Electric Trim

[ltdoyle]

I recently purchased a nicely equipped 1977 M20J.  It has a 430 coupled to a STEC-30 w/alt hold and it makes a great cross country IFR machine.  The one thing I do not have

is an electric trim.  I have learned that this plane likes LOTS of trim for taking off, landing, etc.  (on my approach to landing I am close to full nose up!)  Any suggestions or ideas on what it would

take  to add electric trim?

[Piloto]

I am surprised the STEC-30 does not has trim servo. Without the trim servo the plane could be trim up while the elevator is trying nose down to maintain altitude. This creates a cross control that induces drag and slow down the plane. It also creates the sudden pitch up/down attitude when the A/P is disengaged. The trim and elevator servos work in conjunction to eliminate the above. Check with STEC to see if there is a trim servo option.

José

[markejackson02]

I believe the STEC system has a TRIM light for manually trimmed planes.  It tells you to trim up or down to relieve pressure from the servo.

[M20S Driver]

3 minutes ago, markejackson02 said:

I believe the STEC system has a TRIM light for manually trimmed planes.  It tells you to trim up or down to relieve pressure from the servo.

I have an Stec 30 with electric trim.  There is a light on the autopilot (turn coordinator) that tells me to trim up or down.  I use trim switch on the yoke to correct it.

I don't know the cost to add electric trim but I would be willing to spend a couple of grands to have it.

Driver

[jetdriven]

1 hour ago, markejackson02 said:

I believe the STEC system has a TRIM light for manually trimmed planes.  It tells you to trim up or down to relieve pressure from the servo.

And a beeper that starts out solid tone, then intermittent, to get your attention. ON the J model, its about a 5-7 knots difference between trimmed speed and actual, to trigger the beeper. it rarely goes off in cruise.

[1964-M20E]

I have the STEC 30 with ALT hole and no electric trim.  If you are really out of trim the STEC 30 will tell you it is working harder than it needs to.

My flying routine is once I am at altitude I do a rough trim for level fight let it settle for a minute then engage the alt hold and finish twisting the engine knobs for desired RPM and fuel burn rate.  Then several times I turn the alt hold off and trim that for level flight.  It does not take much to get it perfectly in trim this way.  I will even do it through out the flight to see if less fuel has affected the trim and usually not much at all.

Of course the OP was what would it take to add the electric trim and that I do not know.  I have never had an airplane with electric trim and for small ships I do not see the need for it. JMHO   I do not know how his ship is configured but before I would spend $$AMUs on electric trim I would evaluate all other niceties that I would want  and see which one floats to the top.  He has a J so speed mods are pretty much out maybe  a new radio?

I have flown helicopters with electric cyclic trim for that ship the cyclic trim is very useful.

[kevinw]

I have the Century 21 AP with the S-Tec 60 PSS (Pitch Stabilization System). While I have electric trim it didn't work with the AP so I had to manually trim in flight. This wasn't a big deal in level flight; it was a little more of a problem when shooting approaches because as soon as I intercepted the glideslope it went significantly out of trim. With my system a light would come on indicating trim up or down and I learned to anticipate it on approaches. However, I finally broke down about a year and a half ago and added the S-Tec autotrim. It was an option the previous owner could've added when he installed the PSS but he didn't do it. It works very well and it replaces the entire trim switch on the yoke. I'm sure if you contact S-Tec you can add electric trim to your AP. Here's the bad news, like everything in aviation it doesn't come cheap. It was a little north of $6K to add this to mine but I have no regrets. 

[Piloto]

The auto trim is a must if you are coupling the A/P to the ILS (GS/LOC). Otherwise when you reach DH and disengage the AP you may find the plane pitching up or down suddenly. With auto trim you can gradually reduce power as you approach DH and the AP will trim the plane nicely so when you disengage you are already trimmed for the short approach. The trim switch on the yoke is very handy for gradually pitching up as you flare.

José

[Andy95W]

The original poster said he has an S-TEC 30.

Electric trim, auto trim, and glide slope coupling are not features of this autopilot, and there is not a path available to make it so.

[Marauder]

The auto trim is a must if you are coupling the A/P to the ILS (GS/LOC). Otherwise when you reach DH and disengage the AP you may find the plane pitching up or down suddenly. With auto trim you can gradually reduce power as you approach DH and the AP will trim the plane nicely so when you disengage you are already trimmed for the short approach. The trim switch on the yoke is very handy for gradually pitching up as you flare.

José

I have full autotrim on my plane and it does as José mentions. I can disengage at any point and the plane is trimmed.

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[carusoam]

Odd thing...

