2024 - 2025 Elevator Trim Redesign

Engine overhaul
Electronics/Electrical
Fuel System
Trim System
Fabric Recover


Item #1 from the rebuild page:  The trim is inadequate.  It's barely adequate when I have a full tank and a passenger in the front seat.  Otherwise I run out of nose down trim.  If I take the front windscreen off, the plane wants to dive at the ground even with full nose up trim.  So, the spring biasing trim is going to go away in favor of two Ray Allen trim servos; one mounted in either elevator.  The hinges are already there as it apparently had trim tabs on it in the past, but they were removed for unknown reasons.  I see there is an abandoned bowden cable in the aft fuselage, so I suspect that used to be the trim control.


There are no tabs installed on the elevators, but notice the three hinge points welded to the trailing edge of both elevators.  I plan to take advantage of those hinge points and will use them to mount new trim tabs that will work in sync with each other.


The old trim system.  The handle on the left side of the rear cockpit is the existing the trim system in the plane.  It is a push/pull bowden cable that pulled on a spring (in the photo below) to bias the elevator nose down.  There was no nose up trim.  By myself, depending on the fuel load, the plane wanted to fly at about 80 - 85 mph.  I could pull in some nose down trim, but it was inadequate once I had burned off half of the 20 gallon fuel tank.  Additionally, I have quarter turn fasteners to remove the front windscreen and an aluminum cockpit cover for the front cockpit so I can fly it with a slick front cockpit.  When I tried the slick front cockpit configuration, the plane just wanted to dive at the ground with no ability to trim it nose up.  This spring bias trim system has now been removed from the aircraft.





12/19/2024 - The project to redesign the elevator trim.  It currently has a lever in the rear cockpit that pulls on a spring to bias the elevator nose down.  There is no nose up trim as the plane wants to fly almost down to approach speed hands off.  If I remove the front wind screen, the plane wants to dive at the ground.  With no nose up trim available, I can't fly it slick with the front windscreen off and the front cockpit cover on.  I'm adding an adjustable trim tab to each elevator.  Above, I have the elevators removed, and below I have the outer edges of the trim tabs welded together.   I'll add the bellcrank and internal structure after I cut the elevators open and figure out where and how to mount the trim servos.




12/20/2024 - Today's the day to get after the trim modifications.  I stripped the fabric from the left elevator, so orientation wise, we are looking at the top of the left elevator in the photo above, and the bottom below.  The Ray Allen trim servo is in the bottom left of the corner of the top photo and gets mounted into the elevator from the bottom.  .


First thing was to weld in a brace and frame to mount the trim servo.  Just the two sides would be enough to hold the servo.  The complete picture frame to go around the servo is to give me a place to attach the fabric around the hole.  The outer face of the servo will be exposed on the bottom side of the elevator.


Turned over right side up so we are looking at the top of the elevator.  This part of the servo will be under the fabric.  


Working from the bottom side of the elevator again.  Inner framework is welded into the trim tab and the bellcrank arm has been fabricated and welded to the tab.  The bellcrank is two pieces of .032 4130 steel welded together to make it .064" thick.  I cut them out with my hand held band saw, then welded them together before welding the bellcrank to the trim tab.  


Almost completed assembly.  I still need to add nut plates to the mounting frame for the servo and customize a piece of 10-32 threaded rod to go to the trim tab for control.  I also plan to duplicate this same structure and trim tab on the other elevator and will use dual trim tabs.


12/21/2024 - Rinse and repeat from yesterday.  Fabricated the same servo mount and trim tab structure for the right elevator.


12/23/2024 - I have the Ray Allen trim servo attached to the mounting frame with a cleco clamp.  Rather than drilling and installing nut plates, since this is mounted into 4130 steel plate, I decided to thread the plate with a 6-32 tap and that seems to be a firm mount.


I fabricated the linkage from the servo to the trim tab with 10-32 Stainless threaded rod.  Ray Allen sends #8 threaded rod in the kit, but it was too short to meet my needs and with the longer reach, I wanted a bit stiffer linkage.  I drilled the clevises from #8 to #10 sized and tapped them with a 10-32 tap.  I did the same with the trim on my SuperCub when I built it and it has served me well for the last 10 years.   This is full nose up trim and the photo below is full nose down trim.  I only took photos of one elevator as the other looks just like it; only a mirror image.  Those that look closely will notice the trim tab is not straight.  These things warp and bend like mad while torch welding.  A bit of gentle persuasion with a plenishing hammer on the anvil squared it up.




Time to install the new stick handles to include the trim control.  As always, I get ahead of myself and forget to take pictures, so at this point I have already trimmed the plastic bicycle grip handle off the stick.  I needed to sort out the wiring to the switch in the stick as this plane has a switch activated intercom as well as the PTT in the same switch.  Just toggle it the other way.  It had some strange wiring in the way the switch was wired, but I figured it out and will be ready to splice it to the wiring from the new stick handle.


I cut the top of the stick off with a pipe cutter.  That makes for a nice even cut.


The bushing on the bottom of the stick goes into the pipe, then you match drill a hole in the front of the existing stick to bolt it in.  Once that is fitted to the stick, I also drilled a divot into the front of the stick shaft for the set screw in the front to seat into, firmly locking the stick into place.  


Same treatment for the front cockpit as well.  I thought the front stick was wired for intercom only even though it had been labeled for both Intercom and PTT.  Nope.  Most of the wires connected to the switch were broken.  I guess I'll wire it correctly to give the front seat access to the radio as well.  The red button on the left with be the PTT for the radio and the gray button on the right will be the intercom.  The round button in the center will trim nose down when pushed forward and nose up when pulled back.  There are additional buttons on the stick, but they will be unused.


I really should do something with the paint on this front instrument panel.  That is UGLY!


12/24/2024 -Christmas Eve...   Today's goal was to wire in the switches for the new stick grips.  The switches on the stick control elevator trim, radio transmit, and intercom transmit and all are active from either seat.  I decided to add a terminal block under the  right rear floorboard along with the relay deck for the trim servos that came with the stick grips to enable the trim servos to be controlled from either seat.  You can see the relay deck just under the wiring connected to the terminal block.  I still need to pull a ground wire, +12V wire, and the two servo leads to complete this part of the installation.  I also need to wire in the trim indicators in the instrument panel.  I failed to take a photo, but today I also fabricated a new panel mount for the trim indicators and painted it black.  It will show up in the next round of wiring when I install the indicators.  I'm waiting for some mini-Molex connectors to arrive to complete the connections, although I can pull the wiring to the tail now.  The connectors should arrive on Friday.


12/26/2024 -  The terminal block under the floorboard is completed.


I needed to gain access to the aft fuselage to route the wiring for the trim servos.  I am waiting for some components to arrive to complete the wiring, so I'll do some more disassembly and strip some fabric. 




Tail braces are hanging loose and labeled.


Horizontal stabs removed.


12/29/2024 -  The connectors I've been waiting on arrived in yesterdays mail.  The new trim system is now completed and functional.  Note the trim indicators lit up on the right side of the panel.  Trim is actuated by pushing fore and aft on the button at the top center of the stick.  Both trim tabs are actuated with the same button and run in sync with each other.  If, for some reason, they get out of sync, I can simply run the trim to the end of the travel until both servos register at full travel, then when they go the other way, they will be in sync again.  The control works from either seat, but the indicators are only in the rear seat.