COZY: Strong pitch trim jamming


Marc J. Zeitlin
 

Greg Norman wrote:

All good until I had a friend run the trim to its limit. Now it's jammed again. As advised I have not oiled it and it's clean. For pete's sake does this happen often with these? It's a pia to remove and would be real pissed if this happened in flight.

It's not often, but it can happen - as with many aftermarket stuff for the E-AB world, the design is marginal. When it works, it works reasonably well (although there's too much hysteresis in the system, but given that I've had mine in my plane for 18 years now, and it's still working, I shouldn't look a gift horse in the mouth). I have had it get stuck in flight once - at close to full fwd CG, I ran it into the stop and it got stuck there. A runaway in the elevator TE down (nose up) position is no emergency - it's merely annoying, and requires flying slowly to the nearest airport and maintaining some forward pressure on the stick during landing.

Now, IF you can reach the thing in flight (I sometimes can, if I loosen my shoulder harnesses) you can twist the threaded rod a bit and unstick it.

As James Redmon pointed out, sometimes cranking up the torque level will help with this issue, but not always - sometimes, with the torque set higher, it'll just get itself MORE stuck, rather than having an easier time UNsticking itself.

I'll have to try John Bauer's solution of wrapping safety wire around the last few threads so it can't jam - it seems simple enough.


Vance Atkinson wrote:
 
Yes, if it stuck in full up or down in flight you would be for an "E" coupon ride.

Full TE up (nose down) is far worse than the opposite, as it would require a lot of back pressure on the stick continually to stay in level flight, and even more to land slowly. But this would only happen in a trim runaway - there's no way that the pilot would ever COMMAND full nose down trim (in a COZY MKIV with an O-360, or even an O-540 - maybe in an O-540 Berkut). I don't know about GRT or AFS, but Garmin G3X and Dynon Skyview have trim time limits in their system to prevent full runaways.

It would be nice if any of the electric trim systems had limit switches (and some of the Davenport trim system electric actuators do) in them to ensure that they couldn't jam at the end of throw. I've thought about installing separate limit switches for my Strong system, but...

 You must have an emergency stop in your system somewhere.  I had two in my cozy
 
1. emergency disconnect in which the pilot pulls a "T" pin out (by his left knee) and that disconnects the trim system from the elevator system.

This is only necessary because (with all due respect, and we've talked about this a few times before on list as a warning) the Atkinson trim system as published in the COZY newsletters has the ability to not only increase the trim forces to very high levels, but will also jam the elevator motion so that full range of motion is not available if at one extent or the other. I've never seen that with any other electric trim system.

I've fixed this on three canards (a COZY III, Aerocanard and COZY MKIV) by installing collars on the spring cartridge so that they can only move far enough in the nose down trim direction so that full nose up elevator is still available. There's no reason to disconnect the trim system as long as it can't jam the elevator.

2. emergency electrical switch which shuts off all power to the trim system servo.

This is suboptimal because by the time you recognize what's going on (trim runaway), find the "trim power" switch that you put in a non-obvious location because you NEVER use it it's too late. The trim "time" limit methodology, whereby the trim can't run for more than <x> seconds without shutting off, is, while not perfect, better, as it will never let you get far off of the trim speed without conscious effort (multiple button pushes).

The Strong trim system has always been weak as a trim system in my opinion.

It CANNOT jam the elevator, so in that sense, it's a safe system. It has its faults - it can get gunked up and need cleaning (although I've only had to have mine serviced once in 18 years) and it has the aforementioned hysteresis that can make it a bit hard to trim at high speeds unless you've got a pulse width modulator linked to airspeed (many EFIS's have this, too) making it move more slowly. But all in all, especially for the price, it was a decent system.
 
The main problem is screw drive mechanism.  You need a more reliable screw/ball /drive motor.

Actually, the clutch is the only real issue - if that thing just wouldn't jam itself, it would be fine, if not perfect.

You should email Bernie Siu   <siu1.brn@...> who has made a really nice one.

That he has.

No trim system is perfect in our planes - they all need adjustment and tweaking for a particular aircraft - the Davenport systems certainly do, and so do the spring cartridge versions. Even the manual trim systems can need tweaking - I've had to replace trim springs on LE's to get them to trim to both fast and slow speeds, and I've had to move the neutral point of one Davenport type trim system implemented with metal spring rods in order to get the plane to be trimmable in flight.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace


Greg Norman
 

I wire brushed the threaded rod even though it doesn't need it, chased it with a thread die. Tried light oil. No joy. Best I get to keep it from racheting is dialed up to 14. Likely will not need full travel at once but the threaded rod gets hot. 
I'd remove the tube end and chace that with a tap but it looks like a pressed fit - possibly why it's tight. 
So now two issues with this thing and it hasn't left the ground. 
Alex Strong website gone, no call answer, sent an email. Is anyone still making them?

