One of my recent LSA pilots flew to FL and went for a Tecnam ride. Really liked the airplane but he said something that got my attention.
The Tecnam had stick buttons for elevator trim. On top of the stick.
He was used to the cub where he could rest his hand on the stick top.
During a landing they went around the the airplane pitched up. He said he had the stick well forward near the stop and the airplane continued up. The instructor told him to push the nose down and he replied he already was and getting near full down. The instructor said to get off the trim button and re trimmed the airplane.
Nothing was wrong other than he was accidently pushing the button
Since the feds probably never thought of LSA as having electric trim here are some things that were required for certification on normal category airplanes.
No audible warning. In the certified world a lot of airplanes have a tone that sounds when the electric trim motor runs. This gives you a clue what is going on or if the autopilot is trimming for some reason.
Most certified airplanes need you to push an arming switch to activate the trim. You push the center of the rocker switch down and then either for or aft for up or down trim. This eliminates accidental trimming.
The trim motor is geared very slow to allow some reaction time and make fine tuning the trim easier. Not sure what speed the new LSA trim servos operate.
The electric trim in a certified airplane is backed up by a trim wheel. The electric trim motor has a clutch assembly so you could grab the wheel and over power the trim motor. hit the emergency cutoff and then retrim manually.
Most LSA with electric trim have no manual backup.
The scenario that scares me is you are flying along and hit the trim. The button sticks and it runs full up or down. Without a emergency trim disconnect button it takes a while to figure out what the problem is and also find the right circuit breaker to cut the trim off. Depending on how much trim power your airplane has is how much of a problem you will have.
Try applying trim deflection at a safe altitude and see how much push or pull it takes to hold it. It may surprise you.
You can loop a Citabria with elevator trim.
All failures listed above have happened to me. Including MAC electric trim runaway in a Kitfox. Bad rocker switch. also bad tab indicators which showed different trim settings that where the trim was actually at.
Now every flight during runup I set the trim to takeoff and look out the door or back window to see if the tab agrees with the indicator.
Electric elevator trim
Moderator: drseti
Re: Electric elevator trim
You never flew a Cirrus. It has a trim switch int the stick that works just like the Tecnam. It has not manual backup. It is so fast that trimming is very difficult. It is certified. I much prefered the Tecnam trim which is slower making it possible to actually trim for hands off flight.Cub flyer wrote:The electric trim in a certified airplane is backed up by a trim wheel. The electric trim motor has a clutch assembly so you could grab the wheel and over power the trim motor. hit the emergency cutoff and then retrim manually.
Ahh progress.
Did the Cirrus have a beeper or indicator when the trim motor ran?
What I flew with the beeper was part 25 certified. The autopilot could retrim so that may be a requirement with that system.
You landed the airplane with the trim. Came over the end of the runway closed the throttle and held the trim nose up. Beeeeeeeeeeeeeep and the main wheels touched. the engines were canted up for the shockwave and it landed just like a Lake amphibian. But that was an odd airplane. even the bigger ones can have strange characteristics.
All others you had to push an arming button down first and then the rock the switch forward or back. Piper, Cessna, Beech, all the same.
The Part 25 airplane did not have a mechanical backup wheel but did have a trim cutoff button and a auxiliary trim control switch.
One problem with that system was in Aux mode the limit switches were bypassed so you could run the jackscrew to the mechanical limits. Watch the indicator carefully.
The indicator had marks for percent of wing chord so you figured your CG and then set the trim for that location. Worked well and was always in proper trim for takeoff with that loading.
It would be easy to setup something like that for a LSA with the W/B calculator in the Garmin 296 units and then trim for whatever number it spits out.
But that would be silly on a LSA. the Cub has two marks "dual and solo"
I did a few takeoffs and found where it should be trimmed to climb at VY (55 mph). Wrote in marker on the aluminum plate.
Works great. From cruise to landing takes no more than 3 cranks in either direction. Dual or solo. Big people use the L in dual or O in ) solo for their mark. Small ones use the D in dual and S in solo.
I just changed to a metal prop so I'll have to redo the marks for the extra 12 lbs in the nose.
Old Cub is a precision instrument. very narrow speed and Angle of attack range for best performance.
Did the Cirrus have a beeper or indicator when the trim motor ran?
What I flew with the beeper was part 25 certified. The autopilot could retrim so that may be a requirement with that system.
You landed the airplane with the trim. Came over the end of the runway closed the throttle and held the trim nose up. Beeeeeeeeeeeeeep and the main wheels touched. the engines were canted up for the shockwave and it landed just like a Lake amphibian. But that was an odd airplane. even the bigger ones can have strange characteristics.
