Rudder trim tab

[whee]

I've never intended to install a rudder trim because I to figured I could just set it, using the return springs and cables to adjust it, and forget it. As I've thought about it I'm thinking rudder trim might be nice if it could be don't simply at little weight/complexity cost.

[Rollie]

I just wanted to say that there are some really cool ideas here and this is exactly why I moved over to the experimental world. The guys who want the fully adjustable rudder trim and are willing to design and install it should do it and those who want something simpler should do that. I love having the freedom to modify my plane to exactly what I think I want without needing to see if someone already did it, got an STC approved and is available for me to purchase it from, only to find out that that is only the beginning of the paperwork. Next is getting someone with the proper certificate to inspect your work (if they will let you do it yourself) and make a writeup in your logbook and send in a 337 and whatever else might be required. I'm sure I have done a few mods that most people would look at and think "why?" but really I am having such a blast just putting this thing together exactly how I want it that sometimes I might add things just because I wasn't allowed to on my last couple planes.

[huntaero]

I used the Ray Allen trim in my elevators one in each elevator for redundancy and no mech linkage, welded a a bracket into the elevator at the front torgue tube, mounted with 440 screws and used a piece of 5/16 2024 alum rod threaded internally at each end for 10-32 threaded rod to attach to the servo clevis and trim tab. It will be removable and sticks into the wind about 1/8 inch, mounted from the bottom. The rudder is the same thickness tube and would mount similar. I plan to taper the edges with Pro seal.

[kestrel]

I used the Ray Allen trim in my elevators one in each elevator for redundancy and no mech linkage, welded a a bracket into the elevator at the front torgue tube, mounted with 440 screws and used a piece of 5/16 2024 alum rod threaded internally at each end for 10-32 threaded rod to attach to the servo clevis and trim tab. It will be removable and sticks into the wind about 1/8 inch, mounted from the bottom. The rudder is the same thickness tube and would mount similar. I plan to taper the edges with Pro seal.

That is just about exactly what I've been contemplating as a retrofit to mine. Mine has the older larger trim tabs, so I'm only using one tab and would need only one servo. I was envisioning a fiberglass blister to cover the extra thickness. Eliminates the "servo action" of the stock trim. Eliminates a lot of linkages. Eliminates the flex in the link to the tab.

[huntaero]

Yes it cleans up the elevators and trim linkages, the servo only protrudes about 1/8 in and when you seal the edges it would be weathertite without a blister covering. This would not be the servo tab. You could install one in each elevator and use one as a standby In case of failure.

[Zzz]

I used the Ray Allen trim in my elevators one in each elevator for redundancy and no mech linkage, welded a a bracket into the elevator at the front torgue tube, mounted with 440 screws and used a piece of 5/16 2024 alum rod threaded internally at each end for 10-32 threaded rod to attach to the servo clevis and trim tab. It will be removable and sticks into the wind about 1/8 inch, mounted from the bottom. The rudder is the same thickness tube and would mount similar. I plan to taper the edges with Pro seal.

Are you able to sync them? If they're run independently with no frequently calibration won't they get out of sync possibly causing a differential trim situation?

I've considered this same method as I think it totally cleans up the tail, but have been hesitant for the reason I mentioned.

[huntaero]

If you run them to the end and the return them to neutral they should be in sync for a while if powered together. I might use one side only as main trim and the second side for standby trim, not sure yet. I was also thinking of using 2 switches ganged together with separate power sources with 2 trim indicators then you can sync them anytime in flight or on the ground.

[kestrel]

With the smaller trim tabs on most Bearhawks, you probably want to use both tabs or make a single large tab. I am running a single large tab (old style) with the 2nd tab disconnected and secured. I have seen no problems with "differential trim". Many aircraft use a single tab, including RV's and C-172's. Huntaero's suggestion of a pair of switches and a pair of position sensors should be fine.

[jaredyates]

I've been thinking I might try an electric elevator trim too, and have thought about using just one tab. Even with the smaller tabs, I suspect there would still be plenty of effectiveness, but that hunch is not based on science. If I were to redo the covering on the horizontal stabs I could also add wooden strips to go to the profile shape, and in that case there would be plenty of room for mounting the servo directly to the pushrod. I'd immobilize the tab on the other side. It's easy to see how these little projects creep into bigger ones. Somehow I'm still waist-deep in a Skyview upgrade that has also become an autopilot and heated pitot installation, and maybe the addition of a flap position sensor.

[whee]

I've been thinking I might try an electric elevator trim too, and have thought about using just one tab. Even with the smaller tabs, I suspect there would still be plenty of effectiveness, but that hunch is not based on science. If I were to redo the covering on the horizontal stabs I could also add wooden strips to go to the profile shape, and in that case there would be plenty of room for mounting the servo directly to the pushrod. I'd immobilize the tab on the other side. It's easy to see how these little projects creep into bigger ones. Somehow I'm still waist-deep in a Skyview upgrade that has also become an autopilot and heated pitot installation, and maybe the addition of a flap position sensor.

