Rudder "trim" tab - like it or not?

[Rezrider]

Hey folks, I'm glad you guys are talking about this. I have just bought a 1980 M5-235 and loving it so far.
I noticed the T-handle on the dash but haven't messed with it yet. Does anyone actually use this? Is it connected to the rudder tab? Or does it just hold some rudder pressure for you through tension on the pedal?

The other question I have, when towing it back into the hangar today the tab was deflected, would this be because the airlerons may be turned?

Thanks guys, awesome info here.

RR

[MauleMechanic]

Yes, I understand what you're saying. You also need LH trim for power off descent too... For the difference check out your elev trim, you dial it in at tab, tab stays fixed at same location thru out the travel range, there is NO spring preload to overcome. This is not the case with the rudder, but if you want to call it rudder trim, rudder servo trim, or servo tab, they all do trim job but the servo trim also drives the ailerons with cables attached to aileron cables at wing root which are interconnected to rudder trim cables in tailcone... It's also not as effective as the straight trim. It will also tend to put you into a coordinated RH turn if you take hands off yoke with T pulled all the way out. Straight trim will turn you as well but would be a skidding turn. Proper terminology would be active servo trim tab, the servo part of equation driving ailerons... Or are ailerons driving rudder tab... It all depends upon how much preload against spring under boot cowl / upholstery RH fwd fuselage...

There are four major types of this trailing edge tab control.
( 1 ) An " active anti-servo " trim tab system : Anti-Servo Trim Tab This system of trim utilizes the "race ahead and help push it back" theory of trim. It does this by having the little trim tabs race ahead of the elevator in both directions of travel and aerodynamically force the elevator back to equilibrium. The linkage basically connects the trim tab to a fixed part of the airframe (or servo motor attached to the airframe). The way you get reversed travel is to push on a lever that is ahead of the trim tab's pivot point. From a trimmed position, if you bump the stick, this concept aggressively returns the aircraft to its former state of flying. In general, the tab's position is always up to offset the aerodynamic loads of the elevator. The tab travels farther up as the elevator travels up, and the tab travels down as the elevator travels down. Note: this is the most stable configuration you can come up with. The trim settings (once established) would neutralize elevator forces to the control stick for a very small range of elevator travel. Once the pilot exceeds this little range of neutral (low) forces, the stick loads would load up fast.
( 2 ) An " active " or " motor driven " trim tab system : Active Trim Tab This system of trim utilizes the "motorized bent metal plate" theory of trim. The little tabs are inert as the elevator goes up or down and do not actively assist in returning the elevator to equilibrium. The linkage connects an electric motor (or mechanical trim wheel cable) to the movable trim tab at a point that is aft of the trim tab's hinge point. In general, the tab's position is always up to offset the aerodynamic loads of the elevator. From a trimmed position, if you bump the stick, this concept neither hinders or helps return the aircraft to its former state of flying. Return to equilibrium is achieved by a longer period porpoise effect as the aircraft "seeks its own" based upon power and drag. This type of trim tab system is only slightly better than the " fixed " version in that the servo motor can adjust the tab positions and affect a trim condition for the aircraft. The trim settings (once established) would neutralize elevator forces to the control stick for a small range of elevator travel. Once the pilot exceeds this little range of neutral ( low ) forces, the stick loads would load up fast.
( 3 ) A " passive " or "un-powered" trim tab system : Same as above except that this is just a bent metal plate sticking out in the breeze. It would be the same as above when the servo motors fail. You bend the tab once and it is good for a small range of speeds and elevator settings. There is no pilot control of the pitch trim. Once the pilot exceeds this little range of neutral ( to low ) forces, the stick loads would load up fast.
( 4 ) An " active servo " trim tab system. Servo Trim Tab This system of trim utilizes the "push in the opposite direction and help the elevator to go" theory of trim. It does this by having the little trim tabs work opposite of the elevator and generate aerodynamic forces that aid in the elevators travel. The elevator is helped away from equilibrium. From a trimmed position, if you bump the stick, this system aggressively pulls the aircraft farther into the perturbed state. The linkage essentially connects the trim tabs to some fixed part of the airframe (or servomotor attached to the airframe) at a point that is aft of the trim tab's pivot point. In general, the tab's position is up if the elevator is down, neutral if the elevator is neutral and down if the elevator is up. The tabs travel up as the elevator travels down, and the tabs travel down as the elevator travels up. Stick forces imparted by the elevator would be neutral the whole time. Note : THIS IS AN AERODYNAMICALLY UNSTABLE CONDITION. This type of tab would be a great as a booster for ailerons or really big elevators that overpower the pilot’s best efforts. In effect, this type of trim system is "power steering".

