the autopilot
1. The autopilot is set up incorrectly and doesn’t capture altitude or glideslope or (this is really common) without altitude preselect, the pilot gets distracted and climbs through assigned altitude.

2. Pilot reverts to primary training (fly the airplane) and overpowers the autopilot without engaging CWS or disconnecting the autopilot.

3. The autopilot trims against the pilot’s inputs, increasing stick forces.

4. To alleviate the rapidly increasing stick forces, the pilot disengages the autopilot and away we go!

Autopilot in pitch hold, VS hold or ALT hold with insufficient power available.

1. Pilot reduces power to slow down in ALT hold and gets distracted. 

2. Autopilot continues to pitch and trim up until airplane either stalls or autopilot disconnects at low airspeed with nose up trim.

3. Same thing in a climb with a NA engine especially in VS hold. 

Skip