I have the opposite hunch. In my short 30hrs in a BH I can think of two different flight were I nearly ran out of forward trim; that plane had the large tabs with one disabled. If you mount the servo in the H-stab then you still have the servo action but maybe that doesn't matter to you.

Do you have a hard time figuring out what position your flaps are in

I know we are getting off track here but if I could go back to before I ordered my empannage I'd make my own elevators. I build them with one large tab and mount a servo inside the elevator. I suspect that installing a servo in each elevator to drive each small tab and powering them from one switch would result in a slightly out of sink but completely functional trim system.

[jaredyates]

Yes, we totally off track! Who is supposed to be moderating this place anyway? I'm in the "pro-servo" camp so that's not a concern for me. If a single small tab is not adequate, I like the idea of a fuselage-mounted single servo to control both tabs through the torque tubes. Do you know what kind of deflection your tab had when it wasn't quite enough? This would be a useful datapoint. As for the flap position, the setup is very small and light, and it would allow the electronics to provide an aural alert of a flap overspeed. Perhaps with future software enhancements it might also allow for Vfe indications conditional to flap settings. I'm also interested in seeing how much the flap deflection changes with airspeed. I can see in gopro videos that it is pretty significant, but getting the flap position into the EMS will allow tracking in the recorded data.

[JimParker256]

All this discussion about the elevator trim strikes me as kind of funny, though I'm building a Patrol, and not the 4-place. But one of the things I remember about the Patrol demo flight I took at OSH with Wayne Massey was that he basically adjusted the trim once - to compensate for my weight in the back seat - and then never touched it again. The airplane was incredibly stable at speeds ranging from 140+ mph all the way down to stall speed, with no significantly noticeable or objectionable stick force. Maybe that's a result of the inherent "servo-action" of the stock trim system?

All I know is I'm planning to build mine with the dirt-simple, ultra-lightweight Bob Barrows trim lever. After flying with a similar overhead trim lever in the Champion 7ECA, it's super-easy to tweak the trim, and you quickly learn the set it for takeoff / cruise / landing by "feel." I must admit that I am considering the addition of a wood "kitchen drawer" pull knob to the end of the lever to act as the "handle." I know - those ounces add up! LOL

[jaredyates]

Yes, the Patrol is in a different category when it comes to elevator trim.

[marcusofcotton]

I search the site trying to find pictures of the patrol elevator trim mechanisms, no luck. What is different from the four place?

[kestrel]

Marcus, the 4 place is bigger and heavier. A 4 place flown solo and light on fuel will have a lot more trim change with power or speed changes than a Patrol with someone in the back seat to move the CG back.

[whee]

Do you know what kind of deflection your tab had when it wasn't quite enough? This would be a useful datapoint. As for the flap position, the setup is very small and light, and it would allow the electronics to provide an aural alert of a flap overspeed. Perhaps with future software enhancements it might also allow for Vfe indications conditional to flap settings. I'm also interested in seeing how much the flap deflection changes with airspeed. I can see in gopro videos that it is pretty significant, but getting the flap position into the EMS will allow tracking in the recorded data.

I wish I knew what the measured tab deflection was because you are right, that would be a very useful datapoint but I don't.

I was just razzing you about the flap position indicator.

[Battson]

All this discussion about the elevator trim strikes me as kind of funny, though I'm building a Patrol, and not the 4-place. But one of the things I remember about the Patrol demo flight I took at OSH with Wayne Massey was that he basically adjusted the trim once - to compensate for my weight in the back seat - and then never touched it again. The airplane was incredibly stable at speeds ranging from 140+ mph all the way down to stall speed, with no significantly noticeable or objectionable stick force. Maybe that's a result of the inherent "servo-action" of the stock trim system?

All I know is I'm planning to build mine with the dirt-simple, ultra-lightweight Bob Barrows trim lever. After flying with a similar overhead trim lever in the Champion 7ECA, it's super-easy to tweak the trim, and you quickly learn the set it for takeoff / cruise / landing by "feel." I must admit that I am considering the addition of a wood "kitchen drawer" pull knob to the end of the lever to act as the "handle." I know - those ounces add up! LOL

If you are at aft CG - the Bearhawk is the same - you only set it once. At forward CG, you are adjusting it all the time.

I've had the pleasure of flying both electric trim and manual trim in a Bearhawk, for several hours including some short and difficult landings in each... Personally, I remain in favor of servo-driven electric trim. Each system has pros and cons, and each person their own preferences.