The Microsoft Flight Simulator for the Bravo fails exactly the way Piloto describes.  When you Turn off the AP near the ground, a pitch up or down can really ruin the ILS approach.

This would make for a terrible experience in real IMC near the ground.

Best regards,

-a-

[jetdriven]

2 hours ago, Piloto said:

The auto trim is a must if you are coupling the A/P to the ILS (GS/LOC). Otherwise when you reach DH and disengage the AP you may find the plane pitching up or down suddenly. With auto trim you can gradually reduce power as you approach DH and the AP will trim the plane nicely so when you disengage you are already trimmed for the short approach. The trim switch on the yoke is very handy for gradually pitching up as you flare.

José

I am strongly against trimming in the flare.  Besides being horrible technique, it frequently kills pilots when they firewall it for go-around and the plane rears up and stalls.   Then they try to compensate for one bad technique for another, by only adding partial power during a go-around.  

[N201MKTurbo]

18 minutes ago, jetdriven said:

I am strongly against trimming in the flare.  Besides being horrible technique, it frequently kills pilots when they firewall it for go-around and the plane rears up and stalls.   Then they try to compensate for one bad technique for another, by only adding partial power during a go-around.  

Just because it is not your technique, does that make it a bad technique?

[Bob_Belville]

I have what I think is a common combination. The STEC 50 has no access to pitch trim. It does "feel" the pressure that it is holding on the elevator to maintain ALT. If that pressure is great or prolonged it provides a signal light to advise the pilot to trim the pitch. 

I also have STEC electric trim. Model ST-155, STC SA5279SW-D It is completely independent of the A/P. When activated it turns the manual trim wheel.

FWIW. I have a long time ingrained habit: while in cruise with ALT engaged I will release ALT for a few seconds to see if the pitch trim is neutral. If the plane climbs or descends I will tweak the pitch trim and reengage ALT. 

I do not see that the current owners of the STEC stuff still offers the electric trim add on. 

http://genesys-aerosystems.com/

[gsxrpilot]

1 hour ago, jetdriven said:

I am strongly against trimming in the flare.  Besides being horrible technique, it frequently kills pilots when they firewall it for go-around and the plane rears up and stalls.   Then they try to compensate for one bad technique for another, by only adding partial power during a go-around.  

Speaking of my C...  With full up trim, it will almost land it's self. And I've tested go arounds with the trim in that full up position. It was a non-event. Of course I'm very actively flying the airplane and a fair amount of forward pressure is required.  But even with full power, I was able to hold correct climb attitude while I spin the trim wheel back into take-off position.  No big deal...

[DC_Mooniac]

9 minutes ago, gsxrpilot said:

 With full up trim, it will almost land it's self.

Same with my J.  My best landings are always with full up trim.  Never had issues with go arounds.

[Marauder]

I have what I think is a common combination. The STEC 50 has no access to pitch trim. It does "feel" the pressure that it is holding on the elevator to maintain ALT. If that pressure is great or prolonged it provides a signal light to advise the pilot to trim the pitch. 

I also have STEC electric trim. Model ST-155, STC SA5279SW-D It is completely independent of the A/P. When activated it turns the manual trim wheel.

FWIW. I have a long time ingrained habit: while in cruise with ALT engaged I will release ALT for a few seconds to see if the pitch trim is neutral. If the plane climbs or descends I will tweak the pitch trim and reengage ALT. 

I do not see that the current owners of the STEC stuff still offers the electric trim add on. 

http://genesys-aerosystems.com/

Bob -- you ever note where the trim is set when the AP is holding it trimmed? Here is a picture of mine with the AP engaged and the autotrim trimmed. I do not get an out of trim indication, but do think it is sitting pretty nose down. What do you think?

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[Danb]

Chris when mine is in cruise and properly trimmed my Bravo only shows a little nose down must be difference in the long body?

[Bob_Belville]

29 minutes ago, Marauder said:

Bob -- you ever note where the trim is set when the AP is holding it trimmed? Here is a picture of mine with the AP engaged and the autotrim trimmed. I do not get an out of trim indication, but do think it is sitting pretty nose down. What do you think?

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Yeah, seems to be. But the trim indicator linkage, at least in my older E is, what shall I say, Mickey Mouse?. The lawn mower throttle cable ends with a Z bend the goes through a hole in the piloting indicator that's mounted to the plastic wheel well cover. Start multiplying the slop and I estimate the accuracy as +/- 20%.

And of course neutral pitch trim will vary with CG, right? Looks like to me you might have a couple of your girls in the back with that trim setting.  