Greg Norman

On Sun, Jul 4, 2021, 12:55 AM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Greg Norman wrote:

All good until I had a friend run the trim to its limit. Now it's jammed again. As advised I have not oiled it and it's clean. For pete's sake does this happen often with these? It's a pia to remove and would be real pissed if this happened in flight.

It's not often, but it can happen - as with many aftermarket stuff for the E-AB world, the design is marginal. When it works, it works reasonably well (although there's too much hysteresis in the system, but given that I've had mine in my plane for 18 years now, and it's still working, I shouldn't look a gift horse in the mouth). I have had it get stuck in flight once - at close to full fwd CG, I ran it into the stop and it got stuck there. A runaway in the elevator TE down (nose up) position is no emergency - it's merely annoying, and requires flying slowly to the nearest airport and maintaining some forward pressure on the stick during landing.

Now, IF you can reach the thing in flight (I sometimes can, if I loosen my shoulder harnesses) you can twist the threaded rod a bit and unstick it.

As James Redmon pointed out, sometimes cranking up the torque level will help with this issue, but not always - sometimes, with the torque set higher, it'll just get itself MORE stuck, rather than having an easier time UNsticking itself.

I'll have to try John Bauer's solution of wrapping safety wire around the last few threads so it can't jam - it seems simple enough.


Vance Atkinson wrote:
 
Yes, if it stuck in full up or down in flight you would be for an "E" coupon ride.

Full TE up (nose down) is far worse than the opposite, as it would require a lot of back pressure on the stick continually to stay in level flight, and even more to land slowly. But this would only happen in a trim runaway - there's no way that the pilot would ever COMMAND full nose down trim (in a COZY MKIV with an O-360, or even an O-540 - maybe in an O-540 Berkut). I don't know about GRT or AFS, but Garmin G3X and Dynon Skyview have trim time limits in their system to prevent full runaways.

It would be nice if any of the electric trim systems had limit switches (and some of the Davenport trim system electric actuators do) in them to ensure that they couldn't jam at the end of throw. I've thought about installing separate limit switches for my Strong system, but...

 You must have an emergency stop in your system somewhere.  I had two in my cozy
 
1. emergency disconnect in which the pilot pulls a "T" pin out (by his left knee) and that disconnects the trim system from the elevator system.

This is only necessary because (with all due respect, and we've talked about this a few times before on list as a warning) the Atkinson trim system as published in the COZY newsletters has the ability to not only increase the trim forces to very high levels, but will also jam the elevator motion so that full range of motion is not available if at one extent or the other. I've never seen that with any other electric trim system.

I've fixed this on three canards (a COZY III, Aerocanard and COZY MKIV) by installing collars on the spring cartridge so that they can only move far enough in the nose down trim direction so that full nose up elevator is still available. There's no reason to disconnect the trim system as long as it can't jam the elevator.

2. emergency electrical switch which shuts off all power to the trim system servo.

This is suboptimal because by the time you recognize what's going on (trim runaway), find the "trim power" switch that you put in a non-obvious location because you NEVER use it it's too late. The trim "time" limit methodology, whereby the trim can't run for more than <x> seconds without shutting off, is, while not perfect, better, as it will never let you get far off of the trim speed without conscious effort (multiple button pushes).

The Strong trim system has always been weak as a trim system in my opinion.

It CANNOT jam the elevator, so in that sense, it's a safe system. It has its faults - it can get gunked up and need cleaning (although I've only had to have mine serviced once in 18 years) and it has the aforementioned hysteresis that can make it a bit hard to trim at high speeds unless you've got a pulse width modulator linked to airspeed (many EFIS's have this, too) making it move more slowly. But all in all, especially for the price, it was a decent system.
 
The main problem is screw drive mechanism.  You need a more reliable screw/ball /drive motor.

Actually, the clutch is the only real issue - if that thing just wouldn't jam itself, it would be fine, if not perfect.

You should email Bernie Siu   <siu1.brn@...> who has made a really nice one.

That he has.

No trim system is perfect in our planes - they all need adjustment and tweaking for a particular aircraft - the Davenport systems certainly do, and so do the spring cartridge versions. Even the manual trim systems can need tweaking - I've had to replace trim springs on LE's to get them to trim to both fast and slow speeds, and I've had to move the neutral point of one Davenport type trim system implemented with metal spring rods in order to get the plane to be trimmable in flight.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace


Bulent Aliev
 

Greg,
You should chase the female part also with a tap. It is plastic and shrinks over the years. Mine needed it, and worked fine after that. 
On mine the square shaft was rusted too.
But I was glad to get rid of the Strong unit and install the Davenport fiberglass one.