Thanks Aero.....I am gonna have to digest that for a while.

[MauleMechanic]

...but the servo trim also drives the ailerons with cables attached to aileron cables at wing root which are interconnected to rudder trim cables in tailcone... It's also not as effective as the straight trim. It will also tend to put you into a coordinated RH turn if you take hands off yoke with T pulled all the way out. Straight trim will turn you as well but would be a skidding turn.

So basically if you are in straight and level flight...airplane trimmed.....and you pull the T cable all the way out......that activates the right rudder to move forward thus enabling right rudder input causing the airplane to yaw right. How does this aerodynamic action relate to the movement of the tab that is connected to the ailerons? The questions are in my brain but I can't seem to ask them they way I want.

[aero101]

Read Item #4 for an active servo tab, which is what the maule has got (note- one end of trim cable connected to airframe thru the spring under RH kick panel)... If you keep ailerons straight and level, the tab will give you a right yawing tendency as is needed to counteract P Factor, etc, etc... Now given same position on T handle, neutralize rudder pedals and lock them in that position with feet, what are the ailerons going to do as you release yoke? Of course this all must be done while airborne with air pressure on servo tab or someone mechanically moving servo tab while inside airplane running flight controls... Suggest take airplane for a flight, play around with T handle position as well as locking rudder pedals in neutral, then lock ailerons in neutral after releasing rudders and note the changes about the aircraft axis. If you exaggerate by pulling out T handle all the way, it'll probably be easier to recognize the control inputs it directs. Quite simply the servo tab interfaces with rudder and ailerons, and one end of trim cable connects to fixed airframe thru a spring instead of both ends of trim cable connecting to a trim tab. A true trim tab cable sys would only interface with rudder tab and there could be no interconnect anywhere.

That's about best explanation I'm capable of, suggest you could probably discuss with Shirley Maule, as I believe she's an engineer type? Granted it is kind of confusing, but it's pretty self explanatory if you play with it in flight? This system probably installed on the maule to counteract it's short coupling and help with pilot induced adverse yaw, which the acft still has a good bit of anyway?

JEREMY may also have another explanation easier to understand or to clarify what's already been said?

[pilot]

Hey folks, I'm glad you guys are talking about this. I have just bought a 1980 M5-235 and loving it so far.
I noticed the T-handle on the dash but haven't messed with it yet. Does anyone actually use this? Is it connected to the rudder tab? Or does it just hold some rudder pressure for you through tension on the pedal?

The other question I have, when towing it back into the hangar today the tab was deflected, would this be because the airlerons may be turned?

Thanks guys, awesome info here.

RR

First, congrats on the new ride!

The "rudder trim" t-handle pulls a spring that is attached to the right rudder pedal, it has no connection to the tab on the rudder. The cable can be adjusted behind the kick panel if you need more pull on the spring, just losoen the clamp and pull the cable housing up.

The answer to your other question is yes.