All others you had to push an arming button down first and then the rock the switch forward or back. Piper, Cessna, Beech, all the same.
The Part 25 airplane did not have a mechanical backup wheel but did have a trim cutoff button and a auxiliary trim control switch.
One problem with that system was in Aux mode the limit switches were bypassed so you could run the jackscrew to the mechanical limits. Watch the indicator carefully.
The indicator had marks for percent of wing chord so you figured your CG and then set the trim for that location. Worked well and was always in proper trim for takeoff with that loading.
It would be easy to setup something like that for a LSA with the W/B calculator in the Garmin 296 units and then trim for whatever number it spits out.
But that would be silly on a LSA. the Cub has two marks "dual and solo"
I did a few takeoffs and found where it should be trimmed to climb at VY (55 mph). Wrote in marker on the aluminum plate.
Works great. From cruise to landing takes no more than 3 cranks in either direction. Dual or solo. Big people use the L in dual or O in ) solo for their mark. Small ones use the D in dual and S in solo.
I just changed to a metal prop so I'll have to redo the marks for the extra 12 lbs in the nose.
Old Cub is a precision instrument. very narrow speed and Angle of attack range for best performance.
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CharlieTango
- Posts: 1000
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- Location: Mammoth Lakes, California
I fly both Tecnams and a Cessna 182RG. The Cessna 182 has trim on the top of the yoke. It does not have an audible warning. It is so fast, that 3 seconds will significantly put the plane out of trim. 5 seconds and you can't fly it.
As for the Tecnam, there is a switch that switches the trim power from pilot to co-pilot. This is a great training aid when teaching someone that tends to accidently hit the trim.
Finally, I can have the Tecnam will full trim in either direction and still fly the plane. There are a lot of forces but not enough to overpower a person.
I think good electric trim is an essential for any prolonged straight and level flight. Sky Arrow, Sport Cruiser, and Tecnam all have nice trim options that make the planes easily to level out and enjoy the ride.
As for the Tecnam, there is a switch that switches the trim power from pilot to co-pilot. This is a great training aid when teaching someone that tends to accidently hit the trim.
Finally, I can have the Tecnam will full trim in either direction and still fly the plane. There are a lot of forces but not enough to overpower a person.
I think good electric trim is an essential for any prolonged straight and level flight. Sky Arrow, Sport Cruiser, and Tecnam all have nice trim options that make the planes easily to level out and enjoy the ride.
No indication of any kind.Cub flyer wrote: Did the Cirrus have a beeper or indicator when the trim motor ran?
No arming button. You press it and it moved. Between the PTT, autopilot disable, elevator trim, and aileron trim buttons on the stick there was no place at the top where pressure would not activate or deactivate something.All others you had to push an arming button down first and then the rock the switch forward or back. Piper, Cessna, Beech, all the same.
Not on the Cirrus. All you could do was pull the circuit breaker and then you had no trim.The Part 25 airplane did not have a mechanical backup wheel but did have a trim cutoff button and a auxiliary trim control switch.
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CharlieTango
- Posts: 1000
- Joined: Sat Jun 10, 2006 10:04 am
- Location: Mammoth Lakes, California
gee art, hope your thumb will be ok.
i find the stabilator trim works best with a fingertip as opposed to my thumb.
it is hard to envision the need for all of this trimming in turbulence. you must be chasing the trim up and down, if it is too turbulent to get it perfect, pick a good compromise and let the servo work a little.
i find the stabilator trim works best with a fingertip as opposed to my thumb.
it is hard to envision the need for all of this trimming in turbulence. you must be chasing the trim up and down, if it is too turbulent to get it perfect, pick a good compromise and let the servo work a little.
The trouble with that is after a short period of time it starts with the verbal announcements and I eventually will disengage the autopilot to protect the servos. I have seen an autopilot burn out on a 172 in heavy turbulence from an overheated servo.CharlieTango wrote:it is hard to envision the need for all of this trimming in turbulence. you must be chasing the trim up and down, if it is too turbulent to get it perfect, pick a good compromise and let the servo work a little.
Glad the Tecnam is ok with full trim pressure. I still want to fly one when I can get down near Baltimore.
There may be some specs somewhere in the LSA requirements for electric trim speeds and such.
If the trim light is varying between up and down during turbulence while on autopilot then try slowing down. It might help. Or just turn it off and take the lumps.
Most of the low cost ones can't hold altitude in even minor low level turbulence.
I have not flown any LSA with an autopilot. Never thought of needing one but they are nice for long trips. Bigger airplanes yes and I was remembering the out of trim pressures and wondering what an LSA pilot might get lured into.