This pic was not taken in cruise - I do not recall ever taking one of that area in flight. The trim is set to TO position. (FWIW, landing is normally trimmed full nose up. I think Mike Elliott soiled his britches when he told me to "go around" on short final. In my little E I can, and do, apply full throttle, dump flaps and muscle the nose down while trimming pitch. With hydraulic flaps It is not worth it to try to bleed off to some intermediate position while engage in serious aviating, OSISTM after 2500 hours in this model.) 

[Marauder]

29 minutes ago, Marauder said: Bob -- you ever note where the trim is set when the AP is holding it trimmed? Here is a picture of mine with the AP engaged and the autotrim trimmed. I do not get an out of trim indication, but do think it is sitting pretty nose down. What do you think?

Sent from my iPad using Tapatalk

Yeah, seems to be. But the trim indicator linkage, at least in my older E is, what shall I say, Mickey Mouse?. The lawn mower throttle cable ends with a Z bend the goes through a hole in the piloting indicator that's mounted to the plastic wheel well cover. Start multiplying the slop and I estimate the accuracy as +/- 20%.

And of course neutral pitch trim will vary with CG, right? Looks like to me you might have a couple of your girls in the back with that trim setting.  

This pic was not taken in cruise - I do not recall ever taking one of that area in flight. The trim is set to TO position. (FWIW, landing is normally trimmed full nose up. I think Mike Elliott soiled his britches when he told me to "go around" on short final. In my little E I can, and do, apply full throttle, dump flaps and muscle the nose down while trimming pitch. With hydraulic flaps It is not worth it to try to bleed off to some intermediate position while engage in serious aviating, OSISTM after 2500 hours in this model.) 

The trim on my F is different. I think there is something attached to the jackscrew that moves the indicator. I chase confirmed that I have less than a half turn before the trim is pegged full nose down. It is the same if I am hand flying. Lots of nose down.

I never really looked at it in flight because, like most, I trim to remove pressure and I didn't care where it was set.

I had the control rods going to the tail painted a couple of annuals ago. I wonder if they messed with the trim.

I should probably ask people who have the 1975 F model, like Guitarman and I think Yetti.

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[Marauder]

I will say I was able to determine the problem with my car nosing down too much while braking.

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[Bob_Belville]

4 minutes ago, Marauder said:

The trim on my F is different. I think there is something attached to the jackscrew that moves the indicator. I chase confirmed that I have less than a half turn before the trim is pegged full nose down. It is the same if I am hand flying. Lots of nose down.

I never really looked at it in flight because, like most, I trim to remove pressure and I didn't care where it was set.

I had the control rods going to the tail painted a couple of annuals ago. I wonder if they messed with the trim.

I should probably ask people who have the 1975 F model, like Guitarman and I think Yetti.

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I wonder if your indicator matches the full range of the actual movement of the tailfeathers? Does the indicator go to the full up position when the trim itself bottoms out? Is the take off indication where you trim for take off?

The next time the belly is off verify that the indicator extremes match the trim mechanism stops. It's easy to adjust the indicator unless an end has broken off where it had been bent which made the cable too short but they hooked it up anyway. (You might guess how I would come to know something like that.) 

[Bob_Belville]

10 minutes ago, Marauder said:

I will say I was able to determine the problem with my car nosing down too much while braking.

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I note that FaceBook has recently add a "don't like" choice to their "like". I'm thinking MS needs to do a poll re adding that feature... 

[Marauder]

10 minutes ago, Marauder said: I will say I was able to determine the problem with my car nosing down too much while braking.

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I note that FaceBook has recently add a "don't like" choice to their "like". I'm thinking MS needs to do a poll re adding that feature... 

Be careful what you wish for! If you go negative, "they" might eject you from the forum.

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[Marauder]

4 minutes ago, Marauder said: The trim on my F is different. I think there is something attached to the jackscrew that moves the indicator. I chase confirmed that I have less than a half turn before the trim is pegged full nose down. It is the same if I am hand flying. Lots of nose down.

I never really looked at it in flight because, like most, I trim to remove pressure and I didn't care where it was set.

I had the control rods going to the tail painted a couple of annuals ago. I wonder if they messed with the trim.

I should probably ask people who have the 1975 F model, like Guitarman and I think Yetti.

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I wonder if your indicator matches the full range of the actual movement of the tailfeathers? Does the indicator go to the full up position when the trim itself bottoms out? Is the take off indication where you trim for take off?

The next time the belly is off verify that the indicator extremes match the trim mechanism stops. It's easy to adjust the indicator unless an end has broken off where it had been bent which made the cable too short but they hooked it up anyway. (You might guess how I would come to know something like that.) 

It think it does go full up and will indicate so. I move it to full up when I put my panel guard on. Strange issue. But I got to think it can't be that close to nose down.

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