On Mon, Jul 5, 2021 at 4:06 PM Greg Norman <gnorm76@...> wrote:
I wire brushed the threaded rod even though it doesn't need it, chased it with a thread die. Tried light oil. No joy. Best I get to keep it from racheting is dialed up to 14. Likely will not need full travel at once but the threaded rod gets hot. 
I'd remove the tube end and chace that with a tap but it looks like a pressed fit - possibly why it's tight. 
So now two issues with this thing and it hasn't left the ground. 
Alex Strong website gone, no call answer, sent an email. Is anyone still making them?

Greg Norman

On Sun, Jul 4, 2021, 12:55 AM Marc J. Zeitlin <marc.j.zeitlin@...> wrote:
Greg Norman wrote:

All good until I had a friend run the trim to its limit. Now it's jammed again. As advised I have not oiled it and it's clean. For pete's sake does this happen often with these? It's a pia to remove and would be real pissed if this happened in flight.

It's not often, but it can happen - as with many aftermarket stuff for the E-AB world, the design is marginal. When it works, it works reasonably well (although there's too much hysteresis in the system, but given that I've had mine in my plane for 18 years now, and it's still working, I shouldn't look a gift horse in the mouth). I have had it get stuck in flight once - at close to full fwd CG, I ran it into the stop and it got stuck there. A runaway in the elevator TE down (nose up) position is no emergency - it's merely annoying, and requires flying slowly to the nearest airport and maintaining some forward pressure on the stick during landing.

Now, IF you can reach the thing in flight (I sometimes can, if I loosen my shoulder harnesses) you can twist the threaded rod a bit and unstick it.

As James Redmon pointed out, sometimes cranking up the torque level will help with this issue, but not always - sometimes, with the torque set higher, it'll just get itself MORE stuck, rather than having an easier time UNsticking itself.

I'll have to try John Bauer's solution of wrapping safety wire around the last few threads so it can't jam - it seems simple enough.


Vance Atkinson wrote:
 
Yes, if it stuck in full up or down in flight you would be for an "E" coupon ride.

Full TE up (nose down) is far worse than the opposite, as it would require a lot of back pressure on the stick continually to stay in level flight, and even more to land slowly. But this would only happen in a trim runaway - there's no way that the pilot would ever COMMAND full nose down trim (in a COZY MKIV with an O-360, or even an O-540 - maybe in an O-540 Berkut). I don't know about GRT or AFS, but Garmin G3X and Dynon Skyview have trim time limits in their system to prevent full runaways.

It would be nice if any of the electric trim systems had limit switches (and some of the Davenport trim system electric actuators do) in them to ensure that they couldn't jam at the end of throw. I've thought about installing separate limit switches for my Strong system, but...

 You must have an emergency stop in your system somewhere.  I had two in my cozy
 
1. emergency disconnect in which the pilot pulls a "T" pin out (by his left knee) and that disconnects the trim system from the elevator system.

This is only necessary because (with all due respect, and we've talked about this a few times before on list as a warning) the Atkinson trim system as published in the COZY newsletters has the ability to not only increase the trim forces to very high levels, but will also jam the elevator motion so that full range of motion is not available if at one extent or the other. I've never seen that with any other electric trim system.

I've fixed this on three canards (a COZY III, Aerocanard and COZY MKIV) by installing collars on the spring cartridge so that they can only move far enough in the nose down trim direction so that full nose up elevator is still available. There's no reason to disconnect the trim system as long as it can't jam the elevator.

2. emergency electrical switch which shuts off all power to the trim system servo.

This is suboptimal because by the time you recognize what's going on (trim runaway), find the "trim power" switch that you put in a non-obvious location because you NEVER use it it's too late. The trim "time" limit methodology, whereby the trim can't run for more than <x> seconds without shutting off, is, while not perfect, better, as it will never let you get far off of the trim speed without conscious effort (multiple button pushes).

The Strong trim system has always been weak as a trim system in my opinion.

It CANNOT jam the elevator, so in that sense, it's a safe system. It has its faults - it can get gunked up and need cleaning (although I've only had to have mine serviced once in 18 years) and it has the aforementioned hysteresis that can make it a bit hard to trim at high speeds unless you've got a pulse width modulator linked to airspeed (many EFIS's have this, too) making it move more slowly. But all in all, especially for the price, it was a decent system.
 
The main problem is screw drive mechanism.  You need a more reliable screw/ball /drive motor.

Actually, the clutch is the only real issue - if that thing just wouldn't jam itself, it would be fine, if not perfect.

You should email Bernie Siu   <siu1.brn@...> who has made a really nice one.

That he has.

No trim system is perfect in our planes - they all need adjustment and tweaking for a particular aircraft - the Davenport systems certainly do, and so do the spring cartridge versions. Even the manual trim systems can need tweaking - I've had to replace trim springs on LE's to get them to trim to both fast and slow speeds, and I've had to move the neutral point of one Davenport type trim system implemented with metal spring rods in order to get the plane to be trimmable in flight.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2021                     Burnside Aerospace

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