There may be some specs somewhere in the LSA requirements for electric trim speeds and such.
If the trim light is varying between up and down during turbulence while on autopilot then try slowing down. It might help. Or just turn it off and take the lumps.
Most of the low cost ones can't hold altitude in even minor low level turbulence.
I have not flown any LSA with an autopilot. Never thought of needing one but they are nice for long trips. Bigger airplanes yes and I was remembering the out of trim pressures and wondering what an LSA pilot might get lured into.
I'm a little confused. I don't think the trim servos and AP servos have anything to do with each other, although an AP may manage both of them.
I'm gonna climb out on a limb here, based on my brief experience home building an LSA plane:
I think most if not all LSA's use the Ray Allen trim servos - dinky little plastic things about 70mm square and 20mm deep with a control arm that moves about 3/4 in linearly, not in an arc. It connects directly to the trim tab via a short threaded rod with a clevis on each end. There is zero cabling involved here BTW, and no way to hook any in.
The AP servos are much bigger and more powerful and hook into the control linkages (torque tube or cables) of the control surfaces.
I assume, but don't know that the trim servos on a Cessna are also completely separate from the control surface servos. Another guess, the trim servo that works with the trim control wheel just has a capstan that the trim control cable goes around.
I'd be glad to hear any info counter to this as I'm going to be installing an AP at some point and want to understand the system as well as possible.
Ron
I'm gonna climb out on a limb here, based on my brief experience home building an LSA plane:
I think most if not all LSA's use the Ray Allen trim servos - dinky little plastic things about 70mm square and 20mm deep with a control arm that moves about 3/4 in linearly, not in an arc. It connects directly to the trim tab via a short threaded rod with a clevis on each end. There is zero cabling involved here BTW, and no way to hook any in.
The AP servos are much bigger and more powerful and hook into the control linkages (torque tube or cables) of the control surfaces.
I assume, but don't know that the trim servos on a Cessna are also completely separate from the control surface servos. Another guess, the trim servo that works with the trim control wheel just has a capstan that the trim control cable goes around.
I'd be glad to hear any info counter to this as I'm going to be installing an AP at some point and want to understand the system as well as possible.
Ron
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CharlieTango
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the trim servo is small because it moves to a new location and is done also it takes less force to move a trim tab than an elevator.
the problem is the same with manual or electric trim. if your ap is set to climb, cruise or descend and your trim isn't in perfect agreement the ap servo will have to hold pressure.
in thermals or other turbulence your ap might be fighting the trim off and on.
if the ap is holding pressure it is fighting the trim tab not the trim servo
the problem is the same with manual or electric trim. if your ap is set to climb, cruise or descend and your trim isn't in perfect agreement the ap servo will have to hold pressure.
in thermals or other turbulence your ap might be fighting the trim off and on.
if the ap is holding pressure it is fighting the trim tab not the trim servo
dynon
I see in the newest Sport Aviation there is an ad for Dynon having their own autopilot and servo.
Also Tru Trak has a flight director function with some kind of an approach selection.
Not long ago there were some coreless motor servos used with I believe a Chelton autopilot and hooked to the elevator trim. I looked at this system for my Apache but decided not because of the trim crank whirling around all the time. I don't think the elevator trim system was made with that kind of constant use in mind.
In a Cessna the electric trim motor turns the trim system and also the manual wheel in the cockpit. The autopilot servo has a capstan with a bridle cable wrapped around and it moves the elevator cable directly.
Both are not connected but the trim lights tell you if the Autopilot is fighting the trim.
The Ray allen servo or MAC servos would not work as an autopilot servo.
I guess I would like to have a tone sound in the headsets when I hit the trim button to alert me when something is running.
Also Tru Trak has a flight director function with some kind of an approach selection.
Not long ago there were some coreless motor servos used with I believe a Chelton autopilot and hooked to the elevator trim. I looked at this system for my Apache but decided not because of the trim crank whirling around all the time. I don't think the elevator trim system was made with that kind of constant use in mind.
In a Cessna the electric trim motor turns the trim system and also the manual wheel in the cockpit. The autopilot servo has a capstan with a bridle cable wrapped around and it moves the elevator cable directly.
Both are not connected but the trim lights tell you if the Autopilot is fighting the trim.
The Ray allen servo or MAC servos would not work as an autopilot servo.
I guess I would like to have a tone sound in the headsets when I hit the trim button to alert me when something is running.
"Perfection is finally attained not when there is no longer anything to add but when there is no longer anything to take away." Antoine de Saint Exupery
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owenstrawn
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