[MauleMechanic]

Read Item #4 for an active servo tab, which is what the maule has got (note- one end of trim cable connected to airframe thru the spring under RH kick panel)... If you keep ailerons straight and level, the tab will give you a right yawing tendency as is needed to counteract P Factor, etc, etc... Now given same position on T handle, neutralize rudder pedals and lock them in that position with feet, what are the ailerons going to do as you release yoke? Of course this all must be done while airborne with air pressure on servo tab or someone mechanically moving servo tab while inside airplane running flight controls... Suggest take airplane for a flight, play around with T handle position as well as locking rudder pedals in neutral, then lock ailerons in neutral after releasing rudders and note the changes about the aircraft axis. If you exaggerate by pulling out T handle all the way, it'll probably be easier to recognize the control inputs it directs. Quite simply the servo tab interfaces with rudder and ailerons, and one end of trim cable connects to fixed airframe thru a spring instead of both ends of trim cable connecting to a trim tab. A true trim tab cable sys would only interface with rudder tab and there could be no interconnect anywhere.

That's about best explanation I'm capable of, suggest you could probably discuss with Shirley Maule, as I believe she's an engineer type? Granted it is kind of confusing, but it's pretty self explanatory if you play with it in flight? This system probably installed on the maule to counteract it's short coupling and help with pilot induced adverse yaw, which the acft still has a good bit of anyway?

JEREMY may also have another explanation easier to understand or to clarify what's already been said?

The T handle does not connect to the Airframe unless you are calling the right rudder peddle an "airframe" for this discussion, it connects to the right rudder peddle. I will continue to look into this with Ray and Sherley but what I can say is that the items discussed are taught to students here to only be for the aid to prenvent Adverse Yaw during the initiation of bank/turn.

Thanks for your time trying to explain it to me.

[aero101]

It is connected directly to airframe thru the spring under RH kick panel... Just compare it to elevator connections to see difference in set up... About enough on this subject, bottom line it does what it was designed to do and the rest is just techno stuff that really doesn't matter.

[MauleMechanic]

It is connected directly to airframe thru the spring under RH kick panel....

I am thinking maybe you need to snap a photo and let me take a look. It does not attach directly to the frame at all. The cable runs to a bracket on the frame then down to a spring then to the tab connected to the right rudder peddle cross tube. When the T handle is not in use, there should be enough slack adjustment (no spring tension) as not to interfere with the rudder input.

[MauleWacko]

[MauleWacko]

II post

[aero101]

Jim I like that, hillbilly cruz control, with power steering assist!! Ref MXT7-180 maint manual items 9 and 10 in rigging procedures. It very clearly and precisely explains the difference between rudder trim and elev trim on this airplane. You can't have a trim tab without 2ea direct connections to move and adj that tab like elev has. Rudder servo tab has NO DIRECT control cables connected to tab from trim knob or adjustment T handle... AS the Maint Man states "it MAY BE USED for Rudder Trim in CRUZ... " I am quite familiar with set up on the maule, and yes one end of cable ends up on rudder pedal. A real trim tab does NOT hook up to rudder pedals, or rudder cables, or aileron cables for that matter. You mechanically move tab with cables in opposite direction to assist flight control movement thru this adjustment. I think we've covered all avenues, and I'm done on this subject. It's difficult to explain and understand until it just clicks, "Oh now I understand." Playing with it in flight helps as well, that is, if ya didn't remove it!!

[riverbuggy]

As Jim states the rudder trim is connected to the airframe thru the spring of which tension you can control with the T handle. The connection to airframe is the clamp that holds the cable housing in a fixed position behind the right lower kick panel. The whole system works great for me except I keep forgetting to push the T handle in on approach, and I am left wondering why the aircraft doesn't seem to want to go where I want it to go.

[MAU MAU]

I know the Servo Tab can be confusing, so Maule Air just released this very helpful video which puts its operation into the simplest terms.

http://youtu.be/Ac7G7xOG2Ag

[aero101]

Ha! Ha! That explains it perfectly, PFM!!!

[Beamerpilot]

I have one of six Maules ever built that does not have the turn coordinator tab on the rudder. If you could, would you change out the rudder (when recovering your plane) to add this feature?

My M4 had it installed many years before I bought it, but I thought it was part of the increased gross weight kit, Am I wrong?[/img]